#!/bin/bash
# 
# Developed by Fred Weinhaus 6/1/2009 .......... revised 4/25/2015
#
# ------------------------------------------------------------------------------
# 
# Licensing:
# 
# Copyright © Fred Weinhaus
# 
# My scripts are available free of charge for non-commercial use, ONLY.
# 
# For use of my scripts in commercial (for-profit) environments or 
# non-free applications, please contact me (Fred Weinhaus) for 
# licensing arrangements. My email address is fmw at alink dot net.
# 
# If you: 1) redistribute, 2) incorporate any of these scripts into other 
# free applications or 3) reprogram them in another scripting language, 
# then you must contact me for permission, especially if the result might 
# be used in a commercial or for-profit environment.
# 
# My scripts are also subject, in a subordinate manner, to the ImageMagick 
# license, which can be found at: http://www.imagemagick.org/script/license.php
# 
# ------------------------------------------------------------------------------
#
# USAGE: exposure -a amount infile outfile
# USAGE: exposure [-h or -help]
#
# OPTIONS:
#
# -a amount       amount of exposure change in percent; -100<=amount<=100;
#                 positive will be brighter and negative will be darker; 
#                 default=0 (no change)
#
###
#
# NAME: EXPOSURE 
# 
# PURPOSE: To change the exposure level of an image.
# 
# DESCRIPTION: EXPOSURE changes the exposure level of an image to make  
# it either brighter or darker. It uses -level 0x(100-amount)% to make 
# it brighter and +level 0x(100+amount)% to make it darker.
# 
# OPTIONS: 
#
# -a amount ...  AMOUNT of exposure change in percent. Values are floats 
# between -100 and 100. Positive values increase exposure (make it brighter) 
# and negative values decrease exposure (make it darker darker). The default 
# is zero or no change.
# 
# NOTE: This script requires IM 6.4.2-0 or higher due to the use of 
# +level, if making the image darker.
#
# CAVEAT: No guarantee that this script will work on all platforms, 
# nor that trapping of inconsistent parameters is complete and 
# foolproof. Use At Your Own Risk. 
# 
######
#

# set default values
amount=0

# set directory for temporary files
dir="."    # suggestions are dir="." or dir="/tmp"

# set up functions to report Usage and Usage with Description
PROGNAME=`type $0 | awk '{print $3}'`  # search for executable on path
PROGDIR=`dirname $PROGNAME`            # extract directory of program
PROGNAME=`basename $PROGNAME`          # base name of program
usage1() 
	{
	echo >&2 ""
	echo >&2 "$PROGNAME:" "$@"
	sed >&2 -e '1,/^####/d;  /^###/g;  /^#/!q;  s/^#//;  s/^ //;  4,$p' "$PROGDIR/$PROGNAME"
	}
usage2() 
	{
	echo >&2 ""
	echo >&2 "$PROGNAME:" "$@"
	sed >&2 -e '1,/^####/d;  /^######/g;  /^#/!q;  s/^#*//;  s/^ //;  4,$p' "$PROGDIR/$PROGNAME"
	}


# function to report error messages
errMsg()
	{
	echo ""
	echo $1
	echo ""
	usage1
	exit 1
	}


# function to test for minus at start of value of second part of option 1 or 2
checkMinus()
	{
	test=`echo "$1" | grep -c '^-.*$'`   # returns 1 if match; 0 otherwise
    [ $test -eq 1 ] && errMsg "$errorMsg"
	}

# test for correct number of arguments and get values
if [ $# -eq 0 ]
	then
	# help information
   echo ""
   usage2
   exit 0
elif [ $# -gt 4 ]
	then
	errMsg "--- TOO MANY ARGUMENTS WERE PROVIDED ---"
else
	while [ $# -gt 0 ]
		do
			# get parameter values
			case "$1" in
		  -h|-help)    # help information
					   echo ""
					   usage2
					   exit 0
					   ;;
				-a)    # get amount
					   shift  # to get the next parameter
					   # test if parameter starts with minus sign 
					   #errorMsg="--- INVALID AMOUNT SPECIFICATION ---"
					   #checkMinus "$1"
					   amount=`expr "$1" : '\([-.0-9]*\)'`
					   [ "$amount" = "" ] && errMsg "--- AMOUNT=$amount MUST BE A FLOAT ---"
					   amounttestA=`echo "$amount < -100" | bc`
					   amounttestB=`echo "$amount > 100" | bc`
					   [ $amounttestA -eq 1 -o $amounttestB -eq 1 ] && errMsg "--- AMOUNT=$amount MUST BE A FLOAT BETWEEN -100 AND 100 ---"
					   ;;
				 -)    # STDIN and end of arguments
					   break
					   ;;
				-*)    # any other - argument
					   errMsg "--- UNKNOWN OPTION ---"
					   ;;
		     	 *)    # end of arguments
					   break
					   ;;
			esac
			shift   # next option
	done
	#
	# get infile and outfile
	infile="$1"
	outfile="$2"
fi

# test that infile provided
[ "$infile" = "" ] && errMsg "--- NO INFILE FILE SPECIFIED ---"

# test that outfile provided
[ "$outfile" = "" ] && errMsg "--- NO OUTPUT FILE SPECIFIED ---"

tmpA1="$dir/exposure_A_$$.mpc"
tmpA2="$dir/exposure_A_$$.cache"
trap "rm -f $tmpA1 $tmpA2;" 0
trap "rm -f $tmpA1 $tmpA2; exit 1" 1 2 3 15
trap "rm -f $tmpA1 $tmpA2; exit 1" ERR

# read the input image into the TMP cached image.
convert -quiet "$infile" +repage "$tmpA1" ||
	errMsg "--- FILE $infile NOT READABLE OR HAS ZERO SIZE ---"

# get IM version
im_version=`convert -list configure | \
	sed '/^LIB_VERSION_NUMBER */!d; s//,/;  s/,/,0/g;  s/,0*\([0-9][0-9]\)/\1/g' | head -n 1`

# get sign of amount
sign=`convert xc: -format "%[fx:sign($amount)]" info:`

#echo "amount=$amount; sign=$sign"

# test if IM version compatible with +level
[ "$sign" = "-1" -a "$im_version" -lt "06040200" ] && errMsg "--- IM VERSION IS NOT COMPATIBLE WITH +LEVEL ---"


# set up operation
if [ "$amount" = "0" -o "$amount" = "0.0" ]; then
	operation=""
elif [ "$sign" = "1" -o "$sign" = "+1" ]; then
	amount=`convert xc: -format "%[fx:100-$amount]" info:`
	operation="-level 0%x${amount}%"
elif [ "$sign" = "-1" ]; then
	amount=`convert xc: -format "%[fx:100+$amount]" info:`
	operation="+level 0%x${amount}%"
fi

#echo "amount=$amount; operation=$operation"

# process image
convert $tmpA1 $operation "$outfile"

exit 0