1xscreenshot.sh

# the path where screenshots to save
SS_PATH="/tmp"
# if you want to save them to your desktop, SS_PATH should be "/Users/YOURNAME/Desktop"
 
# a variable of unix timestamp for screenshot file name
NOW=$(date +%s)
 
# execute screen capture command, screenshot$NOW.png is the name of file
screencapture -i -r $SS_PATH/screenshot$NOW@2X.png
 
# then downscale the high resolution screenshot to 50% by imagemagick
# /usr/local/bin/convert $SS_PATH/screenshot$NOW@2X.png -resize 50% $SS_PATH/screenshot$NOW@1X.png
 
# check if screenshot is existing
if [ -f $SS_PATH/screenshot$NOW@2X.png ]; then
    # get the 50% width of screenshot by sips
    WIDTH=$(($(sips -g pixelWidth $SS_PATH/screenshot$NOW@2X.png | cut -s -d ':' -f 2 | cut -c 2-)/2))
    # scale down by sips
    sips --resampleWidth $WIDTH $SS_PATH/screenshot$NOW@2X.png --out $SS_PATH/screenshot$NOW@1X.png
    # rm orginal pic file
    rm $SS_PATH/screenshot$NOW@2X.png
    # copy small one to clipboard by applescript
    osascript -e 'set the clipboard to POSIX file "'$SS_PATH/screenshot$NOW@1X.png'"'
fi