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royter
08-23-2007, 08:19 PM
what this the equivalent of the specular value in the mai_material?
is it the highlight vs refl balannce?

can you turn on specular without having reflectivity off just like you would do in a phong shader?

(regardless og the highlight only option witch i don't want to use)

JasonA
08-26-2007, 03:48 PM
From the mia_material documentation:

In the real world “highlights” are just (glossy) reflections of the light sources. In computer graphics it’s more efficient to treat these separately. However, to maintain physical accuracy the material automatically keeps “highlight” intensity, glossiness, anisotropy etc. in sync with the intensity, glossiness and anisotropy of reflections, hence there are no separate controls for these as both are driven by the reflectivity settings.

maybe a way around this would be to try rendering out a sperate reflection and specular pass by controlly the primary visibility of objects in the environment and the light linking to the object in question to seperate rtelfection from specular.

Olegr
08-27-2007, 08:45 AM
Specularity is reflection, so I do not believe it is possible to have one without the other in mia_material. If you need to tweak specularity like a phong, then I suggest you use a phong.

royter
08-27-2007, 04:06 PM
Specularity is reflection, so I do not believe it is possible to have one without the other in mia_material. If you need to tweak specularity like a phong, then I suggest you use a phong.

i really need to ise the mia_material.

so there is 2 kind of reflections behavior in the mia_material : reflective or reflective glossy (regardless of aniasotropy).

i found it a little poor becose in real life there are a lot of materials with special specular features in addition to those last 2. It's too bad that we can not use specular maps in the mia_material.

MasterZap
08-27-2007, 04:38 PM
i really need to ise the mia_material.
i found it a little poor becose in real life there are a lot of materials with special specular features in addition to those last 2. It's too bad that we can not use specular maps in the mia_material.

You can map both the glossiness and the reflectivity just fine. Since speculars are just the emulation of reflections of the lightsource, they go together (by default) in the mia_material.

But if you really want to adjust that, you have the refl_hl_balance parameter, which you also could apply a map to, if you find that fun.

Generally, tho, I would suggest mapping the reflection glossiness, because that is most akin to what reality does.

/Z

royter
08-27-2007, 05:41 PM
You can map both the glossiness and the reflectivity just fine. Since speculars are just the emulation of reflections of the lightsource, they go together (by default) in the mia_material.

But if you really want to adjust that, you have the refl_hl_balance parameter, which you also could apply a map to, if you find that fun.

Generally, tho, I would suggest mapping the reflection glossiness, because that is most akin to what reality does.

/Z

hello Zap

i have always maped reflectivity, glosiness and specularity before the mia_material by using a phong in combination with a mib_glsossy and it worked grate ( i alsow used to use a maya phong with the mr reflec blur option and it worked good to).

But even if speculars are just the emulation of reflections of the lightsource, i find it very useful to have the control over this attribute.

now, can refl_hl_balance parameter replace the specular attribute? and how it does it?

royter
09-03-2007, 04:29 PM
i am trying to simulate this material, witch is a blurry paint.
i noticed that you can try to get the general reflection aspect of the material by turning on gloss reflec of the mia material. As you can see (in yellow), the blurry enviornement is correctly reproduced in the mia_material.
http://www.aedii.qc.ca/v2/fichiers/uploads/section_4/ex_1.jpg

http://www.aedii.qc.ca/v2/fichiers/uploads/section_4/ex2.jpg



but there is a highlight line in the reference photo (in red) that is not reproduced in the mia material. Is this because of the lack of a specular attribute in the mia_material?
or it can be chieved in another way.


*i have the same environement modeled in front of the metal ramp just like the refrence photo.

*i wonder why i never get the same AO occlusion effect as in the reference image, no matter the ao settings in the mia material the AO is very very weak.

royter
09-03-2007, 11:02 PM
this is the the closer that i can get to the material in the photo.
http://www.aedii.qc.ca/v2/fichiers/uploads/section_4/ramp_1.jpg

http://www.aedii.qc.ca/v2/fichiers/uploads/section_4/ramp_ref.jpg

you can download the scene , and try to get closer to the photo as you can.

scene (http://www.aedii.qc.ca/v2/fichiers/uploads/section_4/ramp_entry.mb)

modernPrimitive
09-06-2007, 08:31 PM
Firstly your light direction is not matched up to the reference. For a start if you want to match it up exactly, you're going to have to match the light source. Check the shadow on the left leg coming down as a reference. It looks like you're using the sun as a backlight from the right side in your scene when in actual fact it is above left. The strong highlight running at the top of the object is not necessarily from the sun, it is probably a fresnel reflection of the sky (increased reflectivity at glancing angle) - so don't use the main light source to get this highlight - rather use the fresnel BRDF attibutes. Check the top left corner to match the main light source.

Secondly I suspect that the highlight you're talking about is merely an increased incandecense in the horizon line of the environment not a "specluar" highlight as you call it. Remember that "specular" is the reflection of the light source - that is all. Phong and Blinn only have this as separate because of historical reasons - precessing power etc. Specular on phong and blinn are just an "emulation" of the reflection of the light source which is usually hundreds or thousands of times brighter than the environment.

Mia is more physically accurate - to get more "specular" you need to up the strength of the light source so that it reflects more. It may not be perfectly accurate though - is any CG perfectly accurate - no. Even Maxwell is not a 100% true physical emuation - and that's after 24 hours of rendering!

To create a "fake" specular you could perhaps try a mix20layer node (free download - www.pixero.com (http://www.pixero.com)) and screen the phong's specular over your mia or render separately and comp in post.

I'm also having a problem with the AO in mia - you can try to plug an mib_amb_occlusion node into diffuse or do a separate pass and comp in post again....

hope this helps. I think your shader is pretty close, I think the environment is not 100% identical.

modernPrimitive
09-06-2007, 09:03 PM
Just checked your scene - the photo looks like it was taken on a slightly overcast day - very different from your physical sky. An overcast day creates a white-grey sky dome and the clouds diffuse the sunlight which creates a much broader key light resulting in a broader "specular". You can only match this shot exactly by changing your light setup.

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