avgLum = average scene luminance;
static const float MIDDLE_GREY = 0.72f;  /// WHY IS THIS 0.72????????  I HATE MAJIK NUMBERS :)
newCol = (MIDDLE_GREY / avgLum) * pxColor;
static const float L_WHITE = 1.5f; // I assume this is just our max value before it's pure white
newCol = newCol * (1.0f + newCol / L_WHITE) / (1.0f + newCol);