Load an image to a GSL matrix - c

Question

Does anyone know about some function that loads a grayscale image into a GSL matrix?
Something like:
gsl_matrix *M;
load_image("./image.jpg", M); // any image extension would also be fine

Answer 1

Something like this works on my PC: allows you to load a grayscale JPG image using libjpeg.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <jpeglib.h>
#include <gsl/gsl_matrix.h>
gsl_matrix *load_jpg_image(const char *pFileName)
{
FILE *pFile;
long jpegSize;
unsigned char *pJpegBytes, *pPixels;
struct jpeg_decompress_struct cinfo;
struct jpeg_error_mgr jerr;
int status, w, h, numComponents, stride, x, y;
gsl_matrix *pMatrix;
pFile = fopen(pFileName, "rb");
if (!pFile)
{
fprintf(stderr, "Can't open file\n");
return NULL;
}
// Get the size of the file
fseek(pFile, 0, SEEK_END);
jpegSize = ftell(pFile);
rewind(pFile);
if (jpegSize == 0)
{
fclose(pFile);
fprintf(stderr, "Empty file\n");
return NULL;
}
// Read it into memory and close file
pJpegBytes = (unsigned char *)malloc(jpegSize);
fread(pJpegBytes, 1, jpegSize, pFile);
fclose(pFile);
// Jpeg decompression starts here
memset(&cinfo, 0, sizeof(struct jpeg_decompress_struct));
cinfo.err = jpeg_std_error(&jerr);
jpeg_create_decompress(&cinfo);
jpeg_mem_src(&cinfo, pJpegBytes, jpegSize);
status = jpeg_read_header(&cinfo, TRUE);
if (status != 1)
{
free(pJpegBytes);
fprintf(stderr, "Invalid JPEG header\n");
return NULL;
}
jpeg_start_decompress(&cinfo);
w = cinfo.output_width;
h = cinfo.output_height;
numComponents = cinfo.output_components;
if (numComponents != 1)
{
free(pJpegBytes);
fprintf(stderr, "Can only handle 1 color component\n");
return NULL;
}
pPixels = (unsigned char *)malloc(w*h);
stride = w*numComponents;
// perhaps this can de done much faster by processing
// multiple lines at once
while (cinfo.output_scanline < cinfo.output_height)
{
unsigned char *buffer_array[1];
buffer_array[0] = pPixels + cinfo.output_scanline * stride;
jpeg_read_scanlines(&cinfo, buffer_array, 1);
}
jpeg_finish_decompress(&cinfo);
jpeg_destroy_decompress(&cinfo);
free(pJpegBytes);
// Now, create and fill in the matrix
pMatrix = gsl_matrix_alloc(h, w);
for (y = 0 ; y < h ; y++)
for (x = 0 ; x < w ; x++)
gsl_matrix_set(pMatrix, y, x, pPixels[x+y*stride]);
return pMatrix;
}
int main(void)
{
gsl_matrix *pMatrix;
int rows, cols;
int i, j;
pMatrix = load_jpg_image("test.jpg");
if (pMatrix == NULL)
{
fprintf(stderr, "Can't load matrix\n");
return -1;
}
//
// Use the matrix
//
gsl_matrix_free(pMatrix);
return 0;
}