Figure weight is a function of artwork type, and the safe dpi floor changes with it. Springer's guidance is the clearest version: photos and fine shading need a minimum of 300 dpi, a mix of halftone and line art needs 600 dpi because the lettering has to stay legible, and scanned line art needs 1200 dpi. Compressing a 1200 dpi line scan down to photo weight is the classic way to make a crisp diagram turn to mush in print. The other lever is resolution above the floor, which buys nothing: PLOS says plainly that figures above 600 dpi may be resized by production, and Nature caps supply at 300 ppi because denser files get too heavy for reviewers to download. So the two moves that actually reduce file size without cost are resizing to the printed width in pixels and dropping resolution above the journal's ceiling — both lossless in terms of what the reader sees. Beyond that, flattening layers and using container-level compression (LZW for TIFF) does more than aggressive JPEG re-encoding. Skwish handles the raster side in the browser with a per-file before/after readout and a batch queue, so you can measure which figures are carrying the weight before touching compression settings. Nothing is uploaded.