is lanczos suitable for upscaling ?

[codemaster]

i'm using MeGUI to encode to xvid. if my source is 720x576 and I want to scale to 640x352, I understand that I should use a filter like Lanczos.

But what if my source is 720x480 and 712x472 after cropping some black borders, and I want to upscale to 854x480 ? Is Lanczos good for upscaling the horizontal resolution from 712 to 854 pixels, and the vertical res from 472 to 480 ? Or should I use other filter than lanczos, perhaps one more suited for upscaling ?

[jagabo]

Lanczos will be sharper than Bicubic (which is sharper than bilinear). The sharper the resizer the more noise will be increased. You also risk oversharpening halos if your source is already very sharp.

[codemaster]

you are saying that there is a tradeoff between sharpness and noise ? meaning if I use the least sharper one, bilinear, the filtered frames will be much closer to the original source frames ? in other words, if I want to preserve the original as much as possible in the encoding process, among other things, I should use bilinear for upscaling or downscaling ?

[poisondeathray]

No, sharpness will only accentuate noise that is already existing, and require more bitrate for a certain level of quality. It won't "generate" noise per se, except haloing (oversharpening artifacts)

There is no such thing as "closer to original source frames" if you are resizing. There are pros / cons to each algorithm of resizing. Bilinear will produce blurrier results, but fewer oversharpening artifacts. Bicubic is in between. Lanczos is sharper. Spline36 is similar to lanczos but very slightly less ringing artifacts

If you wanted to do ""closer to original source frames", encode anamporphic 720x480 (ie. don't resize), but then your playback software will do the resizing on the fly (most usually use bilinear)

[jagabo]

Here are some examples of slight enlargements with the different methods. (After the indicated enlargement method an 8x point resize enlargement was performed so each individual pixel is now an obvious 8x8 block):

Original:



Precise Bilinear:


Precise Bicubic:


Lanczos3:


Of course, real world video doesn't have super sharp details like the original image here. So the sharpening artifacts won't be as strong.