Luminosity damaging in CS2

AY
Posted By
Alexander_Yuferev
Jan 18, 2007
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334
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6
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Closed
Dear friends!

Accidentally I found one critical defect of Photoshop CS2:

after converting a gray-scale image several times to RGB (or Lab) and then back, to grayscale, you get a severe damage of your picture, which looks like a posterization. No defect of such a sort was found in CS.

There are some other errors in CS2 (in Actions, for example) but they are non-critical.

Shu-Yu

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Mathias_Vejerslev
Jan 18, 2007
Try unchecking ‘dither’ in advanced color preferences.
J
jaspoyner
Jan 18, 2007
wrote in message
Dear friends!

Accidentally I found one critical defect of Photoshop CS2:
after converting a gray-scale image several times to RGB (or Lab) and then back, to grayscale, you get a severe damage of your picture, which looks like a posterization. No defect of such a sort was found in CS.
There are some other errors in CS2 (in Actions, for example) but they are non-critical.

Shu-Yu

Perhaps you haven’t fully mastered CS2.
RB
Robert_Barnett
Jan 18, 2007
Duh, it is a lossy process. RGB images can have millions of colors. Grayscale is 256 shades of gray. You go back and forth too much and you get what you see. Don’t do it. There really is no reason to convert a non-web destined image to grayscale. If you want black and white there are dozens of ways of doing it without loosing a ton if image information. The channel mixer is but one of them.

You also get image degradation if you use the transform tools too much. There is a rounding error in Photoshop (nothing that can be fixed as far as I know). But, you can get some interesting effects if you do it enough (a couple of hundred times.

Robert
MR
Mark_Reynolds
Jan 19, 2007
8 bit Lab is destructive and converting your image back and forth will cause breakup. If you need Lab I try and convert the source file to 16 bit first.
AY
Alexander_Yuferev
Jan 20, 2007
Uncheking "dither" gets no effect.

The images for testing have 16 bit/channel, or even 32! And you have forgotten another moment: The intermediate color space (Lab), via which all convertings are made, must have the maximum possible bit depth (even while our picture has got only 8 bit/channel), but it has not in CS2.

Note that no defect occures in CS!!! No defects occures in CS even for 8-bit/channel images. It confirms the fact that intermediate color space has its bit depth in large excess!

Why we are getting this dread in new version? – that is the level of the middle of 90s years… Who likes degradations?

One my friend who got update to 9.0.2 have tested this feature and got the same result…
MD
Michael_D_Sullivan
Jan 20, 2007
What is your default greyscale color space? Is it the same in CS and CS2?

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