Raster graphics
The fundamental strategy underlying the raster data model is the tessellation of a plane, into a two-dimensional array of squares, each called a cell or pixel (from "picture element").
The digital sensors used for remote sensing and astronomy are often able to detect and store wavelengths beyond the visible spectrum; the large CCD bitmapped sensor at the Vera C. Rubin Observatory captures 3.2 gigapixels in a single image (6.4 GB raw), over six color channels which exceed the spectral range of human color vision.
Most computer images are stored in raster graphics formats or compressed variations, including GIF, JPEG, and PNG, which are popular on the World Wide Web.
Headers may also include the number of rows, georeferencing parameters for geographic data, or other metadata tags, such as those specified in the Exif standard.
Thus, the raster above would be represented as: This technique is very efficient when there are large areas of identical values, such as a line drawing, but in a photograph where pixels are usually slightly different from their neighbors, the RLE file would be up to twice the size of the original.
Other algorithms, such as JPEG, are lossy, because the parameterized patterns are only an approximation of the original pixel values, so the latter can only be estimated from the compressed data.
The refresh procedure, being speed critical, is often implemented by dedicated circuitry, often as a part of a graphics processing unit.
The bits of data stored in this block of memory are related to the eventual pattern of pixels that will be used to construct an image on the display.
[9] During the 1970s and 1980s, pen plotters, using Vector graphics, were common for creating precise drawings, especially on large format paper.
Three-dimensional voxel raster graphics are employed in video games and are also used in medical imaging such as MRI scanners.
Examples of fields commonly represented in rasters include: temperature, population density, soil moisture, land cover, surface elevation, etc.
Modern computer-monitors typically display about 72 to 130 pixels per inch (PPI), and some modern consumer printers can resolve 2400 dots per inch (DPI) or more; determining the most appropriate image resolution for a given printer-resolution can pose difficulties, since printed output may have a greater level of detail than a viewer can discern on a monitor.
[12] Raster-based image editors, such as PaintShop Pro, Corel Painter, Adobe Photoshop, Paint.NET, Microsoft Paint, Krita, and GIMP, revolve around editing pixels, unlike vector-based image editors, such as Xfig, CorelDRAW, Adobe Illustrator, or Inkscape, which revolve around editing lines and shapes (vectors).
