mr problem with glass mr material with dielectric

[msamer]

hello every1!

i have a problem with glass material in mental ray,

architectural material glass and raytrace material work fine but i don't seem to get realistic images using them especially reflections.

having mental ray i turned to using mental ray material with

--dielectric set on surface;

--shadow transparency base set on shadow;

--photon basic base set on photon

everything was working fine until i had 3 glass layers or more behind each other in a view, then pixels started appearing on the area where u view more than 2 layers thru it. i have tried everything in the settings from:

increasing trace depth;

playing with the material shadow and photon base settings, even without them;

--changing lights and logarithmic exposure

--trying it with caustics

--increasing gi photons

--even using glass physics_phen as a material; its mentioned somewhere in the user reference that this material is similar to using mental ray material with dielectric set on surface

--etc...

whatever i do a view thru 3 layers or more gives pixels on them.

i hope some1 out there can give an insight to this, i'm sure some of u have encountered the same problem.

i'm new to this forum so i hope i can attach some images to describe the issue more.

thanks in advance!

 

 

image 1 settings

Ies sun 2300 ies sky 0.2

GI 80 phtns/sample radius 5

gi phtns = 8000 decay 1.7

fg 80 samples filter 1 radius max min: 4 0.3

fastlookup is on

 

image 2 same as 1 decay 2

 

image 3 same as 1 but ies sun 2400 no ies sky

 

image 4 logarithmic exposure on ext daylight ticked on

brightness 65 contrast 50 midtones 1

 

image 5 same as 1

fg 120 samples; filter 1 radii 2 0.3 fastlookup off

sampling 1 - 4 box filter 2x2

 

image 6 same as 5 but lancoz filter 4x4

 

image 7 same as 6 fg 200samples filter1 radii 4 1

gi photons 12000

gi 200 phtns per sample radius 6

[AJLynn]

Try increasing image sampling quality. I think this is in the Renderer tab.

[architimmy]

You should use the Lume Glass shader. Increasing the sampling just gives you more spots on your glass with DGS or the Glass(physics_phen). The Glass(lume) shader will give you several options to increase sampling but the default settings should be fine. Do it the way you are doing it, just create a mental ray material and add the Glass(Lume) as the surface shader. Lume shaders come with mental ray in Max 7+ and Viz 2006 and up. Not sure about earlier versions.

[msamer]

thanks for the replies! really appreciate it!

 

ajlynn, went up to 4 and 16 still the artifacts or bright pixels

 

architimmy, i used the glass lume shader previously, but i had another problem with it, when using logarithmic exposure while rendering, the glass turns to almost a mirror! besides it has a lot higher reflections normally, it makes the glass look unrealistic. any comments there since u r recommending it?

thanks guys for ur help!

[architimmy]

You need to put a different surface shader into glass material if you don't like your reflections, in this case a DGS material works fine. This works only as a surface shader so anything happening inside the material (refraction etc...) is on the glass shader. So look at your glass sample, if for example it is frosted or sandblasted glass add that to your surface shader, if the glass is tinted or has some quality that exists throughout the volume of the glass add that to the glass(lume) shader. I attached a sample scene that has a mr-glass(lume-dgs material on the right and architectural glass material on the left. Just play around with it until you get a result you like.

[msamer]

thanks for ur reply again architimmy, tried it ur way in ur file, the glass lume is really good and has a lot of options, but still in log exposure u notice the reflections increase lot, will try to use it without the log exposure in the scene. adding a dgs material to it really increases the render times a LOT! although the differences are subtle.

 

though still researchig to find how to get rid of these bright pixeles using the dielectric material, dunno why but but also found it to work really nicely with just the right amount of reflections and its interaction with the scene.

 

i came across it somewhere where these pixels were mentioned to be related with the cpu type or something, dual processor machines, i'll try to dig it up add add it if i get across it again.

 

still researching....

any1 know a solution of this dielectric pixel issue...

[architimmy]

Interesting... DGS on top of the Glass Lume shader does take a long time. Try the Dielectric material instead it's much quicker and it seems like the reflections are a bit less. Unfortunately, in real life, glass is normally pretty reflective so the shaders are pretty reflective too. If you need absolute control of your reflections use the mental ray Reflect(base) shader as the surface shader for the glass. Black is no reflections and white is 100% reflections.

 

Too bad you aren't using VRay, you could just change the sampling in the material. By the way, you can turn on supersampling with architectural glass to get a smoother result.

[msamer]

hey man thanks again,

these r some test renders i did for my scene, as u can see the 1st 2 images show the difference of reflections i am talking about. excessive reflections from glass lume u can hardly behind it.

 

this view angle (images 1&2) shows the noise i have a problem with on the vase only near the center of the room, but when the view coincides the center glass void and the external window u get noise almost allover! see image 3 notice the noise on the intersection of the view angle with 3 faces of glass! image 3 is with caustics.

 

as for the 4th image its a fast render for the glass lume with less transparency set to .7 ; u notice the glass becomes more whitish and looses some of its transparency to color, the whole area restricts light entering and becomes duller!

 

last image is vray render with vray material, i just prefer mr, i think its a matter of preference... don't wanna start a vray mr thing here....

seems there is no such thing as perfection!

 

but i am gonna stay after this issue till i solve it!!!!!!

 

some 1 out there plz help!

 

oh image 1 is with dielectric material and image 2 is with glass lume.

[msamer]

i was digging out the mr tutorial that came with max, found this scene with the glass and water in it, well i added 3 planes using the glass to air material supplied in the scene and a red ball behind it, u can see the noise thru the 3 layers! hmmmmm....

 

dunno if i am seeing things or.....

 

what do u think?

[architimmy]

hey samer,

using a reflect base is the best thing I can think of to help you with this. it seems pretty obvious that the lume glass shader is the only one that doesn't end up looking a bit spotty when you layer it. just try to think of mental ray shaders as a network of shaders (more like maya) and you should be able to figure most problems out. if you don't like a surface or reflection just throw in a new shader for that parameter and set it to what you want. it's hard to explain but once you get it it becomes pretty easy.

 

I too prefer mental ray over vray (although I use vray more often for interior renderings because it's easier to work with). The results from MR are just nicer I guess. Vray renderings are always too bright and too clean. Not that I want to stary a vray vs. mr thing either. But mental ray is much more difficult to work with because there aren't many tutorials online to help you out with it. Check out lume's documentation on their shaders http://www.lume.com/manual/Contents.html.

The more I work with mental ray the more I use their shaders.