Luminous Landscape Forum

Raw & Post Processing, Printing => Colour Management => Topic started by: erpman on September 20, 2012, 11:26:06 AM

Title: Color profiling while Exposing To The Right
Post by: erpman on September 20, 2012, 11:26:06 AM
Hi!

I just got a color checker passport that I plan to use for making location-specific DNG profiles. In the manual Im being urged to get the exposure right when making the reference shot. But this got me thinking; If I will be doing the actual shoot exposing to the right, which exposure will be correct for the reference shot of the color checker? Correctly according to the camera meter and then overexposing the shoot, or the same exposure for color checker that I plan to use during the shoot? (assuming of course that I dont blow out the highlights on the color checker with neither exposure).
Title: Re: Color profiling while Exposing To The Right
Post by: Schewe on September 20, 2012, 01:23:38 PM
No...if you are going to make DNG profiles your exposure must be correct because the profile software will be expecting the color patches to be within a nominal range. Over or under exposure will alter the accuracy of the DNG profile.
Title: Re: Color profiling while Exposing To The Right
Post by: Scott Martin on September 20, 2012, 05:41:56 PM
Well for starters, exposing to the right isn't "overexposing" and doesn't blow out anything...
Title: Re: Color profiling while Exposing To The Right
Post by: mac_paolo on September 21, 2012, 01:54:23 AM
When shooting the CC24 I always look for a bright histogram.
Relying on the histogram itself watching out for blinkies, I'm pretty sure the final shot won't overexposed (JPG preview is very conservative!)
In the years I got some "Overexposed. Shoot again!" Messages when trying to maximize ETTR, so the point is: get a proper exposure right OOC and stick with it. :)
Title: Re: Color profiling while Exposing To The Right
Post by: MarkM on September 21, 2012, 02:25:23 AM
No...if you are going to make DNG profiles your exposure must be correct because the profile software will be expecting the color patches to be within a nominal range. Over or under exposure will alter the accuracy of the DNG profile.

What is correct exposure for a raw file in this context? If a profile from a ETTR exposure is off, why would we expect a profile from a 'correct' exposure to be right if your workflow depends on ETTR?

In practice I don't think it matters that much because your ETTR exposure isn't going to be that far off when shooting the patches. How far can you really expose to the right before you blow out the white patch? Aren't we talking a half a stop or so for most cameras?
Title: Re: Color profiling while Exposing To The Right
Post by: mac_paolo on September 21, 2012, 02:42:16 AM
What is correct exposure for a raw file in this context? If a profile from a ETTR exposure is off, why would we expect a profile from a 'correct' exposure to be right if your workflow depends on ETTR?

In practice I don't think it matters that much because your ETTR exposure isn't going to be that far off when shooting the patches. How far can you really expose to the right before you blow out the white patch? Aren't we talking a half a stop or so for most cameras?
I know that the DNG PE normalize the exposure when reading the patch. Given that the white patch is quite bright per se, you won't be able to go that far with ETTR, nor it is that useful.
The difference between Adobe Standard (or any other profile) and the CC24 profile is substantial. The difference between normal exposure and ETTR for the CC24 shot is barely nothing. :)
Title: Re: Color profiling while Exposing To The Right
Post by: erpman on September 21, 2012, 07:13:10 AM
Yeah, I guess I wont get that far anyhow since the white patch will blow out pretty soon anywa. ETTR is for lower contrast subjects anyway.

But lets consider the following example: Im shooting a grey stone that fills the entire image. The brightest tones in the stone are mid gray, so I can shift the whole exposure +2 without overexposure. Wont exposing the color checker according to meter be misleading with regard to the actual subject?
Title: Re: Color profiling while Exposing To The Right
Post by: mac_paolo on September 21, 2012, 07:22:45 AM
But lets consider the following example: Im shooting a grey stone that fills the entire image. The brightest tones in the stone are mid gray, so I can shift the whole exposure +2 without overexposure. Wont exposing the color checker according to meter be misleading with regard to the actual subject?
Honestly I can't figure out what you're trying to explain or achieve, sorry :(
Are we talking about the ETTR in general or how to take the CC24 shot for the DNG PE?  ???
Title: Re: Color profiling while Exposing To The Right
Post by: deejjjaaaa on September 21, 2012, 10:45:28 AM
What is correct exposure for a raw file in this context?

check this = http://www.rmimaging.com/information/ColorChecker_Passport_Technical_Report.pdf

i 'd spot meter my camera off neutral patch N5 (has reflectance = ~18-20% and camera's metering is calibrated for ~12-14%) and I will not fill the frame with the target even with aperture stopped down... you need to fill only the area that tests for your lens show very very free from vignetting at stopped down aperture and also use a good tele lens + good hood... filling only central 25% (horizontally) of the image @ F5.8-F11 shall be something suitable... that is regardless of what DNG PE does inside to compensate for difference in illumination... because GIGO.
Title: Re: Color profiling while Exposing To The Right
Post by: RFPhotography on September 21, 2012, 10:55:35 AM
People are missing Jeff's point that "the profile software will be expecting the patches to be within a normal range". 

If you alter exposure of the chart you're going to alter the RGB values of the patches.  If you ETTR by a stop or stop and a half you may throw the RGB values of the patches outside of the range that the profile creation software is expecting. 

Example, I shoot a CC Passport at +1.5 Exp Comp and the light blue patch, top row, third from the left reads 83%, 84%, 94% in LR.  Shooting the Passport at 0 Exp Comp the same patch reads 54%, 55%, 70%.  That's a big difference and may be outside of the range of what the Passport software is expecting in reading the values captured by the camera to create the profile. 
Title: Re: Color profiling while Exposing To The Right
Post by: deejjjaaaa on September 21, 2012, 11:22:32 AM
People are missing Jeff's point that "the profile software will be expecting the patches to be within a normal range". 

If you alter exposure of the chart you're going to alter the RGB values of the patches.  If you ETTR by a stop or stop and a half you may throw the RGB values of the patches outside of the range that the profile creation software is expecting. 

Example, I shoot a CC Passport at +1.5 Exp Comp and the light blue patch, top row, third from the left reads 83%, 84%, 94% in LR.  Shooting the Passport at 0 Exp Comp the same patch reads 54%, 55%, 70%.  That's a big difference and may be outside of the range of what the Passport software is expecting in reading the values captured by the camera to create the profile. 

the question from the person who asked (as I understand it) is how do you exactly meter and what exactly DNG PE expects ideally (to avoid any internal compensation)... your exposure compensation, Bob, is based on what kind of metering exactly ? matrix ? center weight ? spot metering (as I suggested a post earlier) ?

PS: true, you can just simply bracket exposures no matter which method you use for metering and then just select a proper raw based on what ACR (or LR) shows w/ the most neutral settings for conversion for patches in RGB numbers in the particular color space used for such readout (in RPP, for example, for icc profile creation, you do this by checking camera's RGB numbers, those before any color transforms to any color space, for the most bright neutral patch - ACR/LR naturally do not allow to do this)

Title: Re: Color profiling while Exposing To The Right
Post by: RFPhotography on September 21, 2012, 12:38:21 PM
Well, the original question said nothing about DNG PE.  I made the assumption, perhaps incorrectly, that if the OP is using a CC Passport then the Passport software is also being used.  The original question did refer to 'the manual' so I think my assumption is solid.

There was no mention of metering pattern.  I used Matrix but it didn't matter because the target was shot taped to a solid background that was close to neutral in brightness.  If I were shooting it in a different environment I might use a different metering pattern and/or I might fill the viewfinder with the neutral grey patch.  I'd do what I needed to do to get a 'proper' exposure.  That wasn't the point of the original question, I don't believe.  The question was about whether or not the CC Passport target should be ETTR'd or not.  The answer to that, as Jeff pointed out, is no.
Title: Re: Color profiling while Exposing To The Right
Post by: deejjjaaaa on September 21, 2012, 01:26:47 PM
The question was about whether or not the CC Passport target should be ETTR'd or not.  The answer to that, as Jeff pointed out, is no.
whether or not it should be ETTR'd depends on camera and metering... you might have such light and such metering that you have to put some positive exposure adjustment on camera (or change the metering)... but this adjustment certainly shall not bring the most bright patch (w/ the most reflectance) to the very edge of clipping (in raw channels)... so basically the answer shall be - you expose the target so that such and such patch(es) shall be within such and such range (of measurements in your tool, like ACR, using such and such parameters in that tool), whether as a result the shot is w/o exposure compensation on camera or with exposure compensation on camera is not important...

or for example if your shots are then done w/ exposure compensation to achieve some ETTR (for raw), then why you do not want the same for the target shot used to generate profile that will be used to convert those raw files ?...


Title: Re: Color profiling while Exposing To The Right
Post by: RFPhotography on September 21, 2012, 02:35:08 PM
No.  What you're describing is not ETTR.  What you're describing is making and adjustment for the meter reading to 'correct' for the bias of the meter in certain situations.  Two entirely different things.  If I meter a Passport sitting on a snowbank I'm still going to have to add 1.5 to 2 stops of exposure.  That is not ETTR.  That's adjusting for the bias of the metering system to generate a 'proper' exposure.

Why you don't want to ETTR the target goes back to Jeff's original point; which you seem to be missing:  The profiling software expects values for the patches to be within certain a certain range.  If the exposure puts the patch values outside that range the profile won't be accurate.
Title: Re: Color profiling while Exposing To The Right
Post by: erpman on September 21, 2012, 02:58:33 PM
Quote
No.  What you're describing is not ETTR.  What you're describing is making and adjustment for the meter reading to 'correct' for the bias of the meter in certain situations.  Two entirely different things.  If I meter a Passport sitting on a snowbank I'm still going to have to add 1.5 to 2 stops of exposure.  That is not ETTR.  That's adjusting for the bias of the metering system to generate a 'proper' exposure.

Why you don't want to ETTR the target goes back to Jeff's original point; which you seem to be missing:  The profiling software expects values for the patches to be within certain a certain range.  If the exposure puts the patch values outside that range the profile won't be accurate.

This makes sense. Since the passport covers most of the range it wont really be possible to really ETTR it anyway, so we will be forced to a normal exposure. But as you point out with the snow example, adjusting for meter bias is another thing. In that case we would risk underexposing and delivering to the software a patch that was out of range the in the other direction. Spot metering the middle gray patch for the reference shot, and then adjusting for the subject according to histogram/blinking highlights afterwards seems logical in most situations.

Well it certainly makes more sense now, thanks all for the input.
Title: Re: Color profiling while Exposing To The Right
Post by: deejjjaaaa on September 21, 2012, 03:05:11 PM
No.  What you're describing is not ETTR.  What you're describing is making and adjustment for the meter reading to 'correct' for the bias of the meter in certain situations.  Two entirely different things.  If I meter a Passport sitting on a snowbank I'm still going to have to add 1.5 to 2 stops of exposure.  That is not ETTR.  That's adjusting for the bias of the metering system to generate a 'proper' exposure.

that is what I am trying to get - what is proper exposure by numbers or by exact technique for metering...

Why you don't want to ETTR the target goes back to Jeff's original point; which you seem to be missing:  The profiling software expects values for the patches to be within certain a certain range. 

and what is that exactly (numbers) for DNG PE and for XRite's software ?
Title: Re: Color profiling while Exposing To The Right
Post by: deejjjaaaa on September 21, 2012, 03:10:46 PM
This makes sense. Since the passport covers most of the range it wont really be possible to really ETTR it anyway

what if your metering underexposes vs what it shall be from the profile creation standpoint ?


, so we will be forced to a normal exposure. But as you point out with the snow example, adjusting for meter bias is another thing.

ETTR in local (this forum) sense is when you provide the maximum exposure yet do not have any raw channel clipping in your shot... if that is a defintion you can ETTR any target.

In that case we would risk underexposing and delivering to the software a patch that was out of range the in the other direction.

and what is the range ?

Spot metering the middle gray patch for the reference shot, and then adjusting for the subject according to histogram/blinking highlights afterwards seems logical in most situations.

too much depends on camera and light... unless you bracket (immediately or w/ shot review - does not matter) - but then the question is - when you review the raw file in ACR/LR - what are the numbers that you compare some patches with ?

Title: Re: Color profiling while Exposing To The Right
Post by: RFPhotography on September 21, 2012, 04:44:23 PM
Quote
that is what I am trying to get - what is proper exposure by numbers or by exact technique for metering...

I think you're complicating things simply for the sake of complication.  If someone is competent with a meter they will understand how meters work and be able to expose the target properly.

Quote
and what is that exactly (numbers) for DNG PE and for XRite's software ?

I don't know that that information is available for public use.  But given that XRite take care about exposing the target properly and being very careful not to clip any channels it would make sense that it's something just either side of a proper metered exposure (don't bother with the 'what metering method' bravo sierra).

Quote
what if your metering underexposes vs what it shall be from the profile creation standpoint ? ETTR in local (this forum) sense is when you provide the maximum exposure yet do not have any raw channel clipping in your shot... if that is a defintion you can ETTR any target.

Then just as with the snowbank example you're compensating for a bias in the meter.  You're not purposefully increasing exposure from a 'proper' exposure.  And it's not true that any target can be ETTR'd.  If the target contains patches that cover the spectrum from black to white then you can't ETTR the target otherwise you'll clip channels at the top end. 

Quote
too much depends on camera and light... unless you bracket (immediately or w/ shot review - does not matter)

No, too much doesn't depend on the camera and light.  The lighting under which a target should be captured is even light.  Not dappled light.  Not halfway in dark and halfway in sun.  The lighting on the target has to be consistent.  Doing this there should really be no need to bracket. 

Title: Re: Color profiling while Exposing To The Right
Post by: deejjjaaaa on September 22, 2012, 11:07:04 AM
I think you're complicating things simply for the sake of complication.  If someone is competent with a meter they will understand how meters work and be able to expose the target properly.

you are trying to avoid answering the question - what is the proper exposure of the target from the software (that makes a profile) standpoint... I understand that you do not know the answer, only developers know... neither does Schewe... people like Eric Chan know... hence this is an attempt to summon such people.

Then just as with the snowbank example you're compensating for a bias in the meter.  You're not purposefully increasing exposure from a 'proper' exposure.  And it's not true that any target can be ETTR'd.  If the target contains patches that cover the spectrum from black to white then you can't ETTR the target otherwise you'll clip channels at the top end. 

that exactly depends on the definition of ETTR that you are using... if ETTR is about the end result (raw channels histogram) - then every single raw file can be ETTR'd regardless of the target  ;) ... just try to distance yourself from thinking about dialing a positive exposure compensation... you might be in a situation when (based on your camera, light, target, metering) you need actually to dial in a negative exposure compensation to get an ETTR'd raw file... so no matter what you do with camera controls, a raw file is ETTR'd when you have raw channels historgams shifted to the the point of clipping (but no clipping) in any combination of all raw channels (be it 1, 2, 3, etc channels) - hence every shot can be "ETTR'd"

Title: Re: Color profiling while Exposing To The Right
Post by: RFPhotography on September 22, 2012, 11:44:45 AM
You're playing a game of semantics. 
Title: Re: Color profiling while Exposing To The Right
Post by: Ellis Vener on September 24, 2012, 09:58:25 PM
deejjjaaaa, " only developers know... neither does Schewe... people like Eric Chan know." Jeff Schewe knows far more in that direction than you give him credit for.

If you want to involve Eric Chan in this discussion all you have to do is look up his profile here and ask him what his thoughts on the subject are.
Title: Re: Color profiling while Exposing To The Right
Post by: Schewe on September 25, 2012, 12:12:36 AM
you are trying to avoid answering the question - what is the proper exposure of the target from the software (that makes a profile) standpoint... I understand that you do not know the answer, only developers know... neither does Schewe... people like Eric Chan know... hence this is an attempt to summon such people.

Actually, I do know...when making any sort of profile whether DNG or ICC, the photographed (or printed) target chromaticity is evaluated and compared to the expected known target chromaticity and the algorithms calculate what color transforms need to be applied to make the photographed target chromaticity match the expected actual target chromaticity. The further away from the known target chromaticity that a photographed target chromaticity is, the less accurate and less smooth the resulting profiles will be. Obviously, the photographed target chromaticity will be impacted by the photographed targets exposure.

The aim should be an "accurate" exposure that makes the luminance values of the photographed target chromaticity be as close to the expected actual target chromaticity for the best and most accurate (and smoothest) results. Over or under exposing is suboptimal. ETTR of the photographed target chromaticity would be a mistake.
Title: Re: Color profiling while Exposing To The Right
Post by: deejjjaaaa on September 25, 2012, 01:13:46 AM
Actually, I do know...

then where are the numbers, Jeff ? you have a raw file with xrite passport shot, you open it in ACR - please explain how do you evaluate by numbers whether this shot is good or not, starting with the settings in ACR that shall be used for that... like you know - WB set off which patch ? exposure shall be EV0, contrast 0, the rest of sliders @ that tab 0, no sharpening, NR ? all zero ?, tone curve = linear, etc, etc... then what ? you use a color sampler tool and which patch you shall check (first) and what shall be RGB values there, what are the tolerances ?

imagine that you are doing a repro work...

that is what I am trying to understand first of all - how do I evaluate the target shot before actually making a profile... and the only things I hear back are adjectives, but no numbers.

PS: and the next question will be - how do you evaluate that profile you have - and I am not talking about some artistic intents, because you can't argue about tastes - but I 'd assume we shall have something more substantial that your eyesight to see if the profile built off one target can render another target (different type - not like 2 passports) close to the what the colors shall be... otherwise the whole profiling thing is a herbalife and unless you have a really really odd light then you are better off w/ a standard profile from Adobe + proper WB and profiles for artistic intents are better done by just editing a base profile w/o actually shooting a target, are they not ?
Title: Re: Color profiling while Exposing To The Right
Post by: deejjjaaaa on September 25, 2012, 01:15:14 AM
deejjjaaaa, " only developers know... neither does Schewe... people like Eric Chan know." Jeff Schewe knows far more in that direction than you give him credit for.

If you want to involve Eric Chan in this discussion all you have to do is look up his profile here and ask him what his thoughts on the subject are.

I guess he is too busy w/ whatever releases and people in the know shall appear only if the discussion is interesting...
Title: Re: Color profiling while Exposing To The Right
Post by: deejjjaaaa on September 25, 2012, 01:30:59 AM
You're playing a game of semantics.  

I am just asking for some numbers... I understand that a lot of art might be involved but absence of any numbers in the whole profiling thing sounds odd  ::) ... |

Like the recent topic = http://www.luminous-landscape.com/forum/index.php?topic=70491.msg558028#msg558028

"Today I made the usual dual illuminant camera profiles I make for each new model I test.
I find them to be much more accurate than Adobe Standard."

And when I asked how did the author actually found that they are more accurate (how dare I ?!) - I heard the following

Quote
dejjjaaaa, your argumentative and insulting posts add absolutely nothing of substance to this forum, I wish you would just to over to DRP to do your trolling.  This is not that kind of forum.

Quote
Ignore the people with missing brain cells.

 ;D

and topic starter did not post the original raw files (he was asked), I 'd assume he was afraid to show how the target was actually shot  ::) /"You'd see a CC24 covering almost 95% of the frame." - that is the first sign, right... fill the frame with the target/
Title: Re: Color profiling while Exposing To The Right
Post by: Schewe on September 25, 2012, 02:22:58 AM
then where are the numbers, Jeff ? you have a raw file with xrite passport shot, you open it in ACR - please explain how do you evaluate by numbers whether this shot is good or not, starting with the settings in ACR that shall be used for that... like you know - WB set off which patch ? exposure shall be EV0, contrast 0, the rest of sliders @ that tab 0, no sharpening, NR ? all zero ?, tone curve = linear, etc, etc... then what ? you use a color sampler tool and which patch you shall check (first) and what shall be RGB values there, what are the tolerances ?

I use Bruce Lindbloom's (http://www.brucelindbloom.com) ColorChecker Calculator (http://www.brucelindbloom.com/index.html?ColorCheckerCalculator.html) to determine what the target chromaticity should be in ProPhoto RGB and simply read the patches in ACR set to ProPhoto RGB...pretty simple really. Just set the calculator to ProPhoto RGB...

If you are lazy, you can download a synthetic ProPhoto RGB target file (http://colorremedies.com/realworldcolor/downloads/Macbeth_ColorChecker_ProPhoto.jpg.zip) from Chris Murphy's web site (http://colorremedies.com). It gives you the RGB target readouts of ProPhoto RGB. Save it as a TIFF and you can load the photographed target brackets and the synthetic target in ACR and check the readouts for an optimal exposure.

Edited to add Bruce's & Chris' main web site links...
Title: Re: Color profiling while Exposing To The Right
Post by: MarkM on September 25, 2012, 02:35:49 AM
Actually, I do know...when making any sort of profile whether DNG or ICC, the photographed (or printed) target chromaticity is evaluated and compared to the expected known target chromaticity and the algorithms calculate what color transforms need to be applied to make the photographed target chromaticity match the expected actual target chromaticity.
I use Bruce Lindbloom's ColorChecker Calculator to determine what the target chromaticity should be in ProPhoto RGB and simply read the patches in ACR set to ProPhoto RGB...pretty simple really.

This is a little confusing. It's my understanding that DNG profiles differ significantly from ICC profiles in that DNG profiles work with scene referred data.  Suggesting that it expects some RGB target or chromaticity would imply that the DNG profile editor is working with output referred data, but according to Adobe it's not.

Since it's working with linear raw data, I would think (but it's only a guess) that the profile editor would use the grey patches and normalize the exposure before creating the profile. If the data is linear, this should have almost no effect on the final result. So long as you don't clip any channels or introduce too much noise, you would be able to expose however you want.

Title: Re: Color profiling while Exposing To The Right
Post by: Schewe on September 25, 2012, 02:41:18 AM
Since it's working with linear raw data, I would think (but it's only a guess) that the profile editor would use the grey patches and normalize the exposure before creating the profile. If the data is linear, this should have almost no effect on the final result. So long as you don't clip any channels or introduce too much noise, you would be able to expose however you want.

I'm talking about evaluating a raw file in ACR for optimal creation of a DNG profile in either DNG Profile Editor or Passport. The closer you are to an optimal exposure, the better the resulting DNG profile. Pretty simple really...the less transforming a profile must do, the more accurate (and smother) the transformed results. Since exposure is gonna have an impact on the photographed ColorChecker target chromaticity you should pick an optimally exposed DNG to make the profile from. Same deal for using an accurate color temp to shoot the target. Right?
Title: Re: Color profiling while Exposing To The Right
Post by: mac_paolo on September 25, 2012, 03:06:05 AM
I am just asking for some numbers... I understand that a lot of art might be involved but absence of any numbers in the whole profiling thing sounds odd  ::) ... |
Jeff linked those numbers. The same one I found years ago via a 10 seconds google search. You know, sometimes people just don't like to spend time when the speaker is the first to be lazy.

Like the recent topic = http://www.luminous-landscape.com/forum/index.php?topic=70491.msg558028#msg558028

"Today I made the usual dual illuminant camera profiles I make for each new model I test.
I find them to be much more accurate than Adobe Standard."

And when I asked how did the author actually found that they are more accurate (how dare I ?!) - I heard the following

 ;D
I'm the "author" of that thread, which was opened to be helpful, and maybe it reached its goal, taken that almost 30 people got that profile.
I'm not the author of those two comments (which I kinda agree with, time after time), so you're mischievous, at best.

You obviously can check RGB values of the patches against given values. They are objective. What you clearly can't do is to check chromaticity values of colors in a real world scene.
What apparently anyone understood but you, is that these latter tests must be evaluated by eye, and any serious photographer is able to do it.
It doesn't take a genius to figure out which image has more realistic colors and, when the ratio is 9:1 (if not even 10:0) towards the custom DNG corrected, it's not that hard to write a thread like that.

and topic starter did not post the original raw files (he was asked), I 'd assume he was afraid to show how the target was actually shot  ::) /"You'd see a CC24 covering almost 95% of the frame." - that is the first sign, right... fill the frame with the target/
I even lost time to explain that on that very thread an still you keep on this provocateur tone. If you really like to test it's been shot at 1,3", /5, ISO 125 for the indoor and 1/20", /5.6 for the outdoor.
Let me add a last thing, when it seems that no one replies to your [rude] requests, chances are that either no one knows the answers (I do, and certainly much more do both Mr. Chan and Mr. Schewe) or, more simply, people is ignoring you.
Have fun solving the riddle. ;)
Title: Re: Color profiling while Exposing To The Right
Post by: bjanes on September 25, 2012, 06:40:52 AM
I use Bruce Lindbloom's (http://www.brucelindbloom.com) ColorChecker Calculator (http://www.brucelindbloom.com/index.html?ColorCheckerCalculator.html) to determine what the target chromaticity should be in ProPhoto RGB and simply read the patches in ACR set to ProPhoto RGB...pretty simple really. Just set the calculator to ProPhoto RGB...

If you are lazy, you can download a synthetic ProPhoto RGB target file (http://colorremedies.com/realworldcolor/downloads/Macbeth_ColorChecker_ProPhoto.jpg.zip) from Chris Murphy's web site (http://colorremedies.com). It gives you the RGB target readouts of ProPhoto RGB. Save it as a TIFF and you can load the photographed target brackets and the synthetic target in ACR and check the readouts for an optimal exposure.

Edited to add Bruce's & Chris' main web site links...

This is a little confusing. It's my understanding that DNG profiles differ significantly from ICC profiles in that DNG profiles work with scene referred data.  Suggesting that it expects some RGB target or chromaticity would imply that the DNG profile editor is working with output referred data, but according to Adobe it's not.

Since it's working with linear raw data, I would think (but it's only a guess) that the profile editor would use the grey patches and normalize the exposure before creating the profile. If the data is linear, this should have almost no effect on the final result. So long as you don't clip any channels or introduce too much noise, you would be able to expose however you want.

Mark,

That is a good point. For scene referred data, one should look at the raw file, which is scene referred. The problem with using ACR/LR to determine the adequacy of exposure is that the results will be affected by the tone curve and the BaselineExposure value used by those programs. For exposure, one should look at the gray values as you suggest. As those who have struggled to calibrate with the ColorChecker using Bruce Fraser's manual method know, the contrast setting will affect the gray values above and below mid-gray. The saturation will affect the color values.

The Neutral 5 patch has an optical density of 0.70. One can use Bruce Lindbloom's companding calculator to determine the normalized pixel value for this density as shown. A normalized pixel value of 0.1995 corresponds to about 3616 in a linear 14 bit space. One can check the raw values with RawDigger or a similar probram, using the green channels which have a white balance multiplier of unity.

Regards,

Bill

Title: Re: Color profiling while Exposing To The Right
Post by: RFPhotography on September 25, 2012, 07:38:34 AM
I use Bruce Lindbloom's (http://www.brucelindbloom.com) ColorChecker Calculator (http://www.brucelindbloom.com/index.html?ColorCheckerCalculator.html) to determine what the target chromaticity should be in ProPhoto RGB and simply read the patches in ACR set to ProPhoto RGB...pretty simple really. Just set the calculator to ProPhoto RGB...

If you are lazy, you can download a synthetic ProPhoto RGB target file (http://colorremedies.com/realworldcolor/downloads/Macbeth_ColorChecker_ProPhoto.jpg.zip) from Chris Murphy's web site (http://colorremedies.com). It gives you the RGB target readouts of ProPhoto RGB. Save it as a TIFF and you can load the photographed target brackets and the synthetic target in ACR and check the readouts for an optimal exposure.

Edited to add Bruce's & Chris' main web site links...

You also have to choose the illuminant type to use Bruce's calculator, correct Jeff?  One could use the table at the bottom of this page (http://en.wikipedia.org/wiki/Standard_illuminant) to know what the various illuminant types represent in terms of a white balance?  One of the presets in the calculator may not match up exactly with the WB used for the target.  How do you account for the differences?
Title: Re: Color profiling while Exposing To The Right
Post by: madmanchan on September 25, 2012, 08:56:30 AM
The main thing with shooting charts for DNG PE is not to clip any of the patches.  Usually the tool will warn you if that's happened and refuse to proceed.  Since the tool does work off the raw data, it's not subject to rendering-related tags in the DNG format (e.g., BaselineExposure). 

If you have a severely underexposed image, the main detriment that you'll find is simply more noise in the color patches, which means the profile may be off a bit.  But overall that's not a big deal, and if you're concerned about this, the solution is bracket some exposures.   :)

The illuminant used to compute the numbers does matter, of course.  For the single-illuminant profile, DNG PE assumes a D50 illuminant (which is what the normal published numbers assume, too), and for the dual-illuminant profile, DNG PE assumes Standard Illuminant A for the first table, and CIE D65 for the second table (same calibration illuminants that Adobe uses for its Adobe Standard profile).
Title: Re: Color profiling while Exposing To The Right
Post by: bjanes on September 25, 2012, 04:39:48 PM
The main thing with shooting charts for DNG PE is not to clip any of the patches.  Usually the tool will warn you if that's happened and refuse to proceed.  Since the tool does work off the raw data, it's not subject to rendering-related tags in the DNG format (e.g., BaselineExposure). 

If you have a severely underexposed image, the main detriment that you'll find is simply more noise in the color patches, which means the profile may be off a bit.  But overall that's not a big deal, and if you're concerned about this, the solution is bracket some exposures.   :)

The illuminant used to compute the numbers does matter, of course.  For the single-illuminant profile, DNG PE assumes a D50 illuminant (which is what the normal published numbers assume, too), and for the dual-illuminant profile, DNG PE assumes Standard Illuminant A for the first table, and CIE D65 for the second table (same calibration illuminants that Adobe uses for its Adobe Standard profile).

Eric,

Thanks for the definite answer. From your reply, I infer that MarkM was correct: since the profiler deals with the raw data, it can correct for minor exposure differences as long as the data are not clipped. However, one should try to have reasonable ETTR for the best signal:noise (ignoring the semantic issues). My point about using ACR/LR to judge exposure was that the tone curve and BaselineExposure do have an effect on the rendering.

As an example, here is an exposure with the Nikon D3 of the ColorChecker under Solux illumination (approx 4700K, hopefully close enough to 5000K for a single illuminant profile) with the Neutral 5 patch raw green channels near nominal exposure with a raw value of 3170, close to the value determined for this patch by Bruce Lindbloom's companding calculator.

(http://bjanes.smugmug.com/Photography/DNGCalibr/i-WNQN6ks/0/O/MacbethRawDigger.png)

The white patch is well short of clipping.

(http://bjanes.smugmug.com/Photography/DNGCalibr/i-n73Vf4n/0/O/02Patch1RD.png)

The image appears overexposed with ACR 7.1 Process 2012 using the default settings:

(http://bjanes.smugmug.com/Photography/DNGCalibr/i-BBfWb9C/0/O/MacbethPV2012.png)

With PV2010 and a linear tone curve, the exposure appears more reasonable:

(http://bjanes.smugmug.com/Photography/DNGCalibr/i-57q7Gk5/0/O/MacbethPV2010a.png)

Using an exposure value of -0.5 EV to offset the BaselineExposure of +0.5 EV gives close to the correct pixel value in the Neutral 5 patch.

(http://bjanes.smugmug.com/Photography/DNGCalibr/i-htgHxD4/0/O/MacbethPV2010b.png)

My conclusion is that PV2012 with the default settings is not good for evaluating exposure and, with my D3 at least, PV2010 with a linear tone curve and a BaselineExposure compensation gives better results. However, this exposure was rejected by the DNG Profile editor, which reported that the yellow patch (row 3 column 4) was overexposed. Exposing 0.5 EV less gave a valid calibration. Your comments would be welcome.

Best regards,

Bill

PS. I enjoyed very much and learned a lot from your interviews on the LuLa tutorial with Michael and Jeff. I hope they invite you back.

Title: Re: Color profiling while Exposing To The Right
Post by: Schewe on September 25, 2012, 04:48:54 PM
The main thing with shooting charts for DNG PE is not to clip any of the patches.  Usually the tool will warn you if that's happened and refuse to proceed.  Since the tool does work off the raw data, it's not subject to rendering-related tags in the DNG format (e.g., BaselineExposure). 

Do you agree that getting an optimal exposure is best for making DNG profiles? Do you disagree that using a known reference chart (synthetic PPRGB) is a good way of evaluating various exposure of a bracket in ACR?
Title: Re: Color profiling while Exposing To The Right
Post by: deejjjaaaa on September 25, 2012, 05:13:48 PM
Do you agree that getting an optimal exposure is best for making DNG profiles? Do you disagree that using a known reference chart (synthetic PPRGB) is a good way of evaluating various exposure of a bracket in ACR?

Jeff - that was the question - what is the optimal (a word "optimal" is not a number of any kind, it is just an adjective) exposure and what are the tolerances... I can't believe that we have a leeway on one stop more, two stops less (just make sure not to clip any raw channels) and get a profile that will be more accurate (for a regular day light or so - no exotic spectrums) than Adobe's standard... does not sound right, does it ?

Plus - can we really test that using Adobe's own tools (no rawdigger - let us stay kosher!) - I understand that DNG PE will warn - but it is clear it will warn only in case of totally unsuitable shot, but what if I want to be as close to perfection as possible...
Title: Re: Color profiling while Exposing To The Right
Post by: deejjjaaaa on September 25, 2012, 05:18:21 PM
it can correct for minor exposure differences as long as the data are not clipped.

we need to define minor ? shall we... is it 1/3 EV ? is it 1/2 EV ? is it 1 EV ? is it 2 EV ?


However, one should try to have reasonable ETTR for the best signal:noise (ignoring the semantic issues). My point about using ACR/LR to judge exposure was that the tone curve and BaselineExposure do have an effect on the rendering.

but the Adobe's toolset shall be complete - we shall not use any 3rd party tools to evaluate our exposures... so naturally we need to be able to use ACR/LR to make a judgement as to how good our shot is by numbers... that means you select certain raw conversion parameters and take some RGB color readings, right ?

Title: Re: Color profiling while Exposing To The Right
Post by: Rhossydd on September 25, 2012, 05:23:16 PM
If you are lazy, you can download a synthetic ProPhoto RGB target file (http://colorremedies.com/realworldcolor/downloads/Macbeth_ColorChecker_ProPhoto.jpg.zip) from Chris Murphy's web site (http://colorremedies.com). It gives you the RGB target readouts of ProPhoto RGB.
Curiously, the numbers specified on the file don't match the actual measured values of the image.

Not disagreeing with any of your comments on this though.
Title: Re: Color profiling while Exposing To The Right
Post by: MarkM on September 25, 2012, 05:41:11 PM
Sorry if I'm being dense, stubborn, or both, but I would really like to understand this.

It's my understanding that the whole point of ETTR and the reason it works is that we are able to scale the linear raw data without introducing hue/saturation shifts. In other words, there really is no difference, as far as colorimetry is concerned, between exposing and processing normally, and exposing more and bring it down in processing. My own tests have confirmed this for me, and from past reading I think most people here are comfortable with this.

Since we can move the exposure up and down without changing the color, an optimal exposure doesn't really exist. ETTR proponents will say the optimal exposure is the one the captures the most light possible, but this has more to do with shadow noise than color.

So the question is: does profile editor use the grey patches to normalize the exposure?

I would think for it to be useable it would have to. If it didn't, then Schewe's worries would be correct because even a small deviation in exposure would move the patches out of whack. In order to make a truly accurate profile you would need to know exactly what profile editor expects and exactly what your camera's meter is doing. Judging your exposure would require digging into the linear raw data. (Not just measuring processed RGB patches in ACR.)

Since the color picker has everything that profile editor needs to shift the exposure I can see no reason why it wouldn't do it. It should not twist the color and it allows for a lot of flexibility in the exposure, which means users who are not interested in digging into the raw numbers (i.e. most users) will get good results.

So long as you don't clip channels, profile editor will work.
Title: Re: Color profiling while Exposing To The Right
Post by: deejjjaaaa on September 25, 2012, 05:50:16 PM
I use Bruce Lindbloom's (http://www.brucelindbloom.com) ColorChecker Calculator (http://www.brucelindbloom.com/index.html?ColorCheckerCalculator.html) to determine what the target chromaticity should be in ProPhoto RGB and simply read the patches in ACR set to ProPhoto RGB...pretty simple really. Just set the calculator to ProPhoto RGB...

ОК, so you say that ideal exposure for DNG PE profile building is when the raw file loaded in ACR (we assume v7.x), which set is to ProPhoto RGB output, matches the numbers from Bruce Lindbloom's calculator (we make sure to select the proper illuminant there and proper WB in ACR of course) when you take RGB samples in ACR itself... so what is the tolerance now - how many patches do you personally check (all 24 patches ? only one ? few of them), what are possible tolerances for RGB readings vs calculated numbers, what EV adjustment in ACR (if any) you consider to be allowable ? and are there any other settings in ACR to pay attention to (except selecting ProPhoto RGB as the output space for ACR)... and RGB readings in ACR will be in Melissa RGB, right - different gamma.
Title: Re: Color profiling while Exposing To The Right
Post by: deejjjaaaa on September 25, 2012, 05:53:40 PM
Since we can move the exposure up and down without changing the color, an optimal exposure doesn't really exist. ETTR proponents will say the optimal exposure is the one the captures the most light possible, but this has more to do with shadow noise than color.

that is if you think that noise does not affect the color... or that nothing wrong happens near very saturation
Title: Re: Color profiling while Exposing To The Right
Post by: deejjjaaaa on September 25, 2012, 06:04:14 PM
You obviously can check RGB values of the patches against given values. They are objective. What you clearly can't do is to check chromaticity values of colors in a real world scene.
What apparently anyone understood but you, is that these latter tests must be evaluated by eye, and any serious photographer is able to do it.

why shall I trust your eye and not some tools like babelcolor patchtool ?

It doesn't take a genius to figure out which image has more realistic colors and, when the ratio is 9:1 (if not even 10:0) towards the custom DNG corrected, it's not that hard to write a thread like that.

well, first of all "realistic" is subjective... however if the test under a regular (but different) light using a totally different type of a target and proper tools to measure instead of your "eye" shows that multitude of dE's is better for your profile than for Adobe's standard then I have a question to Eric Chan (or whoever does profiles in Adobe) - how come ? we are talking about a generic dual illuminant profile here...



I even lost time to explain that on that very thread an still you keep on this provocateur tone. If you really like to test it's been shot at 1,3", /5, ISO 125 for the indoor and 1/20", /5.6 for the outdoor.


how about just posting these 2 raw files... you share the profile - then you shall not have any issues to post the source, right ? unless.......
Title: Re: Color profiling while Exposing To The Right
Post by: deejjjaaaa on September 25, 2012, 06:34:55 PM
with the Neutral 5 patch raw green channels

why Patch N5 - ideally we shall be checking just one patch - and the one w/ the most reflectance to do both things at once - check how close we are to the clipping and use RGB values of that only patch to comparing with the value from Bruce Lindbloom calculator, as suggested by Jeff Schewe for a source of values from an ideally exposed target for the purpose of DNG PE profile building...
Title: Re: Color profiling while Exposing To The Right
Post by: Schewe on September 25, 2012, 07:20:16 PM
Curiously, the numbers specified on the file don't match the actual measured values of the image.

Not disagreeing with any of your comments on this though.

You need to click on the option to Scale RGB in the calculator then they match the synthetic PP RGB file (the calculator doesn't round to full numbers as the synthetic target does). also, when you are using the color sampler in Photoshop what Sample Size is set in Photoshop? When I open the synthetic target in ACR, all the numbers are within a level or two with all of the luminance patches exactly correct. Since we are talking about picking the optimal exposure, those are the ones that are important to compare.

As I recall, in ACR, the Color Sampler does a sample of 5x5 screen pixels (Eric can correct me if I'm wrong). But the readouts for rgb really are pretty close with generally only one of the tree colors off by a level or two.
Title: Re: Color profiling while Exposing To The Right
Post by: bjanes on September 25, 2012, 08:57:06 PM
why Patch N5 - ideally we shall be checking just one patch - and the one w/ the most reflectance to do both things at once - check how close we are to the clipping and use RGB values of that only patch to comparing with the value from Bruce Lindbloom calculator, as suggested by Jeff Schewe for a source of values from an ideally exposed target for the purpose of DNG PE profile building...

I chose a midgray patch for evaluation with ACR/LR, since the midgray values are less affected by the contrast curve as shown below for PV2012 with ARR 7.1. The graph is self-explanatory.

(http://bjanes.smugmug.com/Photography/ACR7/i-nzjjsq3/0/O/05ContrLogLin.png)

If you are looking at the raw file with Rawdigger, you could use any of the neutral patches, since the sensor response is linear; in this case, the white patch would serve the purposes you suggest. The problem with Mr. Schewe's method is what ACR/LR settings do you use? The results are markedly different with different parameters as shown in my previous post. PV2010 with a linear tone curve and correction for the BaselineExposure appears to give the best results. The BaselineExposure can be obtained from the DNG exif.

The "ideally exposed target" values are usually determined mathematically from the spectral reflectances of the target convolved with the spectrum of the illuminant and not from an actual exposure (see Danny Pascale (http://www.babelcolor.com/main_level/ColorChecker.htm#ColorChecker_data)). Rendered values from an actual target exposed in a camera can never be fully accurate because of metameric failure.

Regards,

Bill
Title: Re: Color profiling while Exposing To The Right
Post by: Schewe on September 25, 2012, 09:47:36 PM
The problem with Mr. Schewe's method is what ACR/LR settings do you use? The results are markedly different with different parameters as shown in my previous post.

You are making this all to complicated (as is your nature). The OP simply wanted to know whether or not to ETTR to create DNG Profiles...a lot of back and forth ensued...since my name was mentioned, I answered the question regarding how to pick an optimal exposure of a photographed ColorChecker chart...when asked how to determine the optimal exposure, I answered that it's optimal to pick a "good" exposure. Eric chimed in that as long as the image isn't underexposed nor any color clipped it was "ok". I still think that an optimal exposure is useful for making accurate and smooth DNG profiles. Do you disagree? Using a synthetic ProPhoto RGB and a photographed ColorChecker target and ACR to check on what would be an optimal exposure works...its what I do. Am I wrong? All I can say is what I do works for me...YMMV.

Don't under or over expose a ColorChecker and the odds are you'll be able to make a good DNG profile. The further to move away from a "good exposure" the less good the profile is likely to be...agreed?
Title: Re: Color profiling while Exposing To The Right
Post by: deejjjaaaa on September 25, 2012, 09:53:31 PM
If you are looking at the raw file with Rawdigger

no, the whole point was to stay in the realm of Adobe tools to evaluate which shot is the best for DNG PE editor... certainly w/ rawdigger I can find out very easy which shot is the most ETTR'd (but then that does not mean that the very most ETTR'd shot is the best one for DNG PE or is it)

, you could use any of the neutral patches, since the sensor response is linear;

and one of rawdigger co-author says that linearity of the camera (not a single sensel responce on die taken w/o consideration of the whole sensor, its toppings and the rest of the signal processing circuitry) is not exactly a given fact within 1/3-1/2 to raw channel clipping, if I am not mistaken, at least not for all cameras (even modern)...

The problem with Mr. Schewe's method is what ACR/LR settings do you use? The results are markedly different with different parameters as shown in my previous post. PV2010 with a linear tone curve and correction for the BaselineExposure appears to give the best results. The BaselineExposure can be obtained from the DNG exif.

it does not really matter which method for as long as an average Joe can stay just within ACR and DNG PE - because that the market where XRite and other vendors are peddling the product... digging for a value of BaselineExposure tag is not nice... Ideally the next version of Adobe's DNG PE shall offer some indication about quality of the source raw file in more certain terms... one can certainly argue that an average Joe can live w/ whatever profile happens, but that's not nice.

Title: Re: Color profiling while Exposing To The Right
Post by: bjanes on September 26, 2012, 07:11:30 AM
no, the whole point was to stay in the realm of Adobe tools to evaluate which shot is the best for DNG PE editor... certainly w/ rawdigger I can find out very easy which shot is the most ETTR'd (but then that does not mean that the very most ETTR'd shot is the best one for DNG PE or is it)

Personally, I see no need to restrict oneself to Adobe tools. ACR/LR are for visual editing and rendering of raw files. If one desires quantitative photometric and colorimetric analysis of the raw file, it is often best to look elsewhere. As my previous post demonstrated, the most ETTRed shot is sometimes not the best for the DNG profile editor, since an ETTR shot without clipping in any channel was rejected by the editor with an error message that the yellow patch was overexposed.

and one of rawdigger co-author says that linearity of the camera (not a single sensel responce on die taken w/o consideration of the whole sensor, its toppings and the rest of the signal processing circuitry) is not exactly a given fact within 1/3-1/2 to raw channel clipping, if I am not mistaken, at least not for all cameras (even modern)...

It is often not documented, but I understand that some cameras do some preprocessing to linearize the data from the sensor that is written to the raw file. One must know one's camera. My previous work with the Nikon D3 does demonstrate that the sensor is reasonably linear right up to clipping as shown below. To the extent that the system response is not linear with higher luminance values, it is best to avoid excessive ETTR and work with the linear portion of the response.

(http://bjanes.smugmug.com/Photography/DNGCalibr/i-mQ4NrBv/0/O/Data.png)

it does not really matter which method for as long as an average Joe can stay just within ACR and DNG PE - because that the market where XRite and other vendors are peddling the product... digging for a value of BaselineExposure tag is not nice... Ideally the next version of Adobe's DNG PE shall offer some indication about quality of the source raw file in more certain terms... one can certainly argue that an average Joe can live w/ whatever profile happens, but that's not nice.

If you want quantitative data concerning the contents of the raw file, the BaselineExposure must be taken into account if you are using ACR/LR. It is a pain to look up the baseline exposure, and it is often easier to use Rawdigger, which also avoids nonlinearities introduced by the tone curve. Personally, I do not like the introduction of the BaselineExposure. It does enable one to get consistent results when using multiple cameras that allow differing amounts of highlight headroom, but if one is primarily using one camera it is a pain.

It would be nice to have some indication of the quality of the source raw file, but, as Eric has indicated, a reasonable exposure without clipping is sufficient and I think he has better things to do than work on such an indicator.

Regards,

Bill

Title: Re: Color profiling while Exposing To The Right
Post by: bjanes on September 26, 2012, 07:26:31 AM
Don't under or over expose a ColorChecker and the odds are you'll be able to make a good DNG profile. The further to move away from a "good exposure" the less good the profile is likely to be...agreed?

I do agree. From what Eric has indicated, a "good exposure" is sufficient and striving for the most ETTRed exposure without clipping needlessly complicates things. Indeed, in my previous experiments such an exposure was rejected by the DNG profile editor.

BTW, I just received my copy of your Digital Negative book and am impressed. Very well done with some great photography for illustration. I have all the previous editions of the RealWorld Camera Raw series and had found that the incremental value of each edition was diminishing since much of the material was repeated. A fresh start is most welcome.

Regards,

Bill
Title: Re: Color profiling while Exposing To The Right
Post by: madmanchan on September 26, 2012, 08:31:33 AM
Do you agree that getting an optimal exposure is best for making DNG profiles?

Yes. 


Quote
Do you disagree that using a known reference chart (synthetic PPRGB) is a good way of evaluating various exposure of a bracket in ACR?

I don't disagree.  I think it's also helpful just to check if the resulting color mapping generated by the table does what you expect.  The main limitation of a synthetic PPRGB chart is that it's usually calculated with one illuminant only (if your source doesn't specify, it's likely D50).  For the dual-illuminant profile, that means the color patches resulting from DNG PE's Chart Wizard probably won't match your synthetic ref chart because the DNG PE uses A/D65 (instead of D50).
Title: Re: Color profiling while Exposing To The Right
Post by: madmanchan on September 26, 2012, 08:37:03 AM
The DNG PE needs to be somewhat conservative in its chart wizard with regards to clipping because color tables are always applied after white balance.  Your raw capture may not have clipped data in its native coordinate system (native RGB, without WB applied), but that data can become clipped after WB is applied.  That leads to problems with the color mapping.  DNG PE will generally detect this case and prevent you from proceeding.

My recommendation is simply to bracket exposures and then pick the brightest one that DNG PE will accept without giving you an error.
Title: Re: Color profiling while Exposing To The Right
Post by: mac_paolo on September 26, 2012, 08:59:17 AM
My recommendation is simply to bracket exposures and then pick the brightest one that DNG PE will accept without giving you an error.
That's exactly what I always do :)
Title: Re: Color profiling while Exposing To The Right
Post by: Schewe on September 26, 2012, 12:38:54 PM
BTW, I just received my copy of your Digital Negative book and am impressed. Very well done with some great photography for illustration. I have all the previous editions of the RealWorld Camera Raw series and had found that the incremental value of each edition was diminishing since much of the material was repeated. A fresh start is most welcome.

Thanks for the kind words...
Title: Re: Color profiling while Exposing To The Right
Post by: Bryan Conner on September 26, 2012, 02:05:38 PM
Thanks for the kind words...

What????!!!!??????  You have a new book and did not tell me (us)?  Shame shame shame.  Just kidding...ok, I have to go buy my kindle edition over at Amazon.de now.  Looking forward to reading and learning....
Title: Re: Color profiling while Exposing To The Right
Post by: bjanes on September 26, 2012, 04:04:05 PM
I use Bruce Lindbloom's (http://www.brucelindbloom.com) ColorChecker Calculator (http://www.brucelindbloom.com/index.html?ColorCheckerCalculator.html) to determine what the target chromaticity should be in ProPhoto RGB and simply read the patches in ACR set to ProPhoto RGB...pretty simple really. Just set the calculator to ProPhoto RGB...

If you are lazy, you can download a synthetic ProPhoto RGB target file (http://colorremedies.com/realworldcolor/downloads/Macbeth_ColorChecker_ProPhoto.jpg.zip) from Chris Murphy's web site (http://colorremedies.com). It gives you the RGB target readouts of ProPhoto RGB. Save it as a TIFF and you can load the photographed target brackets and the synthetic target in ACR and check the readouts for an optimal exposure.

Curiously, the numbers specified on the file don't match the actual measured values of the image.

Not disagreeing with any of your comments on this though.

It is interesting to note that there are two common methods to obtain the color checker values for a given illuminant and color space (which itself has its own white point). The most accurate method is to compute the values directly using the spectral reflectance properties of the target convolved with the spectrum of the light source. This is the method used by Bruce Lindbloom's ColorChecker calculator, and no chromatic adaption is needed as explained here (http://www.brucelindbloom.com/index.html?ColorCheckerCalcHelp.html) by the author. This is the method that Jeff is recommending. Another method would be to download the synthetic chart thus derived (say in L*a*b or ProphotoRGB) and then convert to the desired space in Photoshop, which would use chromatic adaption (the Bradford algorithm by default in Photoshop, I think). This does introduce errors as Bruce explains in the link. I would think that Chris Murphy's synthetic chart in ProphotoRGB also uses the exact calculated values.

If one photographs the chart in D50 illumination and uses a D50 space such as ProphotoRGB, then no chromatic adaptions are needed. Unfortunately there is no standard D50 source, but D50 fluorescent lamps are available. If one photographs the chart under D50 and renders into a D65 space such as sRGB, a chromatic adaption is needed and one would likely obtain results slightly different than if the chart were photographed under D65. Illuminant E (http://en.wikipedia.org/wiki/Standard_illuminant#Illuminant_series_D) (which is not black body and has no color temperature but a CCT of 5455 K) is interesting since the XYZ color matching functions are normalized such that their integrals over the visible spectrum are the same.  You talk about measured values in the image, but I don't think that any measurements are made--the values are calculated.

It is all a bit confusing and I don't claim to understand the details and think this would be a good subject for another thread or tutorial.

Regards,

Bill



Title: Re: Color profiling while Exposing To The Right
Post by: Rhossydd on September 26, 2012, 04:35:25 PM
You talk about measured values in the image, but I don't think that any measurements are made--the values are calculated.
If you view the image (in it's correct colourspace) the measurements reported by PS's eye dropper are different to the values defined in numbers on the image itself.

Maybe it's something to do with JPG compression, but it's a curious issue that suggests you shouldn't get too pedantic over matching exact numbers.
Title: Re: Color profiling while Exposing To The Right
Post by: samueljohnchia on September 26, 2012, 11:20:33 PM
The main limitation of a synthetic PPRGB chart is that it's usually calculated with one illuminant only (if your source doesn't specify, it's likely D50).  For the dual-illuminant profile, that means the color patches resulting from DNG PE's Chart Wizard probably won't match your synthetic ref chart because the DNG PE uses A/D65 (instead of D50).

Hi Eric,

Could you help to verify the illuminant(s) used under the various circumstances when generating the color tables in the DNG PE's Chart Wizard?

Both color tables - Illuminant A for 2850K and D65 for 6500K (as per your post)
6500K table only - D65?
2850K table only - Illuminant A?
6500K first and then 2850K after (or vice versa) - Illuminant A for 2850K and D65 for 6500K?

I noted that the profile that I generated for both color tables at once is slightly different from the one where I generated the 6500k table first and then the 2850K after because the RGB readouts after applying the profiles in Camera Raw (7.1) is different. I did not move the control end points for the target when making the profiles. Is this down to some averaging error?
Title: Re: Color profiling while Exposing To The Right
Post by: Schewe on September 28, 2012, 04:08:55 AM
What????!!!!??????  You have a new book and did not tell me (us)?  Shame shame shame.  Just kidding...ok, I have to go buy my kindle edition over at Amazon.de now.  Looking forward to reading and learning....

Yeah, ya know...I do have a life outside of LuLa...sorry to sneak up on ya!

Yes, I did a new book called The Digital Negative (http://www.amazon.com/The-Digital-Negative-Processing-Lightroom/dp/0321839579)...kinda tried to sneak it in through the back door. Didn't want to make a big deal about it. If ya wanna know it's shipping (in print and ebook form) and has it's own website The Digital Negative Book.com (http://thedigitalnegativebook.com/wp/).

Sorry I didn't make a big deal about it...but now ya know.

Buy one for yourself and a few more for your friends...don't worry, we'll make more!
Title: Re: Color profiling while Exposing To The Right
Post by: Peter_DL on September 28, 2012, 01:55:31 PM
My recommendation is simply to bracket exposures
and then pick the brightest one that DNG PE will accept without giving you an error.

When we create a series of DNG profiles by running the chart wizard on such bracketed exposures (not too bright/clipped or too dark/noisy),
which sort and magnitude of deviations would we have to expect with the resulting Hue/Sat.-corrections per patch ?

Peter

--
Title: Re: Color profiling while Exposing To The Right
Post by: madmanchan on September 29, 2012, 01:55:18 PM
Hi Eric,

Could you help to verify the illuminant(s) used under the various circumstances when generating the color tables in the DNG PE's Chart Wizard?

Both color tables - Illuminant A for 2850K and D65 for 6500K (as per your post)
6500K table only - D65?
2850K table only - Illuminant A?
6500K first and then 2850K after (or vice versa) - Illuminant A for 2850K and D65 for 6500K?

Yes, if you do the 6500k table only, it's D65.  If you do the 2850K table only, it's Std illuminant A.  Regardless of the order you choose to do them in individually, the mapping is always the same.

Quote
I noted that the profile that I generated for both color tables at once is slightly different from the one where I generated the 6500k table first and then the 2850K after because the RGB readouts after applying the profiles in Camera Raw (7.1) is different. I did not move the control end points for the target when making the profiles. Is this down to some averaging error?

This sounds unexpected to me.  How different are the readouts? 
Title: Re: Color profiling while Exposing To The Right
Post by: samueljohnchia on September 30, 2012, 01:34:23 AM
This sounds unexpected to me.  How different are the readouts? 

Thank you for the clarification. The readouts differ from 1 - 3 values. The image of the colorchecker that I used to generate the camera dng profiles is the same as the one that I used to evaluate the differences between the profiles. The readouts are in ProphotoRGB and 16bits/color channel. The patches second row, first on the right (warm yellow) and third row, second from the right (magenta) differ the most - 3 values in the blue channel. A fair number of the other color patches also differ by 1 - 2 points in the R, G or B channel, sometimes in more than one channel. Only the neutral patches remain identical.

The image of the colorchecker was white balanced by using the WB tool in camera raw on the second lightest neutral patch. However, I am not sure that this is ideal as we know that none of the 'neutral' patches are spectrally neutral. Only the large gray patch found on the colorchecker passport is spectrally neutral.

This document (http://www.rmimaging.com/information/ColorChecker_Passport_Technical_Report.pdf) provides evidence of that claim.

There are some other things I noticed when building camera profiles with the DNG PE. I will collate the information and post it in a new thread, to not go off topic here.
Title: Re: Color profiling while Exposing To The Right
Post by: samueljohnchia on September 30, 2012, 05:50:13 AM
Yes, if you do the 6500k table only, it's D65.  If you do the 2850K table only, it's Std illuminant A.  Regardless of the order you choose to do them in individually, the mapping is always the same.

Erm Eric, your post here (http://www.luminous-landscape.com/forum/index.php?topic=59688.msg482472#msg482472) states that a single illuminant profile assumes D50 as the illuminant. Has the behavior of the DNG PE changed?
Title: Re: Color profiling while Exposing To The Right
Post by: erpman on October 21, 2012, 06:18:52 AM
Thought Id revive this thread since I have an assignment that Im a litte puzzled over:

Im going to document an exhibition of paintings, and the artist wants me to produce images that are as close to the original lighting, contrast and color. The pictures will show the paintings in context, the rooms of the museum. The exhibition consists of massive dark black-grey-green paintings with a lot of structure in them. What makes me scratch my head is the lighting. The rooms are lit in a low-key light, almost like twilight. Its very cool, and its making the paintings even heavier and darker, and I want to communicate that muted feeling in the pictures.

Here you can see one of the paintings: http://www.lautom.no/exhibitions/show/1 (http://www.lautom.no/exhibitions/show/1)

But the big question is how to meter and expose to get the contrast right, but at the same time exposing to the right since the main subject is in the far left of the histogram? The easy way would be to spot meter an 18% grey card, but then I wont be exposing to the right. Im thinking that somehow I should be able to use the color checker grayscale as a reference to get the right exposure and contrast when pulling the exposure in ACR?

Would it be reasonable to meter an 18% grey card and then adding one stop and pulling one stop in ACR?? Or am I missing something?