ImageMagick extend canvas with transparent background

Question

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 · Accepted Answer · 2018-03-16T18:08:09.473

111

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]).

edited Mar 16 '18 at 18:08

answered Aug 29 '12 at 21:25

Kurt Pfeifle

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Indeed the order is important, and you got it wrong! You need to put -gravity before -extent, or it will have no effect. Try -gravity SouthEast to see what I mean. – Joshua Smith May 03 '13 at 19:15
2

@jesmith: Thanks for the hint. – Kurt Pfeifle Feb 04 '14 at 18:59
@noɥʇʎPʎzɐɹC: Thx -- fixed. – Kurt Pfeifle Nov 23 '16 at 22:24

score 9 · Answer 2 · answered Jan 31 '14 at 15:05

9

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

answered Jan 31 '14 at 15:05

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

ImageMagick extend canvas with transparent background

2 Answers2