www.pudn.com > imgport.rar > jcprepct.c, change:2008-11-05,size:12427b


/* 
 * jcprepct.c 
 * 
 * Copyright (C) 1994-1996, 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 the compression preprocessing controller. 
 * This controller manages the color conversion, downsampling, 
 * and edge expansion steps. 
 * 
 * Most of the complexity here is associated with buffering input rows 
 * as required by the downsampler.  See the comments at the head of 
 * jcsample.c for the downsampler's needs. 
 */ 
 
#define JPEG_INTERNALS 
#include "jinclude.h" 
#include "jpeglib.h" 
 
 
/* At present, jcsample.c can request context rows only for smoothing. 
 * In the future, we might also need context rows for CCIR601 sampling 
 * or other more-complex downsampling procedures.  The code to support 
 * context rows should be compiled only if needed. 
 */ 
#ifdef INPUT_SMOOTHING_SUPPORTED 
#define CONTEXT_ROWS_SUPPORTED 
#endif 
 
 
/* 
 * For the simple (no-context-row) case, we just need to buffer one 
 * row group's worth of pixels for the downsampling step.  At the bottom of 
 * the image, we pad to a full row group by replicating the last pixel row. 
 * The downsampler's last output row is then replicated if needed to pad 
 * out to a full iMCU row. 
 * 
 * When providing context rows, we must buffer three row groups' worth of 
 * pixels.  Three row groups are physically allocated, but the row pointer 
 * arrays are made five row groups high, with the extra pointers above and 
 * below "wrapping around" to point to the last and first real row groups. 
 * This allows the downsampler to access the proper context rows. 
 * At the top and bottom of the image, we create dummy context rows by 
 * copying the first or last real pixel row.  This copying could be avoided 
 * by pointer hacking as is done in jdmainct.c, but it doesn't seem worth the 
 * trouble on the compression side. 
 */ 
 
 
/* Private buffer controller object */ 
 
typedef struct { 
  struct jpeg_c_prep_controller pub; /* public fields */ 
 
  /* Downsampling input buffer.  This buffer holds color-converted data 
   * until we have enough to do a downsample step. 
   */ 
  JSAMPARRAY color_buf[MAX_COMPONENTS]; 
 
  JDIMENSION rows_to_go;	/* counts rows remaining in source image */ 
  int next_buf_row;		/* index of next row to store in color_buf */ 
 
#ifdef CONTEXT_ROWS_SUPPORTED	/* only needed for context case */ 
  int this_row_group;		/* starting row index of group to process */ 
  int next_buf_stop;		/* downsample when we reach this index */ 
#endif 
} my_prep_controller; 
 
typedef my_prep_controller * my_prep_ptr; 
 
 
/* 
 * Initialize for a processing pass. 
 */ 
 
METHODDEF(void) 
start_pass_prep (j_compress_ptr cinfo, J_BUF_MODE pass_mode) 
{ 
  my_prep_ptr prep = (my_prep_ptr) cinfo->prep; 
 
  if (pass_mode != JBUF_PASS_THRU) 
    ERREXIT(cinfo, JERR_BAD_BUFFER_MODE); 
 
  /* Initialize total-height counter for detecting bottom of image */ 
  prep->rows_to_go = cinfo->image_height; 
  /* Mark the conversion buffer empty */ 
  prep->next_buf_row = 0; 
#ifdef CONTEXT_ROWS_SUPPORTED 
  /* Preset additional state variables for context mode. 
   * These aren't used in non-context mode, so we needn't test which mode. 
   */ 
  prep->this_row_group = 0; 
  /* Set next_buf_stop to stop after two row groups have been read in. */ 
  prep->next_buf_stop = 2 * cinfo->max_v_samp_factor; 
#endif 
} 
 
 
/* 
 * Expand an image vertically from height input_rows to height output_rows, 
 * by duplicating the bottom row. 
 */ 
 
LOCAL(void) 
expand_bottom_edge (JSAMPARRAY image_data, JDIMENSION num_cols, 
		    int input_rows, int output_rows) 
{ 
  register int row; 
 
  for (row = input_rows; row < output_rows; row++) { 
    jcopy_sample_rows(image_data, input_rows-1, image_data, row, 
		      1, num_cols); 
  } 
} 
 
 
/* 
 * Process some data in the simple no-context case. 
 * 
 * Preprocessor output data is counted in "row groups".  A row group 
 * is defined to be v_samp_factor sample rows of each component. 
 * Downsampling will produce this much data from each max_v_samp_factor 
 * input rows. 
 */ 
 
METHODDEF(void) 
pre_process_data (j_compress_ptr cinfo, 
		  JSAMPARRAY input_buf, JDIMENSION *in_row_ctr, 
		  JDIMENSION in_rows_avail, 
		  JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr, 
		  JDIMENSION out_row_groups_avail) 
{ 
  my_prep_ptr prep = (my_prep_ptr) cinfo->prep; 
  int numrows, ci; 
  JDIMENSION inrows; 
  jpeg_component_info * compptr; 
 
  while (*in_row_ctr < in_rows_avail && 
	 *out_row_group_ctr < out_row_groups_avail) { 
    /* Do color conversion to fill the conversion buffer. */ 
    inrows = in_rows_avail - *in_row_ctr; 
    numrows = cinfo->max_v_samp_factor - prep->next_buf_row; 
    numrows = (int) MIN((JDIMENSION) numrows, inrows); 
    (*cinfo->cconvert->color_convert) (cinfo, input_buf + *in_row_ctr, 
				       prep->color_buf, 
				       (JDIMENSION) prep->next_buf_row, 
				       numrows); 
    *in_row_ctr += numrows; 
    prep->next_buf_row += numrows; 
    prep->rows_to_go -= numrows; 
    /* If at bottom of image, pad to fill the conversion buffer. */ 
    if (prep->rows_to_go == 0 && 
	prep->next_buf_row < cinfo->max_v_samp_factor) { 
      for (ci = 0; ci < cinfo->num_components; ci++) { 
	expand_bottom_edge(prep->color_buf[ci], cinfo->image_width, 
			   prep->next_buf_row, cinfo->max_v_samp_factor); 
      } 
      prep->next_buf_row = cinfo->max_v_samp_factor; 
    } 
    /* If we've filled the conversion buffer, empty it. */ 
    if (prep->next_buf_row == cinfo->max_v_samp_factor) { 
      (*cinfo->downsample->downsample) (cinfo, 
					prep->color_buf, (JDIMENSION) 0, 
					output_buf, *out_row_group_ctr); 
      prep->next_buf_row = 0; 
      (*out_row_group_ctr)++; 
    } 
    /* If at bottom of image, pad the output to a full iMCU height. 
     * Note we assume the caller is providing a one-iMCU-height output buffer! 
     */ 
    if (prep->rows_to_go == 0 && 
	*out_row_group_ctr < out_row_groups_avail) { 
      for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 
	   ci++, compptr++) { 
	expand_bottom_edge(output_buf[ci], 
			   compptr->width_in_blocks * DCTSIZE, 
			   (int) (*out_row_group_ctr * compptr->v_samp_factor), 
			   (int) (out_row_groups_avail * compptr->v_samp_factor)); 
      } 
      *out_row_group_ctr = out_row_groups_avail; 
      break;			/* can exit outer loop without test */ 
    } 
  } 
} 
 
 
#ifdef CONTEXT_ROWS_SUPPORTED 
 
/* 
 * Process some data in the context case. 
 */ 
 
METHODDEF(void) 
pre_process_context (j_compress_ptr cinfo, 
		     JSAMPARRAY input_buf, JDIMENSION *in_row_ctr, 
		     JDIMENSION in_rows_avail, 
		     JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr, 
		     JDIMENSION out_row_groups_avail) 
{ 
  my_prep_ptr prep = (my_prep_ptr) cinfo->prep; 
  int numrows, ci; 
  int buf_height = cinfo->max_v_samp_factor * 3; 
  JDIMENSION inrows; 
 
  while (*out_row_group_ctr < out_row_groups_avail) { 
    if (*in_row_ctr < in_rows_avail) { 
      /* Do color conversion to fill the conversion buffer. */ 
      inrows = in_rows_avail - *in_row_ctr; 
      numrows = prep->next_buf_stop - prep->next_buf_row; 
      numrows = (int) MIN((JDIMENSION) numrows, inrows); 
      (*cinfo->cconvert->color_convert) (cinfo, input_buf + *in_row_ctr, 
					 prep->color_buf, 
					 (JDIMENSION) prep->next_buf_row, 
					 numrows); 
      /* Pad at top of image, if first time through */ 
      if (prep->rows_to_go == cinfo->image_height) { 
	for (ci = 0; ci < cinfo->num_components; ci++) { 
	  int row; 
	  for (row = 1; row <= cinfo->max_v_samp_factor; row++) { 
	    jcopy_sample_rows(prep->color_buf[ci], 0, 
			      prep->color_buf[ci], -row, 
			      1, cinfo->image_width); 
	  } 
	} 
      } 
      *in_row_ctr += numrows; 
      prep->next_buf_row += numrows; 
      prep->rows_to_go -= numrows; 
    } else { 
      /* Return for more data, unless we are at the bottom of the image. */ 
      if (prep->rows_to_go != 0) 
	break; 
      /* When at bottom of image, pad to fill the conversion buffer. */ 
      if (prep->next_buf_row < prep->next_buf_stop) { 
	for (ci = 0; ci < cinfo->num_components; ci++) { 
	  expand_bottom_edge(prep->color_buf[ci], cinfo->image_width, 
			     prep->next_buf_row, prep->next_buf_stop); 
	} 
	prep->next_buf_row = prep->next_buf_stop; 
      } 
    } 
    /* If we've gotten enough data, downsample a row group. */ 
    if (prep->next_buf_row == prep->next_buf_stop) { 
      (*cinfo->downsample->downsample) (cinfo, 
					prep->color_buf, 
					(JDIMENSION) prep->this_row_group, 
					output_buf, *out_row_group_ctr); 
      (*out_row_group_ctr)++; 
      /* Advance pointers with wraparound as necessary. */ 
      prep->this_row_group += cinfo->max_v_samp_factor; 
      if (prep->this_row_group >= buf_height) 
	prep->this_row_group = 0; 
      if (prep->next_buf_row >= buf_height) 
	prep->next_buf_row = 0; 
      prep->next_buf_stop = prep->next_buf_row + cinfo->max_v_samp_factor; 
    } 
  } 
} 
 
 
/* 
 * Create the wrapped-around downsampling input buffer needed for context mode. 
 */ 
 
LOCAL(void) 
create_context_buffer (j_compress_ptr cinfo) 
{ 
  my_prep_ptr prep = (my_prep_ptr) cinfo->prep; 
  int rgroup_height = cinfo->max_v_samp_factor; 
  int ci, i; 
  jpeg_component_info * compptr; 
  JSAMPARRAY true_buffer, fake_buffer; 
 
  /* Grab enough space for fake row pointers for all the components; 
   * we need five row groups' worth of pointers for each component. 
   */ 
  fake_buffer = (JSAMPARRAY) 
    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 
				(cinfo->num_components * 5 * rgroup_height) * 
				SIZEOF(JSAMPROW)); 
 
  for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 
       ci++, compptr++) { 
    /* Allocate the actual buffer space (3 row groups) for this component. 
     * We make the buffer wide enough to allow the downsampler to edge-expand 
     * horizontally within the buffer, if it so chooses. 
     */ 
    true_buffer = (*cinfo->mem->alloc_sarray) 
      ((j_common_ptr) cinfo, JPOOL_IMAGE, 
       (JDIMENSION) (((long) compptr->width_in_blocks * DCTSIZE * 
		      cinfo->max_h_samp_factor) / compptr->h_samp_factor), 
       (JDIMENSION) (3 * rgroup_height)); 
    /* Copy true buffer row pointers into the middle of the fake row array */ 
    MEMCOPY(fake_buffer + rgroup_height, true_buffer, 
	    3 * rgroup_height * SIZEOF(JSAMPROW)); 
    /* Fill in the above and below wraparound pointers */ 
    for (i = 0; i < rgroup_height; i++) { 
      fake_buffer[i] = true_buffer[2 * rgroup_height + i]; 
      fake_buffer[4 * rgroup_height + i] = true_buffer[i]; 
    } 
    prep->color_buf[ci] = fake_buffer + rgroup_height; 
    fake_buffer += 5 * rgroup_height; /* point to space for next component */ 
  } 
} 
 
#endif /* CONTEXT_ROWS_SUPPORTED */ 
 
 
/* 
 * Initialize preprocessing controller. 
 */ 
 
GLOBAL(void) 
jinit_c_prep_controller (j_compress_ptr cinfo, boolean need_full_buffer) 
{ 
  my_prep_ptr prep; 
  int ci; 
  jpeg_component_info * compptr; 
 
  if (need_full_buffer)		/* safety check */ 
    ERREXIT(cinfo, JERR_BAD_BUFFER_MODE); 
 
  prep = (my_prep_ptr) 
    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 
				SIZEOF(my_prep_controller)); 
  cinfo->prep = (struct jpeg_c_prep_controller *) prep; 
  prep->pub.start_pass = start_pass_prep; 
 
  /* Allocate the color conversion buffer. 
   * We make the buffer wide enough to allow the downsampler to edge-expand 
   * horizontally within the buffer, if it so chooses. 
   */ 
  if (cinfo->downsample->need_context_rows) { 
    /* Set up to provide context rows */ 
#ifdef CONTEXT_ROWS_SUPPORTED 
    prep->pub.pre_process_data = pre_process_context; 
    create_context_buffer(cinfo); 
#else 
    ERREXIT(cinfo, JERR_NOT_COMPILED); 
#endif 
  } else { 
    /* No context, just make it tall enough for one row group */ 
    prep->pub.pre_process_data = pre_process_data; 
    for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 
	 ci++, compptr++) { 
      prep->color_buf[ci] = (*cinfo->mem->alloc_sarray) 
	((j_common_ptr) cinfo, JPOOL_IMAGE, 
	 (JDIMENSION) (((long) compptr->width_in_blocks * DCTSIZE * 
			cinfo->max_h_samp_factor) / compptr->h_samp_factor), 
	 (JDIMENSION) cinfo->max_v_samp_factor); 
    } 
  } 
}