macOS 8-bit gray-scale bitmap from CGImage

[mqt]

I need an array of pixel data, packed in 8-bit gray-scale format, from a CGImageRef. Here's what I have so far though it seems to be 24-bit RGB:

- (unsigned char *)convertImageToBitmapRep:(NSImage *)image {
    CGImageRef imageRef = 
        [[[NSBitmapImageRep alloc] 
             initWithData:[image TIFFRepresentation]] CGImage];

    NSUInteger width = CGImageGetWidth(imageRef);
    NSUInteger height = CGImageGetHeight(imageRef);
    void *memory = malloc(width * height);

    CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceGray();
    CGContextRef contextRef = CGBitmapContextCreate(memory, 
                                                    width, 
                                                    height, 
                                                    8, 
                                                    width, 
                                                    colorSpaceRef, 
                                                    kCGImageAlphaNone);

    unsigned char *data = (unsigned char *)CGBitmapContextGetData(contextRef);    

    CGColorSpaceRelease(colorSpaceRef);
    CGContextRelease(contextRef);
    free(memory);

    return data;
}

How do I get an 8-bit gray-scale bitmap from CGImage?

 

[Sayer]

How do I get an 8-bit gray-scale bitmap from CGImage?

The Internet is a beautiful thing: http://www.cocoadev.com/index.pl?NSBitmapImageRepFromCGImage