jcsample.c - third_party/libjpeg-turbo - Git at Google

 /*
  * jcsample.c
  *
  * This file was part of the Independent JPEG Group's software:
  * Copyright (C) 1991-1996, Thomas G. Lane.
  * libjpeg-turbo Modifications:
  * Copyright 2009 Pierre Ossman <ossman@cendio.se> for Cendio AB
  * Copyright (C) 2014, MIPS Technologies, Inc., California
  * Copyright (C) 2015, 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"


 /* 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];         /* don't need GETJSAMPLE() here */
       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 */
   JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
   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) GETJSAMPLE(*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)
 {
   /* 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 * DCTSIZE);
 }


 /*
  * 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;
   JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
   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) ((GETJSAMPLE(*inptr) + GETJSAMPLE(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;
   JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
   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) ((GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
                               GETJSAMPLE(*inptr1) + GETJSAMPLE(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;
   JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
   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 = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
                 GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]);
     neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) +
                GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) +
                GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[2]) +
                GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[2]);
     neighsum += neighsum;
     neighsum += GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[2]) +
                 GETJSAMPLE(*below_ptr) + GETJSAMPLE(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 = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
                   GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]);
       /* sum of edge-neighbor pixels */
       neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) +
                  GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) +
                  GETJSAMPLE(inptr0[-1]) + GETJSAMPLE(inptr0[2]) +
                  GETJSAMPLE(inptr1[-1]) + GETJSAMPLE(inptr1[2]);
       /* The edge-neighbors count twice as much as corner-neighbors */
       neighsum += neighsum;
       /* Add in the corner-neighbors */
       neighsum += GETJSAMPLE(above_ptr[-1]) + GETJSAMPLE(above_ptr[2]) +
                   GETJSAMPLE(below_ptr[-1]) + GETJSAMPLE(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 = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
                 GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]);
     neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) +
                GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) +
                GETJSAMPLE(inptr0[-1]) + GETJSAMPLE(inptr0[1]) +
                GETJSAMPLE(inptr1[-1]) + GETJSAMPLE(inptr1[1]);
     neighsum += neighsum;
     neighsum += GETJSAMPLE(above_ptr[-1]) + GETJSAMPLE(above_ptr[1]) +
                 GETJSAMPLE(below_ptr[-1]) + GETJSAMPLE(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;
   JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
   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 = GETJSAMPLE(*above_ptr++) + GETJSAMPLE(*below_ptr++) +
              GETJSAMPLE(*inptr);
     membersum = GETJSAMPLE(*inptr++);
     nextcolsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(*below_ptr) +
                  GETJSAMPLE(*inptr);
     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 = GETJSAMPLE(*inptr++);
       above_ptr++; below_ptr++;
       nextcolsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(*below_ptr) +
                    GETJSAMPLE(*inptr);
       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 = GETJSAMPLE(*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;

   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;
       if (jsimd_can_h2v1_downsample())
         downsample->methods[ci] = jsimd_h2v1_downsample;
       else
         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(__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
       {
         if (jsimd_can_h2v2_downsample())
           downsample->methods[ci] = jsimd_h2v2_downsample;
         else
           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
 }
	/*
	* jcsample.c
	*
	* This file was part of the Independent JPEG Group's software:
	* Copyright (C) 1991-1996, Thomas G. Lane.
	* libjpeg-turbo Modifications:
	* Copyright 2009 Pierre Ossman <ossman@cendio.se> for Cendio AB
	* Copyright (C) 2014, MIPS Technologies, Inc., California
	* Copyright (C) 2015, 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"


	/* 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]; /* don't need GETJSAMPLE() here */
	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 == outcolh_expand /
	JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
	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) GETJSAMPLE(*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)
	{
	/* 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 * DCTSIZE);
	}


	/*
	* 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;
	JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
	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) ((GETJSAMPLE(inptr) + GETJSAMPLE(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;
	JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
	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) ((GETJSAMPLE(inptr0) + GETJSAMPLE(inptr0[1]) +
	GETJSAMPLE(*inptr1) + GETJSAMPLE(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;
	JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
	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 (1-5SF)/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 = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
	GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]);
	neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) +
	GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) +
	GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[2]) +
	GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[2]);
	neighsum += neighsum;
	neighsum += GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[2]) +
	GETJSAMPLE(*below_ptr) + GETJSAMPLE(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 = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
	GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]);
	/* sum of edge-neighbor pixels */
	neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) +
	GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) +
	GETJSAMPLE(inptr0[-1]) + GETJSAMPLE(inptr0[2]) +
	GETJSAMPLE(inptr1[-1]) + GETJSAMPLE(inptr1[2]);
	/* The edge-neighbors count twice as much as corner-neighbors */
	neighsum += neighsum;
	/* Add in the corner-neighbors */
	neighsum += GETJSAMPLE(above_ptr[-1]) + GETJSAMPLE(above_ptr[2]) +
	GETJSAMPLE(below_ptr[-1]) + GETJSAMPLE(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 = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
	GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]);
	neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) +
	GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) +
	GETJSAMPLE(inptr0[-1]) + GETJSAMPLE(inptr0[1]) +
	GETJSAMPLE(inptr1[-1]) + GETJSAMPLE(inptr1[1]);
	neighsum += neighsum;
	neighsum += GETJSAMPLE(above_ptr[-1]) + GETJSAMPLE(above_ptr[1]) +
	GETJSAMPLE(below_ptr[-1]) + GETJSAMPLE(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;
	JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
	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 1-8SF /
	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 = GETJSAMPLE(above_ptr++) + GETJSAMPLE(below_ptr++) +
	GETJSAMPLE(*inptr);
	membersum = GETJSAMPLE(*inptr++);
	nextcolsum = GETJSAMPLE(above_ptr) + GETJSAMPLE(below_ptr) +
	GETJSAMPLE(*inptr);
	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 = GETJSAMPLE(*inptr++);
	above_ptr++; below_ptr++;
	nextcolsum = GETJSAMPLE(above_ptr) + GETJSAMPLE(below_ptr) +
	GETJSAMPLE(*inptr);
	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 = GETJSAMPLE(*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;

	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;
	if (jsimd_can_h2v1_downsample())
	downsample->methods[ci] = jsimd_h2v1_downsample;
	else
	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(__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
	{
	if (jsimd_can_h2v2_downsample())
	downsample->methods[ci] = jsimd_h2v2_downsample;
	else
	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
	}