Artifacts after rendring to interlaced codec? fix?

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Eirik Heim

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Artifacts after rendring to interlaced codec? fix?

PostSat Dec 09, 2017 5:07 pm

Hi,

I am working on a 10 program tv-series. It is mainly shot on Canon C300's and Davinci shows it as XDCAM Mpeg2. There are some shots with other cameras as well, but they have not showed the same problem. The problem is not consistent. Only three clips that has been marked by the broadcasters in one program with I am fixing now for second upload.

This artifact does not show up on my referance monitor working in Davinci or Premiere. It does not show up when I am rendering to a progressive codec. It shows up in both interlaced codecs accepted by the broadcaster: DNxHD and XDCAM.

Any tips? I have tried de-interlaced plugins just for a test, flicker free and stabilised in Davinci or warp in AE.

What to do?
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Fabio Bovenzi

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Re: Artifacts after rendring to interlaced codec? fix?

PostSat Dec 09, 2017 5:31 pm

Which version of Resolve use?... in the latest version, BlackMagic fix the problem about the Field Render for interlaced material.
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Eirik Heim

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Re: Artifacts after rendring to interlaced codec? fix?

PostSat Dec 09, 2017 6:03 pm

I am on 14.1.1?
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Andrew Kolakowski

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Re: Artifacts after rendring to interlaced codec? fix?

PostSat Dec 09, 2017 6:43 pm

Is your source footage interlaced or progressive (the one which is problematic) ?
You have to by eye identify it and interpret properly in Resolve in clip properties.
What is your project set to?
If your source footage is in 95% progressive footage then set project to progressive and turn on deinterlacing (high quality) on all source clips which are interlaced. If broadcast needs files to be marked as interlaced then turn this on when exporting. You should end up with progressive footage, but flagged as interlaced. This is very common these days as outdated "broadcast" can't cope with progressive files- they always scream for interlaced flagging (even if your all source files were progressive).

Another possible issue is fact that progressive sharp sources cause aliasing when watched over interlaced chain (they are in simple word-to sharp/good). In this case you want some antialiasing filter or local very mild blur effect (mainly vertically). Your output is simply to sharp which shows ups on highly detailed areas specially with diagonal, high contrasty lines.


If you have interlaced source and previewing them in Resolve (resized) GUI preview then this is bad practice. For interlaced monitoring you definitely need broadcast monitor or TV over BM card.
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Eirik Heim

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Re: Artifacts after rendring to interlaced codec? fix?

PostSat Dec 09, 2017 7:05 pm

I think I have tried mostly any workflow when it comes to progressive to interlace and deinterlacing interlaced and so on. If it were a interlaced problem I guess it would have showed on more stuff than these three clips. All the clips are on edges, highly contrasted and only happens when it is rendered as interlaced no matter if it is progressiv or interlaced native. Tried both.

So local bluring or anti-alias filter? What do you recommend of filters/plug ins for Davinci then? Or is it tracking/masking and blur locally that counts?
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Andrew Kolakowski

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Re: Artifacts after rendring to interlaced codec? fix?

PostSat Dec 09, 2017 7:09 pm

I don't know Resolve filters.
Is it native resolution source? If your source is downscaled then you can change Resolve global scaling option to soft one.
You need something called low pass filter (sort of blur), which affects only areas with certain sharpness.
With interlaced chain you can't preserve same sharpness in your footage as with progressive one- you always have to make footage bit softer or you will have aliasing problems (same applies when you do e.g. SD master from HD or 4K sources).

If you are down to few problematic places just use local blur with masking.
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Eirik Heim

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Re: Artifacts after rendring to interlaced codec? fix?

PostSat Dec 09, 2017 7:36 pm

Ok. Will try local bluring first. Seems easiest.

Used to deliever stuff in progressive and last time I delievered something like this I did not have this problem, but other interlace problems.

Hope this works ok.
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Andrew Kolakowski

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Re: Artifacts after rendring to interlaced codec? fix?

PostSat Dec 09, 2017 11:06 pm

I actually opened your grabs at 1:1 pixel.

You simply have some resolution lost+ encoding artefacts (is this from XDCAM-HD)?
How did you made these grabs? From Resolve?
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Eirik Heim

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Re: Artifacts after rendring to interlaced codec? fix?

PostSun Dec 10, 2017 1:38 am

The grabs are from screenbrabs from VLC from files rendered from Davinci.
They are originally full HD, but resized to 1600 x 1000 because of file limitation in the forum.

The file almost without the artifact is how it looks lite when I see it in Davinci or render it with a progressive codec.

The other file with the artifacts is how it looks like when I use an interlaced codec as they request. It happens with both DNxHD and XDCAM interlaced. It also happens both from rendering in Davinci and when I try to render it from premiere.
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Andrew Kolakowski

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Re: Artifacts after rendring to interlaced codec? fix?

PostSun Dec 10, 2017 1:58 pm

It's just what you see, due to deinterlacing. Previewing such a files on computer screen is not optimal at all. I don't think it has anything to do with Resolve at all.

Do you see interlacing lines when you bring files to Resolve or in player where you can disable deinterlacing?
Telestream Switch is a good player, you should invest in it. Basic version which is probably enough is cheap. You have to know how to "watch and judge" interlaced files on PC screens. It's not that obvious or easy. The best is proper monitoring on broadcast monitor or fairly good TV.
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Eirik Heim

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Re: Artifacts after rendring to interlaced codec? fix?

PostSun Dec 10, 2017 4:54 pm

I am of course doing this job on a calibrated rec 709 proper broadcast monitor through a Black Magic 4k deckline card. It shows the same results. Looks good in Davinci or in premiere before rendring it to an interlaced codec on both the monitor and the PC screen. It does not show this artifacts when rendering it progressive, on both monitors.

I do not have any of the typical interlace problems in this project. There was three other clips shot with something else, they got fixed by Clip attributes -> deinterlace and then all good.
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Andrew Kolakowski

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Re: Artifacts after rendring to interlaced codec? fix?

PostSun Dec 10, 2017 8:00 pm

Hmmmm....so when you bring interlaced file back to Resolve and watch on broadcast monitor or TV then you have this issue?
When you watch interlaced file back from Resolve do you do it over e.g. 50i or 25p format set in video monitoring?
I think it's just preview issue, but VLC preview is not a way of judging it.

I've tried and Resolve doesn't generate half lines when exporting to interlaced codec from progressive project (source), so this is good. Your files is still progressive, just flagged as interlaced. When you interpret it as progressive then you should still have perfect playback as it would be never rendered as interlaced. This is also some way of validation if it really has some issue or not.
Last edited by Andrew Kolakowski on Sun Dec 10, 2017 8:05 pm, edited 1 time in total.
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Andrew Kolakowski

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Re: Artifacts after rendring to interlaced codec? fix?

PostSun Dec 10, 2017 8:01 pm

Eirik Heim wrote:I do not have any of the typical interlace problems in this project. There was three other clips shot with something else, they got fixed by Clip attributes -> deinterlace and then all good.


Yes, as you seams to work all the way progressive, so when have real interlaced files then you need to deinterlace them.
Always use high quality deinterlacing as standard one is quite poor.
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Eirik Heim

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Re: Artifacts after rendring to interlaced codec? fix?

PostMon Dec 11, 2017 12:23 am

So the only way is to try the bluring actually? Seems like everything is ok with every clip interlaced or progressive except those three that has this artifacts of "beeing to sharp"? No clips are showing the normal interlaced problems after rendering, like stripes or jagged lines.
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Andrew Kolakowski

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Re: Artifacts after rendring to interlaced codec? fix?

PostMon Dec 11, 2017 11:46 am

I don't think anymore that it's problem with video being "to sharp".
You said problem appears when you watch clip in VLC. This is not the way to judge interlaced clip.
For me it's preview problem, not actual video itself.
Play interlaced clip over interlaced chain to broadcast monitor/TV and then check if there is any issue there or not.
"To sharp" problem appears only on proper interlaced chains- broadcast monitor/TV.
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Eirik Heim

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Re: Artifacts after rendring to interlaced codec? fix?

PostMon Dec 11, 2017 12:49 pm

As I already have written, I monitor it on a proper broadcast monitor of course. Can not do the job without it. And it happens on the monitor when bringing the clips back in Davinci again on the monitor, also when rendered to interlaced by premiere/media encoder.

Only the screen grabs where made from VLC as it shows the same as Davinci and the broadcast monitor.
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Andrew Kolakowski

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Re: Artifacts after rendring to interlaced codec? fix?

PostMon Dec 11, 2017 1:43 pm

When you bring clip back to Resolve do you use new interlaced project with interlaced setting for monitoring?

Can you render 5sec of problematic section as progressive and interlace and post here?
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Eirik Heim

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Re: Artifacts after rendring to interlaced codec? fix?

PostWed Dec 13, 2017 12:32 pm

Seems like I have found what the problem is. It is the Canon C300 and horizontal lines. Some times it is just a bad combo. Now I just have to find a nice fix.
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Andrew Kolakowski

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Re: Artifacts after rendring to interlaced codec? fix?

PostWed Dec 13, 2017 12:58 pm

Possible- most often this is due to "shortcuts" in debayering algorithm in camera.
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roger.magnusson

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Re: Artifacts after rendring to interlaced codec? fix?

PostWed Dec 13, 2017 1:34 pm

I've shot a lot with the C300 and haven't seen that kind of issue. I might have used softer lenses though.

FYI the C300 doesn't do line skipping when downsampling from the full sensor readout to 1080p, instead it resamples all the data.

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