[英]Segmentation fault when saving a JPEG file (from an array of RGB data)
I find the follow code on internet for read and write a JPEG file using the library libjpeg . 我在网上找到以下代码,用于使用libjpeg库读取和写入JPEG文件。
I changed the function v oid write_JPEG_file (char * filename, int quality)
to the following: 我将函数oid write_JPEG_file (char * filename, int quality)
更改为以下内容:
void write_JPEG_vetor (JSAMPLE * image_data, int height, int width, int quality)
{
printf("%s\n","write_JPEG_vetor");
/* 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 */
printf ("%s\n","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);
printf ("%s\n","/* 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.
*/
char * filename = {"novo_arquivo.jpeg"};
if ((outfile = fopen(filename, "wb")) == NULL) {
fprintf(stderr, "can't open %s\n", filename);
exit(1);
}
jpeg_stdio_dest(&cinfo, outfile);
printf ("%s\n","/* 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 = width; /* image width and height, in pixels */
cinfo.image_height = height;
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 */);
printf ("%s\n","/* 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);
printf ("%s\n","/* 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 = width * 3; /* JSAMPLEs per row in image_buffer */
while (cinfo.next_scanline < cinfo.image_height) {
printf ("%s\n","Loop WHILE");
/* 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_data[cinfo.next_scanline * row_stride];
(void) jpeg_write_scanlines(&cinfo, row_pointer, row_stride);
}
printf ("%s\n","/* Step 6: Finish compression */");
jpeg_finish_compress(&cinfo);
/* After finish_compress, we can close the output file. */
fclose(outfile);
printf ("%s\n","/* 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! */
}
Now, when I run the program (in a Linux enviroment), I am receiving an error Segmentation Fault. 现在,当我在Linux环境中运行该程序时,出现了错误Segmentation Fault。 Someone can tell why this is happening? 有人可以说出为什么会这样吗? My main suspect is the code: 我主要的怀疑是代码:
while (cinfo.next_scanline < cinfo.image_height) {
printf ("%s\n","Loop WHILE");
/* 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_data[cinfo.next_scanline * row_stride];
(void) jpeg_write_scanlines(&cinfo, row_pointer, row_stride);
}
but i'm not sure about that, and can't find a solution to solve this, despite spend a good time trying. 但是我不确定,尽管花了很多时间,也找不到解决方案。
=== UPDATE === I included the follow debugging code in this part of the code: ===更新===我在代码的这一部分中包含以下调试代码:
while (cinfo.next_scanline < cinfo.image_height) {
printf ("%s\n","Loop WHILE");
/* 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.
*/
printf ("%s\n","parte 1.1");
row_pointer[0] = &image_data[cinfo.next_scanline * row_stride];
printf ("%s\n","parte 1.2");
printf ("%s\n","parte 2.1");
(void) jpeg_write_scanlines(&cinfo, row_pointer, 1);
printf ("%s\n","parte 2.2");
}
And this way the output when running the programa is: 这样,运行programa时的输出为:
Loop WHILE
parte 1.1
parte 1.2
parte 2.1
=== UPDATE 2 === For the record, in my program, this function is receiving the return value of this function: ===更新2 ===记录一下,在我的程序中,此函数正在接收此函数的返回值:
JSAMPLE * inverte_imagem()
{
int tamanho = image_height*image_width*image_colors;
int i;
JSAMPLE * vetor = malloc(sizeof(JSAMPLE)*(image_height*image_width*image_colors));
for( i=0; i<tamanho; i++)
vetor [i] = image_buffer [tamanho - (i+1)];
}
This looks wrong: 这看起来是错误的:
(void) jpeg_write_scanlines(&cinfo, row_pointer, row_stride);
That last parameter is the number of lines to write, not the row length. 最后一个参数是要写入的行数,而不是行长。 You probably want: 您可能想要:
(void) jpeg_write_scanlines(&cinfo, row_pointer, 1);
OK, I solve the problem putting the call for write_JPEG_vector inside the function inverte_imagem(). 好的,我解决了将对write_JPEG_vector的调用放在函数inverte_imagem()中的问题。 I don't know why, but when I make the call to this function from my main function, a memory problem (error segmentation fault on linux) occurs. 我不知道为什么,但是当我从主函数调用此函数时,发生了内存问题(Linux上的错误分段错误)。
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