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What is a raster image?


Basically, a raster images is a bitmap, which in turn is a grid of individual pixels that compose an image as a whole. This kind of graphics render images as a number of countless tiny squares, also called pixels. And each pixel is coded in a specific shade.

Raster images vs. vector images

Unlike raster graphics, vector images are made up of paths, each of which has a mathematical formula that defines its shape and color.

Vectors can be infinitely scaled without loss of quality, so they are excellent for:

  • logos
  • illustrations
  • engravings
  • product artwork 

On the other hand, it's not possible to scale raster images without sacrificing quality; they will either pixelate or become blurry. They are best used for:

  • Non-line art images
  • specifically digitalized photographs
  • scanned artwork
  • detailed graphics

We could say that's the main difference between rasters and vectors. Raster graphics are not scalable.

5 things you need to know about raster images

  1. Screen resolution will probably have an impact on raster files
  2. Scaling can be an issue: raster files are made up of tiny pixels, and when the image is enlarged, the pixel proportion per inch is reduced, as a consequence, the image becomes blurred and pixelated.
  3. They are bulky files, but they look great!
  4. They are everywhere, since they are supported by almost every computer program.
  5. They can be converted into vector files; this enables you to work with the image (vector files are easier to edit), and it makes them scalable, without resolution being an issue.

When to use raster and when to use vector

Let's get one thing clear, some images can only be raster and some can only be vectors. But make sure you use raster when you need high-quality, pixel-perfect images without worrying about the file size. 

Raster graphics are far superior when we talk about color usage; the more pixels there are, the more lifelike the image. However, be sure to check out your file size; more quality equals more data.

The rule of thumb is: if image quality is the top priority, then use raster graphics. Vector can go for everything else 😉.

Example of raster image (FIG. 1) vs. example of vector graphic (FIG. 2)

To wrap it up, a good analogy is painting vs drawing; rasterized images can create complex imagery with a mix of blended colors, like in painting, while vector images are like drawing: they are faster and more convenient for simple shapes, no matter the size.

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