{"componentChunkName":"component---src-templates-blog-post-js","path":"/blog/2008/07/22/tweaking-png-transparency-with-imagemagick/","result":{"data":{"markdownRemark":{"html":"

This took me way too long to find out, so I thought I’d blog here and hopefully save someone else some time.

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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.

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My aim was simple: given a PNG, make the whole thing semi-transparent.

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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.

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The word I was missing was “alpha”, and the magic incantation for changing the opacity of the whole image is:

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convert input.png -channel Alpha -evaluate Divide 2 output.png
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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.

\n","timeToRead":1,"frontmatter":{"title":"Tweaking PNG transparency with ImageMagick","blurb":"A brief article with command-line example using ImageMagick to tweak an image’s transparency","date":"2008-07-22T12:21:32.000Z","modified":"2011-01-03T17:20:14.000Z"}}},"pageContext":{"slug":"/blog/2008/07/22/tweaking-png-transparency-with-imagemagick/","next":{"fields":{"slug":"/blog/2008/08/08/svn-log-message-encoding-problem/"},"frontmatter":{"title":"SVN log message encoding problem"}},"previous":{"fields":{"slug":"/blog/2008/07/21/microformats-dark-data-and-css-part-2/"},"frontmatter":{"title":"Microformats, dark data and CSS - part 2"}}}},"staticQueryHashes":["1192980692"]}