Eric Eric - 6 days ago 6
iOS Question

Convert UIImage to CVImageBufferRef

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

It sounds like it might be that relationship. Possibly have it be a jpg and RGB instead of indexed colors with a png?