iOS：给图片置灰色

/**
 UIImage:去色功能的实现（图片灰色显示）
 @param sourceImage 图片
 */
- (UIImage *)grayImage:(UIImage *)sourceImage
{
   int bitmapInfo = kCGImageAlphaNone;
   int width = sourceImage.size.width;
   int height = sourceImage.size.height;
   CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();
   CGContextRef context = CGBitmapContextCreate (nil,width,height,8,0,colorSpace,bitmapInfo);
   CGColorSpaceRelease(colorSpace);
   if (context == NULL) {
       return nil;
   }
   CGContextDrawImage(context,CGRectMake(0, 0, width, height), sourceImage.CGImage);
   UIImage *grayImage = [UIImage imageWithCGImage:CGBitmapContextCreateImage(context)];
   CGContextRelease(context);
   return grayImage;
}