Blend modes

Blend modes (alternatively blending modes or mixing modes) in digital image editing and computer graphics are used to determine how two layers are blended with each other. The default blend mode in most applications is simply to obscure the lower layer by covering it with whatever is present in the top layer (see alpha compositing); because each pixel has numerical values, there also are many other ways to blend two layers.

Most graphics editing programs, such as Adobe Photoshop and GIMP, allow users to modify the basic blend modes, for example by applying different levels of opacity to the top "layer". The top "layer" is not necessarily a layer in the application; it may be applied with a painting or editing tool. The top "layer" also is called the "blend layer" and the "active layer".

In the formulas shown on this page, values go from 0.0 (black) to 1.0 (white).

Normal blend mode

This is the standard blend mode which uses the top layer alone, without mixing its colors with the layer beneath it:

f

(

a

,

b

)

=

b

{\displaystyle f(a,b)=b}

where a is the value of a color channel in the underlying layer, and b is that of the corresponding channel of the upper layer. The result is most typically merged into the bottom layer using "simple" (b over a) alpha compositing (making the actual formula

f

(

a

,

b

)

=

alpha

⁡

(

b

,

a

)

{\displaystyle f(a,b)=\operatorname {alpha} (b,a)}

), but other Porter-Duff operations are possible. The compositing step results in the top layer's shape, as defined by its alpha channel, appearing over the bottom layer.

Dissolve

The dissolve mode takes random pixels from both layers.