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Author Topic: DSLR testing sites like DXOmark and Imaging Resource use HMI and LEDs for color  (Read 56289 times)

Alexey.Danilchenko

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He really has no clue about this topic and his agenda is not learning or aiding others; ignore his severe misinformed posts and maybe he will go away.
Duly noted - thanks Andrew.
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digitaldog

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No one here is an expert, not even me.
Wrong then absolutely correct; a rare occurrence from your keyboard. Not are you not an expert on color, nor play one on TV, you're generally wrong and without sufficient equipment or knowledge to be posing on this subject. Which is why you're called out and corrected so often from so many....

Now what is it you actually do for a living? Aside from posting a lot of rubbish on the subject of color, proving you're not an expert or sufficient in that topic, do give us an idea of what you believe you are an expert in, other than fiction on the subject of color. A lack of a reply indicates you still live with your parents.  ;D
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digitaldog

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Before I tackle Wyszecki and Stiles again.

Have you considered writing a second edition? 
Yeah, W&S isn't easy, evening reading but a good reference!
No desire to update the book; too much work, too little gain. It's enough work these days dismissing the nonsense from amateurs who think they should write about color in various forums but clearly should not.  ;)
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WayneLarmon

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... where one Lab channel differs by 5 units and we see (numerically via deltaE of 3.88 and visually) ...  after I've corrected them colorimetrically as we see here:

What program are you using?  All I've got is ColorMeter and the various programs in ArgyllCMS.  Which are very good but I don't think I can do the kind of comparative analysis that you did.  (Or maybe I need to add the documentation for ColorMeter and ArgyllCMS to my stack of remedial color science reading.)
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digitaldog

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What program are you using?


CT&A
http://www.babelcolor.com
Love how it shows the various deltaE differences visually (with the text and such).
ColorThink Pro can do the same. But what's great about CT&A unlike ColorThink Pro, is I can enter Lab or RGB values directly into the input fields (after receiving common numeric assumptions from Tim over the years), and actually show visually and numerically, the dE using many differing formulas.
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digitaldog

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Oh, for Doug and the fellow ignoring the colorimetric facts because he has no such tools, here's another set of Lab triplets that only differ 3 units in one channel and have a clear visual difference and a large dE using a differing formula. As I said, that statement about no visual differences when one Lab channel is off by 5 units is utter rubbish and the figment of someone's imagination:
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WayneLarmon

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This is a do-over for my earlier post because "4. Outside..." because 4. was out of focus.  This time I took my tripod out in the driveway and shot it properly.  (Somebody I probably know honked when they drove by.  This isn't helping my "crazy old man" reputation.)

Quote
I shot raw and white balanced on the lower right portion of the WhiBal card. (This is the way I always shoot paintings.)   I adjusted exposure (in ACR) so that this portion of the card was approx. 186.  They are

1. Walmart 75w daylight LED
2. Cree 100w daylight LED
3. Aputure Amaran AL-H198 LED panel
4. Outside under a cloudy sky, about 1:00 PM EDT.  ColorMeter measured the CCT as being about 6000K

I'm attaching the four images.  The three done under artificial light look pretty similar.  The one done outside looks different, 1., because the CCT is higher (shows on the background) and 2., because the angle of the light is different.  (And 3, because the one done outdoors is slightly out of focus because I quickly shot handheld because I felt like a doofus crouching down in my driveway shooting a small white thing balanced on a storage tub.)

This time I have

1. Outside under a cloudy sky, about 12:30 PM EDT.  ColorMeter measured the CCT as being about 6000K
2. Same, only with my Google Pixel 2.  Taken about four minutes after 1.
3. What the clouds looked like.  They were moving so light was changing.
4. ColorMeter done as close to 1. as possible (because of moving clouds.)

Because the Pixel 2 image was an OTC JPEG I didn't attempt to adjust white balance.  I did adjust exposure (pulled up in Curves) so the lower right portion of the WhiBal card was about 186, like the others.

Um, why is the Duv of real sunlight 0.0029?  Shouldn't it be closer to 0?  Is this an indication of measurement error with my ColorMunki (or with ColorMeter)?  Or is there something going on with the sun that the government isn't telling us?  Maybe this is a hint.
« Last Edit: June 08, 2018, 04:37:47 pm by WayneLarmon »
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WayneLarmon

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CT&A
http://www.babelcolor.com
Love how it shows the various deltaE differences visually (with the text and such).
ColorThink Pro can do the same. But what's great about CT&A unlike ColorThink Pro, is I can enter Lab or RGB values directly into the input fields (after receiving common numeric assumptions from Tim over the years), and actually show visually and numerically, the dE using many differing formulas.

Cool.  I downloaded CT&A and am running it in trial mode.  I can't seem to enter Lab values, only RGB.  I used PhotoShop's info tool to get RGB values from the CC yellow patch on 1., the Cree LEDs I shot yesterday and 2., the real daylight shot I did today (that was in focus.)  I attached a screenshot from CC&T.

Is the reason I can't enter Lab values because it is still in trial mode?

It doesn't support my ColorMunki Design.  ArgyllCMS spotread can make CGATS files from ColorMunki spectro readings (I just verified.)  I also don't see any file import in CT&A.  Is this also because it is in trial mode?

Otherwise it looks like a good learning tool.  I still have a lot of color science remedial work to do.

« Last Edit: June 08, 2018, 06:29:29 pm by WayneLarmon »
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Tim Lookingbill

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Wayne, will you post the photo of the family painting colors that aren't reproducing as intended and see if your Aputure lights correct it? This was the impetus of this entire discussion that started with you mentioning these paintings.

And disregard what I said about your using the "Ambient" port for measuring the bulbs. I don't know enough about what's going on with your measurement process nor do I have a spectro. Can't afford one anyway.

It wouldn't help me figure out how to predict what colors will distort with these daylight LED bulbs. The CRI numbers only tell me a progression of yellow and skin tone colors that appear to improve according to the CRI number but it doesn't answer why CCT 5000K daylight LED bulbs show this greenish yellow tint of white when there's nothing on planet Earth that shows this hue of white in any natural lighting situation including flash and direct sunlight.

And Andrew can kiss my ass with his unhelpful comments.
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Doug Gray

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Oh, for Doug and the fellow ignoring the colorimetric facts because he has no such tools

Try L*a*b* values 80,0,90 and 80,0,95 and look at the delta E2000 which is currently the best estimate of whether two patches appear different or not.   ;D

The vast majority of Lab triplets that vary by 5 in either a* or b* are quite visibly different.  But not all.
« Last Edit: June 08, 2018, 06:48:52 pm by Doug Gray »
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Doug Gray

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And disregard what I said about your using the "Ambient" port for measuring the bulbs. I don't know enough about what's going on with your measurement process nor do I have a spectro. Can't afford one anyway.

That's progress. Wayne's comment about how to read an illuminant's spectrum was exactly correct and showed a good understanding of the issues involved.

Wayne:
The ColorMunki Design spectrophotometer I use has two ports for reading.  The one at the top is for reading ambient light through a diffuser.  When it is set up for reading ambient light, I point it right at the light, usually six to eight inches away from the light to swamp out room reflections.
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digitaldog

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Is the reason I can't enter Lab values because it is still in trial mode?
Unless he's made it inoperative in demo, you have to make sure the Lab check boxes on either side is clicked on. Then as you enter values, a little red "go" icon appears which you click on to enter the values. Move from field to field on each side. Then you should see the deltaE mode take place and you can alter the formula as desired. 
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digitaldog

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The vast majority of Lab triplets that vary by 5 in either a* or b* are quite visibly different.  But not all.
Agreed, quite visibly different and I don't believe I suggested none were. Simply that Tim's statement is utterly and consistently bogus; he's speaking of ALL Lab triplets if we make the massive mistake of taking his text seriously.
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WayneLarmon

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Wayne, will you post the photo of the family painting colors that aren't reproducing as intended and see if your Aputure lights correct it? This was the impetus of this entire discussion that started with you mentioning these paintings.

The paintings I struggled with were done a few years ago when I was using CFLs.  The 2nd batch I was shooting recently weren't as out of bounds.  I don't know if it is because the pigments in the paintings fell in a different portion of the spectrum (that the LEDs lit properly), or if the newer LEDs are indeed better.  Several years ago I went through several rounds of having the images of the paintings printed by AdoramaPix (because I don't have a printer that prints 16x20 nor do I plan on buying one) before I went with the "least worst" prints.

I haven't reshot those paintings yet.  I was trying to get a better handle on measuring color rendering before I started up the cycles with AdoramaPix.

And because I have a lot of 100 year old B/W photos to digitize that were also discovered.  Color science isn't needed as much for those.  I'm working on camera scanning techniques so I don't have to use a slow flat bed scanner again.  This is mostly a tripod/copy stand and light stand thing, which is off topic for the color management forum.

Quote
And disregard what I said about your using the "Ambient" port for measuring the bulbs. I don't know enough about what's going on with your measurement process nor do I have a spectro. Can't afford one anyway.

[Edit: A ColorMunki grade spectro is less than the cost of a good lens.  The ColorMeter Android app is about the cost of a nifty fifty. {Flame}Any photographer should already have an Android Pixel 2 because it is the only smartphone that takes images that withstand 100% scrutiny.  P2 image quality ~= a M4/3 sensor.{/flame} A spectro and ColorMeter would be well worth it for any photographer if they can be used to take meaningful measurements of light sources.  Without needing to take a long detour into reading a stack of expensive color science textbooks.]

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It wouldn't help me figure out how to predict what colors will distort with these daylight LED bulbs. The CRI numbers only tell me a progression of yellow and skin tone colors that appear to improve according to the CRI number but it doesn't answer why CCT 5000K daylight LED bulbs show this greenish yellow tint of white when there's nothing on planet Earth that shows this hue of white in any natural lighting situation including flash and direct sunlight.

As I said, I don't pay too much attention to what my eyes can see (tints) because cameras render differently than eyes do.  I pay attention to the image that is displayed on my NEC PA241W (and ultimately on AdoramaPix prints.)  So I don't have any good painting examples now.  I don't think it would be of much value to show the paintings I shot with CFLs several years ago.

I am also trying to understand how the numerical measurements (CRI, TLCI, Duv, and R9, etc.) correlate.  As I have explained, I am refreshing what I used to know about color science, starting with Andrew's book.  I am at a loss how the new Cree bulbs have a TLCI of almost 97 and aren't almost perfect for rendering color shot with a camera (other than that pesky Luther/Ives thing.)

ColorMeter and a ColorMunki grade spectro are useful tools, once I figure out how to use them properly. 
« Last Edit: June 09, 2018, 10:09:18 am by WayneLarmon »
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digitaldog

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And disregard what I said about your using the "Ambient" port for measuring the bulbs. I don't know enough about what's going on with your measurement process nor do I have a spectro. Can't afford one anyway.
Anyone who's read more than a few of your posts on this subject have already disregarded what you wrote about a piece of hardware you know very little of anything about. Hence your silly rant/question to Wayne after which again, I had to correct you then bring you into our world of facts and science. Indeed, the most accurate text you've written in a very long time here is your admission you don't know enough about the measuring process many of the rest of us do clearly understand. And have actually experienced. Now if you'd consider how much you know, you don't know before posting, we'd all get more done in these parts. But you don't know what you don't know even when you're told correctly about how the stuff you have no experience with, actually works by experts who do know how they work. None being color scientists if you can actually believe that fact!
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It wouldn't help me figure out how to predict what colors will distort with these daylight LED bulbs.
Again, you know so little about this topic and how to measure color, your comment, like so many posted here is best ignored. Which is my goal in pointing out again, your massive misunderstandings of this topic along with your own admission of a lack of any experience measuring color.
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The CRI numbers only tell me a progression of yellow and skin tone colors that appear to improve according to the CRI number but it doesn't answer why CCT 5000K daylight LED bulbs show this greenish yellow tint of white when there's nothing on planet Earth that shows this hue of white in any natural lighting situation including flash and direct sunlight.
When you ask stupid questions expect stupid answers. No, that isn't what CRI tells those who understand what CRI is and how rather useless it is.
Quote
And Andrew can kiss my ass with his unhelpful comments.
The comments were never meant to be useful to you; that's not possible as you're a fact denier. The comments were made to correct your misinformed posts for others and the comments at least today, seem to have been successful in getting a newer member who hasn't witnessed your inability to post facts on color science a tip he too should ignore your rants. The kissing the ass part shows you've got to lower yourself down further from an amateur who has so little experience with this topic of color, to someone morphing into a troll here which may deserve moderation due to that comment. I personally don’t care you wrote it, there's no way I could kiss your ass when your own lips seem to be stuck onto that area of anatomy. Perhaps that position is why you are unable to measure an illuminant like some many other's here. Amateurs like you should read more, type less, assuming your newer agenda is to learn this topic. Until that occurs, what is your agenda for regularly posting misinformation that has been regularly dismissed and corrected with facts, by experts and professionals in the field of color and imaging?


Do we need to talk to your mom and dad about taking away your keyboard son? Shorten your curfew? 
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WayneLarmon

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Unless he's made it inoperative in demo, you have to make sure the Lab check boxes on either side is clicked on. Then as you enter values, a little red "go" icon appears which you click on to enter the values. Move from field to field on each side. Then you should see the deltaE mode take place and you can alter the formula as desired.

That worked.  I'm pausing now to watch your sRGB Myths videos.  It covers a lot of what I am asking questions about.

Thanks.
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Alexey.Danilchenko

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I'm also trying to find the value of measuring instruments.  I just bought and measured a Walmart daylight LED

To add to your measurements in this post here are some measurements for Yuji VTC COB LEDs and daylight for comparison. Measurements below show importance of not overheating the LED and include measurement for 4xLEDs run for 10 mins heated up pretty much to max temperature on full power and similarly the same with reduced power (PWM still at full rated current) to 75% which show quite a bit of difference in CCT, CRI and TLCI. Then also included measurement for single LED on large heatsink at full power (it does not go hot) and daylight measurement.

« Last Edit: June 09, 2018, 03:19:44 pm by Alexey.Danilchenko »
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Doug Gray

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Um, why is the Duv of real sunlight 0.0029?  Shouldn't it be closer to 0?  Is this an indication of measurement error with my ColorMunki (or with ColorMeter)?  Or is there something going on with the sun that the government isn't telling us?  Maybe this is a hint.

The Duv value goes along with the CCT. It's a measure of how far off, on CIEuv chromaticity, the measurement is from a black body at the CCT temperature. It's normal for sunlight, and D50, to have an offset. It certainly shouldn't be 0.

Note that the LED is closer to 0. Duv, together with the CCT, is only a measure of chromaticity and is more intuitive than just xy or uv. All are isomorphic, but they say nothing about how spikey the spectrum is. The various rendering indexes do that and to varying degrees of goodness.
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WayneLarmon

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The Duv value goes along with the CCT. It's a measure of how far off, on CIEuv chromaticity, the measurement is from a black body at the CCT temperature. It's normal for sunlight, and D50, to have an offset. It certainly shouldn't be 0.

Black body == Planckian locus, doesn't it? 

Wikipedia:

The relative spectral power distribution (SPD) of a D series illuminant can be derived from its chromaticity coordinates in the CIE 1931 color space.


Daylight locus in the CIE 1960 UCS. The isotherms are perpendicular to the Planckian locus. The two sections of the daylight locus, from 4000–7000 K and 7000–25000 K, are color-coded.
https://en.wikipedia.org/wiki/Standard_illuminant

Does "perpendicular" account for the offset?

I hadn't thought about this.  I was extrapolating that because the CRI of the sun (and of a black body radiator) is a perfect 100, that the Duv should be 0.  But they aren't the same thing.

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Note that the LED is closer to 0. Duv, together with the CCT, is only a measure of chromaticity and is more intuitive than just xy or uv. All are isomorphic, but they say nothing about how spikey the spectrum is. The various rendering indexes do that and to varying degrees of goodness.

The "varying degrees of goodness" is at the root of my posts in this thread.
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Doug Gray

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Black body == Planckian locus, doesn't it? 
Does "perpendicular" account for the offset?

I hadn't thought about this.  I was extrapolating that because the CRI of the sun (and of a black body radiator) is a perfect 100, that the Duv should be 0.  But they aren't the same thing.

Nope, they sure aren't the same. People often think of D50 as the same as blackbody 5,000K but they aren't. While the CCT of D50 is very close to 5,000K, the major difference is that it's offset along the CCT locus. That offset is surprisingly large, on the order of dE 4 or so, so the two "whites," side by side are noticeably different. Apart, you really can't see a difference.

However, the L/I issue relative to camera CFAs is a much bigger factor for most colored objects than these differences in the illuminant. And how good that is depends on both the CFA spectral response and the particular spectrum of whatever objects one is photographing. Those are bigger factors than whether the illuminant is D50, D55, D65, or an incandescent at 5,000K.
« Last Edit: June 09, 2018, 09:56:21 pm by Doug Gray »
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