A really nice MediaComp Image Blending lesson
I got to see this at SIGCSE and was really impressed — both the effect, and how it’s written up. Thanks for letting me share it, Dwight!
A much better effect would be combine the images to give the impression that Bogart’s character, Rick, is thinking about Bergman’s character, Ilsa. This requires blending the images together. When blending images the necessary step required is to combine the colors of corresponding pixels of the images together. The RGB values of the pixels to be blended are added together using a percentage of the color of each pixel. If even blending is desired then 50% of each RGB value of the source pixels is added to 50% of each RGB value of the target pixels to make the color of the blended pixel. In the Bergman/Bogart merging above we do not wish an even blending instead we will use 33% of the Bergman pixel color and 67% of the Bogart pixel color. You should now be able to write a blend33() function to perform this blending. To view the completed function move your mouse over the following paragraph.
via Image Blending.