ImageMagick: resize the image without scaling it

Question

I have an image example.png, which is 50x50 pixels, mostly transparent and some black shape. What I want to achieve with imagemagick is, create a new image, example_output.png, which would be 100x100 pixels with transparent background and original 50x50 image in the center. Is this doable? How?

Answer 1

Check out the extent operation:

convert example.png -gravity center -background none -extent 200%x example_output.png

Answer 2

If you have a 100x100 transparent image already, you can do this:

convert 100x100.png 50x50.png -geometry +25+25 -composite x.png

Otherwise, create the 100x100 first, then add the original:

convert -size 100x100 xc:none 100x100.png
convert 100x100.png 50x50.png -geometry +25+25 -composite x.png