Posterization

Posterization of an image occurs when a region with a continuous gradation of tone is replaced with several regions of fewer tones, resulting in an abrupt change from one tone to another. Unwanted posterization is most evident in pictures of people and makes the skin tones appear blotchy.

To prevent posterization:

• using 16-bits or 24-bits channels instead of 8-bits channels can reduce the risk of posterization, since they provide much more color levels. 8 bits is not enough to allow smooth transitions.
• shoot your images in RAW rather than JPG and convert them to a high bit format. File formats that are not recommended: GIF, 8-bit JPG. Recommended formats: TIFF, 16-bit JPG.
• save your photographs in a lossless format that allow you to do several editings without the damage done through JPEG compression.
• when editing, use adjustment layers (in Photoshop)
• when editing, use Brightness/Contrast instead of Curves to avoid modifying the histogram.
  

To repair a posterized image:

• use dithering (a photographic technique that creates the illusion of color depth)
• add image noise in small quantities to the damaged areas in order to mask the edges of the bands and make them invisible to the eye.
• you can download a Photoshop plug-in to repair posterized histograms.

To successfully get a digital dye sublimation print of an image that is otherwise OK but is posterized on printing:

• make sure the color mode is RGB
• use an ICC profile with little or no black substitution. Try creating an ICC profile with the K limit set to zero.
  

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