The colour chart is overexposed

When shooting the colour chart from the same distance as during data collection, about 60cm, the chart takes up a very small part of the lens’s field of view. Since the floor around the chart is much darker than the chart itself, the camera overexposes the chart.

Example of the colour chart being overexposed

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Normal exposure

Exposure at -1 stop

Exposure at -2 stop

Tests to do

For the first shot of the colour chart, take two more while changing the camera setting to underexpose by 1 stop and by 2 stops respectively:

1. Ev comp: -1
2. Ev comp: -2

Conclusion

Underexpose the shot by -1 stop when calibrating the colours.