PorterDuff Mode

Introduction

PorterDuff is described as a way of combining images as if they were “irregular shaped pieces of cardboard” overlayed on each other, as well as a scheme for blending the overlapping parts

Remarks

“Porter Duff” in itself is an alpha compositing technique named after a paper by Thomas Porter and Tom Duff.

To summarize, the technique takes two images with alpha channel and generates the output image by combining pixels values of two images. The various combining modes result in different output image. For example, in following image, blue shape (source, existing pixels) is combined with Yellow shape (destination, new pixels) in different modes: