Thread: how to save pixel values of a Image in a matrix?

hello guys.
I want to have a algo or c-program that can save image pixel values in a matrix similar like we do in MATLAB
I have a bmp image which black and white only that its pixel values is only 0 or 255 (black or white)
Now I want to save all that pixel values in a 2D matrix in a c-program
so, is there any way to this?
I used Cimg and imagemagick they are very slow.

But my cprogram not reading it.. some type of compression or encryption is used i think. i was using FILE pointer in my cprogram but it doesn't help

so is there any solution u come on?

okeh I am using Ubuntu 14 and gcc compiler. Following is the code:

Code:

main()
{
char ch;
FILE *f;
f=fopen("image.bmp","r");
while((ch=fgetc(f))!=EOF)
{
printf("%c",ch);
}
fclose(f);
}

following is the image that i am using to read:

This is the output i get:
BM6($"
X ������������������������NNN ������}}}��

BMP files are binary, so trying to read and print them as text will not work. I suggest you use "fread()" instead, and for printing, use hexadecimal so you can see the bytes.

If you read the link Salem posted in post #2, you will notice that there is header information in the file before the pixel data. The header contains important information about the image data.

I suggest you first try to understand the file format, then plan the variables you need in order to store the header information. Once you get that working, you can then start planning how to store the pixel data.

okeh thanks Matticus.. But I still do not understand u.. i dont know how to know or read file headers and then u said use hexadecimal, did u mean by %p ??

A binary file is a collection of bytes. What these bytes represent depend upon the definition of the file format. For a BMP file, the first group of bytes (what we call the header) represent information about the image. How many bytes and what they mean are defined as described in the wiki link above.

Here's an analogy. Let's say you have a series of letters: G, Y, R, G, Y, R, G, Y, R.

Without any context, these letters have no discernable meaning.

But if I were to say, "these letters represent the states of a traffic light", then those letters now have meaning (the light starts on Green, goes to Yellow, then to Red, then back to Green, and so on), since a context was defined.

It's the same with a binary file. What the bytes represent depend upon the context in which they're read.

---

"%x" is used for printing hex. This probably isn't necessary, but I personally find it easier to read hex values when working with binary.

Code:

#include <stdio.h>

#define BYTES 8

int main(void)
{
    unsigned char byte[BYTES] = { 0x10, 0x0A, 0xFF, 0x00, 0x35, 0xC8, 0xEF, 0x77 };
    int i;

    printf("Hex  Dec\n\n");

    for(i = 0; i < BYTES; i++)
        printf("%02X = %3d\n", byte[i], byte[i]);

    return 0;
}

Thanks Mr. Matticus you are very helpful to me.
Do you know any better explanation of file headers of different images other than wikipedia. It is very difficult to understand on wikipedia.

It takes some deliberate study to understand some file formats. I wrote a simple BMP "library" once for fun, and had to take a fair bit of notes before I got my head around the file format and how the data worked together. That is programming though - breaking down a problem into smaller pieces that are easy to understand (be it code or concepts).

You can try doing a search for "bmp tutorial", but be warned: a lot of the examples I found were pretty bad. But maybe you can find explanations that will help you understand the file format better.