objective-c: cv::Mat to CVPixelBuffer - ios

Question

Below code converts cv::Mat to CVPixelBufferRef
CVPixelBufferRef getImageBufferFromMat(cv::Mat matimg) {
cv::cvtColor(matimg, matimg, CV_BGR2BGRA);
NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithBool: YES], kCVPixelBufferMetalCompatibilityKey,
[NSNumber numberWithBool: YES], kCVPixelBufferCGImageCompatibilityKey,
[NSNumber numberWithBool: YES], kCVPixelBufferCGBitmapContextCompatibilityKey,
[NSNumber numberWithInt: matimg.cols], kCVPixelBufferWidthKey,
[NSNumber numberWithInt: matimg.rows], kCVPixelBufferHeightKey,
[NSNumber numberWithInt: matimg.step[0]], kCVPixelBufferBytesPerRowAlignmentKey,
nil];
CVPixelBufferRef imageBuffer;
CVReturn status = CVPixelBufferCreate(kCFAllocatorMalloc, matimg.cols, matimg.rows, kCVPixelFormatType_32BGRA, (CFDictionaryRef) CFBridgingRetain(options), &imageBuffer) ;
CVPixelBufferLockBaseAddress(imageBuffer, 0);
void *base = CVPixelBufferGetBaseAddress(imageBuffer);
memcpy(base, matimg.data, matimg.total() * matimg.elemSize());
CVPixelBufferUnlockBaseAddress(imageBuffer, 0);
return imageBuffer;
}
The problem is I am getting half the image
Original Image
After Convertion (i convert CVPixelBufferRef back to UIImage and store it using UIImageWriteToSavedPhotosAlbum just for checking)
Interestingly, the image size of Mat and CVPixelBufferRef are the same.
Now, what I did was resizing the image just before memcopy, where the height is increased by 2 folds
CVPixelBufferLockBaseAddress(imageBuffer, 0);
void *base = CVPixelBufferGetBaseAddress(imageBuffer);
cv::resize(matimg, matimg, cv::Size(), 1 , 2);
memcpy(base, matimg.data, matimg.total() * matimg.elemSize());
CVPixelBufferUnlockBaseAddress(imageBuffer, 0);
Now the image size is still the same...
I want to badly know what's causing this behavior and I am sure I am missing something...

Answer 1

I found a solution to this problem after reading this.
The system likes images to be a multiple of 64 bytes per row, presumably for better performance due to cache line alignment. As image resolution is [1000 × 1000], not multiple of 64 hence bytes per row would default to 27840 don't know why... This was causing the problems.
Anyway, if anyone looking for the solution
CVPixelBufferRef getImageBufferFromMat(cv::Mat matimg) {
cv::cvtColor(matimg, matimg, CV_BGR2BGRA);
int widthReminder = matimg.cols % 64, heightReminder = matimg.rows % 64;
if (widthReminder != 0 || heightReminder != 0) {
cv::resize(matimg, matimg, cv::Size(matimg.cols + (64 - widthReminder), matimg.rows + (64 - heightReminder)));
}
NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithBool: YES], kCVPixelBufferMetalCompatibilityKey,
[NSNumber numberWithBool: YES], kCVPixelBufferCGImageCompatibilityKey,
[NSNumber numberWithBool: YES], kCVPixelBufferCGBitmapContextCompatibilityKey,
[NSNumber numberWithInt: matimg.cols], kCVPixelBufferWidthKey,
[NSNumber numberWithInt: matimg.rows], kCVPixelBufferHeightKey,
[NSNumber numberWithInt: matimg.step[0]], kCVPixelBufferBytesPerRowAlignmentKey,
nil];
CVPixelBufferRef imageBuffer;
CVReturn status = CVPixelBufferCreate(kCFAllocatorMalloc, matimg.cols, matimg.rows, kCVPixelFormatType_32BGRA, (CFDictionaryRef) CFBridgingRetain(options), &imageBuffer) ;
NSParameterAssert(status == kCVReturnSuccess && imageBuffer != NULL);
CVPixelBufferLockBaseAddress(imageBuffer, 0);
void *base = CVPixelBufferGetBaseAddress(imageBuffer);
memcpy(base, matimg.data, matimg.total() * matimg.elemSize());
CVPixelBufferUnlockBaseAddress(imageBuffer, 0);
// UIImageWriteToSavedPhotosAlbum(converts(imageBuffer), nil, nil, nil);
return imageBuffer;
}