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/.gitignore

@@ -0,0 +1,2 @@
+im_error.txt
+out.png

rsrc/remove-bg/apply-alpha.fx

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+aval=u[1]*255;
+bval=u[2]*255;
+
+i==21&&j==8 ? debug(aval) : 1;
+i==21&&j==8 ? debug(bval) : 1;
+
+dist=bval-aval;
+
+i==21&&j==8 ? debug(dist) : 1;
+
+op=u[0].p{i,j}.a;
+
+i==21&&j==8 ? debug(op) : 1;
+
+mdist=op==0 ? 0 : dist/op;
+
+i==21&&j==8 ? debug(mdist) : 1;
+
+mdist/255

rsrc/remove-bg/calc-alpha.fx

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+rback=int(u[1].p{i,j}.r*255);
+gback=int(u[1].p{i,j}.g*255);
+bback=int(u[1].p{i,j}.b*255);
+
+i==21&&j==8 ? debug(rback) : 1;
+i==21&&j==8 ? debug(gback) : 1;
+i==21&&j==8 ? debug(bback) : 1;
+
+rmain=int(u[2].p{i,j}.r*255);
+gmain=int(u[2].p{i,j}.g*255);
+bmain=int(u[2].p{i,j}.b*255);
+
+i==21&&j==8 ? debug(rmain) : 1;
+i==21&&j==8 ? debug(gmain) : 1;
+i==21&&j==8 ? debug(bmain) : 1;
+
+rdiff=rmain - rback;
+gdiff=gmain - gback;
+bdiff=bmain - bback;
+
+i==21&&j==8 ? debug(rdiff) : 1;
+i==21&&j==8 ? debug(gdiff) : 1;
+i==21&&j==8 ? debug(bdiff) : 1;
+
+rgoal=rdiff > 0 ? 255 : 0;
+ggoal=gdiff > 0 ? 255 : 0;
+bgoal=bdiff > 0 ? 255 : 0;
+
+i==21&&j==8 ? debug(rgoal) : 1;
+i==21&&j==8 ? debug(ggoal) : 1;
+i==21&&j==8 ? debug(bgoal) : 1;
+
+rgd=rgoal - rback;
+ggd=ggoal - gback;
+bgd=bgoal - bback;
+
+i==21&&j==8 ? debug(rgd) : 1;
+i==21&&j==8 ? debug(ggd) : 1;
+i==21&&j==8 ? debug(bgd) : 1;
+
+ro=rgd == 0 ? 0 : rdiff / rgd;
+bo=bgd == 0 ? 0 : bdiff / bgd;
+go=ggd == 0 ? 0 : gdiff / ggd;
+
+i==21&&j==8 ? debug(ro) : 1;
+i==21&&j==8 ? debug(go) : 1;
+i==21&&j==8 ? debug(bo) : 1;
+
+max(ro,max(go,bo))

rsrc/remove-bg/remove-bg.sh

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+#!/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