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Transparent background

Discussion in 'General Discussion' started by eager to learn, Feb 1, 2013.

  1. eager to learn

    eager to learn New Member

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    Hi,

    I scanned in my signature signed on a white paper but that white shows up as the background in the scanned signature file.

    How can I set the background in GIMP (XP Pro) so that when I scan something the background is transparent?

    If I've already scanned something in with a white background can I edit that file (e.g. BMP, GIF) later and change the background from white to transparent?

    Thanks so much.
     
  2. ofnuts

    ofnuts Member

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    You can remove the white and replace with transparency:
    - "Layer/Transparency/Add alpha channel"
    - "Colors/Color to Alpha"

    Now, a scan output is usually not completely white, so you can make it a bit more uniform with this technique:
    - Duplicate layer
    - Select bottom copy and "Filters/Blur/Gaussian blur". Use a very large radius (about 1/4th of the width of the scan)
    - Select the top copy and put it in "Grain merge" mode (using the mode selector at top of the Layers list).
    - "Layers/New from visible" (this makes a nbew layer from the result)
    - Using the "Brightness/Contrast" or "Levels tools", make the black blacker (the method above washes it out a bit)
    - Clean remaining spots with a white paint brush
    - Apply Color-to-alpha as above
     
  3. eager to learn

    eager to learn New Member

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    Hi ofnuts,

    I tried your instructions and I'm able to do Layer/Transparency/Add alpha channel but when I go to Colors and look at the drop-down menu the Color to Alpha is all greyed out so if I click on it nothing happens.

    I tried this with a GIF of my signature and then a BMP file of it and got the same results.

    I then tried it on another PC running XP Pro and got the same results.

    I'm using GIMP version 2.8.2 and whatever the latest GIMP version is which I downloaded on the other PC a couple of days ago.

    I tried as regular user and admin but got the same result.

    I'm not sure what's wrong.

    Thanks for your help.
     
  4. ofnuts

    ofnuts Member

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    This i slikely because your scan is a grayscale image (*) (it should say so in the title bar) and not full color. Use "Image/Mode/RGB" to make it full color, then try again.

    (*)A grayscale image for Gimp is an image with only one channel per pixel. A full-color image can also look grayscale if all channels have equal values, but it's not grayscale for Gimp.
     

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