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a WebP encoder
converts PNG & JPEG to WebP This is an experimental early version, with lot of room of later optimizations in both speed and quality. Compile with the usual `./configure && make` Command line example is examples/cwebp Usage: cwebp [options] -q quality input.png -o output.webp where 'quality' is between 0 (poor) to 100 (very good). Typical value is around 80. More encoding options with 'cwebp -longhelp' Change-Id: I577a94f6f622a0c44bdfa9daf1086ace89d45539
This commit is contained in:
Pascal Massimino
370
src/enc/filter.c
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370
src/enc/filter.c
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// Copyright 2011 Google Inc. All Rights Reserved.
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//
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// This code is licensed under the same terms as WebM:
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// Software License Agreement: http://www.webmproject.org/license/software/
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// Additional IP Rights Grant: http://www.webmproject.org/license/additional/
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// -----------------------------------------------------------------------------
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//
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// Selecting filter level
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//
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// Author: somnath@google.com (Somnath Banerjee)
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#include <math.h>
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#include "vp8enci.h"
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// NOTE: clip1, tables and InitTables are repeated entries of dsp.c
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static uint8_t abs0[255 + 255 + 1]; // abs(i)
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static uint8_t abs1[255 + 255 + 1]; // abs(i)>>1
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static int8_t sclip1[1020 + 1020 + 1]; // clips [-1020, 1020] to [-128, 127]
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static int8_t sclip2[112 + 112 + 1]; // clips [-112, 112] to [-16, 15]
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static uint8_t clip1[255 + 510 + 1]; // clips [-255,510] to [0,255]
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static int tables_ok = 0;
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static void InitTables() {
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if (!tables_ok) {
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int i;
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for (i = -255; i <= 255; ++i) {
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abs0[255 + i] = (i < 0) ? -i : i;
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abs1[255 + i] = abs0[255 + i] >> 1;
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}
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for (i = -1020; i <= 1020; ++i) {
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sclip1[1020 + i] = (i < -128) ? -128 : (i > 127) ? 127 : i;
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}
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for (i = -112; i <= 112; ++i) {
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sclip2[112 + i] = (i < -16) ? -16 : (i > 15) ? 15 : i;
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}
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for (i = -255; i <= 255 + 255; ++i) {
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clip1[255 + i] = (i < 0) ? 0 : (i > 255) ? 255 : i;
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}
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tables_ok = 1;
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}
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}
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//-----------------------------------------------------------------------------
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// Edge filtering functions
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// 4 pixels in, 2 pixels out
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static inline void do_filter2(uint8_t* p, int step) {
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const int p1 = p[-2*step], p0 = p[-step], q0 = p[0], q1 = p[step];
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const int a = 3 * (q0 - p0) + sclip1[1020 + p1 - q1];
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const int a1 = sclip2[112 + ((a + 4) >> 3)];
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const int a2 = sclip2[112 + ((a + 3) >> 3)];
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p[-step] = clip1[255 + p0 + a2];
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p[ 0] = clip1[255 + q0 - a1];
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}
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// 4 pixels in, 4 pixels out
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static inline void do_filter4(uint8_t* p, int step) {
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const int p1 = p[-2*step], p0 = p[-step], q0 = p[0], q1 = p[step];
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const int a = 3 * (q0 - p0);
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const int a1 = sclip2[112 + ((a + 4) >> 3)];
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const int a2 = sclip2[112 + ((a + 3) >> 3)];
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const int a3 = (a1 + 1) >> 1;
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p[-2*step] = clip1[255 + p1 + a3];
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p[- step] = clip1[255 + p0 + a2];
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p[ 0] = clip1[255 + q0 - a1];
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p[ step] = clip1[255 + q1 - a3];
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}
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// high edge-variance
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static inline int hev(const uint8_t* p, int step, int thresh) {
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const int p1 = p[-2*step], p0 = p[-step], q0 = p[0], q1 = p[step];
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return (abs0[255 + p1 - p0] > thresh) || (abs0[255 + q1 - q0] > thresh);
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}
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static inline int needs_filter(const uint8_t* p, int step, int thresh) {
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const int p1 = p[-2*step], p0 = p[-step], q0 = p[0], q1 = p[step];
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return (2 * abs0[255 + p0 - q0] + abs1[255 + p1 - q1]) <= thresh;
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}
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static inline int needs_filter2(const uint8_t* p, int step, int t, int it) {
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const int p3 = p[-4*step], p2 = p[-3*step], p1 = p[-2*step], p0 = p[-step];
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const int q0 = p[0], q1 = p[step], q2 = p[2*step], q3 = p[3*step];
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if ((2 * abs0[255 + p0 - q0] + abs1[255 + p1 - q1]) > t)
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return 0;
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return abs0[255 + p3 - p2] <= it && abs0[255 + p2 - p1] <= it &&
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abs0[255 + p1 - p0] <= it && abs0[255 + q3 - q2] <= it &&
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abs0[255 + q2 - q1] <= it && abs0[255 + q1 - q0] <= it;
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}
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//-----------------------------------------------------------------------------
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// Simple In-loop filtering (Paragraph 15.2)
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static void SimpleVFilter16(uint8_t* p, int stride, int thresh) {
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int i;
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for (i = 0; i < 16; ++i) {
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if (needs_filter(p + i, stride, thresh)) {
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do_filter2(p + i, stride);
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}
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}
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}
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static void SimpleHFilter16(uint8_t* p, int stride, int thresh) {
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int i;
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for (i = 0; i < 16; ++i) {
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if (needs_filter(p + i * stride, 1, thresh)) {
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do_filter2(p + i * stride, 1);
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}
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}
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}
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static void SimpleVFilter16i(uint8_t* p, int stride, int thresh) {
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int k;
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for (k = 3; k > 0; --k) {
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p += 4 * stride;
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SimpleVFilter16(p, stride, thresh);
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}
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}
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static void SimpleHFilter16i(uint8_t* p, int stride, int thresh) {
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int k;
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for (k = 3; k > 0; --k) {
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p += 4;
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SimpleHFilter16(p, stride, thresh);
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}
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}
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//-----------------------------------------------------------------------------
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// Complex In-loop filtering (Paragraph 15.3)
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static inline void FilterLoop24(uint8_t* p, int hstride, int vstride, int size,
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int thresh, int ithresh, int hev_thresh) {
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while (size-- > 0) {
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if (needs_filter2(p, hstride, thresh, ithresh)) {
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if (hev(p, hstride, hev_thresh)) {
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do_filter2(p, hstride);
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} else {
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do_filter4(p, hstride);
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}
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}
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p += vstride;
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}
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}
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// on three inner edges
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static void VFilter16i(uint8_t* p, int stride,
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int thresh, int ithresh, int hev_thresh) {
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int k;
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for (k = 3; k > 0; --k) {
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p += 4 * stride;
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FilterLoop24(p, stride, 1, 16, thresh, ithresh, hev_thresh);
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}
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}
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static void HFilter16i(uint8_t* p, int stride,
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int thresh, int ithresh, int hev_thresh) {
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int k;
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for (k = 3; k > 0; --k) {
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p += 4;
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FilterLoop24(p, 1, stride, 16, thresh, ithresh, hev_thresh);
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}
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}
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static void VFilter8i(uint8_t* u, uint8_t* v, int stride,
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int thresh, int ithresh, int hev_thresh) {
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FilterLoop24(u + 4 * stride, stride, 1, 8, thresh, ithresh, hev_thresh);
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FilterLoop24(v + 4 * stride, stride, 1, 8, thresh, ithresh, hev_thresh);
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}
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static void HFilter8i(uint8_t* u, uint8_t* v, int stride,
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int thresh, int ithresh, int hev_thresh) {
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FilterLoop24(u + 4, 1, stride, 8, thresh, ithresh, hev_thresh);
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FilterLoop24(v + 4, 1, stride, 8, thresh, ithresh, hev_thresh);
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}
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//-----------------------------------------------------------------------------
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void (*VP8EncVFilter16i)(uint8_t*, int, int, int, int) = VFilter16i;
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void (*VP8EncHFilter16i)(uint8_t*, int, int, int, int) = HFilter16i;
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void (*VP8EncVFilter8i)(uint8_t*, uint8_t*, int, int, int, int) = VFilter8i;
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void (*VP8EncHFilter8i)(uint8_t*, uint8_t*, int, int, int, int) = HFilter8i;
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void (*VP8EncSimpleVFilter16i)(uint8_t*, int, int) = SimpleVFilter16i;
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void (*VP8EncSimpleHFilter16i)(uint8_t*, int, int) = SimpleHFilter16i;
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//-----------------------------------------------------------------------------
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// Paragraph 15.4: compute the inner-edge filtering strength
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static int GetILevel(int sharpness, int level) {
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if (sharpness > 0) {
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if (sharpness > 4) {
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level >>= 2;
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} else {
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level >>= 1;
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}
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if (level > 9 - sharpness) {
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level = 9 - sharpness;
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}
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}
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if (level < 1) level = 1;
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return level;
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}
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static void DoFilter(const VP8EncIterator* const it, int level) {
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const VP8Encoder* const enc = it->enc_;
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const int ilevel = GetILevel(enc->config_->filter_sharpness, level);
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const int limit = 2 * level + ilevel;
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uint8_t* const y_dst = it->yuv_out2_ + Y_OFF;
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uint8_t* const u_dst = it->yuv_out2_ + U_OFF;
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uint8_t* const v_dst = it->yuv_out2_ + V_OFF;
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// copy current block to yuv_out2_
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memcpy(y_dst, it->yuv_out_, YUV_SIZE * sizeof(uint8_t));
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if (enc->filter_hdr_.simple_ == 1) { // simple
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VP8EncSimpleHFilter16i(y_dst, BPS, limit);
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VP8EncSimpleVFilter16i(y_dst, BPS, limit);
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} else { // complex
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const int hev_thresh = (level >= 40) ? 2 : (level >= 15) ? 1 : 0;
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VP8EncHFilter16i(y_dst, BPS, limit, ilevel, hev_thresh);
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VP8EncHFilter8i(u_dst, v_dst, BPS, limit, ilevel, hev_thresh);
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VP8EncVFilter16i(y_dst, BPS, limit, ilevel, hev_thresh);
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VP8EncVFilter8i(u_dst, v_dst, BPS, limit, ilevel, hev_thresh);
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}
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}
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//-----------------------------------------------------------------------------
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// SSIM metric
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enum { KERNEL = 3 };
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typedef struct {
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double w, xm, ym, xxm, xym, yym;
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} SSIMStats;
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static void Accumulate(const uint8_t* src1, int stride1,
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const uint8_t* src2, int stride2,
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int xo, int yo, int W, int H,
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SSIMStats* const stats) {
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const int ymin = (yo - KERNEL < 0) ? 0 : yo - KERNEL;
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const int ymax = (yo + KERNEL > H - 1) ? H - 1 : yo + KERNEL;
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const int xmin = (xo - KERNEL < 0) ? 0 : xo - KERNEL;
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const int xmax = (xo + KERNEL > W - 1) ? W - 1 : xo + KERNEL;
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int x, y;
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src1 += ymin * stride1;
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src2 += ymin * stride2;
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for (y = ymin; y <= ymax; ++y, src1 += stride1, src2 += stride2) {
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for (x = xmin; x <= xmax; ++x) {
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const int s1 = src1[x];
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const int s2 = src2[x];
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stats->w += 1;
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stats->xm += s1;
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stats->ym += s2;
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stats->xxm += s1 * s1;
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stats->xym += s1 * s2;
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stats->yym += s2 * s2;
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}
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}
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}
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static double GetSSIM(const SSIMStats* const stats) {
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const double xmxm = stats->xm * stats->xm;
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const double ymym = stats->ym * stats->ym;
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const double xmym = stats->xm * stats->ym;
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const double w2 = stats->w * stats->w;
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double sxx = stats->xxm * stats->w - xmxm;
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double syy = stats->yym * stats->w - ymym;
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double sxy = stats->xym * stats->w - xmym;
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double C1, C2;
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double fnum;
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double fden;
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// small errors are possible, due to rounding. Clamp to zero.
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if (sxx < 0.) sxx = 0.;
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if (syy < 0.) syy = 0.;
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C1 = 6.5025 * w2;
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C2 = 58.5225 * w2;
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fnum = (2 * xmym + C1) * (2 * sxy + C2);
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fden = (xmxm + ymym + C1) * (sxx + syy + C2);
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return (fden != 0) ? fnum / fden : 0.;
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}
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static double GetMBSSIM(const uint8_t* yuv1, const uint8_t* yuv2) {
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int x, y;
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SSIMStats s = { .0, .0, .0, .0, .0, .0 };
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// compute SSIM in a 10 x 10 window
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for (x = 3; x < 13; x++) {
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for (y = 3; y < 13; y++) {
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Accumulate(yuv1 + Y_OFF, BPS, yuv2 + Y_OFF, BPS, x, y, 16, 16, &s);
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}
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}
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for (x = 1; x < 7; x++) {
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for (y = 1; y < 7; y++) {
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Accumulate(yuv1 + U_OFF, BPS, yuv2 + U_OFF, BPS, x, y, 8, 8, &s);
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Accumulate(yuv1 + V_OFF, BPS, yuv2 + V_OFF, BPS, x, y, 8, 8, &s);
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}
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}
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return GetSSIM(&s);
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}
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//-----------------------------------------------------------------------------
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// Exposed APIs: Encoder should call the following 3 functions to adjust
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// loop filter strength
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void VP8InitFilter(VP8EncIterator* const it) {
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int s, i;
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if (!it->lf_stats_) return;
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InitTables();
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for (s = 0; s < NUM_MB_SEGMENTS; s++) {
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for (i = 0; i < MAX_LF_LEVELS; i++) {
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(*it->lf_stats_)[s][i] = 0;
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}
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}
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}
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void VP8StoreFilterStats(VP8EncIterator* const it) {
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int d;
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const int s = it->mb_->segment_;
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const int level0 = it->enc_->dqm_[s].fstrength_; // TODO: ref_lf_delta[]
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// explore +/-quant range of values around level0
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const int delta_min = -it->enc_->dqm_[s].quant_;
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const int delta_max = it->enc_->dqm_[s].quant_;
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const int step_size = (delta_max - delta_min >= 4) ? 4 : 1;
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if (!it->lf_stats_) return;
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// NOTE: Currently we are applying filter only across the sublock edges
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// There are two reasons for that.
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// 1. Applying filter on macro block edges will change the pixels in
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// the left and top macro blocks. That will be hard to restore
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// 2. Macro Blocks on the bottom and right are not yet compressed. So we
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// cannot apply filter on the right and bottom macro block edges.
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if (it->mb_->type_ == 1 && it->mb_->skip_) return;
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// Always try filter level zero
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(*it->lf_stats_)[s][0] += GetMBSSIM(it->yuv_in_, it->yuv_out_);
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for (d = delta_min; d <= delta_max; d += step_size) {
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const int level = level0 + d;
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if (level <= 0 || level >= MAX_LF_LEVELS) {
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continue;
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}
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DoFilter(it, level);
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(*it->lf_stats_)[s][level] += GetMBSSIM(it->yuv_in_, it->yuv_out2_);
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}
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}
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void VP8AdjustFilterStrength(VP8EncIterator* const it) {
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int s;
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VP8Encoder* const enc = it->enc_;
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if (!it->lf_stats_) {
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return;
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}
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for (s = 0; s < NUM_MB_SEGMENTS; s++) {
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int i, best_level = 0;
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// Improvement over filter level 0 should be at least 1e-5 (relatively)
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double best_v = 1.00001 * (*it->lf_stats_)[s][0];
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for (i = 1; i < MAX_LF_LEVELS; i++) {
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const double v = (*it->lf_stats_)[s][i];
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if (v > best_v) {
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best_v = v;
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best_level = i;
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}
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}
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enc->dqm_[s].fstrength_ = best_level;
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}
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}
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