Share:

We have updated the forum software 🙂 ! We are now working on upgrading the whole site and the Forum to a dark theme...  so please refresh your internet browser twice to properly update the forum appearance AND functionality... Check your internet browser for the refresh function, on windows, this usually is the F5 button, but it depends on your internet browser.

[Solved] Interpolation artifacts with Lanczos, Catmull-Rom Spline, Mitchell-Netravali, Cubic B-Spline  

  RSS

(@dhkim)
White Dwarf Customer
Joined: 2 years ago
Posts: 15
June 19, 2017 00:52  
Posted by: Dong Hun

Hi Mabula

 

I'm getting little bit of interpolation artifacts for the data set that I'm working with.

artifacts

There are dark pixels at the edge of some stars when I use Lanczos-3 as the interpolation algorithm.

 

In fact the artifacts are a lot worse in Pixinsight.

 

They are much less noticeable with APP.

 

If I use bilinear algorithm, the artifacts go away but the image is not as sharp as one from Lanczos-3(bigger FWHM value).

 

I'm wondering if there is a way to preserve FWHM but remove the artifacts.

 

Thank you very much.

Donghun

 

Hi Donghun,

Yes, I clearly see the artefact. This artefact is known as undershoot. This will always happen with a data interpolation algorithm like Lanczos.

But there is a solution to prevent this in APP. You will need to enable the "no under/overshoot" selectbox below the pixel interpolation filter in 6) INTEGRATE. This should prevent these dark pixels at the star borders due to undershoot.

app NUOS

Let me know if this solves the artefacts with your data.

Mabula

Under and Overshoot happens because a filter like Lanczos has positive and negative lobes see:

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

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

 

 

 


ReplyQuote
(@dhkim)
White Dwarf Customer
Joined: 2 years ago
Posts: 15
June 19, 2017 01:13  

I found the answer!

When I check "no under/over shoot", the artifacts goes away.

APP definitely beat PI on this one.

I was never able to remove these artifacts on PI (such as reducing clamp threshold) unless I used other algorithm such as bilinear.

Thank you very much.

Donghun


ReplyQuote
(@mabula-admin)
Quasar Admin
Joined: 2 years ago
Posts: 2071
June 19, 2017 01:19  

Yes 😉 Indeed, I was just finishing my answer... excellent!

You're most welcome Donghun,

I'll make this a sticky as well.

Mabula

Main developer of Astro Pixel Processor and owner of Aries Productions


ReplyQuote
Share: