What parameters does "convert" (?) need to get this OUTPUT from this INPUT?


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enter image description here

4 Answers 4


As I didn't want the images flush with the right side, I had to use a different approach (ImageMagick's composite tool):

convert -size 500x500 xc:white canvas.png
convert canvas.png in.png -geometry +200+200 -composite out.png

-size should be the final image size you want, canvas.png is a blank white canvas, in.png would be the image you want to pad, and -geometry is the positioning offset.


My ImageMagick version is '6.7.8-0 2012-07-04 Q16'. According to the docu the answer of @kev command should work:

 convert in.png -gravity east -extent 520x352 out.png

However, like with most ImageMagick questions, you can achieve the same goal with different means. You could use montage like this:

 montage null: in.png -tile 2x1 -geometry +17+0 out1.png

This uses the special 'null:' image to concatenate it with the in.png.

It is true that with convert you need to re-compute the values you need to pass to -extent for each input picture that's got a different size.

First use identify -format to get the dimensions of the image:

 identify -format '%Wx%H' in.png

This should return something like:


Ok, now you would need to add your wanted 71 pixels, to get the final 520x352 value. But you don't need to do that calculation in your own brains:

ImageMagick to the rescue!, and its magic calculation capabilities... :-)

You can tell the identify -format command to do that calculation for you:

 identify -format '%[fx:W+71]x%H'

This should now give you a result of:


So assuming you want to just pad/add a 'white strip' of 71 pixels width to the left of any picture, you can use the following single commandline:

 convert \
    in.png \
   -gravity east \
   -background white \
   -extent $(identify -format '%[fx:W+71]x%H' in.png) \

Voila! One commandline (which encapsulates 2 commands, to be honest) and you can let this one loose on all your PNGs, JPEGs, GIFs,... in a directory to auto-magickally add your 71pixels white strip to each of them:

 for i in *.png *.jpeg *jpg *.gif; do
    convert \
       ${i} \
      -gravity east \
      -background white \
      -extent $(identify -format '%[fx:W+71]x%H' ${i}) \
       $(convert ${i} -format "71-pixels-padded-left---%t.%e" info:)

For each image its output remains the same filetype. Of course you can enforce all output to be PNG (or whatever you want). Just replace the %t.%e part of the command with %t.png...


Documentation: http://www.imagemagick.org/Usage/crop/#extent

convert in.png -gravity east -extent 500x352 out.png
  • Thanks!! But what if my picture is not 500x352 - because the size varies? Jul 3, 2012 at 22:44
  • 1
    I just show you how to.
    – kev
    Jul 3, 2012 at 22:58
  • @kev: Your command doesn't exactly do what @gasko peter wanted. You should have used -extend 520x352. +1 for the 'right direction' though :-P Jul 9, 2012 at 18:45
  • sed 's#-extend#-extent#g' Aug 6, 2012 at 20:15
  • I had to add -background transparent to preserve a transparent background.
    – tremby
    Jul 4, 2016 at 23:27

I have this command defined in my .bash_profile. It will automatically compute the final image size from the padding you want in width and height (works with zeros):

# arithmetic with awk
calc() { awk "BEGIN { print $* }"; }

# pad an image
img_pad() {
    local width height pw ph 
    [ $# -lt 3 ] && { echo "Usage: img_pad <Input> <WxH> <Output>"; return; }

    # parse current size and padding
    IFS=x read width height <<< "$(identify "$1" | awk '{print $3}')"
    IFS=x read pw ph <<< "$2"

    # new widht and height
    width=$(calc "$width + 2*$pw")
    height=$(calc "$height + 2*$ph")

    echo "Converting '$1' to '$3' with size ${width}x${height} (+w=${pw}, +h=${ph})."
    convert "$1" -gravity center -extent "${width}x${height}" "$3"

Example usage:

# pad 50px left and right, no vertical padding
img_pad in.png 50x0 out.png 

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