Google Upgrades WebP To Challenge PNG Image Format

New submitter more writes with news that Google has added to its WebP image format the ability to losslessly compress images, and to do so with a substantial reduction in file size compared to the PNG format. Quoting: "Our main focus for lossless mode has been in compression density and simplicity in decoding. On average, we get a 45% reduction in size when starting with PNGs found on the web, and a 28% reduction in size compared to PNGs that are re-compressed with pngcrush and pngout. Smaller images on the page mean faster page loads."

Comments

Re:This is a big deal!

[Trixter]

I didn't realize it was even possible to make such a big improvement in lossless image compression.

You falsely assume that PNG was state-of-the-art in lossless compression. PNG took a great idea (filter the image and take advantage of the 2-D correlation present in most real-world images) and coupled with it a terrible idea (zlib for the back-end compression of the filter output). You're supposed to do order-0 compression (ie. statistical, like Huffman coding) on the filter residuals, not pattern-match searching (zlib). zlib is a great piece of software, but like all tools, there are things it is very well-suited for and others it is not well-suited for. This was a misstep by the PNG team.

The choice the PNG people made was fueled by the Unisys GIF/LZW patent of the time, and at that time IBM also had a patent on range coders. So I guess it's understandable why they didn't use those order-0 methods on the filter residuals. But it was a huge mistake to knee-jerk away from ALL statistical methods and choose zlib as the back-end. They could have used basic Huffman; not sure why they didn't.

Re:NIH

[petermgreen]

One of the key design features of PNG was that any PNG should be able to be read by any decoder. That is why PNG has relatively few options on how the core data is encoded*

Adding optional stuff is ok (unless it's animation......) but if you want to make a key change to the core of the format I suspect the PNG guys would tell you to go make your own format based on PNG but with it's own specification, file extension and "magic number" (as was done for MNG, and JNG).

* a handful of filter types all of which are easy to implement, one compression algorith, one byte order standard, 15 allowed color/bitdepth combintions (the majority of which represent very comon combinations and all of which can be easilly mapped to 24-bit RGB).