Re: [Gimp-user] Change background colour with GIMP 2.10.22 [resent]

[Tom <tomdkat comcast net>]

On 3/25/21 4:27 PM, Liam R E Quin wrote:
> Sending this message again with the image compressed more,  so it gets
> through to the list... (3rd attempt!)
>
>
>
> On Thu, 2021-03-25 at 17:24 +0100, Zoltán Kluik wrote:
> > Dear Liam,
> >
> > Yes, the image is in RGB colour 8 bit.
> > What does it mean?
> Colour means as opposed to greyscale (just grey, no colur allowed).
>
> RGB means that any pixel can be in any colour, as opposed to indexed
> which would mean a fixed list of colours
>
> 8-bit means  each of red,  green, blue (RGB) can take any whole number
> value from 0 to 255 - this is appropriate for JPEG images for example.
>
> With the following image I did this:
>
> (1) open the image in gimp
> (2) select the Fuzzy Select tool from the toolbox
> (3) in Tool Options, make sure the threshold is good - i used 13. The
> higher  this number ,the more the Fuzzy Select tool will select colours
> that are not quite the one you click on.
> (4) i clicked on the green background 9still with fuzzy select). This
> selected eveything except the coin.
> (5) i used select->grow to increase the selection by 2 pixels. This
> makes sure that if e.g. there's a pet hair in the picture, it gets
> selected out. But this also selects the edge of the coin, which we
> don't  want.
> (6) then, i did Select->shrinl and entered 1 pixel, to get back the
> edge of the coin.
> (7) Probably we don't want an ugly hard edge so i used Select->Feather
> by 1.5 pixels to soften the edge of the selection.
> (8) i did edit->cut (or Control-X), to remove the green. If you don't
> have the default black and white colours selected in the two small
> panels  under the toolbox, press d to reset them to defaults and then
> do cut.
> (9) then i did Image->Crop to Content, to get rid of the extra white
> areas.
> (10) finally i exported the image.
>
> This is much faster to do than to describe. Maybe ten seconds at most.
>
> Just before exporting ,i actually also used  Colours->Levelsand pressed
> Auto Input Levels; you may not want that; it makes the dark  parts of
> the image black. You can get a better result by including a photo card
> (you can get them on ebay or from any photography shop) in the picture
> and using the white and the black as white and black points in Levels.
> It's pretty  much instant although then you have to crop the photo card
> out of the picture.
>
> Interesting coin.
>
> slave liam (ankh)

Thanks for posting your process.  Without having seen the original 
image, I have a question: would the "Color to Alpha" function worked 
well here?  Select the green background as the color to eliminate and 
the coin should be all that's left, with a transparent background.

Thanks!

Peace...

Tom