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Ebook Cover File Formats and Color Profiles: JPG, PNG, RGB vs CMYK Explained

An author who spends weeks getting a cover's colors exactly right can still upload a file that looks noticeably duller on the retail page than it did on their own screen. Almost every time, the cause is the same: the file was saved in the wrong color profile, or exported at a quality setting that introduced visible artifacts nobody caught before hitting publish. Neither mistake is visible in your design software's working view — you only see it after the file leaves your hands.

RGB Is the Only Profile That Matters for Ebook Covers

Ebook covers are viewed exclusively on screens — phones, tablets, e-readers, laptop browsers — and every one of those displays renders color in RGB, the additive red-green-blue model that screens use to produce light. CMYK, by contrast, is a subtractive model built for physical ink on paper, and it exists because ink can't reproduce the full range of colors a screen can. If you design or export your ebook cover in CMYK, you're throwing away color range you could have used, and worse, most retail upload systems will either reject a CMYK file outright or convert it automatically using a generic profile that can shift your carefully chosen colors in ways you don't control.

This mistake happens most often to authors who also format print interiors, where CMYK genuinely is correct, and who carry that habit over to the ebook cover file without realizing the two outputs need opposite settings. Check your document's color mode before you even start designing an ebook-only cover, and if you're producing both a print and an ebook version from the same source file, make sure you're exporting two separate files with two separate profiles rather than reusing one.

JPG vs PNG: Picking the Right Format for the Job

JPG uses lossy compression, meaning it discards some image data to shrink file size, and it's what most retailers request for ebook cover uploads because it reliably produces a smaller file without a visible quality loss at reasonable compression settings. PNG uses lossless compression and preserves sharp edges and flat color blocks more faithfully, which matters for covers built around crisp typography, thin line art, or transparent elements, but the resulting file is often several times larger for no visible benefit once it's been re-compressed by the retailer's own system on upload anyway.

In practice, export your working file as a high-quality JPG — quality setting 90 or above, not the default "web" preset many programs offer, which compresses harder than retailers require and can introduce visible blocking around high-contrast title text. Reserve PNG for cases where you specifically need transparency, such as an overlay element you're compositing in another program, not for the final upload file itself. Most platforms cap ebook cover uploads around 50 megabytes, so file size from a properly compressed JPG at full print-quality resolution is rarely a real constraint.

Resolution, DPI, and Why the Number on Screen Is Misleading

DPI — dots per inch — is a print-era measurement and is functionally meaningless for a file that will only ever be displayed on screens. What actually matters for an ebook cover is pixel dimensions: most retailers want a minimum of 2560 pixels on the longest side, with 1.6:1 as the standard height-to-width ratio. A file can say "300 DPI" in its metadata and still be too small in pixel terms, or say "72 DPI" and be plenty large, because DPI only describes a printed size assumption that doesn't apply to digital display at all. If your design software shows a DPI field, treat pixel dimensions as the number that matters and ignore DPI entirely for ebook-only work.

Checking Your Export Before You Upload

Before uploading, open the exported file in a fresh window — not the tab where you were editing it — and zoom to 100% to check for compression artifacts around text edges, banding in gradients, or color shifts compared to your working file. This catches most export mistakes before a retailer's system does it for you and shows you a result you didn't choose. It's a two-minute check that's easy to skip once you're in a hurry to publish, and it's exactly the step most likely to be skipped right before a cover ships with a problem nobody notices until a reader points it out. Pairing a correct color profile with the dimension requirements for your target platform covers the two technical checks that cause the most avoidable upload problems.