Just to clarify, here's something I wrote for the manual (might have to simplify it, not everyone knows calculus
)
To be honest, "A,B,C" should not be used in the exporters, I think we will try and remove that lingo and go just with Quadratic, Scale, and Offset.
A,B,C Values
The A, B, C values are modifiers for the texture map. This is the equation used (for those that have studied calculus this equation will be familiar):
x = ax^2 + bx + c
The A, B, C, values are taken from here. Thus:
A value – Quadratic
You will not often need to use this, usually it easier to get expected results by modifying the texture map with an image editing program.
Scales values by a quadratic, so low values stay low, and larger values become massive!
B value - scale/multiplier
Scales the texture map values. Can be associated with contrast. Maps the value range of 0-255 to 0-1 (for a usual LDR texture), which is then multiplied by this number. For example: a B value of 2 makes a pure red RGB 255,0,0 to 510,0,0.
C value - Offset
Total RGB offset, generally making the texture brighter or darker.
Exponent: Used for converting texture RGB values to display values (gamma). A typical value is thus 2.2. Here is how it fits into the equation:
f(x) = a*g(x)^2 + b*g(x) + c
and
g(x) = exponent
