Le 11/09/2015 22:44, KOVÁCS István a écrit :
Even when fit to the screen (1920x1080), I find the plain 'colour'-blended version (DSC_8834.jpg) less noisy*and* sharper than the HSV-colour-blended one (DSC_8834_01.jpg). Zoomed in, the noise seems more 'patterned' on the HSV-blended version (shows some kinds of structure, patches, homogeneous areas with more defined, thicker borders).
The better noise characteristic you mention (better on DSC_8834.jpg than on DSC_8834_01.jpg) seems pretty clear to me.
From my experience, the pattern you mention have similar size as typical *color* noise patterns in photographs.
I'm not a human vision specialist yet have some past experience during my Ph.D. in robotic vision where the colorspace used for computation has sometimes important impact on the effectiveness/robustness of some algorithms.
In the case of your observation, I would guess it is related to the fact that performing image operations on HSV colorspace misfits/mixes what human vision perceives as luma and chroma. As a consequence, the noise reduction performed on S and V "bleeds" into what the eye perceive as luminance, where it appears as the patterned noise you mention. This theory goes in the same direction as your observation.
For more information, read the paragraphs above and below the turtle photographs on https://en.wikipedia.org/wiki/HSL_and_HSV#Disadvantages
Can anyone elaborate the difference between "color" and "chroma" blending mode in this respect ?
Regards, -- Stéphane Gourichon
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