Good question. I've taken a look at the final revision of the spec ([1]) and it seems that parallelizing a QOI decoder may be non-trivial, because of back refer

Good question. I've taken a look at the final revision of the spec ([1]) and it seems that parallelizing a QOI decoder may be non-trivial, because of back references. More over, it's possible to come up with QOI-encoded images which would see no speedup from any concurrent decoding (for example, if every single pixel refers to the previous). On the other hand, a parallel QOI encoder is relatively straightforward and will only have about 4*N bytes of compression penalty per image, where N is the number of threads, which is a trivial cost, if we talk about megapixel-scale images (as opposed to tiny icons). 1. https://qoiformat.org/qoi-specification.pdf https://qoiformat.org/qoi-specification.pdf