Resolution: why a good-looking image prints badly
An author finds an image, likes it, and sends the cover to print. The proof arrives and the picture is slightly soft — not wrong, not broken, just mushy in a way that makes the book look cheap. Nothing changed between the screen and the paper except the number of inches the same pixels had to cover.
Pixels are a supply, not a size
An image has a fixed number of pixels, and that number never changes on its own. What changes is how far you spread them.
The same 1,200-pixel-wide picture is dense at postage-stamp size and thin across a 6-inch cover. "Is this image big enough?" is not answerable by looking at the image. It is only answerable once you say how many inches it has to fill. Almost every resolution problem in self-publishing comes from skipping that step.
DPI is one division
Dots per inch is exactly what it says: pixels divided by inches.
A 1,800-pixel-wide image across 6 inches is 1,800 ÷ 6 = 300 DPI. The same image across 12 inches is 150 DPI. Over 18 inches it is 100 DPI. One image, three numbers, because DPI is a relationship and not a property.
Commercial book printing targets 300 DPI — the density at which the press stops being the limit and your artwork starts being the limit.
The arithmetic for a 6 × 9
Take the most common trim size in self-publishing. Add the bleed that gets trimmed away — on the outside edges, not at the spine fold — and the front panel alone is 6.125 × 9.25 inches. Multiply each side by 300:
- 6.125 × 300 = 1,838 pixels wide
- 9.25 × 300 = 2,775 pixels tall
So a front cover image for a 6 × 9 book wants to be roughly 1,838 × 2,775 pixels — around 5.1 megapixels, more than most images you find casually and less than any decent camera produces.
A full print wrap needs far more, because it is one sheet spanning back cover, spine and front. For a 300-page 6 × 9 paperback that wrap is about 12.93 inches wide: 3,878 × 2,775 pixels at 300 DPI. If a single photograph has to fill the whole wrap, that is the number to shop for, not the front-panel one. See Book cover dimensions.
In the Cover Maker. Drop in your artwork and it tells you the real DPI at your actual trim size, warns when the front image is under the print guideline, and flags anything under 200 DPI as visibly soft. Start a book → · about the Cover Maker
What under-resolution looks like on paper
It rarely looks like the pixelated blocks people expect. It looks like a slight loss of nerve:
- Soft edges. Where a shape should meet the background with a clean line, it meets it with a faint smear.
- Mushy small type. Any text baked into the image — a series name, a tagline, a fake publisher mark — loses its thin strokes first.
- A slightly blurred face. Eyes and lips go first, and a face that is nearly sharp reads as worse than one that is clearly stylized.
- Flat texture. Fabric, paper grain and foliage turn into an even mush.
Why you didn't see it coming
Because your screen lied to you, politely. When you open a big image in a viewer it is shown fit-to-window: the software throws away pixels to make it fit, and downsizing always looks good. You are judging a shrunken version of the file, which is the one situation where the supply is guaranteed to be sufficient.
The honest check is to view the image at 100 percent — one image pixel per screen pixel — and to compare its pixel dimensions against the inches it has to fill. Not how it looks. The numbers.
What helps, and what doesn't
A bigger original always helps. Rescan, re-render, re-export, re-shoot, or buy the larger size of the stock file. Going back to the source is the only move that adds real detail.
Enlarging invents nothing. Resampling to more pixels cannot recover information that was never captured; it can only make an educated guess about the gaps. Good resampling makes the result perfectly acceptable at modest factors — going up by a half or so is usually invisible on paper. Tripling a small image is not, and no amount of sharpening afterward brings the detail back.
Screenshots, web images and social downloads are the usual culprits. A screenshot contains only as many pixels as your screen had. Images on websites and downloads from social platforms have been deliberately shrunk and recompressed for fast loading. They were made small on purpose, and they cannot be made big again.
Line art and type are less forgiving than photographs
A photograph is mostly gradual change, so softening it costs less. Line art, logos, hand lettering and any drawn type are made of hard edges, and hard edges are what low resolution destroys first.
If your cover is illustrated or type-led, treat the target as a floor rather than a goal — and keep the type as live text rather than part of the picture. Text drawn as vector prints at whatever sharpness the press can manage, at any size.
300 is a target, not a magic number
Nothing collapses at 299. The figure comes from the printer's halftone screen — the grid of dots that makes continuous tone out of solid ink — and 300 DPI supplies comfortably more detail than that grid can resolve.
So the practical ranges are these. At or above 300 you are fine. Between 200 and 300 you are usually fine for photographic artwork and getting risky for anything with edges. Below 200 the softness becomes something a reader notices without knowing why.
In the Cover Maker. If an image is close but short, one click enlarges it to 300 DPI — ordinary high-quality resampling done in your browser, no AI, nothing uploaded — while the title and author stay live vector text that never softens at any size. Start a book → · about the Cover Maker
Make yours
Everything here is built into the tools, and they are free to use: name your book, bring your manuscript or your artwork, and work as long as you like. You only pay when you want the files without the preview watermark.
Next: Hire a cover designer, or do it yourself? · More: Stock images and licensing · AI cover art that works · Book cover dimensions