[MEncoder-users] Codec-independant objective quality measurement

[Loren Merritt]

On Wed, 2 Aug 2006, Nicolas George wrote:
>
> I am looking for a tool (Open Source and command-line, for Unix; I have
> found MSU Video Quality Measurement Tool on the web, but it is neither) 
> to evaluate the quality of a video encoding.
>
> I know the PSNR option of some codecs, and I use it a lot to evaluate 
> the effect of fine encoding options. But it is not satisfactory for the 
> big comparisons:

Attached is an implementation of SSIM. As far as I can tell, this is the 
second most popular metric, behind PSNR.

--Loren Merritt
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/*
 * Copyright (c) 2006 Loren Merritt
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110 USA
 */
/*
 * tiny_ssim.c
 * Computes the Structural Similarity Metric between two rawYV12 video files.
 * original algorithm:
 * Z. Wang, A. C. Bovik, H. R. Sheikh and E. P. Simoncelli,
 *   "Image quality assessment: From error visibility to structural similarity,"
 *   IEEE Transactions on Image Processing, vol. 13, no. 4, pp. 600-612, Apr. 2004.
 *
 * To improve speed, this implementation uses the standard approximation of
 * overlapped 8x8 block sums, rather than the original gaussian weights.
 */

#include <inttypes.h>
#include <math.h>
#include <stdio.h>

double ssim_8x8( const uint8_t *pix1, int stride1,
                 const uint8_t *pix2, int stride2 )
{
    const int c1 = (int)(.01*.01*255*255*64 + .5);
    const int c2 = (int)(.03*.03*255*255*64*63 + .5);
    uint32_t s1=0, s2=0, ss=0, s12=0;
    uint32_t vars;
    int32_t covar;
    int x, y;

    for(y=0; y<8; y++)
        for(x=0; x<8; x++)
        {
            int a = pix1[x+y*stride1];
            int b = pix2[x+y*stride2];
            s1  += a;
            s2  += b;
            ss  += a*a;
            ss  += b*b;
            s12 += a*b;
        }

    vars = ss*64 - s1*s1 - s2*s2;\
    covar = s12*64 - s1*s2;\
    return (double)(2*s1*s2 + c1) * (double)(2*covar + c2)\
           / ((double)(s1*s1 + s2*s2 + c1) * (double)(vars + c2));
}

double ssim_plane( const uint8_t *pix1, const uint8_t *pix2, int width, int height )
{
    int x, y;
    double sum = 0.0;
    for( y = 0; y <= height-8; y += 4 )
        for( x = 0; x <= width-8; x += 4 )
            sum += ssim_8x8( pix1+x+y*width, width,
                             pix2+x+y*width, width );
    return sum / ((width/4-1) * (height/4-1));
}

uint64_t ssd_plane( const uint8_t *pix1, const uint8_t *pix2, int size )
{
    uint64_t ssd = 0;
    int i;
    for( i=0; i<size; i++ )
    {
        int d = pix1[i] - pix2[i];
        ssd += d*d;
    }
    return ssd;
}

double ssd_to_psnr( uint64_t ssd, uint64_t denom )
{
    return -10*log((double)ssd/(denom*255*255))/log(10);
}

int main(int argc, char* argv[])
{
    FILE *f[2];
    uint8_t *buf[2], *plane[2][3];
    uint64_t ssd[3] = {0,0,0};
    double ssim[3] = {0,0,0};
    int frame_size, w, h;
    int frames, seek;
    int i;

    if( argc<4 || 2 != sscanf(argv[3], "%dx%d", &w, &h) )
    {
        printf("tiny_ssim <file1.yuv> <file2.yuv> <width>x<height> [<seek>]\n");
        return -1;
    }

    f[0] = fopen(argv[1], "rb");
    f[1] = fopen(argv[2], "rb");
    sscanf(argv[3], "%dx%d", &w, &h);
    frame_size = w*h*3/2;
    for( i=0; i<2; i++ )
    {
        buf[i] = malloc(frame_size);
        plane[i][0] = buf[i];
        plane[i][1] = plane[i][0] + w*h;
        plane[i][2] = plane[i][1] + w*h/4;
    }
    seek = argc<5 ? 0 : atoi(argv[4]);
    fseek(f[seek<0], seek < 0 ? -seek : seek, SEEK_SET);

    for( frames=0;; frames++ )
    {
        if( fread(buf[0], frame_size, 1, f[0]) != 1) break;
        if( fread(buf[1], frame_size, 1, f[1]) != 1) break;
        for( i=0; i<3; i++ )
        {
            ssd[i]  += ssd_plane ( plane[0][i], plane[1][i], w*h>>2*!!i );
            ssim[i] += ssim_plane( plane[0][i], plane[1][i], w>>!!i, h>>!!i );
        }
    }

    if( !frames ) return 0;

    printf( "PSNR Y:%.3f  U:%.3f  V:%.3f  All:%.3f\n",
            ssd_to_psnr( ssd[0], (uint64_t)frames*w*h ),
            ssd_to_psnr( ssd[1], (uint64_t)frames*w*h/4 ),
            ssd_to_psnr( ssd[2], (uint64_t)frames*w*h/4 ),
            ssd_to_psnr( ssd[0] + ssd[1] + ssd[2], (uint64_t)frames*w*h*3/2 ) );
    printf( "SSIM Y:%.5f U:%.5f V:%.5f All:%.5f\n",
            ssim[0] / frames,
            ssim[1] / frames,
            ssim[2] / frames,
            (ssim[0]*4 + ssim[1] + ssim[2]) / (frames*6) );

    return 0;
}