iOS imageview取色处理

-(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,      // bits per component

                                                  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;

}