Help! Convert map to lines, separated by transparency.

[Starlite]

I have an image that is a map (snippet below). I'd like to use this in Google Sheets, but they don't allow background images. So I have a plan to convert the map, but I need some help.

 

The idea is to use edge detection to strengthen all the edges to black, then somehow select all the other regions and delete them, converting them to transparency. I'm having two issues:

 

1. How do I make the lines strong enough between zones?  (Outline seemed to work, but Edge Detection destroyed that strength.)

2. How do I select all areas under a certain luminance threshold, in order to delete them?

 

I'm happy for the map to be black and white, though starting with colour may have some advantages.

 

Thanks in advance, for any help!

 

PS: Please test your ideas on the image snippet I've provided before suggesting them. That seems the best way to ensure they actually work. :)

[Red ochre]

This may help Tone Gradient Magnitude

 

Reduce background opacity and if needed you can subsequently adjust the opacity of the remaining lines using Alpha-threshold

[Starlite]

Sweet. I'll try it out.

[Ego Eram Reputo]

21 hours ago, Starlite said:

2. How do I select all areas under a certain luminance threshold, in order to delete them?

 

Have you tried the magic wand with the Shift key held down? The Shift key toggles Global selection. Once you've made a selection using the Shift key, fine tune it using the Tolerance setting to include or exclude pixels.