Rasterised vs Vectorised Images - What you need to know

Rasterised vs Vectorised Images - What you need to know

By far the most common issue we face when receiving customer artwork is the quality it is sent to us as. Usually this is because of the difference between vector and raster images. So what are they, why do they matter, and what can you do about them to avoid problems? 

What are rasterised images? 

In short, a raster image is the most common type of image you will have on your computer. Every time you take a photograph - that's a raster image. Every time you take a screenshot - that's a raster image. Raster images are really useful. It's not that they're bad - they're just not great when it comes to printing things professionally because they're not designed for that purpose. If you zoom in on a raster image you will see that much like a TV screen image they are made up of thousands or millions of tiny coloured pixels, or squares. If you take a photo of your black and white cat (there's one sitting with me right now, he's called Neo) the overall image will be made up of a massive grid of those tiny squares. Where the cat has black fur the image will have black pixels. Where the cat has white fur the image will use white pixels. If the cat is sitting on a red chair then where you can see the chair ... yep, you've guessed it - red pixels. It's that easy. This is called rasterised imagery.

File formats which are rasterised are: PNG, JPG, JPEG, BMP, GIF and TIFF.

Why does this matter? 

It matters simply because the pixels will just get bigger and bigger as you enlarge the image. You don't create more pixels as you magnify the image. Instead the size of the pixels enlarges. So what was once a tiny indiscernible pixel making for a nice sharp looking photo, will become a blocky image as the individual pixels become large enough to see. Magnify your nice photo 100 times and suddenly you have a weird looking image made up of big blur bricks and it's a mess. 

But I don't want to magnify my image 100 times

No, of course not. We get that. But printers might need to - in a sense. Your laptop screen is actually very low resolution - 72dpi. That means if you drew a 1 inch square on your screen (please don't do that) and you counted the number of dots or pixels in there you would find it had 72 dots across and 72 dots down across the whole square - that's 72 x 72 or 5,184 dots making up that 1 inch square. A professional printer works at between 300 and 600 dpi usually. A 600 dpi printer will have 600x600 dots of ink in every 1 inch square, that's a staggering 360,000 dots! That's 70x more dots than your raster image at 72dpi is able to give.


SO .... the issue is all those missing pixels or dots. Computers can only guess at the missing information. They will try and process your image to the correct size but at the end of the day it is just a guess. And your image will end up looking blocky and messy. 

What can I do about this?

The first thing you can do is make sure your raster image is saved at the size you want it printed and at a minimum of 150-300dpi. If you can get it higher then great. The higher the resolution and the larger the image size though the bigger your file will be in terms of memory size. A 50kb image can quickly end up being 1Gb (that's a difference between very very small and really GIGANTIC). But if you know you want an A3 sized print on a t-shirt for example, then make sure you send through an A3 sized image SAVED AS 300dpi. That will give you the best results. It means we have all the pixels we need.

OR...you could send your image as a vector!

VECTORS! Vector images work completely differently. Not every image can be a vector though. So it does get a little tricky. A photo is usually rich in detail and colour. Logos on the other hand tend to be shapes - sometimes complex shapes, but shapes nonetheless. A shape usually has a clearly defined edge to it and can be worked out mathematically - a curve, a line, a square, even letters and numbers - all of these are perfect for being treated as vectorised images. 

Ok - I don't get it. Are vectors not dots then?

As you look at them on the screen you will still be seeing the image made up of dots, that's just because it's how your screen works. But the information generating that image on the screen - telling the screen what to show - is totally different. The information can be scaled to ANY SIZE with a vector without any loss of quality. You can type a tiny letter "a" on a laptop screen, save it as a vector in an image file and then a printer could print you a 100m tall letter "a" to go on the side of a building and that letter will scale up perfectly to print to that gigantic size. It's no longer made up in the file out of a map of pixels, rather it's defined by mathematics to be a relationship of lines, curves and angles which can go big or small without changing those relationships. Vectors are lovely in the world of print! 

Vectorised file formats are: EPS, AI, PDF, SVG

But beware!

Although EPS, AI and PDF files can all be vector formats, they are also hybrid formats which means they can include BOTH vector and raster images inside them. So you could put a raster image at 72dpi into a PDF file and send it to us. That won't magically make the low resolution image inside that PDF a beautiful vector. It will still just be a nasty low res raster image hiding inside a PDF package. Same with EPS and AI. They are really just containers. What you put in is what you get out.