Scan line
A scan line is one line, or row, in a raster scanning pattern, such as a line of video on a cathode ray tube display of a television set or computer monitor.
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 a progressive scan signal with below maximum vertical resolution is displayed. This is sometimes used today as a visual effect in computer graphics.
The term is used, by analogy, for a single row of pixels in a raster graphics image.
Scan lines are important in representations of image data, because many image 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. 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.
