Aliasing on Straight Vertical lines with 4k video on A7r3

Started Oct 16, 2018 | Discussions
Chester McCheeserton Regular Member • Posts: 101
Aliasing on Straight Vertical lines with 4k video on A7r3

I'm wondering if anybody has any suggestions or tips for getting rid of whats happening in the straight vertical lines you can see in the green building in this clip. Not trying to fix this clip but trying to prevent it in the future.

https://vimeo.com/295477096

This was shot on an a7r3 in 4k in super 35 mode on a Zhiyun Crane 2. The footage was downsized to instagram sized here, I initially thought it was the thing you see in stills in photoshop when zoomed out that disappears when zoomed in to 100%, but alas I seem to have a problem.  shutter speed was 1/50th of sec, frame rate 24 p 100m, Picture Profile set to  PP5.

Thank you!

Mike Evangelist
Mike Evangelist Contributing Member • Posts: 583
Re: Aliasing on Straight Vertical lines with 4k video on A7r3

That's not aliasing, it's moiré. Here's an article with details about why it happens - http://www.xdcam-user.com/old-stuff/aliasing-and-moire-what-is-it-and-what-can-be-done-about-it/

 Mike Evangelist's gear list:Mike Evangelist's gear list
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Beaverhelmet Senior Member • Posts: 2,296
Re: Aliasing on Straight Vertical lines with 4k video on A7r3

Chester McCheeserton wrote:

I'm wondering if anybody has any suggestions or tips for getting rid of whats happening in the straight vertical lines you can see in the green building in this clip. Not trying to fix this clip but trying to prevent it in the future.

https://vimeo.com/295477096

This was shot on an a7r3 in 4k in super 35 mode on a Zhiyun Crane 2. The footage was downsized to instagram sized here, I initially thought it was the thing you see in stills in photoshop when zoomed out that disappears when zoomed in to 100%, but alas I seem to have a problem. shutter speed was 1/50th of sec, frame rate 24 p 100m, Picture Profile set to PP5.

Thank you!

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.

https://www.cinema5d.com/best-way-downsample-4k-smartphone-footage/

OP Chester McCheeserton Regular Member • Posts: 101
Re: Aliasing on Straight Vertical lines with 4k video on A7r3

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.

OP Chester McCheeserton Regular Member • Posts: 101
Re: Aliasing on Straight Vertical lines with 4k video on A7r3

Mike Evangelist wrote:

That's not aliasing, it's moiré. Here's an article with details about why it happens - http://www.xdcam-user.com/old-stuff/aliasing-and-moire-what-is-it-and-what-can-be-done-about-it/

OK, moiré then, I stand corrected.  If I'm understanding that link correctly, it's saying I wouldn't get it if I just shot HD...also sort of hard to swallow...But Thank you.   Maybe I'll just try not moving the camera when I'm on land.

Entropy512 Veteran Member • Posts: 4,842
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.

This is a known tradeoff/disadvantage of using a camera with no OLPF.  To achieve maximum resolution/sharpness, the OLPF is removed, but this causes a risk of moire.

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RicksAstro
RicksAstro Veteran Member • Posts: 3,879
Re: Aliasing on Straight Vertical lines with 4k video on A7r3
1

Chester McCheeserton wrote:

I'm wondering if anybody has any suggestions or tips for getting rid of whats happening in the straight vertical lines you can see in the green building in this clip. Not trying to fix this clip but trying to prevent it in the future.

https://vimeo.com/295477096

This was shot on an a7r3 in 4k in super 35 mode on a Zhiyun Crane 2. The footage was downsized to instagram sized here, I initially thought it was the thing you see in stills in photoshop when zoomed out that disappears when zoomed in to 100%, but alas I seem to have a problem. shutter speed was 1/50th of sec, frame rate 24 p 100m, Picture Profile set to PP5.

Thank you!

It is actually aliasing like you said, causing a moire pattern.  These really aren't 2 separate things.

Have you examined the output on a 4k monitor?   If you were using APS-C crop mode of the a7rIII, you should not be seeing that much aliasing.   it looks more like you were using full frame, where it's doing line skipping.   Here's a comparison from DPRs video still comparison tool

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Entropy512 Veteran Member • Posts: 4,842
Re: Aliasing on Straight Vertical lines with 4k video on A7r3

RicksAstro wrote:

Chester McCheeserton wrote:

I'm wondering if anybody has any suggestions or tips for getting rid of whats happening in the straight vertical lines you can see in the green building in this clip. Not trying to fix this clip but trying to prevent it in the future.

https://vimeo.com/295477096

This was shot on an a7r3 in 4k in super 35 mode on a Zhiyun Crane 2. The footage was downsized to instagram sized here, I initially thought it was the thing you see in stills in photoshop when zoomed out that disappears when zoomed in to 100%, but alas I seem to have a problem. shutter speed was 1/50th of sec, frame rate 24 p 100m, Picture Profile set to PP5.

Thank you!

It is actually aliasing like you said, causing a moire pattern. These really aren't 2 separate things.

Have you examined the output on a 4k monitor? If you were using APS-C crop mode of the a7rIII, you should not be seeing that much aliasing. it looks more like you were using full frame, where it's doing line skipping. Here's a comparison from DPRs video still comparison tool

Yeah, I would have expected these issues in FF mode, but it should be pretty hard to cause them in APS-C mode, especially since the video is downscaled to 4k from roughly 5k

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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.

OP Chester McCheeserton Regular Member • Posts: 101
Re: Aliasing on Straight Vertical lines with 4k video on A7r3

You can start by dialling down sharpness/detail in your camera if you haven't done it already, all the way down.

Thanks, I will try this.  Any idea where in the 900,000 menu options one find this in the video settings on the A7r3?

am also unsure if my picture profile is adding sharpness....

OP Chester McCheeserton Regular Member • Posts: 101
Re: Aliasing on Straight Vertical lines with 4k video on A7r3

Have you examined the output on a 4k monitor? If you were using APS-C crop mode of the a7rIII, you should not be seeing that much aliasing. it looks more like you were using full frame, where it's doing line skipping.

No I haven't examined the output on 4k monitor, just my laptop. But if it's just a monitor issue, thought it would have gone away when I downsized it.

It's super 35! That's why I'm so frustrated, thought I went through all these hoops to get high quality video, rented a 21mm lens even to get the focal length I wanted in crop mode....

OP Chester McCheeserton Regular Member • Posts: 101
Re: Aliasing on Straight Vertical lines with 4k video on A7r3

Have you examined the output on a 4k monitor? I

Although weirdly, when I watch it through the evf in camera I don't see the moire/aliasing /whatever it's called.

OP Chester McCheeserton Regular Member • Posts: 101
Re: Aliasing on Straight Vertical lines with 4k video on A7r3

All I could find was within the picture profile settings, something called "detail" which I've never touched and was set at "0". Should it be set a negative value?

Beaverhelmet Senior Member • Posts: 2,296
Re: Aliasing on Straight Vertical lines with 4k video on A7r3

Chester McCheeserton wrote:

You can start by dialling down sharpness/detail in your camera if you haven't done it already, all the way down.

Thanks, I will try this. Any idea where in the 900,000 menu options one find this in the video settings on the A7r3?

It's news for most beginners, but videography is vastly more complex than stills photography, and the settings in the semipro A7x cameras can be daunting. Just don't expect to get the hang of it after just a couple of weeks shooting and you'll be fine. It will take a normally talented person many months of practical experimentation and Internet research to even begin to understand how to get good video footage done. I'm pretty sure most people give up and settle for acceptable* video.
(* Acceptable for that person, but not remotely acceptable if it was ever to be included in a production. Many people on the Internet forums are skilled enough to take stills that can be used in newspapers, magazines or billboards without any problems, but few know how to shoot video that's fit to be used for broadcast or commercials.)

am also unsure if my picture profile is adding sharpness....

Every profile adds sharpening unless you dial down "Detail" to -3. Unfortunately, that's how pretty much every amateur/semipro camera are made, they all add sharpness out of the box.

And as someone already pointed out, to judge 4K footage critically, you MUST use a 4K display, or a smaller display with the player set to 100% scale (just giving you a crop of the whole image). Playing a 4K clip in a player that downscales on the fly to your display resolution will add moire/artifacts in many cases.

Beaverhelmet Senior Member • Posts: 2,296
Re: Aliasing on Straight Vertical lines with 4k video on A7r3

Chester McCheeserton wrote:

All I could find was within the picture profile settings, something called "detail" which I've never touched and was set at "0". Should it be set a negative value?

Yup, -3 will virtually kill the sharpening. You can use -2 in many cases as well as long as there are no problem patterns in the frame. NB, you will need to add sharpening in post. How much is depending on the scene and chosen output size.

(Sharpening algorithms are an integral part of all the demosaicing/downsampling/encoding done in the camera, so it can't be shut off entirely per se.)

OP Chester McCheeserton Regular Member • Posts: 101
Re: Aliasing on Straight Vertical lines with 4k video on A7r3

It's news for most beginners, but videography is vastly more complex than stills photography, and the settings in the semipro A7x cameras can be daunting. Just don't expect to get the hang of it after just a couple of weeks shooting and you'll be fine. It will take a normally talented person many months of practical experimentation and Internet research to even begin to understand how to get good video footage done. I'm pretty sure most people give up and settle for acceptable* video.

Every profile adds sharpening unless you dial down "Detail" to -3. Unfortunately, that's how pretty much every amateur/semipro camera are made, they all add sharpness out of the box.

And as someone already pointed out, to judge 4K footage critically, you MUST use a 4K display, or a smaller display with the player set to 100% scale (just giving you a crop of the whole image). Playing a 4K clip in a player that downscales on the fly to your display resolution will add moire/artifacts in many cases.

Okay Thank you.  I am a total beginner at video but not at still photography.  Attempting to make a personal/experimental art piece, and I'm aware it will be impossible to have real professional broadcast quality given my inexperience but trying to do the best I can.

Would you recommend always shooting all video with the detail at minus 3?

and that's a very useful suggestion about viewing the footage in the player at 100% scale, I'll try to figure that out today in Premiere.

Beaverhelmet Senior Member • Posts: 2,296
Re: Aliasing on Straight Vertical lines with 4k video on A7r3

Chester McCheeserton wrote:

It's news for most beginners, but videography is vastly more complex than stills photography, and the settings in the semipro A7x cameras can be daunting. Just don't expect to get the hang of it after just a couple of weeks shooting and you'll be fine. It will take a normally talented person many months of practical experimentation and Internet research to even begin to understand how to get good video footage done. I'm pretty sure most people give up and settle for acceptable* video.

Every profile adds sharpening unless you dial down "Detail" to -3. Unfortunately, that's how pretty much every amateur/semipro camera are made, they all add sharpness out of the box.

And as someone already pointed out, to judge 4K footage critically, you MUST use a 4K display, or a smaller display with the player set to 100% scale (just giving you a crop of the whole image). Playing a 4K clip in a player that downscales on the fly to your display resolution will add moire/artifacts in many cases.

Okay Thank you. I am a total beginner at video but not at still photography. Attempting to make a personal/experimental art piece, and I'm aware it will be impossible to have real professional broadcast quality given my inexperience but trying to do the best I can.

Would you recommend always shooting all video with the detail at minus 3?

No, mostly for "problematic scenes". But you should stay with using a "soft" image setting in the camera. -1, -2 or -3, it all depends on occasion. This is not a set and forget setting I'm afraid (if you really want to learn the trade). Sharpening in post is what pretty much all videographers prefer. Dealing with oversharpenening/moire in post is near impossible.

and that's a very useful suggestion about viewing the footage in the player at 100% scale, I'll try to figure that out today in Premiere.

Yes, very common mistake. We've had several people coming here upset about moire from their new 4K capable camera. Telling them how to properly scrutinize 4k footage has calmed them down more than once.

RicksAstro
RicksAstro Veteran Member • Posts: 3,879
Re: Aliasing on Straight Vertical lines with 4k video on A7r3

Chester McCheeserton wrote:

Have you examined the output on a 4k monitor? I

Although weirdly, when I watch it through the evf in camera I don't see the moire/aliasing /whatever it's called.

Depending on how the downsampling is done, it could definitely introduce aliasing/moire.

Can you do a single frame capture at 4k and see if it's there?

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OP Chester McCheeserton Regular Member • Posts: 101
Re: Aliasing on Straight Vertical lines with 4k video on A7r3
2

Yes, now I feel embarrassed. Just viewed the footage at 100% in premiere and it looks fine.  Thanks for your patience with all of us greenhorns.

It's choppy/ie. not smooth playback but the moire/aliasing is gone, I'm guessing the choppyness has to do with the fact that I'm playing it over a external drive that is not solid state.

OP Chester McCheeserton Regular Member • Posts: 101
Re: Aliasing on Straight Vertical lines with 4k video on A7r3
1

Depending on how the downsampling is done, it could definitely introduce aliasing/moire.

Can you do a single frame capture at 4k and see if it's there?

My bad, I viewed the footage at 100% and it's fine, so I guess the "how to downsize your 4k footage to instagram size" youtube video I watched wasn't what the downsampling professionals use...Thanks anyway

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