jccoefct.c

一套图像处理程序,支持三种图像文件格式,我调试过了,很好用

/*
 * jccoefct.c
 *
 * Copyright (C) 1994, 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 coefficient buffer controller for compression.
 * This controller is the top level of the JPEG compressor proper.
 * The coefficient buffer lies between forward-DCT and entropy encoding steps.
 */

#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"


/* We use a full-image coefficient buffer when doing Huffman optimization,
 * and also for writing multiple-scan JPEG files.  In all cases, the DCT
 * step is run during the first pass, and subsequent passes need only read
 * the buffered coefficients.
 */
#ifdef ENTROPY_OPT_SUPPORTED
#define FULL_COEF_BUFFER_SUPPORTED
#else
#ifdef C_MULTISCAN_FILES_SUPPORTED
#define FULL_COEF_BUFFER_SUPPORTED
#endif
#endif


/* Private buffer controller object */

typedef struct {
  struct jpeg_c_coef_controller pub; /* public fields */

  JDIMENSION MCU_row_num;	/* keep track of MCU row # within image */

  /* For single-pass compression, it's sufficient to buffer just one MCU
   * (although this may prove a bit slow in practice).  We allocate a
   * workspace of MAX_BLOCKS_IN_MCU coefficient blocks, and reuse it for each
   * MCU constructed and sent.  (On 80x86, the workspace is FAR even though
   * it's not really very big; this is to keep the module interfaces unchanged
   * when a large coefficient buffer is necessary.)
   * In multi-pass modes, this array points to the current MCU's blocks
   * within the virtual arrays.
   */
  JBLOCKROW MCU_buffer[MAX_BLOCKS_IN_MCU];

  /* In multi-pass modes, we need a virtual block array for each component. */
  jvirt_barray_ptr whole_image[MAX_COMPONENTS];
} my_coef_controller;

typedef my_coef_controller * my_coef_ptr;


/* Forward declarations */
METHODDEF void compress_data
    JPP((j_compress_ptr cinfo, JSAMPIMAGE input_buf, JDIMENSION *in_mcu_ctr));
#ifdef FULL_COEF_BUFFER_SUPPORTED
METHODDEF void compress_first_pass
    JPP((j_compress_ptr cinfo, JSAMPIMAGE input_buf, JDIMENSION *in_mcu_ctr));
METHODDEF void compress_output
    JPP((j_compress_ptr cinfo, JSAMPIMAGE input_buf, JDIMENSION *in_mcu_ctr));
#endif


/*
 * Initialize for a processing pass.
 */

METHODDEF void
start_pass_coef (j_compress_ptr cinfo, J_BUF_MODE pass_mode)
{
  my_coef_ptr coef = (my_coef_ptr) cinfo->coef;

  coef->MCU_row_num = 0;

  switch (pass_mode) {
  case JBUF_PASS_THRU:
    if (coef->whole_image[0] != NULL)
      ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
    coef->pub.compress_data = compress_data;
    break;
#ifdef FULL_COEF_BUFFER_SUPPORTED
  case JBUF_SAVE_AND_PASS:
    if (coef->whole_image[0] == NULL)
      ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
    coef->pub.compress_data = compress_first_pass;
    break;
  case JBUF_CRANK_DEST:
    if (coef->whole_image[0] == NULL)
      ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
    coef->pub.compress_data = compress_output;
    break;
#endif
  default:
    ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
    break;
  }
}


/*
 * Process some data in the single-pass case.
 * Up to one MCU row is processed (less if suspension is forced).
 *
 * NB: input_buf contains a plane for each component in image.
 * For single pass, this is the same as the components in the scan.
 */

METHODDEF void
compress_data (j_compress_ptr cinfo,
	       JSAMPIMAGE input_buf, JDIMENSION *in_mcu_ctr)
{
  my_coef_ptr coef = (my_coef_ptr) cinfo->coef;
  JDIMENSION MCU_col_num;	/* index of current MCU within row */
  JDIMENSION last_MCU_col = cinfo->MCUs_per_row - 1;
  JDIMENSION last_MCU_row = cinfo->MCU_rows_in_scan - 1;
  int blkn, bi, ci, yindex, blockcnt;
  JDIMENSION ypos, xpos;
  jpeg_component_info *compptr;

  /* Loop to write as much as one whole MCU row */

  for (MCU_col_num = *in_mcu_ctr; MCU_col_num <= last_MCU_col; MCU_col_num++) {
    /* Determine where data comes from in input_buf and do the DCT thing.
     * Each call on forward_DCT processes a horizontal row of DCT blocks
     * as wide as an MCU; we rely on having allocated the MCU_buffer[] blocks
     * sequentially.  Dummy blocks at the right or bottom edge are filled in
     * specially.  The data in them does not matter for image reconstruction,
     * so we fill them with values that will encode to the smallest amount of
     * data, viz: all zeroes in the AC entries, DC entries equal to previous
     * block's DC value.  (Thanks to Thomas Kinsman for this idea.)
     */
    blkn = 0;
    for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
      compptr = cinfo->cur_comp_info[ci];
      blockcnt = (MCU_col_num < last_MCU_col) ? compptr->MCU_width
					      : compptr->last_col_width;
      xpos = MCU_col_num * compptr->MCU_sample_width;
      ypos = 0;
      for (yindex = 0; yindex < compptr->MCU_height; yindex++) {
	if (coef->MCU_row_num < last_MCU_row ||
	    yindex < compptr->last_row_height) {
	  (*cinfo->fdct->forward_DCT) (cinfo, compptr,
				       input_buf[ci], coef->MCU_buffer[blkn],
				       ypos, xpos, (JDIMENSION) blockcnt);
	  if (blockcnt < compptr->MCU_width) {
	    /* Create some dummy blocks at the right edge of the image. */
	    jzero_far((void FAR *) coef->MCU_buffer[blkn + blockcnt],
		      (compptr->MCU_width - blockcnt) * SIZEOF(JBLOCK));
	    for (bi = blockcnt; bi < compptr->MCU_width; bi++) {
	      coef->MCU_buffer[blkn+bi][0][0] = coef->MCU_buffer[blkn+bi-1][0][0];
	    }
	  }
	} else {
	  /* Create a whole row of dummy blocks at the bottom of the image. */
	  jzero_far((void FAR *) coef->MCU_buffer[blkn],
		    compptr->MCU_width * SIZEOF(JBLOCK));
	  for (bi = 0; bi < compptr->MCU_width; bi++) {
	    coef->MCU_buffer[blkn+bi][0][0] = coef->MCU_buffer[blkn-1][0][0];
	  }
	}
	blkn += compptr->MCU_width;
	ypos += DCTSIZE;
      }
    }
    /* Try to write the MCU.  In event of a suspension failure, we will
     * re-DCT the MCU on restart (a bit inefficient, could be fixed...)
     */
    if (! (*cinfo->entropy->encode_mcu) (cinfo, coef->MCU_buffer))
      break;			/* suspension forced; exit loop */
  }
  if (MCU_col_num > last_MCU_col)
    coef->MCU_row_num++;	/* advance if we finished the row */
  *in_mcu_ctr = MCU_col_num;
}


#ifdef FULL_COEF_BUFFER_SUPPORTED

/*
 * Process some data in the first pass of a multi-pass case.
 * We process the equivalent of one fully interleaved MCU row ("iMCU" row)
 * per call, ie, v_samp_factor block rows for each component in the image.
 * This amount of data is read from the source buffer, DCT'd and quantized,
 * and saved into the virtual arrays.  We also generate suitable dummy blocks
 * as needed at the right and lower edges.  (The dummy blocks are constructed
 * in the virtual arrays, which have been padded appropriately.)  This makes
 * it possible for subsequent passes not to worry about real vs. dummy blocks.
 *
 * We must also emit the data to the entropy encoder.  This is conveniently
 * done by calling compress_output() after we've loaded the current strip
 * of the virtual arrays.
 *
 * NB: input_buf contains a plane for each component in image.  All
 * components are DCT'd and loaded into the virtual arrays in this pass.
 * However, it may be that only a subset of the components are emitted to
 * the entropy encoder during this first pass; be careful about looking
 * at the scan-dependent variables (MCU dimensions, etc).
 */

METHODDEF void
compress_first_pass (j_compress_ptr cinfo,
		     JSAMPIMAGE input_buf, JDIMENSION *in_mcu_ctr)
{
  my_coef_ptr coef = (my_coef_ptr) cinfo->coef;