Is it possible to adjust color levels using Core Graphics?
I would like to adjust channels using parametrized curves in the Gimp or other graphic editor style.
You can use this: ios-image-filters (like photoshop)
if you want to manipulate levels, here's your method, built straight onto the UIImage class:
- (UIImage*) levels:(NSInteger)black mid:(NSInteger)mid white:(NSInteger)white
来源：https://stackoverflow.com/questions/7567934/ios-change-color-channels-levels-programmatically