Posterization online

 Posterization is not only a Photoshop correction that allows you to specify a number of tonal levels (brightness values) of the image, needed, for example, to create large monochrome areas in photos, but also an unwanted artifact that occurs when some settings and filters are abused.

Posterization online

This artifact appears when the color depth of the image is greatly reduced, so that it is observed visually. The term comes from the word "Poster", as this effect is similar to the result of printing a poster with a small set of colored inks. That is, with a smooth transition from one color to another, as well as a change in brightness, we have jumps instead of a smooth transition. You can observe this effect in photos that use many color tones, such as sky, fire, etc. In all digital images, color levels are discrete, and the effect of a smooth continuous transition between them is achieved by a large number of these very levels.



We can get this undesirable effect by abusing such necessary and important tools as Levels, Curves, and by changing the color space.

The best way to control posterization is to analyze a histogram, because ordinary visual control is not always effective. Small gaps, peaks or scars appear on the histogram, resembling a comb.

Examples of normal and stretched histograms:

To avoid this undesirable effect, the following rules should be followed:

- Do not use direct layer adjustments with levels and curves (Lewels end Curwes), but use Adjustment layers. Remember that it is the repeated application of adjustments that stretch the histogram that contributes to the appearance of color and brightness jumps.

- The image should be edited in 16-bit per channel mode, even if it is originally eight-bit.

- Also, remember that using a space with a wide color gamut significantly increases the likelihood of a posterization effect

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