programmatically trimming (automatically cropping out transparent boundaries) an image in objective-c / cocoa

Does anyone know how to trim an image (uiimage or cgimage). By trim I mean programatica开发者_JAVA技巧lly cropping to the non-transparent bounds of an image. So if I have the image below:

• 00111000
• 00010000
• 01011110
• 00000000

it would yield:

• 011100
• 001000
• 101111

---

Sum all rows and all columns of your image. You'll get two arrays, in your example looking like this:

3 1 5 0
0 1 1 3 2 1 1 0

Then the first non-zero from the left and the last one near the right is where you have to crop, in each direction.