[Matplotlib-users] How to create an animation of complicated figures without writing each image to file

Thomas Caswell tcaswell at gmail.com
Thu May 31 09:19:45 EDT 2018

I do not know of a vector-based movie format, I think you have to rasterize
at _some_ point.  Try increasing the dpi or adjusting the encoding
parameters /  of ffmpeg (the defaults are not great for plots iirc).

`to_jshtml` writes out movie file and then wraps it in minimal js player.


On Thu, May 31, 2018 at 9:14 AM David Ketcheson <dketch at gmail.com> wrote:

> Thanks for your help!  My replies are interspersed below.
> On Thu, May 31, 2018 at 3:38 PM, Thomas Caswell <tcaswell at gmail.com>
> wrote:
>> If you have no control over the plotting functions, can not update the
>> artists in place, or just have a sequence of Figure objects, the best
>> approach is probably to so save each frame to png and then use an external
>> program to (eg ffmpeg) stitch them together.  Make sure that you are not
>> using `bbox_inches='tight'`, tight_layour, or contrained layout (so every
>> saved figure is the same size and the axes are in the same place).
> That's what I've been doing, but as I mentioned in my first message, the
> output isn't what I want -- there are visible artifacts in the resulting
> movie.  Is there a way to do this without going to a rasterized graphics
> format?
>> If you can re-use the same `Figure` object you can directly use the
>> Writer classes is `matplotlib.animation`, see
>> https://matplotlib.org/api/animation_api.html?highlight=animation#writer-classes .
>> Those instances are bound to a particular Figure, you _may_ be able to just
>> re-set the figure (but not sure what other state we hold based on the
>> initial figure that might need to be updated as well), at a minimum they
>> should be a good starting point to write your self a "concatenate a list of
>> figures into a movie" writer.
> I don't want to write a movie file; my goal is to end up with a
> JSAnimation-style output (i.e., what you get from anim.to_jshtml()).  I
> don't see a writer class for that.
>> On Thu, May 31, 2018 at 4:57 AM David Ketcheson <
>> david.ketcheson at kaust.edu.sa> wrote:
>>> I would like to create an animation from a very complicated plot.  The
>>> plot is created by a lot of functions and it's not feasible for me to pass
>>> back the handles to all the objects that get added to the plot from all of
>>> those functions.  One approach that works is to write each plot to a file
>>> and then create an animation by loading the images.  Unfortunately, this
>>> doesn't look good, presumably because the images are first rasterized and
>>> then the resolution is altered.
>>> So I'd like to create an animation directly from a set of figures, when
>>> all I have are the figures.  I've tried to use get_children() recursively
>>> to get all the artists and then use animation.ArtistAnimation(), but so
>>> far this only leads to an empty (blank) animation.  Is it possible to do
>>> what I'm attempting?
>>> -David
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