Definition of raster scan (original) (raw)

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Displaying or capturing a video image line by line in an earlier CRT display system. CRT-based monitors and TVs used this method whereby electrons were beamed (scanned) onto the phosphor coating on the screen a line at a time from left to right starting at the top-left corner. At the end of the line, the beam was turned off and moved back to the left and down one line, known as the "horizontal retrace." When the bottom-right corner was reached, the electron gun was returned to the top-left corner, known as the "vertical retrace." For TV signals, these "flyback" periods in which the electron beam was moved to a different line were also called the "horizontal" and "vertical blanking intervals."

Capturing Video Is the Opposite

Raster scan video used the same sequence as a monitor, but in reverse. Instead of sending electrons to a material that created light, light was directed to a material that held a charge, and the charge was turned into an electronic signal. The first video cameras used a vacuum tube with a light-sensitive plate at one end. Subsequently, CCD and CMOS chips replaced the tube. See CRT, CCD sensor, CMOS sensor and rasterize.

Raster Scan Tracing Starting at the top-left of the screen and going to the bottom-right, the electron beam is turned on a line at a time (1), then turned off to go back to the next line (2), then off once again to go back up to the top (3).

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