Basic Colour Nodes Discussion

An Exploration of Poser Nodes: Colour,

Maths, and how this stuff all inter-

connects

This is an exploration. I'm not an expert or even understand much about this. I just desperately want to understand. The purpose of this is to put my ignorance out there for all to see so that perhaps some extremely motivated or irritated knowledgeable person will set me right or point me in the right direction. Hasn't happened yet. Anyway, that is the spirit of this undertaking: it is not an authorative work but a bit of a publishing the results of my little material room lab. That's it.

When I undertook to do this, I wanted to have a look at math_function nodes and how they affected other nodes. I felt I knew spots nodes - how they behaved and all that - and so the first thing I did was hook up a spots node (output) to a math_functions Add node (input) Then I hooked the output from the math node to the diffuse_color channel input on the main PoserSurface node.

I changed the values in that math_function Add nodes input_2, expecting to see something happen to the preview picture on the PoserSurface. So, what happened? Nothing. Nothing at all. Thought I'd go ahead and render, just to be sure. The render showed nil change from before.
Well, I puzzled over this and mulled it over.

As far as I can tell, there's no organized official documentation on how Poser nodes work with one another. I'm finding out that if I plug in a math_function node between a spots node and the diffuse_color channel of PoserSurface, it's not going to do diddly... why? Because it's plugged in wrong! Well, how am I to know? I thought the math_functions Add node was a sort of filter, and that one could plug it between the spots node and the diffuse_color channel of the PoserSurface node. Oh, I'm sure that Those-That-Know think me ridiculous, but I'm a Dummie. I can learn, but this stuff has to be documented somewhere or figured out somehow.

So, now what? I'm faced with the inevitable: to sort out the BASIC BEHAVIOUR OF NODES via experimentation. A bit like putting stuff in a pot and tasting it afterwards to see if it goes together. And how much. And when. Gee, be nice if there were a recipe book!

Before we start plugging things together and doing renders, let's consider this titbit gleaned from one of the first threads (that I have access to - I suspect there are older ones) by BagginsBill, answering a question by another bright light in that arena, Cobalt Queen. She was doing essentially what I'm doing - experimenting with nodes - except her approach was considerably more organised and knowledgeable. Bill said:
A word of caution however, I wonder how you plugged these (...nodes...) in? Do you know that plugging into the Diffuse_Color means that it is going through a Diffuse node as well? And that plugging into Alternate_Diffuse does not pass through another node? When you got the blowout on the Alternate_Diffuse, I suspect you had the regular built-in Diffuse_Color/Value still turned on?

The general idea is if you want standard Diffuse and Specular nodes - you don't need to add any nodes at all. Those two are built into the Poser Surface.

But if you want to use alternative approaches to either diffuse or specular, e.g. Clay for diffuse or Blinn for specular, you should turn the corresponding built-in component off completely. Then plug your node into Alternate_Diffuse or Alternate_Specular. Those two inputs assume whatever is plugged in has already done its processing and no post-processing should take place.

Are you reading what I'm reading, here?

Well, there's a lot to read in that thread, actually. Most of the stuff they discuss is completely over my head, but here was this valuable titbit. What I'm seeing here is this:
--If all you are going to use is Diffuse_Color and /or Specular (and no other nodes), use the ones that came on PoserSurface.
--If you are going to use other nodes, turn off the PoserSurface nodes off... assumption being: they will interfere with what you're doing?

So, where do we go from here? I'm going to start with basics. Instead of jumping in adding elaborate textures to surfaces and kinda starting somewhere in the middle, let's start with colour. We have a surface - that sphere from the Spots Node discussion - onto which upper hemisphere we're going to give a colour. That is about as basic as it can get, right?

The Poser 7 Reference Manual defines the diffuse_color attribute as follows:
The Diffuse_Color attribute is the surface color that is multiplied through any light striking the object.

What could possibly be meant by that? Let's break it down:
... surface color
... multiplied
... light

So, diffuse_color is color of a surface that is mathematically affected by light: the closer or brighter the light, the brighter the color. As far as I can read: that's it.
That's not giving us a lot of properties, is it? You would think that's all there is to it... but wait, there's more. We're going to find out how much more with a little experimentation. Let's start with something simple. On our main PoserSurface node, we're going to turn everything off - set all channel values to 0 (zero) - except for the Diffuse_Color channel.

Lights are going to be the ones we had set up in the Skin Nodes discussion. Render settings are the very basic Firefly ones: Auto settings, draft, everything un-ticked except Smooth Polygons.

Let's test it, shall we? What we get is on the right: a white hemisphere. I saved the render as a png file, brought it up in The Gimp, set my background colour to 147,120,120 (to provide a bit of contrast to the object itself) and flattened the image to save it as a jpg.

All channels off, diffuse_color white, diffuse_value 1

Well, that's what it looks like, doesn't it? Something doesn't smell right about this - something to do with the ambient_color channel being turned off. Can't just leave that, can we now?

The Poser 7 Reference Manual indicates:
The Ambient_Color attribute defines the accumulated, indirect light within a scene. This is usually light bounced off other objects or otherwise diffused by elements such as the atmosphere.

What the heck does that mean? It's not talking about the colour of the object's surface at all. Let's break that down:
... light (accumulated indirect bounced-off-objects diffused-by-atmosphere)

Diffuse_Value 0, Ambient_Value 1, same lights

Well, what does that mean in real life? We'll turn OFF the Diffuse_Color channel and turn ON the Ambient_Color and render. Just doing this in the material room gives us what looks like a glowing ball, and the render shows a much brighter upper hemisphere as well.

A hemisphere without shadows - unlike our first render, which shows a bit of colour gradient as we look towards the edge of the sphere. Since the manual says it's a ambient light thing, let's change the light colour and see what happens. We'll go to the Infinite light, which has the following settings:
Red, Green and Blue: 1.000
Intensity: 65%

Light appears to be always a composite of these three colour components. We'll change the Green and Blue to 0, leaving the colour red as the only light colour. We will have to turn off IBL so the only light we have is from the Infinite.

And render.

Huh?

Diffuse_Value 0, Ambient_Value 1, IBL off, Inf 1.0,0,0 (pure red)

Either that definition in the manual is wrong, or we're missing something. I'll vote for the latter. Obviously, whilst perhaps the ambient_color channel has something to do with the colour of the lights, changing the colour of those lights does not affect the surface colours of objects.

Let's try this... let's reset the colour of the Infinite light to white and change the ambient_color to 255,0,0 (red).

What are we to infer from the resultant glowing red upper hemisphere? That regardless of whatever lights and whatever colours exist, the diffuse_color channel dictates the colour of the surface?

Diffuse_Value 0, Ambient_Value 1, Ambient_Color 255,0,0 (Red)
IBL off, Inf Light 1,1,1

How do we sort this out, then? At this point, it really doesn't look like light affects the colour of a surface as much as the Ambient_Color channel does. Will the light intensity affect it? How about changing some values? Let's drop the Infinite light value from 65% to 20%... I want to see a difference, a really noticeable one.

And render.

Yes, there's a difference: in the lower hemisphere, the one where the Diffuse_Color channel is active and working. Nothing has changed in the upper hemisphere at all. That Ambient_Color channel and its associated Ambient_Value channel completely overrides whatever lights exist in the scene completely.

That's my story and I'm sticking to it, so far.

Diffuse_Value 0, Ambient_Value 1, IBL off
Inf 1,1,1 - Intensity 20% (down from 65%)