Scan conversion
Encyclopedia
Scan conversion or scan rate converting 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.
The application of scan conversion is wide and covers video projectors, cinema equipment, TV and video capture
cards, standard and HDTV television
s, LCD monitors and many different aspects of picture processing.
signals.
There are two distinct methods for changing a picture's data rate:
This conversion is done using large numbers of delay cells and is appropriate for analog video.
In this method, a picture is stored in a line or frame buffer with n1 speed (data rate) and is read with n2 speed, several picture processing techniques are applicable when the picture is stored in buffer memory including kinds of interpolation from simple to smart high order comparisons, motion detection and … to improve the picture quality and prevent the conversion artifacts.
and VLSI scales. Timing, interference between digital and analog signals, clocks, noise and exact synchronization have important roles in the circuit.
Digital conversion method needs the analog video signal to be converted to digital data at the first step.
A scan converter can be made in its basic structure using some high speed integrated circuits as a circuit board however there are some integrated circuits which perform this function plus other picture processing functions like scissoring, change of aspect ratio
and … an easy to use example was SDA9401
):
Down conversion (decimation
):
Scan conversion serves as a bridge between TV and computer graphics technology.
Video processing
In electrical engineering and computer science, video processing is a particular case of signal processing, which often employs video filters and where the input and output signals are video files or video streams. Video processing techniques are used in television sets, VCRs, DVDs, video codecs,...
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.
The application of scan conversion is wide and covers video projectors, cinema equipment, TV and video capture
Video capture
Video capture is the process of converting an analog video signal—such as that produced by a video camera or DVD player—to digital video. The resulting digital data are computer files referred to as a digital video stream, or more often, simply video stream...
cards, standard and HDTV television
Television
Television is a telecommunication medium for transmitting and receiving moving images that can be monochrome or colored, with accompanying sound...
s, LCD monitors and many different aspects of picture processing.
Mechanisms and methods
Scan conversion involves changing the picture information data rate and wrapping the new picture in appropriate synchronizationSynchronization
Synchronization is timekeeping which requires the coordination of events to operate a system in unison. The familiar conductor of an orchestra serves to keep the orchestra in time....
signals.
There are two distinct methods for changing a picture's data rate:
- Analog Methods (Non retentive, memory-less or real time method)
This conversion is done using large numbers of delay cells and is appropriate for analog video.
- Digital methods (Retentive or buffered method)
In this method, a picture is stored in a line or frame buffer with n1 speed (data rate) and is read with n2 speed, several picture processing techniques are applicable when the picture is stored in buffer memory including kinds of interpolation from simple to smart high order comparisons, motion detection and … to improve the picture quality and prevent the conversion artifacts.
How to realize
The process in practice is applicable only using integrated circuits in LSILSI
LSI may mean* Lord Steel Industry, a manufacturer of stainless steel tubing and piping* Labour and Socialist International, a former socialist international* Lake Superior and Ishpeming Railroad, a railroad service in Michigan, U.S....
and VLSI scales. Timing, interference between digital and analog signals, clocks, noise and exact synchronization have important roles in the circuit.
Digital conversion method needs the analog video signal to be converted to digital data at the first step.
A scan converter can be made in its basic structure using some high speed integrated circuits as a circuit board however there are some integrated circuits which perform this function plus other picture processing functions like scissoring, change of aspect ratio
Aspect ratio
The aspect ratio of a shape is the ratio of its longer dimension to its shorter dimension. It may be applied to two characteristic dimensions of a three-dimensional shape, such as the ratio of the longest and shortest axis, or for symmetrical objects that are described by just two measurements,...
and … an easy to use example was SDA9401
Some examples
Up conversion (interpolationInterpolation
In the mathematical field of numerical analysis, interpolation is a method of constructing new data points within the range of a discrete set of known data points....
):
- In many LCD monitors there is a native picture mode, however the monitor can display different graphical modes using a scan converter.
- In a 100 Hz/120Hz analog TV, there is a scan converter circuit which converts the vertical frequency (refresh rate) from standard 50/60Hz to 100/120Hz to achieve a low level of flicker which is important in large screen (high inch) TVs.
- An external TV card receives the TV signals and converts them to VGA or SVGA format to display on monitor.
Down conversion (decimation
Decimation (signal processing)
In digital signal processing, decimation is a technique for reducing the number of samples in a discrete-time signal. The element which implements this technique is referred to as a decimator.Decimation is a two-step process:...
):
- Many graphic cards have output for standard-definition televisionStandard-definition televisionSorete-definition television is a television system that uses a resolution that is not considered to be either enhanced-definition television or high-definition television . The term is usually used in reference to digital television, in particular when broadcasting at the same resolution as...
. Here there is a conversion from computer graphical modes to TV standard formats. - Other graphic cards lack an SDTV output, but their VGA outputs can still be connected to an SDTV through an external scan converter (pictured).
Scan conversion serves as a bridge between TV and computer graphics technology.
See also
- Analog-to-digital converterAnalog-to-digital converterAn analog-to-digital converter is a device that converts a continuous quantity to a discrete time digital representation. An ADC may also provide an isolated measurement...
- Digital-to-analog converterDigital-to-analog converterIn electronics, a digital-to-analog converter is a device that converts a digital code to an analog signal . An analog-to-digital converter performs the reverse operation...
- VESAVESAVESA is an international standards body for computer graphics founded in 1989 by NEC Home Electronics and eight other video display adapter manufacturers.VESA's initial goal was to produce a standard for 800×600 SVGA resolution video displays...
- Digital TelevisionDigital televisionDigital television is the transmission of audio and video by digital signals, in contrast to the analog signals used by analog TV...
- International Telecommunication UnionInternational Telecommunication UnionThe International Telecommunication Union is the specialized agency of the United Nations which is responsible for information and communication technologies...
- Video scalerVideo scalerA video scaler is a device for converting video signals from one size or resolution to another: usually "upscaling" or "upconverting" a video signal from a low resolution to one of higher resolution A video scaler is a device for converting video signals from one size or resolution to another:...