When working in a large gamut space, like ProPhoto, higher ISO images tend to have a lot of pixels, due to noise, that are outside a display and printer's gamut even when the actual image is within gamut. These are clipped or remapped to the gamut boundary. but others that have noise pushing them inside the gamut are rendered properly. Because they are so close human vision sees an average over small distances and the apparent colors are rendered less saturated than they would be with a less noisy image.
Hi Doug,
Yes, a good point. But if we use noise reduction before gamut down-sampling, the remapping will include fewer oversaturated (and undersaturated) OOG overshoots (and undershoots). That should give a more average (and correct average chrominance) new gamut boundary.
Seems to me that a selective, noise reduction process that works only near gamut boundary could produce somewhat better prints. Does anyone know of any software that has options to do this?
Other than using a saturation selection mask, and specifically denoising that selection, I do not know of a commercial Denoising application that specifically targets (OOG) saturation (except for Topaz Denoise shadow color). While the better ones can make a specific noise profile for a typical camera and specific conversion settings, they do not allow a specific saturation approach (they are supposed to handle all noise equally, but with basic tweaks).
A program like NeatImage is already highly tuneable, even if based on a normal Raw conversion. The user can make pre-made profiles for different ISO settings per camera model, in case a specific image offers too few clues to make a complete image specific profile. One can boost the Chrominance noise reduction separately from the Luminance noise reduction. Also Topaz Denoise, which makes an automatic per image noise profile, can be set to modify the noise rendition in shadows to avoid overly red shadows (caused by clipped undershoot shadow noise conversions).
Cheers,
Bart