Programming

Hi,

How to decode an image using openGL library libjpeg ..
which are the steps needed to do this using C language..
actually my work is to decode the image, store it on the buffer,
and place it on cube surface..

please guide me,,any answer will appreciated ..

Here is one way of finding source code examples of how to use libjpeg to decode a JPEG image.

Hi,

Thank you so much for your help.. it helps me a lot..
as i am new to openGL. i dont know whether it is a basic question which i am asking know.
the question is :

The program jpeg_sample.c which is there in tar file is executing with out any error ..
i think decompression is done well ,,
but its not displaying any JPEG image after execution ...

Could you tell how to display jpeg image after decoding in openGL

and i am not getting from where it is taking an jpeg image in that code ..

Please guide me , any answer will appreciated..

We cannot see the source code from here.

Given that you do not appear to much experience with the concept of textures in OpenGL, maybe you should use an image library such as DevIL.

Here is a tutorial on DevIL. It includes an example of how to load and display a JPEG using OpenGL.

Hi,

The source code is:

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


unsigned char *raw_image = NULL;

int width = 2000;
int height = 1300;
int bytes_per_pixel = 3;
int color_space = JCS_RGB;



int read_jpeg_file( char *filename )
{

struct jpeg_decompress_struct cinfo;
struct jpeg_error_mgr jerr;



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;
}

cinfo.err = jpeg_std_error( &jerr );

jpeg_create_decompress( &cinfo );

jpeg_stdio_src( &cinfo, infile );

jpeg_read_header( &cinfo, TRUE );


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 );


jpeg_start_decompress( &cinfo );


raw_image = (unsigned char*)malloc( cinfo.output_width*cinfo.output_height*cinfo.num_components );

row_pointer[0] = (unsigned char *)malloc( cinfo.output_width*cinfo.num_components );

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];
}

jpeg_finish_decompress( &cinfo );
jpeg_destroy_decompress( &cinfo );
free( row_pointer[0] );
fclose( infile );

return 1;
}


int write_jpeg_file( char *filename )
{
struct jpeg_compress_struct cinfo;
struct jpeg_error_mgr jerr;


JSAMPROW row_pointer[1];
FILE *outfile = fopen( filename, "wb" );

if ( !outfile )
{
printf("Error opening output jpeg file %s\n!", filename );
return -1;
}
cinfo.err = jpeg_std_error( &jerr );
jpeg_create_compress(&cinfo);
jpeg_stdio_dest(&cinfo, outfile);


cinfo.image_width = width;
cinfo.image_height = height;
cinfo.input_components = bytes_per_pixel;
cinfo.in_color_space = color_space;

jpeg_set_defaults( &cinfo );

jpeg_start_compress( &cinfo, TRUE );

while( cinfo.next_scanline < cinfo.image_height )
{
row_pointer[0] = &raw_image[ cinfo.next_scanline * cinfo.image_width * cinfo.input_components];
jpeg_write_scanlines( &cinfo, row_pointer, 1 );
}

jpeg_finish_compress( &cinfo );
jpeg_destroy_compress( &cinfo );
fclose( outfile );

return 1;
}

int main()
{
char *infilename = "rro1.bmp", *outfilename = "rr.jpg";



if( read_jpeg_file( infilename ) > 0 )
{

if( write_jpeg_file( outfilename ) < 0 ) return -1;
}
else return -1;



return 0;
}



This code is working without any error message. but Displayed image is not decompressed .. Image is not a clear picture after decompressed ..
i need to display a decompressed JPEG image at the out put..

Please help me out with this problem,,,any answer will appreciated ..

Hi,

Sorry for late reply , i got the result of decompressed image, but now i need to insert images on Cylinder surfaces.

Please Help me out ...answer will appreciated ...