A is an algorithmic processing device for converting video signals between one arbitrary resolution/aspect-ratio and another resolution/aspect-ratio. 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. This does not necessarily mean that the picture becomes clearer/more detailed - as scalers in their simplest form only increase the sample points for the original signal resulting in more data points for the original given information. Better scaling devices include other signal conditioning to maintain the original signal details when increasing the resolution. This also does not mean that placing a video scaler before a limited-capability display device will 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). Confusion is caused within the general public, due to how little is understood about video scalers and where they are used. Manufacturers of digital displays (DLP, LCD, LCOS or “SXRD”, Plasma) don’t tell customers that there is a simple video scaler built into their display which accepts a video signal and converts it to what the display is expecting.

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.

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. Since not every video signal in use in the world is exactly the same resolution (and neither are all of the displays), some form of resolution change (video scaling) is required. For example, within the United States, there are NTSC, ATSC, and VESA video standards each with several video formats. 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.