Profiling a GFX 100 with X-rite CC calibration, part 2

Warning! This post was created before I realized that the CC24 patches in the CCSG had different values than the CC24 patches in a real CC24 target.

https://blog.kasson.com/the-last-word/cc24-vs-ccsg-spectra-and-cielab-values/

Yesterday I posted about my experiences using the X-Rite CC24 and CCSG targets and X-Rite’s Color Checker Camera Calibration program in diffuse illumination. Before that test, I made a profile with the CCSG target in direct sunlight at a 45-degree angle to the target. The colors were overly chromatic. Several people said that the CCSG target might be more sensitive to glare than the CC24 — the SG does stand for semigloss — leading to dulling of the patches when the capture used to make the profile is exposed, leading to overly saturated colors when the profile is used.

That makes a kind of internal sense. I did some testing this morning to find out if it’s right. Spoiler: not even close.

I set up the target lit at approximately a 45-degree angle (maybe a bit more oblique than that) by early morning (shortly after eight at about the 35th parallel) sunlight. Here’s the spectrum of the sunlight:

Since the illumination is so close to 5000K blackbody radiation, I defeated the Bradford adaptation in my analysis software. I used Color Checker Camera Calibration to make profiles for the camera, using both the CC24 and CCSG targets. Then I analysed the accuracy of those profiles, throwing Adobe Color Profile into the mix.

1. The first column of numbers is the CC24 patches processed using the Adobe Color Profile
2. The second column is the cropped CCSG patches processed using the Adobe Color Profile
3. The third column is the CC24 patches processed using the CC24 profile
4. The fourth column is the cropped CCSG patches processed using the CCSG profile

Mean Delta E is the average CIELab delta E. Since Delta E can never be negative, errors in one direction don’t cancel out errors in another.

Mean Delta L is the average difference in the CIELab and CIELuv vertical (luminance) channel. Positive Delta L means that the output is brighter than it should be. Negative Delta L means that the output is darker than it should be. Thus Delta L is good for detecting systematic luminance bias.

Mean Gray Delta L is the average difference in the CIELab and CIELuv vertical (luminance) channel for the 6 gray patches. Positive Gray Delta L means that the output is brighter than it should be. Negative Gray Delta L means that the output is darker than it should be. Thus Gray Delta L is good for detecting systematic luminance bias in the gray axis.

Mean Delta A and B are the average differences in the CIELab and CIELuv a and b channels. Positive Delta A or B means that the output is redder or yellower than it should be. Negative Delta A or B means that the output is bluer or more cyan than it should be. These measures are good for detecting systematic color balance bias.

Mean Delta Cab is the average chroma error measured in Lab. A positive number means that the output colors are more saturated than they should be. A negative number means that the output colors are less saturated than they should be.

Mean Non-Gray Delta Cab is the average chroma error measured in Lab for the 18 chromatic patches. Mean Non-Gray Delta Cuv is the average chroma error measured in CIELuv for the 18 chromatic patches. A positive number means that the output colors are more saturated than they should be. A negative number means that the output colors are less saturated than they should be. The sigma metrics track the standard deviation of the 18 samples.

Mean Delta Hab is the average hue angle error measured in Lab, expressed in degrees. The gray patches are excluded from this measure, since their target hue angle is undefined. A positive number means that the output colors have a hue angle higher than they should have. A negative number means that the output colors have a hue angle lower than they should have. Mean Delta Huv is the same measure in CIELuv.  The sigma metrics track the standard deviation of the 18 samples.

Look at the first two columns, which both use the Adobe Color profile, concentrating on the darker yellow rows. The crop of the CCSG patch set is more chromatic than the CC24 set. This is exactly the opposite of the predicted behavior in this sentence at the top of this post: “Several people said that the CCSG target might be more sensitive to glare than the CC24 — the SG does stand for semigloss — leading to dulling of the patches when the capture used to make the profile is exposed…”

Now look at the next two columns, in which the CC24 patches are developed using the X-Rite-generated CC24 profile, and the CCSG patches are developed using the X-Rite-generated CCSG profile. They are both more chromatic than they were with the Adobe Color profile. In addition, the increased chroma in the CCSG target is not calibrated out by the profiling process.

This is going to take some more work. It’s not making it any easier that the X-Rite profile creator is a black box with no knobs. I’m in the process of learning how to use Lumariver Profile Developer, and I’ll be reporting on my experiences with it and both the CC24 and CCSG targets.