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Specular, reflection, bump mapping: what's the difference?

dswo

Charter Member 2011
I know what the words mean (specular < Latin speculum "mirror"), but how are they different?
 
Well for one of them, I can answer... Bump mapping adjusts the texture, lightening it or darkening it to make areas seem raised or recessed above or below the surface "plane" (as in flat area, not necessarily aircraft...)

I've never really understood the difference between the other two myself, as they both affect the reflectiveness of the material/texture presumably?
 
Spec map controls how much sunlight the aircraft illuminates. Say, a badarse Batman matte black compared to a bright/white texture on a sunny day.

Reflection reflects!!! Sort of like what you get with metallic car paint. But without the possibility of your neighbours' cat scratching it!

Bump map adds a visual bump where the surface is not completely smooth. e.g. windows edges, rivets, coat hangers, door knobs, whatever else that you may find on the fuselage!!!
 
And now in Gmax:

The diffuse color defines the base texture of the model
The specular color defines how much light the the model reflects
The bump map applies a layer that shows bumps and dents without having to model them
The reflection map defines what is reflected (mountains/water, whatever)

You must tweak some other settings here and there in the material editor, in order to get the desired result.

See the SDK for more info.

R.
 
The specular map controls the colour of the highlights, the amount of highlight is set in Max to make it appear glossy or matt.
If you look at the default R22 with the Hawaiian paint scheme you'll notice the highlights are a different colour to the base, whereas normally they'd be a lighter shade of it. If you don't have a particularly complicated paint scheme you can just set the specular properties in Max and not bother with a separate texture file.
 
And of course there are the Fresnel ramps and alpha channels and diffuse maps and of course you need to at least have a smattering of physics left over from school and a touch of the colour wheel...

...and how to merge colours.

The three main maps in FSX are:

a. The diffuse map and alpha channel - i.e. the livery and other painted bits. Alpha defines how shiny the skin is (how strongly the surface reflects the terrain - i.e. the environment map)

b. The specular map and alpha channel - how the ambient light is reflected from the surface of the material. Standard paint, flip-flop, chromalusion, metalic, satin. The alpha here dictates the angular diffusion of the light reflected by the material surface

c. Bumpmaps. Pseudo surface 3d modelling. The various colour channels RGB normally 'feed' the height and depth values to the rendering machine. Biggest trouble here is that the lighting is unidirectional and you can have a model where the self-shadows indicate the sun is high and left and yet the bumps try to tell you the sun is high and right. FSX uses the red channel in place of the alpha, so you have to learn how to separate out colours and how to flood fill channels.

I tried to put all that in a nut shell, but I can't even manage walnut, let alone hazelnut. Even a coconut is too small for all the info.

As usual, Microsoft only put enough info in the SDK to get you going...

Just to make things interesting, FSX lets you have emissive textures (for night lighting illumination) and damage textures too. You don't want to get involved...

But yes - it's all in the teapot.

For starters.

Just don't get me started on mood lighting. I have had to do acceptance checks for an airline's cabin mood lighting - then light gets complicated, because we humans are so subjective.

The best recipe is experiment - because on top of ALL that need to know stuff, you have to hope and pray that the modeller even read the SDK the same way you do. All to often a pretty model is fouled up for painters because the modeller tries to be clever and insist on making the mdl define how lighting works.

Painting planes can be simple - until you start trying to get the right luminance values and al the rest....
 
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