Aliasing on Straight Vertical lines with 4k video on A7r3

Started Oct 16, 2018 | Discussions thread
Beaverhelmet Senior Member • Posts: 2,296
Re: Aliasing on Straight Vertical lines with 4k video on A7r3

Chester McCheeserton wrote:

As Mike said, this is a moire issue. Your question is unclear though. If you want to avoid moire in the original 4K footage, use an aperture value that puts the problem areas slightly outside of the focus area. A really small aperture, provoking a small amount of diffraction can also help. In some rare cases even a soft filter is used (common in cinematography).

If you want to address moire when downsampling in post, the result can vary a lot depending on compression settings and software used. This is mainly a computational issue.

Thanks, I want to avoid this in the original 4k footage in the future. Hard to believe I'd have to blur it with diffraction, make it of focus in camera, or put a stocking over the lens.

That downsampling link is way over my head, but I did try to read it.

You can start by dialling down sharpness/detail in your camera if you haven't done it already, all the way down. Pretty much every seasoned videographer shut off in-camera sharpening for this exact reason. Fixing moire in video in post is a nightmare, and you really want to start out your work with files with no added artificial sharpening. You can add the desired amount of sharpening in post instead, with much better control.

Downsampling to a low resolution output like the 360p footage you posted on Vimeo will always be problematic with this kind of geometry present in frame. OLPFs are used in lower resolution cameras to avoid severe moire, and when exporting video to this low a pixel count, it's basically like recording video footage from a very low resolution camera (if you get the principle). Removing all unnecessary sharpening, and testing various downsampling settings is simply a must I'm afraid.

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