"Shutter open" camera parameter not affecting motion blur

[SpawnSP]

Hi all!

I've tracked a footage I shot with a DSLR. In order to match motion blur also, I have to set the "shutter open" parameter to -25%. This way, the rendered motion blur matches the original footage.

Lightwave documentation says this:

Shutter Open - defines the time offset for the start of the render. If the Blur Length is set to 50%, a Shutter Open value of -25% will center the motion blur for each frame.

I've noticed that this parameter only works on the native renderer, having no effect on Octane. Is there any other way to achieve this?
Without this parameter, motion is a bit "jerky", even if object position is OK.

Thanks in advance!

[juanjgon]

Hi,

Sorry, I'm afraid that the Octane plugin doesn't support this parameter. I'll take a look at it to see if this feature can be added to the next plugin build.

Thanks,
-Juanjo

[SpawnSP]

Many thanks for looking at it Juanjo.

I've seen that in Octane there are settings that seem to control motion blur:
viewtopic.php?f=21&t=63552

But I'm not sure if the "Shutter Open" parameter can be translated "as is".

[baltort]

Hi SpawnSP,

I had two ideas for this.

I started on an OSL camera that takes into account the subframe time. That way you can set the LW motion blur to 100% and invalidate rays that happen when you want the shutter closed. I think it slows things down because lots of time samples are thrown away. You also get a corresponding exposure drop that you need to compensate for. It does works though. Another problem is that with a shutter phase of -25% you need to take the first 25% of each frame and the combine it with the last 25% of the previous frame. You'd have to render these out separately and then combine them in post.

Then I had a better idea.

Switch on 'fractional frames' in the LW options and then shift all of your camera keyframes by 0.25 frames. This does the trick more easily!

Cheers,

James.

[SpawnSP]

Switch on 'fractional frames' in the LW options and then shift all of your camera keyframes by 0.25 frames. This does the trick more easily!

Wow, didn't think about this possibility. Definitely worth a try.
I hope that this small shift doesn't affect the actual animation, because with motion blur off, object position is OK.

Thanks!

[baltort]

Hi SpawnSP,

It should work. Depending on your setup, you may need to shift the object keyframes by a quarter frame too.

My golden rule for matching motion blur settings is to approach it logically for about 15 minutes. Then get annoyed and randomly try values. It always works.

Cheers,

J.

[SpawnSP]

Hi! It's me again.

Sorry for the (very) late reply. The project got on hold for a while and now I'm wanting to resume it.
Tried the fractional keyframes trick, by shifting all camera keyframes by 0.25. This matched the motion blur perfectly on the OpenGL preview with motion blur enabled.
But when rendered with F9, motion blur is still not the same. It's different than before shifting the keyframes, but still incorrect. I could try shifting keyframes a bit randomly as suggested, but I tried something first:

I left the fractional keyframes turned off (moving keyframes to their original position), and then exported the entire scene as orbx and opened it in Octane standalone. Then went to the animation settings and changed the "Shutter alignment" to "symmetrical" (as seen on https://docs.otoy.com/StandaloneH_STA/S ... ations.htm ), and this seemed to do the trick.

I've searched on the Lightwave plugin to find this setting, but I didn't find it. Is it available? I would like to avoid doing the export trick and render the shots inside Lightwave...

Thanks!

[juanjgon]

I've searched on the Lightwave plugin to find this setting, but I didn't find it. Is it available? I would like to avoid doing the export trick and render the shots inside Lightwave...

Yes, it is possible. I'll expose this parameter in the LightWave plugin for the next plugin builds to see if it helps.

Thanks,
-Juanjo

[SpawnSP]

I've searched on the Lightwave plugin to find this setting, but I didn't find it. Is it available? I would like to avoid doing the export trick and render the shots inside Lightwave...

Yes, it is possible. I'll expose this parameter in the LightWave plugin for the next plugin builds to see if it helps.

Thanks,
-Juanjo

That will be awesome. Many thanks!