Understanding and writing a JPEG decoder in Python
1–10 of 48 posts
Re: Understanding and writing a JPEG decoder in Python
#2Hi everyone! OP here.
Why write another article on JPEG when there are already hundreds of articles on the internet? Well, normally when you read articles on JPEG, the author just gives you details about what the format looks like. You don’t implement any code to do the actual decompression and decoding. Even if you do write code, it is in C/C++ and not accessible to a wide group of people. I tried to change that through this article. I give you a guided tour of JPEG encoding/decoding process and show you how it can be implemented in Python3.
I mainly focus on decoding baseline encoded JPEG images.
Re: Understanding and writing a JPEG decoder in Python
#3Hi everyone! OP here. Why write another article on JPEG when there are already hundreds of articles on the internet? Well, normally when you read articles on JPEG, the author just gives you details about what the format looks like. You don’t implement any code to do the actual decompression and decoding. Even if you do write code, it is in C/C++ and not accessible to a wide group of people. I tried to change that thr…
This is a cool article. I have always wondered the internals of JPEG and this has lots of details. Just as an FYI it should be a "Show HN:".
Edit: NVM! I didn't realize you didn't post this.
Re: Understanding and writing a JPEG decoder in Python
#4Hi everyone! OP here. Why write another article on JPEG when there are already hundreds of articles on the internet? Well, normally when you read articles on JPEG, the author just gives you details about what the format looks like. You don’t implement any code to do the actual decompression and decoding. Even if you do write code, it is in C/C++ and not accessible to a wide group of people. I tried to change that thr…
I really really like this - especially with all the references you've listed. I think more programmers should have a go at working with various file formats. Well done on this article.
Re: Understanding and writing a JPEG decoder in Python
#5This was a really good read to understand JPEG with the right videos and images included. Thanks!
Re: Understanding and writing a JPEG decoder in Python
#6Hi everyone! OP here. Why write another article on JPEG when there are already hundreds of articles on the internet? Well, normally when you read articles on JPEG, the author just gives you details about what the format looks like. You don’t implement any code to do the actual decompression and decoding. Even if you do write code, it is in C/C++ and not accessible to a wide group of people. I tried to change that thr…
I really really like this - especially with all the references you've listed. I think more programmers should have a go at working with various file formats. Well done on this article.
Thanks! And I completely agree with the idea that more programmers should have a go at working with various file formats. I learned so much about binary file layouts through this one project.
Before writing this article I had no idea that JPEGs use Huffman tables. Now all those Huffman table lectures from college algos classes make sense. I was never told in that class that this is a major use case for Huffman tables. Maybe I would have shown more interest then if I knew this fact.
Re: Understanding and writing a JPEG decoder in Python
#7This was a really good read to understand JPEG with the right videos and images included. Thanks!
Glad to hear that. :) IMO some content is just better suited as visualizations in the form of videos and images.
Re: Understanding and writing a JPEG decoder in Python
#8Hi everyone! OP here. Why write another article on JPEG when there are already hundreds of articles on the internet? Well, normally when you read articles on JPEG, the author just gives you details about what the format looks like. You don’t implement any code to do the actual decompression and decoding. Even if you do write code, it is in C/C++ and not accessible to a wide group of people. I tried to change that thr…
> Even if you do write code, it is in C/C++ and not accessible to a wide group of people.
To be honest, writing a jpeg decoder in C seems easier and more natural than doing it in python.
Re: Understanding and writing a JPEG decoder in Python
#9Thank you for this; lots of details, references and detailed diagrams!
One small note - the first image you mention that we'll need to reference is a bit small to read. Zooming in on the page does not zoom it in due to format of the page. I had to right click -> View image, in a separate tab in order to be able to zoom in enough to read the righthand side of it. edit: this is on the latest version of Firefox
Re: Understanding and writing a JPEG decoder in Python
#10Hi everyone! OP here. Why write another article on JPEG when there are already hundreds of articles on the internet? Well, normally when you read articles on JPEG, the author just gives you details about what the format looks like. You don’t implement any code to do the actual decompression and decoding. Even if you do write code, it is in C/C++ and not accessible to a wide group of people. I tried to change that thr…
> Even if you do write code, it is in C/C++ and not accessible to a wide group of people. To be honest, writing a jpeg decoder in C seems easier and more natural than doing it in python.
As someone who has done it in C, I would both agree and disagree --- reading the file format will definitely be easier since C lets you pick bits/bytes/words/etc. off the stream directly, but on the other hand the high-level structures (looping, etc.) would probably be easier with Python.
Overall, seeing as OP's Python implementation is less than 300 LoC while my C implementation was closer to 750, the Python might be easier. Then again, I followed the algorithms/flowcharts in the spec, which do a faster table-based Huffman decoding than the bit-by-bit of this Python version, and also implemented arbitrary(!) chroma subsampling as the spec allows, so it's not a direct comparison.