And the author is not documenting them either, just announcing his new niche library. It is not like disassembling a few functions to prove that they exist is dark magic. I just don't see any value in the article.
maybe I am missing something but isn't it barely faster than the offical ESP32_JPG? But fair enough, didn't know than JPEG decoding on MCUs is a widespread thing.
The "official" version used in that blog post decodes the JPG all in one go - so it's pretty memory hungry. With JPEG encoders that decode sections of the image at a time you can minimise the amount of RAM that needs to be allocated. It's also possible to stream the display data out to screen using DMA while the next chunk of image data is being decoded.
It's very easy to forget what a range of MCUs there are, from very puny, to very capable. For example the Espressif range of MCUs - which you'll find in all sorts of consumer products - are very powerful. Couple that with a lot of cheap SPI based display modules and you very quickly start wanting to show images.
You need to go back and read it again. I provide links to the relevant Espressif documents and in my next article I provide a simple example to get started. Would you rather have me copy the hundreds of pages of PDF into my blog post instead of providing a link?
There are some numbers here on the performance improvements he’s managed to make.
https://atomic14.substack.com/p/even-faster-jpeg-decoding