Parameters of "Apply Image" : blending operation/scale/offest are never explained in tutorials on Frequency Separation
I understand that for image 8bits (luminance R/V/B coded from 0 to 255), to get high frequencies (structure) we substract low pass image from original, then the result values are from -255 to + 255, so we use a scale of 2 to reduce values to -128 to +127 and then an offset of 128 to get a final 8bits value from 0 to 255.
For 16bits images (luminance R/V/B coded from 0 to 65535) all tutos use without explanation : Addition with inversion of low pass layer, scale 2 , offset 0. I don't understand how it works ?
Furthermore using substract without inversion seems to give the same result (seems to me normal since addition of the inverse is equivalent to a substract), so what is the reason of this choice ?