Question

I have two CVImageBufferRef buffers that correspond to two images grabbed in sequence by AVCaptureSession. I would like to compare both to see if all the pixels are the same. In order to loop thru all pixels of the frame buffer and compare them, I have this:

unsigned char *pixelA = (unsigned char *)CVPixelBufferGetBaseAddress(pixelBufferA);
unsigned char *pixelB = (unsigned char *)CVPixelBufferGetBaseAddress(pixelBufferB);


- (BOOL) isBuffer:(unsigned char *)pixelA equalToBuffer:(unsigned char *)pixelB {
    for( int row = 0; row < bufferHeight; row++ ) {
        for( int column = 0; column < bufferWidth; column++ ) {

            if ((pixelA[0] != pixelB[0]) ||
                (pixelA[1] != pixelB[1]) ||
                (pixelA[2] != pixelB[2]) ){
                return NO; 
                // means at some point pixelA is not equal to pixelB, so
                // pixelBufferA is not equal to pixelBufferB
            }

            pixelA += BYTES_PER_PIXEL;
            pixelB += BYTES_PER_PIXEL;

        }
    }

        // if the method reached here, pixelBufferA is equal to pixelBufferB, so
        return YES; // are equal
}

Obviously it is crashing in the comparison. How do I compare all values in pixelA with pixelB ? thanks

Answer 1

I’ve never actually done what you’re doing, but is there a reason you can’t just compare the buffers in one go, say, with memcmp?

- (BOOL) isBuffer:(unsigned char*)pixelA equalToBuffer:(unsigned char*)pixelB
{
    size_t bufferSize = bufferWidth * bufferHeight * BYTES_PER_PIXEL;

    return memcmp( pixelA, pixelB, bufferSize ) == 0;
}