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Re: Arrow annotation in GIMP.

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On Fri, Aug 16, 2019 at 10:40:59AM -0700, peter@easthope.ca wrote:
> From: Dan Ritter 
> Date: Wed, 14 Aug 2019 08:26:18 -0400
> > Set the background to transparent.
> 

[...]

> Really I don't understand the representation used in GIMP. From what 
> I've read, there are three channels, R, G, B.  OK.  Plus an optional 
> 4th, alpha. What is it?

There are four: RGBA -- [1] should address your other questions. The
alpha channel is useful when you overlay images (like in your arrow
case): you want the arrow be "on top" of your image, but you don't
want the arrow's background obscuring the rest of your image.

You could achieve that with a "mask" (an array of bits of your image's
size with an 1 for each "relevant" pixel and a 0 for each "irrelevant"
one). This is an alpha channel with one bit depth. A deeper alpha
channel allows semi-transparency, where the foreground image could,
for example, merge "softly" into the background.

A neat effect would be to make your arrow semi-transparent: you
would still see through, as if the arrow was smoked glass.

Best you play with that under Gimp, then you'll "get" it quickly.

Cheers

[1] https://en.wikipedia.org/wiki/RGBA
-- t

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Thread

Arrow annotation in GIMP. peter@easthope.ca - 2019-08-14 04:00 +0200
  Re: Arrow annotation in GIMP. Dan Ritter <dsr@randomstring.org> - 2019-08-14 14:30 +0200
    Re: Arrow annotation in GIMP. peter@easthope.ca - 2019-08-16 20:00 +0200
      Re: Arrow annotation in GIMP. <tomas@tuxteam.de> - 2019-08-16 20:30 +0200
  Re: Arrow annotation in GIMP. Tom Browder <tom.browder@gmail.com> - 2019-08-14 18:50 +0200

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