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.