View Full Version : pixel velocity channel

03 March 2005, 09:46 PM

how do you see the pixel velocity channel from a RPF file?

the 3D Channel Extract does not have an option for that. iīve searched everywhere, but could not find it. any ideas?


03 March 2005, 12:19 AM
you can see the channel ID with the " ID MATTE " under the menu effect/3dchannel

I dont no what footage is it but if it a render seq from any 3d package you need to be sure that it is render with the open select in the > Z, Material, object and etc is on


03 March 2005, 01:42 AM
yes, itīs a render pass from 3dsmax. problem is i canīt save ONLY the velocity channel, in max it always saves a RGB channel and any other you specify (z, object id, normal, etc etc). and 3d channel extract does not have the velocity channel listed.

tryed the ID Matte, but could not find the velocity channel in it.

thanks for the answer though!


03 March 2005, 09:39 AM
ok if thats a render from 3dmax you have to be sure that you have setup all the object you need a objects channel NR that can be made by select the object and Right Click mouse choose properties then you see in the popupmenu a option menu (G-buffer/ Object channel ) give some channel nr into it .

you can seperate all object with differend channel NR.

hope that helps ya

03 March 2005, 03:40 PM
hey artisanfx! thanks for the info!!

i finally learned what g-buffer and object id is and where to set it! :thumbsup:

but... that didnīt solved my problem. :D

i donīt need to separate objects in post, i need to see the velocity channel in after effects. i also found out that the velocity channel is often called "motion vector" channel by other softwares. problem is, i can render this channel with max scanline and save it in a RPF channel, but i donīt seem to be able to use it, or even see it, in any other place.

reelsmart have a way to render motion vector in max with mental ray ( and other 3d softwares (, but scanline for rendering a matte and velocity pass is faster than MR. 30 seconds against 3 minutes. its faster to render and to set up with scanline in a RPF channel. it just seem useless because i cant see and use the channel anywhere else!! :cry:


03 March 2005, 10:53 PM
hmm sorry then, I dont understund what you correctly mean with the velocity channel,
what will you try to use on this file?
because you can just edit the object ID and g-buffer that means that you have only the obtion to edit the objects seperate and the z-buffer what can be use to gifed effect like fog and distance blur but i think thats all what you can do in afx ... i think :)


03 March 2005, 08:32 PM

thatīs why our communication wasnīt going so well :)

i need motion vectors for setting motion blur in after effects. RE:Vision Effects ( have an excellent plug-in to add motion blur in post. for most scenes, just rendering a matte of the character works to add motion blur of a character over a background. but when your camera moves a lot, you have to either add track points or have a motion vector pass of your scene so the blur can be correctly added. i will end up going with track points. itīs not easier as just set up another render pass, but oh well...

thanks a lot for the help tho! :thumbsup::thumbsup:


03 March 2005, 03:01 AM
FYI, AE only supports the RLA subset of RPF, hence no support for Pixel Velocities. If you know Max, (as I am not an expert in Max yet), someone was telling me there might be a way to use the G-Buffers viewer in Max to write the Velocity Buffer to a standard image file...


11 November 2005, 09:19 PM
I was exploring Render Elements in Max 8's help and I found out that you can split out the velocity pass now as an image sequence. I don't remember if this was possible or not previously, but it's in there now. So I downloaded and played around with the demo of Reelsmart Motion Blur Pro; the RSMB vectors 3.x plug-in seemed to do the trick.

The flexibilty of rendering a clean pass w/o DoF or motion blur and being able to dial it in later would be awesome for my workflow at my job. No one ever makes the same decision twice here, so it's nice to be able to just turn blur on or off at my whim, rather than wait for another render.

11 November 2005, 09:40 PM
This channel is compatible with Combustion in a .RPF file or separate pass ( render elements) in combustion 4 ( using the G-buffer Builder), I ibelieve in After Effects you can use this file only with plugins.

11 November 2005, 11:01 PM
I believe you're correct on the AE end, Vympel. The only way I've been able to do anything with the Velocity pass in AE is through Re:VisionFX's Reel Smart Motion Blur Pro ( plug-in. The pro version includes a Vectors effect that can access the Velocity pass from Max.

The other thing that is troublesome is that it seems that only Max 8 can export the velocity info from the G-Buffer as something AE can use. You can embed the info into the RPF file, and Combustion can use it, but there was nothing I could find that would let AE recognize it.

I haven't had time to dive into it yet, but if you're running Max 7/7.5, it looks like there might be a way to get something into After Effects. Check out this page ( and look into using the VelocityToBitmap script. I'm guessing that this might be the technique that Pierre was referring to a few posts ago for transferring the velocity info into something AE can use.

I've been working with AE 5.0 Standard this whole time, and I think it's about time to upgrade finally. Up until today I didn't even know any of this was possible. I feel like my head's going to explode any second!

11 November 2005, 03:44 AM
Will if you want to this, update to PRO yes, as 16 bits per channel Motion Vectors element makes a bit precision difference. Also aside it does not support Pixel Velocity, the 3D channel extractor in AE is only 8 bits.

Pierre (

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