Banding In Z Depth With Samplerinfo

[joaomontenegro]

Hello,

I'm rendering a Z pass using the SamplerInfo node. I need the values to be exact (i.e. the Z values must be the actual distance between the camera and the surfaces). I'm having trouble with the output: the z values in the image are banded, instead of smooth transitions i'm having "staircase"-like values. I'm using floating point in the output and tried all the possible configurations in mental ray. I also changed the camera's clipping planes, but nothing seems to change this banding. I guess it is something related with some low resolution representation of the floating point values internally in the SamplerInfo node. Do you have any clue on this? And do you know any other way of creating such a Z pass?

Thank you,
Joao

[joojaa]

QUOTE(Joao Monten @ 08/29/07, 08:37 PM) [snapback]272467[/snapback]
I guess it is something related with some low resolution representation of the floating point values internally in the SamplerInfo node.

No its full resolution (renderers dont do 8 bit calculations internaly), but likelihood is that either you rendered out a 8 bit image despite what you think, then since floating point values dont jitter the band is very accurate, however off course your display is only 8 bit so when you convert it to 8 bit for showing you it becomes banded.

See you doo understand that a 8 bit totaly black and white image bands no questions asked 256 values are just way too little for the output.

Clip planes dont affect sampler info.

PS: if you chek zdepth in the output settings of your camera you get this info for free automatically, the only thing you need is a prog that understands -1/dist values, and unfortunately adobe for example rejects possibility of negative values. (wich is a shame really negatives are SO useful for comp)