reading a UPC barcode from an image - c

Question

i need some guidance on how to get a 12 digit barcode from a bmp file, i'm completely clueless on how approach this.
i started by reading the image into a bitmam, how can i continue?
example: the barcode of the image below is 081034489030.
how to i get these numbers?
void part1() {
int width, height;
unsigned char ** img = NULL;
img = readBMP("package.bmp", &height, &width);
}
unsigned char** readBMP(char* filename, int* height_r, int* width_r)
{
int i, j;
FILE* f;
fopen_s(&f,filename, "rb");
unsigned char info[54];
fread(info, sizeof(unsigned char), 54, f); // read the 54-byte header
// extract image height and width
//from header
int width = *(int*)&info[18];
int height = *(int*)&info[22];
int pad_needed = 4 - (3 * width) % 4; // pad calculation
int paddedRow = 3 * width + ((pad_needed != 4) ? pad_needed : 0);
unsigned char** map2d = (unsigned char**)malloc(width * sizeof(unsigned
char*)); // alocate memory for img 2d array
for (i = 0; i < width; i++) {
map2d[i] = (unsigned char*)malloc(height * sizeof(unsigned char));
}
unsigned char* data = (unsigned char*)malloc(paddedRow * sizeof(unsigned
char)); // allocate memory for each read from file
for (i = 0; i < height; i++) {
fread(data, sizeof(unsigned char), paddedRow, f); //read line from file
for (j = 0; j < width; j++) {
map2d[j][i] = (int)data[3 * j]; // insert data to map2d. jump 3,
//becasue we need only one value of the colors (RGB)
}
}
free(data);
fclose(f);
*width_r = width;
*height_r = height;
return map2d;
}

Answer 1

You need to apply computer vision techniques to:
Segment the barcode from the image
Decode the barcode information so that it can be further used in an application.
There is no single answer to this problem, and it will definitely not be a one-liner.
A way to start is by using a dedicated computer vision library like OpenCV. It will not only handle the image loading on your behalf, but enable you to apply advanced image processing algorithms on the loaded data. It supports C, Python, C#, so you should easily find the version that matches your language of choice.
Once OpenCV is added to your project, it is time to solve point number 1. A good algorithm to start from is described Detecting Barcodes in Images with Python and OpenCV. Don't get distracted by the use of Python, the same OpenCV functions are available in C as well, the idea is to understand the algorithm.
Assuming you now have a working segmentation algorithm, the last step is to decode the barcode itself. Here I would suggest Parts 2 and 3 of this article as a starting point. There are also pre-built libraries (if you Google, there are plenty of UPC decoders written in Java or C# like this one), so with a bit of digging you may be able to find an out-of-the-box solution.
Hope this helps.