Vector and raster graphics - how to tell which kind of file you are dealing with

You are preparing a file for print and you hear the question: do you have it in vector or raster? To a layperson it sounds like jargon from another planet, and yet the answer decides whether a logo comes out sharp or ragged. The good news is that the difference between these two worlds can be understood in a few minutes, without a design degree and without complicated definitions.

Vector and raster are two entirely different ways of storing an image in a computer. One describes shapes using curves and lines, the other builds the image from tiny squares - pixels. This seemingly technical difference has very practical consequences: it decides what can be enlarged endlessly and what will blur at the first attempt. Below we explain it in plain terms and show how to work out for yourself what you are dealing with.

Vector - an image built from curves

Vector graphics do not remember the image as a set of points, but as a description of shapes: here is a circle of a given radius, here a line from point to point, here a fill of a given colour. It is a bit like a recipe by which the computer redraws the image from scratch every time - at any size.

The biggest advantage follows precisely from this. Since the image is a description rather than a ready grid of points, you can enlarge it to fill a whole wall or shrink it to a mark on a pen - and each time the edges stay perfectly smooth. Nothing blurs, nothing loses sharpness. That is why vector is the natural choice for logos, lettering and simple graphic marks that must look good at any size.

Typical vector formats

You can usually guess what you are dealing with from the file extension. Vector formats are most often:

• .ai - the format of a vector graphics program, typical for logo and identity files.
• .eps - an older, universal vector format, still often found in print-ready files.
• .pdf - it can contain vector, though it is sometimes a container for raster graphics too, so the extension alone does not settle the matter.
• .svg - a lightweight vector format, popular on the web, great for simple logos and icons.

Raster - an image made of pixels

Raster graphics work completely differently. Here the image is a grid of tiny squares, each with its own colour. From a distance you do not see the grid - the pixels merge into a smooth image. But when you zoom in too far, the grid reveals itself and the image turns into a mosaic of coloured squares.

This is why raster has limits when scaling. The file contains a finite number of pixels and you cannot conjure more from nothing. Enlarging a photo does not gain you new detail - the computer simply stretches what is there, and the image goes soft and blurry. We expand on this in a separate post on why enlarging a small photo does not improve quality - one of the most common misunderstandings in file preparation.

Typical raster formats

• .jpg - the most popular photo format, heavily compressed and therefore light, but with strong compression it loses detail.
• .png - a raster format with transparency support, good for graphics with sharp edges and a background meant to disappear.
• .tif - a high-quality format without lossy compression, often used for printing photographs.

How to recognise the file type yourself

You do not need to be a designer to tell vector from raster. A few simple observations, which anyone can make on their own computer, are enough.

1. Zoom in hard - this is the most reliable test. Open the file and zoom in as far as it goes. If the edges stay smooth and sharp, it is vector. If steps appear and the image breaks into coloured squares - it is raster.
2. Check the extension - .ai, .eps and .svg are almost always vector; .jpg, .png and .tif are raster. The .pdf extension is ambiguous, so pair it with the zoom test.
3. Think about the origin - where the file came from. A photo from a camera or phone is always raster. A scanned document is raster too. A logo designed from scratch in a graphics program usually exists in a vector version.
4. Look at the file size - this is a supporting clue, not a rule. A simple logotype in vector can be very light despite a large output resolution, because it is only a description of shapes, not millions of pixels.

What suits what

Knowing the difference boils down to one practical rule: match the file type to what it depicts. There is no magic here, just logic that follows from how each of these worlds works.

Logos, text, icons, simple graphic marks and anything with sharp contours and flat colours are best kept as vector. Then the same file will serve both a business card and a huge banner without losing sharpness. That is why, when ordering business cards or posters, it is worth having your logo in vector form.

Photos are always raster - there is no way around it, because a photograph by nature consists of subtle colours and transitions you cannot describe with curves. Here what matters is a suitably high resolution matched to the final print size. If you want a logo to keep a clean, transparent background regardless of format, our post on which file format gives a transparent background in a logo will help.

How not to ruin a file during conversion

The most common trouble comes from trying to turn one type into the other. Conversion is sometimes necessary, but you need to know what to expect from it.

• Raster to vector works no miracles - automatically turning a photo into vector will not recover lost detail. It works reasonably for simple, flat-colour graphics, but turns a photo into a strange, blotchy version of itself.
• Vector to raster is a one-way street - once you save a logo from vector as a .jpg or .png at a particular size, you lose flexibility. From then on it is an ordinary raster, and enlarging it beyond the saved size will blur the edges.
• Keep the original - before you convert anything, set aside the source version. From vector you can always generate a raster at the size you need, but from raster you cannot recreate vector.
• Do not force-enlarge raster - if a file is too small, it is better to find a higher-resolution version than to stretch the existing one.

Finally, the simplest advice: when in doubt, do not guess. Zoom in on the file, look at the edges, check the extension and the origin - these three clues almost always give the answer. And if you still are not sure, take a look at our section on file preparation, or simply attach the best version you have to your order. Understanding the difference between vector and raster is one of those things that, once grasped, saves a great deal of stress on every print project that follows.