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Transparency from Selection

Jun 25, 2012, 16:39
Post: #1
Transparency from Selection
I'm sure there's already a thread on this: please direct me there if so...

That said, I've just sent a frustrating hour trying to select an area ant turn the background transparent. Previously this was simple: select foreground, invert so background selcted, toggle the transparency to 0% and hey presto, transpaent background. Now when I do that it goes white.

I have tried using transparency - add alpha channel, and nothing happens: the menu stays there. Is that a glitch in y version of Gimp? and how can I now isolate the background and turn int transparent?

Andy in Germany
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Jun 26, 2012, 10:08
Post: #2
RE: Transparency from Selection
(Jun 25, 2012 19:32)ofnuts Wrote:  Normally you should have an alpha channel on the layer for this (otherwise you get the background color). And then Select and [Delete] should do the job.

If you are trying to remove a uniform background around a subject, the technique expounded in the "background removal" link in my signature will likely give better results.

Many thanks Ofnuts, but I still seem to be missing something, because I'm getting a different result. Here's the original image:

[Image: Pot_01.jpg]

I want to isolate the pot and the plant, and make the floor transparent. What I'm doing is:

Select the pot and plant using the inteligent scissors.

Invert selection so the background is selected.

Then I press the delete button. This is the result:

[Image: Pot_02.jpg]

What extra command do I need to tell Gimp it should be clear, not white?

Andy in Germany
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Jun 26, 2012, 11:43
Post: #3
RE: Transparency from Selection
(Jun 26, 2012 11:23)ofnuts Wrote:  You don't see white while in Gimp. The white is added back because you save as JPG and JPG doesn't support transparency. If you save as PNG you keep the transparency:

As well as all the above good advice

Still looks like no alpha channel but using your example

Add an alpha channel for transparency. You will see a change in the layer name from bold to normal.

Make your selection, a circular selection is obvious here but cuts off the end of a leaf.

Easiest way for this one is the quick mask -> toggle quick mask on, bottom of the select menu.

Use a white brush to paint over the end of the leaf. Back and toggle quick mask off.

Invert the selection, then edit cut or ctrl-x The transparency shows as a chequer board pattern.

Save as either a gimp xcf file or a png to preserve transparency.

screenshots of the above. http://i.imgur.com/7IVF8.jpg

I did a run down on the select tools some time ago, a bit long at 11 mins but might help.

http://www.youtube.com/watch?v=aUHEI-bVSPo

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Jun 26, 2012, 14:37
Post: #4
RE: Transparency from Selection
(Jun 26, 2012 11:43)rich2005 Wrote:  
(Jun 26, 2012 11:23)ofnuts Wrote:  You don't see white while in Gimp. The white is added back because you save as JPG and JPG doesn't support transparency. If you save as PNG you keep the transparency:

As well as all the above good advice

Still looks like no alpha channel but using your example

Add an alpha channel for transparency. You will see a change in the layer name from bold to normal.

Make your selection, a circular selection is obvious here but cuts off the end of a leaf.

Easiest way for this one is the quick mask -> toggle quick mask on, bottom of the select menu.

Use a white brush to paint over the end of the leaf. Back and toggle quick mask off.

Invert the selection, then edit cut or ctrl-x The transparency shows as a chequer board pattern.

Save as either a gimp xcf file or a png to preserve transparency.

screenshots of the above. http://i.imgur.com/7IVF8.jpg

I did a run down on the select tools some time ago, a bit long at 11 mins but might help.

http://www.youtube.com/watch?v=aUHEI-bVSPo

Many thanks for the help: the missing Alpha channel was apparently the problem, as I was able to make the background transparent without problems. I'll look at the video later...

Previously the background went white in Gimp while I was aorking on the file as a multi-layered XCF, and before I saved it as a Jpeg.

Sorry to go on, but how do I now make the background semi transparent. Or should I look at the video for that?

Andy in Germany
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