Dodging lightens an image, while burning darkens it. But now the image for b=1 is not γ=0.5, but the result of a tonal curve which differs from the curve of γ=0.5 for small values of a: while gamma correction with γ=0.5 may increase the value of a many times, this new curve limits the increase of a by coefficient 4.ĭodge and burn change the lightness of the pictures, inspired by the dodging and burning performed in a darkroom. It is still a linear interpolation between 3 images for b=0, 0.5, 1. This is also the formula used by Cairo, and in earlier PDF documentation. The result is most typically merged into the bottom layer using "simple" (b over a) alpha compositing (making the actual formula f ( a, b ) = a l p h a ( b, a ) 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. In the formulas shown on this page, values go from 0.0 (black) to 1.0 (white). The top "layer" also is called the "blend layer" and the "active layer".
The top "layer" is not necessarily a layer in the application it may be applied with a painting or editing tool. 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 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. A sketch colored digitally with use of several different blend modes in order to preserve the pencil lines and paper texture below the color layers.īlend 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.
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