Is there any way to effectively remove posterization from images in CS? Based on the histogram, even the *slightest* adjustment to the contrast/curve/level value of an image will create some posterization damage. Any way to de-posterize after the fact? (short of applying a blur on everything).
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Yes, adjustments of the kind you mention, which are generally called "tone expansion/compression" result in posterization. That’s because image data is lost. Whether the posterization can be seen is another matter. If the changes are slight, the effect may go unnoticed.
But you are right, it happens. And it is unavoidable on 8 bit files. If you capture data at 12-14 bits in the 16 bit file format, there are enough gray scale steps to "round down" when the file is converted from 16 bit to 8 bit to create real data to fill in the missing data "holes" created by the tone editing.
8 bit files have 256 gray levels. Throw some away, and there is no real data in the file to "fill in" for the missing levels, just pixel replication and averaging which gives the posterization effect. But a 12 bit image has 4096 distinct gray levels. You can lose up to 50% of those, then convert the file "down" to 8 bits with no visible loss. A file with 14 "real" bits of data has 16000 distinct gray levels. Unfortunately, some digital devices claiming 14 bit output have little more clean information in their images than 12 bit devices.
If an image has enough captured data to begin with, even if it’s 8-bit at 300ppi you should be able to properly correct levels or apply a curve without noticable degradation.
Well, these images are older 8 bit RGB images @ 72 ppi created or originally captured in Photoshop 5. I realize the brightness / contrast adjustement is rather blunt but often it is what gives me the desired result. Not for extreme effects either but just adjustments to humm, contrast. The posterization is not visibly noticeable @ 100% view but the histogram does indicate it.
I have found as an alternative using "replace color" to tweek the white levels can work pretty well without getting posterization. Any suggestions for other processes to adjust contrast etc. without using contrast, levels or curves?
Reason then is that the resolution is low. You might be able to play around with multi layers tweaked different ways, combined with adjustment layers and different layer modes.
Is there any way to effectively remove posterization from images in CS?
I’d say you are pretty much screwed. the best you can hope for is making the pics small and hope nobody looks too close. the other thing is to say this is artsy fartsy and just how they are supposed to look.
Best way to remove posterization is to never apply it to your originals.
I’m checking out some of the new stuff in CS and I find the "shadow/highlight" works real well without causing any posterization at all. "brightness/contrast" on the other hand causes posterization (on the histogram) when I take contrast to +2. +1 even in some cases. Looks like "shadow/highlight" is the way to go.
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