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// Copyright 2015 Google Inc. All Rights Reserved.
// Use of this source code is governed by a BSD-style license
// that can be found in the COPYING file in the root of the source
// tree. An additional intellectual property rights grant can be found
// in the file PATENTS. All contributing project authors may
// be found in the AUTHORS file in the root of the source tree.
// -----------------------------------------------------------------------------
// Author: Mislav Bradac (
#include "./delta_palettization.h"
#include "../webp/types.h"
#include "../dsp/lossless.h"
#define MK_COL(r, g, b) (((r) << 16) + ((g) << 8) + (b))
// Format allows palette up to 256 entries, but more palette entries produce
// bigger entropy. In the future it will probably be useful to add more entries
// that are far from the origin of the palette or choose remaining entries
// dynamically.
// Palette used for delta_palettization. Entries are roughly sorted by distance
// of their signed equivalents from the origin.
static const uint32_t kDeltaPalette[DELTA_PALETTE_SIZE] = {
MK_COL(0u, 0u, 0u),
MK_COL(255u, 255u, 255u),
MK_COL(1u, 1u, 1u),
MK_COL(254u, 254u, 254u),
MK_COL(2u, 2u, 2u),
MK_COL(4u, 4u, 4u),
MK_COL(252u, 252u, 252u),
MK_COL(250u, 0u, 0u),
MK_COL(0u, 250u, 0u),
MK_COL(0u, 0u, 250u),
MK_COL(6u, 0u, 0u),
MK_COL(0u, 6u, 0u),
MK_COL(0u, 0u, 6u),
MK_COL(0u, 0u, 248u),
MK_COL(0u, 0u, 8u),
MK_COL(0u, 248u, 0u),
MK_COL(0u, 248u, 248u),
MK_COL(0u, 248u, 8u),
MK_COL(0u, 8u, 0u),
MK_COL(0u, 8u, 248u),
MK_COL(0u, 8u, 8u),
MK_COL(8u, 8u, 8u),
MK_COL(248u, 0u, 0u),
MK_COL(248u, 0u, 248u),
MK_COL(248u, 0u, 8u),
MK_COL(248u, 248u, 0u),
MK_COL(248u, 8u, 0u),
MK_COL(8u, 0u, 0u),
MK_COL(8u, 0u, 248u),
MK_COL(8u, 0u, 8u),
MK_COL(8u, 248u, 0u),
MK_COL(8u, 8u, 0u),
MK_COL(23u, 23u, 23u),
MK_COL(13u, 13u, 13u),
MK_COL(232u, 232u, 232u),
MK_COL(244u, 244u, 244u),
MK_COL(245u, 245u, 250u),
MK_COL(50u, 50u, 50u),
MK_COL(204u, 204u, 204u),
MK_COL(236u, 236u, 236u),
MK_COL(16u, 16u, 16u),
MK_COL(240u, 16u, 16u),
MK_COL(16u, 240u, 16u),
MK_COL(240u, 240u, 16u),
MK_COL(16u, 16u, 240u),
MK_COL(240u, 16u, 240u),
MK_COL(16u, 240u, 240u),
MK_COL(240u, 240u, 240u),
MK_COL(0u, 0u, 232u),
MK_COL(0u, 232u, 0u),
MK_COL(232u, 0u, 0u),
MK_COL(0u, 0u, 24u),
MK_COL(0u, 24u, 0u),
MK_COL(24u, 0u, 0u),
MK_COL(32u, 32u, 32u),
MK_COL(224u, 32u, 32u),
MK_COL(32u, 224u, 32u),
MK_COL(224u, 224u, 32u),
MK_COL(32u, 32u, 224u),
MK_COL(224u, 32u, 224u),
MK_COL(32u, 224u, 224u),
MK_COL(224u, 224u, 224u),
MK_COL(0u, 0u, 176u),
MK_COL(0u, 0u, 80u),
MK_COL(0u, 176u, 0u),
MK_COL(0u, 176u, 176u),
MK_COL(0u, 176u, 80u),
MK_COL(0u, 80u, 0u),
MK_COL(0u, 80u, 176u),
MK_COL(0u, 80u, 80u),
MK_COL(176u, 0u, 0u),
MK_COL(176u, 0u, 176u),
MK_COL(176u, 0u, 80u),
MK_COL(176u, 176u, 0u),
MK_COL(176u, 80u, 0u),
MK_COL(80u, 0u, 0u),
MK_COL(80u, 0u, 176u),
MK_COL(80u, 0u, 80u),
MK_COL(80u, 176u, 0u),
MK_COL(80u, 80u, 0u),
MK_COL(0u, 0u, 152u),
MK_COL(0u, 0u, 104u),
MK_COL(0u, 152u, 0u),
MK_COL(0u, 152u, 152u),
MK_COL(0u, 152u, 104u),
MK_COL(0u, 104u, 0u),
MK_COL(0u, 104u, 152u),
MK_COL(0u, 104u, 104u),
MK_COL(152u, 0u, 0u),
MK_COL(152u, 0u, 152u),
MK_COL(152u, 0u, 104u),
MK_COL(152u, 152u, 0u),
MK_COL(152u, 104u, 0u),
MK_COL(104u, 0u, 0u),
MK_COL(104u, 0u, 152u),
MK_COL(104u, 0u, 104u),
MK_COL(104u, 152u, 0u),
MK_COL(104u, 104u, 0u),
MK_COL(216u, 216u, 216u),
MK_COL(216u, 216u, 40u),
MK_COL(216u, 216u, 176u),
MK_COL(216u, 216u, 80u),
MK_COL(216u, 40u, 216u),
MK_COL(216u, 40u, 40u),
MK_COL(216u, 40u, 176u),
MK_COL(216u, 40u, 80u),
MK_COL(216u, 176u, 216u),
MK_COL(216u, 176u, 40u),
MK_COL(216u, 176u, 176u),
MK_COL(216u, 176u, 80u),
MK_COL(216u, 80u, 216u),
MK_COL(216u, 80u, 40u),
MK_COL(216u, 80u, 176u),
MK_COL(216u, 80u, 80u),
MK_COL(40u, 216u, 216u),
MK_COL(40u, 216u, 40u),
MK_COL(40u, 216u, 176u),
MK_COL(40u, 216u, 80u),
MK_COL(40u, 40u, 216u),
MK_COL(40u, 40u, 40u),
MK_COL(40u, 40u, 176u),
MK_COL(40u, 40u, 80u),
MK_COL(40u, 176u, 216u),
MK_COL(40u, 176u, 40u),
MK_COL(40u, 176u, 176u),
MK_COL(40u, 176u, 80u),
MK_COL(40u, 80u, 216u),
MK_COL(40u, 80u, 40u),
MK_COL(40u, 80u, 176u),
MK_COL(40u, 80u, 80u),
MK_COL(80u, 216u, 216u),
MK_COL(80u, 216u, 40u),
MK_COL(80u, 216u, 176u),
MK_COL(80u, 216u, 80u),
MK_COL(80u, 40u, 216u),
MK_COL(80u, 40u, 40u),
MK_COL(80u, 40u, 176u),
MK_COL(80u, 40u, 80u),
MK_COL(80u, 176u, 216u),
MK_COL(80u, 176u, 40u),
MK_COL(80u, 176u, 176u),
MK_COL(80u, 176u, 80u),
MK_COL(80u, 80u, 216u),
MK_COL(80u, 80u, 40u),
MK_COL(80u, 80u, 176u),
MK_COL(80u, 80u, 80u),
MK_COL(0u, 0u, 192u),
MK_COL(0u, 0u, 64u),
MK_COL(0u, 0u, 128u),
MK_COL(0u, 192u, 0u),
MK_COL(0u, 192u, 192u),
MK_COL(0u, 192u, 64u),
MK_COL(0u, 192u, 128u),
MK_COL(0u, 64u, 0u),
MK_COL(0u, 64u, 192u),
MK_COL(0u, 64u, 64u),
MK_COL(0u, 64u, 128u),
MK_COL(0u, 128u, 0u),
MK_COL(0u, 128u, 192u),
MK_COL(0u, 128u, 64u),
MK_COL(0u, 128u, 128u),
MK_COL(176u, 216u, 216u),
MK_COL(176u, 216u, 40u),
MK_COL(176u, 216u, 176u),
MK_COL(176u, 216u, 80u),
MK_COL(176u, 40u, 216u),
MK_COL(176u, 40u, 40u),
MK_COL(176u, 40u, 176u),
MK_COL(176u, 40u, 80u),
MK_COL(176u, 176u, 216u),
MK_COL(176u, 176u, 40u),
MK_COL(176u, 176u, 176u),
MK_COL(176u, 176u, 80u),
MK_COL(176u, 80u, 216u),
MK_COL(176u, 80u, 40u),
MK_COL(176u, 80u, 176u),
MK_COL(176u, 80u, 80u),
MK_COL(192u, 0u, 0u),
MK_COL(192u, 0u, 192u),
MK_COL(192u, 0u, 64u),
MK_COL(192u, 0u, 128u),
MK_COL(192u, 192u, 0u),
MK_COL(192u, 192u, 192u),
MK_COL(192u, 192u, 64u),
MK_COL(192u, 192u, 128u),
MK_COL(192u, 64u, 0u),
MK_COL(192u, 64u, 192u),
MK_COL(192u, 64u, 64u),
MK_COL(192u, 64u, 128u),
MK_COL(192u, 128u, 0u),
MK_COL(192u, 128u, 192u),
MK_COL(192u, 128u, 64u),
MK_COL(192u, 128u, 128u),
MK_COL(64u, 0u, 0u),
MK_COL(64u, 0u, 192u),
MK_COL(64u, 0u, 64u),
MK_COL(64u, 0u, 128u),
MK_COL(64u, 192u, 0u),
MK_COL(64u, 192u, 192u),
MK_COL(64u, 192u, 64u),
MK_COL(64u, 192u, 128u),
MK_COL(64u, 64u, 0u),
MK_COL(64u, 64u, 192u),
MK_COL(64u, 64u, 64u),
MK_COL(64u, 64u, 128u),
MK_COL(64u, 128u, 0u),
MK_COL(64u, 128u, 192u),
MK_COL(64u, 128u, 64u),
MK_COL(64u, 128u, 128u),
MK_COL(128u, 0u, 0u),
MK_COL(128u, 0u, 192u),
MK_COL(128u, 0u, 64u),
MK_COL(128u, 0u, 128u),
MK_COL(128u, 192u, 0u),
MK_COL(128u, 192u, 192u),
MK_COL(128u, 192u, 64u),
MK_COL(128u, 192u, 128u),
MK_COL(128u, 64u, 0u),
MK_COL(128u, 64u, 192u),
MK_COL(128u, 64u, 64u),
MK_COL(128u, 64u, 128u),
MK_COL(128u, 128u, 0u),
MK_COL(128u, 128u, 192u),
MK_COL(128u, 128u, 64u),
MK_COL(128u, 128u, 128u),
#undef MK_COL
// TODO(skal): move the functions to dsp/lossless.c when the correct
// granularity is found. For now, we'll just copy-paste some useful bits
// here instead.
// In-place sum of each component with mod 256.
static WEBP_INLINE void AddPixelsEq(uint32_t* a, uint32_t b) {
const uint32_t alpha_and_green = (*a & 0xff00ff00u) + (b & 0xff00ff00u);
const uint32_t red_and_blue = (*a & 0x00ff00ffu) + (b & 0x00ff00ffu);
*a = (alpha_and_green & 0xff00ff00u) | (red_and_blue & 0x00ff00ffu);
static WEBP_INLINE uint32_t Clip255(uint32_t a) {
if (a < 256) {
return a;
// return 0, when a is a negative integer.
// return 255, when a is positive.
return ~a >> 24;
// Delta palettization functions.
static WEBP_INLINE int Square(int x) {
return x * x;
static WEBP_INLINE uint32_t Intensity(uint32_t a) {
30 * ((a >> 16) & 0xff) +
59 * ((a >> 8) & 0xff) +
11 * ((a >> 0) & 0xff);
static uint32_t CalcDist(uint32_t predicted_value, uint32_t actual_value,
uint32_t palette_entry) {
int i;
uint32_t distance = 0;
AddPixelsEq(&predicted_value, palette_entry);
for (i = 0; i < 32; i += 8) {
const int32_t av = (actual_value >> i) & 0xff;
const int32_t pv = (predicted_value >> i) & 0xff;
distance += Square(pv - av);
// We sum square of intensity difference with factor 10, but because Intensity
// returns 100 times real intensity we need to multiply differences of colors
// by 1000.
distance *= 1000u;
distance += Square(Intensity(predicted_value)
- Intensity(actual_value));
return distance;
static uint32_t Predict(int x, int y, uint32_t* image) {
const uint32_t t = (y == 0) ? ARGB_BLACK : image[x];
const uint32_t l = (x == 0) ? ARGB_BLACK : image[x - 1];
const uint32_t p =
(((((t >> 24) & 0xff) + ((l >> 24) & 0xff)) / 2) << 24) +
(((((t >> 16) & 0xff) + ((l >> 16) & 0xff)) / 2) << 16) +
(((((t >> 8) & 0xff) + ((l >> 8) & 0xff)) / 2) << 8) +
(((((t >> 0) & 0xff) + ((l >> 0) & 0xff)) / 2) << 0);
if (x == 0 && y == 0) return ARGB_BLACK;
if (x == 0) return t;
if (y == 0) return l;
return p;
static WEBP_INLINE int AddSubtractComponentFullWithCoefficient(
int a, int b, int c) {
return Clip255(a + ((b - c) >> 2));
static WEBP_INLINE uint32_t ClampedAddSubtractFullWithCoefficient(
uint32_t c0, uint32_t c1, uint32_t c2) {
const int a = AddSubtractComponentFullWithCoefficient(
c0 >> 24, c1 >> 24, c2 >> 24);
const int r = AddSubtractComponentFullWithCoefficient((c0 >> 16) & 0xff,
(c1 >> 16) & 0xff,
(c2 >> 16) & 0xff);
const int g = AddSubtractComponentFullWithCoefficient((c0 >> 8) & 0xff,
(c1 >> 8) & 0xff,
(c2 >> 8) & 0xff);
const int b = AddSubtractComponentFullWithCoefficient(
c0 & 0xff, c1 & 0xff, c2 & 0xff);
return ((uint32_t)a << 24) | (r << 16) | (g << 8) | b;
// Find palette entry with minimum error from difference of actual pixel value
// and predicted pixel value. Propagate error of pixel to its top and left pixel
// in src array. Write predicted_value + palette_entry to new_image. Return
// index of best palette entry.
static int FindBestPaletteEntry(uint32_t src, uint32_t predicted_value,
const uint32_t palette[], int palette_size) {
int i;
int idx = 0;
uint32_t best_distance = CalcDist(predicted_value, src, palette[0]);
for (i = 1; i < palette_size; ++i) {
const uint32_t distance = CalcDist(predicted_value, src, palette[i]);
if (distance < best_distance) {
best_distance = distance;
idx = i;
return idx;
static void ApplyBestPaletteEntry(int x, int y,
uint32_t new_value, uint32_t palette_value,
uint32_t* src, int src_stride,
uint32_t* new_image) {
AddPixelsEq(&new_value, palette_value);
if (x > 0) {
src[x - 1] = ClampedAddSubtractFullWithCoefficient(src[x - 1],
new_value, src[x]);
if (y > 0) {
src[x - src_stride] =
ClampedAddSubtractFullWithCoefficient(src[x - src_stride],
new_value, src[x]);
new_image[x] = new_value;
// Main entry point
static WebPEncodingError ApplyDeltaPalette(uint32_t* src, uint32_t* dst,
uint32_t src_stride,
uint32_t dst_stride,
const uint32_t* palette,
int palette_size,
int width, int height,
int num_passes) {
int x, y;
WebPEncodingError err = VP8_ENC_OK;
uint32_t* new_image = (uint32_t*)WebPSafeMalloc(width, sizeof(*new_image));
uint8_t* const tmp_row = (uint8_t*)WebPSafeMalloc(width, sizeof(*tmp_row));
if (new_image == NULL || tmp_row == NULL) {
goto Error;
while (num_passes--) {
uint32_t* cur_src = src;
uint32_t* cur_dst = dst;
for (y = 0; y < height; ++y) {
for (x = 0; x < width; ++x) {
const uint32_t predicted_value = Predict(x, y, new_image);
tmp_row[x] = FindBestPaletteEntry(cur_src[x], predicted_value,
palette, palette_size);
ApplyBestPaletteEntry(x, y, predicted_value, palette[tmp_row[x]],
cur_src, src_stride, new_image);
for (x = 0; x < width; ++x) {
cur_dst[x] = palette[tmp_row[x]];
cur_src += src_stride;
cur_dst += dst_stride;
return err;
// replaces enc->argb_ by a palettizable approximation of it,
// and generates optimal enc->palette_[]
WebPEncodingError WebPSearchOptimalDeltaPalette(VP8LEncoder* const enc) {
const WebPPicture* const pic = enc->pic_;
uint32_t* src = pic->argb;
uint32_t* dst = enc->argb_;
const int width = pic->width;
const int height = pic->height;
WebPEncodingError err = VP8_ENC_OK;
memcpy(enc->palette_, kDeltaPalette, sizeof(kDeltaPalette));
enc->palette_[DELTA_PALETTE_SIZE - 1] = src[0] - 0xff000000u;
enc->palette_size_ = DELTA_PALETTE_SIZE;
err = ApplyDeltaPalette(src, dst, pic->argb_stride, enc->current_width_,
enc->palette_, enc->palette_size_,
width, height, 2);
if (err != VP8_ENC_OK) goto Error;
return err;
WebPEncodingError WebPSearchOptimalDeltaPalette(VP8LEncoder* const enc) {