Targets for camera profiling

Third-party raw photo processing applications need custom input profiles to make nice colour from camera RGB. For a long time now, I have making my own camera profiles with Argyll CMS. For this we need a profiling target (a test chart). All targets are not equal, as you will find in this review.

Profiling targets examined

I have evaluated the following reflective targets which are supported by Argyll CMS. I found reference data on the manufacturers websites for most charts. I don’t quote batch numbers for reference data because I believe the manufacturing is precise.

Chart Number of patches Cost
X-Rite ColorChecker Classic 24 USD 69
X-Rite ColorChecker Digital SG 140 USD 259
LaserSoft DCPro Studio Target 140 EUR 79
Wolf Faust IT8.7/2 C1 288 USD 30
HutchColor HCT (Fuji/Kodak) 528 USD 255
CMP Digital Target 4 570 EUR 92
Summary of camera profiling targets examined

Colour gamut

Modern digital SLR (DSLR) cameras have very wide colour gamuts. A wide gamut test chart is preferred, to exercise the camera’s response.

Below are two-dimensional gamut plots for seven targets (including two from HutchColor). The calculation of xyY is very simple from XYZ reference data. For the X-Rite charts I could only get Lab data and conversion to XYZ and then xyY is more involved (equations on Bruce Lindbloom’s site).

All targets are weak towards green. The HutchColor targets have the widest gamut. The ColorChecker Digital SG and LaserSoft DCPro targets have similar gamuts. The IT8.7/2 target provides satisfactory coverage with 288 patches. Surprisingly, the CMP Digital Target 4, with 570 patches, has a small gamut and is weak in blues and reds. Is the CMP Digital Target 4 simply a home-printed target?

Gamut plot for X-Rite ColorChecker Classic. This chart has rather weak RGB patches.

Gamut plot for X-Rite ColorChecker Digital SG. A decent gamut but this chart is expensive and has just 140 patches.

Gamut plot for LaserSoft DCPro Studio Target. A similar gamut to the X-Rite ColorChecker Digital SG.

Gamut plot for Wolf Faust IT8.7/2 C1. A good result from a simple and inexpensive chart.

Gamut plot for HutchColor HCT (Fuji). The gamut of the chart touches WideGamutRGB in cyans and yellows.

Gamut plot for HutchColor HCT (Kodak). Green is a little less intense than the HCT Fuji chart.

Gamut plot for CMP Digital Target 4. This chart is weak in blues and reds.

Dynamic range and white point

Modern DSLR cameras have very high dynamic range and a high contrast test chart is preferred. The white patch should be bright and neutral. The dark patch is less important because it is difficult to avoid glare.

The graphs below summarise brightness, contrast and white point for the seven targets. The ColorChecker Digital SG seems best overall, with a bright (L* = 96.5), neutral (Delta-ab = 1.1) white patch and not the worst contrast ratio (White/Black = 15).

White patch lightness for the seven targets considered in this review.

Black patch lightness for the seven targets considered in this review.

Also Observe that the medium makes a difference: the HutchColor HCT target on Kodak paper (Delta-ab = 0.7) is more neutral than Fuji paper (Delta-ab = 2.3). The Wolf Faust IT8.7/2 C1 is also printed on Kodak paper (perhaps different to HutchColor) and the white patch is slightly bluish (Delta-ab = 2.2).

White patch deviation from perfect neutral (Delta-ab=0) for the seven targets considered in this review.

Spectral problems

Camera profiling targets are commonly photographed in sunlight, which includes ultraviolet wavelengths (UV). Photographic papers can contain “fluorescent whitener additives” (or “optical brightening agents”) which makes these papers appear more blue. These papers and printed camera profiling targets can show colour shifts towards blue when there is ultraviolet in the light source.

Metamerism is another problem for photographic and printed targets. The processes are optimised to produce colour, usually from just three of four colourants, that look natural to the human eye but actually might be composed of quite different spectra. This is a problem if the camera spectral sensitivities are different to the human eye. ColorChecker targets are made using multiple different pigments, giving reflective spectra that are more representative of the real world.

Conclusions

Modern DSLR cameras surpass the gamut and dynamic range of any camera profiling target. For real world photography, forget about buying the “biggest and best” camera profiling target and consider more general matrix profile models.

I have found the simple and low-cost ColorChecker Classic 24 to be satisfactory for matrix profiles. The bigger ColorChecker Digital SG is expensive, but the increased number of patches may be useful for more detailed modelling (which I am yet to attempt).

ColorChecker charts are made using multiple different pigments, giving reflective spectra that are more representative of the real world. They are not printed and I don’t expect there are any fluorescent whitener additives in the pigments. I sold my Coloraid IT8.7/2 target because the Kodak photographic paper has fluorescent brightening additives.

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6 Responses to Targets for camera profiling

  1. Anonymous says:

    If a profiler is looking to maximize the colors available within the gamut spectrum. (eg. prophoto) What about adding more (different) products or paint swatches to photograph? Or best the swatches are calibrated constructed? (dye optimized)

    In particular, more extension into the green gamut.

    Is there a way in getting more (maximum) green gamut? (camera profile) As well as additional colors?

  2. Anonymous says:

    On a raw workflow, what is the very best color target?

    Hutch Kodak? Hutch reflective print target? (or best usage on just scanners?) Expand the hues on a basic colorchecker passport?
    (can you add more color hues with paint swatches?)

  3. Hi, altough its an old topik I hope you will follow new questions.
    I agree that Color Checker Passport is adequate for easy profiling. Still, colors are close to sRGB.. and it shows when I try to profile for reproduction shooting of paintings. I have the 24 patches pretty good, but light pastels are loosing color. Another problem with the Colorchecker Passport target is that the LAB values are different between tartgets and you dont get a proper measure reference file, so any profiling application is just as good as the variation among the diferent targets allows. Do you happen to have similar assessement data regarding larger gamut originals? Any help is appreciated.

    • bulumakao says:

      You might search the Argyll CMS mailing lists, where there are posts about making your own custom targets:

      http://www.freelists.org/archive/argyllcms

      More patches (hundreds) and a bigger look-up table profile can deliver higher accuracy under controlled lighting.

      Most accurate would be to measure the spectral sensitivity of the camera and the spectrum of the illuminant and to do the detailed colour calculations. However, current raw photo processing software does not support this approach.

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