Changing thick lines to thin

[Steve Austin]

Could someone help me to figure out a way in Gimp 2.10.36
to change thick lines into thinner ones?  Is there a function
that would speed the process?  Currently I am reducing the line
with a digital art pad and I would rather reduce the thickness by 
computer and not by me trying to erase a line.

[sallyanne]

You could try the magic wand on the black and delete it. It will not delete it all as the 'greys' will stay behind, but that will give you thinner lines.
For the white just add another white background to the back to fill in, which you could do first
I'm not sure how you are going to do the colour though. Maybe as you did before, or if you want plain red, just colour pick the red and fill in the spaces that should be that colour.

[Steve Austin]

I appreciate the reply, SallyAnne. Every time I try to do a magic wand and delete, you are right, the greys stay behind.
If I try to "add" back in some black with bucket fill, then I'm right back to where I was.
I am actually trying to make this into a coloring page. I have figured out a process to remove
all the color, but haven't figured out how to thin those thick black lines.

[sallyanne]

After making the black lines thinner you could try threshold on it

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[attachment=10944 Wrote:sallyanne pid='37274' dateline='1703722892']Or you could desaturate after removing the black lines. then use threshold

[Steve Austin]

I've gotten it to this point and it looks good--
black and white.
Just the lines are SO thick.

[sallyanne]

Found another way to  do it for you
If you have the  plugin GMICqt and it is updated, Use the 'Uncanny edges' filter. You will need to invert the result, but I think you may like it.
   

[Steve Austin]

I have found the filter under contours called 
"canny".
Working on the inversion--

[sallyanne]

go back to gimp. Colours >invert

[Steve Austin]

Thank you for that direction.

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Thank you so much--
but now is there a way to darken those lines a little?
I've tried threshold and contours.  
I don't want to go too light--

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Thanks a million Sally Anne.
I think I'm going with your first recommendation--
magic wand and deleting the black.
It seems to look the best on what I am printing.

[sallyanne]

You're welcome. Glad I could have been a little help.

just noticed I gave you wrong name of the filter before too. Glad you were still able to find it