1/*
2 *  Copyright (c) 2014 The WebM project authors. All Rights Reserved.
3 *
4 *  Use of this source code is governed by a BSD-style license
5 *  that can be found in the LICENSE file in the root of the source
6 *  tree. An additional intellectual property rights grant can be found
7 *  in the file PATENTS.  All contributing project authors may
8 *  be found in the AUTHORS file in the root of the source tree.
9 */
10
11#include <limits.h>
12#include <math.h>
13
14#include "vp9/common/vp9_seg_common.h"
15
16#include "vp9/encoder/vp9_segmentation.h"
17
18#define AQ_C_SEGMENTS  3
19#define AQ_C_STRENGTHS  3
20static const int aq_c_active_segments[AQ_C_STRENGTHS] = {1, 2, 3};
21static const double aq_c_q_adj_factor[AQ_C_STRENGTHS][AQ_C_SEGMENTS] =
22  {{1.0, 1.0, 1.0}, {1.0, 2.0, 1.0}, {1.0, 1.5, 2.5}};
23static const double aq_c_transitions[AQ_C_STRENGTHS][AQ_C_SEGMENTS] =
24  {{1.0, 1.0, 1.0}, {1.0, 0.25, 0.0}, {1.0, 0.5, 0.25}};
25
26static int get_aq_c_strength(int q_index, vpx_bit_depth_t bit_depth) {
27  // Approximate base quatizer (truncated to int)
28  const int base_quant = vp9_ac_quant(q_index, 0, bit_depth) / 4;
29  return (base_quant > 20) + (base_quant > 45);
30}
31
32void vp9_setup_in_frame_q_adj(VP9_COMP *cpi) {
33  VP9_COMMON *const cm = &cpi->common;
34  struct segmentation *const seg = &cm->seg;
35
36  // Make SURE use of floating point in this function is safe.
37  vp9_clear_system_state();
38
39  if (cm->frame_type == KEY_FRAME ||
40      cpi->refresh_alt_ref_frame ||
41      (cpi->refresh_golden_frame && !cpi->rc.is_src_frame_alt_ref)) {
42    int segment;
43    const int aq_strength = get_aq_c_strength(cm->base_qindex, cm->bit_depth);
44    const int active_segments = aq_c_active_segments[aq_strength];
45
46    // Clear down the segment map.
47    vpx_memset(cpi->segmentation_map, 0, cm->mi_rows * cm->mi_cols);
48
49    // Clear down the complexity map used for rd.
50    vpx_memset(cpi->complexity_map, 0, cm->mi_rows * cm->mi_cols);
51
52    vp9_clearall_segfeatures(seg);
53
54    // Segmentation only makes sense if the target bits per SB is above a
55    // threshold. Below this the overheads will usually outweigh any benefit.
56    if (cpi->rc.sb64_target_rate < 256) {
57      vp9_disable_segmentation(seg);
58      return;
59    }
60
61    vp9_enable_segmentation(seg);
62
63    // Select delta coding method.
64    seg->abs_delta = SEGMENT_DELTADATA;
65
66    // Segment 0 "Q" feature is disabled so it defaults to the baseline Q.
67    vp9_disable_segfeature(seg, 0, SEG_LVL_ALT_Q);
68
69    // Use some of the segments for in frame Q adjustment.
70    for (segment = 1; segment < active_segments; ++segment) {
71      int qindex_delta =
72          vp9_compute_qdelta_by_rate(&cpi->rc, cm->frame_type, cm->base_qindex,
73                                     aq_c_q_adj_factor[aq_strength][segment],
74                                     cm->bit_depth);
75
76      // For AQ complexity mode, we dont allow Q0 in a segment if the base
77      // Q is not 0. Q0 (lossless) implies 4x4 only and in AQ mode 2 a segment
78      // Q delta is sometimes applied without going back around the rd loop.
79      // This could lead to an illegal combination of partition size and q.
80      if ((cm->base_qindex != 0) && ((cm->base_qindex + qindex_delta) == 0)) {
81        qindex_delta = -cm->base_qindex + 1;
82      }
83      if ((cm->base_qindex + qindex_delta) > 0) {
84        vp9_enable_segfeature(seg, segment, SEG_LVL_ALT_Q);
85        vp9_set_segdata(seg, segment, SEG_LVL_ALT_Q, qindex_delta);
86      }
87    }
88  }
89}
90
91// Select a segment for the current SB64 block.
92// The choice of segment for a block depends on the ratio of the projected
93// bits for the block vs a target average.
94// An "aq_strength" value determines how many segments are supported,
95// the set of transition points to use and the extent of the quantizer
96// adjustment for each segment (configured in vp9_setup_in_frame_q_adj()).
97void vp9_select_in_frame_q_segment(VP9_COMP *cpi,
98                                   int mi_row, int mi_col,
99                                   int output_enabled, int projected_rate) {
100  VP9_COMMON *const cm = &cpi->common;
101
102  const int mi_offset = mi_row * cm->mi_cols + mi_col;
103  const int bw = num_8x8_blocks_wide_lookup[BLOCK_64X64];
104  const int bh = num_8x8_blocks_high_lookup[BLOCK_64X64];
105  const int xmis = MIN(cm->mi_cols - mi_col, bw);
106  const int ymis = MIN(cm->mi_rows - mi_row, bh);
107  int complexity_metric = 64;
108  int x, y;
109
110  unsigned char segment;
111
112  if (!output_enabled) {
113    segment = 0;
114  } else {
115    // Rate depends on fraction of a SB64 in frame (xmis * ymis / bw * bh).
116    // It is converted to bits * 256 units.
117    const int target_rate = (cpi->rc.sb64_target_rate * xmis * ymis * 256) /
118                            (bw * bh);
119    const int aq_strength = get_aq_c_strength(cm->base_qindex, cm->bit_depth);
120    const int active_segments = aq_c_active_segments[aq_strength];
121
122    // The number of segments considered and the transition points used to
123    // select them is determined by the "aq_strength" value.
124    // Currently this loop only supports segments that reduce Q (i.e. where
125    // there is undershoot.
126    // The loop counts down towards segment 0 which is the default segment
127    // with no Q adjustment.
128    segment = active_segments - 1;
129    while (segment > 0) {
130      if (projected_rate <
131          (target_rate * aq_c_transitions[aq_strength][segment])) {
132        break;
133      }
134      --segment;
135    }
136
137    if (target_rate > 0) {
138      complexity_metric =
139        clamp((int)((projected_rate * 64) / target_rate), 16, 255);
140    }
141  }
142
143  // Fill in the entires in the segment map corresponding to this SB64.
144  for (y = 0; y < ymis; y++) {
145    for (x = 0; x < xmis; x++) {
146      cpi->segmentation_map[mi_offset + y * cm->mi_cols + x] = segment;
147      cpi->complexity_map[mi_offset + y * cm->mi_cols + x] =
148        (unsigned char)complexity_metric;
149    }
150  }
151}
152