CGColorSpaceCreateDeviceGray.m

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;  
}