Lanczos and Lanczos4

[pwnsweet]

I can't find any explicit info regarding Lanczos4. Not even the wikipedia entry mentions it.

1. What's the difference between the two and which is better?
2. Is Lanczos resizing used only when upscaling from a lower resolution to a higher resolution or is it also used when downscaling? (ie, when encoding a 1920x1080 source to 1280x720)
3. What's the best downscaling resizer to go from 1920x1080 to 1280x720?

[TheRyuu]

Looks like you might have posted this in the wrong forum.

Lanczos4 is just Lanczos with taps=4. But for downsizing I'd recommend Spline36 over Lanczos.

[J_Darnley]

3. What's the best downscaling resizer to go from 1920x1080 to 1280x720?

There is no best, per rule 12. All resizers besides point and bilinear are just about as good as each other

[pwnsweet]

But for downsizing I'd recommend Spline36 over Lanczos.

I apologize if this is in the wrong forum. If an admin is reading this, please move it to the appropriate location.

Would you mind elaborating on why you recommend Spline36 over Lanczos?

[Astrophizz]

As I understand, Spline36 is not as sharp as Lanczos and so is less likely to introduce aliasing when downscaling.

[LoRd_MuldeR]

Have a look here for a comparison of the different resizing kernels:
* https://www.ligh.de/resamplehq/kernels.html
* http://classic-web.archive.org/web/20060827184031/http://www.path.unimelb.edu.au/~dersch/interpolator/interpolator.html
* https://web.archive.org/web/20180118065553/http://hermidownloads.craqstar.de/videoresizefiltercomparasion/

Some background info about Spline-based Resizers is available here:
http://forum.doom9.org/showthread.php?t=147117

Also please remember rule #12 ;)

[2Bdecided]

Have a look here for a comparison of the different resizing kernels:
* http://svn.int64.org/viewvc/int64/resamplehq/doc/kernels.html
* http://classic-web.archive.org/web/20060827184031/http://www.path.unimelb.edu.au/~dersch/interpolator/interpolator.html
* http://hermidownloads.craqstar.de/videoresizefiltercomparasion/
I love that first link.

Clearly point-resize wins in the last link - it's meant to be some kind of artist tool, right? ;)

Cheers,
David.

[Sagittaire]

There is no best, per rule 12. All resizers besides point and bilinear are just about as good as each other

rule 12 not apply for resize. Spline36 is the best ... simple to show that.

[kypec]

Spline32 is the best ... simple to show that.
Are you implying that Spline16 is inferior and Spline36 is superior to Spline32? :p

[Sagittaire]

Are you implying that Spline16 is inferior and Spline36 is superior to Spline32? :p

Spline36 is superior to bilinear, bicubic, lanczos ...

[Didée]

Spline36 is the best ... simple to show that.
Whatever you might show, you'll always get a contra-example showing that spline36 causes ringing, where (e.g.) spline16 does not.

There is no "best".

[J_Darnley]

rule 12 not apply for resize. Spline36 is the best ... simple to show that.

I would disagree based on the example linked above

[Balling]

ITU-T H series supplement 18 recommends at least Lanczos with 2 taps with chroma siting taken into account being mandatery.

Zscale uses lanczos with 3 taps. https://github.com/sekrit-twc/zimg/blob/90bf82c7202fa5fd37775db3c98799be899231f6/src/zimg/resize/filter.h#L114

[huhn]

i could make a couple of example scales but it has been done a lot here.

the king of downscaling is SSIM.
bicubic 150 with AR is a nice cheap alternative.
spline32 is pretty similar to lanczos 3 (beware there are different ways to count the tabs amd even the word tab is not even used generally there is also lob) lanczos suffers as usual from ringing so an AR algorithm makes quite a difference.

[Katie Boundary]

1. What's the difference between the two and which is better?

Lanczos-4 is sharper than Lanczos-3, and has better antialiasing, but has worse ringing artifacts. In PSNR tests, either one might outperform the other depending on the scaling factor and the content of the image. Spline144 is better than both, though :)

2. Is Lanczos resizing used only when upscaling from a lower resolution to a higher resolution or is it also used when downscaling? (ie, when encoding a 1920x1080 source to 1280x720)

The general rule is that "sharpening" filters, meaning filters with negative lobes, should be used for upscaling, while "smoothing" filters, meaning filters without negative lobes, should be used for downscaling. Lanczos is a sharpening filter at any number of taps other than 1.

3. What's the best downscaling resizer to go from 1920x1080 to 1280x720?

Arearesize.

My personal rule of thumb for downscaling is this: for scaling factors close to 1 (like if rescaling 720x480 to 640x480), I use bilinear. For scaling factors close to 2 (like if rescaling 720x480 to 352x240), I use Hermite. For anything else, use Arearesize.

[rwill]

I don't understand. Why are you all posting in a thread that is over 10 years old ? Sure enough there have been some advances in scaling but....

[huhn]

balling is necroing again sorry my mistake...

[Balling]

I am not "necroing", this post have high visability in google, so google thinks those are important. What is up with people against that, LOL? Do you think I scrolled back to 2011?? LOL, no.

BTW, what does Dolby and LG C9 e.g. uses by default without AI? Spline144? It is insane, I agree! https://forum.doom9.org/showpost.php?p=1829918&postcount=1

[Katie Boundary]

I am not "necroing", this post have high visability in google, so google thinks those are important.

Necroing has nothing to do with what Google thinks is or isn't important.