+ (UIImage *)grayImage:(UIImage *)sourceImage {
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();
CGContextRef context = CGBitmapContextCreate(nil, sourceImage.size.width, sourceImage.size.height, 8, 0, colorSpace, kCGImageAlphaNone);
CGColorSpaceRelease(colorSpace);
if (context == NULL) {
return nil;
}
CGContextDrawImage(context, CGRectMake(0, 0, sourceImage.size.width, sourceImage.size.height), sourceImage.CGImage);
UIImage *grayImage = [UIImage imageWithCGImage:CGBitmapContextCreateImage(context)];
CGContextRelease(context);
return grayImage;
}
