If you want to make digital art, it’s good to be aware of vectors and rasters (sometimes called bitmaps). But what are they?
In short, they determine how your image is built up. See it as one building made of concrete, and another made of bricks. This probably hasn’t really explained yet what they are, so let’s have a closer look at each.
A raster image is made up of pixels. Zoomed out it looks like a smooth image, but if you zoom in really closely on a raster image, you’ll see a grid (or, raster) composed of pixels. Since pixels are the smallest possible size on a computer, resizing a raster image is somewhat problematic. Making it bigger means that what was one pixel suddenly has to be divided over multiple pixels, and making it smaller means that one pixel suddenly has to contain the information of several surrounding pixels. Usually a raster image that’s made smaller will still look good, but once it’s smaller you won’t be able to make it bigger again with it still looking nice. Information was lost upon resizing and can’t be recovered. The image below illustrates this well; the first image is the original, the second a smaller version, and the third is that second image resized again to the size of the first.
On the other hand, when you make the image bigger, it’ll become blurry and weird, similar to the third image. Information that isn’t there has to be filled in; one pixel is spread over multiple pixels, and you start seeing the pixel grid at full size.
When making raster images like digital paintings, it’s best to work at a bigger size than your final work is intended to be. At least double the size works well. You can just resize it to the correct size when you’re done (and that has the added bonus that small mistakes aren’t as visible).
Programs such as Adobe Photoshop, GIMP, Paint Tool Sai etc. are made to work with rasters. Photoshop does have some vector capabilities (perhaps other programs as well, but I haven’t worked with those enough), for instance in its text tool and its pen tool. By default, text in Photoshop is created as vectors, allowing for easy resizing without quality loss. However, once you want to create some effects with it or go somewhat more complicated than cleanly-lined words, it has to be rasterized, thereby losing the vector information.
Vector images are made up of paths. Paths are mathematical formulas made visible; you’ve probably dealt with them in maths class, though they might not have been called vectors. The numbers determine how the path is shaped.
Because they’re all based on numbers and formulas, vector images are easily resized, and to (theoretically) any size imaginable. If an image has to become both business-card sized and billboard-sized (like a logo, for instance), you’ll probably want to work with vectors.
They have their downside, however. Vector files aren’t designed to have a large, complex array of colours. While there are certainly more and more possibilities with them as technology develops further, vector files just aren’t made to have the colour complexity of a raster file.
Vector images can be made by programs such as Adobe Illustrator and Inkscape, among many others. Some of these programs allow you to go into the actual maths, while others are purely graphic.
When to use what
So when should you use which?
Generally speaking, graphic design uses vectors while ‘normal’ art uses rasters. If you need to create an image with relatively few colours which needs to be able to resize to any size, you’ll want to go with vectors. Things like logos, packaging designs, etc. Often when I need to design something I start by sketching in Photoshop (raster-based) and create the actual, final thing in Illustrator (vector-based).
If you want to make a digital painting, however, you’ll probably want to use complex colours, brushes, etc. Rasters are what you’ll want to use then. Photographs, pixel art etc. are all also raster-based images. If you’re not sure how big you want the final thing to be, play it safe and go big.