-fx can not be used for windows ?

[linjuming]

-fx can not be used for windows ?

[Bonzo]

It will work but I think you need to change the ' ' to " " and in so your case \"( r+g+b )/3\"

In your error output you have a back tick and a ' but in your code you just have '

[anthony]

For differences between the UNIX shell CLI and Windows DOS CLI see
http://www.imagemagick.org/Usage/windows/#dos

Also watch out for the "Convert Issue"
http://www.imagemagick.org/Usage/windows/#convert_issue

[linjuming]

thank you !!