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convert input.png -extent 100x100 -gravity center -background white output.png

If the input is 50x50 the surrounding background is white. Can I somehow set this to transparent without declaring any color within input as transparent?

Kurt Pfeifle
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Toby
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2 Answers2

128

Use this instead:

convert               \
      input.png       \
     -background none \
     -gravity center  \
     -extent 100x100  \
      output.png

Note well: The order of the parameters is significant! (To convince yourself, just put -background none at the end of the parameters instead of the start...)

Updated: Thanks to @jesmith who noticed that the commandline I originally provided does no longer work as intended. More recent versions of convert additionally require that the -gravity center is called before -extent 100x100. (This was one of the changes introduced to one ImageMagick's most recent versions [at the time of originally writing this answer]).

Kurt Pfeifle
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10

Kurt's note is ironically spot on, order matters greatly. Kurt's command results in gravity not being applied to the extent, so the transparent 'border' will all be to the bottom and/or right of the image.

Moving gravity before extent will correctly create equal transparent 'borders' on all applicable sides.

convert input.jpg -background none -gravity Center -extent 100x50 output.png

eprothro
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  • **+1** and thanks for your additional answer pointing out the now required command line order for `-gravity center`. I hadn't seen it, nor @jesmith's comment earlier, though he had pointed it out already in May '13. – Kurt Pfeifle Feb 04 '14 at 19:27