am remembering .... a small test during our painting !!!! described earlier, I think.
One way to verify if the lightening is correctly painted, and to visualize the three dimensional effect of a flat painting, is
1) to take a photography in good light conditions (pic 1)
2) to convert the colours to black and white ... (pic 2)
3) Then to adjust the contrast and light to optimize a good balance between lights and shadows (pic 3)
Then compare 2) and 3)
a) Is the three dimensional effect well given in absence of colours?
b) Are contrast correctly optimized, or too strong, or too weak, or is the general aspect "GREY" like winter weather?
In my case, contrasts are still a bit weak, as I had to increase the contrasts to avoid a grey picture ...
But too late now !! I'll do it earlier next time ...
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Exercise to do during painting which can also indicate if the selection of colours is balanced also ...