I second the request. Frequency separation is a very wide used technique, but it works really bad with gaussian blur. Median blur or Dust&sratches filter work so much better. PLEASE add the option of choosing blur method!
Issue solved! This is useful to subtract one layer from the other, for example for Frequency separation.
So this is how I did it for a 8 bits image (16 bits should need a change in the 2 and .5 values bellow)
1 - Create two layers with the same image
2 - Change the layer bellow as you like (gaussian blur, median blur or anything else)
3 - Make the top layer Linear Light (could be done afterwords but if you do it before Applying image, it's easy to see the result as it happens)
4 - Apply image with the following parameters:
Source: layer bellow modified
Blend mode: Normal
Equations: on
DR=(DR-SR)/2+0.5
DG=(DG-SG)/2+0.5
DB=(DB-SB)/2+0.5
DA=DA (no change to the Alpha )
A couple of explanations. In the equations:
DR stands for Destination Red an is the value of the Red in the layer you chose to Apply image (in this case the top Layer)
SR stands for Source Red and is the value of the Red in the source layer (in this case the layer bellow)
The 2 and 0.5 are based on this info: https://helpx.adobe.com/photoshop/using/channel-calculations.html (look for "Add and Subtract blending modes")
When using the frequency separation dialogue, it would be great to be able to chose the type of blur to apply: Gaussian, Median or Bilateral, since each as a different effect on the edges.
Thank you