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Old 14th April 2012, 02:58   #3  |  Link
IanB
Avisynth Developer
 
Join Date: Jan 2003
Location: Melbourne, Australia
Posts: 3,167
All of the inbuilt Avisynth resizers effectively work the same way. The difference between them is how many taps each use and what weight do they apply to each tap. More taps allows for higher sharpening but risks more ripples (ringing). The actual choice of tap weights sets the actual degree of sharpening and risk of ringing. The spline family are generally considers conservative, with emphasis on avoiding ringing. The lanczos family is more aggressive, favouring higher sharpening at the risk of marginally observable ringing, blackman is a lanczos variant that favours a slightly more conservative sharpening for higher tap counts.

The nnedi family are neural net trained edge directed interpolaters. At a single pass they will double the height of the input image. All other size adjustments are made with combinations of 90 degree rotations, multiple passes and a final standard downsize to the actual size required. For up-sizing by a factor of 2 a nnedi interpolation is currently the state of the art.

Your choice of actual resizer used should be subjectively based on the actual content of the material involved. There is no one size fits all. Crystal sharp sources almost certainly do not want any extra sharpening. Soft sources may withstand extreme sharpening particularly with large downsizing ratios. Avisynth provides many resizers so you can choose the best one for your current source material.

Note 1: PointResize implements the nearest neighbour algorithm, so no taps or weighting is involved.

Note 2: BilinearResize and GaussResize only use positive tap coefficients so provide no sharpening and cause no ringing. All the other resizers use some negative coefficients to provide sharpening and risk ringing. GaussResize at it's sharpest P setting is a PointResize. BicubicResize is a 3 tap resizer, user selectable B and C values make it fully tunable to suit any needs.
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