How do blend modes work?
Each blend mode presents a different method of combining (compositing) two or more images. Blend modes work in addition to a layer’s alpha channel and opacity parameter.
To understand the descriptions of each blend mode in this chapter, it’s important to understand that blend modes mix colors from overlapping images based on the brightness values in each color channel in an image. Every image consists of a red, green, and blue channel, and sometimes an additional alpha channel. Each channel contains a range of brightness values that define the intensity of each pixel in the image that uses some of the channel’s color.
The effect that each blend mode has on overlapping layers depends on the range of color values in each layer. The red, green, and blue channels in each overlapping pixel are mathematically combined to yield the final image.
These value ranges can be described as blacks, midrange values, or whites. These regions are loosely illustrated by the chart below.
For example, the Multiply blend mode renders white color values in an image transparent, while black values are left alone. All midrange color values become translucent, with colors in the lighter end of the scale becoming more transparent than the colors in the darker end of the scale.