Hi there,
Ive downloaded the real motion blur plugin demo to test the velocity channel that vray can output, but the results are not very good at all. The blurring is very strange in places.
Does anyone have any experience using this plugin with the velocity channel from vray ?
from vlados post some time ago
REELSMART MOTIONBLUR IN VRAY
--------------------------------------------
There is nothing really specific about this; it’s the same approach as you would take with the scanline renderer:
(*) Add the VRayVelocity render element;
(*) Go to some frame of the animation where objects are moving fast;
(*) Render the frame;
(*) Go to the VRayVelocity render element and check out the “max velocity in last frame” value. Suppose this is, let’s say 36.67;
(*) Set the “max velocity” parameter of the VRayVelocity element to something just above this value, e.g. 40.0 and note this value (it is the “Max. Displace” value that you must enter into RSMB).
(*) Render the scene along with the velocity render element.
In your compositing application (I used Premier evaluation for this):
(*) Load the rgb and velocity sequences and apply a RSMB Vectors effect to the RGB sequence;
(*) In the RSMB Vectors parameters, select the “Motion vector” source to be the velocity sequence;
(*) Set “Max. Displace” to be equal to the “max velocity” parameter in the VRayVelocity render element parameters (e.g. 40.0);
(*) Set the “Vec Scale Y” parameter to -1 as noted in the RSMB manual;
(*) Adjust “Blur Amt” as you wish (for example, 1.0 for motion blur duration of 1 frame);
Ideally this should be all. It seemed to work fine on two scenes that I tested.
Best regards,
Vlado
I think that you have to leave the “Vec Scale Y” parameter at +1 as in the defaults, i think it looks more correct but you have to try it out yourself.
Yep, I think the VRay velocity is already flipped properly (it used to be reversed in older builds).
Best regards,
Vlado
Great, I’ll give that a go. Thanks for the help.
Ok, I have just rendered out a single frame…with a velocity channel. How do I read the max value..all I get is the x,y,z values and the pixel x & y coords…
Update: I did have the velocity pass clamped..Im rendering to a png. Is this correct ? I tried unclamping and the x, y & z values now go above 1. Im assuming this is how I read the max velocity..
Ok. Ive sorted it now. Onto the next stage of testing 
Could you please write out your solution, since this does not make things clearer !
Ok. This is what I did:
1. Add the vrayvelocity pass to the render elements.
2. Turn off clamping in the velocity pass.
3. Render a frame where the motion or movement is estimated to be maximum.
4. Look at the vrayvelocity pass in the vrayframe buffer and note the maximum velocity as shown by the x,y & z readouts.
5. Enter this figure, adding 5 to its value, into the vray velocity max velocity box to make sure that every velocity within the animation would be within this scale. So, for instance if the max velocity readout was 56, I would enter 60 into the max velocity.
6. Render the animation and your vrayvelocity output.
7. Bring the anim into your comp software.
8. Select real motion blur vector blur.
9. Select the vray velocity output that you have just rendered.
10. Make sure that max velocity inside Real motion blur is set to the same velocity you entered into the vrayvelocity max velocity earlier.
11. Adjust the motion blur amount to the desired effect.
Hey preseto
Probably long winded but thats what I did
Is the velocity pass a part of the rgb file(.png) or is it a separate png file that is saved? I only see the rgb .png file in my folder. Sorry for the basic question. I never use render elements. I’m using the pre-pass method for rendering.
Cool. The x, y and z values are the velocity values
Well, if you are using the vray frame buffer and you have added the velocity pass you will be able to select the vray velocity pass from the drop down menu on the top left of the vrayFB. Normally it is RGB and alpha..it should have vray velocity in the dropdown also. If you are using the normal frame buffer, the velocity buffer should display as a seperate buffer once the render is complete. Im not sure if the x,y,z values can be read off from the standard buffer, you may have to use the VFB for this…
Also please bear in mind that you need to save the velocity channel with an alpha and also as a 48bit png or something similar otherwise the motion blur will look incorrect if using something like RMB…
Thanks Steve. I’m new to render elements. But, I have the rsmb plugin for AE and want to learn.
No problem. Let me know if you need any more help.