Selection boundaries don't act as boundaries for effects

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2023-01-24 04:36:42

First, I want to emphasize that this problem is entirely due to my own ignorance. The title explains the problem as I perceive it. I spent a goodly amount of time searching this forum, and going through the reference, trying to figure it out for myself, but I'm so ignorant that I don't even know how to phrase what I'm looking for. I attach an image demonstrating the problem.


On the left is an oddly shaped surface with texture. I want to smooth the texture partially but not completely. That is, I do not desire to have exactly the same color value in each and every pixel. Instead, I want to see some smoothing of the roughness of image. The obvious solution is a blur effect, right? So I select the area in blue and apply a Gaussian blur and I get the result to the immediate right of the leftmost image. The problem is that the Gaussian blur imports pixels from outside the selection area -- transparent pixels. If the area outside the selection area is red, then I'll get mixing of the blue and the red in the Gaussian blur -- even though the red is outside of the selected area. It appears to me, then, that the Gaussian blur (and all the others, too) ignores selection boundaries.

This, it seems to me, makes no sense. I should think that all manipulations inside a selection area take place ONLY inside that area and should not in any way use pixels outside the selected area in their calculations. I want to smooth out ONLY the pixels inside the selection area.

This happens with the smudge and soften tools also.

The closest I can come to my goal is the image on the far right. I obtained this by using the smudge tool with a small diameter and carefully smudging outward from the central regions of the image. The trick is to never, ever smudge inward from the edge -- that smudges transparent pixels into the image. If I only smudge outwards from the center, then I get some smoothing and no interference from outside the selection area. Sad to say, this technique is time-consuming and irregular in its results.

Can anybody set me straight?
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2023-01-25 01:26:13

I came up with a kluge that works in this situation, but it's not a general solution. This image demonstrates the kluge:


In step 1, we start with the image that we require to be partially smoothed.
Step 2: create a slightly larger enclosing rectangle and use the bucket tool to fill it with a "representative" color from image #1.
Step 3: Copy image #1 and paste it into the rectangle, retaining its unique shape-selection.
Step 4: with BOTH layers shown in step 3 selected, apply Gaussian blur. The pixels from the surrounding area blend into the odd-shaped region.
Step 5: Copy the odd-shaped region produced in Step 4 into a separate area. It's independent and blurred properly!