How do I make border color depend on counter color

Goal: to derive border colour colour of the counter.

Relevant reading:

• ImageMagick docs, identify, https://imagemagick.org/script/identify.php
• ImageMagick docs, format identify, https://imagemagick.org/script/escape.php
• StackOverflow, How to set commands output as a variable in a batch file, https://stackoverflow.com/questions/6359820/how-to-set-commands-output-as-a-variable-in-a-batch-file,
• ImageMagick docs, Extracting Image Colors, https://www.imagemagick.org/Usage/quantize/#extract
• SS64: Command line reference, IF: Conditionally perform a command, https://ss64.com/nt/if.html

Consider counters of two sides in a game. You wish to automate process of adding border but you want each side to have border of different colour.

With ImageMagick it is possible to read colour value from specific pixel, modify it and use it as border colour. This method, however, rarely yields eye-pleasing results (i.e. it is not easy to come up with such a colour modification that would, first, give appealing outcome, two, give appealing outcome for all counter types); for a better effect it's advised you use Windows script to set border colour based on a pixel value read from input image.

We will use these two files as input:

We want grey counter to have black border and dark red for the other.

We will use this script:

FOR %%G IN (input\*.png) DO (

        FOR /F "tokens=* USEBACKQ" %%F IN (`magick %%G ^
-crop 1x1+1+1 -format "%%[fx:int(255*r+.5)],%%[fx:int(255*g+.5)],%%[fx:int(255*b+.5)]" info:`) DO (
                SET pcolor=%%F
        )

        IF "!pcolor!"=="161,162,172" SET bcolor=#000000
        IF "!pcolor!"=="181,161,143" SET bcolor=#B14246
        
        magick %%G -bordercolor !bcolor! -border 4 output\%%~nGOutput.png

)

explanation

• FOR %%G IN (input\*.png) DO ( ... ) iterates through all PNGs in input folder;
• FOR /F "tokens=* USEBACKQ" %%F IN (`command`) DO ( ... ) is Windows way of assigning command output to a variable (%F in our case).
• magick %%G -crop 1x1+1+1 -format "%%[fx:int(255*r+.5)],%%[fx:int(255*g+.5)],%%[fx:int(255*b+.5)]" info: is a convoluted way of reading pixel located at coordinates of (1,1) and writing its RGB components to the output. It ensures that ImageMagick will not output name of the colour, should it be one of hundreds that ImageMagick knows;
• SET pcolor=%%F assigns command output to variable pcolor (as in "pixel color");
• IF "!pcolor!"=="161,162,172" SET bcolor=#000000 sets variable bcolor (as in "border color") to value #000000 if RGB components of read pixel colour are equal to specified value. To ensure proper parsing, Windows requires string variables and values to be enclosed in quotes;
• magick %%G -bordercolor !bcolor! -border 4 output\%%~nG-border.png adds 4 pixel border of colour bcolor to input image. In Windows, to use variable with assigned value you enclose it in "!".

result