#!/bin/bash -x
# 
# Set yardmarkers A and B within the lookup table. Lookup table runs
# from 0-256. The length of an interval is C.  With each new image,
# one interval in moved along the lookup table.  The total number of
# intervals used (H) must be as close to D (the total number of files)
# as possible, but not more.  Once yardmarker B is reached the
# intervals are counted down. If yardmarker A is reached then
# intervals are counted up. The way between the yardmarkers A and B
# may be repeated G number of times.  When H is reached we must always
# end up within an interval length of yardmarker A. This is necessary
# for looped animations.

z=+
A=64 # position of first yardmarker
B=192 # position of second yardmarker
C=20 # lenght of one interval
D=`ls $1 | wc -l` # the number intervals used must be as close to a multiple of D as possible, without going over
E=1 # Number of the first and later current image
F=`echo "scale=4; ( ( $B - $A ) * 2 ) / $C" | bc` # Number of images processed per trip from A to B and back
G=`echo "scale=0; $D / $F" | bc` # Number of trips between A and B required
                                 # Rounded down to a whole number
H=`echo "scale=0; $F * $G" | bc | awk '{printf "%.0f",$1}'` # Total number images used
I=`expr $A + $C` #end position after the first interval
J=`expr \( $B - $A \) \* 2` #Double the distance traveled between yardmarkers so we will always end 
                            #at the first yardmarker
L=255       # lightness value for generating the rainbow
S=255       # saturation value for generating the rainbow
tmp0="coloration_0_$$.png"
tmp1="coloration_1_$$.png"
tmp2="coloration_2_$$.png"
tmp3="coloration_3_$$.png"
trap "rm -f $tmpB $tmp0 $tmp1 $tmp2 $tmp3 $tmp4; exit 0" 0
trap "rm -f $tmpB $tmp0 $tmp1 $tmp2 $tmp3 $tmp4; exit 1" 1 2 3 15

# create rainbow lut

# create hue channel
convert -size 1x256 gradient: $tmp0

# create saturation channel
convert -size 1x256 xc:"rgb($S,$S,$S)" -channel Green -separate $tmp1

# create lightness channel
convert -size 1x256 xc:"rgb($L,$L,$L)" -channel Blue -separate $tmp2

# combine channels to form rainbow lut
convert $tmp0 -colorspace HSB $tmp0 \
	-compose CopyRed -composite $tmp1 \
	-compose CopyGreen -composite $tmp2 \
	-compose CopyBlue -composite -colorspace RGB \
	-rotate 90 $tmp3
I2=$I
y=$z

# keep track of when to stop processing and the current position on the color lookup table

while [ $E -le $H ]; do
VAR=`printf "%03d" $E`
    if [ $I -ge $B ]; then
	z="-"
# $I is the current position on the lookup table
	I=`expr $B - \( $I - $B \)`
    elif [ $I -le $A ]; then
	z="+"
	I=`expr $A + \( $A - $I \)`
# $I2 is needed so that we'll always end at Yardmarker A
    elif [ $I2 -ge $J ]; then
	y="-"
	I2=`expr $J - \( $I2 - $J \)`
    elif [ $I2 -le $A ]; then
	y="+"
	I2=`expr $A + \( $A - $I \)`
    fi

# color the grayscale images with the color lookup table
    convert $1/$VAR.png \( $tmp3 -roll -$I+0 \) -clut $VAR.png

    I=`expr $I $z $C`
    I2=`expr $I2 $y $C`
    let E=$E+1
done