chromium/third_party/libvpx/source/libvpx/vp8/encoder/denoising.c

/*
 *  Copyright (c) 2012 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 <limits.h>

#include "denoising.h"

#include "vp8/common/reconinter.h"
#include "vpx/vpx_integer.h"
#include "vpx_mem/vpx_mem.h"
#include "vp8_rtcd.h"

static const unsigned int NOISE_MOTION_THRESHOLD = …;
/* SSE_DIFF_THRESHOLD is selected as ~95% confidence assuming
 * var(noise) ~= 100.
 */
static const unsigned int SSE_DIFF_THRESHOLD = …;
static const unsigned int SSE_THRESHOLD = …;
static const unsigned int SSE_THRESHOLD_HIGH = …;

/*
 * The filter function was modified to reduce the computational complexity.
 * Step 1:
 * Instead of applying tap coefficients for each pixel, we calculated the
 * pixel adjustments vs. pixel diff value ahead of time.
 *     adjustment = filtered_value - current_raw
 *                = (filter_coefficient * diff + 128) >> 8
 * where
 *     filter_coefficient = (255 << 8) / (256 + ((absdiff * 330) >> 3));
 *     filter_coefficient += filter_coefficient /
 *                           (3 + motion_magnitude_adjustment);
 *     filter_coefficient is clamped to 0 ~ 255.
 *
 * Step 2:
 * The adjustment vs. diff curve becomes flat very quick when diff increases.
 * This allowed us to use only several levels to approximate the curve without
 * changing the filtering algorithm too much.
 * The adjustments were further corrected by checking the motion magnitude.
 * The levels used are:
 * diff       adjustment w/o motion correction   adjustment w/ motion correction
 * [-255, -16]           -6                                   -7
 * [-15, -8]             -4                                   -5
 * [-7, -4]              -3                                   -4
 * [-3, 3]               diff                                 diff
 * [4, 7]                 3                                    4
 * [8, 15]                4                                    5
 * [16, 255]              6                                    7
 */

int vp8_denoiser_filter_c(unsigned char *mc_running_avg_y, int mc_avg_y_stride,
                          unsigned char *running_avg_y, int avg_y_stride,
                          unsigned char *sig, int sig_stride,
                          unsigned int motion_magnitude,
                          int increase_denoising) { … }

int vp8_denoiser_filter_uv_c(unsigned char *mc_running_avg, int mc_avg_stride,
                             unsigned char *running_avg, int avg_stride,
                             unsigned char *sig, int sig_stride,
                             unsigned int motion_magnitude,
                             int increase_denoising) { … }

void vp8_denoiser_set_parameters(VP8_DENOISER *denoiser, int mode) { … }

int vp8_denoiser_allocate(VP8_DENOISER *denoiser, int width, int height,
                          int num_mb_rows, int num_mb_cols, int mode) { … }

void vp8_denoiser_free(VP8_DENOISER *denoiser) { … }

void vp8_denoiser_denoise_mb(VP8_DENOISER *denoiser, MACROBLOCK *x,
                             unsigned int best_sse, unsigned int zero_mv_sse,
                             int recon_yoffset, int recon_uvoffset,
                             loop_filter_info_n *lfi_n, int mb_row, int mb_col,
                             int block_index, int consec_zero_last)

{ … }