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How to Make a Transparent Background

Oct 18, 2011, 22:24
Post: #1
How to Make a Transparent Background
hi, i want to be able to use the fussy select tool to remove the Background of a picture so i can paste it over another picture, but whenever i delete the background it doesent become transparent, only into the colour ive recently used, How can i Fix this?
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Oct 18, 2011, 23:35
Post: #2
RE: How to Make a Transparent Background
You have to make sure your layer can be transparent: "Layer/Transparency/Ad alpha channel".

This said, the technique you expound never works very well.

If you have a uniform background (logo/letters), the right technique (with "color to alpha") is explained there: http://gimpforums.com/thread-changing-a-...parent-png

To give you an idea: original/magic wand/color to alpha (the last two over a gray background to demonstrate the problem):
[attachment=701]

If the background is more mixed (photo) things are definitely more difficult, and will depend a lot on the actual picture at hand.

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Oct 25, 2011, 07:54 (This post was last modified: Oct 25, 2011 08:02 by TX_Greenhorn.)
Post: #3
RE: How to Make a Transparent Background
I think I'm having the same problem Extradaemon is having, where "clear" on a selection made by the "color select" tool (on a single-layer image, mind) fills the selection (in my case, with white) instead of making it transparent like it should. I'd been using this method for weeks with no problems up until, inexplicably, tonight. I reinstalled, thinking I may have accidentally ticked a setting here or there, but to no avail.

And while more complicated methods may produce better results, I really, really liked doing it my simple way. Any help making that possible would be greatly appreciated.

edited to add -- it may help Extradaemon to know that right clicking the selection, then choosing "color to alpha" seems to work to create the transparency. (But I still want my original stupid, wrong method back!)
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Oct 25, 2011, 08:20
Post: #4
RE: How to Make a Transparent Background
You get white if the layer has no alpha channel (in other words, cannot be transparent). See "Layer/Transparency/Add alpha channel": if it's grayed, the active layer already has one.

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Oct 26, 2011, 00:49 (This post was last modified: Oct 26, 2011 00:52 by TX_Greenhorn.)
Post: #5
RE: How to Make a Transparent Background
(Oct 25, 2011 08:20)ofnuts Wrote:  You get white if the layer has no alpha channel (in other words, cannot be transparent). See "Layer/Transparency/Add alpha channel": if it's grayed, the active layer already has one.

The pickle is, I had a single image, in a single session, from the same source (my camera) that many of my previous images came from, evidently go from having an alpha channel, to not having an alpha channel, spontaneously. And then no images afterwards having an alpha channel, unlike every other image I'd edited in this way before.

If I didn't know better, I'd think an update was the culprit.
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Oct 26, 2011, 06:22
Post: #6
RE: How to Make a Transparent Background
Image from cameras (jpeg and raw) are loaded as layers without alpha channel, since the file types do not support transparency.

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Oct 27, 2011, 03:46
Post: #7
RE: How to Make a Transparent Background
Well, I won't belabor the point further, but like I said, I was previously able to create transparency on images from my camera without making any adjustments to channels. It suddenly stopped working in the middle of a single session with a single file.

Thanks for trying to help, anyway!
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Oct 27, 2011, 13:35
Post: #8
RE: How to Make a Transparent Background
(Oct 26, 2011 06:22)ofnuts Wrote:  Image from cameras (jpeg and raw) are loaded as layers without alpha channel, since the file types do not support transparency.

Why is it necessary to load alpha channels into image and if it is done for making changes in the image, can the changes be made in the layer itself.
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Oct 27, 2011, 13:54
Post: #9
RE: How to Make a Transparent Background
You don't load an alpha channel in the image... you add an alpha channel to a layer that has none so far. A pixel in a JPEG file is defined by three values, R, G, B. In a layer (or in a PNG file), it should have 4: R, G, B, and A. The A value tells how opaque the pixel is (from 0: fully transparent to 255: fully opaque). This 4th value, in most cases, is treated like a color value (for instance, you can change it across the image using the Curves or Levels tools). "Adding an alpha channel" is just adding this 4th value (initialized to 1: fully opaque) to the pixels of a layer that had none.

When doing basic editing of photographs (color/contrast/clean up), there is usually little need to have a transparent bottom layer, so Gimp won't add the alpha channel by default.

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