Simple image conversion script design create from a double density asset both @2x and @1x versions of said image in JPEG, JPEG2000, WebP for HTML5 picture elements.

imageconversion.sh

# simple image conversion script design create from a double density asset both @2x and @1x versions of said image in JPEG, JPEG2000, WebP for HTML5 picture elements.
# Requires Zenity, ImageMagick with JPEG2000, MozJPEG, and Webp
# brew install imagemagick --with-openjpeg
# brew install webp
# brew install mozjpeg
# brew install zenity
      
file=$(zenity --file-selection --title="Select a File")

datafill=`zenity --forms \
         --title="Example" \
         --add-entry="Select WebP Quality" \
         --add-entry="Select JPEG2000 Quality"  \
         --add-entry="Select JPEG Quality"  \
      --separator="|"`
echo $datafill


arrIN=(${datafill//|/ })
JPEG2000quality=${arrIN[0]}
WebPquality=${arrIN[1]}
JPEGquality=${arrIN[2]}

echo $file
# vars for use later
webpExt=".webp"
jp2Ext=".jp2"
jpgExt=".jpg"
ppmExt=".ppm"
pngExt=".png"
twoX="@2x"
oneX="@1x"

# make half size PNG path name, create a 1x PNG.
halfsizeFile="${file%.*}"$oneX$pngExt
echo $halfsizeFile
convert  $file -resize 50%  $halfsizeFile

# webp
convert $file   -quality $WebPquality "${file%.*}"$twoX$webpExt
convert $halfsizeFile -quality $WebPquality "${file%.png}"$oneX$webpExt

# jpeg2000
convert $file    -quality $JPEG2000quality "${file%.*}"$twoX$jp2Ext
convert $halfsizeFile  -quality $JPEG2000quality "${file%.*}"$oneX$jp2Ext

# ppm temp for MozJPEG
ppm2x="${file%.*}"$twoX$ppmExt
convert $file  $ppm2x
ppm1x="${file%.*}"$oneX$ppmExt
convert $halfsizeFile  $ppm1x

# jpeg (MozJPEG)
cjpeg -quality $JPEGquality $ppm2x > ${ppm2x%.ppm}$twoX$jpgExt
cjpeg -quality $JPEGquality $ppm1x > ${ppm1x%.ppm}$oneX$jpgExt

# remove temp ppm
rm  $ppm2x
rm  $ppm1x