Opening JPEG images.

Started by Axel November 01, 2000 12:30 PM

4 comments, last by Axel 24 years, 3 months ago

Author

122

November 01, 2000 12:30 PM

I have been given a project that includes a .rpc file. In the file is information about a JPEG image and the image itself. I can open this file and get all kinds of information about the image but I don''t know how to display the JPEG image itself. Please help, I have been working on this for over a month. Axel

Axel

rohar

122

November 01, 2000 04:12 PM

libjpeg from http://www.ijg.org/ will let you do what you want in a couple of function calls. I was messing around with it trying to get it to dump the rendering window, and it works really well. I think I will try and modify lesson 6 to read the texture from a jpeg, and post the results if I get it to work.

Anonymous

November 01, 2000 04:47 PM

Rohar,

When you modify what lesson 6 to work with JPEG can you forward me the changes in the code.

Axel

rohar

122

November 01, 2000 06:43 PM

this will prettymuch drop in for loadBMP, and load the texture from a jpeg. It works, but I didn't put alot of time into error checking, I will when I get a chance. There is a whack of info returned from the libjpeg library, which should be error checked for correctness....

You need to link with libjpeg.lib & have the headers. (I built my own libjpeg library from the source @ http://www.ijg.org/ for vc on win98, but it also works on my RH6.2 box with the included libjpeg library)
Make sure you use a 256x256x24 RGB JFIF jpeg... and you should be okey-dokey. (I just converted the NeHe bmp to a jpeg with no changes)
The dumb-assed looking math where I am swapping the buffer is because the image loads upside down. The row pointer array is because libjpeg needs a pointer array, and can return more than 1 line at a time... When I understand the library better, I think that the temp buffer can get turfed, and more than 1 line can be processed at a time. (array of pointers to the output buffer, and change them with each call to jpeg_read_scanlines)

The docs that come with libjpeg are pretty good.

If you don't mind... don't pick on my code, I did this from scratch in an hour and it even works

you'll need to wrap extern "C" { } around the c includes for vc

        #include <jpeglib.h>#include <jerror.h>/* simple loader for 24bit jpeg (data is in rgb-format) */int LoadJPEG(char *filename, textureImage *texture){    FILE *file;    struct jpeg_decompress_struct cinfo;    struct jpeg_error_mgr jerr;    volatile JSAMPROW row = 0;    JSAMPROW rowptr[1];    int i,j,nrows;    cinfo.err = jpeg_std_error(&jerr);    jpeg_create_decompress(&cinfo);    /* make sure the file is there and open it read-only (binary) */    if ((file = fopen(filename, "rb")) == NULL)    {        printf("File not found : %s\n", filename);        return 0;    }    jpeg_stdio_src(&cinfo, file);    jpeg_read_header(&cinfo, TRUE);    jpeg_start_decompress(&cinfo);    texture->width = cinfo.output_width;    texture->height = cinfo.output_height;    printf("Colorspace %d\n",cinfo.jpeg_color_space);	row = (JSAMPROW)calloc(1,cinfo.image_width * cinfo.output_components							* sizeof(JSAMPLE));		texture->data = malloc(cinfo.image_width * cinfo.image_height 			       * cinfo.output_components * sizeof(JSAMPLE));	rowptr[0] = row;    for (i = 0; i < cinfo.output_height; i++) {	nrows = jpeg_read_scanlines(&cinfo, rowptr, 1);	if (nrows != 1) {	    fprintf(stderr, "jpeg_read_scanlines"		    " returns %u, expected 1\n", nrows);	    return 0;	}	for (j = 0; j < cinfo.output_width*cinfo.output_components; j++)	    texture->data[(cinfo.output_height-1-i)*cinfo.output_width*cinfo.output_components+j] = row[j];    }        jpeg_finish_decompress(&cinfo);    jpeg_destroy_decompress(&cinfo);    free(row);       return 1;}

Edited by - rohar on November 1, 2000 7:48:28 PM

122

November 02, 2000 07:40 AM

rohar -> Thanks for your code...
But I couldn''t compile it... I done something wrong when I used it. The linker give me this messages:

"void __cdecl jpeg_destroy_decompress(struct jpeg_decompress_struct *)" (?jpeg_destroy_decompress@@YAXPAUjpeg_decompress_struct@@@Z)
"unsigned char __cdecl jpeg_finish_decompress(struct jpeg_decompress_struct *)" (?jpeg_finish_decompress@@YAEPAUjpeg_decompress_struct@@@Z)
"unsigned int __cdecl jpeg_read_scanlines(struct jpeg_decompress_struct *,unsigned char * *,unsigned int)" (?jpeg_read_scanlines@@YAIPAUjpeg_decompress_struct@@PAPAEI@Z)
"unsigned char __cdecl jpeg_start_decompress(struct jpeg_decompress_struct *)" (?jpeg_start_decompress@@YAEPAUjpeg_decompress_struct@@@Z)
"int __cdecl jpeg_read_header(struct jpeg_decompress_struct *,unsigned char)" (?jpeg_read_header@@YAHPAUjpeg_decompress_struct@@E@Z)
"void __cdecl jpeg_stdio_src(struct jpeg_decompress_struct *,struct _iobuf *)" (?jpeg_stdio_src@@YAXPAUjpeg_decompress_struct@@PAU_iobuf@@@Z)
"void __cdecl jpeg_CreateDecompress(struct jpeg_decompress_struct *,int,unsigned int)" (?jpeg_CreateDecompress@@YAXPAUjpeg_decompress_struct@@HI@Z)
"struct jpeg_error_mgr * __cdecl jpeg_std_error(struct jpeg_error_mgr *)" (?jpeg_std_error@@YAPAUjpeg_error_mgr@@PAU1@@Z)

Or short, the linker couldn''t find the stuff.
I used the Libjpeg.lib (wrong version??) but the linker couldn''t find the stuff.
Can you help me to solve this ''little'' problem?

Thanks

rohar

122

November 06, 2000 08:22 PM

The library is compiled without a extern "C" {...} when linked into c++.

You need to wrap extern "C" around the includes when you compile & link with vc++.

    extern "C"{#include <jpeglib.h>#include <jerror.h>}

This should really be in the jpeglib.h, but it isn't.

Edited by - rohar on November 6, 2000 9:23:39 PM

Opening JPEG images.

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