This took me way too long to find out, so I thought I’d blog here and hopefully save someone else some time.
ImageMagick is a great swiss-army-knife type tool, with a shed-load of options for converting and combining images. Unfortunately, the sheer number of options can make it a bit time-consuming and frustrating trying to find the one you want.
My aim was simple: given a PNG, make the whole thing semi-transparent.
Searching Google using “transparent” and “opacity” drew a blank – all I got was instructions on how to set transparency for certain colours – not what I wanted to do.
The word I was missing was “alpha”, and the magic incantation for changing the opacity of the whole image is:
convert input.png -channel Alpha -evaluate Divide 2 output.png
In my case, I wanted to set the PNG to be 50% transparent (hence “Divide 2″.) Of course, you can change that number to whatever works for you.
thanks, man
you saved my day
Thanks man yr one blog post solved my problem. Thank you for sharing
helped me! thanks.
Thank you!
A quick fix for my problem as well.
Big thx.
Thanks, that was really helpful.
Big thx for the tip
That’s cool! I wonder how much time I would have spent
Thanks so much for having this on the web. I was going crazy trying to do a simple opacity change and was stuck in ImageMagicK syntax hell.
Thanks heaps for posting this. Lifesaver!!!
Another “thanks a lot” up here.
Also, you can say the same with “convert input.png -channel Alpha -evaluate Set 50% output.png”.