imgscalr Documentation

imgscalr allows you to control how images are fitted into target dimensions using Mode. By default, resizing maintains proportions. Use Mode to override this behavior:

• Mode.FIT_EXACT: Forces the image into the specific given dimensions, ignoring orientation and proportions.
• Mode.FIT_TO_WIDTH: Treats width as the primary dimension and recalculates height to fit.
• Mode.FIT_TO_HEIGHT: Treats height as the primary dimension and recalculates width to fit.

To avoid overloading the host system or exhausting the heap in multi-user environments (like web apps), use the AsyncScalr class. It wraps Scalr and submits jobs to an internal ExecutorService.

Key features:

• Rate Limiting: Uses a fixed-size thread pool (default is 2 threads) to queue scaling operations.
• Customization: You can customize the service by extending AsyncScalr and overriding createService() or createService(ThreadFactory).
• Thread Factories: Provides DefaultThreadFactory and ServerThreadFactory (optimized for servers with daemon threads and LOW_PRIORITY).
• Configuration: The number of threads can be tuned via the system property THREAD_COUNT.

Scaling animated GIFs is not supported. For static GIFs, be aware of the following:

1. Transparency: If a GIF has an alpha channel (TYPE_INT_ARGB), saving it as a GIF in older Java runtimes may replace transparency with solid black.
2. Recommendation: Save the resulting BufferedImage as a PNG to maintain transparency and avoid color quantization issues.
3. Avoid Ops on GIFs: Applying BufferedImageOps (like ConvolveOp) to a scaled image before saving it as a GIF can corrupt the file. If you need to apply operations, save the result as a PNG.

Image manipulation requires significant memory because images are decoded into raw ARGB bytes in the BufferedImage instance. If you encounter OutOfMemoryException when processing large images, increase the JVM heap size using the -Xmx flag.

Example:

java -Xmx128m com.site.MyApp

To scale an image to a specific width while maintaining its original proportions and letting the library choose the best scaling method, use Scalr.resize(BufferedImage, int).

BufferedImage srcImage = ImageIO.read(...); // Load image
BufferedImage scaledImage = Scalr.resize(srcImage, 150); // Scale image

You can combine loading, scaling, and writing into a single expression for simple use cases.

ImageIO.write(Scalr.resize(ImageIO.read(...), 150));

Most imgscalr methods accept a variable number of BufferedImageOps as arguments. These operations are applied to the final image result before it is returned.

One common use case is applying a light softening effect (anti-aliasing) using the built-in constant:

• Scalr.OP_ANTIALIAS