#!/bin/bash
#
# divide_vert_bg [options]  image  multi_image
#
# Divide (segment) an image with a known pure a background color horizontally
# into rows of images alternating images of blank background color images, and
# those with non-background colors (the interesting parts).
#
# Options...
#    -i        Don't output (delete) the white gaps between the rows.
#    -b color  Background color to use (defaults to top-left pixel color)
#    -f fuzz   color fuzz factor (percentage)
#
# This script is a faster version of the "divide_vert" script but only works
# with a single background color.
#
# Examples...
#
# Expand the row spacing of some text by 4 pixels (must be a multiple of two)
#
#  magick -size 50x caption:'This is a word wrapped line of text' miff:- |\
#    divide_vert_bg - miff:- |\
#      magick - -splice 0x2 -append  gap_expansion.png
#
# This will remove all gaps between lines of text...
#
#  magick -size 50x caption:'This is a word wrapped line of text' miff:- |\
#    divide_vert_bg -i - miff:- |\
#       magick - -append  gaps-removed.png
#
# Replace all gaps by a fixed amount (5 pixels),
# though this is not a good idea for normal text images.
#
#  magick -size 50x caption:'This is a word wrapped line of text' miff:- |\
#    divide_vert_bg -i - miff:- |\
#      magick - -splice 0x5 -append \
#              -gravity south -splice 0x5  gaps_replaced.png
#
###
#
# Anthony Thyssen    7 September 2010     A.Thyssen_AT_griffith.edu.au
#
PROGNAME=`type $0 | awk '{print $3}'`  # search for executable on path
PROGDIR=`dirname $PROGNAME`            # extract directory of program
PROGNAME=`basename $PROGNAME`          # base name of program
Usage() {                              # output the script comments as docs
  echo >&2 "$PROGNAME:" "$@"
  sed >&2 -n '/^###/q; /^#/!q; s/^#//; s/^ //; 3s/^/Usage: /; 2,$ p' \
          "$PROGDIR/$PROGNAME"
  exit 10;
}

IGNORE_GAPS=''  # don't ignore gaps by default.
coords=0,0;     # where to get background color from
fuzz=0;         # how pure is the background color.

while [  $# -gt 0 ]; do
  case "$1" in
  --help|--doc*) Usage ;;

  -i) IGNORE_GAPS=true ;;      # do not output blank gap images.
  -b) shift; bg_color=$1 ;;    # background_color
  -f) shift; fuzz=$1 ;;        # fuzz factor

  --) shift; break ;;    # end of user options
  -)  break ;;           # STDIN end of user options
  -*) Usage "Unknown option \"$1\"" ;;
  *)  break ;;           # end of user options
  esac
  shift   # next option
done

[ $# -ne 2 ] && Usage "Invalid number of Arguments"

input="$1"  # Read from this IM input file format, may be a pipe
output="$2" # Write to this IM input file format, may be a pipe

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=`echo "$fuzz" | tr -cd '0-9'`  # $remove any '%' leaving just numbers

# ----------------------------------------------------------------------
# The problem is we need to know the height of the image to scale it!
# If it wasn't for this we would not need any temporary files at all.

# Read input image, once only as it may be pipelines, and save a MPC copy of it.
height=`magick "$input" -format '%h' -identify $tmpdir/original.mpc`

if [ "X$bg_color" = 'X' ]; then
  bgcolor=`magick $tmpdir/original.mpc -format "%[pixel:u.p{$coords}]" info:`
fi

# Replace given background color with none, and scale down to a single column
magick $tmpdir/original.mpc \
        -fuzz ${fuzz}% -fill none -draw "matte $coords replace" \
        -scale 1x$height\! \
        -alpha extract -depth 16 txt:- |

# Then use "sed" to define each row as being 'gap' or 'nogap' segments.
sed '1d; s/.*(    0,.*/gap/; s/.....*/nogap/;' |

# Finally use "uniq" to collect the number of rows in each segment.
uniq -c |

#cat; exit 0;
#wc; exit 0;  # debugging - check results of counts

# Divide the image basied on the number of colors (or change in gap color)
while   read height gap;   do
  if [ "$gap" = "nogap" -o ! "$IGNORE_GAPS" ]; then
    magick $tmpdir/original.mpc -crop 0x$height+0+$top +repage miff:-
  fi
  top=`expr $top + $height`
done |

# Now ouput the pipeline of image segments the way the user wants it saved
magick miff:- "$output"