Pixel sort with mix and inverse

# Takes 2 arguments:
# $1 is the original filename
# $2 is the field to order:
#     1 r
#     2 g
#     3 b
#     4 r + g + b

# Example:
# sh sort.sh me.jpg 4

# We first need an uncompressed ppm
convert $1 -compress none image.ppm

# take data and put in one column
cat image.ppm | tail -n+4 | sed 's/ /\n/g' | sed '/^$/d' > 1-column.ppm

# invert colors
# the sed part adds "255-" before each lines
# bc calculates it
cat 1-column.ppm | sed 's/^/255-/g' | bc > 1-column-inverse.ppm

# organise data in 3 columns (r,g,b)
cat 1-column-inverse.ppm | paste -d\  - - - > 3-columns.ppm

# calculate the sum of every (r,g,b) values
cat 3-columns.ppm | sed 's/ /+/g' | bc > sums.ppm

# join (r,g,b) columns with sum column
paste -d\  3-columns.ppm sums.ppm > 4-columns.ppm

# order by given field ($2) and take back only (r,g,b) values
cat 4-columns.ppm | sort -k$2,$2nr | cut -d" " -f1,2,3 > sorted.ppm

# Create a mix of sorted and not sorted
# Just discovered the epicness of awk
paste -d\  sorted.ppm 3-columns.ppm | awk \
'BEGIN {FS = " "}
{
    if(NR %2 == 0){ 
        print $1,$2,$3;
    }
    else{
        print $4,$5,$6;
    }
}' > mix.ppm

#cat final.ppm | awk 'NR %2 == 0: '

# create identical header with first 3 lines
cat image.ppm | head -n 3 > final.ppm

# put sorted data in the file
cat mix.ppm >> final.ppm

# create jpg version
convert final.ppm final.jpg

# put original and result side by side (montage)
montage image.ppm final.ppm montage.jpg

# remove temporary files
rm 3-columns.ppm 4-columns.ppm sums.ppm

# display montage or final image
# display montage.jpg
display final.jpg