jcsample.c

电子书《数字图像处理学》Visual C++实现 郎锐编写 所附源码

#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;
  long 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 += (long) 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