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brenly
03-03-2008, 09:47 AM
Ive noticed when you create a new material that the default value of the diffuse amount is set at 80. I was just wondering if most people leave it at 80 most of the time to get best results. I want to start this thread in a hope to improve my knowledge of Diffuse color. I know that reducing the diffuse amount will darken the texture until you get just black. Would increasing it to 100 allow the texture to reveal its true color? Or will it become slightly over brighten? I know that lighting will affect the final rendered color. I guess what Im trying to get at is why did Modo chose 80?

3dj
03-03-2008, 01:31 PM
Not sure why either, but C4D does the same thing in the color channel. It is seperate from the diffusion channel, but when rendering multi-pass, the color is rendered in the diffuse layer. Anyway, that is another issue I don't completely understand but it is all good. Still, wonder why 80 percent? Is it a physical type of default setting?
-Jim

spaz8
03-04-2008, 05:55 AM
Very few things in the world would have a setting of 100% diffuse, if anything. Light is absorbed, energy is lost. 80 is a good starting point.. skin is around 70%, high 60's.

brenly
03-04-2008, 09:48 AM
thanks spaz8.
just to air my ignorance ..
whats the difference between reducing the value of a color and reducing the diffuse value? Im guessing objects with a low diffuse level reveal thier true color under stronger lights where high diffuse objects do the opposite.

spaz8
03-04-2008, 01:50 PM
Well lower value (darker) is just that, the colour.. select colour value based on what the object looks like in bright conditions, natural environment you would find. Let lighting dictate how dark or bright it renders.. the diffuse parameter is more like a discription of what the object is made out off... metal for example is often a diffuse of 20-40 with a higher spec.. perhaps 60.. a piece of fruit might be close to 80 in the 70s. Is the object dense or soft? does light penetrate it or is it all reflected.. is the surface pores or smooth..

chewedon
03-07-2008, 02:39 PM
Um. . .this is just a guess, but here goes nothing.

When light strikes an object, it gets reflected (bounce back/off) from that object. The reflected light doesn't always reflect at the same angle it got incidented at due to rough surfaces containing bumps, thus scattering and bouncing the light back at different angles. Also some of the light that strikes the object gets absorbed by that object so the light isn't as intense as it originally was.

Diffuse is basically how much that light gets scattered when it bounces off the object that's being lit. The higher the diffuse value, the more the light is scattered, the lower the diffuse value, the less the light is scattered.

The colour of the object is the reflected light we see from the object.

So basically the idea is diffuse = how scattered the light is while colour is what we see being reflected from that object.

Does that sound reasonable ? :)

Edit: sorry, I got the meanings the wrong way around in this post, it is fixed now.

brenly
03-07-2008, 11:30 PM
Thanks Spaz8 and Chewedon for you input I think Im beginning to see the light *how funny am I* .. Ive been thinking about this difficult concept for awhile, what is diffuse. Or how does it work. This is where Im at so far.
lets see if Im getting it right... so diffuse controls the scattering of light from an object. so the higher the value the more direct the light is bounced from the objects surface = less diffusion of light from the surface? the lower the value the more diffusion of light, if the value is low enough the object wont bounce any light back hence the object becomes black.
Could you say that diffusion is like light absorbtion?
sorry if Im repeating whats already been stated ..

chewedon
03-08-2008, 03:37 AM
It's confusing you because the software uses diffuse which I think isn't appropriate.

When I think of diffuse I think of how much the light gets scattered and absorbed by objects.

So a higher diffuse value SHOULD make the light less brighter since the light is already scattered instead of being concentrated when being reflected back to our eyes.

BUT

instead, some softwares like to call it diffuse and make it so that when you drag the diffuse slider higher the thing gets brighter, maybe they had a mental block, I don't know why but this do the OPPOSITE to what diffuse is suppose to mean.

One of the book says this:

"Diffuse Sometimes called falloff, this attribute controls the amount of light reflected back from the surface. At a value of 1, the surface will reflect back 100 percent of the color specified in the color channel. The default value is 0.8"

Notice how they're describing what's happening but using an inappropriate word ?

"diffuse ... controls the amount of light reflected back from the surface"

It should really be:

"reflection ... controls the amount of light reflected back from the surface".

If something is diffuse (diffuse value greater than 0), it means the light that gets reflected back is not as concentrated as it was before it got scattered. Since the light has been scattered, it isn't as intense, thus the object we see isn't as bright.

If there is NO diffuse, (diffuse = 0), the light has NO scattering, hence 100% of the light gets reflected back, having the same intensity it had before being reflected from the surface and so we see the object as bright.

Here are two diagrams:

http://img.photobucket.com/albums/v639/Ryu_Kaiser/some_diffuse.jpg

http://img.photobucket.com/albums/v639/Ryu_Kaiser/no_diffuse.jpg



If you use Blender, it uses the term "reflection" instead of "diffusion" to eliminate this confusion:


http://img.photobucket.com/albums/v639/Ryu_Kaiser/reflection_in_blender.jpg

Notice the sphere on the right with a reflection value of 1.0 i.e. light gets reflected from that object with no scattering whereas the sphere on the left, the reflection value is 0.5 meaning 50% of the light gets reflected, causing it to appear more darker than the sphere on the right.

I think some softwares just find it weird to call the property reflection instead of diffusion because it might cause another confusion with mirror reflection (even though they call that reflectivity) :D

Hope you can understand that.

brenly
03-08-2008, 08:01 AM
chewedon .. Nice one!!!
Youve really cleared up the confusion for me. I always thought the diffuse value sounded a little strange. Awesome! I started this thread in a hope that someone like yourself could clear up the confusion for me .. THANKS!

new2LW
03-13-2008, 10:20 AM
typically, as the diffuse goes down, the reflection goes up. In fact, if check conserve energy, this is forced upon the material in the backround... the diffuse is set inverse of the reflection even if you don't see a change in the numbers.

here is a direct link to modo help conserve energy if you have 301 and the documentation installed. If you have 201 or another version it's probably still there, just a dfferent directory.

C:\Program Files\Luxology\modo 301\Documentation\help\pages\Conserve_Energy.html

This talks about physically based rendering and how spec and reflection should match and be approximatly inverse to diffuse. There's even an animated picture :scream: for an example!!

[edit] a small chunk from the documentation. lol originally posted by..sorry, easily amused.

Anyway, one of the dictionary definitions of diffuse is scatter (...away from the object/surface) So, it would seem to me diffuse is a pretty good definition of the effect. Less diffuse, less light scattered (or opposite, more absorbed) ?

It's funny the way you word that sentence, scattered and absorbed like they are one and the same. Like saying "when I think of transparency I think of clear and opaque." The two end descriptions of transparency are opposite eachother. So, more clear is higher percentage and closer to the actuall definition, opaque less clear and lower percentage and further away from the actuall definition. As with diffuse, 100 percent more light scatter, 10 percent more light absorb. Follow?

Also, it seems more to me that your diagrams would be better describing different material attributes than the difference between reflection/diffuse. In Modo, I'd say this would be the surface roughness and reflection bluring. Just because a surface is perfectly smooth doesn't mean it's perfectly reflected. Stained glass and a mirror glass being an example both can be really smooth and yet have different reflection diffusion values. I think I'm starting to confuse myself.



The basic idea behind energy conservation as it relates to shading is that a given photon hitting an opaque surface can either be absorbed, or it can be scattered in a random direction (diffuse), or it can bounce off in a direction near the mirror angle (specular and reflection). A realistic energy conserving surface can never reflect more photons than are hitting it, but unfortunately that's what the non-physical shaders in most CG programs do. For example it is common for an artist to set a Diffuse value of 80% or more combined with a Specular or Mirror Reflection of 30% or more. The combination of these channels results in more than 100% of the energy being reflected in some way. To make the problem even worse, parametric materials such as Fresnel or other gradients can drive these numbers up behind the users back. All of these things cause a result which is not physically accurate. Conserve Energy helps to correct for this.


P.S. Not trying to come down on you Chewedon. Just saying.. Blenders way of Reflection and Mirror Reflection works just as well.

brenly
03-19-2008, 06:45 AM
New2LW thanks that gives me a better understanding of how Modo uses diffusion although I had a look at Dictionary.com which gave this meaning for diffusion...

Diffusion = The reflection or refraction of radiation such as light or sound by an irregular surface, tending to scatter it in many directions.

This seems to back up Chewdons summary of diffusion.

New2LW I find these 2 sentences confusing, they seem to contradict each other??
'typically, as the diffuse goes down, the reflection goes up'
'Less diffuse, less light scattered (or opposite, more absorbed) ? '

I dont understand how less diffusion will increase absorbtion and increase reflection at the same time.

chewedon
03-19-2008, 07:19 AM
No worries New2LW.

My diagram of the perfectly smooth surface is mean to show that light reflected from a smooth surface or perfectly smooth surface will not cause any scattering of light.

I don't mean to say the light that gets reflected back is 100% of the light that gets incidented onto the surface. (even though my diagram says so ^.^!)

Yes, there would be definitely be some absorbtion or transmission of light (light passes through the medium such as a transparent glass).

My point of the diagram was to show how different surfaces causes different amount of scattering of light.



------------

Brenly,

Reflection and Diffusion is like a pulley system.

When one side goes down, the other side goes up and vice versa.

Don't worry about it really. As long as you can get your art work to look good.

I, myself, prefer creativity over realism. As long as it looks good, it is fine. It doesn't have to match reality. Take Final Fantasy VII Advent Children as an example. Normal humans can't jump that high, stay in the air for that long or swing a big massive sword around like a toy.

If they made it realistic physics, where's the fun or enjoyment in that ?

I might as well watch gymnastics or something like that if I want realism :)

CaptainObvious
03-19-2008, 05:24 PM
In modo, diffuse reflectance (http://en.wikipedia.org/wiki/Diffuse_reflection) and specular reflectance (http://en.wikipedia.org/wiki/Specular_reflection) are dealt with separately.

Diffuse reflectance is light that bounces off in all directions, in a completely diffuse manner. In modo, the diffuse reflectance is split up into diffuse VALUE and diffuse COLOR. They're virtually interchangeable, though: a diffuse value of 50 % and a color of white is the same as a color of 50 % gray and a value of 100 %.

Specular highlights, reflections, transparency, etc, are all unaffected by the values you put into the diffuse color and value. A surface with 0 % diffuse value or black diffuse color will be black, as far as diffuse reflectance is concerned. It will not be shiny just because you put in 0 % diffuse -- in order to make it shiny, you have to make it specular / reflective.

new2LW
03-20-2008, 11:12 AM
they seem to contradict each other??
'typically, as the diffuse goes down, the reflection goes up'
'Less diffuse, less light scattered (or opposite, more absorbed) ? '

I dont understand how less diffusion will increase absorbtion and increase reflection at the same time.

It won't. As captain said, in modo you have to adjust the values separately. I added more absorbed kind of thinking outloud. Kind of thinking that less diffuse shows less color because more energy is being absorbed...with global illumination you will get less color spill with less diffusion, too. Also, the first line you quoted is more real world physics. Conserve energy in modo will auto compinsate the diffuse as you change the reflection/specular.

Diffusion = The reflection or refraction of radiation such as light or sound by an irregular surface, tending to scatter it in many directions.

This seems to back up Chewdons summary of diffusion.

That's what I said it meant..?

while we're at it lets bring in caustics (http://en.wikipedia.org/wiki/Caustic_%28optics%29), kidding, Just tossing the link (http://en.wikipedia.org/wiki/Caustic_%28optics%29) in for a read. Modo doesn't have an option for this yet.

Chewdon and Captain Obvious both have good replies.

If you want white white and not gray then you probably want to bump up the diffuse. And to one of the origial questions, I would say that to get a good representation of the color as you picked it out, higher diffuse looks like a closer match.

Chewdon puts it nicely, "as long as it looks good"

brenly
03-21-2008, 01:02 AM
Don't worry about it really. As long as you can get your art work to look good.

I, myself, prefer creativity over realism. As long as it looks good, it is fine. It doesn't have to match reality. Take Final Fantasy VII Advent Children as an example. Normal humans can't jump that high, stay in the air for that long or swing a big massive sword around like a toy.

One needs to know the rules before you can break them. That was one cool movie, Ill have to pull it out one of these days to watch it again for the 20th time!

Thanks guys for your input is much appreciated!!, I have a much better idea of how modo uses diffuse, even better is now I understand conserve energy. Ill be using that setting from now on.

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