Thumbnail Decoding Challenge

Thumbnail decoding challenge – colin@colino.net

colin@colino.net

2026/08/16<br>About 2 minutes read

Three years I got Quicktake 150’s thumbnail decoding in, and it’s "basically good enough" that one can recognize an image in the 80*60 output:

But as you can see, I think it’s wrong. It is too pixelated. And I can’t figure out what transformation to apply to the values to get a smooth thumbnail, because I absolutely suck at image processing.

I’m quite sure this would be super easy for someone well-versed into various image processing algorithms, so I have setup minimal test rigs for you to test my decoder and, hopefully, make it right!

I uploaded three files that make it easy to setup:

qt150-thumb-challenge.c

qt150-thumb-challenge.py

QT150.thumb

For those of you who prefer C, install libsdl-image-1.2 dev package, and compile and run with:

gcc -I/usr/include/SDL -o qt150-thumb-challenge qt150-thumb-challenge.c -lSDL_image -lSDL && \<br>./qt150-thumb-challenge QT150.thumb

For those of you who prefer Python, pip install pygame, and run with:

python3 qt150-thumb-challenge.py QT150.thumb

My notes about how the data is encoded is in comments at the relevant places in the code.

I hope someone will figure it out… Mostly because I would love to understand it completely.

Update! Henry Asseily figured it out. It is actually a 40×30 pixels thumbnail, encoded as RGGB, with 4 bits of red, 8 bits of green, 4 bits of blue, and with 40*RGG followed by 40*B. This is the result of a correct decoding:

In Quicktake for Apple II, the project being monochrome, I’ve opted to keep only the green values (as they’re 8 bits). This is the result of monochrome decoding:

And this is the result once dithered:

Finally, the actual algorithm: qt150-thumb-challenge-correct.c

Thumbnail Decoding Challenge

Related Articles

Incident with Github.com

(no title)

Scientists reverse brain aging, with a nasal spray

NHS apologises and admits Palantir have access to identifiable patient data

AI has torched the market for junior programmers