Ascan line (alsoscanline) is one line, or row, in araster scanning pattern, such as a line ofvideo on acathode-ray tube (CRT) display of atelevision set orcomputer monitor.[1]
On CRT screens the horizontal scan lines are visually discernible, even when viewed from a distance, as alternating colored lines and black lines, especially when aprogressive scan signal with below maximum vertical resolution is displayed.[2] This is sometimes used today as avisual effect incomputer graphics.[3]
The term is used, by analogy, for a single row ofpixels in araster graphics image.[4]Scan lines are important in representations of image data, because manyimage file formats have special rules for data at the end of a scan line. For example, there may be a rule that each scan line starts on a particular boundary (such as a byte or word; see for exampleBMP file format). This means that even otherwise compatible raster data may need to be analyzed at the level of scan lines in order to convert between formats.
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