how to do manipulation on CVImageBufferRef video frame

how to do manipulation on CVImageBufferRef video frame

- (void)processPixelBuffer: (CVImageBufferRef)pixelBuffer
{
CVPixelBufferLockBaseAddress( pixelBuffer, 0 );
int bufferWidth = CVPixelBufferGetWidth(pixelBuffer);
int bufferHeight = CVPixelBufferGetHeight(pixelBuffer);
unsigned char *pixel = (unsigned char
*)CVPixelBufferGetBaseAddress(pixelBuffer);
for( int row = 0; row < bufferHeight; row++ ) {
for( int column = 0; column < bufferWidth; column++ ) {
pixel[1] = 0; // it sets the green element of each pixel to
zero, which gives the entire frame a purple tint.
pixel += 4;
}
}
CVPixelBufferUnlockBaseAddress( pixelBuffer, 0 );
}
my question is how can i manipulate pixel so dark all brith colour becomes
yellow and all dark colour become blue
thank you so much