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jcsample.c (19963B)

---

/*
* jcsample.c
*
* This file was part of the Independent JPEG Group's software:
* Copyright (C) 1991-1996, Thomas G. Lane.
* Lossless JPEG Modifications:
* Copyright (C) 1999, Ken Murchison.
* libjpeg-turbo Modifications:
* Copyright 2009 Pierre Ossman <ossman@cendio.se> for Cendio AB
* Copyright (C) 2014, MIPS Technologies, Inc., California.
* Copyright (C) 2015, 2019, 2022, D. R. Commander.
* For conditions of distribution and use, see the accompanying README.ijg
* file.
*
* This file contains downsampling routines.
*
* Downsampling input data is counted in "row groups".  A row group
* is defined to be max_v_samp_factor pixel rows of each component,
* from which the downsampler produces v_samp_factor sample rows.
* A single row group is processed in each call to the downsampler module.
*
* The downsampler is responsible for edge-expansion of its output data
* to fill an integral number of DCT blocks horizontally.  The source buffer
* may be modified if it is helpful for this purpose (the source buffer is
* allocated wide enough to correspond to the desired output width).
* The caller (the prep controller) is responsible for vertical padding.
*
* The downsampler may request "context rows" by setting need_context_rows
* during startup.  In this case, the input arrays will contain at least
* one row group's worth of pixels above and below the passed-in data;
* the caller will create dummy rows at image top and bottom by replicating
* the first or last real pixel row.
*
* An excellent reference for image resampling is
*   Digital Image Warping, George Wolberg, 1990.
*   Pub. by IEEE Computer Society Press, Los Alamitos, CA. ISBN 0-8186-8944-7.
*
* The downsampling algorithm used here is a simple average of the source
* pixels covered by the output pixel.  The hi-falutin sampling literature
* refers to this as a "box filter".  In general the characteristics of a box
* filter are not very good, but for the specific cases we normally use (1:1
* and 2:1 ratios) the box is equivalent to a "triangle filter" which is not
* nearly so bad.  If you intend to use other sampling ratios, you'd be well
* advised to improve this code.
*
* A simple input-smoothing capability is provided.  This is mainly intended
* for cleaning up color-dithered GIF input files (if you find it inadequate,
* we suggest using an external filtering program such as pnmconvol).  When
* enabled, each input pixel P is replaced by a weighted sum of itself and its
* eight neighbors.  P's weight is 1-8*SF and each neighbor's weight is SF,
* where SF = (smoothing_factor / 1024).
* Currently, smoothing is only supported for 2h2v sampling factors.
*/

#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
#include "jsimd.h"
#include "jsamplecomp.h"


#if BITS_IN_JSAMPLE != 16 || defined(C_LOSSLESS_SUPPORTED)

/* Pointer to routine to downsample a single component */
typedef void (*downsample1_ptr) (j_compress_ptr cinfo,
                                jpeg_component_info *compptr,
                                _JSAMPARRAY input_data,
                                _JSAMPARRAY output_data);

/* Private subobject */

typedef struct {
 struct jpeg_downsampler pub;  /* public fields */

 /* Downsampling method pointers, one per component */
 downsample1_ptr methods[MAX_COMPONENTS];
} my_downsampler;

typedef my_downsampler *my_downsample_ptr;


/*
* Initialize for a downsampling pass.
*/

METHODDEF(void)
start_pass_downsample(j_compress_ptr cinfo)
{
 /* no work for now */
}


/*
* Expand a component horizontally from width input_cols to width output_cols,
* by duplicating the rightmost samples.
*/

LOCAL(void)
expand_right_edge(_JSAMPARRAY image_data, int num_rows, JDIMENSION input_cols,
                 JDIMENSION output_cols)
{
 register _JSAMPROW ptr;
 register _JSAMPLE pixval;
 register int count;
 int row;
 int numcols = (int)(output_cols - input_cols);

 if (numcols > 0) {
   for (row = 0; row < num_rows; row++) {
     ptr = image_data[row] + input_cols;
     pixval = ptr[-1];
     for (count = numcols; count > 0; count--)
       *ptr++ = pixval;
   }
 }
}


/*
* Do downsampling for a whole row group (all components).
*
* In this version we simply downsample each component independently.
*/

METHODDEF(void)
sep_downsample(j_compress_ptr cinfo, _JSAMPIMAGE input_buf,
              JDIMENSION in_row_index, _JSAMPIMAGE output_buf,
              JDIMENSION out_row_group_index)
{
 my_downsample_ptr downsample = (my_downsample_ptr)cinfo->downsample;
 int ci;
 jpeg_component_info *compptr;
 _JSAMPARRAY in_ptr, out_ptr;

 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
      ci++, compptr++) {
   in_ptr = input_buf[ci] + in_row_index;
   out_ptr = output_buf[ci] + (out_row_group_index * compptr->v_samp_factor);
   (*downsample->methods[ci]) (cinfo, compptr, in_ptr, out_ptr);
 }
}


/*
* Downsample pixel values of a single component.
* One row group is processed per call.
* This version handles arbitrary integral sampling ratios, without smoothing.
* Note that this version is not actually used for customary sampling ratios.
*/

METHODDEF(void)
int_downsample(j_compress_ptr cinfo, jpeg_component_info *compptr,
              _JSAMPARRAY input_data, _JSAMPARRAY output_data)
{
 int inrow, outrow, h_expand, v_expand, numpix, numpix2, h, v;
 JDIMENSION outcol, outcol_h;  /* outcol_h == outcol*h_expand */
 int data_unit = cinfo->master->lossless ? 1 : DCTSIZE;
 JDIMENSION output_cols = compptr->width_in_blocks * data_unit;
 _JSAMPROW inptr, outptr;
 JLONG outvalue;

 h_expand = cinfo->max_h_samp_factor / compptr->h_samp_factor;
 v_expand = cinfo->max_v_samp_factor / compptr->v_samp_factor;
 numpix = h_expand * v_expand;
 numpix2 = numpix / 2;

 /* Expand input data enough to let all the output samples be generated
  * by the standard loop.  Special-casing padded output would be more
  * efficient.
  */
 expand_right_edge(input_data, cinfo->max_v_samp_factor, cinfo->image_width,
                   output_cols * h_expand);

 inrow = 0;
 for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
   outptr = output_data[outrow];
   for (outcol = 0, outcol_h = 0; outcol < output_cols;
        outcol++, outcol_h += h_expand) {
     outvalue = 0;
     for (v = 0; v < v_expand; v++) {
       inptr = input_data[inrow + v] + outcol_h;
       for (h = 0; h < h_expand; h++) {
         outvalue += (JLONG)(*inptr++);
       }
     }
     *outptr++ = (_JSAMPLE)((outvalue + numpix2) / numpix);
   }
   inrow += v_expand;
 }
}


/*
* Downsample pixel values of a single component.
* This version handles the special case of a full-size component,
* without smoothing.
*/

METHODDEF(void)
fullsize_downsample(j_compress_ptr cinfo, jpeg_component_info *compptr,
                   _JSAMPARRAY input_data, _JSAMPARRAY output_data)
{
 int data_unit = cinfo->master->lossless ? 1 : DCTSIZE;

 /* Copy the data */
 _jcopy_sample_rows(input_data, 0, output_data, 0, cinfo->max_v_samp_factor,
                    cinfo->image_width);
 /* Edge-expand */
 expand_right_edge(output_data, cinfo->max_v_samp_factor, cinfo->image_width,
                   compptr->width_in_blocks * data_unit);
}


/*
* Downsample pixel values of a single component.
* This version handles the common case of 2:1 horizontal and 1:1 vertical,
* without smoothing.
*
* A note about the "bias" calculations: when rounding fractional values to
* integer, we do not want to always round 0.5 up to the next integer.
* If we did that, we'd introduce a noticeable bias towards larger values.
* Instead, this code is arranged so that 0.5 will be rounded up or down at
* alternate pixel locations (a simple ordered dither pattern).
*/

METHODDEF(void)
h2v1_downsample(j_compress_ptr cinfo, jpeg_component_info *compptr,
               _JSAMPARRAY input_data, _JSAMPARRAY output_data)
{
 int outrow;
 JDIMENSION outcol;
 int data_unit = cinfo->master->lossless ? 1 : DCTSIZE;
 JDIMENSION output_cols = compptr->width_in_blocks * data_unit;
 register _JSAMPROW inptr, outptr;
 register int bias;

 /* Expand input data enough to let all the output samples be generated
  * by the standard loop.  Special-casing padded output would be more
  * efficient.
  */
 expand_right_edge(input_data, cinfo->max_v_samp_factor, cinfo->image_width,
                   output_cols * 2);

 for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
   outptr = output_data[outrow];
   inptr = input_data[outrow];
   bias = 0;                   /* bias = 0,1,0,1,... for successive samples */
   for (outcol = 0; outcol < output_cols; outcol++) {
     *outptr++ = (_JSAMPLE)((inptr[0] + inptr[1] + bias) >> 1);
     bias ^= 1;                /* 0=>1, 1=>0 */
     inptr += 2;
   }
 }
}


/*
* Downsample pixel values of a single component.
* This version handles the standard case of 2:1 horizontal and 2:1 vertical,
* without smoothing.
*/

METHODDEF(void)
h2v2_downsample(j_compress_ptr cinfo, jpeg_component_info *compptr,
               _JSAMPARRAY input_data, _JSAMPARRAY output_data)
{
 int inrow, outrow;
 JDIMENSION outcol;
 int data_unit = cinfo->master->lossless ? 1 : DCTSIZE;
 JDIMENSION output_cols = compptr->width_in_blocks * data_unit;
 register _JSAMPROW inptr0, inptr1, outptr;
 register int bias;

 /* Expand input data enough to let all the output samples be generated
  * by the standard loop.  Special-casing padded output would be more
  * efficient.
  */
 expand_right_edge(input_data, cinfo->max_v_samp_factor, cinfo->image_width,
                   output_cols * 2);

 inrow = 0;
 for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
   outptr = output_data[outrow];
   inptr0 = input_data[inrow];
   inptr1 = input_data[inrow + 1];
   bias = 1;                   /* bias = 1,2,1,2,... for successive samples */
   for (outcol = 0; outcol < output_cols; outcol++) {
     *outptr++ = (_JSAMPLE)
       ((inptr0[0] + inptr0[1] + inptr1[0] + inptr1[1] + bias) >> 2);
     bias ^= 3;                /* 1=>2, 2=>1 */
     inptr0 += 2;  inptr1 += 2;
   }
   inrow += 2;
 }
}


#ifdef INPUT_SMOOTHING_SUPPORTED

/*
* Downsample pixel values of a single component.
* This version handles the standard case of 2:1 horizontal and 2:1 vertical,
* with smoothing.  One row of context is required.
*/

METHODDEF(void)
h2v2_smooth_downsample(j_compress_ptr cinfo, jpeg_component_info *compptr,
                      _JSAMPARRAY input_data, _JSAMPARRAY output_data)
{
 int inrow, outrow;
 JDIMENSION colctr;
 int data_unit = cinfo->master->lossless ? 1 : DCTSIZE;
 JDIMENSION output_cols = compptr->width_in_blocks * data_unit;
 register _JSAMPROW inptr0, inptr1, above_ptr, below_ptr, outptr;
 JLONG membersum, neighsum, memberscale, neighscale;

 /* Expand input data enough to let all the output samples be generated
  * by the standard loop.  Special-casing padded output would be more
  * efficient.
  */
 expand_right_edge(input_data - 1, cinfo->max_v_samp_factor + 2,
                   cinfo->image_width, output_cols * 2);

 /* We don't bother to form the individual "smoothed" input pixel values;
  * we can directly compute the output which is the average of the four
  * smoothed values.  Each of the four member pixels contributes a fraction
  * (1-8*SF) to its own smoothed image and a fraction SF to each of the three
  * other smoothed pixels, therefore a total fraction (1-5*SF)/4 to the final
  * output.  The four corner-adjacent neighbor pixels contribute a fraction
  * SF to just one smoothed pixel, or SF/4 to the final output; while the
  * eight edge-adjacent neighbors contribute SF to each of two smoothed
  * pixels, or SF/2 overall.  In order to use integer arithmetic, these
  * factors are scaled by 2^16 = 65536.
  * Also recall that SF = smoothing_factor / 1024.
  */

 memberscale = 16384 - cinfo->smoothing_factor * 80; /* scaled (1-5*SF)/4 */
 neighscale = cinfo->smoothing_factor * 16; /* scaled SF/4 */

 inrow = 0;
 for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
   outptr = output_data[outrow];
   inptr0 = input_data[inrow];
   inptr1 = input_data[inrow + 1];
   above_ptr = input_data[inrow - 1];
   below_ptr = input_data[inrow + 2];

   /* Special case for first column: pretend column -1 is same as column 0 */
   membersum = inptr0[0] + inptr0[1] + inptr1[0] + inptr1[1];
   neighsum = above_ptr[0] + above_ptr[1] + below_ptr[0] + below_ptr[1] +
              inptr0[0] + inptr0[2] + inptr1[0] + inptr1[2];
   neighsum += neighsum;
   neighsum += above_ptr[0] + above_ptr[2] + below_ptr[0] + below_ptr[2];
   membersum = membersum * memberscale + neighsum * neighscale;
   *outptr++ = (_JSAMPLE)((membersum + 32768) >> 16);
   inptr0 += 2;  inptr1 += 2;  above_ptr += 2;  below_ptr += 2;

   for (colctr = output_cols - 2; colctr > 0; colctr--) {
     /* sum of pixels directly mapped to this output element */
     membersum = inptr0[0] + inptr0[1] + inptr1[0] + inptr1[1];
     /* sum of edge-neighbor pixels */
     neighsum = above_ptr[0] + above_ptr[1] + below_ptr[0] + below_ptr[1] +
                inptr0[-1] + inptr0[2] + inptr1[-1] + inptr1[2];
     /* The edge-neighbors count twice as much as corner-neighbors */
     neighsum += neighsum;
     /* Add in the corner-neighbors */
     neighsum += above_ptr[-1] + above_ptr[2] + below_ptr[-1] + below_ptr[2];
     /* form final output scaled up by 2^16 */
     membersum = membersum * memberscale + neighsum * neighscale;
     /* round, descale and output it */
     *outptr++ = (_JSAMPLE)((membersum + 32768) >> 16);
     inptr0 += 2;  inptr1 += 2;  above_ptr += 2;  below_ptr += 2;
   }

   /* Special case for last column */
   membersum = inptr0[0] + inptr0[1] + inptr1[0] + inptr1[1];
   neighsum = above_ptr[0] + above_ptr[1] + below_ptr[0] + below_ptr[1] +
              inptr0[-1] + inptr0[1] + inptr1[-1] + inptr1[1];
   neighsum += neighsum;
   neighsum += above_ptr[-1] + above_ptr[1] + below_ptr[-1] + below_ptr[1];
   membersum = membersum * memberscale + neighsum * neighscale;
   *outptr = (_JSAMPLE)((membersum + 32768) >> 16);

   inrow += 2;
 }
}


/*
* Downsample pixel values of a single component.
* This version handles the special case of a full-size component,
* with smoothing.  One row of context is required.
*/

METHODDEF(void)
fullsize_smooth_downsample(j_compress_ptr cinfo, jpeg_component_info *compptr,
                          _JSAMPARRAY input_data, _JSAMPARRAY output_data)
{
 int outrow;
 JDIMENSION colctr;
 int data_unit = cinfo->master->lossless ? 1 : DCTSIZE;
 JDIMENSION output_cols = compptr->width_in_blocks * data_unit;
 register _JSAMPROW inptr, above_ptr, below_ptr, outptr;
 JLONG membersum, neighsum, memberscale, neighscale;
 int colsum, lastcolsum, nextcolsum;

 /* Expand input data enough to let all the output samples be generated
  * by the standard loop.  Special-casing padded output would be more
  * efficient.
  */
 expand_right_edge(input_data - 1, cinfo->max_v_samp_factor + 2,
                   cinfo->image_width, output_cols);

 /* Each of the eight neighbor pixels contributes a fraction SF to the
  * smoothed pixel, while the main pixel contributes (1-8*SF).  In order
  * to use integer arithmetic, these factors are multiplied by 2^16 = 65536.
  * Also recall that SF = smoothing_factor / 1024.
  */

 memberscale = 65536L - cinfo->smoothing_factor * 512L; /* scaled 1-8*SF */
 neighscale = cinfo->smoothing_factor * 64; /* scaled SF */

 for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
   outptr = output_data[outrow];
   inptr = input_data[outrow];
   above_ptr = input_data[outrow - 1];
   below_ptr = input_data[outrow + 1];

   /* Special case for first column */
   colsum = (*above_ptr++) + (*below_ptr++) + inptr[0];
   membersum = *inptr++;
   nextcolsum = above_ptr[0] + below_ptr[0] + inptr[0];
   neighsum = colsum + (colsum - membersum) + nextcolsum;
   membersum = membersum * memberscale + neighsum * neighscale;
   *outptr++ = (_JSAMPLE)((membersum + 32768) >> 16);
   lastcolsum = colsum;  colsum = nextcolsum;

   for (colctr = output_cols - 2; colctr > 0; colctr--) {
     membersum = *inptr++;
     above_ptr++;  below_ptr++;
     nextcolsum = above_ptr[0] + below_ptr[0] + inptr[0];
     neighsum = lastcolsum + (colsum - membersum) + nextcolsum;
     membersum = membersum * memberscale + neighsum * neighscale;
     *outptr++ = (_JSAMPLE)((membersum + 32768) >> 16);
     lastcolsum = colsum;  colsum = nextcolsum;
   }

   /* Special case for last column */
   membersum = *inptr;
   neighsum = lastcolsum + (colsum - membersum) + colsum;
   membersum = membersum * memberscale + neighsum * neighscale;
   *outptr = (_JSAMPLE)((membersum + 32768) >> 16);

 }
}

#endif /* INPUT_SMOOTHING_SUPPORTED */


/*
* Module initialization routine for downsampling.
* Note that we must select a routine for each component.
*/

GLOBAL(void)
_jinit_downsampler(j_compress_ptr cinfo)
{
 my_downsample_ptr downsample;
 int ci;
 jpeg_component_info *compptr;
 boolean smoothok = TRUE;

 if (cinfo->data_precision != BITS_IN_JSAMPLE)
   ERREXIT1(cinfo, JERR_BAD_PRECISION, cinfo->data_precision);

 downsample = (my_downsample_ptr)
   (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
                               sizeof(my_downsampler));
 cinfo->downsample = (struct jpeg_downsampler *)downsample;
 downsample->pub.start_pass = start_pass_downsample;
 downsample->pub._downsample = sep_downsample;
 downsample->pub.need_context_rows = FALSE;

 if (cinfo->CCIR601_sampling)
   ERREXIT(cinfo, JERR_CCIR601_NOTIMPL);

 /* Verify we can handle the sampling factors, and set up method pointers */
 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
      ci++, compptr++) {
   if (compptr->h_samp_factor == cinfo->max_h_samp_factor &&
       compptr->v_samp_factor == cinfo->max_v_samp_factor) {
#ifdef INPUT_SMOOTHING_SUPPORTED
     if (cinfo->smoothing_factor) {
       downsample->methods[ci] = fullsize_smooth_downsample;
       downsample->pub.need_context_rows = TRUE;
     } else
#endif
       downsample->methods[ci] = fullsize_downsample;
   } else if (compptr->h_samp_factor * 2 == cinfo->max_h_samp_factor &&
              compptr->v_samp_factor == cinfo->max_v_samp_factor) {
     smoothok = FALSE;
#ifdef WITH_SIMD
     if (jsimd_can_h2v1_downsample())
       downsample->methods[ci] = jsimd_h2v1_downsample;
     else
#endif
       downsample->methods[ci] = h2v1_downsample;
   } else if (compptr->h_samp_factor * 2 == cinfo->max_h_samp_factor &&
              compptr->v_samp_factor * 2 == cinfo->max_v_samp_factor) {
#ifdef INPUT_SMOOTHING_SUPPORTED
     if (cinfo->smoothing_factor) {
#if defined(WITH_SIMD) && defined(__mips__)
       if (jsimd_can_h2v2_smooth_downsample())
         downsample->methods[ci] = jsimd_h2v2_smooth_downsample;
       else
#endif
         downsample->methods[ci] = h2v2_smooth_downsample;
       downsample->pub.need_context_rows = TRUE;
     } else
#endif
     {
#ifdef WITH_SIMD
       if (jsimd_can_h2v2_downsample())
         downsample->methods[ci] = jsimd_h2v2_downsample;
       else
#endif
         downsample->methods[ci] = h2v2_downsample;
     }
   } else if ((cinfo->max_h_samp_factor % compptr->h_samp_factor) == 0 &&
              (cinfo->max_v_samp_factor % compptr->v_samp_factor) == 0) {
     smoothok = FALSE;
     downsample->methods[ci] = int_downsample;
   } else
     ERREXIT(cinfo, JERR_FRACT_SAMPLE_NOTIMPL);
 }

#ifdef INPUT_SMOOTHING_SUPPORTED
 if (cinfo->smoothing_factor && !smoothok)
   TRACEMS(cinfo, 0, JTRC_SMOOTH_NOTIMPL);
#endif
}

#endif /* BITS_IN_JSAMPLE != 16 || defined(C_LOSSLESS_SUPPORTED) */