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 = "mort";
            String in = "images/";
            String out = "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
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 = "images/"; // location of images
    private final String outDir = "images/tmp/";  // location of created files
    private String inFile;
    private String resizedFile;
    private String asciiFile;
    private String grayScaledFile;
    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) {
        }

        // Changing to go by blocks 2 times as wide as tall
        for (int i = 0; i < img.getHeight(); i+=2) {
            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) {
            }
        }
    }

    // Gray scale method
    public void GrayScale() {
        BufferedImage img = null;
        // Reading file
        try {
            img = ImageIO.read(new File(this.inFile));
        } catch (IOException e) {
        }
        // Iterating through all pixels
        for (int i = 0; i<this.height; i++) {
            for (int j = 0; j<this.width; j++) {
                // For each pixel, getting RGB contents
                int pixel = img.getRGB(j, i);
                // Creating color object out of RGB contents for easy extraction
                Color color = new Color(pixel, true);
                // Using color object's methods to get the R, G, and B values for the pixel
                int red = color.getRed();
                int green = color.getGreen();
                int blue = color.getBlue();
                
                // Averaging R, G, and B
                int avg = (red+green+blue)/3;
                
                // Creating a new color object which has R=G=B=average
                // This is because the average will be a shade of gray
                Color colorGray = new Color(avg, avg, avg);

                // Setting the pixel's actual RGB content in the image to be the grayscaled version.
                img.setRGB(j, i, colorGray.getRGB());
            }
        }
        // Writing the image out
        try{
            ImageIO.write(img, "png", new File("images/tmp/" + "graymort" + ".png") );
          }catch(IOException e){
            System.out.println(e);
          }
    }


    public void GreenScale() {
        BufferedImage img = null;
        // Reading file
        try {
            img = ImageIO.read(new File(this.inFile));
        } catch (IOException e) {
        }
        // Iterating through all pixels
        for (int i = 0; i<this.height; i++) {
            for (int j = 0; j<this.width; j++) {
                // For each pixel, getting RGB contents
                int pixel = img.getRGB(j, i);
                // Creating color object out of RGB contents for easy extraction
                Color color = new Color(pixel, true);
                // Using color object's methods to get the R, G, and B values for the pixel
                int red = color.getRed();
                int green = color.getGreen();
                int blue = color.getBlue();
                
                // Averaging R, G, and B
                int avg = (green)/3;
                
                // Creating a new color object which has R=G=B=average
                // This is because the average will be a shade of gray
                Color colorGreen = new Color(avg, green, avg);

                // Setting the pixel's actual RGB content in the image to be the grayscaled version.
                img.setRGB(j, i, colorGreen.getRGB());
            }
        }
        // Writing the image out
        try{
            ImageIO.write(img, "png", new File("images/tmp/" + "greenmort" + ".png") );
          }catch(IOException e){
            System.out.println(e);
          }
    }


    public void RedScale() {
        BufferedImage img = null;
        // Reading file
        try {
            img = ImageIO.read(new File(this.inFile));
        } catch (IOException e) {
        }
        // Iterating through all pixels
        for (int i = 0; i<this.height; i++) {
            for (int j = 0; j<this.width; j++) {
                // For each pixel, getting RGB contents
                int pixel = img.getRGB(j, i);
                // Creating color object out of RGB contents for easy extraction
                Color color = new Color(pixel, true);
                // Using color object's methods to get the R, G, and B values for the pixel
                int red = color.getRed();
                int green = color.getGreen();
                int blue = color.getBlue();
                
                // Averaging R, G, and B
                int avg = (red)/3;
                
                // Creating a new color object which has R=G=B=average
                // This is because the average will be a shade of gray
                Color colorRed = new Color(red, avg, avg);

                // Setting the pixel's actual RGB content in the image to be the grayscaled version.
                img.setRGB(j, i, colorRed.getRGB());
            }
        }
        // Writing the image out
        try{
            ImageIO.write(img, "png", new File("images/tmp/" + "redmort" + ".png") );
          }catch(IOException e){
            System.out.println(e);
          }
    }


    public void BlueScale() {
        BufferedImage img = null;
        // Reading file
        try {
            img = ImageIO.read(new File(this.inFile));
        } catch (IOException e) {
        }
        // Iterating through all pixels
        for (int i = 0; i<this.height; i++) {
            for (int j = 0; j<this.width; j++) {
                // For each pixel, getting RGB contents
                int pixel = img.getRGB(j, i);
                // Creating color object out of RGB contents for easy extraction
                Color color = new Color(pixel, true);
                // Using color object's methods to get the R, G, and B values for the pixel
                int red = color.getRed();
                int green = color.getGreen();
                int blue = color.getBlue();
                
                // Averaging R, G, and B
                int avg = (blue)/3;
                
                // Creating a new color object which has R=G=B=average
                // This is because the average will be a shade of gray
                Color colorBlue = new Color(avg, avg, blue);

                // Setting the pixel's actual RGB content in the image to be the grayscaled version.
                img.setRGB(j, i, colorBlue.getRGB());
            }
        }
        // Writing the image out
        try{
            ImageIO.write(img, "png", new File("images/tmp/" + "bluemort" + ".png") );
          }catch(IOException e){
            System.out.println(e);
          }
    }


    // 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 mort = new Pics("mort", "png");
        mort.GrayScale();
        mort.GreenScale();
        mort.RedScale();
        mort.BlueScale();
        mort.printStats("Original");
        mort.resize(33);
        mort.printStats("Scaled");
        mort.convertToAscii();


    }
}
Pics.main(null);
Original: 621907 627x622  images/mort.png
Scaled: 122492 207x205  images/tmp/mort.png

redmort bluemort graymort greenmort mort