Showing posts from May, 2021

An embedded-friendly PNG decoder

Intro I wrote my own imaging codecs many years ago for all of the 'standard' file formats available. Over the last couple of years I've been dusting off that code to give it a new life as open source libraries for embedded/Arduino. I wrote blog posts about my JPEG and GIF decoders so I thought it would be useful to write about my new PNG decoding library . What is PNG? The (Portable Network Graphic) specification was created not too long after Unisys started enforcing their LZW patent to collect licensing fees from the use of GIF images. PNG was specifically designed to not infringe any patents and offered the benefit of supporting many more pixel types and an alpha channel. This offered a new feature not found in JPEG and much more functional than GIF's single transparent color. PNG uses the ZIP/FLATE compression scheme which is open source and without any patents attached to it. The FLATE compression by itself isn't drastically better than the LZW compression

The case of the missing SIMD code

Intro Much of the open source software that we all use daily is not optimized, or at least not well optimized. I've talked about this before because it's an issue I feel very strongly about. Code that is run billions of times a day shouldn't be inefficient. In the last 10 years (especially in the last year), more of our lives are spent in front of a computer than ever. Computers have a non-trivial environmental impact. Recently Bitcoin's environmental impact has popped up in the news, but the overall energy use of everyday software in both server farms and homes and offices is significant and steadily rising. There are plenty of people working diligently to make sure the code which runs the world is efficient, but what if some wrong assumptions were holding them back? SIMD  instructions are the key to unlocking efficient software on both PCs and mobile devices, but the problem is that it's not used everywhere that it needs to be. You can find SIMD code in many popu