#!/bin/sh
#
# segment_image  [option] input_image  multi_output_image
#
# Image of solid color areas (segments) separate the image into a sequence
# of images, with each image containing one unconnected color magick segment on a
# transparent background.
#
# For more details see ImageMagcik Forum Discussions...
#   http://imagemagick.org/discourse-server/viewtopic.php?f=1&t=11705
#   http://imagemagick.org/discourse-server/viewtopic.php?f=1&t=18283
#   http://imagemagick.org/discourse-server/viewtopic.php?f=1&t=18683
#
# Future option: limit extraction to a specific color, generally white or
# black Or anything that is 'NOT' the background color (0,0 pixel color?).
#
# The 'fuzz factor' for floodfill removals may not work well, as the starting
# point is on the edge of a segment.  A better way to select segments may be
# to use a 'distance' morphological function, and then remove segments based
# on a larger distance value so as to avoid the magick segment edges.
#
# Anthony Thyssen    18 July 2008
#
PROGNAME=`type $0 | awk '{print $3}'`  # search for executable on path
PROGDIR=`dirname $PROGNAME`            # extract directory of program
PROGNAME=`basename $PROGNAME`          # base name of program

umask 77
tmpdir=`mktemp -d "${TMPDIR:-/tmp}/$PROGNAME-XXXXXXXXXX"` ||
  { echo >&2 "$PROGNAME: Unable to create temporary directory"; exit 10;}
trap 'rm -rf "$tmpdir"' 0   # remove when finished (on end or exit)
trap 'exit 2' 1 2 3 15

fuzz='0%'    # fuzz factor for flood filling sepearte colored areas
             # This may be needed for JPEG image input.

# ----------------------

# Read input image, once only as it may part of a pipeline of commands,
# and save a MPC working image, for fast image reading.
# Actually it may be better to just save as a IM TXT image file instead.
magick "$1" -matte $tmpdir/working.mpc

while true; do

  # Find the first non-transparent pixel in inpit image.
  coords=`magick $tmpdir/working.mpc txt:- | sed '1d; / 0)/d; s/:.*//; q'`

  # If image is now only transparent, all segments found
  [ -z "$coords" ]  && break

  echo >&2 "Extracting magick segment at coord $coords..."
  # Write the image to the output pipeline BEFORE the magick segment is removes
  # Only THEN, remove that magick segment from working image (mask),
  # Write the working image back so we can look for another segment.
  magick $tmpdir/working.mpc   -write miff:-   \
          -fuzz $fuzz -fill none -draw "matte $coords floodfill" \
          $tmpdir/working.mpc

done |
  # Reverse image list so 'segments' are 'added' on each consecutive image,
  # then use 'OptimizeTransparency' to make previously added pixels
  # transparent, leaving just the newly added pixels. Reverse the list back to
  # the order of discovery and output as a multi-image image sequence.
  magick miff:- -reverse -layers OptimizeTransparency -reverse "$2"