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The chart should have at least 9 distinct color patches for 3×3 CCMs (which are generally recommended). Excellent results can usually be achieved with the inexpensive, widely-available 24-patch X-Rite Colorchecker.

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Is there a particular reason that we need at least 9 patches?

I am asking this because I am working on a computer vision project that uses a color card with only 4 patches. I followed the tutorial here. But none of the methods works, which makes me wonder if there is a minimum requirement to find the CCM?

I couldn't find any research to discuss this question, so I came here for help. Any help is appreciated.

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    $\begingroup$ Welcome to SE.SP! Is it as simple as needing at least as many independent measurements as you have things you want to estimate? If you have only four measurements (color patches), but need to find nine entries for the $3 \times 3$ color correction matrix, that seems like an underdetermined system (in linear algebra terms). $\endgroup$
    – Peter K. ♦
    Commented Oct 13, 2022 at 19:13

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Is it as simple as needing at least as many independent measurements as you have things you want to estimate? If you have only four measurements (color patches), but need to find nine entries for the 3×3 color correction matrix, that seems like an underdetermined system (in linear algebra terms).

Remark: Answer by the comment of @Peter K. above.

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