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Comment by rsp1984 | Hacker News Reader

rsp1984

Unfortunately not everything compresses well with QOI. I have considered using it for our company but then did some tests with real images from real (noisy, low-res) cameras. The result is that in many cases QOI did not offer much compression at all over just storing all the raw bytes and in some cases it even increased the size.

The sample images that come with the download look well selected. I encourage everyone to try it on real data and see for themselves. Personally I was quite underwhelmed by the format and we are sticking with PNG for the time being.

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I think the point in the design space makes more sense for game textures than sensor input. When you consider the encoding primitives, it'll only do well on images which have a mix of (a) limited palette, (b) blocks of constant color and (c) smooth gradients.

Reencoding JPGs may not be too bad because of the way DCT creates little blocks of gradients and chroma subsampling reducing local color entropy, but ISTM it'll do best on images generated by humans with drawing tools.

The decode speed is another big point in favour of usage in games.

> images from real (noisy, low-res) cameras

But these won't compress well _losslessly_ in principle, would they?

Or did you manage to find a format that did in fact work well?

PNG works quite well on these kinds of images too.

Do you have any specific examples you can share?

PNG should not be able to compress noisy images well, because noise removes patterning. JPEG obviously can, but exactly because it is lossy.

PNG can't transform noisy images into something more compressible, but it uses better entropy coding compared to QOI.

I haven't evaluated this personally but the (close to?) lossless raw sensor image compression from Dotphoton [1] seems like an interesting approach for getting around the issue of sensor noise in image compression. However the implementation details are disappointly vague, as it's a proprietary product.

[1]https://dotphoton.com/

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