Vector and raster, and why it matters for a cover
Almost every confusing thing about cover files comes back to one technical distinction, and it is not a difficult one. There are two ways a computer can hold a picture, and they behave in opposite ways when you change the size.
Raster: a fixed supply of detail
A raster image is a grid of colored squares. Photographs are raster. Anything scanned is raster. So is almost everything a painting app produces, and so is almost all AI-generated art.
The grid is decided once, when the image is made, and nothing later adds to it. That is the whole story. A raster image has a fixed amount of detail, so enlarging it invents nothing — the software spreads the same information across more squares and guesses at the gaps, which reads on paper as softness. Detail that was never captured cannot be recovered by any tool, whatever the tool claims. Resolution: why a good-looking image prints badly works through the arithmetic of how much you actually need.
Common raster formats: JPEG, PNG, TIFF, and the working files of most photo editors.
Vector: instructions, redrawn at any size
A vector file does not store a picture. It stores a description of one: this curve, from here to here, with this thickness, filled with this color. Nothing is decided about size until something draws it.
Because it is redrawn rather than stretched, vector art is sharp at any scale. The same logo is crisp on a business card and crisp on the side of a van, and the file does not get larger when you enlarge it. Type is the most important vector art on your cover: a font is itself a set of drawing instructions, which is why live text prints cleanly at any size a press can manage.
Common vector formats: SVG, EPS, AI, and PDF when the PDF holds live text and shapes rather than a flattened picture.
Vector is not better. It is better at some things. A photograph cannot be vector in any useful sense, because a photograph is not made of describable shapes — it is a field of subtle tonal change, and that is exactly what a grid of pixels is good at.
What follows, practically
Keep your title as live text for as long as possible. Live text stays sharp at every size, prints as shapes rather than pixels, and — the part that matters more — can be edited. A typo, a subtitle change, a series line added in book three: all of these are a few seconds of work while the type is live, and a return to the artwork once it has been flattened into the picture.
A logo supplied as a small PNG will disappoint you. Publisher marks are usually printed small, often on the spine, where a soft edge is very visible against a solid color. A 200-pixel PNG grabbed from a website has a fixed supply of detail and no way to gain more. The same mark as vector prints cleanly at any spine width you end up with, which is why a mark is worth drawing in vector from the start — see Designing a publisher mark.
A photograph cannot be rescued by enlargement. Not by sharpening, not by a paid upscaler, not by anything. Go back to the source file and get the larger version.
In the Cover Maker. Your title, series line and author name stay live vector text throughout, so they never soften and stay editable to the last minute. For photographs it flags art under 200 DPI and offers one-click enlargement to 300 DPI — ordinary resampling done in your browser, no AI, nothing uploaded — which cannot invent detail that was never captured. Start your cover → · about the Cover Maker
Where it actually bites
Two situations account for most of the damage.
Someone sends you a screenshot of a logo. An imprint, an award seal, an association mark. What arrives is a raster grab at screen size, and screen size is small. It looks fine in the email and soft on the printed spine. Ask for the original. The organization almost always has one, because whoever designed it worked in vector.
A finished cover comes back as a flat image with the title baked in. Now your page count changes — you cut a chapter, you switch paper, you move printers — and the spine is a different width. The design no longer fits the wrap, and there is nothing to move, because the title is not an object any more. It is a region of pixels in a picture. Every fix goes back to whoever made the file, and back into their schedule. See Changing your page count on purpose for how often that number moves, and Designing a spine people can read on a shelf for what it does to the spine.
What to ask for when you commission
Whether you hire a designer or use someone's template, the thing to agree before money changes hands is what you receive at the end.
- The layered source file, not only a flattened export. That is the file that can be changed.
- Any vector assets — the logo, the drawn ornament, custom lettering — as their own files.
- The fonts named in writing, so a future edit can match the original. You may need your own license for them.
- The full-resolution artwork, at the size it was worked at rather than the size it was exported to.
A designer who works properly has all of this already. Asking costs nothing and saves the second edition. Writing a cover brief, for a designer or for yourself covers the rest of that conversation.
What the printer receives
None of this changes the file you upload. A print-ready cover PDF holds both kinds of content: your photograph as pixels at its own resolution, your type and shapes as vector instructions. That is normal and correct. The distinction matters during the work, when one kind can still be changed freely and the other cannot.
If a printer's reply comes back talking about flattening, live type or rasterizing and you are not sure which half of your file they mean, The words printers use translates the vocabulary.
Make your cover
The Cover Maker is free to use: name your book, bring your artwork, and it draws the full wrap — front, spine and back — to your printer's own measurements. You only pay when you want the files without the preview watermark.
Next: The five photo edits a cover usually needs · More: Resolution: why a good-looking image prints badly · Hand lettering and custom type · Why print files get rejected, and how to not be rejected