How to read and write images in Java

In this post, I will show you how to read and write image files in Java. I will demonstrate 2 different ways of doing this. The first is with the ImageIO, and the second is with our JDeli image library.

If you are just looking for an Image Viewer, JDeli includes a built-in Image Viewer.

How to read and write images in Java

Java provides a single type of object called a BufferedImage for images in Java.

A BufferedImage can be read from lots of different image types (ie BMP, HEIC, etc). Not all of these are supported by ImageIO itself but there are plugins to extend ImageIO, and other libraries such as Apache Imaging and JDeli.

In Java itself all the complexity of different image types is hidden – you work on a BufferedImage. Java allows direct access to the image pixels and colour information as well as allowing transformations and image processing.

Here is a list of how to read and write common Image file formats in Java.

How to read an image in Java with ImageIO

Step 1 Create a File handle, InputStream or URL pointing to the raw image.
Step 2 ImageIO will now be able to read an image file into a BufferedImage. This syntax is like so:

BufferedImage image = ImageIO.read(fileOrInputStreamOrURL)

How to read an image in Java with JDeli

Step 1 Add JDeli to your class or module path. (download the trial jar).
Step 2 Create a File, InputStream pointing to the raw image. You can also use a byte[] containing the image data.
Step 3 Read the image into a BufferedImage

BufferedImage image = JDeli.read(file);

How to write out an image in ImageIO

This example shows the exact settings for a PNG image.
Step 1 Create a File (or OutputStream) object

File file = new File("/path/to/outputFile.png"));

Step 2 Pass image, PNG type and File (or OutputStream) object into write method

ImageIO.write(bufferedImage, "PNG", file);

How to write out an image with JDeli

This example shows the exact settings for a PNG image.
Step 1 Add JDeli to your class or module path. (download link to the trial jar).

Step 2 Create a File (or OutputStream) object

File file = new File("/path/to/outputFile.png"));

Step 3 Pass image, PNG type and File (or OutputStream) object into write method

JDeli.write(bufferedImage, "PNG", file);

In JDeli you can also use a typesafe version

JDeli.write(bufferedImage, OutputFormat.PNG, file);

or pass in a PngEncoderOptions object for more control over image output.

PngEncoderOptions options = new PngEncoderOptions();
JDeli.write(bufferedImage, options, file);

Start reading and writing images with one line of code

Read: BufferedImage image = JDeli.read(streamOrFile);

Write: JDeli.write(myBufferedImage, OutputFormat.HEIC, outputStreamOrFile)

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