A strange glitch experiment

degrade.sh

roll() 
{
#  echo "convert ${1} -roll +${2}+${3} $1"
  convert ${1} -roll +${2}+${3} $1
}
roll_h() 
{
  roll $1 $((($RANDOM+1) % $2)) 0
}
roll_v() 
{
  roll $1 0 $((($RANDOM+1) % $2))
}
roll_b()
{

  roll $1 $((($RANDOM+1) % $2)) $((($RANDOM+1) % $3))
}
resize()
{
#  echo "convert $1 -alpha set \( +clone -background $2 $3 \) -gravity center -compose Src -composite $1"
  convert $1 -alpha set \( +clone -background $2 $3 \) -gravity center -compose Src -composite $1
}
rotate()
{
  resize $1 $3 "-rotate $2"
}
skew_h() 
{
   skew $1 $2 0 $3
}
skew_v() 
{
   skew $1 0 $2 $3
}
skew()
{
  resize $1 $4 "-shear ${2}x${3}"
}
FILE=$(basename "$1")

FILENAME="${FILE%.*}"
EXTENSION=${FILE##*.}

DEGRADED_FILE="${FILENAME}_degraded.${EXTENSION}"
WIDTH=$(identify -format "%[fx:w]" $FILE)
HEIGHT=$(identify -format "%[fx:h]" $FILE)
GEO="$WIDTHx$HEIGHT"
TEMP_FILENAME="${FILENAME}-temp"

cp $FILE $DEGRADED_FILE

#echo convert $DEGRADED_FILE -resize 1x1 ${TEMP_FILENAME}-color.${EXTENSION}
convert $DEGRADED_FILE -resize 1x1 ${TEMP_FILENAME}-color.${EXTENSION}
COLOR=$(convert ${TEMP_FILENAME}-color.${EXTENSION} -format '%[pixel:p{1,1}]' info:-)

MAX=1000
DELTA=$(python -c "print 40.0/$MAX")
for VARIABLE in $(seq 1 $MAX);
do
  PREV="${FILENAME}_degraded_prev.jpg"
  cp $DEGRADED_FILE $PREV

#  echo "# Degradation $VARIABLE"
  QUAL=$(python -c "from math import floor; print 81 - long(floor($DELTA * $VARIABLE))")
#  echo "convert $DEGRADED_FILE -quality $QUAL $DEGRADED_FILE"
  convert $DEGRADED_FILE -quality $QUAL $DEGRADED_FILE

  CHOICE=$(($RANDOM % 10))

  if [ $CHOICE == 0 ]; then
#    roll_h $DEGRADED_FILE $WIDTH
#  elif [ $CHOICE == 1 ]; then
#    roll_v $DEGRADED_FILE $HEIGHT
#  elif [ $CHOICE == 2 ]; then
    roll_b $DEGRADED_FILE $HEIGHT $WIDTH
  elif [ $CHOICE == 1 ]; then
    rotate $DEGRADED_FILE $((($RANDOM+1) % 360)) $COLOR
#  elif [ $CHOICE == 5 ]; then
#    rotate $DEGRADED_FILE $((-1 * ($RANDOM+1) % 360)) $COLOR
#  elif [ $CHOICE == 6 ]; then
#    skew_h $DEGRADED_FILE $((($RANDOM+1) % $WIDTH)) $COLOR
#  elif [ $CHOICE == 7 ]; then
#    skew_v $DEGRADED_FILE $((($RANDOM+1) % $HEIGHT)) $COLOR
#  elif [ $CHOICE == 8 ]; then
#    skew $DEGRADED_FILE $((($RANDOM+1) % $WIDTH)) $((($RANDOM+1) % $HEIGHT)) $COLOR
  elif [ $CHOICE == 2 ]; then
    BLEND=$(($RANDOM % 100))
#    echo "composite -blend $BLEND $FILE $DEGRADED_FILE $DEGRADED_FILE"
    composite -blend $BLEND $FILE $DEGRADED_FILE $DEGRADED_FILE
  fi
  
  BLEND=$(($RANDOM % 100))
#  echo "composite -blend $BLEND $PREV $DEGRADED_FILE $DEGRADED_FILE"
  composite -blend $BLEND $PREV $DEGRADED_FILE $DEGRADED_FILE
#  BLEND=$(($RANDOM % 50))
#  echo "composite -blend $BLEND $FILE $DEGRADED_FILE $DEGRADED_FILE"
#  composite -blend $BLEND $FILE $DEGRADED_FILE $DEGRADED_FILE

done
#echo "composite -blend 50 $FILE $DEGRADED_FILE ${FILENAME}_degraded_final.${EXTENSION}"
composite -blend 50 $FILE $DEGRADED_FILE ${FILENAME}_degraded_final.${EXTENSION}