Read RGB values from PNG in C++

Question

Basically, what I am trying to is learn how to open an image manually WITHOUT LIBRARIES and see the RGB contents.

I want to do this so I can calculate the Hue and Saturation of the RGB to write back a 2D array image.

So far I have got this:

#include <iostream>
#include <stdio.h>      /* printf */
#include <math.h>       /* acos */
#include <fstream>      /* for file I/O */

using namespace std;

int main() {
        FILE* fp = NULL;
        fp = fopen("soccerball.png", "rb");
        cout << "done" << endl;
        return 0;
}

I know it is not much, as I'm used to Python more. But I honestly don't know where to start. And there are literally no examples of this it seems on the internet.

So I read an image. Now I want something like:

img[Height][width]

so I can get

img_r[h][w], img_g[h][w], img_b[h][w]

So I can use those values to calculate a Hue 2d array in same format.

img_hue[h][w]

Thanks

Solution

You can't easily open a PNG file without libraries.

Here is sample of opening a PNG WITH a library... and it's already a lot of code http://zarb.org/~gc/html/libpng.html

The thing is that PNG is compressed format. There's a lot of "mathemagics" happening to compress the RGB values into the special format.

A .BMP (Windows bitmap for example) is a very easy way for you to start parsing manually, if you are doing this for training, but other formats you need a library.

Of couse, you CAN do everything from scratch... but will take a while and by the question you did, you are a little far from it.