Video scaler

Video scaler

A 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 (e.g. standard definition) to one of higher resolution (e.g. high definition television).

Video scaler devices can be found embedded in:

* Computer monitors
* Televisions
* Video editing and broadcasting equipment
* Other audio/visual devices

Video scalers can also be a completely separate box, often providing simple video switching capabilities. These units are commonly found as part of home theatre or projected presentation systems. Home theatre uses might include converting a standard definition DVD or video game signal into high-definition for display on a LCD or plasma television while obtaining the best picture quality possible. Scalers can also be found in schools, lecture theatres and modern churches, where numerous video sources (e.g. DVD video, live camera feeds, DVI/VGA output from a computer) need to be switched between, while the highest possible resolution is maintained.

Video scalers are primarily a digital device, however they can be combined with an analog-to-digital converter (ADC, or digitizer) and a digital-to-analog converter (DAC) to support analog inputs and outputs.

Scaling a signal to match the display

The "native resolution" of a display is how many physical pixels make up each row and column of the visible area on the display's output surface. There are many different video signals in use in the world which are not the same resolution (neither are all of the displays), thus some form of resolution adaptation (video scaling) is required to properly frame a video signal to a display device. For example, within the United States, there are NTSC, ATSC, and VESA video standards each with several different resolution video formats.



The most common example of a video scaler implementation is within a standard LCD desktop monitor, which converts a VGA signal (640x480 pixels) from a computer into a digital signal with a digitizer and then sends the 640x480 pixels into the video scaler to be upscaled to SXGA (1280x1024 pixels) for display on a monitor with 1280x1024 physical pixels on the TFT glass. In this case the resolution outputted by the computer would only use approximately 25% of the actual pixels without a scaler. By upscaling the computer’s output to the native resolution of the TFT glass, the image fills the whole screen without any black pixels surrounding the image content. Usually, the picture is no clearer or more detailed, only larger. The least expensive type of scaler does "pixel replication" where a pixel is copied into the next pixel to double the image resolution. Better scaling devices include other processing and filtering techniques to maintain the original details when increasing the resolution.

TVs also typically employ some kind of overscan correction which internally upscales a received image by around four percent (this value varies by manufacturer and display technology) primarily due to historical broadcast reasons (see Safe area) - this ensures that any artifacts that are a result of the broadcast are not seen by the display customer. Some televisions support an option not to do this, often called "dot-by-dot", "Just" or "1:1" modes. In these modes, a display will attempt to place every pixel it received on the viewable area of the display. Overscan is best described as "zoom", where the top, bottom, and both sides are cut off.

Image Artifacts/Errors Related to Video Scaling

* Banding or posterization
* Scaler ringing
* Double scaling - When a source device is used which upscales to a resolution not native to a television's display, the TV can scale the image a second time which unnecessarily reduces the final output quality.

Display Limitations

Placing a video scaler before a limited-capability display device will not remove the limitations of that display device (for instance, you can’t make a 720p display take a 1080p signal and expect to see all 1920x1080 pixels on the 1280x720 display surface). A common misconception of consumers is that if you upscale to 1080p from a 720p source and the TV downscales to 854x480 internally (like within a plasma display), that you would end up with a better image. Since the final display surface does not contain the necessary pixel amount to display the 720p content in its entirety, there is a loss in the vertical and horizontal resolution in the final displayed image. It is preferred to send the display the exact resolution that it needs to output a final display image. Some displays may have a further problem when displaying native resolution however, when sent the exact native resolution image, the display may be programmed to assume that it is receiving a signal from a PC - which will cause it to reduce its output brightness (this is a protection mechanism which display manufacturers like Pioneer have installed to prevent or reduce image phosphor burn in).

Upscaling/Upconverting DVD

Upscaling/Upconverting DVD (Digital Versatile Disc) Players contain a scaler, which allows the user to convert lower resolution content into a signal that the display device will handle as high definition content. Depending on the quality of the scaling that is done within the upscaling/upconverting DVD player, the resultant output quality of the video displayed may or may not be improved. The idea behind upconverting DVD players is that when a DVD player is connected to an HDTV, especially one of the fixed pixel display type such as LCD, Plasma display, or DLP and Lcos projection TV, scaling happens anyway, either inside the player or inside the TV. By performing the scaling closer to the source inside the DVD player, the video scaler gets to work with the original signal without the concern of transmission error or interference. There exists independent benchmark test [] verifying that some upconverting DVD players do produce better video quality. However, remember under no circumstances will an upscaling/upconverting DVD player provide "high-definition content", since video information can only be retained or lost in each successive conversion step, but not created. Companies such as Denon, Pioneer Electronics, Panasonic and OPPO Digital are among the first to make upconverting DVD players. Later on almost all consumer electronics brands have this product category. Computer software DVD-Video players like PowerDVD and WinDVD tap into a computer's video card in order to upscale a video frame from the DVD content to the user's set output resolution.

A properly designed upconverting DVD player should have these key parts all with good quality: MPEG decoder, deinterlacing component, and video scaler. Among those, the deinterlacing component is the most important one. If the deinterlacer assembles the video frame in an incorrect manner, no matter how good the video scaler is, it still cannot produce the correct video. A typical example of a well-designed upconverting DVD player is the OPPO Digital DV-983H. It uses an MPEG decoder chip made by MediaTek, a deinterlacer chip ABT102 and a video scaler ABT1018, both made by Anchor Bay Technologies, Inc. (Later revised to use an ABT2010 chip that contains both the deinterlacer and the scaler.) [ [ OPPO Digital - What features of the "VRS by Anchor Bay" video processing technology are utilized by the DV-983H?] ] On the other hand, some upconverting DVD players use a single chip that contains the MPEG decoder, deinterlacing component and video scaler. This type of chip is often called SoC (System-on-a-Chip). Low cost upconverting DVD players usually feature the SoC design.

Video processor

Video scalers are often combined with other video processing devices or algorithms to create a video processor that improves the apparent definition of video signals. These other devices may include the ability for:
* deinterlacing
* aspect ratio control
* digital zoom and pan
* brightness/contrast/hue/saturation/sharpness/gamma adjustments
* frame rate conversion
* color point conversion (601 to 709 or 709 to 601)
* color space conversion (Component to RGB or RGB to Component)
* mosquito noise reduction
* block noise reduction
* detail enhancement
* edge enhancement
* motion compensation
* primary and secondary color calibration (including hue/saturation/luminance controls independently for each)

These can either be in chip form, or as a stand alone unit to be placed between a source device (like a DVD player or set-top-box) and a display with less-capable processing. The most widely recognized video processor companies in the market as of June 2007 are:

* Genesis Microchip (with the FLI chipset)
* Sigma Designs (with the VXP chipset - was Gennum, Sigma Designs purchased the Image Processing group from Gennum on February 8, 2008)
* Silicon Optix (with the HQV chipset and Teranex system products)
* Anchor Bay (with the VRS chipset and DVDO system products)

All of these companies chips are in devices ranging from DVD upconverting players (for Standard Definition) to HD DVD/Blu-Ray Disc players and set-top boxes, to displays like plasmas, DLP (both front and rear projection), LCD (both flat-panels and projectors), and LCOS/”SXRD”. Their chips are also becoming more available in stand alone devices (see "External links" below for links to a few of these).

See also

* Display resolution
* Deinterlacing
* Video display standards
* Stretch-o-Vision


External links

* Chipsets:
** [ Anchor Bay VRS]
** [ Silicon Optix HQV]
** [ Sigma Designs VXP] (Formerly Gennum VXP)
** [ Genesis Microchip FLI]

* Standalone Video Processors:
** [ Algolith Upscaling Technology] FPGA Based
** [ Algolith Video Scaling Technology] IP Based
** [ VRS Based (DVDO)]
** [ HQV Based]
** [ both FLI and VXP Based]

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