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How to outline a blurred gradient section?

Fabien G Posted messages 139 Registration date   Status Member Last intervention   -  
breadart Posted messages 1 Status Member -

Hello,

I use a Mac,

in the absence of Photoshop, I am starting to use Gimp.

I have two basic questions...:

1) When I open a photo, I can select an area and apply a filter (e.g., blur).

I have a sharp part / a blurry part.

But I can't find out how to make the transition from the sharp part to the blurry part in a slight gradient.

Can you tell me the method?

2) When I use the selection tool (lasso), I can create a shape, move it (by holding down the option key), but when I release the button, the shape 'disappears'.

If I select the outline of a blue object and want to move it to a red area to select with the same shape, it doesn't work.

The selection area seems to still be present in the layers panel, to the left of the image (round shape on a black background), but even when I select this layer, if I do copy/paste, it doesn't copy the area I created, but the entire image.

So how can I move my selection shape and be able to copy my background?

Thank you in advance.

Best regards

4 answers

  1.
    Bruno83200_6929 Posted messages 724 Registration date   Status Member Last intervention   170
     

    Hello,

    Having a smooth transition between sharp and blurry (selection feathering)

    By default, a selection has hard edges (either everything or nothing). To achieve a gradual transition (like in photography with depth of field), you need to soften the edges of your selection:

    Make your selection (rectangle, ellipse, lasso, etc.).

    Go to the Select menu → Feather… (Feather in English).

    Choose a radius (for example 20 or 50 pixels, depending on the size of your image).

    Then apply your filter (e.g., Filters → Gaussian Blur).

    Result: the edges of your selection become gradual and the blurry area smoothly blends into the sharp area.

    Even more flexible variant: instead of applying the blur directly, add a layer mask to your image and paint on it with a black/white gradient. This allows you to adjust the mix between sharp/blurry without starting over.

    Moving / reusing a selection made with the lasso

    What happens in your case:

    You create a selection with the lasso → GIMP keeps the selection active.

    When you hold down Option (Alt) and drag, you move the content of the selected image, not the selection itself (and that can be confusing).

    When you release, the selection stays in place, but if you copy/paste, it’s normal that it’s the whole image (because you might be on the wrong layer or the selection is empty in that area).

    The solutions:

    Move only the selection (and not its content)

    Active selection tool → go to the tool options bar (at the bottom).

    Uncheck Move Layer and check Move Selection.

    Now you can move the selection shape wherever you want, it won't disappear.

    Reusing a selection later

    Once your shape is created, go to Select → Save to Selection.

    It will be stored in the Windows menu → Dockable Windows → Channels.

    You can reload it at any time (right-click → Channel to Selection).

    Copy only the selected area

    Make sure you are on the correct layer (in your layers list).

    Then go to Edit → Copy → it only takes the content inside the selection.

    If it takes the whole image, it’s because your selection is either empty or applied to a layer without pixels in the area.

    So, for your example:

    You make your lasso around the blue object.

    You check move selection.

    You move this selection over the red area.

    You do Edit → Copy then Paste → you will only have the area defined by your selection.

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  2. Fabien G Posted messages 139 Registration date   Status Member Last intervention   4
     

    Hello,

    Thank you very much for your super detailed response!

    The step-by-step guide is really perfect for those who don't know much about computers.

    I really appreciate the time you took and the kind tone, it's great.

    I will test this out and I'll get back to you to confirm that everything is working, and I’m confident about it!

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  3. Miguel_Pineau Posted messages 4 Registration date   Status Member Last intervention  
     

    Hello,
    I suggest the video "How to blur the background of a portrait of a dog with GIMP" https://youtu.be/sv657EBTtys

    or method 3: circular fade with the radial gradient in GIMP https://youtu.be/n3-zSp_oVxg+

    For the second question:
    point of caution about selection and deselection in GIMP
    https://youtu.be/GZbs494OquQ

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  4. breadart Posted messages 1 Status Member
     

    Thanks for these links, super useful!
    The background blur with the circular fade seems really handy to keep the focus on the subject. And thanks also for the tip on selection/deselection, it saves a lot of hassle.

    https://snake-game.io

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