Highlight A Region / Inverse Region

Hello everyone,

 

I'm a new user to ImageMagick and I'm testing it out to see if it can all
the image functions that we require in order to consider it as a replacement
for our current system.  The current thing I'm attempting to do is
'highlight' a particular area on an image.  When I say highlight I'm really
referring to keeping that specified area 'normal' and putting a 50% black on
everything else [RGBA(0,0,0,0.5)].  This essentially gives the effect that
everything is 'grayed out' and the highlight area pops.

 

I've experimented with the '-region' operator to select the highlight region
but I can't seem to find a way to grab the 'inverse' of that region to draw
my 50% black on the rest of the image.  Here is what I have so far:

 

convert -size 1000x1000 xc:red -region "500x500+100+100" -stroke
"rgba(0,0,0,0.5)" -fill rgba(0,0,0,0.5) -strokewidth 1 -draw "rectangle 0,0
500,500" output.jpg

-- This essentially gives me a shaded area 500x500 in the image.  I need
essentially the opposite (the other area is shaded but the 500x500 is left
unaltered).

 

Is there a way to specify a region then perhaps put something like a ! or ^
to indicate the 'inverse' of the selected region?  Or perhaps a way to
combine several regions?  Can someone perhaps offer some insight or point me
to the proper commands to achieve this?

 

Thanks,

 

Matt