Video scaler

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A video scaler is a numerical processing device for converting video signals between one arbitrary resolution or aspect-ratio and another resolution or aspect-ratio. These devices are primarily digital, however – a video scaler 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. In their most common application they are "upscaling" or "upconverting", taking a low resolution (Standard Definition) video and increasing the resolution to a high resolution (High Definition) video.

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[edit] Scaling for Displays - To Achieve Native Resolution

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 (this "resolution" is NOT the physical size of the display it is shown on).

This is a blow-up of a small section of a 1024x768 (VESA XGA) resolution image. Notice the picture is actually made up from very small squares - these are pixels.

This is a comparison of several different video format resolutions. The lowest resolution is 480p/i, while the highest is 4K (DCI). Since the same content is placed in more pixels for the large formats, the finer detail is preserved.

The most common example of a video scaler implementation is within a standard desktop monitor, which converts a VGA (640x480 pixels) signal 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 pixel 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 active image content.

This does not necessarily mean that the picture becomes clearer or more detailed - as scalers in their simplest form only increase the sample points for the original signal, resulting in more data sample points from the same original conent information. 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 signal conditioning and filtering to maintain the original signal details when increasing the resolution.

(an image showing the difference between pixel replication, linear interpolation, and filtered scaling will be placed here)

TVs also typically employ some kind of overscan correction which internally upscales a received image by around four percent (this value varries 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.

[edit] Artifacts (Errors) Related to Video Scaling

  • Banding
(content and pictures will be added here)
  • Scaler Ringing
(content and pictures will be added here)
  • Double Scaling
It is important to note, as mentioned above, that since most flat panel televisions internally employ upscaling functionality to scale various input resolutions to their target resolutions and to enable overscan for safe areas, when a source device is used which upscales - but the output resolution of the source is not what the TV will display as a final image - double scaling can occur which may reduce the final output image fidelity.
(a content describing and illustrating double scaling will be placed here later)

[edit] 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 from 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).

[edit] 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. Under no circumstances does an Upscaling/Upconverting DVD Player provide "high-definition content"; video information can only be lost in each successive conversion step. 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 - however, since the common CRT computer display is typically a Multisync type, there is no double scaling (digital displays can be an exception to this however).

[edit] 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 or functions may include Deinterlacing, Aspect Ratio Control, 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) and other features that the video processor manufacturer has elected to include. 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 Gennum on February 8, 2008), Silicon Optix (with the HQV chipset and Teranex system products), and 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).

[edit] External links