Lanczos3

Lanczos3 is a specific instance of the Lanczos resampling filter, a high‑quality algorithm for image scaling and interpolation. The general Lanczos function is defined as a sinc function multiplied by a window function of a chosen width, usually denoted by a number (e.g., 2 or 3). Lanczos3 uses a window width of three, meaning that the kernel spans six samples on either side of the target pixel; it is therefore called the Lanczos‑3 filter. The mathematical form is L(x)=sinc(x)·sinc(x/3) for |x|<3, and L(x)=0 otherwise. Because the sinc component exactly reproduces band‑limited signals in theory, the filter provides very good frequency preservation while the window limits side‑lobes to reduce ringing artefacts.

The filter was first described by Leonid Lanczos in the 1960s and later adopted by various image processing libraries. It is commonly available in software such as ImageMagick, GIMP, and Photoshop, and in hardware video encoders and decoders. Lanczos3 is often chosen for high‑quality resizing because it trades slight computational cost for sharper results compared with simpler nearest‑neighbour or bilinear filters. Compared with Lanczos2, the extra support width allows better elimination of aliasing, but it can introduce more pronounced ringing near high‑contrast edges; Lanczos4 offers further attenuation at the expense of more blur.

In practice, Lanczos3 is favored for tasks that demand minimal visual distortion, such as printing, print‑media scaling, and high‑resolution photographic restoration. It is also a common reference point in benchmark studies that compare interpolation methods. The algorithm remains a staple in both proprietary and open‑source image processing environments due to its balance of performance and visual fidelity.