Jtdcftul

In Chipaca's answer to Managing files and sync scenarios there's a screenshot with certain highlights. The highlights are the following:

1. A row of a GUI list is highlighted by the other parts of the screenshot being darker.


2. A check mark is highlighted by being circled by what looks like a (orange) crayon.

How do I create both of these highlights on a screenshot? Is there an automated process?

The screenshot I'm referring to looks like this:

Here's a guide for The Gimp :

Create Higlighted Rectangle

1. 
   

   Select Rectangle Tool:

   
   
   
   
   
   • tick Feather Edges choose Radius e.g. 5.0 pixels for smooth borders
   
   
   • tick Highlight to highlight the selection
   
   
   
   

   

   
   



2. Select area to highlight



3. 
   Select -> None to remove selection.

The selection is now highlighted

Note: in some versions of GIMP the highlighting may be removed as soon as we select another tool or save the image. In this case we can proceed as follows to keep the area highlighted:

4. Invert the selection (Select --> Invert or Ctrl+i).


5. Bucket fill the background with black 30% opacity.

Create Crayon

5. 
   Select Ellipse Tool to select area for crayon


6. 
   Select -> Border e.g. with 8 pixels


7. 
   Paintbrush Tool choose brush e.g. Galaxy, choose color e.g. yellow


8. Paint selection until happy

You can do this in editors such as Pinta, Shutter*, the GIMP, etc.

The process may vary, but one way to do it, would be to place a translucent square/rectangle in a second layer above the image, and then to cut out the part that you want to glow.

Example workflow:

• Open your screenshot in Pinta.
  
  
  
  
  1. Create a new layer.
  
  
  2. Select the new layer
  
  
  3. Choose the paintbucket tool.
  
  
  4. Change the colour to black, but set the opacity to 150.
  
  
  5. Now use the rectangle selection tool to select the area you want to highlight.
  
  
  6. Fill the layer with this colour.
  
  
  7. Hit delete.
  
  
  
  


• The image should now be highlighted.

* Shutter is more for accomplishing the reverse effect.

1. 
   

   Take a screenshot

   
   
   

   I use shutter and gnome-screenshot to take screenshot, you may use any one of them.To install them, use the commands.

   
   
   

   sudo apt-get install shutter
   
   sudo apt-get install gnome-screenshot
   
   

   
   


2. 
   

   Install gimp
   
   We will need this for the editing.Install it with

   
   
   

   sudo apt-get install gimp
   
   

   
   



3. Get the screenshot into gimp
   I dragged the image into gimp.You may use file -->open



4. 
   

   The fun begins

   
   
   
   
   
   • We first select the part we want white.We can hold Shift to select multiple areas. Then we invert the selection using Ctrl+I
     
     
   
   
   • Then we select the paintbrush tool.
     
     
   
   
   • Now we change the opacity and increase size.
     
     
   
   
   • Paint everything.If it's darker, change opacity and try again.For me, 50% was fine.
     And the end result is.
     
     
   
   
   
   

NOTE: The options for gimp were available easily for me because I have customised it a lot. Use some gimp tutorial to learn how to use it.

Whenever you have a workflow like the ones shown in the other answers for the GIMP, it's somewhat easy to automate them at least partially (with the restrictions that scripts have compared to plugins) by writing some Script-Fu (so, Scheme), or Python. If the script is written to respect undo/redo, this also makes experimenting with the values a little bit easier, because it's just a keypress away to remove all traces of the effect again.

Here's a script automates the highlighting part, because I might use that myself going forwards.

Scripts go into ~/.gimp-2.10/scripts (respectively other version numbers), then you only have to start the program, or use Filters > Script-Fu > Refresh Scripts if the file was added when it was already running.

Afterwards, select something and use Filters > Light and Shadow > Highlight Area... to create a new highlight (well, shadow really) layer:

This is also how the highlights would look with 5px of feather applied.

Feathering is optional, after all you can achieve the same effect by using the feather option of the selection tool; using layer opacity can make fiddling with the colour a bit easier, but if you want to paint on top it's easier to go with alpha fill (alternatively another layer would have to be added).