Aliasing Question

[Myoung Jin Chun]

I recently shot some footage with a R1MX and I noticed some aliasing when reviewing the footage. Shot in 4k Redcode 42 and my screen resolution is 1080p. Is 4k resolution + OLPF supposed to prevent aliasing entirely, or just reduce the amount? Can this be prevented? Or is it just because the footage is being played back 1080?

 

[ericyoung]

It's highly unlikely that the R1MX footage is aliasing - the Red OLPFs are on the conservative side because Red just can't abide aliasing/moire.

It's far more likely that your display downscaling is the cause. You can check by viewing the part of the frame which is showing the aliasing at 100% (i.e. 1 pixel on your screen is 1 pixel in your footage). If it's still aliasing, check your deBayer settings are set to full quality.

 

[David Mullen ASC]

Even footage shot on film can alias on a TV monitor if the image contains fine lines of the right size to interact with the pixel grid of the display. There are anti-aliasing tools in post to deal with downsamples to various formats.

You can easily check your original 4K frames to see if the aliasing is there or if it is occurring downstream.

 

[Graeme Nattress]

It's very most likely an issue in how you're downsampling the 4k to HD. It should be avoidable with the right choice of downsampling filter in whatever tool you're using to downsample the image to 1080p.

Graeme

 

[Myoung Jin Chun]

I figured it was a downsampling issue. Thanks for the help gents!