Label: AV VGA
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How much do you know about VGA video signals and AV video signals?
VGA video signal
The bandwidth of a VGA display refers to the total number of pixels scanned by the electron gun per second, which is equal to "horizontal resolution x vertical resolution x field rate (number of picture refreshes)". Compared to the line frequency, the bandwidth is more comprehensive and more directly reflects the display performance. However, the horizontal bandwidth calculated by the above formula is only a theoretical value. In practical applications, in order to avoid signal attenuation at the edge of the image and keep the image clear around, the scanning capability of the electron gun needs to be larger than the resolution size, and the horizontal direction is usually 25% larger and vertical. The direction is 8% larger, so the actual video bandwidth is calculated as “horizontal resolution x125% x vertical resolution x108%â€, ie “row frame x135%. Still taking the above standard as an example: 1024x768x85Hz image mode, the actual bandwidth is about It is "1024x768x85x135%=90.2MHz".
Normal video (AV)
In general, we believe that the baseband transmission bandwidth of a normal video signal is 6M. From the technical point of view of the monitor, the 1MHZ video bandwidth of the general picture tube corresponds to the horizontal definition of 52 lines, and the video bandwidth displayed by the color monitor is 300/52=5.76MHZ.
The video bandwidth represents the amount of information carried by the video signal per unit time, and the ratio of the VGA video signal 1024x768/85Hz to the normal video signal carrying information is about 15:1.
in conclusion
The bandwidth of the two signals is different, and the amount of information carried is different. Therefore, when the AV-VGA is used, the amount of information carried by the AV video signal cannot satisfy the amount of information required for the VGA video display, and the image is not clear, and the image details such as text cannot be displayed. .
The above comparison shows that in the two technical indicators of video signal: display resolution and signal bandwidth, ordinary video is far behind VGA video, so in today's increasingly demanding video, VGA video is used in various display system projects. The display has become a consensus.
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