When QOI meets XZ | MaskRay
QOI's key advantages is its simplicity. Being a byte-oriented format without entropy encoding, it can be further compressed with generic data compression programs like lz4, xz, and zstd. PNG, on the other hand, uses DEFLATE compression internally and is typically resistant to further compression. By applying a stronger compression algorithm on QOI output, you can often achieve a smaller file size compared to PNG.
Lasse Collin has shared some effective options for compressing uncompressed BMP/TIFF files. I tested them on the QOI benchmark images.
While compressing QOI with XZ (.qoi.xz) can achieve good results, using a delta filter directly on the uncompressed BMP format (.bmp.xz) can sometimes lead to even smaller files. (TIFF and PPM/PAM, when compressed, can achieve similar file sizes to .bmp.xz.) This suggests that QOI is probably not better than a plain delta filter.
It's important to note that uncompressed BMP/TIFF files are huge. This can be problematic if the decompressed data can't be streamed directly into the program's internal structures. In such cases, a large temporary buffer would be needed, wasting memory.
