Overbright Cards In Reflections
By Neil Blevins
Aug 13th 2007

Go here to read this tutorial in Russian.

Lets say you have a reflective object (like a car). You want to show off it's brilliant material and beautiful contours. One standard trick that photographers have used for years is to place large bright panels above the vehicle to appear in the reflections.

Notice the nice white reflections on the side of the car.

See the original photo here.

Notice the large bright white panel above the car giving those reflections.

See the original photo here.

So lets try the same thing in cg. First lets make a surface that's somewhat reflective, like our car, and then make a self illuminated plane that has a color of pure white (in this circumstance, the plane is referred to as a card).

But wait, something is wrong. The reflection isn't bright enough. Is the material not reflective enough? Probably not. More likely the problem is that your card isn't bright enough. In CG, we generally deal with colors from pure black (0,0,0) to pure white (1,1,1). But in the real world, something like the panel about the car is not pure white, it's several hundred times brighter than white. This principal is frequently referred to as HDR, or High Dynamic Range.

So lets get back to our scene. At any given point, say the maximum reflectivity of the object is 0.25. Our plane has a maximum brightness of pure white, 1.0. So if you do the math, our card brightness value of 1.0 is multiplied by the maximum reflection on your surface, which was 0.25, to get a final color of 0.25, which isn't very bright. To get a brighter reflection, you will need to give your object a color value of larger than 1. These sorts of cards are often referred to as an "overbright card" or "brighter-than-white card card".

Every 3d app has it's own way to make an overbright card, in 3dsmax, you do this using an output map. Place an Output map into the color value of your card material, then set the RGB Level to 10.

Now the color on your card is 10 times the brightness of white. And 10 times a reflectivity of 0.25 equals 2.5 times white in the final image. Sure enough, your reflection is way brighter.

One last thing to consider, if your card looks too harsh in the reflection, you could go about softening it up some. Place a Gradient Ramp inside the Opacity slot of your overbright material to get soft edges.

Here's the gradient applied to the opacity of the material...

And here's the final result...

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