int im_gammacorrect(in, out, exponent)
IMAGE *in, *out;
double exponent;
DESCRIPTION
im_gammacorrect performs gamma correction to in. The result in written in out.
The correction is carried out by creating a lookup table using the double
exponent and mapping in through it. The exponent is applied on a ramp lut and
the resultant lut is scaled. All channels of im are mapped through the lookup
table.