near_lossless_enc.c (5396B)
1 // Copyright 2014 Google Inc. All Rights Reserved. 2 // 3 // Use of this source code is governed by a BSD-style license 4 // that can be found in the COPYING file in the root of the source 5 // tree. An additional intellectual property rights grant can be found 6 // in the file PATENTS. All contributing project authors may 7 // be found in the AUTHORS file in the root of the source tree. 8 // ----------------------------------------------------------------------------- 9 // 10 // Near-lossless image preprocessing adjusts pixel values to help 11 // compressibility with a guarantee of maximum deviation between original and 12 // resulting pixel values. 13 // 14 // Author: Jyrki Alakuijala (jyrki@google.com) 15 // Converted to C by Aleksander Kramarz (akramarz@google.com) 16 17 #include <assert.h> 18 #include <stdlib.h> 19 #include <string.h> 20 21 #include "src/dsp/lossless_common.h" 22 #include "src/webp/types.h" 23 #include "src/enc/vp8li_enc.h" 24 #include "src/utils/utils.h" 25 #include "src/webp/encode.h" 26 27 #if (WEBP_NEAR_LOSSLESS == 1) 28 29 #define MIN_DIM_FOR_NEAR_LOSSLESS 64 30 #define MAX_LIMIT_BITS 5 31 32 // Quantizes the value up or down to a multiple of 1<<bits (or to 255), 33 // choosing the closer one, resolving ties using bankers' rounding. 34 static uint32_t FindClosestDiscretized(uint32_t a, int bits) { 35 const uint32_t mask = (1u << bits) - 1; 36 const uint32_t biased = a + (mask >> 1) + ((a >> bits) & 1); 37 assert(bits > 0); 38 if (biased > 0xff) return 0xff; 39 return biased & ~mask; 40 } 41 42 // Applies FindClosestDiscretized to all channels of pixel. 43 static uint32_t ClosestDiscretizedArgb(uint32_t a, int bits) { 44 return 45 (FindClosestDiscretized(a >> 24, bits) << 24) | 46 (FindClosestDiscretized((a >> 16) & 0xff, bits) << 16) | 47 (FindClosestDiscretized((a >> 8) & 0xff, bits) << 8) | 48 (FindClosestDiscretized(a & 0xff, bits)); 49 } 50 51 // Checks if distance between corresponding channel values of pixels a and b 52 // is within the given limit. 53 static int IsNear(uint32_t a, uint32_t b, int limit) { 54 int k; 55 for (k = 0; k < 4; ++k) { 56 const int delta = 57 (int)((a >> (k * 8)) & 0xff) - (int)((b >> (k * 8)) & 0xff); 58 if (delta >= limit || delta <= -limit) { 59 return 0; 60 } 61 } 62 return 1; 63 } 64 65 static int IsSmooth(const uint32_t* const prev_row, 66 const uint32_t* const curr_row, 67 const uint32_t* const next_row, 68 int ix, int limit) { 69 // Check that all pixels in 4-connected neighborhood are smooth. 70 return (IsNear(curr_row[ix], curr_row[ix - 1], limit) && 71 IsNear(curr_row[ix], curr_row[ix + 1], limit) && 72 IsNear(curr_row[ix], prev_row[ix], limit) && 73 IsNear(curr_row[ix], next_row[ix], limit)); 74 } 75 76 // Adjusts pixel values of image with given maximum error. 77 static void NearLossless(int xsize, int ysize, const uint32_t* argb_src, 78 int stride, int limit_bits, uint32_t* copy_buffer, 79 uint32_t* argb_dst) { 80 int x, y; 81 const int limit = 1 << limit_bits; 82 uint32_t* prev_row = copy_buffer; 83 uint32_t* curr_row = prev_row + xsize; 84 uint32_t* next_row = curr_row + xsize; 85 memcpy(curr_row, argb_src, xsize * sizeof(argb_src[0])); 86 memcpy(next_row, argb_src + stride, xsize * sizeof(argb_src[0])); 87 88 for (y = 0; y < ysize; ++y, argb_src += stride, argb_dst += xsize) { 89 if (y == 0 || y == ysize - 1) { 90 memcpy(argb_dst, argb_src, xsize * sizeof(argb_src[0])); 91 } else { 92 memcpy(next_row, argb_src + stride, xsize * sizeof(argb_src[0])); 93 argb_dst[0] = argb_src[0]; 94 argb_dst[xsize - 1] = argb_src[xsize - 1]; 95 for (x = 1; x < xsize - 1; ++x) { 96 if (IsSmooth(prev_row, curr_row, next_row, x, limit)) { 97 argb_dst[x] = curr_row[x]; 98 } else { 99 argb_dst[x] = ClosestDiscretizedArgb(curr_row[x], limit_bits); 100 } 101 } 102 } 103 { 104 // Three-way swap. 105 uint32_t* const temp = prev_row; 106 prev_row = curr_row; 107 curr_row = next_row; 108 next_row = temp; 109 } 110 } 111 } 112 113 int VP8ApplyNearLossless(const WebPPicture* const picture, int quality, 114 uint32_t* const argb_dst) { 115 int i; 116 const int xsize = picture->width; 117 const int ysize = picture->height; 118 const int stride = picture->argb_stride; 119 uint32_t* const copy_buffer = 120 (uint32_t*)WebPSafeMalloc(xsize * 3, sizeof(*copy_buffer)); 121 const int limit_bits = VP8LNearLosslessBits(quality); 122 assert(argb_dst != NULL); 123 assert(limit_bits > 0); 124 assert(limit_bits <= MAX_LIMIT_BITS); 125 if (copy_buffer == NULL) { 126 return 0; 127 } 128 // For small icon images, don't attempt to apply near-lossless compression. 129 if ((xsize < MIN_DIM_FOR_NEAR_LOSSLESS && 130 ysize < MIN_DIM_FOR_NEAR_LOSSLESS) || 131 ysize < 3) { 132 for (i = 0; i < ysize; ++i) { 133 memcpy(argb_dst + i * xsize, picture->argb + i * picture->argb_stride, 134 xsize * sizeof(*argb_dst)); 135 } 136 WebPSafeFree(copy_buffer); 137 return 1; 138 } 139 140 NearLossless(xsize, ysize, picture->argb, stride, limit_bits, copy_buffer, 141 argb_dst); 142 for (i = limit_bits - 1; i != 0; --i) { 143 NearLossless(xsize, ysize, argb_dst, xsize, i, copy_buffer, argb_dst); 144 } 145 WebPSafeFree(copy_buffer); 146 return 1; 147 } 148 #else // (WEBP_NEAR_LOSSLESS == 1) 149 150 // Define a stub to suppress compiler warnings. 151 extern void VP8LNearLosslessStub(void); 152 void VP8LNearLosslessStub(void) {} 153 154 #endif // (WEBP_NEAR_LOSSLESS == 1)