[XviD-devel] PSNR question/bug

[Marco "elcabesa" Belli]

looking inside image.c i found psnr fouction, after calc of sum of  (diff)^2  
you make  psnr_y=255*255/result
andthen SNR = 10 log10(psnr_y)

is this right??

isn't better do

psnr_y =sum (diff)^2
s= sum (original pixel) ^2

snr= s/psnr;
SNR =10 log10(snr);

a code doing this is this

image_psnr(IMAGE * orig_image,
		   IMAGE * recon_image,
		   uint16_t stride,
		   uint16_t width,
		   uint16_t height)
{
	int32_t diff, x, y, quad = 0;
	uint8_t *orig = orig_image->y;
	uint8_t *recon = recon_image->y;
	float psnr_y;
	float s=0;



	for (y = 0; y < height; y++) {
		for (x = 0; x < width; x++) {
			diff = *(orig + x) - *(recon + x);
			quad += diff * diff;
			s+=*(orig + x)**(orig + x);
		}
		orig += stride;
		recon += stride;
	}


	psnr_y = quad;

	if (psnr_y) {
		psnr_y = s/psnr_y;
		psnr_y = 10 * (float) log10(psnr_y);
	} else
		psnr_y = (float) 99.99;

	return psnr_y;
}