Converting a data URL (aka data URI) to an image on the commandline (Mac OS X)

This is trivial, but was awfully hard to find via Google Search. Eventually had to give up and actually think about it. :-)

So, a data-URI looks something like the following:

data:image/png;base64,[and a stream of base64 characters here]

The part after the comma is literally the contents of the file (image or whatever), encoded in base64, so all you need to do is run base64 --decode on that part.

For example, with the whole data URL copied to the clipboard, I can do:

pbpaste | sed -e 's#data:image/png;base64,##' | base64 --decode > out.png

to get it into a png file.

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Using Stellarium to make an animation / video

(I don’t have a solution yet.)

I just wanted to show what the sky looks like over the course of a week.

On a Mac with Stellarium installed, I ran the following

/Applications/Stellarium.app/Contents/MacOS/stellarium --startup-script stellarium.ssc

with the following stellarium.ssc:

// -*- mode: javascript -*-
core.clear('natural');  // "atmosphere, landscape, no lines, labels or markers"
core.wait(5);
core.setObserverLocation('Ujjain, India');
core.setDate('1986-08-15T05:30:00', 'utc');
core.wait(5);
for (var i = 0; i < 2 * 24 * 7; i += 1) {
    core.setDate('+30 minutes');
    core.wait(0.5);
    core.screenshot('uj');
    core.wait(0.5);
}
core.wait(10);
core.quitStellarium();

It took a while (some 10–15 minutes) and created those 336 images in ~/Pictures/Stellarium/uj*, occupying a total size of about 550 MB. This seems a start, but Imagemagick etc. seem to choke on creating a GIF from such large data.

Giving up for now; would like to come back in future and figure out something better, that results in a smaller GIF.