third_party/libwebp/dec/quant.c

   1 // Copyright 2010 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 // Quantizer initialization
  11 //
  12 // Author: Skal (pascal.massimino@gmail.com)
  13
  14 #include "./vp8i.h"
  15
  16 static WEBP_INLINE int clip(int v, int M) {
  17   return v < 0 ? 0 : v > M ? M : v;
  18 }
  19
  20 // Paragraph 14.1
  21 static const uint8_t kDcTable[128] = {
  22   4,     5,   6,   7,   8,   9,  10,  10,
  23   11,   12,  13,  14,  15,  16,  17,  17,
  24   18,   19,  20,  20,  21,  21,  22,  22,
  25   23,   23,  24,  25,  25,  26,  27,  28,
  26   29,   30,  31,  32,  33,  34,  35,  36,
  27   37,   37,  38,  39,  40,  41,  42,  43,
  28   44,   45,  46,  46,  47,  48,  49,  50,
  29   51,   52,  53,  54,  55,  56,  57,  58,
  30   59,   60,  61,  62,  63,  64,  65,  66,
  31   67,   68,  69,  70,  71,  72,  73,  74,
  32   75,   76,  76,  77,  78,  79,  80,  81,
  33   82,   83,  84,  85,  86,  87,  88,  89,
  34   91,   93,  95,  96,  98, 100, 101, 102,
  35   104, 106, 108, 110, 112, 114, 116, 118,
  36   122, 124, 126, 128, 130, 132, 134, 136,
  37   138, 140, 143, 145, 148, 151, 154, 157
  38 };
  39
  40 static const uint16_t kAcTable[128] = {
  41   4,     5,   6,   7,   8,   9,  10,  11,
  42   12,   13,  14,  15,  16,  17,  18,  19,
  43   20,   21,  22,  23,  24,  25,  26,  27,
  44   28,   29,  30,  31,  32,  33,  34,  35,
  45   36,   37,  38,  39,  40,  41,  42,  43,
  46   44,   45,  46,  47,  48,  49,  50,  51,
  47   52,   53,  54,  55,  56,  57,  58,  60,
  48   62,   64,  66,  68,  70,  72,  74,  76,
  49   78,   80,  82,  84,  86,  88,  90,  92,
  50   94,   96,  98, 100, 102, 104, 106, 108,
  51   110, 112, 114, 116, 119, 122, 125, 128,
  52   131, 134, 137, 140, 143, 146, 149, 152,
  53   155, 158, 161, 164, 167, 170, 173, 177,
  54   181, 185, 189, 193, 197, 201, 205, 209,
  55   213, 217, 221, 225, 229, 234, 239, 245,
  56   249, 254, 259, 264, 269, 274, 279, 284
  57 };
  58
  59 //------------------------------------------------------------------------------
  60 // Paragraph 9.6
  61
  62 void VP8ParseQuant(VP8Decoder* const dec) {
  63   VP8BitReader* const br = &dec->br_;
  64   const int base_q0 = VP8GetValue(br, 7);
  65   const int dqy1_dc = VP8Get(br) ? VP8GetSignedValue(br, 4) : 0;
  66   const int dqy2_dc = VP8Get(br) ? VP8GetSignedValue(br, 4) : 0;
  67   const int dqy2_ac = VP8Get(br) ? VP8GetSignedValue(br, 4) : 0;
  68   const int dquv_dc = VP8Get(br) ? VP8GetSignedValue(br, 4) : 0;
  69   const int dquv_ac = VP8Get(br) ? VP8GetSignedValue(br, 4) : 0;
  70
  71   const VP8SegmentHeader* const hdr = &dec->segment_hdr_;
  72   int i;
  73
  74   for (i = 0; i < NUM_MB_SEGMENTS; ++i) {
  75     int q;
  76     if (hdr->use_segment_) {
  77       q = hdr->quantizer_[i];
  78       if (!hdr->absolute_delta_) {
  79         q += base_q0;
  80       }
  81     } else {
  82       if (i > 0) {
  83         dec->dqm_[i] = dec->dqm_[0];
  84         continue;
  85       } else {
  86         q = base_q0;
  87       }
  88     }
  89     {
  90       VP8QuantMatrix* const m = &dec->dqm_[i];
  91       m->y1_mat_[0] = kDcTable[clip(q + dqy1_dc, 127)];
  92       m->y1_mat_[1] = kAcTable[clip(q + 0,       127)];
  93
  94       m->y2_mat_[0] = kDcTable[clip(q + dqy2_dc, 127)] * 2;
  95       // For all x in [0..284], x*155/100 is bitwise equal to (x*101581) >> 16.
  96       // The smallest precision for that is '(x*6349) >> 12' but 16 is a good
  97       // word size.
  98       m->y2_mat_[1] = (kAcTable[clip(q + dqy2_ac, 127)] * 101581) >> 16;
  99       if (m->y2_mat_[1] < 8) m->y2_mat_[1] = 8;
 100
 101       m->uv_mat_[0] = kDcTable[clip(q + dquv_dc, 117)];
 102       m->uv_mat_[1] = kAcTable[clip(q + dquv_ac, 127)];
 103
 104       m->uv_quant_ = q + dquv_ac;   // for dithering strength evaluation
 105     }
 106   }
 107 }
 108
 109 //------------------------------------------------------------------------------
 110