Raster images vs Vector images – a brief primer

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A so-called raster-based source image is one that is defined in terms of individual pixels. Each single pixel is defined in terms of its individual colour and intensity, and bears no logical relationship to any other pixels in the image. The most obvious example of a raster-based source image is a digital or digitised photograph. Raster-based file formats include BMP, JPG and PNG.

So-called vector-based source images are defined by mathematical formulae in terms of a collection of shapes and fills, all of which relate to each other in terms of “two-and-a-half-dimensional” positioning. The most common examples of vector-based source images are company logos, although modern 2D and 3D vector-based editing software is capable of producing highly complex and even photo-realistic images. Vector-based file formats include EPS and AI.

Many contemporary image source file editors are able to handle both raster and vector images. Examples are Adobe Photoshop, which is raster-oriented with some vector capabilities, and Adobe Illustrator, which is vector-based with some raster capabilities.

Note that all web and digitally printed images are, in the end, raster images. Some of them are direct renditions of raster-based source images, while some of them are rendered by editing software from vector-based source images. In the 3D modelling world, a 3D "vector-based" wireframe model is developed and various effects (textures, perspectives, lighting etc.) are applied to it in the editing environment. A 2D raster image is then rendered from the model.

An interesting special case of vector-based source files is the ubiquitous Flash animation, which employs vector-based source images to render monitor-friendly raster images at runtime. This is possible because the highly compact vector definitions can be delivered to the web browser in small, efficient files.

The primary benefit of using vector-based source images is that, because they are expressed as a set of mathematical formulae rather than individual pixels, they may be scaled and manipulated to a far greater degree without loss of image fidelity.

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