How to Control JPEG Compression Level Using ImageIO in Java?

Setting JPEG Compression Level Using ImageIO in Java

In Java, ImageIO is a versatile library for image manipulation. However, it lacks an explicit method to set the JPEG compression level when writing images. This article addresses this limitation by demonstrating how to adjust compression quality using the ImageIO API.

Solution

To control JPEG compression, one approach is to utilize the ImageWriteParam class. The following steps outline the process:

1. Obtain the ImageWriter object for the JPEG format.
2. Retrieve the default ImageWriteParam for the ImageWriter.
3. Set the compression mode to ImageWriteParam.MODE_EXPLICIT.
4. Specify the desired compression quality between 0.0f (maximum compression) and 1.0f (maximum quality).
5. Create an ImageOutputStream to handle the output.
6. Set the ImageWriter output to the ImageOutputStream.
7. Create an IIOImage object with the image data.
8. Write the IIOImage to the ImageOutputStream using the custom ImageWriteParam.
9. Dispose of the ImageWriter.

Example Code:

<code class="java">ImageWriter jpgWriter = ImageIO.getImageWritersByFormatName("jpg").next();
ImageWriteParam jpgWriteParam = jpgWriter.getDefaultWriteParam();
jpgWriteParam.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
jpgWriteParam.setCompressionQuality(0.7f);

ImageOutputStream outputStream = new FileImageOutputStream(new File("output.jpg"));
jpgWriter.setOutput(outputStream);
IIOImage outputImage = new IIOImage(image, null, null);
jpgWriter.write(null, outputImage, jpgWriteParam);
jpgWriter.dispose();</code>

This code snippet explicitly sets the compression quality to 0.7, producing an image with a balance between quality and file size.

Note:

The examples assume the existence of an image variable and a File object for writing the output. Additionally, the MemoryCacheImageOutputStream class is an alternative to FileImageOutputStream when writing to a memory buffer.

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