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Interpolation algorithms

(resampler comparison)




Nearest neighbor (simple)


A pixel becomes a square 2×2 block of the same color, then a 4×4, ...

Main advantage of this system: no calculation is necessary, so it is blazing fast. This is actually the way your browser upsizes images.


Windows Background Switcher Resize effect: no interpolation


Hermite filter


This is slightly better than the naive method. For mathematical details, check the Hermite Interpolating Polynomial.


Windows Background Switcher Resize effect: Hermite filter

Triangle/tent filter


Bilinear interpolation considers the closest 2×2 neighborhood of known pixel values surrounding the unknown pixel. It then takes a weighted average of these 4 pixels to arrive at its final interpolated value. This results in much smoother looking images than nearest neighbor.


Windows Background Switcher Resize effect: Triangle filter



B-spline filter


Acceptable quality. Images are sometimes too smooth.


Windows Background Switcher Resize effect: B-spline filter



Lanczos filter


Lanczos is the most complex, and slowest method, which should give the best results.


Windows Background Switcher Resize effect: Lanczos filter


So here's a roundup of some interpolation algorithms for making images bigger. Keep in mind that larger resolutions cause larger files. An image good enough for A0 printing (14000 x 10000 pixels) could amount to a 800MB TIFF file. Don't send them through email.

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