Raster graphics
A raster graphics, and pixel graphics (English raster graphics image, digital image, bitmap or pixmap ), is a form of description of an image in the form of computer-readable data. Raster graphics are composed of a grid- like arrangement of so-called pixels ( picture elements ), which a color is assigned to each. The main characteristics of a raster graphics are therefore the image size ( width and height measured in pixels, commonly known as resolution) and color depth.
The production and processing of raster graphics fall within the field of computer graphics and image processing. Another way to describe images are vector graphics.
Applications
Raster graphics are suitable for displaying complex images such as photographs, can not be described with vector graphics. Raster graphics can from existing material - digitized or created with image editing software - such as a scanner or a digital camera.
The pixels of a raster image can only contain information such as the color. In the latter application areas have raster data to vector data over the disadvantage that they are relatively inaccurate and poorly suitable for topological analysis.
Minimalistic pixel graphics have become a popular art form. The spectrum of the so-called pixel art ranges from Logos on websites to TV spots and billboards. By their very nature are similar to traditional pixel graphics techniques such as mosaic and cross embroidery.
Dissemination and problems
Today's computer screens are sold exclusively through a raster graphics, which is stored in the frame buffer and contains the entire screen content driven. Therefore, vector graphics must be rasterized before output. When printing to some printers, a raster image processor takes this step. All printer with linear paper feed are suitable for playback of pixel graphics while Plotter with line-oriented vector graphics should be controlled.
The best-known graphic formats for raster graphics are BMP, GIF, JPEG / JFIF, PNG and TIFF. Some of these formats apply lossless or lossy image compression.
One of the disadvantages of raster versus vector graphics is one of the most relatively high memory consumption. Since raster graphics consist of only a limited number of pixels, two-dimensional geometric shapes are approximate only. Here, the staircase effect or even the aliasing is revealed, which can be attenuated by anti-aliasing. In geometric transformations of a raster graphic, such as scaling, information can be lost or tones are generated, which previously did not exist.
Conversion
The conversion of a vector graphic into a raster graphic is called rasterization. This process takes place every time a vector graphic is displayed or printed on the screen.
The reverse path, called vectorization of raster graphics is much more difficult. It can be done manually by tracing, or by special functions of a vector graphics program such as the Trace Bitmap from Inkscape function, or by specialized programs such as Corel Power Trace or Potrace. This route is also often flawed because graphical primitives such as lines, circles or curves in the raster image are shown only inaccurate and therefore can not be detected accurately. Particularly large problems arise can be approximated by insufficient color or brightness gradient on raster images which when tracing only as discrete bands ( banding ).