+/**
+ * Compute Rec.709 gama correction of value val
+ */
+static double compute_gammaval709(void *opaque, double gamma)
+{
+ LutContext *s = opaque;
+ double val = s->var_values[VAR_CLIPVAL];
+ double minval = s->var_values[VAR_MINVAL];
+ double maxval = s->var_values[VAR_MAXVAL];
+ double level = (val - minval) / (maxval - minval);
+ level = level < 0.018 ? 4.5 * level
+ : 1.099 * pow(level, 1.0 / gamma) - 0.099;
+ return level * (maxval - minval) + minval;
+}
+