de-pixelate

#!/bin/sh
#
# de-pixelate [-limit N]  input_image  output_image
#
# Try to find and remove any row/columns in the image that are duplicates of
# the previous row/column.  That is remove the extra pixelating rows and
# columns so as to reduce enlarged 'pixel boxes' down to a single pixel.
#
# Option
#   -limit N    Merge at most N rows/columns into a single row/column
#               Can be used to prevent a naturally occuring duplicate
#               row/columns from being merged into a single line/column
#               For example using "-limit 1" will no-op this whole script!
#               N should be equal to or slightly larger that the 'pixel'
#               size that is present in the input image.
#
# NOTE: If the actual number of 'pixel boxes' is known, as faster solution
# is to simply resize the image using "-sample".  However if the size is
# unknown, then you are better off using this script.
#
####
#
#  Anthony Thyssen  2007
#
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
tmp=`mktemp -d "${TMPDIR:-/tmp}/$PROGNAME.XXXXXXXXXX"` ||
  { echo >&2 "$PROGNAME: Unable to create temporary file"; exit 10;}
trap 'rm -rf "$tmp"' 0
trap 'exit 2' 1 2 3 15

# Get limit option
limit=0   # limit will never be reached
if [ "x$1" = "x-limit" ]; then
  shift; limit=$1; shift
fi

# Read input image, once only as it may be pipelines, and save a MPC copy of
# each individual row of pixels as temporary files.
magick "$1" -crop 0x1 +repage "$tmp/rows_%06d.mpc"

# remove duplicate rows (by removing its .mpc index file)
last=""
for pic in $tmp/rows_*.mpc; do
  count=`expr $count + 1`
  if [ "$last" ] && [ $count -ne $limit ] &&
     [ `magick compare -dissimilarity-threshold 100% \
           -metric AE $pic $last null: 2>&1` -eq 0 ]; then
    rm $pic
  else
    last=$pic count=0
  fi
done

# Rejoin and re-split image into columns
magick $tmp/rows_*.mpc -append -crop 1x0 +repage $tmp/cols_%06d.mpc

# lets save some disk space as we are finished with the row images
rm -f $tmp/rows_*.mpc $tmp/rows_*.cache

# remove duplicate columns
last="" count=0
for pic in $tmp/cols_*.mpc; do
  count=`expr $count + 1`
  if [ "$last" ] && [ $count -ne $limit ] &&
     [ `magick compare -dissimilarity-threshold 100% \
           -metric AE $pic $last null: 2>&1` -eq 0 ]; then
    rm $pic
  else
    last=$pic count=0
  fi
done

# Rejoin the columns and return the de-pixelated image...
magick $tmp/cols_*.mpc +append "$2"

# not realy needed, but lets clean up anyway
rm -f $tmp/cols_*.mpc $tmp/cols_*.cache
rm -rf $tmp