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Erasing 2 layers simultaneously

Discussion in 'General GIMP help' started by Whirler, Jan 29, 2013.

  1. Whirler

    Whirler Member

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    I did not find a direct answer searching for this, so perhaps someone can clarify. I have two layers, A and B, on which the same image has been brushed into an intricate prior Fuzzy selection obtained from a bitmap image on a 3rd layer. Layer A is pure black. Layer B is 273d2d green. The unpainted areas of these layers are Alpha Layer.

    I am cleaning up some "over-spray" as the selection had been done using the Fuzzy Select tool, and here and there it got overly aggressive and "leaked out" into undesired areas. Easily remedied with careful inspection and the Eraser tool. But I have to erase the unwanted pixels in a spot on layer A, then switch to layer B and do the same spot, because I don't yet know of a better way.

    But I see the little chain icons on these layers in the Layer dialog. And although trying to find how to do what I want in the manuals has not resulted in telling me what I need to know (I probably don't know what terms to search for) I am guessing there is a way to tie multiple layers together and have what the eraser removes on layer A also get removed on layer B. Or, when I am painting the original selection on Layer A, I could possibly also paint the same color simultaneously on Layer B (when required) instead of doing them one at a time during that step of the project.

    So, how does one join two layers to make this happen? I tried clicking the chain icon on both layers, but what I erased on layer A did not get erased on layer B.
     
  2. ofnuts

    ofnuts Member

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    The "link" only applies to "transforms": move/scale/rotate/shear/flip/perpective/cage.

    If you want to perform the same paint/erase on layers, do a selection, apply on first layer, and keep the selection and apply on second. If both layers should have the same transparent pixels, you can:
    - on the "reference" layer: "Layer/Transparency/Alpha to selection"
    - then on the "copy" layer:
    -- "Layer/Mask/Add layer mask" and transfer layer alpha channel
    -- "Layer/Mask/Delete layer mask" (this removes all transparent pixels)
    -- "Layer/Mask/Add layer mask" and initialize to Selection
    -- "Layer/Mask/Apply layer mask"

    The first add/delete is normally necessary because otherwise the new mask is composed with the old one.
     
  3. Whirler

    Whirler Member

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    Rats. So it can't be done. Well, thanks for the reply. The eraser editing has to be done without the selection ants because I am working on dark colors over dark colors, often at the level of a single pixel. I can't tell if it is erased unless I turn off the selection ants, so I can spot a black pixel on dark colors.
     
  4. ofnuts

    ofnuts Member

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    Use Ctrl-T (shortcut for "View/Show selection") to toggle the display of the ants without losing the selection.
     
  5. Whirler

    Whirler Member

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    Thanks! I had not realized this was possible. :) Is there any other indication, besides the marching ants, that I have something selected when I've used this feature? I can see times where I might have something selected and then have to leave my desk, and when I eventually return and try to do something else it won't work because I have an active selection and forgot about it in the interim. Actually I've had this happen WITH the ants visible, if the selection is a small area toward the edge of an image.
     
  6. ofnuts

    ofnuts Member

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    None I could find. And it can be quite treacherous because the ants really define the limit between places where the selection is above 50% and places where it is under 50%. So if all your pixels are partially selected, and all on the same side of the 50% fence you won't get the ants.
     

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