JPEG encoder and decoder

[jonnor]

When working on image classification (like with the emlearn Convolutional Neural Network), it is desirable to be able to work with standard image formats. Both on PC (for evaluation, testing) and on device (for data collection, verification). The most relevant file format is JPEG, as is widely implemented in hardware cameras, and a very practical and simple format with good levels of compression.

[jonnor]

I think these should be native modules, to have decent performance. There also seems to be very few well-supported, liberally licensed JPEG implementations for MicroPython - but a fair amount of them in C.

For the encoder, these are alternatives:

• https://github.com/bitbank2/JPEGENC
• https://github.com/noritsuna/JPEGEncoder4Cortex-M
• https://github.com/Moodstocks/jpec

For the decoder, these are alternatives:

• https://github.com/bitbank2/JPEGDEC
• https://github.com/Bodmer/TJpg_Decoder
• https://github.com/richgel999/picojpeg