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Author Topic: X-Rite ColorChecker Passport  (Read 22930 times)
Jonathan Wienke
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« Reply #40 on: November 19, 2009, 07:53:41 AM »
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I find it hilarious that people are complaining about lack of "color accuracy" and using non-linear tone curves, etc. Clipping blacks to boost contrast is a valid creative image adjustment, but it has nothing to do with accuracy. The same is true of using S-curves to boost contrast. If you want "accurate" colors, all of the "creative" adjustments have to be TURNED OFF.
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neil snape
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« Reply #41 on: November 19, 2009, 08:22:29 AM »
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Quote from: Jonathan Wienke
I find it hilarious that people are complaining about lack of "color accuracy" and using non-linear tone curves, etc. Clipping blacks to boost contrast is a valid creative image adjustment, but it has nothing to do with accuracy. The same is true of using S-curves to boost contrast. If you want "accurate" colors, all of the "creative" adjustments have to be TURNED OFF.
You are absolutely right. There will be a lot of confusion by the naming involved and the comprehension of what the expected colours will be.
I think it is used to correlate what the camera sees as a base into LR/CR. What controls you apply in LR/CR to the raw files certainly do affect the balance. That said if you look at the passport profiles there will be certain colours with certain cameras that will have an exaggerated saturation in some areas, which may or may not be to your liking. For me it's okay as I am not counting on accuracy for scene rendering to working space, rather a nice balance close to what I see in the scene to it's working space that I know I can work with for reproduction.


I haven't seen any visual differences of DE >25 , as that would show up like a sore thumb.
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digitaldog
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« Reply #42 on: November 19, 2009, 08:25:02 AM »
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In this kind of context, “accuracy” is a BS marketing term that can’t be defined because we’re dealing with output referred imagery. By that very context, its not accurate, its pleasing. You can’t put a matrix on pleasing, certainly not using something like deltaE!
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Andrew Rodney
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Eric Myrvaagnes
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« Reply #43 on: November 19, 2009, 09:13:44 AM »
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"Accurate" = "Boring," IMHO. 
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-Eric Myrvaagnes

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probep
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« Reply #44 on: November 19, 2009, 09:20:06 AM »
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Quote from: Jonathan Wienke
I find it hilarious that people are complaining about lack of "color accuracy" and using non-linear tone curves, etc. Clipping blacks to boost contrast is a valid creative image adjustment, but it has nothing to do with accuracy. The same is true of using S-curves to boost contrast. If you want "accurate" colors, all of the "creative" adjustments have to be TURNED OFF.
Hm... What's about the "Camera Neutral" DNG profile with "Medium contrast" tone curve that is set as default? Colors are almost accurate there. If I set the tone curve to linearized type, I get undersaturated colors.
I do not see logic: to get accurate colors in one case I must set linearized tone curve, in another - "Medium Contrast" tone curve.
« Last Edit: November 19, 2009, 09:50:37 AM by probep » Logged
digitaldog
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« Reply #45 on: November 19, 2009, 09:52:15 AM »
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Quote from: probep
Hm... What's about the "Camera Neutral" DNG profile with "Medium contrast" tone curve that is set as default? Colors are almost accurate there.

Accurate how? How are you defining the term? How can output referred be accurate when you can’t actually measure the scene colorimetry and compare it to the values in the output referred capture?

This may help the definition of accurate:
http://www.color.org/ICC_white_paper_20_Di...ment_basics.pdf
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Andrew Rodney
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probep
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« Reply #46 on: November 19, 2009, 10:24:26 AM »
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Quote from: digitaldog
Accurate how? How are you defining the term? How can output referred be accurate when you can’t actually measure the scene colorimetry and compare it to the values in the output referred capture?
Why I can't? When I shoot a ColorChecker SG in studio, I can. I try to get small deltas.
There are almost no problems with ICC input profiles. In studio, of course.
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digitaldog
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« Reply #47 on: November 19, 2009, 10:31:11 AM »
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Quote from: probep
Why I can't? When I shoot a ColorChecker SG in studio, I can. I try to get small deltas.
There are almost no problems with ICC input profiles. In studio, of course.

Again, I think your methodology is flawed but I’m open to hearing how you gauge this. You’ve got a target. You’ve measured the values in the scene and have Lab values? You’ve got rendered values of that image which are output referred. You’re comparing scene referred values to output referred values. Apples to oranges. Read the ICC article. It explains why scene referred looks butt ugly until its output referred. Eric explained this above too.

If anything, ICC profiles which are output referred, (the reason Adobe went another direction with DNG profiles) are farther from the goal of comparing scene and captured colorimetry.
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Andrew Rodney
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probep
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« Reply #48 on: November 19, 2009, 11:08:43 AM »
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Quote from: digitaldog
Again, I think your methodology is flawed but I’m open to hearing how you gauge this. You’ve got a target. You’ve measured the values in the scene and have Lab values? You’ve got rendered values of that image which are output referred. You’re comparing scene referred values to output referred values.
Yes, you are almost right (we measure spectral data of lighting also). But it does not matter at all.
Do you really think that this approach is always wrong? For all cases? (What's about digital art reproductions for example?)
Thank you, I read the ICC article earlier.
« Last Edit: November 19, 2009, 11:10:46 AM by probep » Logged
digitaldog
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« Reply #49 on: November 19, 2009, 11:16:55 AM »
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Quote from: probep
Do you really think that this approach is always wrong? For all cases? (What's about digital art reproductions for example?)

The issue is, using a term accuracy, you need a measured matrix (which was deltaE above and which has a slew of issues all its own). Outside measuring, we can say “visually the reproduction and original match” but its nearly impossible to put a measured matrix on this when the colorimetry (the measurements of the original art work and your Epson print) don’t sync up. And someone can say “these match perfectly” and someone else can say “They are close”. Its subjective. Just as pleasing color is subjective. That being the case, using a term “accuracy” has way too much fudge factor for my taste.
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Andrew Rodney
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probep
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« Reply #50 on: November 19, 2009, 11:32:16 AM »
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digitaldog
Andrew, thank you for for the clarification.
« Last Edit: November 19, 2009, 11:33:00 AM by probep » Logged
Professional
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« Reply #51 on: November 19, 2009, 01:03:25 PM »
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Question: I have a color Checker already from X-Rite [both small and standard sizes], also a GrayScale from them, so what will this CChecker Passport give me more?
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madmanchan
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« Reply #52 on: November 19, 2009, 02:20:58 PM »
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I believe you can use the Passport software with your existing ColorChecker.

The advantage of the Passport hardware is in its design. It is better for field use because it can be snapped shut to keep debris off the patches. It can also be propped up and oriented at various angles. There are also additional patches as mentioned in Michael's review which can act as additional "white balance presets" -- creative warming/cooling, etc.

On the whole concept of accuracy and evaluation, one of the problems with doing numeric evaluations is inherent limitations of the color matching model. For example, L*a*b* comparisons via Delta E 1976, or any of the newer metrics, are based solely on colorimetry with assumed viewing conditions which often do not match the actual photographed scene conditions (e.g., photographing a ColorChecker in bright daylight versus in a dim room may lead to very similar reported L*a*b* values but very different actual appearance of the chart). You may have noticed that if you try downloading a reference ColorChecker image (Google search should turn up a few) and view it on your display, even with a well-profiled display whose gamut contains all of the patches, the tonal contrast does not look the same as the real thing.

The other problem is that optimizing for chart reproduction does not necessarily lead to better results on real images. Obviously if there is a significant problem with an existing profile (e.g., blues are coming out green) then a custom-built profile from a chart you've shot will fix that. But when one starts getting into nuances of exactly what shade of red you're looking for, it's not so clear. There are cases where optimizing for the chart (e.g., red patch) will give you a perfect hue reproduction of that patch but not so good reproduction of other real-world red colors. This can result from camera metamerism and cannot be addressed by a single color transform (profile).
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bjanes
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« Reply #53 on: November 19, 2009, 03:40:43 PM »
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Quote from: madmanchan
If you are trying to measure output-referred values (e.g., in Photoshop) and compare them to published reference values, they will likely be far off. In general the auto profiles created by the DNG Profile Editor and X-Rite software do not adjust the tone curve. Therefore, using these profiles within CR/LR will result in using the default tone curve within CR/LR, which has a fair amount of brightening and contrast added. Also the Blacks setting of 5 (default value in CR/LR) will step on the shadows a bit and also result in punched up colors. You can use a linearized tone curve within CR/LR by setting Brightness, Contrast, and Blacks to zero, and setting Point Curve to linear. You can then adjust Exposure so that the gray values match up reasonably well with the published chart values, assuming reasonably uniform illumination on the chart. The result will be closer to published values, but if you try to use these settings on real images, they will not look so good ...
Eric,

A very informative post. I used the profile for my D3 that I made with the DNG profile editor using Adobe Standard as the starting point and then rendered an image of the Colorchecker into aRGB with ACR default settings and then with ACR set to linear as you suggested and looked at the results with Imatest. The results are shown below graphically and the linear version closer to the nominal values:

[attachment=18055:CompositeProfiles.png]

As an interesting aside, I did note that an exposure offset of -0.5 EV is needed with the ACR defaults, whereas no offset is needed with the linear settings. Is this typical?

Bill
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Jonathan Wienke
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« Reply #54 on: November 19, 2009, 03:46:57 PM »
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Quote from: bjanes
As an interesting aside, I did note that an exposure offset of -0.5 EV is needed with the ACR defaults, whereas no offset is needed with the linear settings. Is this typical?

Bill

It's not surprising, given that a tone curve's main purpose is to alter luminance. Depending on the exact curve used, the net effect could be to increase or decrease overall luminance.
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neil snape
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« Reply #55 on: November 19, 2009, 03:50:31 PM »
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Quote from: Professional
Question: I have a color Checker already from X-Rite [both small and standard sizes], also a GrayScale from them, so what will this CChecker Passport give me more?


THE PASSPORT CHART HAS A FOLDING WELL DESIGNED PLASTIC CASE FOR PROTECTED HANDLING WHEN USED. THE PATCHES ARE BETTER WEATHER PROTECTED, AND THERE ARE OF COURSE THE WARMING AND COOLING PATCHES INCLUDED FOR FAST CUSTOMISATION OF YOUR SHOOTING CONDITIONS.

Ooops caps lock.


I still have some mini color checker charts, but I don't think they will see much use. Yet if you have one already then go ahead and use the X-Rite software and try out what it will do with the standard chart. The Passport really is made to be tossed in the kit bag, and becomes an accessory that is unobtrusive, but there when you need it. I still have a large SG chart but it's too big for my small gear bag, so has always been in my i1 Pro bag, usually far from any shoots outside of the studio.
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neil snape
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« Reply #56 on: November 19, 2009, 03:51:41 PM »
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Quote from: Jonathan Wienke
It's not surprising, given that a tone curve's main purpose is to alter luminance. Depending on the exact curve used, the net effect could be to increase or decrease overall luminance.
Is it to alter L* or gamma?
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bjanes
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« Reply #57 on: November 19, 2009, 04:14:53 PM »
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Quote from: Jonathan Wienke
It's not surprising, given that a tone curve's main purpose is to alter luminance. Depending on the exact curve used, the net effect could be to increase or decrease overall luminance.
That is obvious, but the extent of the exposure compensation needed with the ACR default TRC can be confusing. The BaselineExposure for the D3 is +0.5 EV. Proponents of ETTR looking at the histogram in ACR may assume that they have overexposed when the highlights are clipped and cut back on exposure for future pictures. Many have complained about Adobe's using a BaselineExposure for this reason. However, one can avoid this pitfall merely by looking at the histogram with a linear TRC. Such an exposure is not present with Nikon's own raw converter.

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teddillard
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« Reply #58 on: November 21, 2009, 05:37:45 AM »
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Quote from: eronald
Yes, I consulted for Xrite on the photographic aspects of this product, and I stressed the importance of robust packaging and in-use protection for a tool that needs to be taken to location and used there.

Edmund

Edmund.  I thank you from the bottom of my heart.  And camera bag.    

This, (and maybe a color-fast T-Shirt with a target printed on it) could well be something that gets a Colorchecker into the hands of many, many photographers who should be using it, but don't.  

I think the Lightroom plugin is brilliant.  The ACR integration is a little lacking, esp. having to restart Photoshop and all, but this takes me back to the Kodak camera software, where you could build a profile right in the workflow- making it so easy and seamless that it truly made camera profiling practical.  (Too bad their cameras weren't as good...    )

I've posted some stuff here, in addition to everything else out there and here too...  

... an intro to the thing
http://www.h2hreviews.com/blog/X-Rite-Passport.html

a brief Lightroom explanation:
http://www.h2hreviews.com/blog/X-Rite-Pass...12;Part-2-.html

and I did a little Youtube number on how you can use it.
http://www.h2hreviews.com/blog/X-Rite-Passport--Part-3-.html
« Last Edit: November 21, 2009, 07:21:13 AM by teddillard » Logged

Ted Dillard
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