How to read and write image files with Java

There is code in the Java standard runtime library to do loading and saving, but the range of functionality depends heavily on the Java version that you are using. If you cannot assume any Java versions because your code is supposed to run even with older Java virtual machines, there is nothing but loading GIF and JPEG files.

In addition quite a few third-party libraries exist. I've assembled a list of libraries to read and write pixel and vector image files. If you find Java code to read or write images that is not linked on that page, please tell me!

Some additional hints for picking a library—trying each and every one of them seems to be a rather time-consuming task.

First of all, think about the image file formats that your code must be able to understand. The libraries differ quite a bit in what they support. If you can decide yourself which formats to use in your application and if you are unclear on that topic, read tips on choosing a pixel image file format. Either way, once you know which formats you want to be able to read or write, you can hopefully eliminate quite a few entries from the above mentioned list. It mentions for each library which formats are read and written.
Avoid external libraries if you can. No need to add 3rd-party-code to your program if all you need is already in the standard runtime library.
- If you want to read JPEG and GIF files, java.awt.Toolkit has createImage methods which will do that for you (since Java 1.0). You might want to use a MediaTracker to make sure an image is loaded completely before continuing. I have written a small demo program that shows how to load images with Toolkit and MediaTracker.
- If you are using Swing, there is a convenient ImageIcon constructor that takes a file name as argument and does all the rest.
- If you can be sure that your application is run under Java 1.3 or higher, reading PNG files is supported by Toolkit as well.
- If you can assume that Java 1.4 is available, the javax.imageio hierarchy also lets you write PNG and JPEG. This program demonstrates how to write a BufferedImage to a PNG file with javax.imageio.ImageIO. Note that there is a bug with JPEG writing in javax.imageio which has been fixed since 1.4.1: bug 4415068 in the bug parade (developer connection login required).
- Since Java 1.5 you can assume reading and writing support for the following formats: JPEG, PNG, Microsoft Windows BMP and WBMP. In addition, reading GIF is supported as well.
- Some Sun JDKs / JREs version 1.2 and higher come with the package com.sun.image.codec.jpeg which lets you read and write JPEG files. Here is a sample program for writing JPEG files with this package.
Note that there are some unusual JPEG subtypes supported by ImageIO. Depending on which image pixel type you are using (e.g. TYPE_INT_RGBA) in your Java application, you may inadvertently create a JPEG file which is not properly read by quite a few other applications. There is a section in the ImageIO JPEG metadata documentation which covers this issue.
Sun's JIMI library deserves to be mentioned here as well. It is not a core library, but it can be used for free, is available from Sun and is written in pure 1.1 Java, so it should work for most Java developers. It reads and writes quite a few file formats. Download it from http://java.sun.com/products/jimi/.
Regard the license under which a certain library comes. You don't want to use GPL'd code in your closed-source commercial program. Make sure that you are allowed to use code that you found somewhere - just because you couldn't find information on that topic on the code's homepage or in the README doesn't mean that you're automatically allowed to use it.
Execution speed. The image loading code that is built into Toolkit typically uses native code for JPEG, PNG and GIF that is relatively fast. At least one of the libraries in my list also uses native code - you'll probably get a speed-up, but you are no longer platform-independent. If you have several choices for the file format you need, you may want to test if they are all sufficient when it comes to speed.
Make sure that the library you choose supports the subtype / file format flavor that you require. You will read often that library X supports format Y, and that's it. However, the more complicated file formats will not be supported fully in many cases. So, as an example, if you know that you need support for TIFF / LZW, make sure that the TIFF library that you pick really supports that. Similar points: support for a certain color depth, compression algorithm, transparency information, access of multiple images etc.

A note to readers who prefer German:

In der FAQ der deutschsprachigen Java-Newsgroup de.comp.lang.java gibt es auch einen Abschnitt zum Thema Laden und Speichern von Bildern (alternativ: http://www.faqs.org/faqs/de/comp-lang-java/faq/).