www.pudn.com > imgport.rar > jcsample.c, change:2008-11-05,size:19398b


/* 
 * 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; 
  JPEG_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 += (JPEG_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; 
  JPEG_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; 
  JPEG_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 
}