Nature's final-submission guidance contains a rule that reads backwards until you see the reason: figures should be supplied at a maximum of 300 ppi, and file size should not exceed 10 MB. The stated reasoning is that exceeding 300 ppi makes files too big and viewers may time out before they can view or download them. So unlike a lot of image advice, the ceiling here is deliberate and the failure mode is a reader who never sees the figure. Layered PSD or TIFF is the accepted container, and 300-600 dpi is the range for photographic images — the upper end is for source quality, not for what you ship. The practical consequence is that a 400 MB composite figure straight out of a confocal or a 60-megapixel camera is not a flex, it is a file the reviewer bounces. Export at your final printed width, flatten, check the byte count, and only then decide whether to re-compress. Skwish reads and compresses JPG, PNG and WebP in the browser with a per-file before/after readout and a batch queue, so a figure set can be brought into range in one pass before you assemble the submission archive. Nothing is uploaded.