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I want to blur a selected area of my image using Gimp, however the standard filters sample from outside the selected pixels to calculate the new shade.

e.g.

enter image description here

Starting with the image on the left, I want to get the image in the middle, but when I apply an elipse select then gaussian blur, I get the image on the right - it has an inverted halo near the edge.

I know I can create a copy / fill in the background, apply the filter then select / copy and paste the object back into my original layer (that's how I created the middle image) this is rather combersome.

Is there a way to blur using only pixels sampled from the selection?

  • I tested with your images and found that the halo was caused by bleeding from the background. There may be other ways to do it, but I got your centre image by selecting the inner white ellipse using elliptical select before applying the Gaussian blur. Making the background transparent may have a similar effect, but I've not tried this. – AFH Oct 2 '18 at 20:53
  • That really only works for small, simple areas. Making the background transparent has the same effect. The FX-Foundry filters all one to specify how selection boundaries should be sampled in filters (Convolution matrix -> Exxtend/crop/wrap) which is exactly what I want, but I can't get an effective blur radius of more than 4 or 5 pixels :( – symcbean Oct 2 '18 at 21:11
  • Try as I might, I can't get any closer to your desired image. Sorry. – AFH Oct 2 '18 at 21:45
  • Copy you initial image to another layer below the blured one – Tinmarino Nov 20 '19 at 1:55
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A solution (of sorts) is to select the region which is to blurred, copy and paste it, but DO NOT anchor the layer, then apply the blur operation to the floating layer. It trims the convolutoin matrix at the edges of the selection.

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