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separating an image from it's background

Jun 15, 2011, 19:50
Post: #1
separating an image from it's background
Tried using this tutorial: http://docs.gimp.org/2.6/en/gimp-tutoria...arate.html

trying to separate non-contiguous letters from a backround so as to make the background transparent. I've used various methods including the gimp tutorial referenced above, and am having problems both selecting everything I need and with the transparency.

When I use the foreground select tool as in the tutorial, I can select the first line, 1812, but not the next two. Color values off some??? Anyway, after successfully selecting at least the 1812 part, I do the next steps: invert the selection, add alpha channel, del background; and end up with a transparent background and a 'kind of' transparent 1812. If I try to save it as a png and open it in any other program it's just empty or black.

Way a newbie here. Hope someone can help. I've spent stupid amounts of time on this.    
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Jun 15, 2011, 21:03
Post: #2
RE: separating an image from it's background
See this thread (which is flagged as "important thread" in this same section):
http://gimpforums.com/thread-changing-a-...parent-png

However, since you start from a photograph, things are a bit less simple and you need to pre-process your picture:

1) crop to the really useful part
2) convert to monochrome: use Colors/Components/Channel mixer. You want to remove as much as the background texture without removing the characters detail. Removing the blue seems to be the most effective
3) adjust lightness and contrast for maximum contrast but still keeping smooth edges on the letters (and the finer parts of some of the smaller letters). With too much contrast you will get blocky edges and missing small bits.

Once you have a decent monochrome pic, use the method expounded in the reference thread:
- wand-select the BG
- grow selection by a couple of pixels
- color-to-alpha

If you want to recover all characters, you can do it in several passes on several copied of the layer:
- one for the bigger ones (grow selection by two pixels)
- one for the middle-size ones (grow selection by one pixel)
- one for the small ones (do not grow selection)

Then erase the irrelevant parts in each and merge them.

Now answering your questions on
https://Gimp-Forum.net
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Jun 16, 2011, 03:02
Post: #3
RE: separating an image from it's background
Wow. I'm such a newbie that I didn't know where most of the commands you referred to are, but I think I might have actually done it, except that I couldn't recolorize the letters to the original dark blue. That was an amazing tutorial, and never once did I use the fg/bg tool which I have been fighting with for two days. I'll check it out in another program and see if it works. THANKS
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Jun 16, 2011, 06:45
Post: #4
RE: separating an image from it's background
(Jun 16, 2011 03:02)rbyrone Wrote:  except that I couldn't recolorize the letters to the original dark blue.
To restore the color once you have the letters on transparent background:
- use the color picker to set the foreground color from the characters in the original image
- lock the "alpha channel" of the layer ("lock" check box next to checkerboard square at top of the layers list in the layers dialog)
- bucket-fill the layer.

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