ImageMagick change image width and height

Question

I am using ImageMagick to resize image resolution by using below command-line option

convert abc.png -set units PixelsPerInch -density 75 abc_a.png

I am in need of this: if any images has more than 300 width OR more than 100 height, I want to convert it to width 300 width and 100 height, with changing above dpi (i.e. 75dpi).

Can any one help me on this?

Mark Setchell Mark Setchell · Accepted Answer · 2014-10-25T08:30:49

If you are on Linux/OSX, you can get the image dimensions like this:

identify -format "%w %h" input.jpg

So, if you want the width and height in variables w and h, do this:

read w h < <(identify -format "%w %h" input.jpg)

Now you can test the width and height and do further processing if necessary:

[ $w -gt 300 -o $h -gt 100 ] && convert input.jpg -set units ...

Or, if you want to be more verbose:

if [ $w -gt 300 -o $h -gt 100 ]; then
    convert ...
fi

So, the total solution I am proposing looks like this:

#!/usr/bin/bash
read w h < <(identify -format "%w %h" input.jpg)
[ $w -gt 300 -o $h -gt 100 ] && convert input.jpg -set units ...

JPEG or PNG makes no difference, so just replace my JPG with PNG if that is the format of your choice.

Updated for Windows

Ok, no-one else is helping so I will get out my (very) rusty Windows skills. Get the image width something like this under Windows:

identify -format "%w" input.png > w.txt
set /p w=<w.txt

Now get the height:

identify -format "%h" input.png > h.txt
set /p h=<h.txt

You should now have the width and height of image input.png in 2 variables, w and h, check by typing

echo %w%
echo %h%

Now you need to do some IF statements:

if %w% LEQ 300 GOTO SKIP
if %h% LEQ 100 GOTO SKIP
convert ....
:SKIP

Note:: You may need ^ in front of the percent sign in Windows.

Note: You may need double @ signs in scripts because Windows is illogical.

ImageMagick change image width and height

2 Answers