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improve integer version of filter

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the lookup table is based on floating point calculations (see source)

by moving the *3 before the downshift and adding the rounding bit, the
delta (LUT - integer) goes from:
______________________________________
__ 1__ 1______________________________
__ 1__ 1______________________________
____ 1______ 1________________________
____ 1 2__ 2 1________________________
______ 1 1 2__ 2__ 2__ 2 1 1__________
________ 1 1 2 2__ 1 2 3 1 2__ 2__ 2__
to:
__-1__-1______________________________
______________________________________
____-1______-1________________________
______________________________________
________-1______________-1____________
______________________________________

it's important to be able to use the integer version because the LUT
more or less precludes SIMD optimizations

Change-Id: I45a81127dc7b72a06fba951649135d9d918386c0
This commit is contained in:
Johann 2010-12-22 11:15:56 -05:00
parent 4b6219cb33
commit 20b855c33e
1 changed files with 18 additions and 13 deletions
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17
vp8/encoder/temporal_filter.c
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@ -36,11 +36,18 @@
#define ALT_REF_MC_ENABLED 1 // dis/enable MC in AltRef filtering #define ALT_REF_MC_ENABLED 1 // dis/enable MC in AltRef filtering
#define ALT_REF_SUBPEL_ENABLED 1 // dis/enable subpel in MC AltRef filtering #define ALT_REF_SUBPEL_ENABLED 1 // dis/enable subpel in MC AltRef filtering
#define USE_FILTER_LUT 0 // use lookup table to improve filter
#define USE_FILTER_LUT 1
#if VP8_TEMPORAL_ALT_REF #if VP8_TEMPORAL_ALT_REF
#if USE_FILTER_LUT #if USE_FILTER_LUT
// for (strength = 0; strength <= 6; strength++) {
// for (delta = 0; delta <= 18; delta++) {
// float coeff = (3.0 * delta * delta) / pow(2, strength);
// printf("%3d", (int)roundf(coeff > 16 ? 0 : 16-coeff));
// }
// printf("\n");
// }
static int modifier_lut[7][19] = static int modifier_lut[7][19] =
{ {
// Strength=0 // Strength=0
@ -140,16 +147,14 @@ void vp8_temporal_filter_apply_c
int pixel_value = *frame2++; int pixel_value = *frame2++;
#if USE_FILTER_LUT #if USE_FILTER_LUT
// LUT implementation --
// improves precision of filter
modifier = abs(src_byte-pixel_value); modifier = abs(src_byte-pixel_value);
modifier = modifier>18 ? 0 : lut[modifier]; modifier = modifier>18 ? 0 : lut[modifier];
#else #else
modifier = src_byte; modifier = src_byte - pixel_value;
modifier -= pixel_value;
modifier *= modifier; modifier *= modifier;
modifier >>= strength;
modifier *= 3; modifier *= 3;
modifier += 1 << (strength - 1);
modifier >>= strength;
if (modifier > 16) if (modifier > 16)
modifier = 16; modifier = 16;