It is a JPEG decoder supporting sequential and progressive DCT-based encoding. Restart is not supported. I write it to test that I have understood how JPEG works.
If you are interested in how JPEG works or are trying to write a JPEG codec, I hope the code and wiki in this repository can help you.
To use it, open the directory jpeg-py, and run decoder.py. The detail of the input image is printed, the input image is decoded to a matrix of [Y, Cb, Cr], and a new image is generated using this matrix. You can add you own jpg image to the directory, and change the argument of function decode().
The IDCT is not optimized, so it's time consuming. For the images I provide to test, it may cost 30s, be patient please :)