UIImage循环通过像素非常低效？

Currently I am using this method to loop through every pixel, and insert a value into a 3D array based upon RGB values. I need this array for other parts of my program, however it is extraordinarily slow. When run on a 50 x 50 picture, it is almost instant, but as soon as you start getting into the hundreds x hundreds it takes a long time to the point where the app is useless. Anyone have any ideas on how to speed up my method?Currently I am using this method to loop throug