| // 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; |
| } |