fromgreytext.sh

#!/bin/bash
#------------------------------------------------
# A way to send images over thin text-based
# mediums.
#
# This one is "fromgreytext.sh"
# get "togreytext.sh" here: https://pastebin.com/XLFaVVdB
#
# Following the concept of SSTV (Slow Scan TV),
# that images do not need to be perfect or large
# when transmitted over thin mediums, I have made
# This pair of scripts.
#
# The first one, "togreytext.sh" converts an image
# into a small 26-grays grayscale image composed
# of a substitution of letters for numbers in a PGM
# uncompressed image file.
#
# ./togreytext.sh "infile.jpg" 128
#
# This "compressed" PGM can then be sent over LoRa
# or text transmission methods.
#
# Once on the other side, "fromgreytext.sh" can
# be run on the resulting file. It will expand
# the letter back into numbers and set the
# header correctly again.
#
# ./fromgreytext.sh captured.txt>outfile.pgm
#
# That file is then a valid uncompressed PGM
# though grayscale and smaller than the original.
# That PGM can then be converted to your image
# format of choice.
#
# ~HowToPhil 2024/02/21 00:04 EST
#------------------------------------------------

# Put the args in pretty vars
FILE="$1"

# Expand the header into a proper line-returned pgm header
head -n 1 "$FILE" |tr [:space:] "\n"; echo

# Expand the letters into their "clamped" grayscale values
cat "$FILE"|tail -n +1|sed 's/./& /g'\
|sed "s/A/0/g"\
|sed "s/B/10/g"\
|sed "s/C/20/g"\
|sed "s/D/30/g"\
|sed "s/E/40/g"\
|sed "s/F/50/g"\
|sed "s/G/60/g"\
|sed "s/H/70/g"\
|sed "s/I/80/g"\
|sed "s/J/90/g"\
|sed "s/K/100/g"\
|sed "s/L/110/g"\
|sed "s/M/120/g"\
|sed "s/N/130/g"\
|sed "s/O/140/g"\
|sed "s/P/150/g"\
|sed "s/Q/160/g"\
|sed "s/R/170/g"\
|sed "s/S/180/g"\
|sed "s/T/190/g"\
|sed "s/U/200/g"\
|sed "s/V/210/g"\
|sed "s/W/220/g"\
|sed "s/X/230/g"\
|sed "s/Y/240/g"\
|sed "s/Z/255/g"