Mapping CoreGraphics Blend Modes to Porter-Duff

Question

I have an iPhone app that does image manipulation via blending two UIImage objects via CoreGraphics, specifically CGContextSetBlendMode. I am currently researching porting it to Android. I've gone through the process of combining to Bitmap objects on Android using PorterDuff modes. However, I want much more complicate compositing. For example, I'm using kCGBlendModeHardLight for many blends:

Either multiplies or screens colors, depending on the source image sample color. If the source image sample color is lighter than 50% gray, the background is lightened, similar to screening. If the source image sample color is darker than 50% gray, the background is darkened, similar to multiplying. If the source image sample color is equal to 50% gray, the source image is not changed. Image samples that are equal to pure black or pure white result in pure black or white. The overall effect is similar to what you’d achieve by shining a harsh spotlight on the source image. Use this to add highlights to a scene.

But don't know of anyway (if it's even possible) to emulate this via Porter-Duff. Does Android not support better Image Manipulation algorithms out of the box? Is it possible to use Porter-Duff in some way to emulate more advanced blend modes?

Answer 1

In addition to the 12 Porter-Duff blending equations, Android supports Lighten, Darken, Multiply, Screen and soon Overlay. Unfortunately this means HardLight is not available and you would have to implement it yourself.