Long shutter motionblur, only trail behind, not infront?

[kosso_olli]

Forget the last post. After some more testing, this is getting weirder and weirder.
By using different types of cameras, you can get two different results, all for the same settings used. Scene file is attached below.

Same setup as above, sphere moving from upper left to lower right over 100 frames.

Result with Physical camera at Frame 0, 100 frame duration:


Result with standard Max camera at Frame 0, using the same settings as physical camera, but in the Vray Camera settings:



It seems the Physical Camera is sampling ahead of time, while the standard time samples ahead and backwards.

Also, the settings for Interval Center and Bias do not have any effect whatsoever with the Physical Camera. I'm not sure I looked everywhere, but this does not seem to be documented in the docs at all.
This is extremely confusing, to say the least.

sparkler_motionblur_TEST.zip

[fixeighted]

Try this. https://www.dropbox.com/s/vkwtfmu4tl...0copy.max?dl=0
Your version crahed me so I stripped it of all but the helix and cam and sphere as it's simpler to share.
I think I have reproduced what Corona does, albeit much more clunkily.
Some nice falloff and a controllable tail length, yet still missing what I would expect, which is the bright light source where it should be in time along the path.
Even when it physically comes to rest it is not fully bright but instead fades up to bright as the tail dies - Corona does this too.
Sure, that can be another layer but shouldn't it appear on each frame if we've forced the blur to be behind the whole way?
Going back to this curtain sync technique, there's another called dragged shutter which is similar - the image is in focus at the beginning and end with the blur in between.
This is what I believe should be possible.

I notice also that the shutter can go minus but why infinitely?, if, as happens, it can only realistically be maximum -1,
working with the duration (of course in a different panel...grrrr) of the blur.

[hermit.crab]

The main thing I can't seem to do is get the motionblur to happen only behind the object when using a very long amount of motion blur (100+ frames in my case). I've fiddled around with it a good bit and haven't found any way to do it. Not sure if it's possible or not.

A negative bias (Render Setup>V-Ray>Camera) should be able to solve your scenario since it would concentrate the lighting towards the most recent movement of an object, whilst the blur from the movement's beginning would dim out. Note that the bias parameter does not affect physical cameras (not physically accurate), so this solution works only with Free/Target Max native cameras or perspective views. Another solution that may produce the desired effect is through a V-Ray Physical camera's "Latency" parameter (set the V-Ray camera to Video cam to make it available), because of the video camera's integrated, but fixed bias.

[Buck]

A negative bias (Render Setup>V-Ray>Camera) should be able to solve your scenario since it would concentrate the lighting towards the most recent movement of an object, whilst the blur from the movement's beginning would dim out. Note that the bias parameter does not affect physical cameras (not physically accurate), so this solution works only with Free/Target Max native cameras or perspective views. Another solution that may produce the desired effect is through a V-Ray Physical camera's "Latency" parameter (set the V-Ray camera to Video cam to make it available), because of the video camera's integrated, but fixed bias.

I don't think I was using the physical camera, but I'll check. I did set the bias and interval parameters as high and as low as they would go, and could not get the motion blur to stay behind the object. It works when the motionblur is at a reasonable amount (like 0.5 frames), but not when its at very large values (100 frames for example).

I'll upload a test scene in a bit. I'm in Maya, BTW.

[hermit.crab]

I don't think I was using the physical camera, but I'll check. I did set the bias and interval parameters as high and as low as they would go, and could not get the motion blur to stay behind the object. It works when the motionblur is at a reasonable amount (like 0.5 frames), but not when its at very large values (100 frames for example).

I'll upload a test scene in a bit. I'm in Maya, BTW.

Seems to work fine in Maya. Make sure there are enough Geometry samples as well. If that doesn't help, do send the scene to support@chaosgroup.com so we can take a look (or attach one here). Mention this thread in the e-mail along with your V-Ray and host platform versions.

[fixeighted]

Both kosso_olli and I have attatched scenes to no avail.
Is this because it is originally Buck 's post and you can only reply to his questions?
I see his query relates to Maya, which may differ considerably from Max.
If so then that's totally fine and I can begin another post on the topic

[kosso_olli]

hermit.crab We did try something like that in Max, it does not work at all. The bias parameter does not have any effect whatsoever, neither with a standard camera, nor in perspective view. Can you please take a look at the scenes that were attached in this thread as well?

[Buck]

hermit.crab

Sorry for the delay, have been very busy at work.

Anyway, here's a simple scene. motionblur.ma.zip

The ball is traveling from the bottom to the top in this arc, taking 200 frames to get from start to finish. I have the motionblur set to 100 frames, and 100 geometry samples. I render in the middle of the frame range where the ball is in the middle of it's path. No matter how I set the settings, I can never get the motionblur to be only behind the ball. Maybe I don't have the right combination of settings, or maybe it's not possible?

The exact number of frames is not really important. Other than it being a larger number.



Here's a screenshot:



And here's a photoshop edit of what I am ideally trying to accomplish:



Thanks for taking a look at this, I don't know if it's possible or not, but i'd love to be able to do this

[fixeighted]

I'm in Max but this scene is the same.
This uses the video camera, which seems to be the only way I have found to do this.
The information came very late and it's really not obvious at all.
There is some confusion but it works.

The camera latency parameter is the only thing that controls the effect 'within' the camera.
The other settings is what confuses things unless they are known about.
Note that Motion blur is unchecked in the render settings - we don't need it to be checked for the blur to work in a general sense.
However, crucially, leaving it unchecked means we cannot access the other controls - only the geometry samples.
We do however need to access these controls, as the latency parameter alone will not work - we need to offset the 'shutter efficiency'
in order to dictate where the blur happens.
In this example, setting it to 1.0 makes the blur be where we want it to be.

This example is perfect to illustrate the general confusion with settings being separated and there not being sufficient info, examples or explanations of
limitations etc. in the docs to come to rational conclusions

By the way, I wrote it this way so I can access the info in the future, as I will certainly forget

[Buck]

Hey right on, I had not tried physical camera with Video, I'll give that a shot

[fixeighted]

No, I hadn't really either, as I believe I and everyone else just assumed it would work with what we've all been using for years LOL
I also didn't realise the two had to be linked in the way I described.
So, really, pure luck
I hope it does what you need anyway, and I can stop spending so many hours thinking about it

I don't think it'll do the rear/front curtain sync thing, but that is not a problem really, as it can be faked easily enough if necessary.

[kosso_olli]

This example is perfect to illustrate the general confusion with settings being separated and there not being sufficient info, examples or explanations of
limitations etc. in the docs to come to rational conclusions

I have been a user of V-Ray for Max for a good 13 years now, none of this was known to me. It is completely undocumented.

[fixeighted]

Yeah they are a bit hit/miss in many places.
What is annoying is that in just this converstion it took so long to get
a result, after what felt like being drip-fed information.
I get that the people are busy but I think that proper documentation is crucial in
such a well established software, especially when the path to results can
be further obscured by a sometimes illogical UI design, as noted here.

It must be noted, Chaos folks, that I'm just being constructively critical here - it's in no way meant
to be personal
We all love Vray and we all demand increasingly more of it (as any software); any relative failure drives innovation

[kosso_olli]

Yeah they are a bit hit/miss in many places.
What is annoying is that in just this converstion it took so long to get
a result, after what felt like being drip-fed information.
I get that the people are busy but I think that proper documentation is crucial in
such a well established software, especially when the path to results can
be further obscured by a sometimes illogical UI design, as noted here.

It must be noted, Chaos folks, that I'm just being constructively critical here - it's in no way meant
to be personal
We all love Vray and we all demand increasingly more of it (as any software); any relative failure drives innovation

Sums up this thread to 100%.
I'm leaning far out of the window here, but I assume even Chaos staff did not knew this.
Anyway, here is the result of the scene posted earlier. It works, but I would have never tried the Video Camera mode in the VrayPhysCam.

[fixeighted]

Hehe, yeah we got there in the end.

I think some knew, generally, that there was something that may or may not work, but unfortunately nobody from Chaos
was available to definitively say what needed to be used to achieve it.
I looked into the video camera quite early on but it didn't appear to offer the capability. As there was no information on it I naturally
assumed I was correct. It was not mentioned in this thread until eight days in, I think.
It was only by chance that I then realised that combined settings from both the camera rollout and the render settings needed to be used.

All in all an exhausting almost 10 day exercise, which should have been as simple to solve on day one as it clearly is