jcmarker.c

JPEG压缩和解压程序和一些相关的说明文档 内容比较全

/*
 * jcmarker.c
 *
 * 
 *
 * This file contains routines to write JPEG datastream markers.
 */


#include "commondecls.h"



typedef enum {			/* JPEG marker codes */
  M_SOF0  = 0xc0,
  M_SOF1  = 0xc1,
  M_SOF2  = 0xc2,
  M_SOF3  = 0xc3,
  
  M_SOF5  = 0xc5,
  M_SOF6  = 0xc6,
  M_SOF7  = 0xc7,
  
  M_JPG   = 0xc8,
  M_SOF9  = 0xc9,
  M_SOF10 = 0xca,
  M_SOF11 = 0xcb,
  
  M_SOF13 = 0xcd,
  M_SOF14 = 0xce,
  M_SOF15 = 0xcf,
  
  M_DHT   = 0xc4,
  
  M_DAC   = 0xcc,
  
  M_RST0  = 0xd0,
  M_RST1  = 0xd1,
  M_RST2  = 0xd2,
  M_RST3  = 0xd3,
  M_RST4  = 0xd4,
  M_RST5  = 0xd5,
  M_RST6  = 0xd6,
  M_RST7  = 0xd7,
  
  M_SOI   = 0xd8,
  M_EOI   = 0xd9,
  M_SOS   = 0xda,
  M_DQT   = 0xdb,
  M_DNL   = 0xdc,
  M_DRI   = 0xdd,
  M_DHP   = 0xde,
  M_EXP   = 0xdf,
  
  M_APP0  = 0xe0,
  M_APP1  = 0xe1,
  M_APP2  = 0xe2,
  M_APP3  = 0xe3,
  M_APP4  = 0xe4,
  M_APP5  = 0xe5,
  M_APP6  = 0xe6,
  M_APP7  = 0xe7,
  M_APP8  = 0xe8,
  M_APP9  = 0xe9,
  M_APP10 = 0xea,
  M_APP11 = 0xeb,
  M_APP12 = 0xec,
  M_APP13 = 0xed,
  M_APP14 = 0xee,
  M_APP15 = 0xef,
  
  M_JPG0  = 0xf0,
  M_JPG13 = 0xfd,
  M_COM   = 0xfe,
  
  M_TEM   = 0x01,
  
  M_ERROR = 0x100
} JPEG_MARKER;




/*
 * Basic output routines.
 *
 * Note that we do not support suspension while writing a marker.
 * Therefore, an application using suspension must ensure that there is
 * enough buffer space for the initial markers (typ. 600-700 bytes) before
 * calling jpeg_start_compress, and enough space to write the trailing EOI
 * (a few bytes) before calling jpeg_finish_compress.  Multipass compression
 * modes are not supported at all with suspension, so those two are the only
 * points where markers will be written.
 */

void
empty_output_buffer (j_compress_ptr cinfo)
{
  jpeg_destination_mgr *dest =  cinfo->dest;

  if (JFWRITE(cinfo->outputfile, cinfo->outbuffer, OUTPUT_BUF_SIZE) !=
      (size_t) OUTPUT_BUF_SIZE)
    exit(0);

  dest->next_output_byte = cinfo->outbuffer;
  dest->free_in_buffer = OUTPUT_BUF_SIZE;

  
}





void
emit_byte (j_compress_ptr cinfo, int val)
/* Emit a byte */
{
  jpeg_destination_mgr *dest = cinfo->dest;

  *(dest->next_output_byte)++ = (JOCTET) val;
  if (--dest->free_in_buffer == 0) 
    empty_output_buffer (cinfo);
    
}


LOCAL(void)
emit_marker (j_compress_ptr cinfo, JPEG_MARKER mark)
/* Emit a marker code */
{
  emit_byte(cinfo, 0xFF);
  emit_byte(cinfo, (int) mark);
}


LOCAL(void)
emit_2bytes (j_compress_ptr cinfo, int value)
/* Emit a 2-byte integer; these are always MSB first in JPEG files */
{
  emit_byte(cinfo, (value >> 8) & 0xFF);
  emit_byte(cinfo, value & 0xFF);
}


/*
 * Routines to write specific marker types.
 */









/*
 * Write datastream header.
 * This consists of an SOI and optional APPn markers.
 * We recommend use of the JFIF marker, but not the Adobe marker,
 * when using YCbCr or grayscale data.  The JFIF marker should NOT
 * be used for any other JPEG colorspace.  The Adobe marker is helpful
 * to distinguish RGB, CMYK, and YCCK colorspaces.
 * Note that an application can write additional header markers after
 * jpeg_start_compress returns.
 */

void
write_file_header (j_compress_ptr cinfo)
{
  
  /*emit_marker(cinfo, M_SOI);*/	/* first the SOI */
  /*emit_2bytes(cinfo,cinfo->image_width);
    emit_2bytes(cinfo,cinfo->image_height);*/
  emit_byte(cinfo,cinfo->image_width & 0xFF);
  emit_byte(cinfo,(cinfo->image_width>>8) & 0xFF);
  emit_byte(cinfo,cinfo->image_height & 0xFF);
  emit_byte(cinfo,(cinfo->image_height>>8) & 0xFF);
}






/*
 * Write datastream trailer.
 */

void
write_file_trailer (j_compress_ptr cinfo)
{
  /*emit_marker(cinfo, M_EOI);*/
}