Raster vs Vector Graphics: A Simple Guide for Researchers

Look, we get it, you’re a scientist. You’re really smart! You know lots of stuff, but you don’t know everything. So occasionally you get thrown a curveball, someone asks you for something and not only do you not understand the question, but you’ve never even heard those words before.

The conference organisers have asked you for something called a “vector file” of your poster design. A journal editor has just emailed you and asked you to re-submit your figures at “300dpi or greater”, whatever the hell that is. Meanwhile the lab shirts you ordered have been delivered and they look terrible; the logo is blurry and pixellated and you don’t understand why! It can be hard to ask for help sometimes.

It’s OK, it happens to us all. This is simply what happens when the daily grind of being a researcher collides head-on with the daily grind of graphic designers.

You’re just speaking different languages, and we’re here to help you make sense of it as plainly and simply as possible. We’re going to do it using bananas, so bear with me.

All these problems come down to how computers manage image files. There are two main categories of image files, raster and vector. There are also endless different file types for both, but forget about that for now, just remember those two words. Raster. Vector.

What on earth are they? Well, here’s a side-by-side comparison.

Raster graphics

Raster graphics are like the left-hand side of the banana. They are image files made up of many small pixels. Zoom in really close and you can see all the individual squares, each with a different colour value. But from afar, the pixels are all small, and blend together to make a coherent image.

To make sure that your image looks right and isn’t pixellated it needs a sufficiently high resolution. This is where ‘dpi’ comes in, or ‘dots per inch’, or sometimes pixels per inch. Why don’t they just use the one term? And why isn’t it a metric scale? Who knows. Pfft, Americans, am I right? For now I’ll stick with dpi.

To look good on a digital screen an image needs a resolution of at least 72dpi, so an image 72 pixels across will be 1 inch in diameter at full resolution on a screen.

For printing however you need a much higher resolution of at least 300dpi, which means much more detail and bigger file sizes. So if your image needs to be printed 6 inches across, it needs to be at least 1800 pixels wide.

Vector graphics

Vector graphics however are like the right-hand side of the banana. The data underneath these image files isn’t stored in pixels, it’s stored as a series of mathematical functions that describe points, shapes and curves. Remember in high school maths when you had to draw differently shaped curves on a graph based on different equations? Like that, but these equations draw a banana.

So which banana do you want?

I mean, which type of image file do you need? Both bananas are great. They are both very useful and are rich in potassium.

The vector graphic is really nice and crisp, isn’t it? The great thing about vector graphics is that they can scale infinitely. Because the data isn’t in pixel form, that curvy banana equation stays the same no matter what size the image is. This is why vector graphics are great for large scale printing like conference posters, or even billboards! But it looks a bit weird, doesn’t it? It’s very artificial looking, you probably wouldn’t want to eat that banana.

If you want a nice natural-looking banana, with subtle colour variations, plenty of surface texture (but not overripe), and complex shadows then you need a raster file. These types of image files are great for depicting photorealistic images like, well, photos obviously. If you want to do digital illustrations where you draw or paint with a pen and tablet, rather than clicking with a mouse, you’ll probably be working with raster files.

If it helps here’s a quick rundown.

Raster graphics

What are they?

Images made of many small pixels

What are some raster file types?

.JPG, .BMP, .PNG, etc.

When will you use them?

Digital photos, scanned documents, on-screen graphics, digital illustrations with a hand-drawn feel. If you know the size that your final image will be, and where it’s going (screen or printed) you can make a raster graphic to the right size and resolution.

Pros

Great for complex details and textures. Easily handled by most software.

Cons

Limited in how much they can be enlarged without pixellating.

Vector graphics

What are they?

Images made of shapes defined by mathematical functions.

What are some vector file types?

.SVG, .PDF, .AI, .AF, .EPS, etc.

When will you use them?

Large scale printing. Crisp clean geometric designs, like corporate logos. If you don’t know what size something will eventually be printed or shown, vector graphics are a safe option.

Pros

Infinitely scalable! You could, theoretically, print an infinitely large banana without losing resolution quality. Great for clean, professional looking designs.

Cons

Some programs just can’t handle vector files.  Vector file designs generally look artificial, so aren’t that useful for photorealism.

👉 Quick recap: Raster equals pixels, best for detail, texture and photorealism. Vector equals maths, best for scaling and clean printed designs. Match the file type to the job, and you’ll never get caught out by a conference organiser or journal editor again.

You can make them yourself!

So now that you know what banana you need, how do you make them?

In the olden days like, I dunno, last year, you needed different programs to manipulate vector and raster graphics; e.g. Photoshop for raster graphics, Illustrator for vector graphics. Doing complex graphic design used to mean doing lots of importing and exporting as you jumped between different programs. But, the times are-a-changing and we finally have a program that can seamlessly handle both raster and vector graphics simultaneously – Affinity! It’s completely free and we’re now using it for all of our in-house design work.

Knowing the difference between raster and vector is step one. Actually being able to create and edit both, confidently, in one program, is the real skill upgrade. That’s exactly what we teach in our new course, Learn to Design in Affinity: for Researchers, by Researchers, built specifically for researchers who want professional looking posters, figures and graphics without hiring a designer every time.

Now go eat a banana, open Affinity, and make some graphics.

Yours creatively,

Dr James O’Hanlon