Main.java

import javax.imageio.ImageIO;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.File;

public class Main {
    
    public static void main(String[] args) throws Exception{
        BufferedImage img = createImageWithID(255*3*3);
        System.out.println(getImageID(img));
        File outputfile = new File("C:\\Users\\stein\\Desktop\\encoded.png");
        ImageIO.write(img, "png", outputfile);
    }
    
    public static BufferedImage createImageWithID(int id){
        BufferedImage buffImg = new BufferedImage(300,300,BufferedImage.TYPE_INT_RGB);
        Graphics graphics = buffImg.getGraphics();
        graphics.setColor(Color.BLACK);
        graphics.fillRect(0,0,buffImg.getWidth(),buffImg.getHeight());
        graphics.setColor(Color.BLACK);
        graphics.fillRect(0,0,buffImg.getWidth() / 5, buffImg.getWidth() / 5);
        drawBlock(graphics,id,1,0);
        return buffImg;
    }


    public static int drawBlock(Graphics g, int val, int x, int y){
        double width = 300;
        double pixelSize = width / 5;
        int valLeft = val;
        int red = 0, green = 0, blue = 0;

        for(int i = 0; i<valLeft; i++){
            if(blue < 255)
                blue++;
            else if(green < 255)
                green++;
            else if(red < 255)
                red++;
            else{
                if((x + 1) * pixelSize < width){
                    drawBlock(g, val - (255 * 3), x + 1, y);
                }
                else{
                    drawBlock(g,val - (255 * 3), 0, y + 1);
                }
                break;
            }
        }

        Color c = new Color(red,green,blue);
        g.setColor(c);
        g.fillRect((int)(x * pixelSize), (int)(y * pixelSize), (int)(pixelSize), (int)pixelSize);
        return 0;
    }

    public static int getImageID(BufferedImage img){
        int pixelSize = img.getWidth() / 5;
        int num = 0;
        for(int i = 0; i<5; i++){
            for(int j = 0; j<5; j++){
                int clr=  img.getRGB(i * pixelSize,j * pixelSize);
                int  red   = (clr & 0x00ff0000) >> 16;
                int  green = (clr & 0x0000ff00) >> 8;
                int  blue  =  clr & 0x000000ff;
                num+= red + green + blue;
            }
        }
        return num;
    }
}