How to Control JPEG Compression Level When Saving Images Using ImageIO in Java?

How to Set JPEG Compression Level Using ImageIO in Java

ImageIO, a part of the Java API for Image I/O (JAII), provides a convenient way to read and write images in various formats, including JPEG. However, by default, ImageIO does not offer direct control over the JPEG compression level. This article explores how to overcome this limitation and set the desired compression level while saving a BufferedImage as a JPEG file.

Java Function to Save a BufferedImage as JPEG

The provided Java function, getScreenShot, captures a BufferedImage and saves it as a JPEG file. However, it does not specify any compression settings.

<code class="java">public static void getScreenShot(BufferedImage capture, Path folder, String filename) {
        try {
            ImageIO.write(capture, "jpeg", new File(folder.toString()+"/"+filename+".jpg"));
        } catch (AWTException | IOException ex) {
            Logger.getLogger(ScreenShotMaker.class.getName()).log(Level.SEVERE, null, ex);
        }
}</code>

Setting the JPEG Compression Level

To set the JPEG compression level, you need to access the ImageWriteParam object, which contains parameters controlling the image encoding process. Here's a more detailed snippet:

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

By setting the compressionMode to MODE_EXPLICIT, you explicitly control the compression level. The value passed to compressionQuality determines the desired compression level, with 1.0f representing maximum quality and 0.0f representing maximum compression.

Additional Considerations

• ImageWriter.setOutput should be passed an ImageOutputStream.
• FileImageOutputStream and MemoryCacheImageOutputStream are preferred implementations for most cases.

By incorporating these enhancements, you can customize the JPEG compression level to meet your specific requirements while saving images using ImageIO in Java.

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