Google| Subject | Re: Is RGB to Lab lossy? - was(Re: Lenses and sharpening) |
| From | PeterN |
| Date | 10/06/2014 15:19 (10/06/2014 09:19) |
| Message-ID | <m0u4sc02ak@news1.newsguy.com> |
| Client | |
| Newsgroups | rec.photo.digital |
| Follows | Alan Browne |
| Followups | Alan Browne (36m) Martin Brown (2h & 14m) |
On 10/5/2014 10:37 PM, Alan Browne wrote:
Alan BrowneIt 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.
On 2014.10.05, 20:55 , PeterN wrote:PeterNAlan Browne
On 10/5/2014 6:57 PM, Alan Browne wrote:Alan BrownePeterN
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.PeterNAlan Browne
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.
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
09/13/2014-
