Vray Motionblur versus Fusion Vector Motion Blur versus Reelsmart Motionblur

[Robert1977]

Dear all,

I have recognized that the motionblur of Vray seems to be really good and has a good relation of blurred foreground and less blurred background based on the physical camera settings of a movie cam. I used the default values of 180 degrees shutter angle.

When I render out a Vray Velocity render element with a max displacement of 100 and put this as input bitmap in a Vector motion blur of Eyeon Fusion, I get a different result. Here, the foreground seems to be less blurred, the background more than the vray motionblur. This seems awkward and the 24p footage is showing more "shuttering" effect than the vray example.

Does anybody know why there is such a difference and how to compensate for this?

Another example is the Reelsmart Motionblur (now Twixtor Reelsmart), it behaves the same way as the vray motionblur, when I don't use a velocity channel as input.

Would be great if anybody can help.

Cheers Robert

[henning]

You have to offset the velocity values by -0.5 for Fusion's Vector Blur. I generally just put a BC node with a brightness of -0.5 right after the Velocity Channel Loader.

[Robert1977]

Thanks Henning, I did this already, but still there is a slight difference.
Without offsetting the velocity values, it would look totally wrong.

[vlado]

Is it possible that you have some color correction on the velocity channel?

Best regards,
Vlado

[Robert1977]

Dear Vlado,

no I hope not that something with color space etc. is wrong. I didn't do any color correction on the velocity channel beside substracting the rgb value 0.5 0.5 0.5 from the image so that vector motion blur works in Fusion.

My impression is, that the Reelsmart motionblur is nearly the same as the vray motion blur, when I wire the vray velocity channel as input, with a shift of the velocity channel footage of one frame.

But the fusion motionblur blurs just less in the front and more in the back, so that for my taste the background is too much blurred if I want to have a smooth movement in the front of the image, also with the vray velocity channel.

In reelsmart I don't need to substract rgb 0.5 0.5 0.5 from the velocity channel.

I will post some renderings to show the differences. These are nuances, but the motions are somehow smoother with reelsmart or vray motion blur.

[Robert1977]

There are two different methods for substracting the rgb 0.5 0.5 0.5 from the velocity channel for fusion, both have the same result:

1. using an "ADD" node with blend = -1.0 so that it becomes a "substract" node.
2. using a brightness contrast node with a brightness = -0.5

I will post the images this evening.

[Robert1977]

The different attachments.

[vlado]

Thanks, will try to look into it; we don't have Fusion here so it might take a while to set it up. Is there a description somewhere of what Fusion expects to find in the velocity channel?

Best regards,
Vlado

[henning]

here: http://www.vfxpedia.com/index.php?ti...or_Motion_Blur

[Robert1977]

Dear all,

found that the right preferences in After Effects solved the problem. I needed to switch on "linearize colorspace" in the project settings, so that the hdr-velocity-channel didn't needed to be gamma corrected. Also I assigned a color profile "sRGB" to the project and the footage, but this obviously didn't have an effect. The hdr footage had the assignment "interprete as linear light" for 32bit-footage.

Best regards

Robert

[vlado]

Good to know, thanks for sharing

Best regards,
Vlado

[tammo]

Robert, this is great news.
I never got anything useful from the velocity channel in after effects.
So you used the realsmart motion vector plugin?
What options did you set in the vray rollout?
Did you clamp velocity, or set the max value by testing the fastest part the animation?
Did you have to invert any channels?

[Robert1977]

Dear Tammo, I did the following:

-my footage was in fullhd (1920 x 1080)
-motion blur inside the rendering has to be turned off, otherwise no velocity is rendered
-render the vray velocity as .hdr-file (output gamma 1.0), clamping off, max displacement was 100 for me (estimation based on testing fastest part of the animation).
-To do without testing, you could also just adjust the image width as max displacement - here 1920, since the hdr-images can store very detailed floating point values, this would be the same result from my opinion. Only with very large values, if a max displacement of 1.0 is set and the file stores values of 200 for example, exr seems to be the better format, hdr then has artifacts (at least what i saw in fusion).
-vrayvelocity is forward velocity, while max velocity seems to be backward velocity
-render the velocity together with the multimattes (gi switched off etc. to save rendertime)
-in After Effects, project settings, set the composition to 32bit, project color space sRGB, but most important: switch on linearize color space ("Arbeitsfarbraum linearisieren")
-interprete footage: tell the vrayvelocity-footage to be color space sRGB as well. Switch "keep RGB" off. And adjust to "interprete as linear light on for 32bit images".
-use motion blur with the Revision Reelsmart Motion Blur Vectors In plugin: set max displacement to the one adjusted in 3dstudio Max (100 in my case), vec scale x and y are 1.0, no inversion (I compared it with the vray-motionblur). Blur amount is 0.5 (based on a shutter angle of 180.0 degree, which is the default value).
-make a sub-composition out of the velocity-channel, and apply an effect to it: in German called: "Feld weichzeichnen" = field blur, smart blur?, with a radius of 20.0, 1 iteration and a check on repeat border pixels. This will smooth the velocity-channel a bit, since it has hard edges which would be somehow visible in the motionblur
-the sub-composition is your velocity-channel for reelsmart motionblur.

Note: on the edges of the image some wipe artifacts may occur, but these are hardly noticeable in the final movie. This is because it is hard to estimate for the effect where neighbouring pixels are, if the pixels go out or come in into the image. For the next project, i would render the movie with some overscan of maybe 10 pixels at each side of the frame which will be cut after application of motion blur or retiming.

Cheers

Robert

[Dave_Wortley]

A small note on calculating Max Velocity, if you do a render test at say half resolution, you might get a value in your last render value of say 50.0, however if you do the same test at full resolution you will get a value of 100.0 so be aware you have to calculate this value at full resolution.

[tammo]

Thanks, this is a great way to save render time.
I have a small 12 PC renderfarm, but now everyone wants FullHD and the rendertimes get to long for my setup.

I once even tried to render my scene again with colored checker textures applied-
in order to make it easier for Rs MBlur to guess the optical flow,
but this new method is just perfect.
Thanks a lot!