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// Copyright 2014 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.
// -----------------------------------------------------------------------------
//
// Near-lossless image preprocessing adjusts pixel values to help
// compressibility with a guarantee of maximum deviation between original and
// resulting pixel values.
//
// Author: Jyrki Alakuijala (jyrki@google.com)
// Converted to C by Aleksander Kramarz (akramarz@google.com)
#include <stdlib.h>
#include "../dsp/lossless.h"
#include "../utils/utils.h"
#include "./vp8enci.h"
#define MIN_DIM_FOR_NEAR_LOSSLESS 64
#define MAX_LIMIT_BITS 5
// Computes quantized pixel value and distance from original value.
static void GetValAndDistance(int a, int initial, int bits,
int* const val, int* const distance) {
const int mask = ~((1 << bits) - 1);
*val = (initial & mask) | (initial >> (8 - bits));
*distance = 2 * abs(a - *val);
}
// Clamps the value to range [0, 255].
static int Clamp8b(int val) {
const int min_val = 0;
const int max_val = 0xff;
return (val < min_val) ? min_val : (val > max_val) ? max_val : val;
}
// Quantizes values {a, a+(1<<bits), a-(1<<bits)} and returns the nearest one.
static int FindClosestDiscretized(int a, int bits) {
int best_val = a, i;
int min_distance = 256;
for (i = -1; i <= 1; ++i) {
int candidate, distance;
const int val = Clamp8b(a + i * (1 << bits));
GetValAndDistance(a, val, bits, &candidate, &distance);
if (i != 0) {
++distance;
}
// Smallest distance but favor i == 0 over i == -1 and i == 1
// since that keeps the overall intensity more constant in the
// images.
if (distance < min_distance) {
min_distance = distance;
best_val = candidate;
}
}
return best_val;
}
// Applies FindClosestDiscretized to all channels of pixel.
static uint32_t ClosestDiscretizedArgb(uint32_t a, int bits) {
return
(FindClosestDiscretized(a >> 24, bits) << 24) |
(FindClosestDiscretized((a >> 16) & 0xff, bits) << 16) |
(FindClosestDiscretized((a >> 8) & 0xff, bits) << 8) |
(FindClosestDiscretized(a & 0xff, bits));
}
// Checks if distance between corresponding channel values of pixels a and b
// is within the given limit.
static int IsNear(uint32_t a, uint32_t b, int limit) {
int k;
for (k = 0; k < 4; ++k) {
const int delta =
(int)((a >> (k * 8)) & 0xff) - (int)((b >> (k * 8)) & 0xff);
if (delta >= limit || delta <= -limit) {
return 0;
}
}
return 1;
}
static int IsSmooth(const uint32_t* const prev_row,
const uint32_t* const curr_row,
const uint32_t* const next_row,
int ix, int limit) {
// Check that all pixels in 4-connected neighborhood are smooth.
return (IsNear(curr_row[ix], curr_row[ix - 1], limit) &&
IsNear(curr_row[ix], curr_row[ix + 1], limit) &&
IsNear(curr_row[ix], prev_row[ix], limit) &&
IsNear(curr_row[ix], next_row[ix], limit));
}
// Adjusts pixel values of image with given maximum error.
static void NearLossless(int xsize, int ysize, uint32_t* argb,
int limit_bits, uint32_t* copy_buffer) {
int x, y;
const int limit = 1 << limit_bits;
uint32_t* prev_row = copy_buffer;
uint32_t* curr_row = prev_row + xsize;
uint32_t* next_row = curr_row + xsize;
memcpy(copy_buffer, argb, xsize * 2 * sizeof(argb[0]));
for (y = 1; y < ysize - 1; ++y) {
uint32_t* const curr_argb_row = argb + y * xsize;
uint32_t* const next_argb_row = curr_argb_row + xsize;
memcpy(next_row, next_argb_row, xsize * sizeof(argb[0]));
for (x = 1; x < xsize - 1; ++x) {
if (!IsSmooth(prev_row, curr_row, next_row, x, limit)) {
curr_argb_row[x] = ClosestDiscretizedArgb(curr_row[x], limit_bits);
}
}
{
// Three-way swap.
uint32_t* const temp = prev_row;
prev_row = curr_row;
curr_row = next_row;
next_row = temp;
}
}
}
static int QualityToLimitBits(int quality) {
// quality mapping:
// 0..19 -> 5
// 0..39 -> 4
// 0..59 -> 3
// 0..79 -> 2
// 0..99 -> 1
// 100 -> 0
return MAX_LIMIT_BITS - quality / 20;
}
int VP8ApplyNearLossless(int xsize, int ysize, uint32_t* argb, int quality) {
int i;
uint32_t* const copy_buffer =
(uint32_t*)WebPSafeMalloc(xsize * 3, sizeof(*copy_buffer));
const int limit_bits = QualityToLimitBits(quality);
assert(argb != NULL);
assert(limit_bits >= 0);
assert(limit_bits <= MAX_LIMIT_BITS);
if (copy_buffer == NULL) {
return 0;
}
// For small icon images, don't attempt to apply near-lossless compression.
if (xsize < MIN_DIM_FOR_NEAR_LOSSLESS && ysize < MIN_DIM_FOR_NEAR_LOSSLESS) {
WebPSafeFree(copy_buffer);
return 1;
}
for (i = limit_bits; i != 0; --i) {
NearLossless(xsize, ysize, argb, i, copy_buffer);
}
WebPSafeFree(copy_buffer);
return 1;
}
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