jpeg_rw.cpp File Reference

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "jpeglib.h"
#include <setjmp.h>

Include dependency graph for jpeg_rw.cpp:

Classes
struct	my_error_mgr

Typedefs
typedef struct my_error_mgr *	my_error_ptr

Functions
void	write_JPEG_file (char *filename, int quality, J_COLOR_SPACE in_color_space, int image_width, int image_height, JSAMPLE *image_buffer)
static void	my_error_exit (j_common_ptr cinfo)
int	read_JPEG_file (const char *filename, JSAMPLE *image_buffer)
int	read_JPEG_file (const char *filename, vector< vector< uint8_t > > &image_buffer)

Typedef Documentation

typedef struct my_error_mgr* my_error_ptr

Function Documentation

void write_JPEG_file	(	char *	filename,
		int	quality,
		J_COLOR_SPACE	in_color_space,
		int	image_width,
		int	image_height,
		JSAMPLE *	image_buffer
	)

{
    /* 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.
   * Note that this struct must live as long as the main JPEG parameter
   * struct, to avoid dangling-pointer problems.
   */
    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 to a
   * stdio stream.  You can also write your own code to do something else.
   * VERY IMPORTANT: use "b" option to fopen() if you are on a machine that
   * requires it in order to write binary files.
   */
    if ((outfile = fopen(filename, "wb")) == NULL) {
        fprintf(stderr, "can't open %s\n", filename);
        exit(1);
    }
    jpeg_stdio_dest(&cinfo, outfile);

    /* Step 3: set parameters for compression */

    /* First we supply a description of the input image.
   * Four fields of the cinfo struct must be filled in:
   */
    cinfo.image_width = image_width;    /* image width and height, in pixels */
    cinfo.image_height = image_height;
    if(in_color_space==JCS_RGB) {
        cinfo.input_components = 3;     /* # of color components per pixel */
    } else {
        cinfo.input_components = 1;     /* # of color components per pixel */
    }
    cinfo.in_color_space = in_color_space;  /* colorspace of input image */
    /* Now use the library's routine to set default compression parameters.
   * (You must set at least cinfo.in_color_space before calling this,
   * since the defaults depend on the source color space.)
   */
    jpeg_set_defaults(&cinfo);
    /* Now you can set any non-default parameters you wish to.
   * Here we just illustrate the use of quality (quantization table) scaling:
   */
    jpeg_set_quality(&cinfo, quality, TRUE /* limit to baseline-JPEG values */);

    /* Step 4: Start compressor */

    /* TRUE ensures that we will write a complete interchange-JPEG file.
   * Pass TRUE unless you are very sure of what you're doing.
   */
    jpeg_start_compress(&cinfo, TRUE);

    /* Step 5: while (scan lines remain to be written) */
    /*           jpeg_write_scanlines(...); */

    /* Here we use the library's state variable cinfo.next_scanline as the
   * loop counter, so that we don't have to keep track ourselves.
   * To keep things simple, we pass one scanline per call; you can pass
   * more if you wish, though.
   */
    if(in_color_space==JCS_RGB) {
        row_stride = image_width * 3;   /* JSAMPLEs per row in image_buffer */
    } else {
        row_stride = 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] = & image_buffer[cinfo.next_scanline * row_stride];
        (void) jpeg_write_scanlines(&cinfo, row_pointer, 1);
    }

    /* Step 6: Finish compression */

    jpeg_finish_compress(&cinfo);
    /* After finish_compress, we can close the output file. */
    fclose(outfile);

    /* Step 7: release JPEG compression object */

    /* This is an important step since it will release a good deal of memory. */
    jpeg_destroy_compress(&cinfo);

    /* And we're done! */
}

static void my_error_exit ( j_common_ptr  cinfo )

static

{
    /* cinfo->err really points to a my_error_mgr struct, so coerce pointer */
    my_error_ptr myerr = (my_error_ptr) cinfo->err;

    /* Always display the message. */
    /* We could postpone this until after returning, if we chose. */
    (*cinfo->err->output_message) (cinfo);

    /* Return control to the setjmp point */
    longjmp(myerr->setjmp_buffer, 1);
}

int read_JPEG_file	(	const char *	filename,
		JSAMPLE *	image_buffer
	)

{
    FILE *infile;
/* This struct contains the JPEG decompression parameters and pointers to
   * working space (which is allocated as needed by the JPEG library).
   */
    struct jpeg_decompress_struct cinfo;
    /* We use our private extension JPEG error handler.
   * Note that this struct must live as long as the main JPEG parameter
   * struct, to avoid dangling-pointer problems.
   */
    struct my_error_mgr jerr;
    /* More stuff */
    JSAMPARRAY buffer;      /* Output row buffer */
    int row_stride;     /* physical row width in output buffer */

    /* In this example we want to open the input file before doing anything else,
     * so that the setjmp() error recovery below can assume the file is open.
     * VERY IMPORTANT: use "b" option to fopen() if you are on a machine that
     * requires it in order to read binary files.
     */

    if ((infile = fopen(filename, "rb")) == NULL) {
        fprintf(stderr, "can't open %s\n", filename);
        return 0;
    }

    /* Step 1: allocate and initialize JPEG decompression object */

    /* We set up the normal JPEG error routines, then override error_exit. */
    cinfo.err = jpeg_std_error(&jerr.pub);
    jerr.pub.error_exit = my_error_exit;
    /* Establish the setjmp return context for my_error_exit to use. */
    if (setjmp(jerr.setjmp_buffer))
    {
        /* If we get here, the JPEG code has signaled an error.
     * We need to clean up the JPEG object, close the input file, and return.
     */
        jpeg_destroy_decompress(&cinfo);
        fclose(infile);
        return 0;
    }
    /* Now we can initialize the JPEG decompression object. */
    jpeg_create_decompress(&cinfo);

    /* Step 2: specify data source (eg, a file) */

    jpeg_stdio_src(&cinfo, infile);

    /* Step 3: read file parameters with jpeg_read_header() */

    (void) jpeg_read_header(&cinfo, TRUE);
    /* We can ignore the return value from jpeg_read_header since
   *   (a) suspension is not possible with the stdio data source, and
   *   (b) we passed TRUE to reject a tables-only JPEG file as an error.
   * See libjpeg.doc for more info.
   */

    /* Step 4: set parameters for decompression */

    /* In this example, we don't need to change any of the defaults set by
   * jpeg_read_header(), so we do nothing here.
   */

    /* Step 5: Start decompressor */

    (void) jpeg_start_decompress(&cinfo);
    /* We can ignore the return value since suspension is not possible
   * with the stdio data source.
   */

    /* We may need to do some setup of our own at this point before reading
   * the data.  After jpeg_start_decompress() we have the correct scaled
   * output image dimensions available, as well as the output colormap
   * if we asked for color quantization.
   * In this example, we need to make an output work buffer of the right size.
   */
    /* JSAMPLEs per row in output buffer */
    row_stride = cinfo.output_width * cinfo.output_components;
    /* Make a one-row-high sample array that will go away when done with image */
    buffer = (*cinfo.mem->alloc_sarray)
            ((j_common_ptr) &cinfo, JPOOL_IMAGE, row_stride, 1);

    /* Step 6: while (scan lines remain to be read) */
    /*           jpeg_read_scanlines(...); */

    /* Here we use the library's state variable cinfo.output_scanline as the
   * loop counter, so that we don't have to keep track ourselves.
   */
    while (cinfo.output_scanline < cinfo.output_height) {
        /* jpeg_read_scanlines expects an array of pointers to scanlines.
     * Here the array is only one element long, but you could ask for
     * more than one scanline at a time if that's more convenient.
     */
        (void) jpeg_read_scanlines(&cinfo, buffer, 1);
        /* Assume put_scanline_someplace wants a pointer and sample count. */
        //put_scanline_someplace(buffer[0], row_stride);
        memcpy((void *)image_buffer, (const void *)buffer[0], row_stride);
        image_buffer += row_stride;
    }

    /* Step 7: Finish decompression */

    (void) jpeg_finish_decompress(&cinfo);
    /* We can ignore the return value since suspension is not possible
   * with the stdio data source.
   */

    /* Step 8: Release JPEG decompression object */

    /* This is an important step since it will release a good deal of memory. */
    jpeg_destroy_decompress(&cinfo);

    /* After finish_decompress, we can close the input file.
   * Here we postpone it until after no more JPEG errors are possible,
   * so as to simplify the setjmp error logic above.  (Actually, I don't
   * think that jpeg_destroy can do an error exit, but why assume anything...)
   */
    fclose(infile);

    /* At this point you may want to check to see whether any corrupt-data
   * warnings occurred (test whether jerr.pub.num_warnings is nonzero).
   */

    /* And we're done! */
    return 1;
}

int read_JPEG_file	(	const char *	filename,
		vector< vector< uint8_t > > &	image_buffer
	)

{
    FILE *infile;
/* This struct contains the JPEG decompression parameters and pointers to
   * working space (which is allocated as needed by the JPEG library).
   */
    struct jpeg_decompress_struct cinfo;
    /* We use our private extension JPEG error handler.
   * Note that this struct must live as long as the main JPEG parameter
   * struct, to avoid dangling-pointer problems.
   */
    struct my_error_mgr jerr;
    /* More stuff */
    JSAMPARRAY buffer;      /* Output row buffer */
    int row_stride;     /* physical row width in output buffer */

    /* In this example we want to open the input file before doing anything else,
     * so that the setjmp() error recovery below can assume the file is open.
     * VERY IMPORTANT: use "b" option to fopen() if you are on a machine that
     * requires it in order to read binary files.
     */

    if ((infile = fopen(filename, "rb")) == NULL) {
        fprintf(stderr, "can't open %s\n", filename);
        return 0;
    }

    /* Step 1: allocate and initialize JPEG decompression object */

    /* We set up the normal JPEG error routines, then override error_exit. */
    cinfo.err = jpeg_std_error(&jerr.pub);
    jerr.pub.error_exit = my_error_exit;
    /* Establish the setjmp return context for my_error_exit to use. */
    if (setjmp(jerr.setjmp_buffer))
    {
        /* If we get here, the JPEG code has signaled an error.
     * We need to clean up the JPEG object, close the input file, and return.
     */
        jpeg_destroy_decompress(&cinfo);
        fclose(infile);
        return 0;
    }
    /* Now we can initialize the JPEG decompression object. */
    jpeg_create_decompress(&cinfo);

    /* Step 2: specify data source (eg, a file) */

    jpeg_stdio_src(&cinfo, infile);

    /* Step 3: read file parameters with jpeg_read_header() */

    (void) jpeg_read_header(&cinfo, TRUE);
    /* We can ignore the return value from jpeg_read_header since
   *   (a) suspension is not possible with the stdio data source, and
   *   (b) we passed TRUE to reject a tables-only JPEG file as an error.
   * See libjpeg.doc for more info.
   */

    /* Step 4: set parameters for decompression */

    /* In this example, we don't need to change any of the defaults set by
   * jpeg_read_header(), so we do nothing here.
   */

    /* Step 5: Start decompressor */

    (void) jpeg_start_decompress(&cinfo);
    /* We can ignore the return value since suspension is not possible
   * with the stdio data source.
   */

    /* We may need to do some setup of our own at this point before reading
   * the data.  After jpeg_start_decompress() we have the correct scaled
   * output image dimensions available, as well as the output colormap
   * if we asked for color quantization.
   * In this example, we need to make an output work buffer of the right size.
   */
    /* JSAMPLEs per row in output buffer */
    row_stride = cinfo.output_width * cinfo.output_components;
    /* Make a one-row-high sample array that will go away when done with image */
    buffer = (*cinfo.mem->alloc_sarray)
            ((j_common_ptr) &cinfo, JPOOL_IMAGE, row_stride, 1);

    /* Step 6: while (scan lines remain to be read) */
    /*           jpeg_read_scanlines(...); */

    /* Here we use the library's state variable cinfo.output_scanline as the
   * loop counter, so that we don't have to keep track ourselves.
   */
//    while (cinfo.output_scanline < cinfo.output_height)
    image_buffer.resize(cinfo.output_height);
    for (size_t ih=0; ih<cinfo.output_height; ++ih)
    {
        /* jpeg_read_scanlines expects an array of pointers to scanlines.
     * Here the array is only one element long, but you could ask for
     * more than one scanline at a time if that's more convenient.
     */
        (void) jpeg_read_scanlines(&cinfo, buffer, 1);
        /* Assume put_scanline_someplace wants a pointer and sample count. */
        //put_scanline_someplace(buffer[0], row_stride);
        image_buffer[ih].resize(cinfo.output_width * cinfo.output_components);
        memcpy((void *)image_buffer[ih].data(), (const void *)buffer[0], row_stride);
    }

    /* Step 7: Finish decompression */

    (void) jpeg_finish_decompress(&cinfo);
    /* We can ignore the return value since suspension is not possible
   * with the stdio data source.
   */

    /* Step 8: Release JPEG decompression object */

    /* This is an important step since it will release a good deal of memory. */
    jpeg_destroy_decompress(&cinfo);

    /* After finish_decompress, we can close the input file.
   * Here we postpone it until after no more JPEG errors are possible,
   * so as to simplify the setjmp error logic above.  (Actually, I don't
   * think that jpeg_destroy can do an error exit, but why assume anything...)
   */
    fclose(infile);

    /* At this point you may want to check to see whether any corrupt-data
   * warnings occurred (test whether jerr.pub.num_warnings is nonzero).
   */

    /* And we're done! */
    return 1;
}