source: liacs/MIR2010/SourceCode/cximage/jpeg/jcsample.c@ 422

/*

 * jcsample.c

 *

 * Copyright (C) 1991-1996, Thomas G. Lane.

 * This file is part of the Independent JPEG Group's software.

 * For conditions of distribution and use, see the accompanying README 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"





/* Pointer to routine to downsample a single component */

typedef JMETHOD(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;

  INT32 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 += (INT32) 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;

  INT32 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;

  INT32 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;

      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) {

        downsample->methods[ci] = h2v2_smooth_downsample;

        downsample->pub.need_context_rows = TRUE;

      } 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

}