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

[Jay Smith <jay JaySmith com>]

Zoltán,

I am eager to know what other users have to say, whether on the list or 
directly to you, Zoltán.

I have a similar application (stamps for collectors).  I have 
experimented with various "green screen" techniques for years, and using 
other programs as well, but I have never been able to find anything that 
can fully do what I need to do.  The problem for me is that sometimes 
the printed design of the stamp (which can be various colors), or the 
cancellation/postmark on the stamp goes to/over the edge of the stamp 
paper.  Thus at that point (near the edge) there are problems with 
selections "eating into" the stamp area, etc., such as the selection 
following the area of the postmark into the stamp.  We have also not 
been able to completely eliminate all vestiges of background color right 
up to the edge of the stamp's paper (keep in mind that on old stamps, 
not all edges are absolutely clear cut as they are on a modern stamp) -- 
this may be similar to Zoltán's problems at the edges of coins if the 
edge of the coin is not perfectly smooth.

Since we never found a satisfactory solution in "old" GIMP we did not 
attempt to automate it back then (as Zoltán did), thus we don't have the 
problem of the automation no longer working well or quickly.

However, our original problem remains as much as ever.  We can get "sort 
of close", but that's just not good enough.  And we need something we 
can use for making tens of thousands of stamp images.

I will watch this thread with interest.

Zoltán, I welcome learning any advice you can give as you solve your 
problem.

Jay Smith


On 03/23/2021 07:15 PM, Zoltán Kluik via gimp-user-list wrote:
> Dear GIMP users,
>
> I would like to ask your help regarding removing background and change it
> to white.
> I'm dealing with coin pictures mainly medieval silver coins. I take the
> photo about coins with green / dark green background. In the past on Ubuntu
> I used the GIMP 2.8.16 version where I applied the foreground selection
> tool. Here I just simple rounded the coin, press enter and the program
> after some seconds selected my coin. I loved this method, because it takes
> only seconds to select the coin.
>
> Last year I have upgraded GIMP to version 2.10.22, but from this time I
> have a big problem with time consumption and also with the quality of the
> changing the background. Now in 2.10.22 I open a picture, using foreground
> selection tool, but in this version there is a motor feature where I can
> select Global- and Levin matting. I use both with iteration value 1. First
> Global is selected, coin is rounded, pressing enter, selecting the
> foreground with the mouse, again pressing enter. Here the problem is that
> under the coin where the green background’s colour was a little bit darker
> there are green dots. So after Global,  I apply the Levin matting. With
> this the dots are deleted, good, but where it is not selected the coin,
> there the surface (mainly at the edge) is not the original, blurred or not
> as the original was. Here I can use the adding to background selection or
> adding to the background within extra zoom possibility to make sharper the
> edges. Finally after 10 minutes however it is the same result as in 2.8.16
> was 30 seconds and automatically.
>
> So what did I wrong or how I should do to make this process easier and
> faster as it was in the earlier version?
>
> Thank You in advance for Your advice!
>
> Zoltan
>
> Zoltán Kluik <numizmatikakz gmail com> ezt írta (időpont: 2021. márc. 23.,
> K 14:10):
>
> > Dear GIMP users,
> >
> > I would like to ask your help regarding removing background and change it
> > to white.
> > I'm dealing with coin pictures mainly medieval silver coins. I take the
> > photo about coins with green / dark green background. In the past on Ubuntu
> > I used the GIMP 2.8.16 version where I applied the foreground selection
> > tool. Here I just simple rounded the coin, press enter and the program
> > after some seconds selected my coin. I loved this method, because it takes
> > only seconds to select the coin.
> >
> > Last year I have upgraded GIMP to version 2.10.22, but from this time I
> > have a big problem with time consumption and also with the quality of the
> > changing the background. Now in 2.10.22 I open a picture, using foreground
> > selection tool, but in this version there is a motor feature where I can
> > select Global- and Levin matting. I use both with iteration value 1. First
> > Global is selected, coin is rounded, pressing enter, selecting the
> > foreground with the mouse, again pressing enter. Here the problem is that
> > under the coin where the green background’s colour was a little bit darker
> > there are green dots. So after Global,  I apply the Levin matting. With
> > this the dots are deleted, good, but where it is not selected the coin,
> > there the surface (mainly at the edge) is not the original, blurred or not
> > as the original was. Here I can use the adding to background selection or
> > adding to the background within extra zoom possibility to make sharper the
> > edges. Finally after 10 minutes however it is the same result as in 2.8.16
> > was 30 seconds and automatically.
> >
> > So what did I wrong or how I should do to make this process easier and
> > faster as it was in the earlier version?
> >
> > Thank You in advance for Your advice!
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