src_ImageDisplay.java

import javax.swing.*;
import java.awt.*;
import java.awt.image.BufferedImage;

public class ImageDisplay extends JFrame {
    private BufferedImage image;
    public ImageDisplay(BufferedImage image){
        this.image = image;
        setTitle("Image Display");
        setBounds(0,0,image.getWidth(),image.getHeight());
        setVisible(true);
    }
    @Override
    public void paint(Graphics graphics){
        graphics.drawImage(image,0,0, null);
    }
}

src_ImageModification.java

import javax.imageio.ImageIO;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.util.List;

public class ImageModification {
    public static BufferedImage grayScale(BufferedImage img){
        BufferedImage grayScale = new BufferedImage(img.getWidth(),img.getHeight(),img.getType());
        Graphics2D g = grayScale.createGraphics();
        for(int i = 0; i<img.getWidth(); i++){
            for(int j = 0; j<img.getHeight(); j++){
                int pixel = img.getRGB(i,j);
                int red = (pixel >> 16) & 0xff;
                int green = (pixel >> 8) & 0xff;
                int blue = (pixel) & 0xff;
                int rgb = (int)((red + green + blue) / 3.0);
                g.setColor(new Color(rgb,rgb,rgb));
                g.fillRect(i,j,1,1);
            }
        }
        return grayScale;
    }
    
    public static BufferedImage pixelize(BufferedImage image, int pixelSize){
        Graphics g = image.createGraphics();
        for(int x = 0; x<image.getWidth(); x+=pixelSize){
            for(int y = 0; y<image.getHeight();y+=pixelSize){
                double brightness = 0;
                for(int i = 0; i<pixelSize; i++){
                    for(int j = 0; j<pixelSize; j++){
                        if( i + x >= image.getWidth() || j + y >= image.getHeight() ) continue;
                        brightness += (image.getRGB(i + x, y + j) >> 16) & 0xff;
                    }
                }
                brightness /= pixelSize * pixelSize;
                Color color = new Color((int)brightness,(int)brightness,(int)brightness);
                g.setColor(color);
                g.fillRect(x,y,pixelSize,pixelSize);
            }
        }
        return image;
    }
    
    public static BufferedImage createDiceImage(BufferedImage pixelizedImage, int pixelSize, boolean invertColors, List<String> lines) throws Exception{
        BufferedImage one = ImageIO.read(ImageDisplay.class.getResource("images/1.png"));
        BufferedImage two = ImageIO.read(ImageDisplay.class.getResource("images/2.png"));
        BufferedImage three = ImageIO.read(ImageDisplay.class.getResource("images/3.png"));
        BufferedImage four = ImageIO.read(ImageDisplay.class.getResource("images/4.png"));
        BufferedImage five = ImageIO.read(ImageDisplay.class.getResource("images/5.png"));
        BufferedImage six = ImageIO.read(ImageDisplay.class.getResource("images/6.png"));

        double ratio = 122.0 / pixelSize;
        
        BufferedImage diceImage = new BufferedImage((int)(pixelizedImage.getWidth() * ratio), (int)(pixelizedImage.getHeight() * ratio), pixelizedImage.getType());
        Graphics diceGraphics = diceImage.createGraphics();
        for(int x = 0; x<pixelizedImage.getWidth(); x += pixelSize){
            String line = "";
            for(int y = 0; y<pixelizedImage.getHeight(); y += pixelSize){
                int brightness = (pixelizedImage.getRGB(x, y ) >> 16) & 0xff;
                if(invertColors){
                    if(brightness <= 42.5 * 1){
                        diceGraphics.drawImage(five,(int)(x * ratio), (int)(y * ratio), null);
                        line += "5 ";
                    }
                    else if(brightness <= 42.5 * 2){
                        diceGraphics.drawImage(six,(int)(x * ratio), (int)(y * ratio), null);
                        line += "6 ";
                    }
                    else if(brightness <= 42.5 * 3){
                        diceGraphics.drawImage(four,(int)(x * ratio), (int)(y * ratio), null);
                        line += "4 ";
                    }
                    else if(brightness <= 42.5 * 4){
                        diceGraphics.drawImage(three, (int)(x * ratio), (int)(y * ratio), null);
                        line += "3 ";
                    }
                    else if(brightness <= 42.5 * 5){
                        diceGraphics.drawImage(two,(int)(x * ratio), (int)(y * ratio), null);
                        line += "2 ";
                    }
                    else if(brightness <= 42.5 * 6){
                        diceGraphics.drawImage(one,(int)(x * ratio), (int)(y * ratio), null);
                        line += "1 ";
                    }
                }
                else {
                    if(brightness <= 42.5 * 1){
                        diceGraphics.drawImage(one,(int)(x * ratio), (int)(y * ratio), null);
                        line += "1 ";
                    }
                    else if(brightness <= 42.5 * 2){
                        diceGraphics.drawImage(two,(int)(x * ratio), (int)(y * ratio), null);
                        line += "2 ";
                    }
                    else if(brightness <= 42.5 * 3){
                        diceGraphics.drawImage(three,(int)(x * ratio), (int)(y * ratio), null);
                        line += "3 ";
                    }
                    else if(brightness <= 42.5 * 4){
                        diceGraphics.drawImage(four, (int)(x * ratio), (int)(y * ratio), null);
                        line += "4 ";
                    }
                    else if(brightness <= 42.5 * 5){
                        diceGraphics.drawImage(six,(int)(x * ratio), (int)(y * ratio), null);
                        line += "6 ";
                    }
                    else if(brightness <= 42.5 * 6){
                        diceGraphics.drawImage(five,(int)(x * ratio), (int)(y * ratio), null);
                        line += "5 ";
                    }
                }
            }
            lines.add(line);
        }
        return diceImage;
    }
}

src_Main.java

import javax.imageio.ImageIO;
import javax.swing.*;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.FileWriter;
import java.util.ArrayList;
import java.util.List;

public class Main {
    public static void main(String[] args) throws Exception{
        File imageFile = new File(JOptionPane.showInputDialog("Please enter the file path of the image:\nIMAGE WIDTH & HEIGHT MUST BE A MULTIPLE OF 7"));
        BufferedImage img = ImageIO.read(imageFile);
        new ImageDisplay(img);
        BufferedImage grayScale = ImageModification.grayScale(img);
        new ImageDisplay(grayScale);
        BufferedImage pixelizedImage = ImageModification.pixelize(grayScale,6);
        new ImageDisplay(pixelizedImage);
        List<String> lines = new ArrayList<>();
        BufferedImage diceScale = ImageModification.createDiceImage(pixelizedImage, 6, true, lines);
        String fileName  = imageFile.getParentFile().getAbsolutePath() + "\\DICE-IMAGE-" + System.currentTimeMillis();
                ImageIO.write(diceScale, "png", new File(fileName + ".png"));
        JOptionPane.showMessageDialog(null,"File has been exported...");
        FileWriter writer = new FileWriter(fileName + "-INSTRUCTIONS.txt");
        for(String str: lines) {
            writer.write(str + "\n");
        }
        writer.close();
        System.exit(0);
    }
}