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Changing a white background to transparent (.png)

Mar 29, 2011, 22:35 (This post was last modified: Mar 29, 2011 22:36 by ofnuts.)
Post: #16
RE: Changing a white background to transparent (.png)
Work for me (2.6.8 for Linux). What version are you using?
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Mar 30, 2011, 00:35
Post: #17
RE: Changing a white background to transparent (.png)
(Mar 29, 2011 22:35)ofnuts Wrote:  Work for me (2.6.8 for Linux). What version are you using?
I'm on 2.6.11 (Win XP Pro SP3).

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Jun 22, 2011, 07:46
Post: #18
RE: Changing a white background to transparent (.png)
(Feb 20, 2011 00:24)ofnuts Wrote:  The canonical way is to use Color/Color to alpha and give the background color, but that doesn't work too well with white because it makes a lot of things semi-transparent. To avoid this, you have to protect most of the logo with a selection that excludes it. So:

- use select by color tool, with treshold of 0, no feathering and no antialiasing. Click on the background. This will select only pure white pixels in the background
- grow the selection by 2 pixels. The selection now includes the background, and the border pixels (anti-aliasing)
- use Color/Color to alpha with white (it will only applies to background and logo border)

Done.

whres color/color? having trouble finding it (srrry im a noob)
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Jun 22, 2011, 08:28
Post: #19
RE: Changing a white background to transparent (.png)
This is "Colors"/"Color to alpha", Where "Colors" is in the menu bar of your image window, and "Color to alpha" is somwhere in the last group in the dropdown menu.

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Dec 10, 2011, 17:18
Post: #20
RE: Changing a white background to transparent (.png)
Okay 2 questions Smile
1. How do I grow the selection by 2 pixels?
2. When I do your steps minus the grow the selection by 2 It takes all the white away, except for a little circle down at the bottom.


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Dec 10, 2011, 20:08
Post: #21
RE: Changing a white background to transparent (.png)
1) Via the menu "Select/Grow..."

2) there is indeed a smear at the bottom (this image isn't mine) which is not white and so doesn't get selected. Crop the image to exclude it or paint over it with white or delete it...

But if you don't do the "grow selection", the edges of the logo won't be clean. You'll obtain a whitish outline that will be very visible if you use a dark background.

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Dec 11, 2011, 15:25
Post: #22
RE: Changing a white background to transparent (.png)
Thank you for your reply! I just realized that my number 2 was not an actual question :-p So thank you for answering it for me anyway.

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Dec 29, 2011, 21:26
Post: #23
RE: Changing a white background to transparent (.png)
Some of the stuff in this thread is now better explained there:

http://gimpforums.com/thread-proper-subj...d-painting

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Mar 9, 2012, 23:55 (This post was last modified: Mar 9, 2012 23:56 by Pl3th0r4x.)
Post: #24
RE: Changing a white background to transparent (.png)
@Virago that must be because of RGB setting image/mode/RGB. This happen to me once and then it was selectable.. possibly a similar setting.

*Edit* -o fiddle faddle that was last March.

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