Technical points to consider when uploading a picture in the forum gallery?

Hm I just uploaded a closeup of my last piece:

But it still got re-encoded at much lower quality, original was 690KiB (that’s 92% quality in Krita, “1x1, 1x1, 1x1” subsampling).

Whatever those 99% in discourse mean, it’s much lower than libjpeg…