Weird artifacts when blurring video w/Alpha

Get answers to your questions about color grading, editing and finishing with DaVinci Resolve.
  • Author
  • Message
Offline
User avatar

Ben Slavens

  • Posts: 28
  • Joined: Thu Jun 01, 2017 8:07 am
  • Location: Los Angeles, CA

Weird artifacts when blurring video w/Alpha

PostTue Jan 15, 2019 8:55 pm

I'm having an odd problem with Resolve (15.2.2 Studio). I've got a DNxHR 444 12-bit (with Alpha exported from Resolve, .mov container) that imports fine, interprets the alpha channel fine (premultiplied, same as export settings), and drops onto the timeline fine as well. However whenever I try to apply any kind of blur effect (both OFX and the Blur/Sharpen tab), I get these strange artifacts around the edges. If I right click the clip and go to Clip Attributes and turn off the Alpha Channel Setting ("None"), the artifacts completely disappear. However obviously this is unusable since it brings back the black background.

Edit Tab:
Image

Color Tab:
Image

Edit Tab (Alpha Channel Set To 'None'):
Image

Any Ideas what's causing this? I have no other color correction or filters applied.
http://Chromatron.Digital
MOBO ASUS m5a99fx pro r2.0
CPU AMD FX-8350
RAM 32GB 1866 DDR3 (non-ecc)
GPU Slot 0 - GTX 1070 Strix 8GB (Compute only)
Slot 1 - GTX 1060 6GB (Display only)
Offline

Peter Cave

  • Posts: 1052
  • Joined: Thu Aug 23, 2012 6:45 am
  • Location: Melbourne, Australia

Re: Weird artifacts when blurring video w/Alpha

PostWed Jan 16, 2019 12:51 am

Pre-multiplied alpha is intended to blend at 100% and includes blending with the background used during the 3d object render. I would try using a straight alpha version of your clip.
Resolve 15.2.4
Mac OSX 10.13.6
Hackintosh i7 32gb
GTX 1060 6GB
Offline
User avatar

Ben Slavens

  • Posts: 28
  • Joined: Thu Jun 01, 2017 8:07 am
  • Location: Los Angeles, CA

Re: Weird artifacts when blurring video w/Alpha

PostWed Jan 16, 2019 1:06 am

I tried exporting the clip using Alpha as Straight, and my clip renders with a red background and severe noise/dithering around the edges...

Image
http://Chromatron.Digital
MOBO ASUS m5a99fx pro r2.0
CPU AMD FX-8350
RAM 32GB 1866 DDR3 (non-ecc)
GPU Slot 0 - GTX 1070 Strix 8GB (Compute only)
Slot 1 - GTX 1060 6GB (Display only)
Offline
User avatar

Ben Slavens

  • Posts: 28
  • Joined: Thu Jun 01, 2017 8:07 am
  • Location: Los Angeles, CA

Re: Weird artifacts when blurring video w/Alpha

PostWed Jan 16, 2019 1:15 am

Ok, so disregard the last post, the red background was ignored when I Imported the clip into Resolve, however once I apply a blur to the clip it still has the odd artifacts on the edges. I'll post a closer pic for detail:

Image
http://Chromatron.Digital
MOBO ASUS m5a99fx pro r2.0
CPU AMD FX-8350
RAM 32GB 1866 DDR3 (non-ecc)
GPU Slot 0 - GTX 1070 Strix 8GB (Compute only)
Slot 1 - GTX 1060 6GB (Display only)
Offline
User avatar

Ben Slavens

  • Posts: 28
  • Joined: Thu Jun 01, 2017 8:07 am
  • Location: Los Angeles, CA

Re: Weird artifacts when blurring video w/Alpha

PostWed Jan 16, 2019 1:17 am

Also, the blur does not extend past the edges of the keyed matte. I'm an old time After Effects user, so in this case I would attempt to pre-compose the clip and apply the blur to the pre-composition so that it doesn't interfere with the key. However I'm not sure how to do this in Resolve/Fusion.
http://Chromatron.Digital
MOBO ASUS m5a99fx pro r2.0
CPU AMD FX-8350
RAM 32GB 1866 DDR3 (non-ecc)
GPU Slot 0 - GTX 1070 Strix 8GB (Compute only)
Slot 1 - GTX 1060 6GB (Display only)
Offline

Peter Cave

  • Posts: 1052
  • Joined: Thu Aug 23, 2012 6:45 am
  • Location: Melbourne, Australia

Re: Weird artifacts when blurring video w/Alpha

PostWed Jan 16, 2019 1:30 am

The artefacts in your rendered clip is the main issue, so solve that problem first.
Always render your clip with a similar background to the final composite to avoid edge issues.
Use a blur effect that has alpha support, or create a node tree that can process the alpha channel.
Compound clips are unnecessary.
Resolve 15.2.4
Mac OSX 10.13.6
Hackintosh i7 32gb
GTX 1060 6GB
Offline
User avatar

Ben Slavens

  • Posts: 28
  • Joined: Thu Jun 01, 2017 8:07 am
  • Location: Los Angeles, CA

Re: Weird artifacts when blurring video w/Alpha

PostWed Jan 16, 2019 2:30 am

I'm not rendering my clip with any background. Ok, maybe I should layout my steps I've taken so far:

1. Was provided with a ProRes 422 (.mov container) clip containing the pre-animated 3D object over a solid chromakey green background.
2. Imported it into resolve, created a new timeline from clip, went to fusion and applied DeltaKeyer, which provided a very clean key with default settings (after setting the background color of course)
3. Exported the timeline as DNxHR 444 12-bit (one Premultiplied and one Straight Alpha)
4. Reimported the clips, put one on timeline above video clips, and tried to apply all kinds of blurs (built-in blue, Gaussian blur, Lens Blur) all of which produce this odd effect.

For reference, here's the original clip I used to key:
Image
http://Chromatron.Digital
MOBO ASUS m5a99fx pro r2.0
CPU AMD FX-8350
RAM 32GB 1866 DDR3 (non-ecc)
GPU Slot 0 - GTX 1070 Strix 8GB (Compute only)
Slot 1 - GTX 1060 6GB (Display only)
Offline

Peter Cave

  • Posts: 1052
  • Joined: Thu Aug 23, 2012 6:45 am
  • Location: Melbourne, Australia

Re: Weird artifacts when blurring video w/Alpha

PostWed Jan 16, 2019 3:49 am

Any reason you are not doing the complete composite in Fusion? You will have way more control.
I can't see any benefit in exporting the chromakeyed clip and then re-importing.

Also, can the supplied clip be re-supplied with it's matching matte or embedded alpha? It's very unusual to use chromakey for this kind of rendered animation.

PS As soon as you blur the alpha, pixels beyond the edge of the 3d model become visible. You will need to use a matte choker to control this. It's common for the 3d animator to create the correct amount of alpha blur for the final composite.

If you can post a link to the original clip I can test for you.
Resolve 15.2.4
Mac OSX 10.13.6
Hackintosh i7 32gb
GTX 1060 6GB
Offline
User avatar

Ben Slavens

  • Posts: 28
  • Joined: Thu Jun 01, 2017 8:07 am
  • Location: Los Angeles, CA

Re: Weird artifacts when blurring video w/Alpha

PostWed Jan 16, 2019 4:29 am

Sure, thing, that'd be much appreciated! Uploading now I'll DM you a link
http://Chromatron.Digital
MOBO ASUS m5a99fx pro r2.0
CPU AMD FX-8350
RAM 32GB 1866 DDR3 (non-ecc)
GPU Slot 0 - GTX 1070 Strix 8GB (Compute only)
Slot 1 - GTX 1060 6GB (Display only)
Offline
User avatar

Ben Slavens

  • Posts: 28
  • Joined: Thu Jun 01, 2017 8:07 am
  • Location: Los Angeles, CA

Re: Weird artifacts when blurring video w/Alpha

PostWed Jan 16, 2019 5:02 am

http://Chromatron.Digital
MOBO ASUS m5a99fx pro r2.0
CPU AMD FX-8350
RAM 32GB 1866 DDR3 (non-ecc)
GPU Slot 0 - GTX 1070 Strix 8GB (Compute only)
Slot 1 - GTX 1060 6GB (Display only)
Offline

Peter Cave

  • Posts: 1052
  • Joined: Thu Aug 23, 2012 6:45 am
  • Location: Melbourne, Australia

Re: Weird artifacts when blurring video w/Alpha

PostWed Jan 16, 2019 9:01 am

Using the 3D keyer in the qualifier works fine here. No edge issues. No need to output the clip with alpha.

My node tree...
Screen Shot 2019-01-16 at 7.53.58 pm.png
Screen Shot 2019-01-16 at 7.53.58 pm.png (157.65 KiB) Viewed 150 times
Resolve 15.2.4
Mac OSX 10.13.6
Hackintosh i7 32gb
GTX 1060 6GB
Offline
User avatar

Ben Slavens

  • Posts: 28
  • Joined: Thu Jun 01, 2017 8:07 am
  • Location: Los Angeles, CA

Re: Weird artifacts when blurring video w/Alpha

PostThu Jan 17, 2019 12:21 am

Thanks for the help! I ended up doing the whole thing in Fusion. Turns out it was just my lack of depth when it comes to Fusion (aka user error :P )
http://Chromatron.Digital
MOBO ASUS m5a99fx pro r2.0
CPU AMD FX-8350
RAM 32GB 1866 DDR3 (non-ecc)
GPU Slot 0 - GTX 1070 Strix 8GB (Compute only)
Slot 1 - GTX 1060 6GB (Display only)

Return to DaVinci Resolve

Who is online

Users browsing this forum: Carsten Sellberg, gobacktogo, Haryanto, Shrinivas Ramani, Synth and 41 guests