vpx/vp9/encoder/vp9_picklpf.c

/*
 *  Copyright (c) 2010 The WebM project authors. All Rights Reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE 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.
 */

#include <assert.h>
#include <limits.h>

#include "./vpx_scale_rtcd.h"

#include "vpx_mem/vpx_mem.h"

#include "vp9/common/vp9_loopfilter.h"
#include "vp9/common/vp9_onyxc_int.h"
#include "vp9/common/vp9_quant_common.h"

#include "vp9/encoder/vp9_encoder.h"
#include "vp9/encoder/vp9_picklpf.h"
#include "vp9/encoder/vp9_quantize.h"

static int get_max_filter_level(const VP9_COMP *cpi) {
  if (cpi->pass == 2) {
    return cpi->twopass.section_intra_rating > 8 ? MAX_LOOP_FILTER * 3 / 4
                                                 : MAX_LOOP_FILTER;
  } else {
    return MAX_LOOP_FILTER;
  }
}


static int try_filter_frame(const YV12_BUFFER_CONFIG *sd, VP9_COMP *const cpi,
                            int filt_level, int partial_frame) {
  VP9_COMMON *const cm = &cpi->common;
  int filt_err;

  vp9_loop_filter_frame(cm, &cpi->mb.e_mbd, filt_level, 1, partial_frame);
  filt_err = vp9_get_y_sse(sd, cm->frame_to_show);

  // Re-instate the unfiltered frame
  vpx_yv12_copy_y(&cpi->last_frame_uf, cm->frame_to_show);

  return filt_err;
}

static int search_filter_level(const YV12_BUFFER_CONFIG *sd, VP9_COMP *cpi,
                               int partial_frame) {
  const VP9_COMMON *const cm = &cpi->common;
  const struct loopfilter *const lf = &cm->lf;
  const int min_filter_level = 0;
  const int max_filter_level = get_max_filter_level(cpi);
  int filt_direction = 0;
  int best_err, filt_best;

  // Start the search at the previous frame filter level unless it is now out of
  // range.
  int filt_mid = clamp(lf->filter_level, min_filter_level, max_filter_level);
  int filter_step = filt_mid < 16 ? 4 : filt_mid / 4;
  // Sum squared error at each filter level
  int ss_err[MAX_LOOP_FILTER + 1];

  // Set each entry to -1
  vpx_memset(ss_err, 0xFF, sizeof(ss_err));

  //  Make a copy of the unfiltered / processed recon buffer
  vpx_yv12_copy_y(cm->frame_to_show, &cpi->last_frame_uf);

  best_err = try_filter_frame(sd, cpi, filt_mid, partial_frame);
  filt_best = filt_mid;
  ss_err[filt_mid] = best_err;

  while (filter_step > 0) {
    const int filt_high = MIN(filt_mid + filter_step, max_filter_level);
    const int filt_low = MAX(filt_mid - filter_step, min_filter_level);
    int filt_err;

    // Bias against raising loop filter in favor of lowering it.
    int bias = (best_err >> (15 - (filt_mid / 8))) * filter_step;

    if ((cpi->pass == 2) && (cpi->twopass.section_intra_rating < 20))
      bias = (bias * cpi->twopass.section_intra_rating) / 20;

    // yx, bias less for large block size
    if (cm->tx_mode != ONLY_4X4)
      bias >>= 1;

    if (filt_direction <= 0 && filt_low != filt_mid) {
      // Get Low filter error score
      if (ss_err[filt_low] < 0) {
        filt_err = try_filter_frame(sd, cpi, filt_low, partial_frame);
        ss_err[filt_low] = filt_err;
      } else {
        filt_err = ss_err[filt_low];
      }
      // If value is close to the best so far then bias towards a lower loop
      // filter value.
      if ((filt_err - bias) < best_err) {
        // Was it actually better than the previous best?
        if (filt_err < best_err)
          best_err = filt_err;

        filt_best = filt_low;
      }
    }

    // Now look at filt_high
    if (filt_direction >= 0 && filt_high != filt_mid) {
      if (ss_err[filt_high] < 0) {
        filt_err = try_filter_frame(sd, cpi, filt_high, partial_frame);
        ss_err[filt_high] = filt_err;
      } else {
        filt_err = ss_err[filt_high];
      }
      // Was it better than the previous best?
      if (filt_err < (best_err - bias)) {
        best_err = filt_err;
        filt_best = filt_high;
      }
    }

    // Half the step distance if the best filter value was the same as last time
    if (filt_best == filt_mid) {
      filter_step /= 2;
      filt_direction = 0;
    } else {
      filt_direction = (filt_best < filt_mid) ? -1 : 1;
      filt_mid = filt_best;
    }
  }

  return filt_best;
}

void vp9_pick_filter_level(const YV12_BUFFER_CONFIG *sd, VP9_COMP *cpi,
                           LPF_PICK_METHOD method) {
  VP9_COMMON *const cm = &cpi->common;
  struct loopfilter *const lf = &cm->lf;

  lf->sharpness_level = cm->frame_type == KEY_FRAME ? 0
                                                    : cpi->oxcf.sharpness;

  if (method == LPF_PICK_FROM_Q) {
    const int min_filter_level = 0;
    const int max_filter_level = get_max_filter_level(cpi);
    const int q = vp9_ac_quant(cm->base_qindex, 0);
    // These values were determined by linear fitting the result of the
    // searched level, filt_guess = q * 0.316206 + 3.87252
    int filt_guess = ROUND_POWER_OF_TWO(q * 20723 + 1015158, 18);
    if (cm->frame_type == KEY_FRAME)
      filt_guess -= 4;
    lf->filter_level = clamp(filt_guess, min_filter_level, max_filter_level);
  } else {
    lf->filter_level = search_filter_level(sd, cpi,
                                           method == LPF_PICK_FROM_SUBIMAGE);
  }
}