Choosing the Best RGB Space as a Source for Channel Blending

Rick Gordon

It might be an interesting test to see if sRGB would normally be better for extracting channels for blending. My own sense is that, since channel blending is likely to be called for when there is missing detail in a current channel (i.e., either clipped or nearly clipped to either black or white), that the most suitable channel to blend with would be one that has sufficient latitude at both extremes, and that a wide-gamut space such as ProPhoto RGB would be the most serviceable.

This is a different argument than the argument that a wide-gamut space is always preferable as a composite RGB space. I generally concur with Dan's assessment that a smaller space may be a better tool for that if the gamut required is not excessive. However, since I opt to edit in 16-bit (though not necessarily use as final), I believe that the argument — that banding is more likely to occur when the values are compressed within a smaller range of gray values — may be mitigated by the 16-bit workflow. (But I dare not open that can of worms again.)

But I do think that some real-world testing of that hypothesis might be informative, in terms of the value of generally using a high-gamut space (e.g., ProPhoto RGB) as a source to derive unclipped individual channels.

Rick Gordon

On May 20, 2020 at 5:57:25 PM [-0700], Dan Margulis Via wrote in an email entitled "Re: [colortheory] The group's techniques, 2":
In more normal work it wouldn’t make a difference, and if it did sRGB would likely be a better choice than ProPhoto.