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Author Topic: Color Checker adjustment with Camera Profiler  (Read 3259 times)
dmward
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« on: August 14, 2008, 06:24:24 PM »
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I want to be able to make fine tuning adjustments to a color checker either in the camera profiler package or in LR so that when an image in imported into LR it is accurate based on the bottom two rows of a Color Checker. Thus, once I have have a camera/lighting profile, if I shoot a color checker and import the raw file, the RGBYMC color wedges will be accurate to the Color Checker itself.

I found in CS3 that a curves layer and a selective color layer could be used for fine tuning.

Unfortunately, the RGB references in LF develop module are in % and there seems to be no way to control each channel individually. (If its in the LL Tutorial I missed it on the first viewing.)

The purpose for this effort is to be able to document works of art, works on paper as well as oil paintings and sculptures based on reference standard color "chips" based on the Macbeth Color Checker bottom two rows.

Naturally, doing this in LR has significant workflow benefits compared to going into CS3.

Hopefully this was a reasonable clear question: How can I fine tune the RGBYMC, and six gray scale wedges in LR develop module after making a camera profile using the Profile editor?

The objective is to get them to within .5% of the reference color checker that was photographed for the camera calibration.

Thanks for suggestions.

David
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ErikKaffehr
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« Reply #1 on: August 14, 2008, 08:17:23 PM »
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Hi,

You may be interested in the article below:

http://www.photoactivity.com/Pagine/Artico...l%20sole_en.asp

The calibration scripts use ACR in Photoshop but settings can be used in Lightroom

Have you checked out this? You can use an Color Checker for this, too.

http://www.luminous-landscape.com/reviews/...-profiles.shtml

Erik

Quote
I want to be able to make fine tuning adjustments to a color checker either in the camera profiler package or in LR so that when an image in imported into LR it is accurate based on the bottom two rows of a Color Checker. Thus, once I have have a camera/lighting profile, if I shoot a color checker and import the raw file, the RGBYMC color wedges will be accurate to the Color Checker itself.

I found in CS3 that a curves layer and a selective color layer could be used for fine tuning.

Unfortunately, the RGB references in LF develop module are in % and there seems to be no way to control each channel individually. (If its in the LL Tutorial I missed it on the first viewing.)

The purpose for this effort is to be able to document works of art, works on paper as well as oil paintings and sculptures based on reference standard color "chips" based on the Macbeth Color Checker bottom two rows.

Naturally, doing this in LR has significant workflow benefits compared to going into CS3.

Hopefully this was a reasonable clear question: How can I fine tune the RGBYMC, and six gray scale wedges in LR develop module after making a camera profile using the Profile editor?

The objective is to get them to within .5% of the reference color checker that was photographed for the camera calibration.

Thanks for suggestions.

David
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dmward
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« Reply #2 on: August 14, 2008, 09:14:43 PM »
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Erik,
the Fors scripting is what I used before the release of the DNG profiler.

That is what I am using to generate the base camera profile.
The result is an image that is reasonably accurate but well short of the accuracy that I am looking for. As was the Fors script. It was after using that script that I used the selective color and curves layers for fine tuning.

Now I am looking for a way to do the fine tuning in LightRoom.

David


Quote
Hi,

You may be interested in the article below:

http://www.photoactivity.com/Pagine/Artico...l%20sole_en.asp

The calibration scripts use ACR in Photoshop but settings can be used in Lightroom

Have you checked out this? You can use an Color Checker for this, too.

http://www.luminous-landscape.com/reviews/...-profiles.shtml

Erik
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ErikKaffehr
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« Reply #3 on: August 15, 2008, 12:22:29 AM »
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Hi,

I think that the "Tindemans script" has more options than the "Fors script". There is also an issue that  there is some variations in the Xrite Color Checker (what used to be MBCC) itself.

The DNG profiler lets you adjust color for each patch individually, I think. As far as I understand you can have some kind of automatic optimization but I think you can do a final tuning by hand. I have not done it myself. See attached screendump.

You also need to consider color spaces. If you do things by the numbers I guess LAB is what is needed. If you use perceptual rendering the colors will be shifted around when you convert between color spaces, so you probably need to work in relative colorimetric. Sorry for mentioning this, I'm sure you already paid consideration to this, but the information may be useful for some other reader.

Best regards
Erik


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Erik,
the Fors scripting is what I used before the release of the DNG profiler.

That is what I am using to generate the base camera profile.
The result is an image that is reasonably accurate but well short of the accuracy that I am looking for. As was the Fors script. It was after using that script that I used the selective color and curves layers for fine tuning.

Now I am looking for a way to do the fine tuning in LightRoom.

David
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« Last Edit: August 15, 2008, 08:57:20 AM by ErikKaffehr » Logged

bjanes
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« Reply #4 on: August 15, 2008, 07:17:20 AM »
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You also need to consider color spaces. If you do things by the numbers I guess LAB is what is needed. If you use perceptual rendering the colors will be shifted around when you convert between color spaces, so you probably need to work in relative colorimetric. Sorry for mentioning this, I'm sure you already paid consideration to this, but the information may be useful for some other reader.
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A small point, but perceptual rendering is not available with matrix color spaces such as aRGB, ProPhotoRGB, etc, since they don't have the necessary lookup tables to perform the task. Conversion between these matrix profiles is always relative colorimetric even though Photoshop will allow you to choose perceptual.

The new PE uses lookup tables in addition to tweaking matrix coefficients, so it should be able to perform a more accurate calibration than any of the scripts previously used for this purpose.

Bill
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madmanchan
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« Reply #5 on: August 15, 2008, 07:55:12 AM »
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The reason the DNG Profile Editor's Chart Wizard isn't giving you your "within 0.5% of reference chart value" tolerance is likely because it ignores tonality (i.e., it doesn't try to match the gray levels of the gray patches of the chart). This is by design. We decided to leave tonality under user control, rather than profile control (although users are welcome to adjust the default tone curve in the Profile Editor by hand).
« Last Edit: August 15, 2008, 07:55:37 AM by madmanchan » Logged

dmward
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« Reply #6 on: August 15, 2008, 02:24:01 PM »
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Eric,
The comment about tonality is useful. However, even without regard to tonality, is there a way to get the RGBYMC color samples to be consistent with a reference chart?

For our purposes tonality is also important but that can be handled with a tone curve rather easily. Its getting the proper RGB components set for each color square that is frustrating me at the moment.

Erik mentioned the tweaking associated with the screen capture. I am having trouble figuring out how to do that based on a reference RGB value.

Suggestions?

Thanks.

Quote
The reason the DNG Profile Editor's Chart Wizard isn't giving you your "within 0.5% of reference chart value" tolerance is likely because it ignores tonality (i.e., it doesn't try to match the gray levels of the gray patches of the chart). This is by design. We decided to leave tonality under user control, rather than profile control (although users are welcome to adjust the default tone curve in the Profile Editor by hand).
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seangirard
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« Reply #7 on: August 15, 2008, 03:10:22 PM »
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Eric,

Could you say a little bit about the decision to leave tonality out of the profile? I don't mean to imply that it is a bad call or anything; just curious about the reasoning.

-sean
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