Raster scan
Although often a great deal faster, it is similar in the most general sense to how one's gaze travels when one reads lines of text.
In most modern graphics cards the data to be drawn is stored internally in an area of semiconductor memory called the framebuffer.
The resulting tilt in the scan lines is very small, and is dwarfed in effect by screen convexity and other modest geometrical imperfections.
As discussed above, this does not exactly happen: the vertical sweep continues at a steady rate over a scan line, creating a small tilt.
These create a sawtooth wave: steady movement across the screen, then a typically rapid move back to the other side, and likewise for the vertical sweep.
A linear change in current would swing the beams at a constant rate angularly; this would cause horizontal compression toward the center.
Computer text is mostly created from font files that describe the outlines of each printable character or symbol (glyph).
These perceptually steady still images are then pieced together to produce a moving picture, similar to a movie projector.
To clear up possible confusion: Referring to the magnetic deflection fields, if there were none, all beams would hit the screen near the center.
After one line has been created on the screen and the beams are blanked, the magnetic field reaches its designed maximum.
A similar process occurs for the vertical scan, but at the display refresh rate (typically 50 to 75 Hz).
Vertical retrace is comparatively slow, occurring over a span of time required for several tens of horizontal scans.
In analog CRT TVs, setting brightness to maximum typically made the vertical retrace visible as zigzag lines on the picture.
In analog TV, originally it was too costly to create a simple sequential raster scan of the type just described with a fast-enough refresh rate and sufficient horizontal resolution, although the French 819-line system had better definition than other standards of its time.
Search and weather radars have a circular display (Plan Position Indicator, PPI) that covers a round screen, but this is not technically a raster.
[1] The concept of raster scanning was inherent in the original mechanical disc-scanning television patent of Paul Nipkow in 1884.
[2] Similar terminology was used in German at least from 1897; Eder[3] writes of "die Herstellung von Rasternegativen für Zwecke der Autotypie" (the production of raster negatives for halftones).
Max Dieckmann and Gustav Glage were the first to produce actual raster images on a cathode-ray tube (CRT); they patented their techniques in Germany in 1906.
The first use of raster specifically for a television scanning pattern is often credited to Baron Manfred von Ardenne who wrote in 1933:[8] "In einem Vortrag im Januar 1930 konnte durch Vorführungen nachgewiesen werden, daß die Braunsche Röhre hinsichtlich Punktschärfe und Punkthelligkeit zur Herstellung eines präzisen, lichtstarken Rasters laboratoriumsmäßig durchgebildet war" (In a lecture in January 1930 it was proven by demonstrations that the Braun tube was prototyped in the laboratory with point sharpness and point brightness for the production of a precise, bright raster).
[9] The mathematical theory of image scanning was developed in detail using Fourier transform techniques in a classic paper by Mertz and Gray of Bell Labs in 1934.
