Of Specs, Bumps and Other Practical Things

On the principle that a day without learning something new is a day wasted, I guess I am now entitled to "Prof. Emeritus", because I have been learning like Billy-O. FSX has done some interesting new things for us painters, and not all of them nice. A texture set for an aircraft now has up to four sheets. OK, the emissive map we don't need to touch (those are the "night textures"), but now we have specular lighting and bump mapping to play with.

"Ah well," the pundits might say, "you don't need to create a new bump map or specular when you repaint a model." and this is generally true - if the people who made the plane also made a sensible bump and spec set.

So what, in simple terms, is a "Spec" and a "Bump"

Let's start with "specular" and say a prayer of thanks to Wikipedia, because the answer is pretty easy:

Specular reflection is the perfect, mirror-like reflection of light (or sometimes other kinds of wave from a surface, in which light from a single incoming direction is reflected into a single outgoing direction. Such behaviour is described by the law of reflection, which states that the direction of outgoing reflected light and the direction of incoming light make the same angle with respect to the surface normal; this is commonly stated as θ_i = θ_r.

So... is that all clear now? No? I thought not. Nor for me. Oh the quote makes sense enough, but what does the specular image do in FSX? Why do Microsoft's default aircraft have such funny hued images as their "Specs"?

Let me see now, metal reflects differently to plastic or glass or a silvered mirror... OK... and a red surface reflects differently to a green surface... Riiigggghhhht... (google gooogle goooogle...) I found one interesting reference somewhere, where the author wrote something like "I have found the best specular for me is a 180 shift..."

...and it was that "180 shift" that finally got me going in the right direction. Whoever it was, he (or she) was talking about degrees, and 180 means opposite - as in the opposite side of the colour wheel, as in colour wheel in your paint program. For those fashion conscious among you - think "complimentary colours". Look in your graphics program and you'll probably see a section where you can edit the colours, and one of the options there will show a circle with options to pick out different kinds of complimentary or opposite colours.

Anyway - I don't want to make this too long. Just suffice to say that the specular component of a texture set defines how the model shines. A polished paint surface will reflect white light as white light, so your specular needs to be "180 shifted". A slightly matt (satin finish, for instance) surface will add its base colour to the reflected light. So here you'd need to tone your spec image differently.

So for shiny airplanes, all you need to do is to flatten your image and then shift the colours by 180 degrees.

That, in essence, is what it's all about - finding the right section of the colour circle and shifting your specular image to suit. There is more - brightness for one thing. A spec image also carries an alpha component, which is not like the alpha we know from FS9. No, in FS9 the dark part of the alpha means more reflectivity. It's the other way round in FSX for the specular. A darker alpha for the spec map will make the reflection less harsh and a lighter one... well, let's put it this way - if you have too harsh an alpha for your specular, you'll end up seeing all the polygons on your model.

Lord, so many words already and I still haven't gotten anywhere. My suggestion is to read the SDK and try to remember. Here's what I have written on a note pad on my desk:

Specular - a two part image (base plus alpha). Shift the base colour by 180 for reflected light. Make the alpha channel grey scale. Experiment with different values of light and dark until you find some you are happy with. My values - 180 clour shift, 35 - 50% lighter for the colour image, save copy as-is but grey scale and use as alpha

Bump map - "flatten" a copy of the texture sheet (remove things like text, logos, emblems and other parts of the skin that don't usually have depth). Go to your "effects" section and choose the "Emboss" effect. Not too high. Select target colour to "greyscale" - that way the height map separates out into thre channels - RGB. MS have declared that the red channel is used for the alpha, so click off the blue and green channels and make the red into an alpha channel (grey). Back to the RGB channels and flood fill RED with black colour. Then flood fill the BLUE with white. Switch on all channels again and you are left with a blue toned image, just like the microsoft bump maps.