Replace living statue and crystal soul graphics with versions that don't have a background

- Also included is details on how this was done, in case someone else can improve on it.
- Living statue attack graphic is derived from Exile III.

rsrc/remove-bg/remove-bg.sh

@@ -0,0 +1,41 @@
+#!/bin/bash
+
+# EXPLANATION
+#############
+#
+# This script was used to strip out the backgrounds from the living statue
+# and crystal soul monster graphics. It takes as input three images:
+#
+# 1. back.png contains the backgrounds to be stripped out.
+# 2. fore.png contains the original images.
+# 3. mask.png contains black pixels where the original image should be assumed opaque.
+#
+# The actual magic that does this is contained in the two .fx scripts
+# included in this directory.
+#
+# The script produces out.png containing the images with the background removed.
+# Overall it works quite well; the regular crystal soul (normal and attack graphics)
+# and the non-attacking living statue look pretty good with no additional
+# manual adjustment. The other two crystal souls require a little noise removal,
+# and the living statue attacks still require quite a bit of editing to get 
+# a usable result. Also, though the crystal soul attack looked pretty good,
+# I used GIMP's levels tool to make it look closer to the original.
+# (Red down to 240, Green up to 80, Blue up to 80, Alpha down to 230)
+#
+# As might be obvious from the below commands, running this script
+# requires that ImageMagick is installed.
+#
+# Note that this script is not at all generic. If you wanted to use it
+# on other images you would at minimum have to edit the canvas size
+# specified in the command.
+#
+
+convert \
+	-size 113x148 canvas:white -alpha set \
+	back.png fore.png -channel A -fx "@calc-alpha.fx" \
+	back.png fore.png -channel RGB -fx "@apply-alpha.fx" \
+	intermediate.png 2>| im_error.txt
+
+convert intermediate.png fore.png mask.png -composite out.png
+
+rm intermediate.png