Posterization Effect in Photoshop CS2

AY
Posted By
Alexander_Yuferev
Mar 13, 2007
Views
360
Replies
3
Status
Closed
I have repeated my previous topic with another heading because many of readers, as I see, cannot realize what the effect this error consist in. It is not related to color gamut at all and is fundamental one, for it touches one of the most basic program features.

I want to draw your attention to the fact that there was no such a defect in previous versions of Photoshop.

See the effect at <http://www.photographer.ru/nonstop/picture.htm?id=448617>
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GH
Gernot_Hoffmann
Mar 13, 2007
Alexander,

nobody responds. My experience is limited to PhS7.
Your test image shows that the banding (CS2) is IMO
a result of not equal spacing of R=G=B along the
horizontal axis.

Please check, how the pages 16,17 and 18 of this doc
appear in PhS CS2:
<http://www.fho-emden.de/~hoffmann/optigray06102001.pdf>

Mode: RGB
Resolution: 144 ppi

The PDFs are pixel-synchronized either for 72 ppi or
for 144 ppi.

Best regards –Gernot Hoffmann
AY
Alexander_Yuferev
Mar 14, 2007
Dear Gernot,

if I understand you correctly, you mean a monitor representation effects? If so, these matters are evidently take place but I can easily separate them by using any temporary Adjustment layer (Curves, or Brightness/Contrast) which parameters I slightly change, and watch moving of the bands. The bands which belong to the very image (to the image itself) are not moving.

And I confined myself with Photoshop 8 where all its errors are able to be circumvented. (For example, in Add/Subtract commands where any negative Offset value causes an error in 16-bit mode. But I change Subtract to Add and switch Invert – all becomes good).

In CS2 I bumped to the problem that I have no way to avoid. For example, you want to colorize a grayscale image – and immediately get its little damage! If one has a grainy image, these damaging is practically not visible. But the better image he has, the more sensible deterioration he gets.

Another example: it is well known that when scanning negative films with Nikon scanner using Negative option one gets rough color breakings. The only way to precisely scan them is to use Positive option. But you get another problem: non-realistic colors. To correct them it is very useful to go to Lab, blur "a" and "b" channels, get blurred a/b differences and apply them to original (sharp a/b values). Then I am to return to RGB. How could I do this without changing color mode? So you can see how dirty trick we have got…

It is not vexing that the program has errors – all programs have them, but it is sad that Adobe’s programmers ceased to observe the basic features which represent the very face of this firm.
GH
Gernot_Hoffmann
Mar 14, 2007
Alexander,

my test images are mathematically correct.
They don’t show banding artifacts:
neither in Adobe Reader nor in PhS7, not on
a CRT, not on a TFT.
What happens if you show them by CS2 without
any calculation ? What happens if you apply
tiny variations ? Are the the banding artifacts
appearing in mode 8bpc and in mode mode 16bpc ?
Any differences if color management is off ?
Answers to these questions might help to
locate the source of errors.

Best regards –Gernot Hoffmann

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