### Sage does not see Imagemagick

I am trying out the animation thing in http://doc.sagemath.org/html/en/reference/plotting/sage/plot/animate.html.

But Sage keep saying

```
Error: Neither ImageMagick nor ffmpeg appears to be installed.
```

And indeed

```
from sage.misc.sage_ostools import have_program
have_program('convert')
```

returns false.

But I do have ImageMagick installed by homwbrew.
i.e. it works perfectly in Terminal.

What Could Possibly Go Wrong?

(macOS 10.13; Sage 8.3; Imagemagick 7.0.8.)