我在 RHEL 6.0 x86_64 机器上使用以下版本的 libjpeg。
[mehoggan@hogganz400 jpeg_to_raw.c]$ rpm -qa libjpeg
libjpeg-6b-46.el6.x86_64
我有以下代码，它以一个 .jpeg 文件作为输入，并写出一个 .raw 文件。当我运行该程序时，文件的大小会扩大，这让我相信该程序正在运行:
[mehoggan@hogganz400 jpeg_to_raw.c]$ ls -l
total 600
-rwxrwxr-x 1 mehoggan mehoggan 10113 Dec 1 10:32 jpeg_to_raw
-rw-rw-r-- 1 mehoggan mehoggan 3311 Dec 1 10:32 jpeg_to_raw.c
-rw-rw-r-- 1 mehoggan mehoggan 75 Dec 1 10:27 Makefile
-rw-rw-r-- 1 mehoggan mehoggan 215205 Dec 1 09:19 test.jpg
-rw-rw-r-- 1 mehoggan mehoggan 374850 Dec 1 10:32 test_out.raw
然而，当我使用 Irfanview(和相关插件)打开文件时，只有一小部分图像打开。代码可以在下面找到:
#include <stdio.h>
#include <jpeglib.h>
#include <stdlib.h>
#include <unistd.h>
/* we will be using this uninitialized pointer later to store raw, uncompressd image */
unsigned char *raw_image = NULL;
unsigned int size;
/**
* print the information for what was stored in the JPEG File
**/
void print_jpeg_info(struct jpeg_decompress_struct cinfo)
{
printf("JPEG File Information: \n");
printf("Image width and height: %d pixels and %d pixels.\n", cinfo.image_width, cinfo.image_height);
printf("Color components per pixel: %d.\n", cinfo.num_components);
printf("Color space: %d.\n", cinfo.jpeg_color_space);
printf("Raw flag is: %d.\n", cinfo.raw_data_out);
}
/**
* read_jpeg_file Reads from a jpeg file on disk specified by filename and saves into the
* raw_image buffer in an uncompressed format.
*
* \returns positive integer if successful, -1 otherwise
* \param *filename char string specifying the file name to read from
**/
int read_jpeg_file(char *filename)
{
/* these are standard libjpeg structures for reading(decompression) */
struct jpeg_decompress_struct cinfo;
struct jpeg_error_mgr jerr;
/* libjpeg data structure for storing one row, that is, scanline of an image */
JSAMPROW row_pointer[1];
FILE *infile = fopen(filename, "rb");
unsigned long location = 0;
int i = 0;
if (!infile) {
printf("Error opening jpeg file %s\n!", filename);
return -1;
}
/* here we set up the standard libjpeg error handler */
cinfo.err = jpeg_std_error(&jerr);
/* setup decompression process and source, then read JPEG header */
jpeg_create_decompress(&cinfo);
/* this makes the library read from infile */
jpeg_stdio_src(&cinfo, infile);
/* reading the image header which contains image information */
jpeg_read_header(&cinfo, TRUE);
print_jpeg_info(cinfo);
jpeg_start_decompress(&cinfo);
/* allocate memory to hold the uncompressed image */
size = cinfo.output_width*cinfo.output_height*cinfo.num_components;
raw_image = (unsigned char*)malloc(size);
/* now actually read the jpeg into the raw buffer */
row_pointer[0] = (unsigned char *)malloc(cinfo.output_width*cinfo.num_components);
/* read one scan line at a time */
while (cinfo.output_scanline < cinfo.image_height) {
jpeg_read_scanlines( &cinfo, row_pointer, 1 );
for (i=0; i<cinfo.image_width*cinfo.num_components;i++) {
raw_image[location++] = row_pointer[0][i];
}
}
/* wrap up decompression, destroy objects, free pointers and close open files */
jpeg_finish_decompress(&cinfo);
jpeg_destroy_decompress(&cinfo);
free(row_pointer[0]);
fclose(infile);
/* yup, we succeeded! */
return 1;
}
int main(int argc, char *argv[])
{
char *infilename = "test.jpg";
if (read_jpeg_file(infilename) > 0) {
size_t count = size / sizeof(unsigned char*);
fprintf(stdout, "The number of unsigned chars in raw_image = %d\n", (int)count);
FILE *ofile = fopen("test_out.raw", "w+");
ssize_t data_out = fwrite(raw_image, count, sizeof(unsigned char), ofile);
fprintf(stdout, "%d", (int)data_out);
fclose(ofile);
}
else
return -1;
return 0;
}
您如何看待程序没有写出所有数据的原因？或者为什么它可能会破坏数据？
用于构建这个简单应用程序的 makefile 是:
jpeg_to_raw : jpeg_to_raw.c
gcc jpeg_to_raw.c -Wall -o jpeg_to_raw -ljpeg
最佳答案
size_t count = size/sizeof(unsigned char*);
只得到写入原始数据的 1/4(实际上，在 64 位模式下只有 1/8)。 计数应该与大小相同(计算字符，而不是指针)
关于c - libjpeg 解压缩到 RAW 不工作，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/8346800/