resize.sh

#!/bin/bash

# Edit the settings below:

# Output sizes - 
# Please note the format: each size is wrapped with quotes, width and height are separated with space.
output=("800 600" "1024 768" "1152 864" "1280 960" "1280 1024" "1400 1050" "1440 960" "1600 1200" "1920 1440" "1024 600" "1366 768" "1440 900" "1600 900" "1680 1050" "1280 800" "1920 1080" "1920 1200" "2560 1440" "2560 1600" "2880 1800")

# If you frequently use the same source file (f.e. "~/Desktop/src.jpg"), 
# set it in "default_src"
default_src="src.jpg";

# If you frequently use the same destination
# (f.e. "~/Desktop/Some_folder/%.jpg"), set it in "default_dst"
# Destination must include "%", it will be replaced by output size, f.e. "800x600"
default_dst="%.jpg";

# Add signature? 
default_sign='y'

# If you frequently use the same signature file (f.e. "~/Desktop/sig.png"), 
# set it in "default_sig"
default_sig="sig.png";

# Gravity is for cropping left/right edges for different proportions (center, east, west)
default_gravity="center"

# Output JPG quality: maximum is 100 (recommended)
quality=100

# ======
# Do not edit below.
# ======
# Welcome to Smashing resizer!
# Written by Vlad Gerasimov from http://www.vladstudio.com
# 
# This script takes one "source" image and saves it in different sizes.
# 
# Requires:
# * imagemagick - http://www.imagemagick.org/
# * python - I'm sure your PC already has it!



# Unfortunately, bash is awful at math operations.
# We'll create a simple function that handles math for us.
# Example: $(math 2 * 2)

function math(){
	echo $(python -c "from __future__ import division; print $@")
}



# To make our script short and nice, here is the "save()" function.
# We'll use it to save each size.

function save(){

	# read target width and height from function parameters
	local dst_w=${1}
	local dst_h=${2}

	# calculate ratio 
	local ratio=$(math $dst_w/$dst_h);

	# calculate "intermediate" width and height
	local inter_w=$(math "int(round($src_h*$ratio))")
	local inter_h=${src_h}

	# which size we're saving now
	local size="${dst_w}x${dst_h}"
	echo "Saving ${size}..."

	#crop intermediate image (with target ratio)
	convert ${src} -gravity ${gravity} -crop ${inter_w}x${inter_h}+0+0 +repage temp.psd

	# apply signature
	if [ "${sign}" == "y" ]; then
	convert temp.psd ${sig} -gravity southeast -geometry ${sig_w}x${sig_h}+24+48 -composite temp.psd
	fi

	## For best quality, I resize image 80%, sharpen 3 times, then repeat.

	# setup resize filter and unsharp parameters (calculated through trial and error)
	local arguments="-interpolate bicubic -filter Lagrange"
	local unsharp="-unsharp 0.4x0.4+0.4+0.008"

	# scale 80%, sharpen, repeat until less than 150% of target size
	local current_w=${dst_w}

	# pardon moi for such ugly while condition!
	while [ $(math "${current_w}/${dst_w} > 1.5") = "True" ]; do
		current_w=$(math ${current_w}\*0\.80)
		current_w=$(math "int(round(${current_w}))")
		arguments="${arguments} -resize 80% +repage ${unsharp} ${unsharp} ${unsharp} "
	done

	# final resize
	arguments="${arguments} -resize ${dst_w}x${dst_h}! +repage ${unsharp} ${unsharp} ${unsharp} -density 72x72 +repage"

	# final convert! resize, sharpen, save
	convert temp.psd ${arguments} -quality ${quality} ${dst/\%/${size}}

}

# Ask for source image, or use default value
echo "Enter path to source image, or hit Enter to keep default value (${default_src}): "
read src
src=${src:-${default_src}}

# ask for destination path, or use default value
echo "Enter destination path, or hit Enter to keep default value (${default_dst})."
echo "must include % symbol, it will be replaced by output size, f.e. '800x600'"
read dst
dst=${dst:-${default_dst}}

# Ask for signature image, or use default value
echo "Apply signature? (hit Enter for 'yes' or type 'n' for 'no') "
read sign
sign=${sign:-${default_sign}}

# Ask for signature image, or use default value
echo "Enter path to signature image, or hit Enter to keep default value (${default_sig}): "
read sig
sig=${sig:-${default_sig}}

# ask for gravity, or use default value
echo "Enter gravity for cropping left/right edges (center, east, west), or hit Enter to keep default value (${default_gravity}): "
read gravity
gravity=${gravity:-${default_gravity}}


# detect source image width and height
src_w=$(identify -format "%w" "${src}")
src_h=$(identify -format "%h" "${src}")

# detect signature width and height
if [ "${sign}" == "y" ]; then
	sig_w=$(identify -format "%w" "${sig}")
	sig_h=$(identify -format "%h" "${sig}")
fi

# loop throught output sizes and save each size
for i in "${output[@]}"
do
	save ${i}
done

# Delete temporary file
rm temp.psd

# Done!
echo "Done!"