Raster graphics, also known as bitmap graphics, are a sort of digital image in which an image is represented by small rectangular pixels, or picture elements, organized in a grid configuration. These individual elements can be and often are stored directly on disk or in memory devices such as RAM. When required for display, the entire image is read into memory at once.
The word "raster" comes from the fact that early images were created by scanning paper with an optical device called a rasterizer. The word "bitmap" was originally an acronym for "block-interleaved binary file". Today these terms generally refer to two-dimensional arrays of bytes, usually but not limited to 8-bits per pixel, arranged in rows and columns. However some sources differentiate between "rasters" and "bitmaps", with the former being a single scan of the screen, and the latter being a sequence of scans that makes up the whole image.
Although the term "raster image" came first, modern computers store their images in vector formats. A vector image is one where the location of each element is defined by coordinates in mathematical form, rather than by physical positions on a surface. The most common vector format is the polygon model, which consists of a set of vertices with associated coordinates that define the shape of the object being displayed.
A bitmap (sometimes known as a "raster") graphic is made up of rows of various colored pixels that form a picture. The more colors, the richer the image.
Bitmaps are stored in computer memories as patterns of on/off switches for individual pixels. To be read by the screen, the image must be scanned back and forth across it. This is done with a cursor controlled by the keyboard; when you press a key, the cursor moves to the next cell on the screen.
The most common type of bitmap image format is the pixel map. Each cell of the screen has an address which determines what color it will display. Pressing any key causes that address to be displayed as a color at its corresponding location.
Pixmaps are bitmaps that are treated as images rather than as collections of pixels. That means they can have transparency, shadows, and other image effects applied to them.
Vector graphics are very similar to pixmaps but instead of using cells with addresses, they use elements with coordinates. These elements can be lines, circles, shapes, etc and are described by mathematical formulas used by vector graphics programs. When changed slightly, these formulas produce exactly the same result every time.
When you think about pictures, you usually think of raster (or bitmap) images. These are the pictures that are created while scanning or photographing an item. Raster pictures are made up of pixels, or small dots, each with its own color and tone information, which are then combined to produce the image. Pixels are the smallest unit of image information that can be used by a computer for printing, storing on disk or pixelating again.
Images also include vector (or outline) files. These are drawings made up of lines and curves that define shapes. When you click the Print Screen button, your computer creates a vector image of what is on screen. This can be edited with any graphics program or online at sites like Pixlr.com. Vector images are printed exactly as they are drawn, so even tiny details can be seen clearly. They don't get fuzzed up when printed at high quality settings.
Raster images look different when viewed at different resolutions because the pixels become smaller. For example, if you zoom in on a raster image 100 percent, it will look the same as it did at first view. But if you zoom in further, the pixels will begin to run together until only large areas of color are visible.
Vector images do not change shape when viewed at different resolutions.
A visual depiction of anything is what an image is. Vector graphics and raster graphics are two ways to describe a picture. A raster image is also referred to as a bitmap. An image map is a file that contains information that links distinct points on a certain image. These points are known as hotspots. The link between each hotspot and its corresponding part of the image is called a pixel. Web pages often contain both vector and raster images.
In computing, digital images are represented by means of vectors or rasters. Vectors are mathematical objects that define shapes by specifying positions for a set number of points. Each position is given as a fraction of the width of the shape, where 0<=x<1. A point with x=0 is called a vertex, a point with x=1 is called an end point, and so on. Vectors can be used to define lines, circles, ellipses, polygons, and more complex shapes. Rasters are rectangular arrays of pixels. Pixels are the smallest unit of color in an image file; colors are composed of combinations of pixels (e.g., red, green, blue) or groups of pixels (e.g., solid white).
Vectors and rasters can be combined to create composite images.