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Is RGB to Lab lossy? - was( Lenses and sharpening)
On 10/5/2014 10:37 PM, Alan Browne wrote:
On 2014.10.05, 20:55 , PeterN wrote: On 10/5/2014 6:57 PM, Alan Browne wrote: On 2014.10.05, 14:42 , PeterN wrote: We went through all this some many months ago. I demonstrated clearly that the amount of 'loss' was negligible in practical terms. I would use the terem "color change." anstead of loss. Any change is a quality loss. Whether that is colour difference, tone, brightness, sharpness ... whatever, it's a loss. Then you are using a different definition of quality. Not at all. A non lossy process would have: RGB-A -- X-format -- RGB-B with RGB-A identical to RGB-B But - the fact is that with Lab RGB-A -- Lab -- RGB-B RGB-A =/= RGB-B, therefore there was quality loss. It seems to me that the assumption in that logic is: the quality of RGB-A quality of RGB-B. LAB has a larger color gamut than RGB. If there is no processing in LAB I would think that there would be no need for interpolation on the return trip. Do the round trip x + 10 times without processing and one might see a difference. It is doubtful that there will be a noticable difference from 10 round trips. Meanwhile there are color modification processes that are easier to perform in LAB than RGB. I would think that if the changes made in LAB created color outside the RGB gamut there would have to be some interpolation. The interpolation coud mae a better image, or it could make the changed image horrific. In another area, I have found images to be fine with a color cast, but when I remove the cast, to my eye the image looks horrific. -- PeterN |
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