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I selected an area in the picture right next to a white wall, and then applied a Gaussian blur to the selection. Problem is some of the white from the wall spilled into the selected area as a result of the Gaussian blur, even though no part of the white wall was in the selection. Now how do I remove this white cast from the area next to the white wall ?

Alternatively, how do I apply a blur to a selection and prevent pixels from outside the selection to come in and contaminate the selected area ?

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This is the original image:

enter image description here

Screenshot of the contaminated result of the blurring

enter image description here

Screenshot of the available result if countermeasures are applied:

enter image description here

The procedure:

Cut and paste the area that you like to be blurred into 2 new layers. Use Paste special > Paste in place to avoid shift. You should save the selection because it vanishes too soon. Save also a spare of the cutted and pasted area into a third, hidden layer. You, at least in the beginning, will miss it.

You must load the selection back before blurring. If you do not, the blur spreads. Probably you want the blur to spread somewhere. There you should expand the selection before blurring. Draw the expasion area by polygonal lasso or other selection tool and press Shift simultaneously.

Blur the upper of the new layers Erase another new layer partially by eraser; you probably like to save something near the selection border, because there is anyway some transparency contamination (as you say) from outside. Quite surely you must reduce the opacity of the lower new layer or use the eraser with smooth brush and reduced opacity (say 25%) to retain continuous look near the border.

If you want only to get rid of contamination and don't care discontinuity, then leave the partially deleted layer off. The contamination will be replaced by the background.

  • AWESOME ! Thank you very much. And for this picture where the white contamination has already occurred, any idea how to get rid of this white haze ? Otherwise I have to start over from scratch on that picture. – user83522 Jan 6 '17 at 12:01
  • you can reduce its brightness and increase the contrast, if needed. You must do this by adding an adjustment layer and limit the affected area by layer mask; there mostly black, more white mask , ehere more effect is needed. Decreasing the brightness reduces white cast, but contrast suffers and should be compensated. – user287001 Jan 6 '17 at 12:40

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