Told your cover is RGB and needs to be CMYK? What that means, and a free converter
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R. S. Breed Founder
If a printer or a forum post has told you your cover or interior images need to be CMYK, here's the short version:
- IngramSpark asks for it: its file guide says cover images and colour interior images must be CMYK, with total ink no more than 240%. It converts RGB itself before printing, which can shift colours.
- KDP recommends it for print covers ("should be in CMYK"), but doesn't say RGB is rejected.
- Lulu prefers RGB, so don't bother there.
- Ebook covers should stay RGB. Only convert files that are going to be printed.
The free converter does it properly: https://bervet.com/tools/rgb-to-cmyk-converter
- It uses a real print colour profile (GRACoL 2013, the US standard for coated paper), the way design software does, not a quick formula.
- It keeps the darkest areas within IngramSpark's 240% ink limit.
- It keeps every pixel: same size and resolution, so the picture places at the same printed size. It warns you if the image is under 300 ppi.
- You can see what changes before you save. It shows your image on screen next to roughly how it prints, and can highlight the areas that shift most. Neon greens and bright blues are usually the ones that dull down: ink can't reach every screen colour, whoever converts it.
You get a CMYK TIFF for your layout program, or a one-page PDF. If it's your whole wrap-around cover going to KDP or IngramSpark, use the cover image to print PDF tool instead: it also checks the cover is the right size for your page count.
It runs in your browser; your image isn't uploaded. The preview is open to everyone; saving the file is free for members. Whatever you use, order a printed proof before you publish.