What gets checked
- Resolution. Effective DPI under cover fit, the same maths as the DPI checker. Warns under 295, errors under 200.
- Shape. If the image shape is far enough from the page shape that filling the page crops about 13% or more of it, you are told how much.
- Missing bleed. Art shaped like the trim rather than trim-plus-bleed was almost certainly drawn without bleed. Enlarging it to fill the bleed box cuts about 1.8% off every edge of a standard comic page. The tool offers to synthesise the bleed band instead.
- Page count. Interiors must be a multiple of four.
- Colour mode. Browsers decode PNG, JPEG and WebP as RGB; the report reminds you to plan a CMYK conversion if your printer wants one. Like the flattening note, it is a reminder and never stops a page passing.
Extending bleed
Mirror reflects the outer band of the art outward and is invisible after trimming for most styles. Stretch smears the outermost row of pixels, best for flat colours and gradients. White only works if the page already has a white border. The band width is the bleed distance at the PPI implied by your image (image width divided by trim width), rounded to whole pixels, so a 1988 px wide trim-size page gets a 38 px band on each edge. The Extend bleed button appears on pages flagged as missing bleed. On a book with no bleed at the spine, such as IngramSpark's, the band goes on the outer edge only: the right of odd pages and the left of even pages, counted in file order.
Everything runs in your browser. Files are sorted by name with natural number ordering, so page_2 comes before page_10. Drop a whole folder, subfolders included; hidden files such as .DS_Store are skipped, and later drops join the same order.