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Photoshop plug-ins for retouching

Posterizer

Quick introduction

This Photoshop plug-in lets you posterize images in any given number of luminance levels or color tones. Create equidistant scales. This is the Posterizer plug-in’s control panel. Click on the image for a larger view. It works with the following image modes: 8 & 16 bit/channel: RGB, CMYK, Grayscale, Duotone, Lab.

Brightness levels

Divisions   lets you set how many value divisions the image should be divided into.
Here is an example of five equidistant value divisions created with the plug-in.
Normally three value divisions is the most aesthetically pleasing as art history has proven to us, but five is also often used. Usually odd numbers are preferred so you get a midtone. Art history has shown that 2,3 and 5 are the most useful. More than five becomes difficult to distinguish. At about 70 the eye can no longer distinguish between them and perceives a gradient as a smooth one.
Force black  will make the darkest pixels as dark as possible. Force white  will make the brightest pixels as bright as possible. The value divisions are then calculated from that range. Greyscale  will output a colorless result. Colorize grey  will assign equidistant colors to the given greys. The colors will approximate the given colors in the image.

Color levels

Divisions lets you set how many distinct hues the image should be divided into.
Selection shift 50%
3 divisions
Original
In the examples to the right we have divided a snap of a regular colorpicker into three distinct hues. Selection shift   lets you change the basic hues to be selected throughout a full color circle, as you can see in the example. Brightness levels  was set to 1.

Output

Amount   determines how much the changed image will be mixed with the original image. 100% means nothing is left of the original. Mode   will set various modes of combining the original with the edited image. We have Normal + 12 modes, most of which are well known from Photoshop. Hue change , unlike   Selection shift , will preserve the given selection of hues, but will rotate their colors throughout the color circle.
Hue change 100%
Original
3 divisions

Blending modes

In this example we turned off brightness divisions by setting the Divisions slider to 0. Here is the output with Normal blending. Brightness divisions = 0 Hue divisions = 1 Selection shift 90 (to turn from yellowish to soft orange) Output amount = 70%
Original
Normal
Multiply
Screen
Overlay
Soft light
Hard light
Darken
Lighten
Negate
Color dodge
Color burn
Inverse dodge
Pastel

Greyscale & Colorize Grey

By converting the image to greyscale and colorizing the levels, you get exact control over the number of distinct levels and hues in the image.
2 levels
3 levels
4 levels