iOS裡產生灰化（黑白）映像

代碼的目的是根據一個UIImage產生對應的灰化（黑白）UIImage.

以下代碼源自stackoverflow裡的一個回複，可惜原文連結已經找不到了。

- (UIImage*) convertImageToGreyScale:(UIImage*) image{    // Create image rectangle with current image width/height    CGRect imageRect = CGRectMake(0, 0, image.size.width, image.size.height);        // Grayscale color space    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();        // Create bitmap content with current image size and grayscale colorspace    CGContextRef context = CGBitmapContextCreate(nil, image.size.width, image.size.height, 8, 0, colorSpace, kCGImageAlphaNone);        // Draw image into current context, with specified rectangle    // using previously defined context (with grayscale colorspace)    CGContextDrawImage(context, imageRect, [image CGImage]);        // Create bitmap image info from pixel data in current context    CGImageRef imageRef = CGBitmapContextCreateImage(context);        // Create a new UIImage object    UIImage *newImage = [UIImage imageWithCGImage:imageRef];        // Release colorspace, context and bitmap information    CGColorSpaceRelease(colorSpace);    CGContextRelease(context);    CFRelease(imageRef);        // Return the new grayscale image    return newImage;}