The Sinclair QL Forum

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#! /bin/bash

INFILE="$1"
OUTFILE="$2"

CONVERTED=`magick "$INFILE" -dither FloydSteinburg -resize 256x256\!  -remap ql-palette.png txt:`

if [ -f "$OUTFILE" ]; then
    rm "$OUTFILE"
fi

y=-1
s=0
hashstring="#"

IFS=$'\n'
for line in $CONVERTED
do
    if [ $y -lt 0 ]; then
        y=$[$y+1]
        continue
    fi

    rest=${line#*$hashstring}
    position=$(( ${#line} - ${#rest} - ${#searchstring} ))

    pixel=${line:$[position]:6}

    if [ $s -eq 0 ]; then
        byte1=0
        byte2=0
    fi

    if [ $[0x$pixel & 0xFF00] -ne 0 ]; then
        byte1=$[($byte1 << 2) | 0x02]
    else
        byte1=$[$byte1 << 2]
    fi

    if [ $[0x$pixel & 0xFF0000] -ne 0 ]; then
        byte2=$[($byte2 << 1) | 0x01]
    else
        byte2=$[$byte2 << 1]
    fi

    if [ $[0x$pixel & 0xFF] -ne 0 ]; then
        byte2=$[($byte2 << 1) | 0x01]
    else
        byte2=$[$byte2 << 1]
    fi

    s=$[$s+1]
    if [ $s -eq 4 ]; then
        byte1out=$(printf "%x" $byte1)
        byte2out=$(printf "%x" $byte2)

        printf "\x$byte1out" >> "$OUTFILE"
        printf "\x$byte2out" >> "$OUTFILE"

        s=0
    fi

done