iPhone How-to：图片的灰度处理

UIImage *grayImage(UIImage *source)
{
int width = source.size.width;
int height = source.size.height;

CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();

CGContextRef context = CGBitmapContextCreate (nil,
width,
height,
8,      // bits per component
0,
colorSpace,
kCGImageAlphaNone);

CGColorSpaceRelease(colorSpace);

if (context == NULL) {
return nil;
}

CGContextDrawImage(context,
CGRectMake(0, 0, width, height), source.CGImage);

UIImage *grayImage = [UIImage imageWithCGImage:CGBitmapContextCreateImage(context)];
CGContextRelease(context);

return grayImage;
}