VrayVelocity pass - negative values

[lichtmaschine]

Hi there,

when objects are moving in certain directions, the velocity value can turn negative and the velocity channel will render black (not in the VrayFramebuffer), am I right ? Is there a way to compensate that like the VrayFramebuffer is doing ?

Best regards
Ingo

[joconnell]

What are you using your velocity pass with? In the case of nuke I don't think it minds negative values, it just means the object is moving left instead of right.

[lichtmaschine]

I`m using After Effects with the RSMB plugin. But anyway, a totally black velocity pass is useless in any software, I guess ?

[joconnell]

If it's float then no. Something like nuke or fusion can use those negative values happily. In the case of something that can't use negative values, you can turn on clamp for the velocity element, and use the max value to let it know what range of values it has to try and fit into the colour space of a normal 0 - 255 rgb image. Take a look through your shot and take a good guess what your fastest moving object is and at what frame. Render that frame and then have a look at the velocity element. It'll show you what the max value was in that particular frame. Stick this value into your max velocity value and your velocity element should have enough data for reelsmart. Here's a note from their support that might be useful too:

Scroll down to the bottom of the Render Element settings and you will see the settings available for the Velocity Render Element. You'll see a setting for Max Velocity; this setting corresponds to the Max Displace value seen in RE:Vision Effects' products= The default Max Velocity is set to 1.0, which means the maximum that can be encoded in the output file is 1.0 pixel in either the X or Y direction which is not very useful . You should change this to a value that encompasses the maximum motion, in pixels, for any object in the scene. If you don't know what this may be, a good value to start with is 2048.0. You also need to specify what the output file sequence is for the velocity-encoded images. Make sure to use a 16 bit or floating point image format that does no compression or lossless compression (for example: 16 bit TIFF files with no compression, or 16 bit SGI files).

IMPORTANT NOTE: 3ds Max renders out velocity images assuming that the y index for pixels of an image increases as you go down the image, and our plugins assume that the y index of images increasses as you go UP the image. As such you will want to use a Vec Scale Y of -1 when using our plugins when rendering out velocity images from Max 8.

[lichtmaschine]

Thanks for answering,

but my problem is the simple fact that the velocity channel in my erx file doesn`t contain any data. When I´m rendering the image and save the velocity channel via the "render elements" tab, the render pass looks fine. But if I´m saving the image as multichannel exr via the "Render to V-Ray raw image file" in the Vray Frame buffer section, the velocity channel is just black, no data. I wonder how I can change this ?

[vlado]

Works fine for me here on a simple test. Which application are you using to view the file? The V-Ray velocity channel is a XYZ channel (as opposed to a RGB one).

Best regards,
Vlado

[lichtmaschine]

It seems that Nuke can read the channel properly, but the RSMB Plugin in After Effects can`t...