Designing

What are Raster Images?

Raster images are made up of pixels – blocks of colour that blend when viewing from a distance. Let’s dive deep into what they actually are and when we should use it.

What is a Raster Image?
Pros & Cons of Raster Images
1. Pros
2. Cons
When to use a raster image format?
Raster Image software and file types

Raster images are made up of pixels – blocks of colour that blend when viewing from a distance. Let’s dive deep into what they actually are and when we should use it.

What is a Raster Image?

A raster image is any digital graphic that is made out of pixels arranged on a static grid. A pixel is a square of solid colour made from the combination of red, green and blue light (also known as subpixels).

Think of a raster like a mosaic: from up close it just looks like a series of squares but from further away from an image forms. Although the pixel grid is not visible, designers add to it when creating graphics in a raster program like Photoshop. Whenever you use the brush tool to create a digital illustration, every brushstroke adds pixels along the brush path—the number of pixels dependent on the size of the Photoshop document and the radius of the brush you are using. When taking a photo or shooting a video, the lens translates the reflected light into tiny coloured pixels that combine to form a realistic digital image.

Because each pixel is designated to a space on the grid, raster images are resolution-dependent. This means that raster images cannot be resized without distortion because the number of pixels is fixed. The more pixels, the higher quality (or resolution) the image is, given that there is more opportunity for colour blending when viewed from a distance. At the same time, fewer pixels means that an image will show up as tiny or will ‘pixelate’ when resized because there are not enough pixels to provide seamless shading.

Pros & Cons of Raster Images

Pros

Raster images are ideal to use when you want to show the subtleties of colour gradients and shading—for example when you are editing photographs or painting photorealistic illustrations—due to the amount of colour information they can hold.
You are able to zoom in and edit each pixel for finer editing.
Many advanced texture effects work best (or only) with raster images.

Cons

The amount of pixel and colour information means that specific parts of the image can be difficult to isolate without complex masking.
File sizes tend to be larger than vector formats.
Raster images have limitations with scalability. For example, a large scale print like a billboard would require a huge file with a high pixel density.
You have to pre-determine the intended size of your image which makes it hard to adapt if an unexpected change in the project comes up.

When to use a raster image format?

Raster is the default format for photography, video, and web-based media. When it comes to illustration, raster is ideal for photorealism and larger-scale images due to the amount of detail possible. On the other hand, raster cannot be used for logos and are dependent on a high resolution when used for print.

Here is a general guide of which projects would better suit raster images: