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Horizontal scan rate, or horizontal frequency, usually expressed in kilohertz, is the number of times per second that a raster-scan video system transmits or displays a complete horizontal line, as opposed to vertical scan rate, the number of times per second that an entire screenful of image data is transmitted or displayed.
Scan rate is a term used when discussing raster-scan video, describing the speed at which the image is transmitted or displayed. There are two types: There are two types: Horizontal scan rate , the number of times per second that a single horizontal line of image data is transmitted or displayed
In a CRT, the vertical scan rate is the number of times per second that the electron beam returns to the upper left corner of the screen to begin drawing a new frame. [3] It is controlled by the vertical blanking signal generated by the video controller, and is partially limited by the monitor's maximum horizontal scan rate.
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. [2] This is sometimes used today as a visual effect in computer graphics. [3]
In a raster scan, an image is subdivided into a sequence of (usually horizontal) strips known as "scan lines".Each scan line can be transmitted in the form of an analog signal as it is read from the video source, as in television systems, or can be further divided into discrete pixels for processing in a computer system.
Early home computers output video to ordinary televisions or composite monitors, utilizing television display standards such as NTSC, PAL or SECAM.These display standards had fixed scan rates, and only used the vertical and horizontal sync pulses embedded in the video signals to ensure synchronization, not to set the actual scan rates.
Scan conversion or scan converting rate is a video processing technique for changing the vertical / horizontal scan frequency of video signal for different purposes and applications. The device which performs this conversion is called a scan converter .
In the NTSC television standard, horizontal blanking occupies 10.9 μs out of every 63.6 μs scan line (17.2%). In PAL, it occupies 12 μs out of every 64 μs scan line (18.8%). Some modern monitors and video cards support reduced blanking, standardized with Coordinated Video Timings. [3]