What Does the oxipng Level Setting Control?
oxipng is a dedicated lossless PNG optimizer, and its "level" parameter controls how many compression strategies it tries during optimization — a higher level tries more strategies, potentially producing a smaller file, at the cost of more processing time.
oxipng and PNG quantize are two different things
These two parameters often get discussed together, but they do completely different jobs: PNG quantize is lossy — it trades away some color palette precision for a smaller file. The oxipng level is purely lossless — it never changes any pixel data, it just tries harder to find a more compact way to pack the exact same pixel data. No matter how high the level, image quality never changes.
Should you adjust this manually?
Everyday use doesn't need to touch this — the four presets already strike a reasonable balance between speed and size. It's only worth understanding what value each preset uses if you specifically want the smallest possible file at the same quality and are willing to wait a bit longer for it, or the opposite — a quick result where a slightly larger file is fine — and you want to pick the preset accordingly.
References
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