Blend Mode

Blend modes in digital image editing are used to determine how two Layers are blended into each other. The default blend mode in most applications is simply to hide the lower layer with whatever is present in the top layer. However, as each pixel has a numerical representation, a large number of ways to blend two layers is possible. Note that the top layer is not necessarily called a "layer" in the application. It may be applied with a painting or editing tool.

The blending mode specified in the options bar controls how pixels in the image are affected by a painting or editing tool. Itís helpful to think in terms of the following colors when visualizing a blending modeís effect:

The following types of blend mode can be found from PDF Reference, 5th Edition, Page 513.

Normal

Selects the source color, ignoring the backdrop.

Multiply

Multiplies the backdrop and source color values.  The result color is always at least as dark as either of the two constituent colors. Multiplying any color with black produces black;  Multiplying with white leaves the original color unchanged. Painting successive overlapping objects with a color other than black or white produces progressively darker colors.

Screen

Multiplies the complements of the backdrop and source color values, then complements the result. The result color is always at least as light as either of the two constituent colors. Screening any color with white produces white; screening with black leaves the original color unchanged. The effect is similar to projecting multiple photographic slides simultaneously onto a single screen.

Overlay

Multiplies or screens the colors, depending on the backdrop color. Source colors overlay the backdrop while preserving its highlights and shadows. The backdrop color is not replaced but is mixed with the source color to reflect the lightness or darkness of the backdrop.

Darken

Selects the darker of the backdrop and source colors. The backdrop is replaced with the source where the source is darker; Otherwise, it is left unchanged.

Lighten

Selects the lighter of the backdrop and source colors. The backdrop is replaced with the source where the source is lighter; Otherwise, it is left unchanged.

ColorDodge

Brightens the backdrop color to reflect the source color. Painting with black produces no change.

ColorBurn

Darkens the backdrop color to reflect the source color. Painting with white produces no change

HardLight

Multiplies or screens the colors, depending on the source color value. If the source color is lighter than 0.5, the backdrop is lightened as if it were screened; this is useful for adding highlights to a scene. If the source color is darker than 0.5, the backdrop is darkened as if it were multiplied; this is useful for adding shadows to a scene. The degree of lightening or darkening is proportional to the difference between the source color and 0.5; if it is equal to 0.5, the backdrop is unchanged. Painting with pure black or white produces pure black or white. The effect is similar to shining a harsh spotlight on the backdrop.

SoftLight

Darkens or lightens the colors, depending on the source color value. If the source color is lighter than 0.5, the backdrop is lightened as if it were dodged; this is useful for adding highlights to a scene. If the source color is darker than 0.5, the backdrop is darkened as if it were burned in. The degree of lightening or darkening is proportional to the difference between the source color and 0.5; if it is equal to 0.5, the backdrop is unchanged. Painting with pure black or white produces a distinctly darker or lighter area but does not result in pure black or white. The effect is similar to shining a diffused spotlight on the backdrop.

Difference

Subtracts the darker of the two constituent colors from the lighter color. Painting with white inverts the backdrop color; painting with black produces no change.

Exclusion

Produces an effect similar to that of the Difference mode but lower in contrast. Painting with white inverts the backdrop color; painting with black produces no change.

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