Bump Map Question using GI

[DIEDBLUE]

Can anyone explain to me why a bump map will show up on my model when global illumination is turned off and using one omni light in the scene, and then doesn't when global illumination is turned on? Very strange!

[Matt_3D]

Not sure of the exact reasoning behind it, but try using displacment instead.

-Matt

[natty]

i think its because bump mainly works on Specular highlights to make it look as if bumpy...

[DIEDBLUE]

Thanks for the replies!

But I have another query regarding displacement maps!

Take a sphere as the object being displaced!

1 - If I want to displace the whole shell of the sphere then I use the 3d mapping technique? yes?

2 - If I want to displace a part of the shell of the sphere I use 2d mapping? and how is this done? Do I use polyselect to select the polys I want and then use the Displacement modifier using 2d mapping and copy the map over from material editor to the tex map slot and hit render? or doI have to use a UVW map aswell?

Thanks for your patience in this matter, it's just that I have tried and failed and need to know the correct way to do this!

[trixian]

Natty got close to the answer
The reason the bump seems to disappear is because sky light (and bounced light to an extent) have less of a direction onto where it is being shone. Therefore the sometimes omni-directional sky light will seem to swallow up the bump features, where as an omni/point light comes from the distinct direction from where it was placed.
Appart from this, low GI settings often cause the bump to get "interpolated away", but this can be solved by upping your GI settings either in the contrast threshhold or the subdivisions.

[DIEDBLUE]

Thanks for that! I understand about the bump being dispersed by the light comming from all directions. I will try as you have suggested to see if it solves the problem!

[egz]

http://www.chaoticdimension.com/foru...?p=19425#19425

and

http://vray.info/entry.asp?entryID=105

[samuel_bubat]

because of the bump map
this seems to be a vray only issue/problem !!

little example. take a sphere, add a bump map and
set your environment color to white or something.
render with vray gi and you will see nothing.
do the same thing with lighttracer and it works (brazil should work, too).

But, as soon as you have for example a gradient in your
environment slot vray will produce bumpmaps as well.
And if i compare these bumpmaps with the one lighttracer produces
in this case.... imo the vray bumpmaps look much better.

[LuKa]

because of the bump map
this seems to be a vray only issue/problem !!

little example. take a sphere, add a bump map and
set your environment color to white or something.
render with vray gi and you will see nothing.
do the same thing with lighttracer and it works (brazil should work, too).

But, as soon as you have for example a gradient in your
environment slot vray will produce bumpmaps as well.
And if i compare these bumpmaps with the one lighttracer produces
in this case.... imo the vray bumpmaps look much better.

I've tried this thing with all renderers (VRay, FR, Brazil and MR(using XSI)) and none was capable of doing this, which seems very logical to me, since bump map is not geometry. Bumps appear nearby other objects (floor for example) and if you use another lightsource (like sun).

[samuel_bubat]

[quote="LuKa"]

I've tried this thing with all renderers (VRay, FR, Brazil and MR(using XSI)) and none was capable of doing this ....

sorry i disagree at this point !! take a look at the pictures below.
I just quickly rendered these pics. And I´m very surprized how
different the bumpmaps are calculated.
All use a the same "dent" map as bumpmap.
The brazil pics are rendered without the "enhance bump shadow" option.
However I still think that this Vray gradient environment pic looks
most realistic. The Lighttracer bumps look very artificial and the brazil
bump are somehow to uniform. In most cases you don´t
use a single coloured environment for lighting so for my part
I DON´T think there should be something changed inside vray.

All these pics were rendered with basic settings. Just actived the gi of the
particular renderer.

Vray Isotropic Env.


Lighttracer Isotropic Env.


Brazil Rio Isotropic Env.


Vray gradient Env.


Lighttracer gradient Env.


Brazil Rio gradient Env.



cheers

[mike_kennedy]

I almost always use an HDRI instead of a solid color if I am doing a sky light only lighting situtation.....

[Long John]

sorry i disagree at this point !! take a look at the pictures below.
I just quickly rendered these pics. And I´m very surprized how
different the bumpmaps are calculated.

there is a tutorial available for brazil customers that show the problems brazil has with bump mapping and GI.

your example is not very good and much to simple, you should have a darker part on the sphere where the diffuse light has problems to illuminate the sphere.
put the sphere on a floor and one side wall to block the skylight.

brazils enhanced bump mapping has nothing to do with GI, it´s for shadows that represent the bump mapping.

i have not seen a GI engine that was able to render bump maps out correctly. it alway look not correct when the main light comes from diffuse light (skylight).