Image Processing in Java: Libraries and Code Examples

Working with Images in Java: Complete Overview of Libraries and Tools

Java provides powerful tools for working with raster images — from simple loading and saving to complex processing using filters and neural networks. In this article, we will cover three main approaches: the built-in Java 2D library, the specialized ImageJ, and the industry standard OpenCV. You will learn how to choose the right tool and see working code examples.

1. Built-in Java 2D Library (javax.imageio, java.awt)

Java 2D is part of the standard Java library (JDK). It requires no additional dependencies and is ideal for basic operations: loading, resizing, cropping, text overlay, and simple filters.

Main Classes:

• javax.imageio.ImageIO — reading and writing images (PNG, JPEG, BMP, GIF, WBMP).
• java.awt.image.BufferedImage — in-memory image representation with pixel access.
• java.awt.Graphics2D — drawing context (scaling, rotation, overlay).
• java.awt.image.BufferedImageOp — interface for filters (blur, contrast, color correction).

Example 1: Loading, Resizing, and Saving

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

public class ImageResizer {    public static void main(String[] args) throws IOException {        // Load the original image        BufferedImage original = ImageIO.read(new File("input.jpg"));

        // New dimensions (e.g., resize to 300x200)        int newWidth = 300;        int newHeight = 200;

        // Create a new image with the desired dimensions        BufferedImage resized = new BufferedImage(newWidth, newHeight, BufferedImage.TYPE_INT_RGB);        Graphics2D g2d = resized.createGraphics();

        // Draw the original image with scaling        g2d.drawImage(original, 0, 0, newWidth, newHeight, null);        g2d.dispose();

        // Save the result        ImageIO.write(resized, "jpg", new File("output.jpg"));        System.out.println("Done! Size changed.");    }}

Example 2: Applying a Built-in Filter (Blur)

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

public class BlurFilter {    public static void main(String[] args) throws Exception {        BufferedImage img = ImageIO.read(new File("input.jpg"));

        // 3x3 blur kernel (box blur)        float[] blurKernel = {            1f/9f, 1f/9f, 1f/9f,            1f/9f, 1f/9f, 1f/9f,            1f/9f, 1f/9f, 1f/9f        };        Kernel kernel = new Kernel(3, 3, blurKernel);        ConvolveOp convolve = new ConvolveOp(kernel, ConvolveOp.EDGE_NO_OP, null);        BufferedImage blurred = convolve.filter(img, null);

        ImageIO.write(blurred, "jpg", new File("blurred.jpg"));    }}

2. ImageJ Library — for Scientific and Medical Images

ImageJ is a popular image processing tool originally written in Java. It provides hundreds of ready-made plugins, macros, and a powerful API. It is well-suited for microscopy analysis, satellite imagery, and any tasks requiring pixel statistics.

Dependency (Maven):

<dependency>    <groupId>net.imagej</groupId>    <artifactId>ij</artifactId>    <version>1.53t</version></dependency>

Example: Histogram Analysis and Thresholding

import ij.IJ;import ij.ImagePlus;import ij.