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A video scaler is a system that converts video signals from one display resolution to another; typically, scalers are used to convert a signal from a lower resolution (such as 480p standard definition) to a higher resolution (such as 1080i high definition), a process known as "upconversion" or "upscaling" (by contrast, converting from high to low resolution is known as "downconversion" or "downscaling").
Video scalers are typically found inside consumer electronics devices such as , video game consoles, and DVD or Blu-ray players, but can also be found in other AV equipment (such as video editing and television broadcasting equipment). Video scalers can also be completely separate devices, often providing simple video switching capabilities. These units are commonly found as part of home theatre or projected presentation systems. They are often combined with other video processing devices or algorithms to create a video processor that improves the apparent definition of video signals.
Video scalers are primarily a digital data 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.
While scaling a video signal does allow it to match the size of a particular display, the process can result in an increased number of visual artifacts in the signal, such as ringing artifact and posterization.
When the U.S. cable network TNT introduced an HD feed in 2004, it controversially employed a stretching system known as FlexView (which was also offered to other broadcasters). FlexView used a nonlinear system to stretch more near the edges of the screen than in the center of it. The practice was imposed by the senior vice president of broadcast engineering at TNT, Clyde D. Smith, who argued that pillarboxing led to inconsistency between programs for viewers, could cause phosphor burn-in on plasma televisions, some older HDTVs could not stretch 4:3 content automatically, and the quality of stretching on some displays was poor. Despite TNT's intentions, the system was frequently criticized by viewers of high definition channels, with some nicknaming the effect "Stretch-O-Vision".
In 2014, FXX faced similar criticism for its use of cropping and scaling on reruns of The Simpsons (which only started producing episodes in HD beginning in its 20th season), as its cropping method caused various to be lost. In February 2015, FXX announced that in response to these complaints, it would present these episodes in their original 4:3 aspect ratio on its video-on-demand service.
Some series that were originally shot on 35 mm film—such as Friends and Seinfeld—have been converted to high-definition in a similar manner, cropping a widescreen image from the 4-perf pulldown.
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