Incorrect image from my Quite OK Image (.qoi) decoder,stumped for hours

Help with Snap! Snap! Editor
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1

I'm implementing a decoder for https://qoiformat.org/qoi-specification.pdf that takes a list of numbers in 0..255. https://piglinpotatoes.github.io/testcard_rgba.qoi is decoding as:

costume
costume256×256 17.1 KB

Here's ImageMagick displaying that image:
image
image494×489 53.2 KB

2

Good work so far :slight_smile:

I love trying to implement things like this from just the specification :slight_smile:

I did an animated GIF one

3

Every chunk must be decoded to full RGBA.
QOI_OP_RGB, DIFF, LUMA must recreate the last used A value.

I've not done it; I just found that the output is not a square RGBA matrix.

4

@dardoro I just came here to say that :slight_smile: my current progress as not quite there yet

image
image278×274 23.4 KB

Closer but still no coconut :slight_smile:

image
image258×273 19.9 KB

5

Success :slight_smile:

image
image268×286 16.7 KB

As well as the missing alphas, the QOI_OP_LUMA code was missing a mod 256

image
image806×436 67.7 KB

6

Thanks cymplecy and dardoro. There's a shorter way to keep the previous pixel's alpha in DIFF and LUMA: adding the previous pixel to a list where the fourth item is 0 after going through surrounding operators.

image
image655×668 97.8 KB

7

Shift :gear: Live coding ... makes this script 10 time faster i.e. 4 compared to 40 s

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i tried my hand at speeding it up. lots of cursed hyperblocks but worth it for the lower block count

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