MAX velocity -> Nuke

[capitanred]

Hi

I'm actually working with the nuke trial and am sticked on the vector blur. I know, there are several discussions out there poiniting to plugins and what else for MAYA!

But what is with Max and Vray?

I did this little test to show that everything I do does wrong m-Blur. For some reason the orthogonal renders have a correct blur as long you watch from a predefined view like front,top,left etc.
Max velocity-RenderElement does somethig Nuke can't read.
The openEXR velocity channel looks pretty good, but neighter from vray or default rendering, nuke can't read it right. Am I doing something wrong? or is the translation between max and nuke not correct?

files:
http://www.megalomania.ch/capitanred...ts/VelTest.rar (0.5 MB)

[jan_dee]

hi there... i am not sure and I haven't reviewed your example but last time I used Vray vel.Channel I had to flip the Y-axis. You can do that by simply using an multiply node and multiplying the y axis by -1... try that. as soon as I have more time I can get back to your example and have a look...
cheers, J.

[capitanred]

hey, tanx for the input
I tried multypling Y by -1. but as the blur is somehow like rotated 90° in local space of the objects, it just fliped it to the other side. I tried some other values and -.3 worked it out. but i'm not sure if this is worth for all directions, or only for this scene. I'll do some tests.

[jan_dee]

...that sounds really weird. try to shuffle your vel.channels. sounds more like some swapped axis issue.. are you using vRay?

[capitanred]

yes, I'm using vray and default...they seem to have some differences.
btw, you were right with multypling Y by -1. but still some issues

I did this new test. now arrows are going in nearly all directions. rendered with default or Vray to openEXR with a velocity channel works nicly. when multiplyed Y by -1 the blur is correct and looks sweet.
but when rendered to vrimg and then converted to exr, the blur goes to a different direction. any axis multyplied by any value gave a incorrect result. perhaps there is something else that has to be done before sending data to vector blur.

http://www.megalomania.ch/capitanred...Directions.rar (1.1MB)

just one more question...

I read alot about unpremulting and premulting stuff, that should be done before the blur and after. am I doing this right here?

[jan_dee]

I can't follow you without checking ur example (no time)...
btw... all filter ops (vectorblur is one) should be done with premultiplied images. otherwise ur going to filter unpremulted stuff which will result in unwanted things... hope that helps
cheers, J.

deadstupid question: are u using the right channels for the vectorblur?

[capitanred]

lol...I hope so

I'm absolutely new to nuke. got it yesterday
but I read alot about it in forums, so i have some little understanding what's going on.

well, there are not alot channels which i can use so i think these are the right ones.

when rendering directly to exr with velocity channel, nuke gives me channel 'other'. There are also channel 'backward' and 'forward', but with no data inside. also when i move the mouse over them in the viewer, it does not diplay anything where normaly the pixels rgba values are shown(bottom in the viewer).

when rendering to vrimg and then converting to exr, there is a channel 'vrayVelocity'(hit me if this is not the right one ). the colors inside are the same to the ones in the 'other' channel of the other renders. but the blur isn't the same.
in this .exr the 'other','frward', and 'backward' channels have no data.

I read about 'uv' channel, but seems that this has been changed to 'other'...

I hope i don't take to much of your time and apperciate your help

[hugo_guerra]

Hi, I am having similar difficulties, maybe someone can help me also.

Both a VRAY velocity pass gives me bad Motion Blur, but also the Scan line render in MAX also gives me a bad Velocity pass.

The Scanline velocity pass appears in the Alpha channels as Vel.x and Vel.y, should I do a new channel with that, what is the way t correctly extract a good velocity pass.

As for the look of the pass, it is always changing very rapidly in colors, so it gives me a poor Motion Blur and with up´s and down´s. Should I grade the Velocity pass to correct that?

All of best

Hugo

[capitanred]

how did you do the velocitypass/channel?

in the files above i did them by rendering to .exr and adding a velocity channel, inside this .exr. this works fine for me.
I did not output a velocity render element.

[tus]

hi
do the vector channel in 3ds max you can refer to this thread:
http://forums.cgsociety.org/showthre...or+motion+blur

[capitanred]

http://www.revisionfx.com/support/fa.../#3d%20Max%208

there is the way to go! I'm so ashamed little bit more reading the manual would have done it

I didn't set any value into the velocity render element. when doing this, the element produces a nice m-blur, as the channel in the exr does too.

________________
EDIT:

Well...shame again! it was a lucky strike that the m-blur was right. in other images it was not...
sorry for that.