text: /*
   * Copyright (c) 2013-2014 Clément Bœsch
   *
   * This file is part of FFmpeg.
   *
   * FFmpeg is free software; you can redistribute it and/or
   * modify it under the terms of the GNU Lesser General Public
   * License as published by the Free Software Foundation; either
   * version 2.1 of the License, or (at your option) any later version.
   *
   * FFmpeg is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   * Lesser General Public License for more details.
   *
   * You should have received a copy of the GNU Lesser General Public
   * License along with FFmpeg; if not, write to the Free Software
   * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
   */
  
  /**
   * A simple, relatively efficient and slow DCT image denoiser.
   *
   * @see http://www.ipol.im/pub/art/2011/ys-dct/
   *
   * The DCT factorization used is based on "Fast and numerically stable
   * algorithms for discrete cosine transforms" from Gerlind Plonkaa & Manfred
   * Tasche (DOI: 10.1016/j.laa.2004.07.015).
   */
  
  #include "libavutil/avassert.h"
  #include "libavutil/eval.h"
  #include "libavutil/opt.h"
  #include "internal.h"
  
  static const char *const var_names[] = { "c", NULL };
  enum { VAR_C, VAR_VARS_NB };
  
  #define MAX_THREADS 8
  
  typedef struct DCTdnoizContext {
      const AVClass *class;
  
      /* coefficient factor expression */
      char *expr_str;
      AVExpr *expr[MAX_THREADS];
      double var_values[MAX_THREADS][VAR_VARS_NB];
  
      int nb_threads;
      int pr_width, pr_height;    // width and height to process
      float sigma;                // used when no expression are st
      float th;                   // threshold (3*sigma)
      float *cbuf[2][3];          // two planar rgb color buffers
      float *slices[MAX_THREADS]; // slices buffers (1 slice buffer per thread)
      float *weights;             // dct coeff are cumulated with overlapping; these values are used for averaging
      int p_linesize;             // line sizes for color and weights
      int overlap;                // number of block overlapping pixels
      int step;                   // block step increment (blocksize - overlap)
      int n;                      // 1<<n is the block size
      int bsize;                  // block size, 1<<n
      void (*filter_freq_func)(struct DCTdnoizContext *s,
                               const float *src, int src_linesize,
                               float *dst, int dst_linesize,
                               int thread_id);
      void (*color_decorrelation)(float **dst, int dst_linesize,
                                  const uint8_t **src, int src_linesize,
                                  int w, int h);
      void (*color_correlation)(uint8_t **dst, int dst_linesize,
                                float **src, int src_linesize,
                                int w, int h);
  } DCTdnoizContext;
  
  #define MIN_NBITS 3 /* blocksize = 1<<3 =  8 */
  #define MAX_NBITS 4 /* blocksize = 1<<4 = 16 */
  #define DEFAULT_NBITS 3
  
  #define OFFSET(x) offsetof(DCTdnoizContext, x)
  #define FLAGS AV_OPT_FLAG_FILTERING_PARAM|AV_OPT_FLAG_VIDEO_PARAM
  static const AVOption dctdnoiz_options[] = {
      { "sigma",   "set noise sigma constant",               OFFSET(sigma),    AV_OPT_TYPE_FLOAT,  {.dbl=0},            0, 999,          .flags = FLAGS },
      { "s",       "set noise sigma constant",               OFFSET(sigma),    AV_OPT_TYPE_FLOAT,  {.dbl=0},            0, 999,          .flags = FLAGS },
      { "overlap", "set number of block overlapping pixels", OFFSET(overlap),  AV_OPT_TYPE_INT,    {.i64=-1}, -1, (1<<MAX_NBITS)-1, .flags = FLAGS },
      { "expr",    "set coefficient factor expression",      OFFSET(expr_str), AV_OPT_TYPE_STRING, {.str=NULL},                          .flags = FLAGS },
      { "e",       "set coefficient factor expression",      OFFSET(expr_str), AV_OPT_TYPE_STRING, {.str=NULL},                          .flags = FLAGS },
      { "n",       "set the block size, expressed in bits",  OFFSET(n),        AV_OPT_TYPE_INT,    {.i64=DEFAULT_NBITS}, MIN_NBITS, MAX_NBITS, .flags = FLAGS },
      { NULL }
  };
  
  AVFILTER_DEFINE_CLASS(dctdnoiz);
  
  static void av_always_inline fdct8_1d(float *dst, const float *src,
                                        int dst_stridea, int dst_strideb,
                                        int src_stridea, int src_strideb)
  {
      int i;
  
      for (i = 0; i < 8; i++) {
          const float x00 = src[0*src_stridea] + src[7*src_stridea];
          const float x01 = src[1*src_stridea] + src[6*src_stridea];
          const float x02 = src[2*src_stridea] + src[5*src_stridea];
          const float x03 = src[3*src_stridea] + src[4*src_stridea];
          const float x04 = src[0*src_stridea] - src[7*src_stridea];
          const float x05 = src[1*src_stridea] - src[6*src_stridea];
          const float x06 = src[2*src_stridea] - src[5*src_stridea];
          const float x07 = src[3*src_stridea] - src[4*src_stridea];
          const float x08 = x00 + x03;
          const float x09 = x01 + x02;
          const float x0a = x00 - x03;
          const float x0b = x01 - x02;
          const float x0c = 1.38703984532215f*x04 + 0.275899379282943f*x07;
          const float x0d = 1.17587560241936f*x05 + 0.785694958387102f*x06;
          const float x0e = -0.785694958387102f*x05 + 1.17587560241936f*x06;
          const float x0f = 0.275899379282943f*x04 - 1.38703984532215f*x07;
          const float x10 = 0.353553390593274f * (x0c - x0d);
          const float x11 = 0.353553390593274f * (x0e - x0f);
          dst[0*dst_stridea] = 0.353553390593274f * (x08 + x09);
          dst[1*dst_stridea] = 0.353553390593274f * (x0c + x0d);
          dst[2*dst_stridea] = 0.461939766255643f*x0a + 0.191341716182545f*x0b;
          dst[3*dst_stridea] = 0.707106781186547f * (x10 - x11);
          dst[4*dst_stridea] = 0.353553390593274f * (x08 - x09);
          dst[5*dst_stridea] = 0.707106781186547f * (x10 + x11);
          dst[6*dst_stridea] = 0.191341716182545f*x0a - 0.461939766255643f*x0b;
          dst[7*dst_stridea] = 0.353553390593274f * (x0e + x0f);
          dst += dst_strideb;
          src += src_strideb;
      }
  }
  
  static void av_always_inline idct8_1d(float *dst, const float *src,
                                        int dst_stridea, int dst_strideb,
                                        int src_stridea, int src_strideb,
                                        int add)
  {
      int i;
  
      for (i = 0; i < 8; i++) {
          const float x00 =  1.4142135623731f  *src[0*src_stridea];
          const float x01 =  1.38703984532215f *src[1*src_stridea] + 0.275899379282943f*src[7*src_stridea];
          const float x02 =  1.30656296487638f *src[2*src_stridea] + 0.541196100146197f*src[6*src_stridea];
          const float x03 =  1.17587560241936f *src[3*src_stridea] + 0.785694958387102f*src[5*src_stridea];
          const float x04 =  1.4142135623731f  *src[4*src_stridea];
          const float x05 = -0.785694958387102f*src[3*src_stridea] + 1.17587560241936f*src[5*src_stridea];
          const float x06 =  0.541196100146197f*src[2*src_stridea] - 1.30656296487638f*src[6*src_stridea];
          const float x07 = -0.275899379282943f*src[1*src_stridea] + 1.38703984532215f*src[7*src_stridea];
          const float x09 = x00 + x04;
          const float x0a = x01 + x03;
          const float x0b = 1.4142135623731f*x02;
          const float x0c = x00 - x04;
          const float x0d = x01 - x03;
          const float x0e = 0.353553390593274f * (x09 - x0b);
          const float x0f = 0.353553390593274f * (x0c + x0d);
          const float x10 = 0.353553390593274f * (x0c - x0d);
          const float x11 = 1.4142135623731f*x06;
          const float x12 = x05 + x07;
          const float x13 = x05 - x07;
          const float x14 = 0.353553390593274f * (x11 + x12);
          const float x15 = 0.353553390593274f * (x11 - x12);
          const float x16 = 0.5f*x13;
          dst[0*dst_stridea] = (add ? dst[ 0*dst_stridea] : 0) + 0.25f * (x09 + x0b) + 0.353553390593274f*x0a;
          dst[1*dst_stridea] = (add ? dst[ 1*dst_stridea] : 0) + 0.707106781186547f * (x0f + x15);
          dst[2*dst_stridea] = (add ? dst[ 2*dst_stridea] : 0) + 0.707106781186547f * (x0f - x15);
          dst[3*dst_stridea] = (add ? dst[ 3*dst_stridea] : 0) + 0.707106781186547f * (x0e + x16);
          dst[4*dst_stridea] = (add ? dst[ 4*dst_stridea] : 0) + 0.707106781186547f * (x0e - x16);
          dst[5*dst_stridea] = (add ? dst[ 5*dst_stridea] : 0) + 0.707106781186547f * (x10 - x14);
          dst[6*dst_stridea] = (add ? dst[ 6*dst_stridea] : 0) + 0.707106781186547f * (x10 + x14);
          dst[7*dst_stridea] = (add ? dst[ 7*dst_stridea] : 0) + 0.25f * (x09 + x0b) - 0.353553390593274f*x0a;
          dst += dst_strideb;
          src += src_strideb;
      }
  }
  
  
  static void av_always_inline fdct16_1d(float *dst, const float *src,
                                         int dst_stridea, int dst_strideb,
                                         int src_stridea, int src_strideb)
  {
      int i;
  
      for (i = 0; i < 16; i++) {
          const float x00 = src[ 0*src_stridea] + src[15*src_stridea];
          const float x01 = src[ 1*src_stridea] + src[14*src_stridea];
          const float x02 = src[ 2*src_stridea] + src[13*src_stridea];
          const float x03 = src[ 3*src_stridea] + src[12*src_stridea];
          const float x04 = src[ 4*src_stridea] + src[11*src_stridea];
          const float x05 = src[ 5*src_stridea] + src[10*src_stridea];
          const float x06 = src[ 6*src_stridea] + src[ 9*src_stridea];
          const float x07 = src[ 7*src_stridea] + src[ 8*src_stridea];
          const float x08 = src[ 0*src_stridea] - src[15*src_stridea];
          const float x09 = src[ 1*src_stridea] - src[14*src_stridea];
          const float x0a = src[ 2*src_stridea] - src[13*src_stridea];
          const float x0b = src[ 3*src_stridea] - src[12*src_stridea];
          const float x0c = src[ 4*src_stridea] - src[11*src_stridea];
          const float x0d = src[ 5*src_stridea] - src[10*src_stridea];
          const float x0e = src[ 6*src_stridea] - src[ 9*src_stridea];
          const float x0f = src[ 7*src_stridea] - src[ 8*src_stridea];
          const float x10 = x00 + x07;
          const float x11 = x01 + x06;
          const float x12 = x02 + x05;
          const float x13 = x03 + x04;
          const float x14 = x00 - x07;
          const float x15 = x01 - x06;
          const float x16 = x02 - x05;
          const float x17 = x03 - x04;
          const float x18 = x10 + x13;
          const float x19 = x11 + x12;
          const float x1a = x10 - x13;
          const float x1b = x11 - x12;
          const float x1c =   1.38703984532215f*x14 + 0.275899379282943f*x17;
          const float x1d =   1.17587560241936f*x15 + 0.785694958387102f*x16;
          const float x1e = -0.785694958387102f*x15 + 1.17587560241936f *x16;
          const float x1f =  0.275899379282943f*x14 - 1.38703984532215f *x17;
          const float x20 = 0.25f * (x1c - x1d);
          const float x21 = 0.25f * (x1e - x1f);
          const float x22 =  1.40740373752638f *x08 + 0.138617169199091f*x0f;
          const float x23 =  1.35331800117435f *x09 + 0.410524527522357f*x0e;
          const float x24 =  1.24722501298667f *x0a + 0.666655658477747f*x0d;
          const float x25 =  1.09320186700176f *x0b + 0.897167586342636f*x0c;
          const float x26 = -0.897167586342636f*x0b + 1.09320186700176f *x0c;
          const float x27 =  0.666655658477747f*x0a - 1.24722501298667f *x0d;
          const float x28 = -0.410524527522357f*x09 + 1.35331800117435f *x0e;
          const float x29 =  0.138617169199091f*x08 - 1.40740373752638f *x0f;
          const float x2a = x22 + x25;
          const float x2b = x23 + x24;
          const float x2c = x22 - x25;
          const float x2d = x23 - x24;
          const float x2e = 0.25f * (x2a - x2b);
          const float x2f = 0.326640741219094f*x2c + 0.135299025036549f*x2d;
          const float x30 = 0.135299025036549f*x2c - 0.326640741219094f*x2d;
          const float x31 = x26 + x29;
          const float x32 = x27 + x28;
          const float x33 = x26 - x29;
          const float x34 = x27 - x28;
          const float x35 = 0.25f * (x31 - x32);
          const float x36 = 0.326640741219094f*x33 + 0.135299025036549f*x34;
          const float x37 = 0.135299025036549f*x33 - 0.326640741219094f*x34;
          dst[ 0*dst_stridea] = 0.25f * (x18 + x19);
          dst[ 1*dst_stridea] = 0.25f * (x2a + x2b);
          dst[ 2*dst_stridea] = 0.25f * (x1c + x1d);
          dst[ 3*dst_stridea] = 0.707106781186547f * (x2f - x37);
          dst[ 4*dst_stridea] = 0.326640741219094f*x1a + 0.135299025036549f*x1b;
          dst[ 5*dst_stridea] = 0.707106781186547f * (x2f + x37);
          dst[ 6*dst_stridea] = 0.707106781186547f * (x20 - x21);
          dst[ 7*dst_stridea] = 0.707106781186547f * (x2e + x35);
          dst[ 8*dst_stridea] = 0.25f * (x18 - x19);
          dst[ 9*dst_stridea] = 0.707106781186547f * (x2e - x35);
          dst[10*dst_stridea] = 0.707106781186547f * (x20 + x21);
          dst[11*dst_stridea] = 0.707106781186547f * (x30 - x36);
          dst[12*dst_stridea] = 0.135299025036549f*x1a - 0.326640741219094f*x1b;
          dst[13*dst_stridea] = 0.707106781186547f * (x30 + x36);
          dst[14*dst_stridea] = 0.25f * (x1e + x1f);
          dst[15*dst_stridea] = 0.25f * (x31 + x32);
          dst += dst_strideb;
          src += src_strideb;
      }
  }
  
  static void av_always_inline idct16_1d(float *dst, const float *src,
                                         int dst_stridea, int dst_strideb,
                                         int src_stridea, int src_strideb,
                                         int add)
  {
      int i;
  
      for (i = 0; i < 16; i++) {
          const float x00 =  1.4142135623731f  *src[ 0*src_stridea];
          const float x01 =  1.40740373752638f *src[ 1*src_stridea] + 0.138617169199091f*src[15*src_stridea];
          const float x02 =  1.38703984532215f *src[ 2*src_stridea] + 0.275899379282943f*src[14*src_stridea];
          const float x03 =  1.35331800117435f *src[ 3*src_stridea] + 0.410524527522357f*src[13*src_stridea];
          const float x04 =  1.30656296487638f *src[ 4*src_stridea] + 0.541196100146197f*src[12*src_stridea];
          const float x05 =  1.24722501298667f *src[ 5*src_stridea] + 0.666655658477747f*src[11*src_stridea];
          const float x06 =  1.17587560241936f *src[ 6*src_stridea] + 0.785694958387102f*src[10*src_stridea];
          const float x07 =  1.09320186700176f *src[ 7*src_stridea] + 0.897167586342636f*src[ 9*src_stridea];
          const float x08 =  1.4142135623731f  *src[ 8*src_stridea];
          const float x09 = -0.897167586342636f*src[ 7*src_stridea] + 1.09320186700176f*src[ 9*src_stridea];
          const float x0a =  0.785694958387102f*src[ 6*src_stridea] - 1.17587560241936f*src[10*src_stridea];
          const float x0b = -0.666655658477747f*src[ 5*src_stridea] + 1.24722501298667f*src[11*src_stridea];
          const float x0c =  0.541196100146197f*src[ 4*src_stridea] - 1.30656296487638f*src[12*src_stridea];
          const float x0d = -0.410524527522357f*src[ 3*src_stridea] + 1.35331800117435f*src[13*src_stridea];
          const float x0e =  0.275899379282943f*src[ 2*src_stridea] - 1.38703984532215f*src[14*src_stridea];
          const float x0f = -0.138617169199091f*src[ 1*src_stridea] + 1.40740373752638f*src[15*src_stridea];
          const float x12 = x00 + x08;
          const float x13 = x01 + x07;
          const float x14 = x02 + x06;
          const float x15 = x03 + x05;
          const float x16 = 1.4142135623731f*x04;
          const float x17 = x00 - x08;
          const float x18 = x01 - x07;
          const float x19 = x02 - x06;
          const float x1a = x03 - x05;
          const float x1d = x12 + x16;
          const float x1e = x13 + x15;
          const float x1f = 1.4142135623731f*x14;
          const float x20 = x12 - x16;
          const float x21 = x13 - x15;
          const float x22 = 0.25f * (x1d - x1f);
          const float x23 = 0.25f * (x20 + x21);
          const float x24 = 0.25f * (x20 - x21);
          const float x25 = 1.4142135623731f*x17;
          const float x26 = 1.30656296487638f*x18 + 0.541196100146197f*x1a;
          const float x27 = 1.4142135623731f*x19;
          const float x28 = -0.541196100146197f*x18 + 1.30656296487638f*x1a;
          const float x29 = 0.176776695296637f * (x25 + x27) + 0.25f*x26;
          const float x2a = 0.25f * (x25 - x27);
          const float x2b = 0.176776695296637f * (x25 + x27) - 0.25f*x26;
          const float x2c = 0.353553390593274f*x28;
          const float x1b = 0.707106781186547f * (x2a - x2c);
          const float x1c = 0.707106781186547f * (x2a + x2c);
          const float x2d = 1.4142135623731f*x0c;
          const float x2e = x0b + x0d;
          const float x2f = x0a + x0e;
          const float x30 = x09 + x0f;
          const float x31 = x09 - x0f;
          const float x32 = x0a - x0e;
          const float x33 = x0b - x0d;
          const float x37 = 1.4142135623731f*x2d;
          const float x38 = 1.30656296487638f*x2e + 0.541196100146197f*x30;
          const float x39 = 1.4142135623731f*x2f;
          const float x3a = -0.541196100146197f*x2e + 1.30656296487638f*x30;
          const float x3b = 0.176776695296637f * (x37 + x39) + 0.25f*x38;
          const float x3c = 0.25f * (x37 - x39);
          const float x3d = 0.176776695296637f * (x37 + x39) - 0.25f*x38;
          const float x3e = 0.353553390593274f*x3a;
          const float x34 = 0.707106781186547f * (x3c - x3e);
          const float x35 = 0.707106781186547f * (x3c + x3e);
          const float x3f = 1.4142135623731f*x32;
          const float x40 = x31 + x33;
          const float x41 = x31 - x33;
          const float x42 = 0.25f * (x3f + x40);
          const float x43 = 0.25f * (x3f - x40);
          const float x44 = 0.353553390593274f*x41;
          dst[ 0*dst_stridea] = (add ? dst[ 0*dst_stridea] : 0) + 0.176776695296637f * (x1d + x1f) + 0.25f*x1e;
          dst[ 1*dst_stridea] = (add ? dst[ 1*dst_stridea] : 0) + 0.707106781186547f * (x29 + x3d);
          dst[ 2*dst_stridea] = (add ? dst[ 2*dst_stridea] : 0) + 0.707106781186547f * (x29 - x3d);
          dst[ 3*dst_stridea] = (add ? dst[ 3*dst_stridea] : 0) + 0.707106781186547f * (x23 - x43);
          dst[ 4*dst_stridea] = (add ? dst[ 4*dst_stridea] : 0) + 0.707106781186547f * (x23 + x43);
          dst[ 5*dst_stridea] = (add ? dst[ 5*dst_stridea] : 0) + 0.707106781186547f * (x1b - x35);
          dst[ 6*dst_stridea] = (add ? dst[ 6*dst_stridea] : 0) + 0.707106781186547f * (x1b + x35);
          dst[ 7*dst_stridea] = (add ? dst[ 7*dst_stridea] : 0) + 0.707106781186547f * (x22 + x44);
          dst[ 8*dst_stridea] = (add ? dst[ 8*dst_stridea] : 0) + 0.707106781186547f * (x22 - x44);
          dst[ 9*dst_stridea] = (add ? dst[ 9*dst_stridea] : 0) + 0.707106781186547f * (x1c + x34);
          dst[10*dst_stridea] = (add ? dst[10*dst_stridea] : 0) + 0.707106781186547f * (x1c - x34);
          dst[11*dst_stridea] = (add ? dst[11*dst_stridea] : 0) + 0.707106781186547f * (x24 + x42);
          dst[12*dst_stridea] = (add ? dst[12*dst_stridea] : 0) + 0.707106781186547f * (x24 - x42);
          dst[13*dst_stridea] = (add ? dst[13*dst_stridea] : 0) + 0.707106781186547f * (x2b - x3b);
          dst[14*dst_stridea] = (add ? dst[14*dst_stridea] : 0) + 0.707106781186547f * (x2b + x3b);
          dst[15*dst_stridea] = (add ? dst[15*dst_stridea] : 0) + 0.176776695296637f * (x1d + x1f) - 0.25f*x1e;
          dst += dst_strideb;
          src += src_strideb;
      }
  }
  
  #define DEF_FILTER_FREQ_FUNCS(bsize)                                                        \
  static av_always_inline void filter_freq_##bsize(const float *src, int src_linesize,        \
                                                   float *dst, int dst_linesize,              \
                                                   AVExpr *expr, double *var_values,          \
                                                   int sigma_th)                              \
  {                                                                                           \
      unsigned i;                                                                             \
      DECLARE_ALIGNED(32, float, tmp_block1)[bsize * bsize];                                  \
      DECLARE_ALIGNED(32, float, tmp_block2)[bsize * bsize];                                  \
                                                                                              \
      /* forward DCT */                                                                       \
      fdct##bsize##_1d(tmp_block1, src, 1, bsize, 1, src_linesize);                           \
      fdct##bsize##_1d(tmp_block2, tmp_block1, bsize, 1, bsize, 1);                           \
                                                                                              \
      for (i = 0; i < bsize*bsize; i++) {                                                     \
          float *b = &tmp_block2[i];                                                          \
          /* frequency filtering */                                                           \
          if (expr) {                                                                         \
              var_values[VAR_C] = fabsf(*b);                                                  \
              *b *= av_expr_eval(expr, var_values, NULL);                                     \
          } else {                                                                            \
              if (fabsf(*b) < sigma_th)                                                       \
                  *b = 0;                                                                     \
          }                                                                                   \
      }                                                                                       \
                                                                                              \
      /* inverse DCT */                                                                       \
      idct##bsize##_1d(tmp_block1, tmp_block2, 1, bsize, 1, bsize, 0);                        \
      idct##bsize##_1d(dst, tmp_block1, dst_linesize, 1, bsize, 1, 1);                        \
  }                                                                                           \
                                                                                              \
  static void filter_freq_sigma_##bsize(DCTdnoizContext *s,                                   \
                                        const float *src, int src_linesize,                   \
                                        float *dst, int dst_linesize, int thread_id)          \
  {                                                                                           \
      filter_freq_##bsize(src, src_linesize, dst, dst_linesize, NULL, NULL, s->th);           \
  }                                                                                           \
                                                                                              \
  static void filter_freq_expr_##bsize(DCTdnoizContext *s,                                    \
                                       const float *src, int src_linesize,                    \
                                       float *dst, int dst_linesize, int thread_id)           \
  {                                                                                           \
      filter_freq_##bsize(src, src_linesize, dst, dst_linesize,                               \
                          s->expr[thread_id], s->var_values[thread_id], 0);                   \
  }
  
  DEF_FILTER_FREQ_FUNCS(8)
  DEF_FILTER_FREQ_FUNCS(16)
  
  #define DCT3X3_0_0  0.5773502691896258f /*  1/sqrt(3) */
  #define DCT3X3_0_1  0.5773502691896258f /*  1/sqrt(3) */
  #define DCT3X3_0_2  0.5773502691896258f /*  1/sqrt(3) */
  #define DCT3X3_1_0  0.7071067811865475f /*  1/sqrt(2) */
  #define DCT3X3_1_2 -0.7071067811865475f /* -1/sqrt(2) */
  #define DCT3X3_2_0  0.4082482904638631f /*  1/sqrt(6) */
  #define DCT3X3_2_1 -0.8164965809277261f /* -2/sqrt(6) */
  #define DCT3X3_2_2  0.4082482904638631f /*  1/sqrt(6) */
  
  static av_always_inline void color_decorrelation(float **dst, int dst_linesize,
                                                   const uint8_t **src, int src_linesize,
                                                   int w, int h,
                                                   int r, int g, int b)
  {
      int x, y;
      float *dstp_r = dst[0];
      float *dstp_g = dst[1];
      float *dstp_b = dst[2];
      const uint8_t *srcp = src[0];
  
      for (y = 0; y < h; y++) {
          for (x = 0; x < w; x++) {
              dstp_r[x] = srcp[r] * DCT3X3_0_0 + srcp[g] * DCT3X3_0_1 + srcp[b] * DCT3X3_0_2;
              dstp_g[x] = srcp[r] * DCT3X3_1_0 +                        srcp[b] * DCT3X3_1_2;
              dstp_b[x] = srcp[r] * DCT3X3_2_0 + srcp[g] * DCT3X3_2_1 + srcp[b] * DCT3X3_2_2;
              srcp += 3;
          }
          srcp   += src_linesize - w * 3;
          dstp_r += dst_linesize;
          dstp_g += dst_linesize;
          dstp_b += dst_linesize;
      }
  }
  
  static av_always_inline void color_correlation(uint8_t **dst, int dst_linesize,
                                                 float **src, int src_linesize,
                                                 int w, int h,
                                                 int r, int g, int b)
  {
      int x, y;
      const float *src_r = src[0];
      const float *src_g = src[1];
      const float *src_b = src[2];
      uint8_t *dstp = dst[0];
  
      for (y = 0; y < h; y++) {
          for (x = 0; x < w; x++) {
              dstp[r] = av_clip_uint8(src_r[x] * DCT3X3_0_0 + src_g[x] * DCT3X3_1_0 + src_b[x] * DCT3X3_2_0);
              dstp[g] = av_clip_uint8(src_r[x] * DCT3X3_0_1 +                         src_b[x] * DCT3X3_2_1);
              dstp[b] = av_clip_uint8(src_r[x] * DCT3X3_0_2 + src_g[x] * DCT3X3_1_2 + src_b[x] * DCT3X3_2_2);
              dstp += 3;
          }
          dstp  += dst_linesize - w * 3;
          src_r += src_linesize;
          src_g += src_linesize;
          src_b += src_linesize;
      }
  }
  
  #define DECLARE_COLOR_FUNCS(name, r, g, b)                                          \
  static void color_decorrelation_##name(float **dst, int dst_linesize,               \
                                         const uint8_t **src, int src_linesize,       \
                                         int w, int h)                                \
  {                                                                                   \
      color_decorrelation(dst, dst_linesize, src, src_linesize, w, h, r, g, b);       \
  }                                                                                   \
                                                                                      \
  static void color_correlation_##name(uint8_t **dst, int dst_linesize,               \
                                       float **src, int src_linesize,                 \
                                       int w, int h)                                  \
  {                                                                                   \
      color_correlation(dst, dst_linesize, src, src_linesize, w, h, r, g, b);         \
  }
  
  DECLARE_COLOR_FUNCS(rgb, 0, 1, 2)
  DECLARE_COLOR_FUNCS(bgr, 2, 1, 0)
  
  static av_always_inline void color_decorrelation_gbrp(float **dst, int dst_linesize,
                                                        const uint8_t **src, int src_linesize,
                                                        int w, int h)
  {
      int x, y;
      float *dstp_r = dst[0];
      float *dstp_g = dst[1];
      float *dstp_b = dst[2];
      const uint8_t *srcp_r = src[2];
      const uint8_t *srcp_g = src[0];
      const uint8_t *srcp_b = src[1];
  
      for (y = 0; y < h; y++) {
          for (x = 0; x < w; x++) {
              dstp_r[x] = srcp_r[x] * DCT3X3_0_0 + srcp_g[x] * DCT3X3_0_1 + srcp_b[x] * DCT3X3_0_2;
              dstp_g[x] = srcp_r[x] * DCT3X3_1_0 +                          srcp_b[x] * DCT3X3_1_2;
              dstp_b[x] = srcp_r[x] * DCT3X3_2_0 + srcp_g[x] * DCT3X3_2_1 + srcp_b[x] * DCT3X3_2_2;
          }
          srcp_r += src_linesize;
          srcp_g += src_linesize;
          srcp_b += src_linesize;
          dstp_r += dst_linesize;
          dstp_g += dst_linesize;
          dstp_b += dst_linesize;
      }
  }
  
  static av_always_inline void color_correlation_gbrp(uint8_t **dst, int dst_linesize,
                                                      float **src, int src_linesize,
                                                      int w, int h)
  {
      int x, y;
      const float *src_r = src[0];
      const float *src_g = src[1];
      const float *src_b = src[2];
      uint8_t *dstp_r = dst[2];
      uint8_t *dstp_g = dst[0];
      uint8_t *dstp_b = dst[1];
  
      for (y = 0; y < h; y++) {
          for (x = 0; x < w; x++) {
              dstp_r[x] = av_clip_uint8(src_r[x] * DCT3X3_0_0 + src_g[x] * DCT3X3_1_0 + src_b[x] * DCT3X3_2_0);
              dstp_g[x] = av_clip_uint8(src_r[x] * DCT3X3_0_1 +                         src_b[x] * DCT3X3_2_1);
              dstp_b[x] = av_clip_uint8(src_r[x] * DCT3X3_0_2 + src_g[x] * DCT3X3_1_2 + src_b[x] * DCT3X3_2_2);
          }
          dstp_r += dst_linesize;
          dstp_g += dst_linesize;
          dstp_b += dst_linesize;
          src_r += src_linesize;
          src_g += src_linesize;
          src_b += src_linesize;
      }
  }
  
  static int config_input(AVFilterLink *inlink)
  {
      AVFilterContext *ctx = inlink->dst;
      DCTdnoizContext *s = ctx->priv;
      int i, x, y, bx, by, linesize, *iweights, max_slice_h, slice_h;
      const int bsize = 1 << s->n;
  
      switch (inlink->format) {
      case AV_PIX_FMT_BGR24:
          s->color_decorrelation = color_decorrelation_bgr;
          s->color_correlation   = color_correlation_bgr;
          break;
      case AV_PIX_FMT_RGB24:
          s->color_decorrelation = color_decorrelation_rgb;
          s->color_correlation   = color_correlation_rgb;
          break;
      case AV_PIX_FMT_GBRP:
          s->color_decorrelation = color_decorrelation_gbrp;
          s->color_correlation   = color_correlation_gbrp;
          break;
      default:
          av_assert0(0);
      }
  
      s->pr_width  = inlink->w - (inlink->w - bsize) % s->step;
      s->pr_height = inlink->h - (inlink->h - bsize) % s->step;
      if (s->pr_width != inlink->w)
          av_log(ctx, AV_LOG_WARNING, "The last %d horizontal pixels won't be denoised\n",
                 inlink->w - s->pr_width);
      if (s->pr_height != inlink->h)
          av_log(ctx, AV_LOG_WARNING, "The last %d vertical pixels won't be denoised\n",
                 inlink->h - s->pr_height);
  
      max_slice_h = s->pr_height / ((s->bsize - 1) * 2);
      s->nb_threads = FFMIN3(MAX_THREADS, ff_filter_get_nb_threads(ctx), max_slice_h);
      av_log(ctx, AV_LOG_DEBUG, "threads: [max=%d hmax=%d user=%d] => %d\n",
             MAX_THREADS, max_slice_h, ff_filter_get_nb_threads(ctx), s->nb_threads);
  
      s->p_linesize = linesize = FFALIGN(s->pr_width, 32);
      for (i = 0; i < 2; i++) {
          s->cbuf[i][0] = av_malloc_array(linesize * s->pr_height, sizeof(*s->cbuf[i][0]));
          s->cbuf[i][1] = av_malloc_array(linesize * s->pr_height, sizeof(*s->cbuf[i][1]));
          s->cbuf[i][2] = av_malloc_array(linesize * s->pr_height, sizeof(*s->cbuf[i][2]));
          if (!s->cbuf[i][0] || !s->cbuf[i][1] || !s->cbuf[i][2])
              return AVERROR(ENOMEM);
      }
  
      /* eval expressions are probably not thread safe when the eval internal
       * state can be changed (typically through load & store operations) */
      if (s->expr_str) {
          for (i = 0; i < s->nb_threads; i++) {
              int ret = av_expr_parse(&s->expr[i], s->expr_str, var_names,
                                      NULL, NULL, NULL, NULL, 0, ctx);
              if (ret < 0)
                  return ret;
          }
      }
  
      /* each slice will need to (pre & re)process the top and bottom block of
       * the previous one in in addition to its processing area. This is because
       * each pixel is averaged by all the surrounding blocks */
      slice_h = (int)ceilf(s->pr_height / (float)s->nb_threads) + (s->bsize - 1) * 2;
      for (i = 0; i < s->nb_threads; i++) {
          s->slices[i] = av_malloc_array(linesize, slice_h * sizeof(*s->slices[i]));
          if (!s->slices[i])
              return AVERROR(ENOMEM);
      }
  
      s->weights = av_malloc(s->pr_height * linesize * sizeof(*s->weights));
      if (!s->weights)
          return AVERROR(ENOMEM);
      iweights = av_calloc(s->pr_height, linesize * sizeof(*iweights));
      if (!iweights)
          return AVERROR(ENOMEM);
      for (y = 0; y < s->pr_height - bsize + 1; y += s->step)
          for (x = 0; x < s->pr_width - bsize + 1; x += s->step)
              for (by = 0; by < bsize; by++)
                  for (bx = 0; bx < bsize; bx++)
                      iweights[(y + by)*linesize + x + bx]++;
      for (y = 0; y < s->pr_height; y++)
          for (x = 0; x < s->pr_width; x++)
              s->weights[y*linesize + x] = 1. / iweights[y*linesize + x];
      av_free(iweights);
  
      return 0;
  }
  
  static av_cold int init(AVFilterContext *ctx)
  {
      DCTdnoizContext *s = ctx->priv;
  
      s->bsize = 1 << s->n;
      if (s->overlap == -1)
          s->overlap = s->bsize - 1;
  
      if (s->overlap > s->bsize - 1) {
          av_log(s, AV_LOG_ERROR, "Overlap value can not except %d "
                 "with a block size of %dx%d\n",
                 s->bsize - 1, s->bsize, s->bsize);
          return AVERROR(EINVAL);
      }
  
      if (s->expr_str) {
          switch (s->n) {
          case 3: s->filter_freq_func = filter_freq_expr_8;  break;
          case 4: s->filter_freq_func = filter_freq_expr_16; break;
          default: av_assert0(0);
          }
      } else {
          switch (s->n) {
          case 3: s->filter_freq_func = filter_freq_sigma_8;  break;
          case 4: s->filter_freq_func = filter_freq_sigma_16; break;
          default: av_assert0(0);
          }
      }
  
      s->th   = s->sigma * 3.;
      s->step = s->bsize - s->overlap;
      return 0;
  }
  
  static int query_formats(AVFilterContext *ctx)
  {
      static const enum AVPixelFormat pix_fmts[] = {
          AV_PIX_FMT_BGR24, AV_PIX_FMT_RGB24,
          AV_PIX_FMT_GBRP,
          AV_PIX_FMT_NONE
      };
      AVFilterFormats *fmts_list = ff_make_format_list(pix_fmts);
      if (!fmts_list)
          return AVERROR(ENOMEM);
      return ff_set_common_formats(ctx, fmts_list);
  }
  
  typedef struct ThreadData {
      float *src, *dst;
  } ThreadData;
  
  static int filter_slice(AVFilterContext *ctx,
                          void *arg, int jobnr, int nb_jobs)
  {
      int x, y;
      DCTdnoizContext *s = ctx->priv;
      const ThreadData *td = arg;
      const int w = s->pr_width;
      const int h = s->pr_height;
      const int slice_start = (h *  jobnr   ) / nb_jobs;
      const int slice_end   = (h * (jobnr+1)) / nb_jobs;
      const int slice_start_ctx = FFMAX(slice_start - s->bsize + 1, 0);
      const int slice_end_ctx   = FFMIN(slice_end, h - s->bsize + 1);
      const int slice_h = slice_end_ctx - slice_start_ctx;
      const int src_linesize   = s->p_linesize;
      const int dst_linesize   = s->p_linesize;
      const int slice_linesize = s->p_linesize;
      float *dst;
      const float *src = td->src + slice_start_ctx * src_linesize;
      const float *weights = s->weights + slice_start * dst_linesize;
      float *slice = s->slices[jobnr];
  
      // reset block sums
      memset(slice, 0, (slice_h + s->bsize - 1) * dst_linesize * sizeof(*slice));
  
      // block dct sums
      for (y = 0; y < slice_h; y += s->step) {
          for (x = 0; x < w - s->bsize + 1; x += s->step)
              s->filter_freq_func(s, src + x, src_linesize,
                                  slice + x, slice_linesize,
                                  jobnr);
          src += s->step * src_linesize;
          slice += s->step * slice_linesize;
      }
  
      // average blocks
      slice = s->slices[jobnr] + (slice_start - slice_start_ctx) * slice_linesize;
      dst = td->dst + slice_start * dst_linesize;
      for (y = slice_start; y < slice_end; y++) {
          for (x = 0; x < w; x++)
              dst[x] = slice[x] * weights[x];
          slice += slice_linesize;
          dst += dst_linesize;
          weights += dst_linesize;
      }
  
      return 0;
  }
  
  static int filter_frame(AVFilterLink *inlink, AVFrame *in)
  {
      AVFilterContext *ctx = inlink->dst;
      DCTdnoizContext *s = ctx->priv;
      AVFilterLink *outlink = inlink->dst->outputs[0];
      int direct, plane;
      AVFrame *out;
  
      if (av_frame_is_writable(in)) {
          direct = 1;
          out = in;
      } else {
          direct = 0;
          out = ff_get_video_buffer(outlink, outlink->w, outlink->h);
          if (!out) {
              av_frame_free(&in);
              return AVERROR(ENOMEM);
          }
          av_frame_copy_props(out, in);
      }
  
      s->color_decorrelation(s->cbuf[0], s->p_linesize,
                             (const uint8_t **)in->data, in->linesize[0],
                             s->pr_width, s->pr_height);
      for (plane = 0; plane < 3; plane++) {
          ThreadData td = {
              .src = s->cbuf[0][plane],
              .dst = s->cbuf[1][plane],
          };
          ctx->internal->execute(ctx, filter_slice, &td, NULL, s->nb_threads);
      }
      s->color_correlation(out->data, out->linesize[0],
                           s->cbuf[1], s->p_linesize,
                           s->pr_width, s->pr_height);
  
      if (!direct) {
          int y;
          uint8_t *dst = out->data[0];
          const uint8_t *src = in->data[0];
          const int dst_linesize = out->linesize[0];
          const int src_linesize = in->linesize[0];
          const int hpad = (inlink->w - s->pr_width) * 3;
          const int vpad = (inlink->h - s->pr_height);
  
          if (hpad) {
              uint8_t       *dstp = dst + s->pr_width * 3;
              const uint8_t *srcp = src + s->pr_width * 3;
  
              for (y = 0; y < s->pr_height; y++) {
                  memcpy(dstp, srcp, hpad);
                  dstp += dst_linesize;
                  srcp += src_linesize;
              }
          }
          if (vpad) {
              uint8_t       *dstp = dst + s->pr_height * dst_linesize;
              const uint8_t *srcp = src + s->pr_height * src_linesize;
  
              for (y = 0; y < vpad; y++) {
                  memcpy(dstp, srcp, inlink->w * 3);
                  dstp += dst_linesize;
                  srcp += src_linesize;
              }
          }
  
          av_frame_free(&in);
      }
  
      return ff_filter_frame(outlink, out);
  }
  
  static av_cold void uninit(AVFilterContext *ctx)
  {
      int i;
      DCTdnoizContext *s = ctx->priv;
  
      av_freep(&s->weights);
      for (i = 0; i < 2; i++) {
          av_freep(&s->cbuf[i][0]);
          av_freep(&s->cbuf[i][1]);
          av_freep(&s->cbuf[i][2]);
      }
      for (i = 0; i < s->nb_threads; i++) {
          av_freep(&s->slices[i]);
          av_expr_free(s->expr[i]);
      }
  }
  
  static const AVFilterPad dctdnoiz_inputs[] = {
      {
          .name         = "default",
          .type         = AVMEDIA_TYPE_VIDEO,
          .filter_frame = filter_frame,
          .config_props = config_input,
      },
      { NULL }
  };
  
  static const AVFilterPad dctdnoiz_outputs[] = {
      {
          .name = "default",
          .type = AVMEDIA_TYPE_VIDEO,
      },
      { NULL }
  };
  
  AVFilter ff_vf_dctdnoiz = {
      .name          = "dctdnoiz",
      .description   = NULL_IF_CONFIG_SMALL("Denoise frames using 2D DCT."),
      .priv_size     = sizeof(DCTdnoizContext),
      .init          = init,
      .uninit        = uninit,
      .query_formats = query_formats,
      .inputs        = dctdnoiz_inputs,
      .outputs       = dctdnoiz_outputs,
      .priv_class    = &dctdnoiz_class,
      .flags         = AVFILTER_FLAG_SUPPORT_TIMELINE_GENERIC | AVFILTER_FLAG_SLICE_THREADS,
  };
  