github.com/cellofellow/gopkg@v0.0.0-20140722061823-eec0544a62ad/image/webp/libwebp/src/dec/quant.c (about)

     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