The Blend Subtract Extension

The Blend Subtract Extension

The blend subtract extension, EXT_blend_subtract, provides two additional blending equations that can be used by glBlendEquationEXT(). These equations are similar to the default blending equation, but produce the difference of its left- and right-hand sides, rather than the sum. See the reference page for glBlendEquationEXT() for a detailed description.

Image differences are useful in many image-processing applications; for example, comparing two pictures that may have changed over time.