libjpeg库分析----2.jpg与bmp格式的相互转换

参照jpeg-6b/example.c这个demo可以很容易的在jpeg与bmp之间进行转换
1.将bmp转为jpg

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

#pragma pack(1)
typedef struct __BITMAPFILEHEADER__
{
    u_int16_t bfType;
    u_int32_t bfSize;
    u_int16_t bfReserved1;
    u_int16_t bfReserved2;
    u_int32_t bfOffBits;
}BITMAPFILEHEADER;

typedef struct __BITMAPINFOHEADER
{
    u_int32_t biSize;
    u_int32_t biWidth;
    u_int32_t biHeight;
    u_int16_t biPlanes;
    u_int16_t biBitCount;
    u_int32_t biCompression;
    u_int32_t biSizeImage;
    u_int32_t biXPelsPerMeter;
    u_int32_t biYPelsPerMeter;
    u_int32_t biClrUsed;
    u_int32_t biClrImportant;
}BITMAPINFOHEADER;


/******************** 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:
 */
#if 0
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 */
#endif


/*
 * 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 * jpgfile, char* bmpfile, int quality)
{
    int w, h, bpp; //bpp-->byte_per_pix
    int len;
    char* image_buffer = NULL;
    BITMAPFILEHEADER bmphead;
    BITMAPINFOHEADER infohead;
    /* 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 * out_jpgfile;        /* target file */
    FILE * in_bmpfile;        /* input 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 ((out_jpgfile = fopen(jpgfile, "wb")) == NULL) {
        fprintf(stderr, "can't open jpg %s\n", jpgfile);
        exit(1);
    }
    if ((in_bmpfile = fopen(bmpfile, "rb")) == NULL) {
        fprintf(stderr, "can't open bmp=%s\n", bmpfile);
        exit(1);
    }
    len = sizeof(bmphead)+sizeof(infohead);
    printf("len=%d\n",len);
    image_buffer = (char*)malloc(len*sizeof(char));
    if(image_buffer == NULL)
    {
        printf("malloc error\n");
        return ;
    }
    fread(image_buffer, len, 1, in_bmpfile);
    memcpy(&bmphead, image_buffer, sizeof(bmphead));
    memcpy(&infohead, image_buffer+sizeof(bmphead), sizeof(infohead));
    if(bmphead.bfType != 0x4D42) //must be 0x4D42='BM'
    {
        printf("not a bmp file\n");
        return ;
    }
    if(infohead.biBitCount != 24)  //这儿只支持bit_pre_pix=24的bmp格式
    {
        printf("error: now bitCount=%d not 24bit\n", infohead.biBitCount);
        return ;
    }
    free(image_buffer);
    w = infohead.biWidth;
    h = infohead.biHeight;
    bpp = infohead.biBitCount/8;
    printf("w=%d,h=%d,bitcount=%d\n", w, h, bpp);
    image_buffer = (char*)malloc(w*h*bpp);
    if(image_buffer == NULL)
    {
        printf("malloc w*h*bpp error\n");
        return ;
    }
    fread(image_buffer, w*h*bpp, 1, in_bmpfile);
    jpeg_stdio_dest(&cinfo, out_jpgfile);

    /* 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 = w;     /* image width and height, in pixels */
    cinfo.image_height = h;
    cinfo.input_components = 3;        /* # of color components per pixel */
    cinfo.in_color_space = JCS_RGB;     /* 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.
     */
    row_stride = w* 3;    /* 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.
         */
        //因为bmp图像的数据存储格式是从左下到右上，若直接处理生成的图像是倒的，所以这儿需要从下往上处理图像
        //row_pointer[0] = & image_buffer[cinfo.next_scanline * row_stride];
        row_pointer[0] = & image_buffer[(cinfo.image_height-cinfo.next_scanline-1) * 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(out_jpgfile);
    fclose(in_bmpfile);
    free(image_buffer);
    /* 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 */
}



int main ( int argc, char *argv[] )
{
    char bmpfile[] = "./640_480.bmp";
    char jpgfile[] = "./640_480.jpg";
    write_JPEG_file(jpgfile, bmpfile, 100);
    printf("read over\n");
    return EXIT_SUCCESS;
}

2.将jpg转为bmp

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

#pragma pack(1)
typedef struct __BITMAPFILEHEADER__
{
    u_int16_t bfType;
    u_int32_t bfSize;
    u_int16_t bfReserved1;
    u_int16_t bfReserved2;
    u_int32_t bfOffBits;
}BITMAPFILEHEADER;

typedef struct __BITMAPINFOHEADER
{
    u_int32_t biSize;
    u_int32_t biWidth;
    u_int32_t biHeight;
    u_int16_t biPlanes;
    u_int16_t biBitCount;
    u_int32_t biCompression;
    u_int32_t biSizeImage;
    u_int32_t biXPelsPerMeter;
    u_int32_t biYPelsPerMeter;
    u_int32_t biClrUsed;
    u_int32_t biClrImportant;
}BITMAPINFOHEADER;

#define BYTE_PER_PIX 3
int create_bmp_header(BITMAPFILEHEADER* bmphead, BITMAPINFOHEADER* infohead, int w, int h)
{
    bmphead->bfType = 0x4D42; //must be 0x4D42='BM'
    bmphead->bfSize= w*h*BYTE_PER_PIX+14+40;
    bmphead->bfReserved1= 0x00;
    bmphead->bfReserved2= 0x00;
    bmphead->bfOffBits = 14+40;

    infohead->biSize = sizeof(BITMAPINFOHEADER);
    infohead->biWidth = w;
    infohead->biHeight = -h;
    infohead->biPlanes = 1;
    infohead->biBitCount = BYTE_PER_PIX*8;
    infohead->biCompression= 0;
    infohead->biSizeImage= w*h*BYTE_PER_PIX;//640 * 480 * 3;
    infohead->biXPelsPerMeter= 0x0;
    infohead->biYPelsPerMeter= 0x0;
    infohead->biClrUsed = 0;
    infohead->biClrImportant = 0;
    return 0;
}



struct my_error_mgr {
  struct jpeg_error_mgr pub;    /* "public" fields */

  jmp_buf setjmp_buffer;    /* for return to caller */
};

typedef struct my_error_mgr * my_error_ptr;

/*
 * Here's the routine that will replace the standard error_exit method:
 */

METHODDEF(void)
my_error_exit (j_common_ptr cinfo)
{
  /* 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);
}


/*
 * Sample routine for JPEG decompression. We assume that the source file name
 * is passed in. We want to return 1 on success, 0 on error.
 */

int read_JPEG_file (char* bmpfile, char * jpgfile)
{
    BITMAPFILEHEADER bmphead;
    BITMAPINFOHEADER infohead;
    FILE * bmp_fp = NULL;
  /* 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 */
  FILE * jpg_file;        /* source file */
  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 ((jpg_file= fopen(jpgfile, "rb")) == NULL) {
    fprintf(stderr, "can't open jpgfile=%s\n", jpgfile);
    return 0;
  }

  //prepare for bmp write
  if (NULL == (bmp_fp = fopen(bmpfile,"wb")))
  {
      fprintf(stderr, "can't open bmpfile=%s\n", bmpfile);
      return -1;
  }

  /* 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(jpg_file);
    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, jpg_file);

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

  (void) jpeg_read_header(&cinfo, TRUE);
  printf("w=%d,h=%d\n", cinfo.image_width, cinfo.image_height);

  create_bmp_header(&bmphead, &infohead, cinfo.image_width, cinfo.image_height);
  fwrite(&bmphead, 14, 1, bmp_fp);
  fwrite(&infohead, 40, 1, bmp_fp);
  /* 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);
    fwrite(buffer[0],row_stride,1, bmp_fp);
  }
  fclose(bmp_fp);

  /* 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(jpg_file);

  /* 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 */
  return 1;
}


int main ( int argc, char *argv[] )
{
    //char filename[] = "./testimg.jpg";
    char jpgfile[] = "./640_480.jpg";
    char bmpfile[] = "./640_480.bmp";
    read_JPEG_file(bmpfile, jpgfile);
    printf("read over\n");
    return EXIT_SUCCESS;
}