New DGS question

[sebast1an2]

hi, it's quite simple...
i u want a diffuse material(like lambert), you connect it to the diffuse value, if you want a reflective material(like blinn) you connect it to the specular value ...and if u want to use the shiny option (for blurry reflections), you connect it to the glossy channel...

greetings sebastian;)

[johnnynightlife]

thanks sebastion, but what about figuring out the values for the file i add in say the diffuse channel? that was my main question i guess:)

[bmcaff]

I guess that the values would be derived on a per-pixel basis from the texture file (seems logical, right?). Since you will probably be using a standard range image no pixel will have a value above 1. The difficulty arises when you combine a diffuse and specular map. The combination value of the two maps (or values) should not go over 1. You can use any image editing package to determine roughly the max colour value for the texture and then use colour balance to control the overall value.

EG. take a simple black and white checker texture. The values are 0 (black) and 1(white). Now you want the floor to have an overall reflectance of about 10% so we want a specular value of 0.1. So in the colour balance of the checker texture you set the colour gain to 0.9 so that the max value of the texture is now 0.9 .. Of course this is a really simple example and for more control you may have to tailor the texture maps in you fav editing package to get exactly what you want.

Hope this is what you are looking for.

[johnnynightlife]

bmcaff, i follow what your saying, but i wonder how to precisely calculate the overall value of the file, so i can make up a total value of one, between Diffuse Glossy, and Specular. maybe i am reaeding into it too much, but i was just going by the tutorials that say do not exceed total value of one, for the three channels.:shrug:

[bmcaff]

I would not be too worried about the accuracy of the overall value as this DGS sum of 1 is for physical correctness (it means that the shader can only reflect 100% of the light it receives, a value of over 1 means it reflects more than 100% which is not possible in reality). If you are only after a visual effect and not too concerned with this "physical accuracy" then you can just eyeball it. You can get pretty cose by just doing a quick value check in photoshop or Maya (with Colour Chooser).

Photoshop info window will give you the values (using HSB readout) and you can compare the same spots in two different files (diffuse & specular) to determine if the value is over 1. Then adjust levels to get the right balance. It will be obviously easrier if you use a solid colour for one of the DGS channels as you only need to get the maximum value in the file texture.

[Daniel Whitton]

I think I follow what your saying. I was pondering this just the other night.
This may not be correct cause I haven't tried it yet but here goes.

Say if you want your Diffuse channel to have an intensity of .8 and your Glossy channel to have a reflectivity of .2. Both are cumaltive to 1.0
Now you want to add an image to the Diffuse channel but the texture loads at 1.0

This is what I thoguht of doing instead of passing the texture lookup directly to the Diffuse channel. You need to create and mib_intensity.
Map your file texture to the lookup>intensity, set the factor to.8> then map the intensity to the Diffuse channel.
NOw the texture should have a value of .8

I'm going out on a limb, but it might just work.

[bmcaff]

Yes, adjusting the colour balance of the file texture won't work for a custom mental ray file texture (but will work for a standard maya file node).

But for custom MR textures the MIB_color_intensity (this is the one you refered to, Daniel?) is a data conversion node for converting to greyscale so would not work in this case. You could try using the MIB_color_mix node, set you texture to the colour 0 and set colour 1 black and then adjust the weight and mix mode to adjust the overall effect. (Maybe there is an easier way?? anyway there is an example of this in the MR book).

[Daniel Whitton]

Thanks for the info bmcaff. Interesting to know. Maybe I should buy the book instead of beating my head into the wall with just experimenting.

[bmcaff]

Welcome, but be prepare to continue beating the wall with your head even with the book.. It is very useful as a reference but doesn't have all the answers.. which brings you right back to good old experimentation.

[johnnynightlife]

It is very useful as a reference but doesn't have all the answers..

bmcaff,
would you be talking about the Rendering With Mental Ray book by Driemeyer? if not which one are you referring too?

[bmcaff]

That's the one..

[johnnynightlife]

ok,:) i just got that book for x-mas, and theres a LOT of sourse code that to me is confusing, and unusable, as i am not proficient with the code. how do utilize what they are trying to explain, and then translate it in maya?

[bmcaff]

Er, it's kinda big into what looks like code but actually if you look closely you will see that the code is usually what you see as an interface in Maya. There is also lots of useful background info on the features and shaders which can help you out.

It's really like any other manual in that it teaches the basics and give simple examples of usage but applying it to your real work takes experimentation and alot of testing.

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