Displacement issue in V-ray

nomeradona

@nomeradona said:

i myself still lokkin on the mapping issue and hope you could further shed some lights here to how displacemnent works.

What mapping issue?
how the displacement maps work in Vray. How the gray scale will be displace. its a kinda small test im doing here. i am setting 11 colors from white to black (9 grays in between from white to black) i have also list down the RGB numbers. I am planning to measure how the displacement behave.

i just plan base on visual, but i know you have your test in mathematical forms. so if you have some thoughts to shed lights on this, i will appreciate.

thomthom

Seems to be exponential. Wonder if it's possible to make it linear. Need to experiment. Maybe ask Damien.

I noted that turning off the filtering of the displacement map made it smoother. When it was on MipMap I got some weird artefacts.

Displacement.skp

thomthom

I was wondering if there was any of the other settings that would make V-Ray treat the grayscale values linear instead of exponential. But I've yet to find it.

thomthom

hmm.... could it be because I use 24bit images... Wonder if HDRI images will differ in behaviour...

thomthom

I was correct in my suspicion.

When I converted the 8bit/color image to 32bit/color the medium 8bit gray (RGB 128,128,128) did not convert to 32bit medium gray (RGB 0.5, 0.5, 0.5) Instead it came out as RGB 0.216, 0.216, 0.216.

When I created a new grayscale image. This time in 32bit per channel, going from 0.0 to 1.0 with 0.1 increment I got a steady displacement.

32bit .HDR displacement map

thomthom

But I wonder why I got the strange streaks in the displacement. I saw them in the 8bit version before I turned of filtering...

nomeradona

@thomthom said:

But I wonder why I got the strange streaks in the displacement. I saw them in the 8bit version before I turned of filtering...
i guess that one could not be perfected, that is why blurrying a bit the displacement is a key one. but even you do this streaks will still be there. waht about vray max? any idea.

thomthom

Don't have V-Ray for Max.

nomeradona

i made a similar test, and i found out a lot of things how vray behave with the grayscale. its smilar with yours thom thom. i will post later my images..

but these are the following facts.

that the pure white with the multiplier 1 will be displace one inch perpendicular to the face.
vray works in inches. not centimeters
if you want to remove artifacts, use non filter and add blur in your displacement map. I found using Normal map seems better. i can prove it yet. but the amount of detail is excellent.
see this post http://www.sketchucation.com/forums/scf/viewtopic.php?f=81&t=18336

nomeradona

ah ok. anyone? let me find also in the Filipino forum.

thomthom

FYI, the reason the 8-bit image has a curve is because the default V-Ray settings is to apply a 2.2 gamma correction.

thomthom

@thomthom said:

FYI, the reason the 8-bit image has a curve is because the default V-Ray settings is to apply a 2.2 gamma correction.

The 2.2 correction stems from the General Switches I think. You can override the displacement gamma for that material with the inverse gamma - in the case of 2.2 you would have to enter 0.4545 in order to make the 8-bit displacement linear.

bhbarchitects

ThomThom

Brilliant piece of info

Possible use as disp for roof tiles, if you can calculate the increase in height of the plane?

Roof tile disp