image_size.c

包含了对于灰度图像的8种jpeg无损压缩的预测方法

#include <stdio.h>
#include <sys/stat.h>
#include <malloc.h>          /* for halloc */

/*******************************************************************************
*NOTICE:                                                                       *
*This code is believed by the author to be bug free.  You are free to use and  *
*modify this code with the understanding that any use, either direct or        *
*derivative, must contain acknowledgement of its author and source.  The author*
*makes no warranty of any kind, expressed or implied, of merchantability or    *
*fitness for a particular purpose.  The author shall not be held liable for any*
*incidental or consequential damages in connection with or arising out of the  *
*furnishing, performance, or use of this software.  This software is not       *
*authorized for use in life support devices or systems.                        *
********************************************************************************/


int image_size(char file[], int *r, int *c)
{
/*
Written by James R. Nau, 6-Oct-89

Attempt to find the size of an image in file pointed to by *file.
Number of rows (down), and the number of columns (across) is returned.
Uses a stat call to find the size of the file.  Then, attempts to find
a pertinent number of rows and columns that we normally use.  Currently

supported formats:

   row x column  size        Format

    128x128    16,384        Small Image
    320x200    64,000        IBM VGA Style
    256x256    65,536        Standard NASA Image (small)
    256x384    98,304        IVG Low-Res Image
    512x384   196,608        IVG High-Res Image
    512x512   262,144        Standard NASA Image (large)
    640x480   307,200        Super VGA (from GIF usually)
    720x480   345,600
    576x720   414,720	     JPEG images

Parameters:
         *file: pointer to filename containing image
          *row: pointer to the number of rows we decided on
       *column: pointer to number of columns we decided on

Return values:
        0: ok
       -1: Couldn't use stat function
       -2: Unknown image size
*/

   struct stat status;
   int res;
   long img_len;

   res = stat (file, &status);
   if (res != 0)
   {
      return (-1);
   }
   img_len = status.st_size;

   if (img_len == 16384L)       /* For BUD's images */
   {
      *r = 128;
      *c = 128;
   }
   else if (img_len == 64000L)  /* IBM VGA Screen */
   {
      *r = 200;
      *c = 320;
   }
   else if (img_len == 65536L)  /* Standard */
   {
      *r = 256;
      *c = 256;
   }
   else if (img_len == 98304L)  /* Low-Res IVG images */
   {
      *r = 256;
      *c = 384;
   }
   else if (img_len == 196608L) /* Hi-Res IVG images */
   {
      *r = 512;
      *c = 384;
   }
   else if (img_len == 262144L) /* Standard, but large... */
   {
      *r = 512;
      *c = 512;
   }
   else if (img_len == 307200L) /* SVGA Hi-Res from GIFs */
   {
      *r = 480;
      *c = 640;
   }
   else if (img_len == 345600L) /* mpeg frame 720 x 480 */
   {
      *r = 720;
      *c = 480;
   }
   else if (img_len == 414720L) /* jpeg test image 576 x 720 */
   {
      *r = 576;
      *c = 720;
   }
   else                         /* oops */
   {
      fprintf(stderr, "\nError, unknown image size: %ld\n", img_len);
      return (-2);
   }
   return (0);
}