What does raster mean?
A raster is a digital representation of an image as a rectangular grid of pixels. Each pixel records a small part of the image, including its position and, usually, its colour or brightness. Raster images are widely used for photographs, scanned pages, screen graphics, and printed output because they reproduce complex tones and textures effectively. Their central limitation is that enlarging them beyond their native resolution can reveal the individual squares and make the image look pixelated. In computing and graphics, the term contrasts with a vector image, which uses mathematical descriptions of lines and shapes and can usually be scaled without loss of clarity. The related verb “raster” means to scan an image or convert it into a pixel-based representation, although the verb is less common outside technical contexts.
An image, graphic, or representation formed from a regular grid of pixels.
"A high-resolution raster preserves more detail when printed than a low-resolution one."
Often used attributively, as in “raster image.” The term is principally technical.
To scan an image or convert an image into a pixel-based representation.
"The device rasters each slide before sending it to the printer."
This verb is specialized and occurs mainly in imaging, scanning, and computer-graphics contexts.
The plural is used when referring to individual raster images or representations; in technical contexts, raster is also commonly used as a mass noun.
"The editor compared the two rasters before choosing one for publication."
Zoom far enough into a raster image and its apparently continuous picture gives way to a mosaic of tiny, independently coloured squares.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does raster come from?
The word comes from German Raster, meaning “grid” or “lattice,” a technical term associated with image scanning and early raster displays. German Raster was borrowed from Latin rastrum, an archaeological and printing term for a rake, and this is related to the Latin root radere, “to scrape.” The same root underlies English words such as erase, rasp, and abrasion, although the development of the technical sense through German printing and imaging terminology is distinctive.
Related word forms
How raster is actually used
Raster is primarily a technical term used in computing, graphics, printing, and scanning. In digital imaging, it contrasts with vector graphics; in general publishing, it may be treated as a mass noun rather than a count noun.
Easily confused with raster
A raster image is made from individual pixels, whereas a vector image is defined by mathematical paths and can be scaled without pixelation.
Raster refers to the pixel-grid representation of an image, not to the depicted subject itself.