Posterize Node

The Posterize node remaps the pixels of an input image to a reduced palette of colors to create large areas of solid color.

For example, if you reduce an image to 16 colors per channel, for each pixel in the image the Posterize node will examine the value of the red channel and reassign that value to the nearest red value in a predetermined set of 16 available reds. Then it will do the same for the green channel, substituting the nearest green value in a predetermined set of 16 greens, and so on. The resulting output image will have a maximum of 16 different values assigned to each channel.

You can specify the number of colors per channel to use, as well as which channels of the input to modify. The Posterize node accepts 8- or 16-bit linear or floating point data. (For floats, the Posterize node allows a maximum of 65536 colors.)

Posterize Parameter Tab

Output Colors

This parameter enables you to specify the number of colors per channel to use for the output. The default is 16 colors per channel for 8-bit inputs and 4096 for 16-bit.

You can specify any value in the range of 1-256, for 8-bit images, or 1-65536, for 16-bit and floating point images, by keying a number into the data entry field or by using the mouse to set the tuner to the desired value.

Channel Mask

The Channel Mask parameter enables you to inhibit the modification of any channel by deselecting the Red, Green, Blue, Alpha, or Other channel icons.

Control Image Parameters

The Control Action and Control Channel menus enable you to specify how an optional control image input will govern the node operation.

The Control Channel menu enables you to specify which channel in the control image will be used to govern the control action.

The Control Action menu lets you select a control method: On/Off or Mix. When the On/Off method is selected any control pixel with a nonzero value will "turn on" filtering of the corresponding pixel in the primary input. The Mix method, on the other hand, uses the specific value of each control pixel to determine the extent to which the primary pixels will be affected by the node operation.

If you need more information, refer to Using Control Images with Filter Nodes at the beginning of chapter 18.




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