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Vector Motion Blur With Vrayvelocity


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#1 Miaz3

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Posted 23 February 2013 - 10:32 AM

Hi,
just some test again, after waste many hour on the web to find how is it possible de composite Velocity Vray pass... As you know vray make you a strange vector.
normaly i cheked velocity on my .exr file and its works fine. So with the extra .exr i've put the vray velocity channel too and no result append with the vectorMotionblur tool.
But with the plugin RSMB vector work fine... really do not understand.
here a screenshoot, with a .tga file(Vray velocity) in 32bits and Channel boolean to convert R to vX and G to vY and a VectorMotionblur.
The second is a simple .exr file autogenerate velocity.

Posted Image

#2 pingking

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Posted 23 February 2013 - 02:02 PM

tga can only be 8bit by defnition

i think the vray velocity has its zero motion point 0.5 and backward motion beneath and forward motion up to one. so its normalized between 0 and 1. thats also the format that rsmb expects
so you have substract a value of 0.5 and multiply by the factor you defined as max motion in 3d


#3 Miaz3

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Posted 24 February 2013 - 08:00 AM

Even if the .tga is in 32bits, it can be only a 8bit ? but with the channelBoolean i convert R to vX and G to vY , how can is possible to nothing append...
i've tested with 0.5 value to the VrayVelocity render, and the result is the same.
I think to explain the best i can, i attach these two's screenshoot.

First with the .exr file (backvectors), works fine:
Posted Image


The second with the VrayVelocity buffer on .exr file won't work even if i Flip the X or Y ...
Posted Image

Thank in advance

#4 Gringo

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Posted 24 February 2013 - 11:18 AM

TGA can only store color in 8 bits per channel. RGBA all together are 8*4=32 bits then.
For data like motion vectors you should better use 32 bits per channel.

You can get some more details about different motion vector storage formats here: http://vfxpedia.com/...n_Vector_Passes

Try to play with the scale parameter. Sometimes you only achieve any visible effect when it's set to some hundreds.

#5 pingking

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Posted 24 February 2013 - 02:59 PM

after you subtracted 0.5 from the vray velocity pass what numbers are in there and what numbers are inside the exr vector pass?

#6 ChadCapeland

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Posted 24 February 2013 - 06:38 PM

Do an A|B split on a 3D Histogram viewer with the two velocity passes. Should help clear up what is different between them.

#7 Miaz3

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Posted 25 February 2013 - 11:51 AM

@pingking: i really don't know what numbers are in....i just put 0.5 on the velocityValue in 3D renderer. And i don't know how to view the numbers inside the exr vectorPass?
@Gringo: I've try too xtract velocity from my exr, and to force Brightness to -0.5 and i have the similar pass.

Why Eyeon fusion vectorMotionblur is so different ? is an headache.

#8 Tilt

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Posted 25 February 2013 - 02:56 PM

Fusion's vectors totally make sense:
0 is no motion, +1.0 is one pixel foward/right/up and -1.0 is one pixel left/back/whatever :-)

The motion vectors your 3D app generates are a workaround that comes from a time, when there was no proper storage and rendering for floating point numbers, so it was done in an image from 0 to 255 with 127 (or 0.5) being the normal point. ReelSmart's motion blur plugin comes from a similar time.

You can see what numbers are inside a vector pass by switching on the color inspector subview (SubV button below viewers).
http://www.vfxpedia....bviews#Subviews

#9 ChadCapeland

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Posted 25 February 2013 - 04:25 PM

For Vray, you might be getting vectors from the VRayVelocity, which for whatever reason must be internally normalized, even if you save out to something like EXR. Either crank up the maximum velocity (I feel ill just mentioning this) or use the GBuffer output (which is conveniently unclamped).




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