123 lines
4.1 KiB
C
123 lines
4.1 KiB
C
// Copyright 2014 Google Inc. All Rights Reserved.
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//
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// Use of this source code is governed by a BSD-style license
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// that can be found in the COPYING file in the root of the source
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// tree. An additional intellectual property rights grant can be found
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// in the file PATENTS. All contributing project authors may
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// be found in the AUTHORS file in the root of the source tree.
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// -----------------------------------------------------------------------------
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//
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// Near-lossless image preprocessing adjusts pixel values to help
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// compressibility with a guarantee of maximum deviation between original and
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// resulting pixel values.
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//
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// Author: Jyrki Alakuijala (jyrki@google.com)
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// Converted to C by Aleksander Kramarz (akramarz@google.com)
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#include <assert.h>
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#include <stdlib.h>
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#include "../dsp/lossless.h"
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#include "../utils/utils.h"
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#include "./vp8enci.h"
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#define MIN_DIM_FOR_NEAR_LOSSLESS 64
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#define MAX_LIMIT_BITS 5
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// Quantizes the value up or down to a multiple of 1<<bits (or to 255),
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// choosing the closer one, resolving ties using bankers' rounding.
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static int FindClosestDiscretized(int a, int bits) {
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const int mask = (1 << bits) - 1;
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const int biased = a + (mask >> 1) + ((a >> bits) & 1);
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assert(bits > 0);
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if (biased > 0xff) return 0xff;
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return biased & ~mask;
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}
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// Applies FindClosestDiscretized to all channels of pixel.
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static uint32_t ClosestDiscretizedArgb(uint32_t a, int bits) {
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return
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(FindClosestDiscretized(a >> 24, bits) << 24) |
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(FindClosestDiscretized((a >> 16) & 0xff, bits) << 16) |
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(FindClosestDiscretized((a >> 8) & 0xff, bits) << 8) |
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(FindClosestDiscretized(a & 0xff, bits));
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}
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// Checks if distance between corresponding channel values of pixels a and b
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// is within the given limit.
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static int IsNear(uint32_t a, uint32_t b, int limit) {
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int k;
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for (k = 0; k < 4; ++k) {
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const int delta =
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(int)((a >> (k * 8)) & 0xff) - (int)((b >> (k * 8)) & 0xff);
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if (delta >= limit || delta <= -limit) {
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return 0;
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}
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}
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return 1;
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}
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static int IsSmooth(const uint32_t* const prev_row,
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const uint32_t* const curr_row,
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const uint32_t* const next_row,
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int ix, int limit) {
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// Check that all pixels in 4-connected neighborhood are smooth.
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return (IsNear(curr_row[ix], curr_row[ix - 1], limit) &&
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IsNear(curr_row[ix], curr_row[ix + 1], limit) &&
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IsNear(curr_row[ix], prev_row[ix], limit) &&
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IsNear(curr_row[ix], next_row[ix], limit));
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}
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// Adjusts pixel values of image with given maximum error.
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static void NearLossless(int xsize, int ysize, uint32_t* argb,
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int limit_bits, uint32_t* copy_buffer) {
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int x, y;
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const int limit = 1 << limit_bits;
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uint32_t* prev_row = copy_buffer;
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uint32_t* curr_row = prev_row + xsize;
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uint32_t* next_row = curr_row + xsize;
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memcpy(copy_buffer, argb, xsize * 2 * sizeof(argb[0]));
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for (y = 1; y < ysize - 1; ++y) {
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uint32_t* const curr_argb_row = argb + y * xsize;
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uint32_t* const next_argb_row = curr_argb_row + xsize;
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memcpy(next_row, next_argb_row, xsize * sizeof(argb[0]));
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for (x = 1; x < xsize - 1; ++x) {
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if (!IsSmooth(prev_row, curr_row, next_row, x, limit)) {
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curr_argb_row[x] = ClosestDiscretizedArgb(curr_row[x], limit_bits);
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}
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}
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{
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// Three-way swap.
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uint32_t* const temp = prev_row;
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prev_row = curr_row;
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curr_row = next_row;
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next_row = temp;
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}
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}
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}
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int VP8ApplyNearLossless(int xsize, int ysize, uint32_t* argb, int quality) {
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int i;
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uint32_t* const copy_buffer =
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(uint32_t*)WebPSafeMalloc(xsize * 3, sizeof(*copy_buffer));
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const int limit_bits = VP8LNearLosslessBits(quality);
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assert(argb != NULL);
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assert(limit_bits >= 0);
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assert(limit_bits <= MAX_LIMIT_BITS);
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if (copy_buffer == NULL) {
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return 0;
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}
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// For small icon images, don't attempt to apply near-lossless compression.
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if (xsize < MIN_DIM_FOR_NEAR_LOSSLESS && ysize < MIN_DIM_FOR_NEAR_LOSSLESS) {
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WebPSafeFree(copy_buffer);
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return 1;
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}
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for (i = limit_bits; i != 0; --i) {
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NearLossless(xsize, ysize, argb, i, copy_buffer);
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}
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WebPSafeFree(copy_buffer);
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return 1;
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}
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