Benefits
of the plugin

Posterize lightness-values
Posterize color hues
Shift selection colors
Change output colors
Blend the posterized with the original

The Posterization filter plugin works with these image modes (Windows and Mac)...
8 & 16 bit / channel: RGB, Grayscale, Duotone, CMYK, Multichannel, Lab.

Posterization
filter controls

This is the Posterization plug-ins control panel at one third size. Click on the photo or the links to see the plug-in at full size.

The filter has three sets of controls:

1. Brightness levels - how many levels to split to
2. Color levels - how many colors to split to
3. Output - blending modes, colorchange

Example - one color and full range of brightness levels

The Posterization plugin lets you posterize color and brightness independently.

Here we preserved a full brightness range and reduced hues to one color only.

The Brightness Levels control-group

Value divisions

This determines how many equidistant brightness-levels to divide the image into. If you set it to 0, you turn value dividing off (retain all levels as they are). The slider ranges from 1 to 128, but you will find the eye can't comprehend more divisions than about 50 levels, while 70 levels appear as a smooth gradation. Even just ten levels are hard to distinguish. Five is easy, as you can see from the illustration below.

If you have too many levels, then instead of being an aesthetic factor in the image, they will appear as poor gradients. Three to five work the best.

Force Black

Force White

Force Black will set the darkest level to be as near black as possible. Force white will similarly set the brightest to near white. This is usefull as a basic contrast enhancement.

The Color Levels control set

Hue divisions

Like value divisions, this Hue divisions divides the image into equidistant groups, but now the criteria is color hue and the hues placement in a full colorcircle. If you set it to 0, then you turn hue divisions off.

Example of equidistant hues

Selection shift

This slider changes the criteria for selecting areas of the original image. If you shift three divisions 50% you go from selecting cyan, magenta and yellow, to selecting red, green and blue. See illustration above.

This gives you full control over which primary colors to reduce the image to and also how many. The plugin filter will by itself make sure they are equidistant.

The Output control-set

The output controls does two things:
1. It mixes the filtered image with the original.
2. It changes the colors

Amount

Mode

Amount determines if and how much the posterized image should be mixed with the original. Mode determines in what way they should be mixed.
Less than 100% will mix more or less with the original.
100% is pure filtered image.
Above 100% enhances the filtereffect.

Hue change

Hue change will alter the output colors, not the selection. If you have selected cyan, magenta, yellow, then you can change these to red, green, blue, for example, but it will still be the same parts of the original image. If you have a colorcircle and set the value divisions and hue divisions to 0, you can see this slider rotate the colors inside the colorwheel.

Mode

This is a menu with the relevant standard Photoshop blending modes. It determines how to mix the posterized image with the original. The algorithms for these were pubished by Adobe some years ago on the internet.

Instead of doing Amount and Mode here, you could do the same in Photoshop by working on a layer that is a copy of the original. Filter it 100% and as Normal. Then in Photoshops Layers panel you can set the mode there and transparency (amount of blending).

Whats nice about having it in the plugin, is you can do it all in one go and see the effect of various posterization settings for a specific blending mode. Otherwise you would have to create many layers and filter each individually.

Examples of hue division

Illustrating
hue divisions

In these examples we set value divisions to 0, which will preserve all brightness values intact.

Images like this have their own beauty, but are most usefull as a layer blended with the original to articulate its main masses of color.

Examples of blending modes

The posterization

The posterization to the right was created with these settings...

Value divisions = 0
Hue divisions = 1
Selection shift 90 (to turn from yellowish to soft orange)
Output amount = 70%

By posterizing to the single most dominating color and blending with that, you can achieve fine harmonies with an elegant overall tone.

The blending modes

Further information

Watercolor

Please go to the tutorial Creating a watercolor look for an example of a specific use of the posterizer in combination with other Power Retouches.