A raster graphic is an image made of hundreds (or thousands or millions) of tiny squares of colour information, referred to as either pixels or dots. Technically pixels refer to colour blocks viewed on an electronic monitor whereas dots refer to the ink dots on a printed piece.
The most common type of raster graphic? A photograph.
Popular raster file format extensions include: jpg/jpeg, psd, png, tiff, bmp and gif.
Pros of Raster Images
Rich Detail: Ever wondered what the term “dpi” stands for? It means, “dots per inch,” a measurement of how much detailed colour information a raster image contains. Say you have a 25mm x 25mm square image at 300 dpi—that’s 300 individual squares of colour that provide precise shading and detail in your photograph. The more dpi your image contains, the more subtle details will be noticeable and the sharper your image will appear.
Cons of Raster Images
Blurry When Enlarged: The biggest downfall to raster images is that they become pixelated (grainy) when enlarged. Why is this? Well, there is a finite number of pixels in all raster images. When you enlarge a photo, the computer takes its best guess as to what specific colours should fill in the gaps. This interpolation of data causes the image to appear blurry since the computer has no way of knowing the exact shade of colours that should be inserted.
A vector graphic uses maths to draw shapes using points, lines and curves. So whereas a raster image of a 25mm x 25mm square at 300 dpi will have 300 individual pieces of information, a vector image will only contain four points, one for each corner. The computer will use maths to “connect the dots” and fill in all of the missing information.
The most common types of vector graphics? Fonts and logos.
Popular vector file format extensions include: eps, ai and pdf.
Pros of Vector Images
Infinitely Scalable: Vector files can be scaled up or down as much as you want without losing any image quality. An important consideration with regard to signage artwork.
Smaller File Size: Using our previous 25mm x 25mm square example, a vector file needs only four points of data to recreate a square versus 300 individual pixels for a raster image. For simple graphics, like geometric shapes or typography, this means a much smaller file size and faster processing speed.
Edibility: Unlike popular raster-based formats, such as a jpg or png, vector files are not “flattened”. When you open them back up in a program such as Adobe Illustrator, all of the original shapes exist separately on different layers. This means you can modify individual elements without affecting other objects in the image.
Cons of Vector Images
Limited Effects: By definition, vector graphics are created from simple points and lines. This means they can’t handle certain styling effects, like blurring or a drop shadow, that are available with raster images.