How does lanczo interpolation work

Report · Feb 23, 2022

I m looking for an explaination on how Lanczo interpolation actually works in Premiere and what it does to the nearest pixels. NN, Bilinear and Bicubic seem to all have a clear definition as to what it does and how it works. I need to be able to explain the interpolation process to others. thanks.

Report · Feb 23, 2022

the best way I can help ( cause I'm an idiot ) is to explain what the basics are... and how each digital iteration of doing it with computers is going to be different ( and a secret probably due to marketing and selling product ).

In the days of film ( before you were born probably ) a person could shoot with a 35mm camera ( using real plastic film ). Some people shot stuff that was gonna be made into national advertising BILLBOARDS along highway 66 and big cities and so on... by the person who hired the photographer.

Joel Meyerowitz used to shoot cigarette ads to make money and got hired by famous advertising companies to make it happen... cause Joel was fantastic and making young people have fun throwing fall leaves at each other in central park and having FUN ! But he shot with a 35mm leica and was really good at making young people ( models ) have fun !

So, eventually, that photo, along with text to make it plain to people that you were looking at what it's like to smoke some brand of cigarette, would end up in magazines and billboards all over the U.S. and it paid his rent.

You probably see ads that say the same kind of thing even today. The geico ads with the cute salamander is a good example ??

Artists have to make money to survive and many of them do commercial work.

So, in film it was copy camera stuff using 35mm to shoot 4x5 negative ( enlarge it ). process it and shoot THAT, and make an 8x10 negative with copy camera. After THAT use giant projector to expose the PRINT to paste on billboard.

basically it is INCREMENTAL increases from the original to a product that looks OK. especially from a distance ( like a billboard, if you climb up there, will look a little blurry, but from a car on highway it looks pretty nice ).

that's what digital interolation does.... it use STEPS to gradually increase the SIZE of the original and intead of using optics ( copy cameras with film etc. ) it does it digitally sampling pixels and trying to reproduce them relative to other nearby pixels. This is tricky cause there is 4.2.0, 4.2.2, 4.4.4 and different bit depth ( 8 bit, 10 bit etc. ).

Now you know the basics... it's incrimental INCREASE of size of original in STEPS.

Report · Feb 23, 2022

Salvo,

Thanks for the fun history lesson! I appreciate the insight. I am keenly aware of how digital interpolation works, especially in photoshop and after effects. What i'm trying to get is a clear definition of what lanczo resampling is (premiere pro defaults to this interpolation) when it comes to resizing an image or video. NN takes the adjacent pixel data and duplicates the color value of it, while bilinear and bucubic takes color data from the nearest pixel of an object and introduces transitional values to the added pixel resampling. Premiere stated that,

"Currently, Premiere uses the Lanczos method for intrinsic scale and rotation. Lanczos is an exceptionally high-quality interpolation method which generally yields better results than bicubic, bilinear, or nearest neighbor. For upscaling, I suggest looking at the Detail-Preserving Upscale effect in After Effects. It does a really good job and gives you some parameters to tweak to fit your specific content."

They just dont explain how its better and how the interpolation is happening.

Report · Feb 23, 2022

https://en.wikipedia.org/wiki/Lanczos_resampling

Report · Feb 23, 2022

Well, I'm going to take a chance and give you some links to something that may help you; I found a VERY helpful document at frame.io

The Ultimate Guide to Premiere Pro's Render Quality Settings (frame.io)

There are some things within that document that I believe properly explain how resizing works; There is lots of useful info linked all over on the frame.io 'insider' site; Here is the text I thought may help you with your search:

You may have to layer some info from other sources to completly address your question, but I hope this elevates your knowledge in the areas of your interest.

What I found helpfull in this document was the explanations of 'max render' settings effects.....

I think the answer to your questions was the text that reads (to make it searchable).

"Lanczos 2 low-pass sampled with bicubic. Also described as modified bicubic with a scale-dependent pre-filter."

I hope this was helpfull....

Report · Feb 24, 2022

wow, this article has a lot of great information. It was certainly helpful. Thanks!

Report · Feb 24, 2022

Glad it helps. And I agree there is some very deep thinking and tests to validate the thinking within that document. I hope you find an answer to your question soon. From my interpretation it seems like there is no 'one way' that it is processing resize/rotation etc, it (appears to) picks a way in which to do it based on some rules (which I would love to see) for the 'preprocess' filters if I read this correctly. Could be why a straightforward answer to your question was harder to come by.

Enjoy the article, there is some real wisdom on many parts of the dark art of how premier works within it.

Report · Feb 24, 2022

Also; does this help you:

raster - What is Lanczos resampling useful for in a spatial context? - Geographic Information System...

It focuses on GIS systems, but they have some interesting insights into the different resample methods:

They also have notes on Downsample in the link....

Report · Feb 25, 2022

yes! This helps a lot actually. It goes in depth of resampling each visual algoritm. This is a great article. You've helped tremdously. Thank you, FFF!

Report · Feb 25, 2022

@canonshop Glad it helped you... and thank you for the feedback!

Report · Feb 25, 2022

Flying,

Awesome work through this thread, thanks a bunch!

Neil

Report · Feb 25, 2022

NP. I had some time, and the question was interesting to me (and I guess others!).

The online community in general is rather good for sharing ideas and knowledge and if it helps someone connect to something like both these professionally written documents / articles I'm happy too (I have done my fair share of taking (of information) and giving back is part of the deal). The people that wrote them I am sure are pleased for the review/linking.