Changing A Color

[Ricebug]

I have a map of Salem, Oregon, and am trying to trace the railroad tracks with a different color. In the map, the tracks are barely legible. Is there a way to pick the color and then globally change the map so that the tracks show up better?

I realize that other parts of the map may be affected. Not an issue, as I'm only focused on the RR tracks themselves. Not an issue, as I'm only focused on the RR tracks themselves.

[rich2005]

Can you post (part of) that image so that suggestions can be made. Otherwise just guessing.

and

What OS are you using and which version of Gimp, those questions are not for nothing, they can determine the result.

[Ricebug]

(10-10-2018, 06:19 PM)rich2005 Wrote: Can you post (part of) that image so that suggestions can be made. Otherwise just guessing.

and

What OS are you using and which version of Gimp, those questions are not for nothing, they can determine the result.

The faint gray lines are the tracks. I want to switch that color to plain black to make them stand out.

Windows 10; GIMP v.2.10.6

[dinasset]

(10-10-2018, 11:31 PM)Ricebug Wrote:

(10-10-2018, 06:19 PM)rich2005 Wrote: Can you post (part of) that image so that suggestions can be made. Otherwise just guessing.

and

What OS are you using and which version of Gimp, those questions are not for nothing, they can determine the result.

The faint gray lines are the tracks. I want to switch that color to plain black to make them stand out.

Windows 10; GIMP v.2.10.6

I used first Brightness/Contrast -75/+75

Then selected the colour by picking
Then coloured used the blue FG
   

[Blighty]

1) Duplicate the Original layer. Rename this duplicated layer to Threshold.

2) On the Threshold layer, apply Threshold, value 220

3) On the Threshold layer use the Fuzzy select tool to select the railroad tracks. Make the Threshold layer invisible.

4) Create a new transparent layer and name it Railroad.

5) On the Railroad layer bucket fill the selection with black.

See attached xcf

[Ricebug]

Thanx, Blighty. Mission accomplished. I was using Corel Draw and it could not handle the map (30,000 x 30,000 pixels). I was getting ready to buy PhotoShop and discovered GIMP instead.