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Arrow annotation in GIMP.

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  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

#212767 — Arrow annotation in GIMP.

Hi, 

Can anyone recommend a means for adding an arrow to 
an image in GIMP?

The article here describes something called ArrowsCreator.
https://graphicdesign.stackexchange.com/questions/44797/how-do-i-insert-arrows-into-a-picture-in-gimp
Is it advisable?

Any other recommendations?

Thanks,                           ... P.



-- 
https://en.wikibooks.org/wiki/Oberon
Tel: +1 604 670 0140            Bcc: peter at easthope. ca

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#212786

peter@easthope.ca wrote: 
> 
> Hi, 
> 
> Can anyone recommend a means for adding an arrow to 
> an image in GIMP?
> 
> The article here describes something called ArrowsCreator.
> https://graphicdesign.stackexchange.com/questions/44797/how-do-i-insert-arrows-into-a-picture-in-gimp
> Is it advisable?
> 
> Any other recommendations?

Open a new image. Set the background to transparent. Draw an
arrow. Save it. Don't close it.

Open your primary image. Figure out where the arrow goes. Create
a new layer on top. Cut and paste the arrow into the primary
image. Move it around until you like it. Save. Export to the
format you want.

Next time you want an arrow, you've already got the same one, so
you can be consistent.

-dsr-

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#212883

From: Dan Ritter 
Date: Wed, 14 Aug 2019 08:26:18 -0400
> Set the background to transparent.

Menus: Layer > Tranparency > Add Alpha Channel. The new viewer remains 
black.  Might be transparent. Might not.  (If all else fails, will see 
what happens when the arrow is dropped on the image layer.  If the 
result has the appearance of the arrow layer, the arrow background is 
not transparent and my image is obscured.)

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?

What is the point of alpha? Transparent should be simply no marking.  
RGB = (0,0,0). What does alpha represent?  

Thanks,                         ... P.

-- 
https://en.wikibooks.org/wiki/Oberon
Tel: +1 604 670 0140            Bcc: peter at easthope. ca

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#212885

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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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#212803

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On Tue, Aug 13, 2019 at 20:51 <peter@easthope.ca> wrote:

>
> Hi,
>
> Can anyone recommend a means for adding an arrow to
> an image in GIMP?
>
> The article here describes something called ArrowsCreator.
>
> https://graphicdesign.stackexchange.com/questions/44797/how-do-i-insert-arrows-into-a-picture-in-gimp
> Is it advisable?
>
> Any other recommendations?


If you're adventurous and want to be able to add more overlays to images
you could use ImageMagick and write a wrapper program to do exactly what
you wish. I have done so using Perl 6 (aka Raku) and plan to make it public
when I get the time.

Check out https://perl6.org for more info on the language.

Best regards,

-Tom

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