togreytext.sh

#!/bin/bash

#------------------------------------------------
# A way to send images over thin text-based
# mediums.
#
# This one is "togreytext.sh"
# get "fromgreytext.sh" here: https://pastebin.com/eSGZ8ZVD
#
# 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.
#
# ./togreyutext.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 into pretty vars
FILE="$1" #The image file to convert for transmission
SQUARE="$2" #The squared geometry of the sent image

#Preserve the pgm header but convert the line-returns to spaces for compactness
convert "$FILE" -scale $SQUAREx$SQUARE -compress none pgm: |head -n3| tr "\n" " "|sed 's/^[ \t]*//;s/[ \t]*$//';echo

# Convert the image to a scaled-down version.
# Make the image greyscale.
# This will be in uncompressed PGM format.
# Clamp grey values into 26 groups which will
# be represented by upper-case letters.
# Also remove all the spaces after the number-to-letters
# but is done.
# This essentially compresses and compacts the image
# for transmission as text.

convert "$FILE" -scale $SQUAREx$SQUARE -compress none pgm: |sed -e 1,3d\
|sed "s/\b[0-9]\b/A/g" \
|sed "s/\b1[0-9]\b/B/g"\
|sed "s/\b2[0-9]\b/C/g"\
|sed "s/\b3[0-9]\b/D/g"\
|sed "s/\b4[0-9]\b/E/g"\
|sed "s/\b5[0-9]\b/F/g"\
|sed "s/\b6[0-9]\b/G/g"\
|sed "s/\b7[0-9]\b/H/g"\
|sed "s/\b8[0-9]\b/I/g"\
|sed "s/\b9[0-9]\b/J/g"\
|sed "s/\b10[0-9]\b/K/g"\
|sed "s/\b11[0-9]\b/L/g"\
|sed "s/\b12[0-9]\b/M/g"\
|sed "s/\b13[0-9]\b/N/g"\
|sed "s/\b14[0-9]\b/O/g"\
|sed "s/\b15[0-9]\b/P/g"\
|sed "s/\b16[0-9]\b/Q/g"\
|sed "s/\b17[0-9]\b/R/g"\
|sed "s/\b18[0-9]\b/S/g"\
|sed "s/\b19[0-9]\b/T/g"\
|sed "s/\b20[0-9]\b/U/g"\
|sed "s/\b21[0-9]\b/V/g"\
|sed "s/\b22[0-9]\b/W/g"\
|sed "s/\b23[0-9]\b/X/g"\
|sed "s/\b24[0-9]\b/Y/g"\
|sed "s/\b25[0-9]\b/Z/g"\
|sed 's/[[:space:]]//g'