Contrast Node

The Contrast node enables you to vary the contrast of an image, or individual image channels, effectively compressing or expanding the color range. The Contrast node includes a Pivot parameter that allows you to specify a pivot point about which the compression or expansion of pixel values will fluctuate.

The following illustration shows a graph in which the Contrast parameter is set to 1.5 and the Pivot parameter is set to 0.5 (default, left) and to .25 (right).

The Contrast node performs the following computation:

V = ((V - Pivot) * Contrast) + Pivot

This formula has the effect of increasing or decreasing the range of color values in the image.

Contrast Parameter Tab

Contrast

You set the Contrast parameter by keying in a numerical value in the preferred range of 0 to 5.0 (though the parameter is unconstrained) or by using the mouse to set the tuner to the desired value. The default value is 1.0.

Pivot

You set the Pivot parameter by keying in a numerical value in the preferred range of -1.0 to 1.0 (though the parameter is unconstrained) or by using the mouse to set the tuner to the desired value. The default value is 0.5.

The Pivot parameter allows you to determine the pivot point about which the compression or expansion of pixel values will fluctuate. It lets you tune the contrast adjustment according to values of a particular image. (See the illustration at the top of this node description).

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, as explained in "Using Control Images with Filter Nodes ."




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