displacement - probs with 50% grey and shift

[joconnell]

Hi Folks,

I've got a mesh that I'm rotoscoping over an actors body and I'm treating the surface with vray displacement to get a cracked, rocky texture like desert earth. The texture map came from Zbrush so 50% grey means no surface change, black means pull the surface back in and white is to push out. What I've been finding is that with vray in my scene that when I use an amount of 4 and a shift of -2 (to make sure my 50% means that nothing happens) it's still pulling the surface back a tad. The displacement map is an ifl sequence of the map being gradually colour corrected down to 50% grey so it should have an effect of gradually returning the surface to no displacement at all. what I'm finding in a lot of cases though is that it is having an effect on my surface - even when the map is at 128 grey and thus should have no effect on the surface. Has anyone else encountered this or am I doing something quite stupid due to tiredness? Am I correct in my thinking of how vray is assigning the displacement amounts?

Cheers!

John

[simmsimaging]

I had this problem once before. In that case it was a gamma issue. If you use Photoshop change your grescale to gamma 2.2 in the colour settings and reconvert the map to greyscale (or apply the profile) and try that. Might help.


b

[jacksc02]

Brett is on the right track there.
Rather than doing it in potatochop you can change the gamma of the incoming bitmap in the bitmap loader.....

But im sure you know that John

[joconnell]

Hmm - not using any gamma stuff at all in my copy of max (normally I use the cheaty lwf button at the minute) and the colour value is reading as 128 in the viewports - I'll do a closer investigation though - cheers for the pointer!

[vlado]

Keep in mind that a color value of 128 is not exactly 0.5, but slightly more (128/255=0.501960784); a value of 127 on the other hand is slightly below (127/255=0.498039216). This will probably not matter for smaller displacement values, but it might be a problem in some cases.

Best regards,
Vlado

[sv]

another thing to check would be the scale of the model? Particuarly if you are bringing in displacement maps from another package (mudbox / zbrush)

[joconnell]

Cheers for that vlado - I did a simple test on a sphere beside a copied sphere to see if the silhouettes remained the same which they did - I went into my non behaving scene, rendered and the model was being distorted as expected. I copied over a vray color map with the default 0.5 color and everything went back to being okay - 50% grey was effectively doing nothing with displace 4 and shift -2. I then copied a frame from my animated map where a colour picker reads all the values as 128 grey and again it worked fine - then loaded back in the full animated sequence and it behaved - very odd!

Edit - still happening - it's as if it resets withy the ifl file - very annoying.