x264的PSNR是如何计算出来的

x264中psnr的计算代码如下：

static double x264_psnr( double sqe, double size )

{

double mse = sqe / (PIXEL_MAX*PIXEL_MAX * size);

if( mse <= 0.0000000001 ) /* Max 100dB */

return 100;

return -10.0 * log10( mse );

}

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而输入参数sqe即ssd的计算代码为：

uint64_t x264_pixel_ssd_wxh( x264_pixel_function_t *pf, pixel *pix1, intptr_t i_pix1,

pixel *pix2, intptr_t i_pix2, int i_width, int i_height )

{

uint64_t i_ssd = 0;

int y;

int align = !(((intptr_t)pix1 | (intptr_t)pix2 | i_pix1 | i_pix2) & 15);

#define SSD(size) i_ssd += pf->ssd[size]( pix1 + y*i_pix1 + x, i_pix1, \

pix2 + y*i_pix2 + x, i_pix2 );

for( y = 0; y < i_height-15; y += 16 )

{

int x = 0;

if( align )

for( ; x < i_width-15; x += 16 )

SSD(PIXEL_16x16);

for( ; x < i_width-7; x += 8 )

SSD(PIXEL_8x16);

}

if( y < i_height-7 )

for( int x = 0; x < i_width-7; x += 8 )

SSD(PIXEL_8x8);

#undef SSD

#define SSD1 { int d = pix1[y*i_pix1+x] - pix2[y*i_pix2+x]; i_ssd += d*d; }

if( i_width & 7 )

{

for( y = 0; y < (i_height & ~7); y++ )

for( int x = i_width & ~7; x < i_width; x++ )

SSD1;

}

if( i_height & 7 )

{

for( y = i_height & ~7; y < i_height; y++ )

for( int x = 0; x < i_width; x++ )

SSD1;

}

#undef SSD1

return i_ssd;

}

static void pixel_ssd_nv12_core( pixel *pixuv1, intptr_t stride1, pixel *pixuv2, intptr_t stride2,

int width, int height, uint64_t *ssd_u, uint64_t *ssd_v )

{

*ssd_u = 0, *ssd_v = 0;

for( int y = 0; y < height; y++, pixuv1+=stride1, pixuv2+=stride2 )

for( int x = 0; x < width; x++ )

{

int du = pixuv1[2*x] - pixuv2[2*x];

int dv = pixuv1[2*x+1] - pixuv2[2*x+1];

*ssd_u += du*du;

*ssd_v += dv*dv;

}

}

void x264_pixel_ssd_nv12( x264_pixel_function_t *pf, pixel *pix1, intptr_t i_pix1, pixel *pix2, intptr_t i_pix2,

int i_width, int i_height, uint64_t *ssd_u, uint64_t *ssd_v )

{

pf->ssd_nv12_core( pix1, i_pix1, pix2, i_pix2, i_width&~7, i_height, ssd_u, ssd_v );

if( i_width&7 )

{

uint64_t tmp[2];

pixel_ssd_nv12_core( pix1+(i_width&~7), i_pix1, pix2+(i_width&~7), i_pix2, i_width&7, i_height, &tmp[0], &tmp[1] );

*ssd_u += tmp[0];

*ssd_v += tmp[1];

}

}

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****************************************************************************

* pixel_satd_WxH: sum of 4x4 Hadamard transformed differences

****************************************************************************/

static NOINLINE int x264_pixel_satd_4x4( pixel *pix1, intptr_t i_pix1, pixel *pix2, intptr_t i_pix2 )

{

sum2_t tmp[4][2];

sum2_t a0, a1, a2, a3, b0, b1;

sum2_t sum = 0;

for( int i = 0; i < 4; i++, pix1 += i_pix1, pix2 += i_pix2 )

{

a0 = pix1[0] - pix2[0];

a1 = pix1[1] - pix2[1];

b0 = (a0+a1) + ((a0-a1)<<BITS_PER_SUM);

a2 = pix1[2] - pix2[2];

a3 = pix1[3] - pix2[3];

b1 = (a2+a3) + ((a2-a3)<<BITS_PER_SUM);

tmp[i][0] = b0 + b1;

tmp[i][1] = b0 - b1;

}

for( int i = 0; i < 2; i++ )

{

HADAMARD4( a0, a1, a2, a3, tmp[0][i], tmp[1][i], tmp[2][i], tmp[3][i] );

a0 = abs2(a0) + abs2(a1) + abs2(a2) + abs2(a3);

sum += ((sum_t)a0) + (a0>>BITS_PER_SUM);

}

return sum >> 1;

}

static NOINLINE int x264_pixel_satd_8x4( pixel *pix1, intptr_t i_pix1, pixel *pix2, intptr_t i_pix2 )

{

sum2_t tmp[4][4];

sum2_t a0, a1, a2, a3;

sum2_t sum = 0;

for( int i = 0; i < 4; i++, pix1 += i_pix1, pix2 += i_pix2 )

{

a0 = (pix1[0] - pix2[0]) + ((sum2_t)(pix1[4] - pix2[4]) << BITS_PER_SUM);

a1 = (pix1[1] - pix2[1]) + ((sum2_t)(pix1[5] - pix2[5]) << BITS_PER_SUM);

a2 = (pix1[2] - pix2[2]) + ((sum2_t)(pix1[6] - pix2[6]) << BITS_PER_SUM);

a3 = (pix1[3] - pix2[3]) + ((sum2_t)(pix1[7] - pix2[7]) << BITS_PER_SUM);

HADAMARD4( tmp[i][0], tmp[i][1], tmp[i][2], tmp[i][3], a0,a1,a2,a3 );

}

for( int i = 0; i < 4; i++ )

{

HADAMARD4( a0, a1, a2, a3, tmp[0][i], tmp[1][i], tmp[2][i], tmp[3][i] );

sum += abs2(a0) + abs2(a1) + abs2(a2) + abs2(a3);

}

return (((sum_t)sum) + (sum>>BITS_PER_SUM)) >> 1;

}

#define PIXEL_SATD_C( w, h, sub )\

static int x264_pixel_satd_##w##x##h( pixel *pix1, intptr_t i_pix1, pixel *pix2, intptr_t i_pix2 )\

{\

int sum = sub( pix1, i_pix1, pix2, i_pix2 )\

+ sub( pix1+4*i_pix1, i_pix1, pix2+4*i_pix2, i_pix2 );\

if( w==16 )\

sum+= sub( pix1+8, i_pix1, pix2+8, i_pix2 )\

+ sub( pix1+8+4*i_pix1, i_pix1, pix2+8+4*i_pix2, i_pix2 );\

if( h==16 )\

sum+= sub( pix1+8*i_pix1, i_pix1, pix2+8*i_pix2, i_pix2 )\

+ sub( pix1+12*i_pix1, i_pix1, pix2+12*i_pix2, i_pix2 );\

if( w==16 && h==16 )\

sum+= sub( pix1+8+8*i_pix1, i_pix1, pix2+8+8*i_pix2, i_pix2 )\

+ sub( pix1+8+12*i_pix1, i_pix1, pix2+8+12*i_pix2, i_pix2 );\

return sum;\

}

PIXEL_SATD_C( 16, 16, x264_pixel_satd_8x4 )

PIXEL_SATD_C( 16, 8, x264_pixel_satd_8x4 )

PIXEL_SATD_C( 8, 16, x264_pixel_satd_8x4 )

PIXEL_SATD_C( 8, 8, x264_pixel_satd_8x4 )

PIXEL_SATD_C( 4, 16, x264_pixel_satd_4x4 )

PIXEL_SATD_C( 4, 8, x264_pixel_satd_4x4 )

static NOINLINE int sa8d_8x8( pixel *pix1, intptr_t i_pix1, pixel *pix2, intptr_t i_pix2 )

{

sum2_t tmp[8][4];

sum2_t a0, a1, a2, a3, a4, a5, a6, a7, b0, b1, b2, b3;

sum2_t sum = 0;

for( int i = 0; i < 8; i++, pix1 += i_pix1, pix2 += i_pix2 )

{

a0 = pix1[0] - pix2[0];

a1 = pix1[1] - pix2[1];

b0 = (a0+a1) + ((a0-a1)<<BITS_PER_SUM);

a2 = pix1[2] - pix2[2];

a3 = pix1[3] - pix2[3];

b1 = (a2+a3) + ((a2-a3)<<BITS_PER_SUM);

a4 = pix1[4] - pix2[4];

a5 = pix1[5] - pix2[5];

b2 = (a4+a5) + ((a4-a5)<<BITS_PER_SUM);

a6 = pix1[6] - pix2[6];

a7 = pix1[7] - pix2[7];

b3 = (a6+a7) + ((a6-a7)<<BITS_PER_SUM);

HADAMARD4( tmp[i][0], tmp[i][1], tmp[i][2], tmp[i][3], b0,b1,b2,b3 );

}

for( int i = 0; i < 4; i++ )

{

HADAMARD4( a0, a1, a2, a3, tmp[0][i], tmp[1][i], tmp[2][i], tmp[3][i] );

HADAMARD4( a4, a5, a6, a7, tmp[4][i], tmp[5][i], tmp[6][i], tmp[7][i] );

b0 = abs2(a0+a4) + abs2(a0-a4);

b0 += abs2(a1+a5) + abs2(a1-a5);

b0 += abs2(a2+a6) + abs2(a2-a6);

b0 += abs2(a3+a7) + abs2(a3-a7);

sum += (sum_t)b0 + (b0>>BITS_PER_SUM);

}

return sum;

}

static int x264_pixel_sa8d_8x8( pixel *pix1, intptr_t i_pix1, pixel *pix2, intptr_t i_pix2 )

{

int sum = sa8d_8x8( pix1, i_pix1, pix2, i_pix2 );

return (sum+2)>>2;

}

static int x264_pixel_sa8d_16x16( pixel *pix1, intptr_t i_pix1, pixel *pix2, intptr_t i_pix2 )

{

int sum = sa8d_8x8( pix1, i_pix1, pix2, i_pix2 )

+ sa8d_8x8( pix1+8, i_pix1, pix2+8, i_pix2 )

+ sa8d_8x8( pix1+8*i_pix1, i_pix1, pix2+8*i_pix2, i_pix2 )

+ sa8d_8x8( pix1+8+8*i_pix1, i_pix1, pix2+8+8*i_pix2, i_pix2 );

return (sum+2)>>2;

}

static NOINLINE uint64_t pixel_hadamard_ac( pixel *pix, intptr_t stride )

{

sum2_t tmp[32];

sum2_t a0, a1, a2, a3, dc;

sum2_t sum4 = 0, sum8 = 0;

for( int i = 0; i < 8; i++, pix+=stride )

{

sum2_t *t = tmp + (i&3) + (i&4)*4;

a0 = (pix[0]+pix[1]) + ((sum2_t)(pix[0]-pix[1])<<BITS_PER_SUM);

a1 = (pix[2]+pix[3]) + ((sum2_t)(pix[2]-pix[3])<<BITS_PER_SUM);

t[0] = a0 + a1;

t[4] = a0 - a1;

a2 = (pix[4]+pix[5]) + ((sum2_t)(pix[4]-pix[5])<<BITS_PER_SUM);

a3 = (pix[6]+pix[7]) + ((sum2_t)(pix[6]-pix[7])<<BITS_PER_SUM);

t[8] = a2 + a3;

t[12] = a2 - a3;

}

for( int i = 0; i < 8; i++ )

{

HADAMARD4( a0, a1, a2, a3, tmp[i*4+0], tmp[i*4+1], tmp[i*4+2], tmp[i*4+3] );

tmp[i*4+0] = a0;

tmp[i*4+1] = a1;

tmp[i*4+2] = a2;

tmp[i*4+3] = a3;

sum4 += abs2(a0) + abs2(a1) + abs2(a2) + abs2(a3);

}

for( int i = 0; i < 8; i++ )

{

HADAMARD4( a0,a1,a2,a3, tmp[i], tmp[8+i], tmp[16+i], tmp[24+i] );

sum8 += abs2(a0) + abs2(a1) + abs2(a2) + abs2(a3);

}

dc = (sum_t)(tmp[0] + tmp[8] + tmp[16] + tmp[24]);

sum4 = (sum_t)sum4 + (sum4>>BITS_PER_SUM) - dc;

sum8 = (sum_t)sum8 + (sum8>>BITS_PER_SUM) - dc;

return ((uint64_t)sum8<<32) + sum4;

}