Gary Dunning
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Gary Dunning got a reaction from Alfred in Saturation Masks - a simple method
The purity of a colour can be computed by converting from RGB to HSV and then multiplying S by V (which is effectively what the Selective Colour adjustment does), where S and V are defined as follows:
min = min(r,g,b)
max = max(r,g,b)
S = (max - min) / max
V = max
Therefore,
S * V = (max - min) * max / max = max - min
That's why the same effect can be achieved with Affinity Photo's Apply Image filter.
DR = max(SR,SG,SB) - min(SR,SG,SB)
DG = max(SR,SG,SB) - min(SR,SG,SB)
DB = max(SR,SG,SB) - min(SR,SG,SB)
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Gary Dunning got a reaction from Metin Seven in Remove Black / White Matte
To remove white matte, use Apply Image with the following settings:
DR = 1 - (1 - SR) / SA
DG = 1 - (1 - SG) / SA
DB = 1 - (1 - SB) / SA
DA = SA
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Gary Dunning got a reaction from wgphoto in RC1 HSL HSV Missing
To create a saturation mask, use the selective colour adjustment as follows:
1. Deselect relative.
2. For the red, yellow, green, cyan, magenta and blue colours, set all the sliders to -100.
3. For the whites, neutrals and blacks, set all the sliders to +100.
N.B. This solution requires Photo 1.7.