Output all colors of an image in a file

compile.bat

# Open a command prompt and type the following lines:
cd C:\type\the\path\to\the\folder\containing\the\cs\file
C:\Windows\Microsoft.NET\Framework\v3.5\csc.exe extract-colors.cs /reference:System.Drawing.dll
extract-colors.exe > result.txt

extract-colors.cs

using System;
using System.Drawing;
using System.Collections.Generic;

public static class Program
{
    public static void Main(string[] args)
    {

        // Create a set to store the colors
        var colors = new HashSet<Color>();

        // Load the image
        var image = new Bitmap(
            @"C:\image.png", 
            true
        );

        // Loop through the images pixels to get their color.
        for(var x=0; x<image.Width; x++)
        {
            for(var y=0; y<image.Height; y++)
            {
                var pixelColor = image.GetPixel(x, y);
                // add the color to the set of colors if it is not fully transparent
                if(pixelColor.A != 0)
                {
                    colors.Add(pixelColor);
                }
            }
        }

        // Loop through the colors and display them in the console
        foreach(var color in colors)
        {
            Console.WriteLine("#" + color.R.ToString("x2") + color.G.ToString("x2") + color.B.ToString("x2"));
        }

    }
}