TYPES OF RASTER DATA: -
Raster data can be categorized in following types: -(i) Satellite Imagery: - Remotely sensed satellite data are recorded in raster format. The pixel value in a satellite image represents light energy reflected or emitted from earth�s surface. By analyzing the pixel values, an image processing system can extract a variety of themes from satellite images, such as land use and land cover, hydrography, water quality and other areas. Satellite images can be displayed in black and white or in color. Satellite images can also simulate color photographs if they have pixel values from the red green and blue spectral bands. The image looks like a color photograph if bands 3,2 and 1 are assigned to red , green and blue respectively, and a color infrared photograph if bands 4,3 and 2 are assigned to red, green and blue respectively.
(ii) Binary Scanned Files: - In this type of raster data a scanned image contains value of 0 or 1.
(iii) Graphics Files: - In this type of raster data we can include maps, photographs and images which can be stored as digital graphic files. Major popular graphic files in raster format are GIF (Graphic Interchange Format), TIFF (Tagged Image File Format), JPEG ( Joint Photographic Experts Group).
(iv) Digital Elevation Models: -A digital elevation model (DEM) consist of an array of uniformly spaced elevation data. A DEM is point-based, but it can easily be converted to raster data by placing each elevation point at the center of a cell.
(v) Digital Orthophotos: - A digital orthophoto quad (DOQ) is a digitized image prepared from an aerial photographs or other remotely sensed data, in which the displacement caused by camera tilt and terrain relief has been removed. A digital orthophoto is geo-referenced and can be registered with topographic and other maps.
