Saving PNG to GIF

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

public class ImageIOTest {    

    public static void main(String[] args){
       BufferedImage img = null;  // buffer type 
        try {
            // Name of file and directories
            String name = "monalisa";
            String in = "ghtop_images/";
            String out = "ghtop_images/tmp/";

            // Either use URL or File for reading image using ImageIO
            File imageFile = new File(in + name + ".png");
            img = ImageIO.read(imageFile);  // set buffer of image data

            // ImageIO Image write to gif in Java
            // Documentation https://docs.oracle.com/javase/tutorial/2d/images/index.html
            ImageIO.write(img, "gif", new File(out + name + ".gif") );  // write buffer to gif

        } catch (IOException e) {
              e.printStackTrace();
        }
        System.out.println("Success");
    }
}
ImageIOTest.main(null);
Success

Scaling Images and Converting to ASCII

import java.awt.Color;
import java.awt.image.BufferedImage;
import java.awt.Image;
import java.awt.Graphics2D;

import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

import javax.imageio.stream.ImageOutputStream;
import javax.imageio.stream.ImageInputStream;
import javax.imageio.metadata.IIOMetadata;
import javax.imageio.IIOImage;
import javax.imageio.ImageIO;
import javax.imageio.ImageWriteParam;
import javax.imageio.ImageWriter;
import javax.imageio.ImageReader;
import javax.imageio.ImageTypeSpecifier;

public class Pics {
    private final String inDir = "ghtop_images/"; // location of images
    private final String outDir = "ghtop_images/tmp/";  // location of created files
    private String inFile;
    private String resizedFile;
    private String asciiFile;
    private String ext;   // extension of file
    private long bytes;
    private int width;
    private int height;

    // Constructor obtains attributes of picture
    public Pics(String name, String ext) {
        this.ext = ext;
        this.inFile = this.inDir + name + "." + ext;
        this.resizedFile = this.outDir + name + "." + ext;
        this.asciiFile = this.outDir + name + ".txt";
        this.setStats();
    }

    
    // An image contains metadata, namely size, width, and height
    public void setStats() {
        BufferedImage img;
        try {
            Path path = Paths.get(this.inFile);
            this.bytes = Files.size(path);
            img = ImageIO.read(new File(this.inFile));
            this.width = img.getWidth();
            this.height = img.getHeight();
        } catch (IOException e) {
        }
    }

    // Console print of data
    public void printStats(String msg) {
        System.out.println(msg + ": " + this.bytes + " " + this.width + "x" + this.height + "  " + this.inFile);
    }

    // Convert scaled image into buffered image
    public static BufferedImage convertToBufferedImage(Image img) {

        // Create a buffered image with transparency
        BufferedImage bi = new BufferedImage(
                img.getWidth(null), img.getHeight(null),
                BufferedImage.TYPE_INT_ARGB);

        // magic?
        Graphics2D graphics2D = bi.createGraphics();
        graphics2D.drawImage(img, 0, 0, null);
        graphics2D.dispose();

        return bi;
    }
    
    // Scale or reduce to "scale" percentage provided
    public void resize(int scale) {
        BufferedImage img = null;
        Image resizedImg = null;  

        int width = (int) (this.width * (scale/100.0) + 0.5);
        int height = (int) (this.height * (scale/100.0) + 0.5);

        try {
            // read an image to BufferedImage for processing
            img = ImageIO.read(new File(this.inFile));  // set buffer of image data
            // create a new BufferedImage for drawing
            resizedImg = img.getScaledInstance(width, height, Image.SCALE_SMOOTH);
        } catch (IOException e) {
            return;
        }

        try {
            ImageIO.write(convertToBufferedImage(resizedImg), this.ext, new File(resizedFile));
        } catch (IOException e) {
            return;
        }
        
        this.inFile = this.resizedFile;  // use scaled file vs original file in Class
        this.setStats();
    }
    
    // convert every pixel to an ascii character (ratio does not seem correct)
    public void convertToAscii() {
        BufferedImage img = null;
        PrintWriter asciiPrt = null;
        FileWriter asciiWrt = null;

        try {
            File file = new File(this.asciiFile);
            Files.deleteIfExists(file.toPath()); 
        } catch (IOException e) {
            System.out.println("Delete File error: " + e);
        }

        try {
            asciiPrt = new PrintWriter(asciiWrt = new FileWriter(this.asciiFile, true));
        } catch (IOException e) {
            System.out.println("ASCII out file create error: " + e);
        }

        try {
            img = ImageIO.read(new File(this.inFile));
        } catch (IOException e) {
        }

        for (int i = 0; i < img.getHeight(); i++) {
            for (int j = 0; j < img.getWidth(); j++) {
                Color col = new Color(img.getRGB(j, i));
                double pixVal = (((col.getRed() * 0.30) + (col.getBlue() * 0.59) + (col
                        .getGreen() * 0.11)));
                try {
                    asciiPrt.print(asciiChar(pixVal));
                    asciiPrt.flush();
                    asciiWrt.flush();
                } catch (Exception ex) {
                }
            }
            try {
                asciiPrt.println("");
                asciiPrt.flush();
                asciiWrt.flush();
            } catch (Exception ex) {
            }
        }
    }

    // conversion table, there may be better out there ie https://www.billmongan.com/Ursinus-CS173-Fall2020/Labs/ASCIIArt
    public String asciiChar(double g) {
        String str = " ";
        if (g >= 240) {
            str = " ";
        } else if (g >= 210) {
            str = ".";
        } else if (g >= 190) {
            str = "*";
        } else if (g >= 170) {
            str = "+";
        } else if (g >= 120) {
            str = "^";
        } else if (g >= 110) {
            str = "&";
        } else if (g >= 80) {
            str = "8";
        } else if (g >= 60) {
            str = "#";
        } else {
            str = "@";
        }
        return str;
    }

    // tester/driver
    public static void main(String[] args) throws IOException {
        Pics monaLisa = new Pics("monalisa", "png");
        monaLisa.printStats("Original");
        monaLisa.resize(33);
        monaLisa.printStats("Scaled");
        monaLisa.convertToAscii();
    }
}
Pics.main(null);
Original: 3299776 1470x1530  ghtop_images/monalisa.png
Scaled: 470918 485x505  ghtop_images/tmp/monalisa.png

Grayscale Hacks

package _notebooks;

import java.awt.Color;
import java.awt.image.BufferedImage;

import java.io.File;
import java.io.IOException;
import java.nio.file.Files;

import javax.imageio.ImageIO;

public class ColorScale extends ImageData {
    
    public ColorScale(String name, String color, String ext) {
        super(name, ext);
        this.colorFile = this.outDir + name + color + ".png";
    }

    public ColorScale(String name, String color) {
        super(name, color);
        this.colorFile = this.outDir + name + color + ".png";
    }

    @Override //child class method is over-writing its base class method.
    protected void scale(String color) {
        BufferedImage img = null;
        PrintWriter asciiPrt = null;
        FileWriter asciiWrt = null;
        Color col = null;
        
        
        // Deletes previously named file if exists 
        try {
            File file = new File(this.colorFile);
            Files.deleteIfExists(file.toPath()); 
        } catch (IOException e) {
            System.out.println("Delete File error: " + e);
        }

        try {
            img = ImageIO.read(new File(this.inFile));
        } catch (IOException e) {
            e.printStackTrace();
        }

        if (color.equals("Gray")){
            for (int i = 0; i < this.height; i++){
                for (int j = 0; j < this.width; j++){
                    Color col = new Color(img.getRGB(j,i));
                    img.setRGB(j, i, rgb);
                }
            }
        }

        if(color.equals("ASCII")){
            final int XLENGTH = 1;
            final int YLENGTH = 2;

            for (int i = 0; i < img.getHeight(); i += 4) {
                for (int j = 0; j < img.getWidth(); j += 2) {
                    double colorSum = 0;
                    int counter = 0;
    
                    for (int k = 0; k < XLENGTH; k++) {
                        for (int l = 0; l < YLENGTH; l++) {
                            if (k < img.getWidth() && l < img.getHeight()) {
                                counter++;
                                col = new Color(img.getRGB(j + k, i + l));  
                            }
                        }
                    }
    
                    double average = colorSum / counter;
                    try {
                        asciiPrt.print(asciiChar(average));
                        asciiPrt.flush();
                        asciiWrt.flush();
                    } catch (Exception ex) {
                    }
    
                }

        }



        try {
            ImageIO.write(img, "png", new File(this.colorFile) );
        } catch (IOException e) {
            e.printStackTrace();
        }

        
    }
// changes the cake regular png into a grayscale version of the photo
    public static void main(String[] args) {
        ColorScale cake = new ColorScale("cake", "png");
        BlueSunset.scale("Gray");
    }

}