Updownscaling

Updownscaling is a term used in signal processing to describe the process of converting data between different sampling rates or resolutions, typically through a combination of upsampling and downsampling. It can refer to moving from one resolution to a higher one (upscaling) and then to a lower one (downscaling), or to a direct resampling path that uses both steps in sequence to reach a target rate or size. The goal is to adapt data for display, storage, or processing while controlling artifacts such as aliasing and blurring.

In imaging and video, updownscaling often involves first increasing the pixel grid with an interpolation method (nearest neighbor, bilinear, bicubic, or Lanczos) and then applying a low-pass filter before reducing to the target resolution. This helps prevent high-frequency components from folding into lower frequencies during downsampling. Conversely, some pipelines perform downsampling after an initial upsampling step to smooth the data and reduce aliasing, especially when the final size is smaller than the original.

In audio, updownscaling refers to resampling audio data to a different sample rate. Upsampling inserts new samples via interpolation, followed by a reconstruction filter; downsampling uses a low-pass filter to avoid aliasing before discarding samples. Multi-rate processing and polyphase filter banks are common techniques to perform updownscaling efficiently.

Applications include display scaling for monitors, image and video compression, audio sample-rate conversion, and any workflow requiring data to be converted across incompatible resolutions. The choice of algorithm and order of operations significantly affects artifacts, computation, and fidelity.