resizing filters

[Vslayer3000]

another stupid question :) lol in gknot when you go to encode there is a list of resize filters: bilinear, soft bicubic, neutral bicubic, sharp bicubic, and simple. whats the difference between the different filters and what do they do? i've been using the neutral bicubic one just cause i aguide i read said it's a good one to use but i would like to know what the other ones do and so on... any info would be apreciated :)

[rmatei]

Experience will teach you. Sharper to softer: sharp > neutral > soft > bilinear. Simpleresize you probably shouldn't use. Sharp is usually to sharp and can lead to edge enhancement artifacts. A basic guideline would be to use neutral for high bitrate rips (2cds, compressible 1cd), and soft bicubic for lower bitrate rips, because a softer filter will make the image more compressible.

[Suzahara]

Bilinear blurs the outlines slightly (or more) making it more compressible.

Soft Bicubic is a very *soft* (meaning doesn't make it very sharp) setting of bicubic.
Neutral Bicubic *tries* to do nothing to the video.
Sharp Bicubic sharpens the video.
These three are just modified values of BicubicResize(x,y).

More on bicubic (can be found in avisynth documentation):
BicubicResize is similar to BilinearResize, except that instead of a linear filtering function it uses the Mitchell-Netravali two-part cubic.
The parameters b and c can be used to adjust the properties of the cubic, they are sometimes referred to as `blurring' and `ringing,' respectively.

With b = 0 and c = 0.75 the filter is exactly the same as VirtualDub's "precise bicubic," and the results are identical except for the VirtualDub scaling problem mentioned above. The default is b = 1/3 and c = 1/3, which were the values recommended by Mitchell and Netravali as yielding the most visually pleasing results in subjective tests of human beings. Larger values of b and c can produce interesting op-art effects--for example, try b = 0 and c = -5.

If you are magnifying your video, you will get much better-looking results with BicubicResize than with BilinearResize. However, if you are shrinking it, you are probably just as well off, or even better off, with BilinearResize. Although VirtualDub's bicubic filter does produce better-looking images than its bilinear filter, this is mainly because the bicubic filter sharpens the image, not because it samples it better. Sharp images are nice to look at--until you try to compress them, at which point they turn nasty on you very quickly. The BicubicResize default doesn't sharpen nearly as much as VirtualDub's bicubic, but it still sharpens more than the bilinear. If you plan to encode your video at a low bitrate, I wouldn't be at all surprised if BilinearResize yields better quality.

You have to set
b + 2 * c = 1
for the numerically most accurate filter.
This gives for b = 0 the maximum value for c = 0.5, which is the Catmull-Rom spline and a goog suggestion for sharpness.

From c>0.6 the filter starts to "ring". You won't get real sharpness, what you'll get is crispening like on a TV set.
No negative values are allowed for b. Then stay on b=0.

SimpleResize does nothing to the video at all except resizing.

More on SimpleResize (found with simpleresize docs):
Okay, on to business. SimpleResize is an Avisynth filter that will do a very simple
2 tap linear interpolation. It is unfiltered which means it will not soften much.

It's main advantage is that it will run somewhat faster than some of the others.

[Suzahara]

Originally posted by rmatei
Experience will teach you. Sharper to softer: sharp > neutral > soft > bilinear. Simpleresize you probably shouldn't use. Sharp is usually to sharp and can lead to edge enhancement artifacts. A basic guideline would be to use neutral for high bitrate rips (2cds, compressible 1cd), and soft bicubic for lower bitrate rips, because a softer filter will make the image more compressible.

I disagree on the simpleresize comment. It's sometimes hard to judge how compressed the video will be if you use any of the other resizes and sometimes you don't want the video sharpened or softened (most dvds now IMHO, unless anime, don't need to be sharpened or softened unless the filesize doesn't hit its mark or you're looking for a very small size). This is when you want to use simple. And if you want to sharpen, I believe there are better ways than using Bicubic (as you said because it leaves artifacts). These ways are MSharpen (a sharpening filter) and another resize filter, LanczosResize (built-in with the latest avisynths). These give a nice sharp picture with a minimum of artifacts.

[Vslayer3000]

cool thanks for all the info :D i understood about half of it lol but it's an improvment from the 0 i understood a month ago :) but at least i understood the parts i needed to. i'm gonna have to save that in notepad cause there's alot of good info in there that i'm gonna have to learn :)

[jorel]

lanczosresize is very good,don't "soft" the image.