Add a option to trace color "by size"

[v1nce]

We got a lot of complaint @ inkscapeforum about color being dull after tracing.

I guess it's because of the color reduction algorithm.

I think we should provide an option to use a dumbest algorithm that will consider color only by their areas.
I think it will behave better on clipart image.

Here's a quick shell I wrote
It uses the histogram function of imagemagick to get the most significant colors and then it potraces every of them and join them in a final svg

#!/bin/bash
input=$1
output=$2
histogram="$2.tmp.histo"
tmpsvg="$2.tmp.svg"
tmpmask="$2.tmp.ppm"

convert $input -format %c -depth 8 histogram:info:"$histogram"
sed -i '$d' "$histogram"
sort -n -k1,1 -r -o "$histogram" "$histogram"
echo "<?xml version='1.0' standalone='no'?>" > "$output" ;
echo "<svg version='1.0' xmlns='http://www.w3.org/2000/svg'><g>" >> "$output" ;

i=1;
 while IFS= read -r line; do
  color="${line:27:6}";
  echo "processing color $color $i"
  i=$(($i+1))
  convert "$input" \
  -transparent "#$color" \
  -alpha extract \
  "$tmpmask"
  potrace -s "$tmpmask" -o "$tmpsvg"
  sed -ni '/transform/,/g>/p' "$tmpsvg"
  sed -i "s/#000000/#$color/" "$tmpsvg"
  cat "$tmpsvg" >> "$output"
done < "$histogram"
echo "</g></svg>" >> "$output"
rm "$histogram"
rm "$tmpsvg"
rm "$tmpmask"