it's a secret

gistfile1.m

            int bufferWidth = CVPixelBufferGetWidth(pixelBuffer);
            int bufferHeight = CVPixelBufferGetHeight(pixelBuffer);
            uint8_t *pixel = CVPixelBufferGetBaseAddress(pixelBuffer);

            uint8_t * baseAddressGray = (uint8_t *) malloc(bufferWidth*bufferHeight);
            intrinsicBGRAtoGrayscale(baseAddressGray, pixel, bufferWidth*bufferHeight);

            for (int i = 0; i < (bufferWidth * bufferHeight); i++) {
                pixel[0] = baseAddressGray[0];
                pixel[1] = baseAddressGray[0];
                pixel[2] = baseAddressGray[0];
                pixel += BYTES_PER_PIXEL;
                baseAddressGray += 1;
            }

            free(baseAddressGray);