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writejpeg.c

#include <stdio.h>
#include <stdlib.h>

/* jpeg includes */
/* Note that jpeglib.h also requires jconfig.h and jmorecfg.h to be
   in the same directory as jpeglib.h */

#include <jpeglib.h>

extern JSAMPLE * image_buffer;      /* Points to large array of R,G,B-order data */
int image_height; /* Number of rows in image */
int image_width;        /* Number of columns in image */
int image_quality;      /* Compression Quality */

FILE *out;

extern void write_JPEG_file (JSAMPLE *scan, FILE *out)
{
  extern int image_width, image_height, image_quality;
  struct jpeg_compress_struct cinfo;
  struct jpeg_error_mgr jerr;
  JSAMPROW row_pointer[1];    /* pointer to JSAMPLE row[s] */
  int row_stride;       /* physical row width in image buffer */

  cinfo.err = jpeg_std_error(&jerr);
  /* Now we can initialize the JPEG compression object. */
  jpeg_create_compress(&cinfo);

  jpeg_stdio_dest(&cinfo, out);
  cinfo.image_width = image_width;  /* image width and height, in pixels */
  cinfo.image_height = image_height;
  cinfo.input_components = 1;       /* # of color components per pixel */
  cinfo.in_color_space = JCS_GRAYSCALE;   /* colorspace of input image */
  jpeg_set_defaults(&cinfo);
  jpeg_set_quality(&cinfo, image_quality, TRUE /* limit to baseline-JPEG values */);
  jpeg_start_compress(&cinfo, TRUE);
  row_stride = cinfo.input_components*image_width;    /* JSAMPLEs per row in image_buffer */
  while (cinfo.next_scanline < cinfo.image_height) {
    /* jpeg_write_scanlines expects an array of pointers to scanlines.
     * Here the array is only one element long, but you could pass
     * more than one scanline at a time if that's more convenient.
     */
    row_pointer[0] = & scan[cinfo.next_scanline * row_stride];
    (void) jpeg_write_scanlines(&cinfo, row_pointer, 1);
  }
  jpeg_finish_compress(&cinfo);
  jpeg_destroy_compress(&cinfo);
}

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