Luminous Landscape Forum

Raw & Post Processing, Printing => Adobe Camera Raw Q&A => Topic started by: BobD on May 19, 2010, 09:44:42 am

Title: Dual Illuminant Profiles
Post by: BobD on May 19, 2010, 09:44:42 am
Trying to understand how ACR uses a dual-illuminant camera profile?   According to X-rite, “when you select a dual illuminant profile, your Adobe Raw software will use both light source tables to adapt the profile to match the image’s illuminant.

My specific questions are:
1)  How does ACR “adapt” a “Dual illuminant” [D65 and 2850] camera profile?  (e.g. for an image shot on a cloudy day)

2)  What are the benefits (and repeatability*) of using a “Dual illuminant” camera profile?
.........2a) *repeatability - if there is a subtle change in color temp. (sun moving in and out of clouds), will a common object have a "color shift" because of “adapting” dual-illuminant LUTs?

3) Is it better to use a single-illuminant profile that is closest to the actual shooting color temperature?

4) How critical are the color temperatures (D65 and 2850) illuminating the 24 patch Graytag-MacBeth target when creating files for a Dual-Illuminate camera profile?

Thanks
Title: Dual Illuminant Profiles
Post by: jpegman on May 19, 2010, 01:31:24 pm
I have the same question - apparently, Photoshop ACR started this dual profile methology and it has filtered down to X-Rites Passport Profiler product, with little explanation on when it is recommended or not.

Eric, do you know the history and theory behind this dual point approach and situations where it might be better to use a single point calibration?

Jpegman
Title: Dual Illuminant Profiles
Post by: madmanchan on May 19, 2010, 01:31:28 pm
1. Interpolates between the two tables based on your white balance setting. Specific method is inverse correlated color temperature. See DNG Specification if you wish to see the details & mathematics.

2. Improved color reproduction over a wider range of scenes. Degree of improvement depends on the camera model. If the scene lighting conditions (e.g., office fluorescent) varies greatly from the two illuminants used to build the profile (e.g., Solux bulb and natural cloudy daylight) then all bets are off. You will get something "ok" but results will be better under the unusual lighting condition by building a profile for that condition.

3. It's not the shooting temperature that matters, but the spectrum of the illumination. This is more complex and not easily measurable. General advice: if you tend to photograph under daylight, not worth building profile for each flavor of daylight, regardless of the color temp. There will be minor variations between ~D50 and ~D75 lighting (roughly 5000 K and 7500 K CCT) but this tends to get eliminated once WB is considered. If you photograph under unusual artifical lighting often, consider building a profile for that lighting.

4. Not too important. X-Rite's software will tag the profile appropriately.
Title: Dual Illuminant Profiles
Post by: BobD on May 19, 2010, 04:08:22 pm
Quote from: madmanchan
#1. Interpolates between the two tables based on your white balance setting.

#3. It's not the shooting temperature that matters, but the spectrum of the illumination.
Eric thanks for the info... I have a few more questions.  

In #1 when you say ACR “Interpolates between the two tables based on your white balance setting.”...
- What WB setting are you referring to: the WB of the scene at time of shooting; the WB set on the camera when shooting the raw file or the WB set in ACR?  I was under the assumption that the camera's WB setting was a suggestion not part of the raw data but used only as a starting point if the ACR WB default was set to “As Shot”.

In #3 when you say “It's not the shooting temperature that matters, but the spectrum of the illumination."...
- Are you talking in wavelength or in Color Rendering Index?

Thanks Again,
Bob DiNatale
Title: Dual Illuminant Profiles
Post by: madmanchan on May 19, 2010, 04:59:38 pm
Hi Bob,

For #1: the WB set in ACR.  Initially, this is the "As Shot" WB which is usually the camera's suggestion, as you say (though it could be a fixed WB setting if you chose a manual WB using the in-camera settings).  As an example, suppose you created a profile for 2 illuminants, approximately A (2856 K) and D65 (about 6500 K). If you drag the temperature slider in ACR towards 6500 K, you'll end up using more of the color matrix and color table for the D65 "half" of the profile, and if you drag the temperature slider in ACR towards 2856 K, you'll end up using the color matrix & table for the A "half" of the profile. And if you're somewhere in between, like 5000 K, you'll use a mix of both.

For #3:  The wavelength. There are infinitely many lights that map to the same correlated color temperature (e.g., 5500 K). In practice, for example, you may have a flavor of natural daylight (some mix of sun & clouds) that gives you 5500 K CCT. You can also have fluorescent tubes that will get you about 5500 K, too. But the color rendering produced by the two lights can (and often will) be quite different, for certain materials. This poses a problem if you're trying to use a color profile made for one illuminant (e.g., the daylight one) for images shot under the other (e.g., the fluorescent one). In short, the CCT (or even a temp/tint pair) is not enough to describe the illumination. Having a spectrum of the overall ambient illumination (i.e., relative power at each wavelength) would help a lot, but this information is generally not easily available.
Title: Dual Illuminant Profiles
Post by: Tim Lookingbill on May 26, 2010, 12:37:33 pm
Here's a comparison showing the difference between using a single and dual illuminant table profiling my Pentax K100D using Adobe's DNG Profile Editor Wizard.

•The first image on the left is my eyeballing the actual appearance of the incandescent lights I used.

•The center As Shot WB image is the one used to build the second 2800K table in DNG Profile Editor CCchart Wizard. Its WB was established using the incamera "Incandescent" WB setting whose cast appearance ACR's As Shot interprets as shown.

•The third version on the right is neutralized using ACR's WB eyedropper tool on the gray patch next to white.

As you can see what a dual table appears to do is maintain the spectral reflectance characteristics (hue/saturation/luminosity) of color relationships no matter what the WB and spectral qualities of light used as long as the color wavelengths of the lights used have no abrupt spikes. From what I've observed the embedded algorithms seem to concentrate on correcting for red/green biases between 2800K-6500K influences.

The red patch in the single 6500K illuminant profile is way too orange and desaturated. The dual table version below looks more accurate though a bit over saturated with a slight magenta bias in the red which I believe is the happy medium between the two illuminants. My camera's AWB also tends to deliver a red bias balancing outdoor daylight.

I've also included the original daylight target image used to build the 6500K table. It has the single illuminant table profile applied which shows a correct looking red compared to the incandescent image.


[attachment=22208:DualSing...DifferLL.jpg]

[attachment=22209:SingleTa...ylightLL.jpg]
Title: Dual Illuminant Profiles
Post by: BobD on May 26, 2010, 02:50:06 pm
Quote from: tlooknbill
…comparison showing the difference between using a single and dual illuminant table profiling my Pentax K100D using Adobe's DNG Profile Editor Wizard.

...As you can see what a dual table appears to do is maintain the spectral reflectance characteristics (hue/saturation/luminosity) of color relationships no matter what the WB and spectral qualities of light used as long as the color wavelengths of the lights used have no abrupt spikes. From what I've observed the embedded algorithms seem to concentrate on correcting for red/green biases between 2800K-6500K influences.

...The red patch in the single 6500K illuminant profile is way too orange and desaturated…
tlook... thanks for the effort

Do you think a single illuminant profile has 2 (dual) daylight LUTs or do you think there is a void in the 2nd LUT area?  I would tend to think that it has 2 of the same “single” illuminant LUT. (Eric?)

Eric says: “If you drag the temperature slider in ACR towards 6500 K, you'll end up using more of the color matrix and color table for the D65 "half" of the profile, and if you drag the temperature slider in ACR towards 2856 K”.  Posing the question, “what would happen if you dragged the slider towards the second illuminant area and there was a void or no LUT?

... “(your) camera's AWB also tends to deliver a red bias balancing outdoor daylight.”
If you are shooting in raw, I would think your camera’s “red bias” is a function of the chip’s bias and not the AWB.  Isn't that why we create a profile in the first place… to remove the camera bias?  Maybe your "…slight magenta bias in the red” is more accurate.  I would hope it's more accurate because if “you drag the temperature slider in ACR towards 2856 K” and it creates a “slightly magenta biased” then I would have a concern that the color, although unique to the dual illuminant profile, would not be accurate.

..."…dual table (profiles)… maintain the spectral reflectance characteristics…no matter what the WB and spectral qualities of light used as long as the color wavelengths of the lights used have no abrupt spikes."
Again, it is my understanding that the camera’s WB has no effect on the profile when shooting a raw file.  The quality of light not having any “abrupt spikes” can be determined by the “Color Rendering Index” (CRI) specification of the light source.
Title: Dual Illuminant Profiles
Post by: Tim Lookingbill on May 26, 2010, 05:31:29 pm
All I can tell is if I slide the color temp slider on the Daylight CCchart target image with the single illuminant profile from default As Shot 5100K to 7500K the Hue/Saturation/Luminance relationship between warm and cool colors change proportionally whether I use a dual or single table profile.

If I slide the color temp to 4500K with the single table profile decreasing overall luminance and saturation, changing to a dual table afterward brightened certain colors mainly in the pinks and magenta when it didn't do this at 7500K.

Now color behaves differently doing this on the incandescent shot, so the light source illuminating the initial image is going to have far more influence over whether you use a dual or single table profile. But in my experience a dual table works best with scenes lit under incandescent lighting because there is far more improvement in maintaining HSL when neutralizing or adjusting to taste this type of color cast.

If all you shoot is under daylight such as in landscapes then a single table is all that's necessary.
Title: Dual Illuminant Profiles
Post by: BobD on June 07, 2010, 01:33:29 pm
Quote from: madmanchan
...As an example, suppose you created a profile for 2 illuminants, approximately A (2856 K) and D65 (about 6500 K). If you drag the temperature slider in ACR towards 6500 K, you'll end up using more of the color matrix and color table for the D65 "half" of the profile, and if you drag the temperature slider in ACR towards 2856 K, you'll end up using the color matrix & table for the A "half" of the profile. And if you're somewhere in between, like 5000 K, you'll use a mix of both.
Eric, recently I have been creating dual illuminant profiles using Xrite's ColorChecker Passport software.  The dual illuminants are Daylight and Tungsten A.  However, sometimes these illuminates fall into different LUT tables e.g. “Daylight" resides in Illuminant 1 & "Tungsten A" in Illuminant 2 AND sometime visa versa (see inset)  
(http://theuncarvedblock.com/images/DualProfiles.jpg)

Previously you mentioned “…dragging the temperature slider towards one or the other (Illuminant) will use more of that color matrix and color table, …if you're somewhere in between, …you'll use a mix of both.”  That being said, here are my questions:
...1 Does it make a difference which Illuminant goes into which look-up table?
.............i.e.  “should the Daylight Illuminant always in Illuminant 1 LUT?”
...2  What happens when there is only a single illuminant profile, what happens when you drag the slider towards the “void” color matrix and color table?
...3 Does the “Adobe Standard” delivered with Lightroom and ACR have “dual illuminants”?
Bob DiNatale
Title: Re: Dual Illuminant Profiles
Post by: mac_paolo on May 08, 2012, 03:42:09 am
I restart this topic with a simple question.
Taken into account that the temperature alone means a little as it doesn't specify nothing about the actual spectrum, how do we chose the hotter temperature for the dual illuminant?

Is it D65 or 6500 K?
Is it better a cloudy day or the specific hour of the afternoon when the sun produces 6500 K light?

The colder illuminant is easier to achieve with a tungsten bulb :)
Title: Re: Dual Illuminant Profiles
Post by: Tim Lookingbill on May 10, 2012, 01:16:19 am
I restart this topic with a simple question.
Taken into account that the temperature alone means a little as it doesn't specify nothing about the actual spectrum, how do we chose the hotter temperature for the dual illuminant?

Is it D65 or 6500 K?
Is it better a cloudy day or the specific hour of the afternoon when the sun produces 6500 K light?

The colder illuminant is easier to achieve with a tungsten bulb :)

I think you're making this too complicated.

If you note in the image samples I posted above I established D65/6500K illuminant table from the CC chart lit by noon day sun (close enough to establish R=G=B neutrality). The important thing is you need to use a light source with the fullest color spectrum and you can't get any closer than direct sunlight. All lights including natural and artificial (and overcast) will impose various levels of color errors within a certain range of memory colors with sunlight showing the least color shifts over a wider range of colors compared to other light sources.

The tungsten lit shot was to show the difference between what happens to certain colors (in particular the red patch) neutralizing a tungsten lit scene with a single verses a dual illuminant profile.

Did you notice the slightly less saturated orangish red patch of the single D65/6500K illuminant profile on the top far right compared to the proper red patch appearance using the dual illuminant profile below it after applying the same color temp edit to both?

So the issue isn't really about establishing exact appearance of color temperature, which can become an interpretive experience editing an image due to the adaptive nature of human vision, but it's more about coming up with two different types of profiles that influence color appearance when neutralizing, editing or adjusting ACR/LR's Color Temp sliders using the gray reference shot under completely different illuminants for the best possible color balance appearance.

This is the true goal behind camera profiles, not accuracy to some color temp appearance associated with a Kelvin number. If you stared at any one of those color patches for at least a minute, I can guarantee the appearance of the gray patch used as neutral reference will noticeably change hue even if it read R=G=B. So much for accuracy to some color temp appearance. Accuracy to a balanced appearance? Yes.

Read up on the subject of "color constancy" and what it does to the perception of color balance associated with color temperature.
Title: Re: Dual Illuminant Profiles
Post by: digitaldog on May 10, 2012, 12:35:39 pm
Is it D65 or 6500 K?

If you want to get real picky...

6500K is a range of colors. D65 was developed using actual color measurements but a lot of em (622) over the course of time in differing locations around the world with differing instruments. So the likelihood you’re exactly getting D65 is questionable.
Title: Re: Dual Illuminant Profiles
Post by: Tim Lookingbill on May 10, 2012, 03:10:57 pm
Examine the various appearances of so called 5000K and 6500K on this site's review of desktop/print viewing stations:

http://www.northlight-images.co.uk/reviews/lighting/viewing-pdv3.html
Title: Re: Dual Illuminant Profiles
Post by: mac_paolo on May 10, 2012, 04:07:52 pm
So why explicitly ask for a 6500 K white when a plain common daylight is most probably the best choice?
6500 K is quite uncommon for daylight here and there.
Title: Re: Dual Illuminant Profiles
Post by: Tim Lookingbill on May 11, 2012, 06:10:08 am
So why explicitly ask for a 6500 K white when a plain common daylight is most probably the best choice?
6500 K is quite uncommon for daylight here and there.

How do you know what color is 6500K daylight? As Andrew pointed out the actual appearance of a spectrally flat white/gray target lit by sunlight can vary depending what area of the globe one resides.

It's just a number that color management software algorithms reference against to compare to their core connection space, Lab D50, which again is an artificially mathematical construct of how humans perceive color under a full spectrum light source. They need the number for mathematical calculation for controlling color appearance assuming a neutral looking viewing display environment.

The appearance of 6500K white on a display can be compared to white formless overcast clouds backlit by noon sun, but again a display is not a full spectrum light source. That particular hue of 6500K display white is only mimicking full spectrum light by tweaking hue/saturation color tables of tagged images (color constancy optical effect) that gives the impression the person is viewing a daylight environment. It's still artificial but it manages to convince us otherwise due to the adaptive nature of human vision.
Title: Re: Dual Illuminant Profiles
Post by: mac_paolo on May 11, 2012, 07:04:46 am
How do you know what color is 6500K daylight? As Andrew pointed out the actual appearance of a spectrally flat white/gray target lit by sunlight can vary depending what area of the globe one resides.
I just shoot a WhiBal under direct sunlight, which should mean full spectrum, and measure it back into Lightroom.
I'll try to explain better my point: as for the most part of the globe the direct sunlight is always way below 6500 K, why did Adobe/others explicitly ask for 6500 K instead of 5000/5500 K?

I mean, I know the difference is not that huge, it's more just curiosity. :)
Title: Re: Dual Illuminant Profiles
Post by: Tim Lookingbill on May 11, 2012, 07:47:08 am
You'ld have to ask Adobe. Like I said it's just a number used for mathematical calculation for controlling color appearance in the artificially neutral looking editing environment of the display.

Below is an image I shot of some food items lit by a regular 100 watt GE soft white tungsten light bulb as an example of how tweaks to WB hue in relation to color table hue/sat tweaks can change the perception of the appearance of Kelvin based defined daylight.

It's not just about color cast. It's about mimicking the spectral reflectance effects of a full spectrum light source along with the color cast/color temp appearance and what it does to our perception of color balance and why focusing on the definition of a Kelvin/D number is pretty much pointless.

The three images are pretty much self explanatory with the last one pushing neutrals to an unnatural hue that compliment overall appearance of the red tomato, the fresh green lettuce leaf and the toasty warm hue of the cracker. It required more than just using a dual illuminant profile. The first one is VERY ACCURATE to the scene but looks butt ugly.

The last one is the most freshest and desirable looking but very inaccurate and way off any natural appearance of daylight whether Kelvin or D65/50. The hue/sat tweaks were applied in ACR's Hue/Sat panel.
Title: Re: Dual Illuminant Profiles
Post by: digitaldog on May 11, 2012, 09:38:12 am
I'll try to explain better my point: as for the most part of the globe the direct sunlight is always way below 6500 K, why did Adobe/others explicitly ask for 6500 K instead of 5000/5500 K?

The numbers are kind of meaningless in this context once you understand a boat load of colors correlate to any single kelvin value.

See: http://www.ppmag.com/reviews/200512_rodneycm.pdf

See the lines of correlated color temp that run magenta to green? Any color on that line could be specified as 6500K.
Title: Re: Dual Illuminant Profiles
Post by: bjanes on May 11, 2012, 10:24:34 am
I just shoot a WhiBal under direct sunlight, which should mean full spectrum, and measure it back into Lightroom.
I'll try to explain better my point: as for the most part of the globe the direct sunlight is always way below 6500 K, why did Adobe/others explicitly ask for 6500 K instead of 5000/5500 K?

There is an important difference between sunlight and daylight, and this is well explained in an article on the Handprint (http://www.handprint.com/HP/WCL/color1.html) web site (scroll down to the section Variations in Natural Light). Sunlight comes directly from the sun and can be visualized by a shaft of sunlight entering a darkened room through a window or skylight. The aperture of the window obstructs skylight (light diffused by the sky and having a bluish color). Daylight is the combination of sunlight and skylight and is what you would measure by taking a WhiBal reading. Daylight sometimes takes into account light reflected from foliage or buildings.

Noon sunlight is approximately 5500K and noon daylight about 6500K, but varies with latitude and atmospheric conditions.

Regards,

Bill
Title: Re: Dual Illuminant Profiles
Post by: julianv on May 13, 2012, 07:08:21 am
There is an important difference between sunlight and daylight, and this is well explained in an article on the Handprint (http://www.handprint.com/HP/WCL/color1.html) web site (scroll down to the section Variations in Natural Light). Sunlight comes directly from the sun and can be visualized by a shaft of sunlight entering a darkened room through a window or skylight. The aperture of the window obstructs skylight (light diffused by the sky and having a bluish color). Daylight is the combination of sunlight and skylight and is what you would measure by taking a WhiBal reading. Daylight sometimes takes into account light reflected from foliage or buildings.

Noon sunlight is approximately 5500K and noon daylight about 6500K, but varies with latitude and atmospheric conditions.

I read the relevant text on the Handprint web site, and I'm afraid that I am still a bit unclear on the distinctions used when referring to daylight, sunlight, and skylight.  I do understand that daytime SPD measurements vary, depending on how much light is received directly from the sun, how much is received via Rayleigh scattering (from a blue sky), how much is filtered through clouds, dust, and pollution, etc.

The part that I don't understand is the advice given for photographing the ColorChecker.  Certainly, the ideal method is to shoot it in the same light that falls on the subject, and to build a profile specific for the scene conditions.  But if I want to build a general purpose camera profile for daytime outdoor conditions, I need to shoot under sunlight.  And that's where I have been reading conflicting advice.  Some sources advise shooting in direct noon sunlight.  Others recommend "open shade", but do not explain what that means.  I have also read comments that the exact conditions do not matter much.

I interpreted "open shade" as follows.  I shot the CC in a location that was shielded from direct sunlight, and only received light from a cloudless mid-day sky.  I tried to minimize exposure to reflected light from other sources, such as foliage.  Is this a proper way to shoot the target for a general purpose single-illuminant profile?

I used the CC Passport software to build custom "open shade" profiles for a D700 and D800.  I processed raw files with ACR and PS CS5, viewing on a calibrated NEC PA271W.  On the D700, the results from using the profile were mixed.  In many cases my shots came out with reds, blues and purples that appear over-saturated.  On the D800 the custom profile gave better results - almost indistinguishable from the Adobe Standard profile for that camera.

Here's an interesting observation: if I load the "open shade" shot of the CC that I made with the D800 and measure the white balance of the lightest gray patch (with the WB eyedropper tool in ACR), I get about 6700K.  If I measure the white patch I get exactly 6500K (and 245/245/245).
Title: Re: Dual Illuminant Profiles
Post by: bjanes on May 13, 2012, 08:35:52 am
I read the relevant text on the Handprint web site, and I'm afraid that I am still a bit unclear on the distinctions used when referring to daylight, sunlight, and skylight.  I do understand that daytime SPD measurements vary,
I interpreted "open shade" as follows.  I shot the CC in a location that was shielded from direct sunlight, and only received light from a cloudless mid-day sky.  I tried to minimize exposure to reflected light from other sources, such as foliage.  Is this a proper way to shoot the target for a general purpose single-illuminant profile?

That sounds reasonable to me. Reflected light from other sources would not affect the results if the reflector were spectrally neutral. An ideal setup would be a skylight admitting clear blue sky with the walls painted neutral gray.

Here's an interesting observation: if I load the "open shade" shot of the CC that I made with the D800 and measure the white balance of the lightest gray patch (with the WB eyedropper tool in ACR), I get about 6700K.  If I measure the white patch I get exactly 6500K (and 245/245/245).

The white patch is not spectrally neutral, since it is difficult to make a neutral paint with high reflectance. See Bruce Lindbloom's color checker page. This is why it is recommended to white balance on the patch just to the right of the white patch.

Regards,

Bill
Title: Re: Dual Illuminant Profiles
Post by: bjanes on May 13, 2012, 09:09:46 am
The numbers are kind of meaningless in this context once you understand a boat load of colors correlate to any single kelvin value.

See: http://www.ppmag.com/reviews/200512_rodneycm.pdf

See the lines of correlated color temp that run magenta to green? Any color on that line could be specified as 6500K.

If 6500K is meanlingless, you would have a hard time making a profile using this illuminant. Rather than throwing up you hands in failure, you could use light source whose radiance is that of a black body radiator. If the radiator's emissions lie on the Planckian locus (http://en.wikipedia.org/wiki/Planckian_locus), color temperature and CCT (correlated color temperature) will be the same. For practical work, a D65 emulator is often used since daylight varies so much. One approach would be to use a wide spectrum D65 florescent lamp with a high CRI (color rendering index). Hunter labs (http://www.hunterlab.com/appnotes/an05_05.pdf) has a paper giving some useful information on CIE illuminants.

If the source lies on or close to the Planckian locus, white balance in ACR can be achieved with the temperature slider, and the tint slider slider will be at zero.

Regards,

Bill

Title: Re: Dual Illuminant Profiles
Post by: digitaldog on May 13, 2012, 12:49:07 pm
If 6500K is meanlingless, you would have a hard time making a profile using this illuminant.

First off, notice I said in ‘this context’ (that of the OP’s need to understand that an exact definition of the actual illuminant isn’t necessary or even useful/possible).

Quote
Rather than throwing up you hands in failure, you could use light source whose radiance is that of a black body radiator.

The theoretical construct** or something that is real? I’m not throwing up my hands, I’m simply stating that a great deal of this discussion is based on theoretical not real world sources.

Quote
If the radiator's emissions lie on the Planckian locus

Yes if. A big if.

Quote
One approach would be to use a wide spectrum D65 florescent lamp with a high CRI (color rendering index).

IF again you put much credence in CRI.

**http://en.wikipedia.org/wiki/Black_body
Quote
A black body is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence.

So are we talking about an exact color for the purposes of this discussion with the OP or some theoretical value? I submit the later.
Title: Re: Dual Illuminant Profiles
Post by: digitaldog on May 13, 2012, 12:53:11 pm
Certainly, the ideal method is to shoot it in the same light that falls on the subject, and to build a profile specific for the scene conditions. 

Some would like you to believe that is the case. But is it in practice? I’d like to see proof that is necessary.

Quote
But if I want to build a general purpose camera profile for daytime outdoor conditions, I need to shoot under sunlight.
 

Yes. And again, that is probably all you’ll need.

Quote
And that's where I have been reading conflicting advice.  Some sources advise shooting in direct noon sunlight.  Others recommend "open shade", but do not explain what that means.  I have also read comments that the exact conditions do not matter much.

I’d suggest that open shade and daylight are quite different but aside from those two conflicting examples, Direct noon sun, direct 2pm sun etc, you’ll be fine.

Quote
Here's an interesting observation: if I load the "open shade" shot of the CC that I made with the D800 and measure the white balance of the lightest gray patch (with the WB eyedropper tool in ACR), I get about 6700K.  If I measure the white patch I get exactly 6500K (and 245/245/245).

And there is more to all this than simply building a loading the camera profile. If you load that raw into 3 different raw converters, you get the same reported values? I suspect not.
Title: Re: Dual Illuminant Profiles
Post by: Tim Lookingbill on May 13, 2012, 05:07:24 pm
If you shoot the CC chart in the shade to build your profile from, then the camera sensor's response to the true spectral reflectance characteristics of full spectrum sunlight on each colored patch won't be recorded and measured from. We're talking major hue/saturation and luminance shifts between these two lighting situations. You can see it with your own eyes.

I haven't found one shaded environment that didn't make the gray patches go wonky from the odd color casts associated with bouncing blue light from the sky or greenish/beige from overcast clouded light or tree foliage not to mention the shifts to yellow and blue in hue and/or saturation.

Sunlight is the only light that makes the gray patches look neutral and provides even illumination and hue/sat appearance across all the patches.

You're attempting to measure the camera sensor's response with regard to color gamut and dynamic range capture capability.
Title: Re: Dual Illuminant Profiles
Post by: Schewe on May 13, 2012, 05:58:28 pm
If you shoot the CC chart in the shade to build your profile from, then the camera sensor's response to the true spectral reflectance characteristics of full spectrum sunlight on each colored patch won't be recorded and measured from. We're talking major hue/saturation and luminance shifts between these two lighting situations. You can see it with your own eyes.

Actually, that's not really true...while it's clear that there will be a difference in the white balance, the sensor's spectral response won't be all that different. As long as you are "close" (D50, D55, D65) the resulting profile will work fine. Where's it's important to control the light color when shooting targets is when doing dual-illuminate profiles. The camera's response to tungsten light will be vastly different than pretty much any sort of daylight. Ideally, you should use color accurate tungsten lighting when shooting the target.

For a given camera, a single dual-illuminate profile with daylight and tungsten will be all you really b=need for a camera. The only other profiles you may want to create are profiles for special lighting such as white-light LED (which doesn't really match daylight), fluorescent (accurate daylight bulbs will still have spectral spikes) or mercury vapor–all of which have very different spectral illumination than daylight or tungsten.
Title: Re: Dual Illuminant Profiles
Post by: Tim Lookingbill on May 13, 2012, 08:58:20 pm
Quote
...while it's clear that there will be a difference in the white balance, the sensor's spectral response won't be all that different.

I really don't understand how what I see with my eyes which clearly shows a difference in appearance of the CC chart in the shade compared to sunlight translates to what profile building software is deriving from the sensor response data captured from the CC chart under that specific light to correct for in a profile. I have to admit most of the DNG profiles I build of fluorescent and other oddball lights create profiles that don't make much of change over profiles built from full spectrum light source. Using either dual and single illuminant profiles make the biggest difference more so than the type of light shot images are captured under and the profile is applied afterward. See the sample below.

I've never made a profile from a CC chart captured in shade which doesn't seem would provide ideal light levels without higher ISO settings for decent shutter speed to be building a profile from when there's sunlight easily available. Why shoot under shade if you have sunlight?

JulianV indicated:

Quote
I used the CC Passport software to build custom "open shade" profiles for a D700 and D800.  I processed raw files with ACR and PS CS5, viewing on a calibrated NEC PA271W.  On the D700, the results from using the profile were mixed.  In many cases my shots came out with reds, blues and purples that appear over-saturated.  On the D800 the custom profile gave better results - almost indistinguishable from the Adobe Standard profile for that camera.


What's causing the over saturation? It's usually the exact opposite for me where a dual illuminant profile built from tungsten bulb and sunlight CC chart causes over saturation over a single 6500K table profile. Are these just transform errors?
Title: Re: Dual Illuminant Profiles
Post by: Schewe on May 13, 2012, 09:32:33 pm
I really don't understand how what I see with my eyes which clearly shows a difference in appearance of the CC chart in the shade compared to sunlight translates to what profile building software is deriving from the sensor response data captured from the CC chart under that specific light to correct for in a profile.

First off, the DNG profile ain't being made to profile your eyes...what you see has ZERO to do with profiling your sensor...the sensor has no white adaptation, no ability to adapt to wide dynamic ranges. It's a friggin' sensor with a single set of tri-color RGGB filters over it that dictates a certain response based on a certain illumination. Daylight is daylight. The sun is pretty consistent regardless of the atmospherics that may impact the white balance of the light. Different light sources other than daylight is not so consistent–hence the reason for doing dual-illuminate profiles. Sensors do actually have metameric failure  due to the differences in the way a sensor responds to different  spectral power distributions...daylight is daylight and tungsten is tungsten which is why it's useful to do a dual-illuminate DNG profile.
Title: Re: Dual Illuminant Profiles
Post by: Tim Lookingbill on May 14, 2012, 12:20:45 am
First off, the DNG profile ain't being made to profile your eyes...what you see has ZERO to do with profiling your sensor...the sensor has no white adaptation, no ability to adapt to wide dynamic ranges. It's a friggin' sensor with a single set of tri-color RGGB filters over it that dictates a certain response based on a certain illumination. Daylight is daylight. The sun is pretty consistent regardless of the atmospherics that may impact the white balance of the light. Different light sources other than daylight is not so consistent–hence the reason for doing dual-illuminate profiles. Sensors do actually have metameric failure  due to the differences in the way a sensor responds to different  spectral power distributions...daylight is daylight and tungsten is tungsten which is why it's useful to do a dual-illuminate DNG profile.

We're not just talking about frickin' white balance, bud. We're talking about what characteristics are inherent within an illuminant that seems to have to be profiled for how an RGGB sensor reacts to it.

What's so specific about an illuminant A,B,C,D,E,F,G,H,I,J,K whatever the hell these color scientists are describing that needs to be measured and corrected for in a profile.

You don't seem to be able to make it make sense even in your terse A-hole style response.
Title: Re: Dual Illuminant Profiles
Post by: Tim Lookingbill on May 14, 2012, 12:43:02 am
Here's the single 6500K illuminant profile I made from a spectrally spikey "5500K" Ottlite CFL. Not much difference from the single 6500K illuminant made from full spectrum sunlight posted above.

Title: Re: Dual Illuminant Profiles
Post by: Schewe on May 14, 2012, 01:55:16 am
What's so specific about an illuminant A,B,C,D,E,F,G,H,I,J,K whatever the hell these color scientists are describing that needs to be measured and corrected for in a profile.

Standard Illuminate A is about 2856 K...However, the R, G, G, B tri-color Bayer array of a lot (most) of sensors are tuned to "daylight" which has a full spectrum between 400nm (ultraviolet) and 700nm (infrared).

The problem with spectral illumination that has different relative amounts of colored light that is different than daylight is that the tri-color photosite filters vary considerably in efficiency...so while the blue of a tricolor filter may pass enough photons to make a reasonable RGB color image under daylight, that same blue filter may block most if not almost all blue light when shooting under tungsten because first of all, tungsten has a lot of IR (which sensors are more sensitive to) and very little blue light component. This leads to far more noise because of less blue light and a real difficulty in demosaicing because of the blue photosite color errors. So, the spectral response of a sensor will vary considerably based upon the spectral distribution of various colors of light. Which is why it's a good idea to profile under both daylight and tungsten...and any other really odd light source (but not waste your time profiling every potential light source).

Sensors are very sensitive to IR and almost blind to UV (which is why it's stupid to stick a UV filter on a lens for a digital camera). The exact formula for filtering for a tri-color filter separation is a tweaky thing. The designers must design the sensor system for the most reasonable expectation which is daylight. Hence various colors of daylight will be well profiled using a D-50 thru D-65 daylight standard. Whether you have more sun vs. skylight is not an issue for profiling a sensor's daylight response, it's an issue for white balance.

With tungsten which has far more IR and whose red tri-color filter may let in more or too much red/IR light and not nearly enough blue light, you have a totally different sensor response. Hence the metameric failure or inability to profile a sensor under daylight and use it reliably for tungsten.

ACR/LR "tweens" white balance between the Standard Illuminate A (2856K) and D-65. The closer you are to either end of the spectrum, the more the ACR/LR white balance must adjust for the interpolation between the two ends of the white balance scale.

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You don't seem to be able to make it make sense even in your terse A-hole style response.

If I'm not making sense, there is two potential reasons, either I'm not making myself clear or you do not understand the fundamentals...but nothing I've written in this thread is my typical "A-hole" you friggin' idiot (see, you wanna push my buttons, I'll respond) I'm just rying to explain why it's important to do a dual-illuminate profile for daylight and tungsten or other weird light sources which may be spiky and incomplete with their full spectrum of light...

And yes, if you understood the way sensors respond to light you would realize the vast majority of the color corrections issues are white balance, not DNG profiles.
Title: Re: Dual Illuminant Profiles
Post by: mac_paolo on May 14, 2012, 02:56:52 am
ACR/LR "tweens" white balance between the Standard Illuminate A (2856K) and D-65. The closer you are to either end of the spectrum, the more the ACR/LR white balance must adjust for the interpolation between the two ends of the white balance scale.
...that leads me to a conclusion where Adobe should have really said: take a photo under mid-watt tungsten bulb and another one under daylight.
Everything else is overkill.
Maybe custom DNG profiles for insane artificial lights are the ones where we should put more efforts. :)
Title: Re: Dual Illuminant Profiles
Post by: julianv on May 14, 2012, 04:26:27 am
Some would like you to believe that is the case. But is it in practice? I’d like to see proof that is necessary.

OK, my statement was obviously too simplistic. Building a profile specific for every scene condition is overkill, except perhaps for those who suffer from OCD (obsessive color-calibration disorder).  :)

I'm trying to sift through the heavy tech talk, to come up with a plan for building a general purpose dual-illuminant profile.  So far, I've gathered the following.  Please correct me, if I am going astray.

1) Make one shot of the CC target under daylight.  Shooting in either direct sunlight or open shade are both acceptable.

2) Make another shot of the target under color correct incandescent light.  I'm assuming that a 3500K Solux is OK for this.  Better to use a lower K?

About a year ago, I created a web gallery (http://julianv.zenfolio.com/p564329719) to compare the variations in color rendition produced by using Adobe's canned profiles, or a custom single-iluminant profile built with CC Passport.  The sample photos were taken with a Nikon D700, and converted with ACR 6.4.  If you visit this page, you can expand your browser window to get the largest image size, and use keyboard right/left arrow keys to switch quickly between images.  To my eyes, the color differences were mostly significant in the blues and reds, which became significantly more saturated with the custom profile. The results were acceptable for these test shots, but were sometimes over-the-top with other images.  Are these results typical?  As noted in my earlier post, the profile that I built for a D800 was much closer to Adobe Standard.
Title: Re: Dual Illuminant Profiles
Post by: Nigel Johnson on May 14, 2012, 07:04:57 am
About a year ago, I created a web gallery (http://julianv.zenfolio.com/p564329719) to compare the variations in color rendition produced by using Adobe's canned profiles, or a custom single-iluminant profile built with CC Passport.  The sample photos were taken with a Nikon D700, and converted with ACR 6.4.  If you visit this page, you can expand your browser window to get the largest image size, and use keyboard right/left arrow keys to switch quickly between images.  To my eyes, the color differences were mostly significant in the blues and reds, which became significantly more saturated with the custom profile. The results were acceptable for these test shots, but were sometimes over-the-top with other images.  Are these results typical?  As noted in my earlier post, the profile that I built for a D800 was much closer to Adobe Standard.

Julian

If I remember correctly the CC Passport software tends to produce more saturated images than the automatic profiles generated by the Adobe DNG Profile Editor (DNG PE) - some people prefer one and some the other. I don't know if you have tried the DNG PE but you can use it on the same profiling images used with the CC Passport software and can generate both single and dual illuminant profiles. The DNG PE is available free from Adobe Labs at http://labs.adobe.com/wiki/index.php/DNG_Profiles (http://labs.adobe.com/wiki/index.php/DNG_Profiles).

Nigel

PS The DNG PE is due to be updated to allow editing of the latest DNG profiles, however the current version can still generate profiles that can be used with the latest versions of LR or ACR.
Title: Re: Dual Illuminant Profiles
Post by: bjanes on May 14, 2012, 07:58:02 am
Standard Illuminate A is about 2856 K.

...ACR/LR "tweens" white balance between the Standard Illuminate A (2856K) and D-65.

I'm just trying to explain why it's important to do a dual-illuminate profile for daylight...

Jeff,

In the context of photometry, illuminate (http://dictionary.reference.com/browse/illuminate) is a verb. The noun is illuminant. According to the above linked reference, illuminate used as noun refers to a person who is or affects to be specially enlightened.

Just a bit of constructive criticism.

Regards,

Bill
Title: Re: Dual Illuminant Profiles
Post by: digitaldog on May 14, 2012, 09:29:50 am
Maybe custom DNG profiles for insane artificial lights are the ones where we should put more efforts. :)

That has been my experience. I’m sure others will pipe in.
Title: Re: Dual Illuminant Profiles
Post by: Tim Lookingbill on May 14, 2012, 12:19:03 pm
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With tungsten which has far more IR and whose red tri-color filter may let in more or too much red/IR light and not nearly enough blue light, you have a totally different sensor response. Hence the metameric failure or inability to profile a sensor under daylight and use it reliably for tungsten.

So the richer, deeper looking red of the tomato and overall slightly increased saturation using the dual illuminant profile is intended as an attempt to compensate the metameric failure of the dull, orangish looking red caused by the orangy yellow tungsten light?

I'm trying to distinguish the way my camera records the real affects of light on an object from how the software interprets it and whether the unexpected results in the preview is intended or metameric failure and whether it should be fixed in front of the camera or in post for better workflow efficiency. Color science jargon often does not effectively connect the dots in explaining the results we get in our previews.

I have to rely on my observations of how sunlight (not mixed skylight) tends to make objects more vibrant and well defined over any other type of light. And so I have to assume color science is aware of this behavior as well but often find it doesn't make clear when color goes wrong.

You say friggin', I say frickin', no big whoop. Consider both our buttons pushed.

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About a year ago, I created a web gallery to compare the variations in color rendition produced by using Adobe's canned profiles, or a custom single-iluminant profile built with CC Passport.  The sample photos were taken with a Nikon D700, and converted with ACR 6.4.  If you visit this page, you can expand your browser window to get the largest image size, and use keyboard right/left arrow keys to switch quickly between images.  To my eyes, the color differences were mostly significant in the blues and reds, which became significantly more saturated with the custom profile. The results were acceptable for these test shots, but were sometimes over-the-top with other images.  Are these results typical?  As noted in my earlier post, the profile that I built for a D800 was much closer to Adobe Standard.

Most of the differences I see in your parade shot is similar to what I demonstrated in the food shot where I artificially made the gray plate look blue while maintaining warmth in the food which is my understanding of how to demonstrate the effects of color constancy.

Note in your Camera Standard shot the street highlight sheen is greenish while the darker parts are bluish while maintaining R=G=B white while the others tweak this and mostly maintain the same hue/sat appearance in the vibrant primary colors while making the street all neutral or all green. I can see slight tweaks to warm hues in the skin tone of the woman upfront far right.

Which version is derived from the real response of the camera sensor or just software/profile tweaks is anyone's guess. All four look fine.
Title: Re: Dual Illuminant Profiles
Post by: sandymc on May 14, 2012, 12:57:29 pm
This seems to be causing huge confusion - it may be helpful to understand how "dual illuminants" are actually used in processing:

In concept, processing from camera to finished image is in two steps:

Step 1: Convert from sensor readings (aka raw data) to "absolute" color values, in principle in an XY-type space. Critical point is that these are "absolute" values; they depend on the actual color of the light - the wavelength. So in the situation where you shine a tungsten light on a white sheet of paper, what you're measuring is the color of the tungsten light, not that the sheet of paper is white.

Step 2: Convert the absolute (XY) light values to something humans recognize - this is the white balance step, taking into account the fact that the light was tungsten, and adjusting the color of the sheet of paper in the final image to be white, white being what we see.

Dual illuminates are ONLY used in step 1 - they're just a way of better interpreting what the raw data converts to in XY type values. Dual illuminants play no role in step 2. They might give you a slightly better white balance, but that's only because they delivered a better measure of what the light reflected off various parts of the scene was, not because they're playing any role in white balance process.

Put another way, if the sensor in your camera was perfect, dual illuminants would make no difference at all. What they do is allow the software to better estimate what the scene actually looked like from what an imperfect sensor measured.

The reason why Adobe recommends D65 as an end-stop is probably just because that's where color temperatures pretty much cease to make sense as a practical photographic measure. Anything "more blue" is likely not a continuous spectrum light source.

Here's what I'd recommend:

1. For scenes lit by something with a continuous spectrum (daylight, tungsten lights), dual illuminant profiles make good sense, basically because color temperature makes sense for those lights.

2. For lights that don't have approximately continuous spectrums (sodium vapor, some fluorescents, etc) dual illuminant profiles won't really help, because color temperature starts to be fairly useless in isolation - to get a good while balance, you're going to need tint as well. So if the image is important, create a single illuminant profile with that light source.

Finally, bear in mind that dual illuminant profiles are just an optimization - so far as I am aware, no other camera company/raw developer has found the improvement compelling enough to adopt the idea.

Sandy

Title: Re: Dual Illuminant Profiles
Post by: digitaldog on May 14, 2012, 01:20:18 pm
So in the situation where you shine a tungsten light on a white sheet of paper, what you're measuring is the color of the tungsten light, not that the sheet of paper is white.
If I understand what you’re saying, this would be akin to measuring the color of the light with say an EyeOne Pro using ambient head. IOW, you’re mesuring just the light, not the effect of the paper.
Title: Re: Dual Illuminant Profiles
Post by: sandymc on May 14, 2012, 01:50:40 pm
If I understand what you’re saying, this would be akin to measuring the color of the light with say an EyeOne Pro using ambient head. IOW, you’re mesuring just the light, not the effect of the paper.

Exactly so.

Sandy
Title: Re: Dual Illuminant Profiles
Post by: Schewe on May 14, 2012, 03:29:44 pm
Finally, bear in mind that dual illuminant profiles are just an optimization - so far as I am aware, no other camera company/raw developer has found the improvement compelling enough to adopt the idea.

Do you mean other companies don't think it's worth it or don't know how to do it? As far as I can tell, the concept of using two profiles for two different illuminants is somewhat unique to ACR...other companies understand that different profiles are needed for daylight and tungsten though. For example Phase One provides separate daylight (actually multiple flavors) and tungsten (multiple flavors) of ICC camera profiles. Capture One simply doesn't try to tween between them and requires the user to select the correct single profile to use. The white balance comes AFTER the correct profile is selected.
Title: Re: Dual Illuminant Profiles
Post by: sandymc on May 14, 2012, 03:42:26 pm
Do you mean other companies don't think it's worth it or don't know how to do it? As far as I can tell, the concept of using two profiles for two different illuminants is somewhat unique to ACR...other companies understand that different profiles are needed for daylight and tungsten though. For example Phase One provides separate daylight (actually multiple flavors) and tungsten (multiple flavors) of ICC camera profiles. Capture One simply doesn't try to tween between them and requires the user to select the correct single profile to use. The white balance comes AFTER the correct profile is selected.

Hi Jeff,

Given that everything anybody might ever want to know about dual illuminate profiles is in the DNG spec, I'd say its "don't think its worth it". Separate profiles are quite common - I don't think that anyone would argue with their place. Temperature based interpolation  - well, if it involves rewriting your core processing algos it would need to deliver something pretty substantial, and I think (maybe wrongly) that the industry consensus is that clever idea though it may be, the cost doesn't justify the difficulty.

But that's just my outside-looking-in perspective.

Regards,

Sandy

Title: Re: Dual Illuminant Profiles
Post by: Tim Lookingbill on May 14, 2012, 05:40:43 pm
Sandy, what is your take on the tweaks to neutrals and primaries in julianV's image gallery profile comparison I described above? Clearly the color tables are being manipulated separately from R=G=B white in the parade image.

I wonder what the engineers measured from or based their tweaks in building Camera Standard and other canned profiles. The thing is the changes between the profiles are so subtle I can't figure why the profiles were necessary if just to attempt to copy the manufacturer's color rendering. Or maybe it's just more evident in that particular parade image.
Title: Re: Dual Illuminant Profiles
Post by: Schewe on May 14, 2012, 06:11:31 pm
Temperature based interpolation  - well, if it involves rewriting your core processing algos it would need to deliver something pretty substantial, and I think (maybe wrongly) that the industry consensus is that clever idea though it may be, the cost doesn't justify the difficulty.

I don't disagree that it is/was difficult but when you have a guy like Thomas Knoll and his sidekick Eric Chan, "difficult" takes on a new meaning, ya know? What may be very difficult for some isn't always so difficult for others.

And I do agree that other app developers who didn't try temperature based profile interpolation when they were developed would find it very difficult to re-write their apps to do so. There was a lot of discussion at the time when ACR was released WHY Thomas didn't use ICC camera profiles and part of his reasoning (as I recall) was that it made temperature based profile interpolation very difficult :~)
Title: Re: Dual Illuminant Profiles
Post by: 32BT on May 14, 2012, 07:17:02 pm
Finally, bear in mind that dual illuminant profiles are just an optimization - so far as I am aware, no other camera company/raw developer has found the improvement compelling enough to adopt the idea.

They are not an "optimization", they are a "convenience". They are specific to Adobe's contorted way of processing, and should therefore never have been part of the DNG specs.
Title: Re: Dual Illuminant Profiles
Post by: 32BT on May 14, 2012, 07:19:11 pm
There was a lot of discussion at the time when ACR was released WHY Thomas didn't use ICC camera profiles and part of his reasoning (as I recall) was that it made temperature based profile interpolation very difficult :~)

Would be interesting to know what the exact logic was behind that thinking. If you could ask him, that would be nice. As stated, it makes no sense.
Title: Re: Dual Illuminant Profiles
Post by: 32BT on May 14, 2012, 07:27:13 pm
I would additionally like to add:

For very rough reference in order of temp:

tungsten or sunset: <3000K (very warm red tint)
sunny: ~5500K
cloudy (white): ~6500K
cloudy (gray): ~7500K
shade: as high as 10000K (very cold blue tint)

Therefore, if "open shade" means Cloudy with white clouds, then, yes, that would be the preferred condition for shooting the target.
if "open shade" means something else, then it is not the best condition. Neither is sunny…

And also: the Original Gretag MacBeth used to be "directionally sensitive". The color changed based on the direction of the incident light. It would therefore be useful to rotate the target and combine several shots. I don't know whether the current crop of color checkers still suffer this problem. I also don't know in how far this affects the results of any profiling solution…


Title: Re: Dual Illuminant Profiles
Post by: Tim Lookingbill on May 14, 2012, 07:53:55 pm
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Therefore, if "open shade" means Cloudy with white clouds, then, yes, that would be the preferred condition for shooting the target.
if "open shade" means something else, then it is not the best condition. Neither is sunny…

Can you prove (with images) what happens to the color rendering applying a camera profile built from a CC chart lit from sunny, open shade or suboptimal lighting condition compared to optimal white cloudy conditions?
Title: Re: Dual Illuminant Profiles
Post by: 32BT on May 14, 2012, 08:08:20 pm
Can you prove (with images) what happens to the color rendering applying a camera profile built from a CC chart lit from sunny, open shade or suboptimal lighting condition compared to optimal white cloudy conditions?

Yes, but only for my own profiling solution for my own RAW converter. I obviously have no idea what other applications are doing in this respect. Given that there are at least 3 aspects involved:

1. the profiling application which creates the profiles
2. the raw converter which uses the profiles
3. the raw conversion procedure which applies the profiles

Since 1 en 3 are usually different applications, from different manufacturers, I have no idea whether it even makes sense to try and mess with the profiles as provided by the manufacturer. But, if people here ask what the preferred lighting condition is for D65, and the answer is "open shade" then the previously mentioned table may help limit any confusion.
Title: Re: Dual Illuminant Profiles
Post by: julianv on May 14, 2012, 08:52:21 pm
Sandy, what is your take on the tweaks to neutrals and primaries in julianV's image gallery profile comparison I described above? Clearly the color tables are being manipulated separately from R=G=B white in the parade image.

I wonder what the engineers measured from or based their tweaks in building Camera Standard and other canned profiles. The thing is the changes between the profiles are so subtle I can't figure why the profiles were necessary if just to attempt to copy the manufacturer's color rendering. Or maybe it's just more evident in that particular parade image.

Let me add a brief comment, just in case some people are wondering why I adjusted exposure when converting the files in that gallery.  This was a year ago, so my recollections are a bit fuzzy.  There was a point in time when Adobe's Camera Standard profile for the D700 was optimized to work best with a +3ev adjustment to exposure.  So I fiddled with exposure to get the images matched at a neutral mid tone.  I was only interested in comparing color effects.  Unfortunately, I don't have my notes on this anymore, and I don't remember which ones were adjusted which way.

I believe that the recent Camera Standard profiles do not require an exposure adjustment.
Title: Re: Dual Illuminant Profiles
Post by: julianv on May 15, 2012, 03:44:05 am
I wonder what the engineers measured from or based their tweaks in building Camera Standard and other canned profiles. The thing is the changes between the profiles are so subtle I can't figure why the profiles were necessary if just to attempt to copy the manufacturer's color rendering. Or maybe it's just more evident in that particular parade image.

Just a heads-up, in case you did not read the notes in the intro page of that gallery.  Those images are tagged with AdobeRGB.  To get the best view of the color differences, you need to be using a color-managed browser, and a calibrated wide-gamut display.  Better yet, download the files (use the "Share" link) and view offline.  Web sites and browsers sometimes mess with the colors.  Anyway, some of those files differ to a degree that I would not describe as "subtle."  It's particularly obvious when comparing Adobe's Camera Standard and the CC Passport "open shade" profiles (although some of that difference may be due to different tone curves).

By the way, I have another D700 custom profile from CC Passport that was made under direct mid-day sunlight.  I did not put images made with that profile up on the web gallery.  What I see is that the reds and blues become even more saturated than they appear when converted with the "open shade" profile.
Title: Re: Dual Illuminant Profiles
Post by: sandymc on May 15, 2012, 05:44:42 am
Sandy, what is your take on the tweaks to neutrals and primaries in julianV's image gallery profile comparison I described above? Clearly the color tables are being manipulated separately from R=G=B white in the parade image.

I wonder what the engineers measured from or based their tweaks in building Camera Standard and other canned profiles. The thing is the changes between the profiles are so subtle I can't figure why the profiles were necessary if just to attempt to copy the manufacturer's color rendering. Or maybe it's just more evident in that particular parade image.

I would guess, and I think that what Julian has said supports, that the differences are more in the color tables and small differences in exposure than in the dual illuminant stuff. The issue with LR3 and later is that there are hue twists in the Adobe profiles, and content-aware processing going on later in the chain. All of those mean that quite small changes in exposure, black level, etc can have an out of proportion effect, so its really difficult to isolate what exactly caused a change without a whole lot of painfully detailed experimentation.

Sandy
Title: Re: Dual Illuminant Profiles
Post by: sandymc on May 15, 2012, 05:52:33 am
There was a lot of discussion at the time when ACR was released WHY Thomas didn't use ICC camera profiles and part of his reasoning (as I recall) was that it made temperature based profile interpolation very difficult :~)

Yes. Although I think there were also other considerations. E.g, ICC profiles have no clue about CFAs, sensor calibration, etc. So in order to encapsulate all the information you needed to decode an image, you'd need an ICC profile plus something else. Something else being either another file, or embedding private data in the ICC profile. But if standard parts of the ICC profile can't represent everything you need, then why bother with it? Better to a custom container that's designed for purpose. DNG Camera Profiles do have the advantage over ICC profiles that they use EXIF formatting, and every raw converter already can decode EXIF, so they're easy to add.

Sandy
Title: Re: Dual Illuminant Profiles
Post by: 32BT on May 15, 2012, 11:35:22 am
Yes. Although I think there were also other considerations. E.g, ICC profiles have no clue about CFAs, sensor calibration, etc. So in order to encapsulate all the information you needed to decode an image, you'd need an ICC profile plus something else.

No, you don't.

Something else being either another file, or embedding private data in the ICC profile. But if standard parts of the ICC profile can't represent everything you need, then why bother with it? Better to a custom container that's designed for purpose.

That's the kind of thinking that results in tons of proprietary RAW formats no?

You should be aware that there have been a lot of very smart people working on the ICC standard, smarter than Thomas and Eric combined, dare I say? And there is a lot of solid color science behind the technology and thinking in ICC profiles. It is useful to stick to that standard initially in the same way that it is useful to consider that most color-correction requirements are attributable to white-balancing in the vast majority of the cases.

Stick to the basics initially, then further down the pipeline you can always give users the opportunity to eff it up again.

DNG Camera Profiles do have the advantage over ICC profiles that they use EXIF formatting, and every raw converter already can decode EXIF, so they're easy to add.

If that would be even remotely a consideration in development, then it's useful to know that the ICC profiles use TIFF formatting…
Title: Re: Dual Illuminant Profiles
Post by: Tim Lookingbill on May 15, 2012, 11:42:59 am
Just a heads-up, in case you did not read the notes in the intro page of that gallery.  Those images are tagged with AdobeRGB.  To get the best view of the color differences, you need to be using a color-managed browser, and a calibrated wide-gamut display.  Better yet, download the files (use the "Share" link) and view offline.  Web sites and browsers sometimes mess with the colors.  Anyway, some of those files differ to a degree that I would not describe as "subtle."  It's particularly obvious when comparing Adobe's Camera Standard and the CC Passport "open shade" profiles (although some of that difference may be due to different tone curves).

By the way, I have another D700 custom profile from CC Passport that was made under direct mid-day sunlight.  I did not put images made with that profile up on the web gallery.  What I see is that the reds and blues become even more saturated than they appear when converted with the "open shade" profile.

julian, I viewed the parade images in color managed Safari. That's not the issue anyway. When I say subtle differences I'm referring to the lack of extreme overall off balance of color appearance. You have no blooming and loss of detail in the saturated primaries.

My tomato image is a demonstration of these extremes showing the dual illuminant's deepening and added magenta hue over the single illuminant's original orangish red tomato rendering which I find both aesthetically pleasing over whether they're accurate. My line of questioning to be to the point in this discussion is finding out if these are intended hue shifts through the software's interpretation of the spectral characteristics of the scene recorded by the sensor or possible metameric failure caused by tungsten light's weak blue spectrum as Jeff pointed out.

The level of saturation you should be gauging as in the parade image should be based on whether the profile causes detail to be lost in the form of posterization through "blooming". I don't see that happening in any version of your parade image. I get much worse blooming using a dual illuminant profile but easily fix by switching to single illuminant in similarly lit shots as yours. See the orange flower demo below.

But the one thing about dual illuminant profiles I can't live without is the way they maintain hue/sat levels over a wider range of colors shot under all kinds of oddball lights which I can easily fix pushing the WB slider to extreme ends as I demonstrated in the bluish WB of the tomato image. If that doesn't work I switch to Adobe Standard which neutralizes the entire tonal scale of the image where I have to adjust WB, usually the Green/Magenta tint slider.
Title: Re: Dual Illuminant Profiles
Post by: digitaldog on May 15, 2012, 11:48:06 am
You should be aware that there have been a lot of very smart people working on the ICC standard, smarter than Thomas and Eric combined, dare I say?

I don’t want to say one is ‘smarter’ than the other but a really smart fellow, Eric Walowit who happens to be on the ICC digital photo committee has for years had a very interesting idea of how to do this with current ICC profile technology. It isn’t easy in that we’d need a small Spectrophotometer of similar device built into the camera to measure the illuminant of the scene and we’d need the spectral characteristics of the sensor and we’d have to write this as metadata into the raw data to build an on the fly profile.

This public post by Eric on the ColorSync user list in 2008 might be useful (I find any post by Eric has some useful information):

Quote
Subject:    Camera profiling with ICC et al
Date:    September 11, 2008 9:07:42 AM MDT


Chris, Edmund, Uli, Eric, and others,

Forgive me for coming into this thread late. I've been very remote and will
be again till next week. A couple comments:
1) I have the new camSpecs monochromator from Image Engineering designed
specifically for profiling by measuring camera spectral sensitivities out to the
near IR. Compared to lab-grade monos, its fast, inexpensive, repeatably, and
easy. I have no financial affiliation with IE except that I am a happy customer
and helped design it. I have measured all my cameras, compared the results to
lab-grade monos, and obtained very similar results. I've not seen near IR
issues with any recent cameras.
2) Once the camera spectral sensitivities, linearity, training data, etc. are
known then it is a simple and very accurate matter to determine the optimal
profile for any given illumination.
3) However, an ICC profile can only handle one illumination condition at a
time, though this does not preclude mixed (though not spatially varying in terms
of SPD) illumination if it is adequately characterized. This is a limitation
of ICC, though it is easily circumvented by building and embedding profiles
on-the-fly based on the scene illumination metadata or precomputing and storing
multiple profiles.
4) In my understanding, fundamentally, it is the latter approach that
underpins and is an advantage of Adobe's method compared with a
single-illumination-only ICC profile. Though Adobe doesn't use the ICC-wrapper, the Adobe profile
data itself is fundamentally similar (and probably not incompatible with some
massaging) to using multiple well-constructed ICC profiles. Adobe should be
commended for their approach, not berated.
5) Assuming that rendering from scene-referred to output-referred is turned
off (frequently not an easy assumption to check) it takes a very carefully
designed, controlled, and executed experiment to objectively evaluate the profile,
Adobe, ICC or otherwise. Much of what I have seen described here is simply
inadequate for validating profile quality.
Thanks,
Eric Walowit
Tahoe
Title: Re: Dual Illuminant Profiles
Post by: sandymc on May 15, 2012, 11:57:56 am
No, you don't.

Ok, I'll bite on that bait ;D

Where would you put e.g., the bayer green split, to randomly select my least favorite part of the DNG camera profile?

Sandy
Title: Re: Dual Illuminant Profiles
Post by: 32BT on May 15, 2012, 01:32:06 pm
This public post by Eric on the ColorSync user list in 2008 might be useful (I find any post by Eric has some useful information):


Yes, but what is described there seems like overkill for most users. As a photographer, we generally don't want to *correct* the on-scene lighting conditions, instead we want to capture the mood of the on-scene lighting.

If I am in a forest with a lot of green light surrounding me, I generally want to preserve the green light, not completely correct it out of the image. Or if I capture a sunset scene, I generally want to preserve the warm colors dominating the atmosphere. While it would be useful to know the character of the light so I can correct it, perhaps just partially, we already know that that can be done quite adequately using tri-color profiles, and mostly very basic whitebalance tricks like a graycard or a white plastic lenscap/cup .

And the sunset example would be my preferred example to show that dual-illuminant profiles are merely a convenience, and may be confusing the actual capture process: i.e. we want to capture the atmosphere of a low temp scene by selecting the normal daylight response and only correcting the graybalance partially.

Whether this "normal daylight" response + graybalance correction is adequate under most circumstances, even tungsten, is indeed an interesting question. IIRC Magne Nilssen was the original creator of the capture one profiles, and he used to mention something to that effect in posts at the time.
Title: Re: Dual Illuminant Profiles
Post by: digitaldog on May 15, 2012, 01:34:23 pm
Yes, but what is described there seems like overkill for most users. As a photographer, we generally don't want to *correct* the on-scene lighting conditions, instead we want to capture the mood of the on-scene lighting.

I don’t know Eric is trying to correct anything but rather initially describe. This is supposed to work in a raw converter which doesn’t circumvent rendering to taste.
Title: Re: Dual Illuminant Profiles
Post by: 32BT on May 15, 2012, 01:56:24 pm
Can you prove (with images) what happens to the color rendering applying a camera profile built from a CC chart lit from sunny, open shade or suboptimal lighting condition compared to optimal white cloudy conditions?

Just for illustrative purposes, I have attached a profiling example for Sunny daylight condition in my own calibrator.

Image 1 shows the result of combining 4 shots of the color checker rotating it 90degr. each time.
Image 2 show a single rotation sample, where the both the skin tone patch as well as the dark gray patch show significant deviation.

I'll try to find the cloudy daylight version as well, or some other version for comparative purposes. I have to immediately add that the resulting profiles were calculated based on variable blackpoint, which is not a useful method for Canon camera's. (One of the very important steps to consider in the entire processing pipeline, with significant effect on the end result).
Title: Re: Dual Illuminant Profiles
Post by: 32BT on May 15, 2012, 02:13:50 pm
I don’t know Eric is trying to correct anything but rather initially describe. This is supposed to work in a raw converter which doesn’t circumvent rendering to taste.

I understand. Using a monochromator for characterizing a camera may be useful. Capturing an on-scene spectrum currently has little or no meaning, neither for image processing, nor for the photographer.

Just to think about it without going too much into technical detail, but if you capture an on-scene spectrum, does it represent the scene average, weighted average, or perhaps point metering value? Does that point-metering value represent the actual light, the on-scene lighting condition, something else? Can the resulting spectrum or its derived tri-color be used for gray balancing? Would it yield a different result if the tri-color was derived by conventional methods?

Would a photographer that actual needed such precision perhaps be helped by simply carrying a spectrophoto meter?

I'm just wondering. I'm not in particular questioning what Eric W and the others are developing here. Do you know the current status of those developments are?

Title: Re: Dual Illuminant Profiles
Post by: digitaldog on May 15, 2012, 02:43:25 pm
Capturing an on-scene spectrum currently has little or no meaning, neither for image processing, nor for the photographer.
No but I think Eric is using that to build a unique on-the-fly profile using that data. That and the spectral sensitivities of the chip are key to his creating this ‘profile’ of camera+scene if I’m explaining his concept correctly. The photographer doesn’t have any access to this metadata nor do they need it.

Quote
Do you know the current status of those developments are?
I’m sure it has been proposed through the ICC and the committee Eric is on but other than that, I don’t know that anything as progress since that post 4 years ago. Heck, look how long we’re waiting on actual V4 ICC support.
Title: Re: Dual Illuminant Profiles
Post by: Tim Lookingbill on May 15, 2012, 03:29:30 pm
Oscar, I saw your "Sunny" lit CC chart samples and I have to say your camera and/or your ACR/LR settings are definitely different compared to the results I get working with my Pentax K100D DSLR. I don't have your skin tone and neutral gray issues using a sunlit CC chart source to build my profile.

The biggest problem I have in getting low Delta E readings applying the final profile to the source CCchart primarily centers around contrast induced saturation issues amplified by using ACR's default settings of Medium Tone Curve and 25 Contrast. Luminance goes off by as much as 7L, some less than others, on almost all patches.

I have to pick either setting Contrast to '0' or setting Medium Tone Curve to Linear but not both to get more accurate Luminance numbers.
Title: Re: Dual Illuminant Profiles
Post by: mac_paolo on May 25, 2012, 07:16:43 pm
I'm trying to chose which one is better to create a DNG profile between Xrite's Lightroom plugin and DNG Profile Editor by Adobe.
They are so different in color rendition. The whole "calibration" term doesn't seem to fit well. I mean, how can the both be valid profiles?  ::)

Here they are...

#1
-removed-

#2
-removed-

Which one do You think is the most accurate? I'll keep my opinion for the last. :)
Title: Re: Dual Illuminant Profiles
Post by: sandymc on May 26, 2012, 02:41:10 am
I'm trying to chose which one is better to create a DNG profile between Xrite's Lightroom plugin and DNG Profile Editor by Adobe.
They are so different in color rendition. The whole "calibration" term doesn't seem to fit well. I mean, how can the both be valid profiles?  ::)

Which one do You think is the most accurate? I'll keep my opinion for the last. :)

White balance is different between the two shots; no way to compare.

Sandy
Title: Re: Dual Illuminant Profiles
Post by: mac_paolo on May 26, 2012, 03:02:09 am
White balance is different between the two shots; no way to compare.

Sandy
I'm pretty sure I set the WB for both of the version by clicking on the second grey patch from left.
I'll check again later. :)
Title: Re: Dual Illuminant Profiles
Post by: mac_paolo on May 26, 2012, 03:25:35 am
White balance is different between the two shots; no way to compare.

Sandy
You're right. The first one way quite a bit off balance.
I regenerated the AdobeRGB preview and reimported right away into Lightroom. Trying to re-balance the previews I found that they where still a bit off, but nothing to worry about.

#1  (Temp: 2500 K, Tint: +15)
(http://cl.ly/3W3r2o2H3N1E1p1N002Z/cc%20xrite.jpg)

#2  (Temp: 2550 K, Tint: +15)
(http://cl.ly/1t3t3d1i330p3E3R2q21/cc%20dng-pe.jpg)

Which one do you prefer, now? :)
Title: Re: Dual Illuminant Profiles
Post by: sandymc on May 26, 2012, 04:02:50 am
Which one do you prefer, now? :)

Well, "prefer" is personal choice. I can tell you that the second one is technically much more accurate compared to a synthetic GM24 image. Especially in the reds.

Sandy
Title: Re: Dual Illuminant Profiles
Post by: mac_paolo on May 26, 2012, 05:04:02 am
Well, "prefer" is personal choice. I can tell you that the second one is technically much more accurate compared to a synthetic GM24 image. Especially in the reds.

Sandy
The term "prefer" comes from the fact that none is perfect, but one is more similar to the target than the other.
I agree with you: the second one is better.
#1 -> Xrite Plugin
#2 -> DNG Profile Editor

I didn't expect so much difference here. I relied a lot to the easier Xrite solution. I'll rebuild all the profiles in the double flavor and make a choice.
I still have to test the dual illuminant DNG Profile, but for the single illuminant, DNG Profile Editor is my choice.
Title: Re: Dual Illuminant Profiles
Post by: Schewe on May 26, 2012, 03:26:26 pm
I didn't expect so much difference here. I relied a lot to the easier Xrite solution. I'll rebuild all the profiles in the double flavor and make a choice.

The X-rite solution is fast and easy, the DNG Profile Editor is geeky and complicated but more powerful and in my experience more "accurate"...but either solution is better than using one of the canned DNG profiles _IF_ your particular camera is different than the one Adobe tested to make the DNG profiles for ACR/LR.

Personally, there have only been a couple of times I have _HAD_ to make DNG profiles and they were done because the camera back I was using only had "preliminary" support in ACR/LR.

I have used DNG Profile Editor more than the Passport software. When I was doing the profiles for my P-65+ back, the Passport software couldn't accept the 60 MP P-65+ capture-it hung.m So, I used the DNG Profile Editor.

I've used the editor to tweak some profiles and make some specialty profiles but for most of my cameras I really don't feel the need to use anything other tan Adobe Standard...
Title: Re: Dual Illuminant Profiles
Post by: mac_paolo on May 26, 2012, 03:37:12 pm
The X-rite solution is fast and easy, the DNG Profile Editor is geeky and complicated but more powerful and in my experience more "accurate"...but either solution is better than using one of the canned DNG profiles _IF_ your particular camera is different than the one Adobe tested to make the DNG profiles for ACR/LR.

Personally, there have only been a couple of times I have _HAD_ to make DNG profiles and they were done because the camera back I was using only had "preliminary" support in ACR/LR.

I have used DNG Profile Editor more than the Passport software. When I was doing the profiles for my P-65+ back, the Passport software couldn't accept the 60 MP P-65+ capture-it hung.m So, I used the DNG Profile Editor.

I've used the editor to tweak some profiles and make some specialty profiles but for most of my cameras I really don't feel the need to use anything other tan Adobe Standard...
I agree and thanks for the response. I tested 4 different artificial light settings, i.e. four rooms in my home :)
There are mixed light with tungsten, alogen and God only know what else. The Adobe Standard was way off each and every single time.
FWIW, I almost never felt that Adobe Standard could work for me, even in daylight situations. Are we sure that Adobe Standard is the CC24 dual illuminant profile or just an average not-to-bad-in-every-condition profile?
I like to start from scratch while working on my photos. These DNG Profile Editor profiles seems to me the bast way to achieve that. :)
Title: Re: Dual Illuminant Profiles
Post by: Schewe on May 26, 2012, 03:50:36 pm
Are we sure that Adobe Standard is the CC24 dual illuminant profile or just an average not-to-bad-in-every-condition profile?

We are sure that the Adobe Standard profile for cameras are very accurate dual-illuminant profiles that are hand tuned by Eric Chan or Thomas Knoll using tools and software well beyond DNG Profile Editor (which Eric wrote). But, it's based on a very small number of camera samples (usually just one) and statistically, there is no way for Eric to know where that camera falls in the range of thousands of cameras that a particular model may sell. Generally, in beta testing Eric will find out if certain DNG profiles are a problem–usually by getting additional sample files from users. But it's been my experience that at least for my cameras (with the exception of the Phase backs) Adobe Standard is fine.
Title: Re: Dual Illuminant Profiles
Post by: mac_paolo on May 26, 2012, 05:51:12 pm
We are sure that the Adobe Standard profile for cameras are very accurate dual-illuminant profiles that are hand tuned by Eric Chan or Thomas Knoll using tools and software well beyond DNG Profile Editor (which Eric wrote). But, it's based on a very small number of camera samples (usually just one) and statistically, there is no way for Eric to know where that camera falls in the range of thousands of cameras that a particular model may sell. Generally, in beta testing Eric will find out if certain DNG profiles are a problem–usually by getting additional sample files from users. But it's been my experience that at least for my cameras (with the exception of the Phase backs) Adobe Standard is fine.
You obviously know much more than me. I own a D300 and previously owned a D40. Adobe standard is quite washed out, if you understand what I'm trying to explain. Not a huge deal for "easy" well lit daylight scenes; a lot worse for more difficult scenes; almost unusable for those artificial lights with non full spectrum.
Maybe it's just my bad luck, and both of my DSLRs have very different sensors from those that Eric and his collegues managed to test.
Just my .02€ :)
Title: Re: Dual Illuminant Profiles
Post by: deejjjaaaa on May 29, 2012, 02:41:40 pm
Are we sure that Adobe Standard is the CC24 dual illuminant profile or just an average not-to-bad-in-every-condition profile?

read this thread -> http://forums.adobe.com/thread/780605?tstart=180

they were less than perfect before and not all of them are perfect now (that is w/o hand-tuning of the standard profile for you own purposes).

PS: but very few people can do a generic profile better...
Title: Re: Dual Illuminant Profiles
Post by: Schewe on May 29, 2012, 03:00:22 pm
they were less than perfect before and not all of them are perfect now (that is w/o hand-tuning of the standard profile for you own purposes).

For the most part that thread dealt with vender matching DNG profiles not Adobe Standard profiles...primarily for Nikon cameras. And as can be seen, the elves are still fine tuning and improving as time allows.
Title: Re: Dual Illuminant Profiles
Post by: deejjjaaaa on May 30, 2012, 01:01:23 pm
And as can be seen, the elves are still fine tuning and improving as time allows.

exactly the point ! but makes one to wonder why such outfit as Adobe Labs does that "as time allows" instead of procuring somebody to do that on a full time basis.
Title: Re: Dual Illuminant Profiles
Post by: Schewe on May 30, 2012, 01:08:12 pm
...but makes one to wonder why such outfit as Adobe Labs does that "as time allows" instead of procuring somebody to do that on a full time basis.

Eric is only one guy (I don't think Thomas does any profiling any more though he could pitch in). As to why it's hard for Adobe to get engineers, well, there aren't a lot as talented and hard working as the ACR team which is actually very small. As for the comment "as time allows" I mean that...they just released ACR 7.1 LR 4.1 which occupied a lot of time recently.

And personally, I do not really care about vender matching profiles since I use either custom or Adobe Standard. I really couldn't care less what the camera makers think is a "look", ya know?