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1 line
16 KiB
C
1 line
16 KiB
C
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/*
* example.c
*
* This file illustrates how to use the IJG code as a subroutine library
* to read or write JPEG image files. You should look at this code in
* conjunction with the documentation file libjpeg.doc.
*
* This code will not do anything useful as-is, but it may be helpful as a
* skeleton for constructing routines that call the JPEG library.
*
* We present these routines in the same coding style used in the JPEG code
* (ANSI function definitions, etc); but you are of course free to code your
* routines in a different style if you prefer.
*/
#include <stdio.h>
/*
* Include file for users of JPEG library.
* You will need to have included system headers that define at least
* the typedefs FILE and size_t before you can include jpeglib.h.
* (stdio.h is sufficient on ANSI-conforming systems.)
* You may also wish to include "jerror.h".
*/
#include "jpeglib.h"
/*
* <setjmp.h> is used for the optional error recovery mechanism shown in
* the second part of the example.
*/
#include <setjmp.h>
/******************** JPEG COMPRESSION SAMPLE INTERFACE *******************/
/* This half of the example shows how to feed data into the JPEG compressor.
* We present a minimal version that does not worry about refinements such
* as error recovery (the JPEG code will just exit() if it gets an error).
*/
/*
* IMAGE DATA FORMATS:
*
* The standard input image format is a rectangular array of pixels, with
* each pixel having the same number of "component" values (color channels).
* Each pixel row is an array of JSAMPLEs (which typically are unsigned chars).
* If you are working with color data, then the color values for each pixel
* must be adjacent in the row; for example, R,G,B,R,G,B,R,G,B,... for 24-bit
* RGB color.
*
* For this example, we'll assume that this data structure matches the way
* our application has stored the image in memory, so we can just pass a
* pointer to our image buffer. In particular, let's say that the image is
* RGB color and is described by:
*/
extern JSAMPLE * image_buffer; /* Points to large array of R,G,B-order data */
extern int image_height; /* Number of rows in image */
extern int image_width; /* Number of columns in image */
/*
* Sample routine for JPEG compression. We assume that the target file name
* and a compression quality factor are passed in.
*/
GLOBAL void
write_JPEG_file (char * filename, int quality)
{
/* This struct contains the JPEG compression parameters and pointers to
* working space (which is allocated as needed by the JPEG library).
* It is possible to have several such structures, representing multiple
* compression/decompression processes, in existence at once. We refer
* to any one struct (and its associated working data) as a "JPEG object".
*/
struct jpeg_compress_struct cinfo;
/* This struct represents a JPEG error handler. It is declared separately
* because applications often want to supply a specialized error handler
* (see the second half of this file for an example). But here we just
* take the easy way out and use the standard error handler, which will
* print a message on stderr and call exit() if compression fails.
*/
struct jpeg_error_mgr jerr;
/* More stuff */
FILE * outfile; /* target file */
JSAMPROW row_pointer[1]; /* pointer to JSAMPLE row[s] */
int row_stride; /* physical row width in image buffer */
/* Step 1: allocate and initialize JPEG compression object */
/* We have to set up the error handler first, in case the initialization
* step fails. (Unlikely, but it could happen if you are out of memory.)
* This routine fills in the contents of struct jerr, and returns jerr's
* address which we place into the link field in cinfo.
*/
cinfo.err = jpeg_std_error(&jerr);
/* Now we can initialize the JPEG compression object. */
jpeg_create_compress(&cinfo);
/* Step 2: specify data destination (eg, a file) */
/* Note: steps 2 and 3 can be done in either order. */
/* Here we use the library-supplied code to send compressed data
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