Javascript lossless image compression

Question

I am looking for a way to encoding a bmp image as a tiff or some other standard, compressed but lossless format in a browser (javascript). I guess if worst comes to worst I can write a library myself (getting the data from a canvas element) but I was hoping either: there's a better way to do it or someone else has already written something similar (I can't find a library).

I have users wanting to upload ~ 4mb (8-bit monochrome) bmp files, which I can losslessly compress to ~700kb tiff files with LZW (or even better ~300kb lossless JPEG-2000). I'd like to do this before the files are uploaded to save transfer costs/time.

Before you ask, I'm not being anal about the lossless encoding instead of just using high bitrate JPEG. These are astronomy photos that are used for analysis so they can't handle any compression artifacts being introduced.

Thanks, Jonny

Answer 1

Use PNG. It's lossless and uses zlib compression. There are even programs like pngcrush that will optimize the image for size (only problem is it takes a while for this).

Is there any reason you're using JavaScript of all things for this process? Wouldn't it be easier in the long run if you did it in a Java applet (using a library that interfaces with the java.awt.Image class), or uploaded it to a server that did the image processing and returned the compressed image?

Edit: Please don't use a Java applet; the technology isn't well-supported anymore.

Answer 2

If you are willing to experiment something new, you could try a new lossless compression algorithm I created; through a Java applet it is possible to visualize the compressed images in a browser. You could use Javascript to trigger the loading of the applet, or manipulate directly the Java code (the program is open source). For many images, the compression ratio will be better than lossless Jpeg 2000. The address of the website is http://www.researchandtechnology.net/bcif/ .

If instead you want to use some well-known standard, then I'd agree with amphetamachine: using PNG would be the best choice.

So long, Stefano