Convert UIImage to CVImageBufferRef

Question

This code mostly works, but the resulting data seems to loose a color channel (is what I am thinking) as the resulting image data when displayed is tinted blue!

Here is the code:

UIImage* myImage=[UIImage imageNamed:@"sample1.png"];
CGImageRef imageRef=[myImage CGImage];
CVImageBufferRef pixelBuffer = [self pixelBufferFromCGImage:imageRef];

The method pixelBufferFromCGIImage was grabbed from another post on stackoverflow here: How do I export UIImage array as a movie? (although this application is unrelated to what I am trying to do) it is

+ (CVPixelBufferRef)pixelBufferFromCGImage:(CGImageRef)image
{
    CGSize frameSize = CGSizeMake(CGImageGetWidth(image), CGImageGetHeight(image));
    NSDictionary *options = @{
                              (__bridge NSString *)kCVPixelBufferCGImageCompatibilityKey: @(NO),
                              (__bridge NSString *)kCVPixelBufferCGBitmapContextCompatibilityKey: @(NO)
                              };
    CVPixelBufferRef pixelBuffer;
    CVReturn status = CVPixelBufferCreate(kCFAllocatorDefault, frameSize.width,
                                          frameSize.height,  kCVPixelFormatType_32ARGB, (__bridge CFDictionaryRef) options,
                                          &pixelBuffer);
    if (status != kCVReturnSuccess) {
        return NULL;
    }

    CVPixelBufferLockBaseAddress(pixelBuffer, 0);
    void *data = CVPixelBufferGetBaseAddress(pixelBuffer);
    CGColorSpaceRef rgbColorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(data, frameSize.width, frameSize.height,
                                                 8, CVPixelBufferGetBytesPerRow(pixelBuffer), rgbColorSpace,
                                                 (CGBitmapInfo) kCGImageAlphaNoneSkipLast);
    CGContextDrawImage(context, CGRectMake(0, 0, CGImageGetWidth(image),
                                           CGImageGetHeight(image)), image);
    CGColorSpaceRelease(rgbColorSpace);
    CGContextRelease(context);
    CVPixelBufferUnlockBaseAddress(pixelBuffer, 0);

    return pixelBuffer;
}

I am thinking it has something to do with the relationship between kCVPixelFormatType_32ARGB and kCGImageAlphaNoneSkipLast though I have tried every combination and get either the same result or a application crash. Once again, this gets the UIImage data into CVImageBufferRef but when I display the image on screen, it appears to loose a color channel and shows up tinted blue. The image is a png.

Answer 1

The solution is that this code works perfectly as intended. :) The issue was in using the data in creating an OpenGL texture. Completely unrelated to this code. Anyone searching for how to Convert UIImage to CVImageBufferRef, your answer is in the above code!

Answer 2

If anyone is still looking for a solution to this problem, I solved it by switching the BOOLs in the pixelBuffer's options:

NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
                     [NSNumber numberWithBool:NO], kCVPixelBufferCGImageCompatibilityKey,
                     [NSNumber numberWithBool:NO], kCVPixelBufferCGBitmapContextCompatibilityKey,
                     nil];

From NO to YES:

NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
                     [NSNumber numberWithBool:YES], kCVPixelBufferCGImageCompatibilityKey,
                     [NSNumber numberWithBool:YES], kCVPixelBufferCGBitmapContextCompatibilityKey,
                     nil];

Answer 3

I encounter the same problem and find some samples: http://www.cakesolutions.net/teamblogs/2014/03/08/cmsamplebufferref-from-cgimageref
try to change

CGBitmapInfo  bitmapInfo = (CGBitmapInfo)kCGBitmapByteOrder32Little |
                  kCGImageAlphaPremultipliedFirst)