Java convert image format with low memory footprint

Question

I'm writing a Web application that let user upload images in several formats (eg png,jpg,bmp). After the image has been uploaded the system should convert it to "png" and scale it to a predefined resolution.

To convert the image I use the handy method:

javax.imageio.ImageIO.write(im, type, baos);

Here's where the problem start. The first argument of Image javax.imageio.ImageIO.write is a RenderedImage . The Java Doc states that the only known implementation is BufferedImage .

I try to find a way to convert a java.awt.Image to a BufferedImage, but it doesn't seems possible. However, it is possible to draw an image on a BufferedImage .

The problem is that creating a new BufferedImage each time is very memory expensive. I can start creating a pool of BufferedImage but I'm looking for clever/news ideas.

Answer 1

Try Thumbnailator library: http://code.google.com/p/thumbnailator/

Example code:

Thumbnails.of("large-picture.jpg")
        .scale(1.0)
        .outputFormat("png")
        .toOutputStream(os);

Library offers also much more like scaling, sizing, cropping, rotating, watermarking etc.

Answer 2

There's a bunch of Java libraries and SO posts about this. Did you check them out?

• http://www.fightingquaker.com/sanselan/
• http://sourceforge.net/projects/jiu/
• http://rsbweb.nih.gov/ij/
• What is the best java image processing library/approach?

Answer 3

您可以一遍又一遍地重复使用一个缓冲图像，在使用ImageIO.write方法时使用子图像适当调整大小

Answer 4

You could look at the implementation of BufferedImage and implement your own (A file-based implementation perhaps?). These classes are generally pretty straight-forward to read, often 50-70% comments and clearly written.

They give out the sources, why not make use of 'em?

Answer 5

启动netpbm或imagemagick等本机转换器。