Spatial Up-scaler with Nonlinear Edge Enhancement for Rational Factors

Spatial image resizing is an important issue for pixel oriented displays with variable input formats. A typical scaling factor of two allows non-linear up-scaling from standard definition (SD) to high definition (HD) format with known parameters in the frequency domain. Nonlinear signal processing enables the creation of higher harmonics to enhance the image sharpness, but it may create annoying alias artefacts. We investigated an up-scaler for rational factors with nonlinear signal processing. The scaling method is based on an economic approach using diamond shaped filters. The additional frequency space in the up-scaled image is filled with higher harmonics created from the detail signal by non-linear signal processing. The creation of higher harmonics is bandwidth limited to prevent aliasing. A carefully chosen design keeps the overall algorithms simple and flexible for a wide range of applications.