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Colour -> Alpha

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Colour -> Alpha chris.danx 04 Sep 21:59
  Colour -> Alpha Sven Neumann 07 Sep 13:41
  Colour -> Alpha David Neary 07 Sep 18:40
  Colour -> Alpha Jeff Trefftzs 07 Sep 19:59
chris.danx
2003-09-04 21:59:45 UTC (over 20 years ago)

Colour -> Alpha

Hi,

Is it possible to make all pixels of a given colour transparent? I've just started playing with the gimp and am a bit stuck. Basically I want to duplicate a selection in the background layer, put it in a transparent layer with only the non-white pixels opaque. Maybe there's a better way to do this?

Cheers, Chris

Sven Neumann
2003-09-07 13:41:12 UTC (over 20 years ago)

Colour -> Alpha

Hi,

"chris.danx" writes:

Is it possible to make all pixels of a given colour transparent?

Yes, select by color and clear that selection. There is a tool to select pixels by color.

Sven

David Neary
2003-09-07 18:40:20 UTC (over 20 years ago)

Colour -> Alpha

chris.danx wrote:

Hi,

Is it possible to make all pixels of a given colour transparent? I've just started playing with the gimp and am a bit stuck. Basically I want to duplicate a selection in the background layer, put it in a transparent layer with only the non-white pixels opaque. Maybe there's a better way to do this?

Add layer mask, Select by colour on layer, activate mask, fill selection with black.

Or, select by colour, quickmask, copy the mask (in the channels dialog), and apply that mask as a layer mask.

Cheers, Dave.

Jeff Trefftzs
2003-09-07 19:59:06 UTC (over 20 years ago)

Colour -> Alpha

On Thu, 2003-09-04 at 12:59, chris.danx wrote:

Hi,

Is it possible to make all pixels of a given colour transparent? I've just started playing with the gimp and am a bit stuck. Basically I want to duplicate a selection in the background layer, put it in a transparent layer with only the non-white pixels opaque. Maybe there's a better way to do this?

Sorry for the delay - it's now Sunday and this post only just arrived.

Short answer: Image/Select/Select by Color should do it. If you want to make the selected (or not selected) pixels transparent, make sure you have an alpha channel. You can't do this on the background layer.

An alternative is the Image/Filters/Colors/Color_to_alpha plug-in.

Experiment with both of these and see what works for you.