[libcamera-devel] [PATCH v4] py: cam.py: Provide live graph of request metadata

[Tomi Valkeinen]

Hi,

On 02/02/2023 17:03, Daniel Oakley wrote:
> Metadata is very useful when improving specific camera configurations.
> Currently, there is an argument to display the metadata in text form,
> however this can be hard to visualise and spot changes or patterns over
> time. Therefore this proposed patch adds an argument to display this
> metadata in graph form.
> 
> The metadata graph has 3 optional parameters:
>   - refresh, number of times a second to update the graph
>   - buffer, amount of historic/previous data to show
>   - graphs, number of graphs to split the metadata between
>   - autoscale, whether or not to autoscale the axis so all the data fits
> 
> Displaying the graph does have some performance penalty, however this
> has been mostly mitigated through the refresh parameter. Despite this,
> graphing might not the best of ideas when using the camera to record or
> save data. This is mainly for debugging purposes.
> 
> Suggested-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
> Signed-off-by: Daniel Oakley <daniel.oakley at ideasonboard.com>
> ---
> This is the 4th version of my graph-metadata patch.
> v3: hopefully addressing the issue of there being a lot of additional
> code in the main cam.py which is optional. Most of the code has been
> moved into a cam_metadata_graph.py file, which is imported at the start
> of cam.py (as opposed to importing it twice throughout the code to make
> the GraphDrawer and process the arguments). I have slightly tweaked the
> error handling with the metadata-graph's arguments to catch a division
> by zero error for refresh=0 and added a comment explanation for the
> metadata-graph argument processor.
> v4: I forgot to add the copywrite information to the new file, hopefully
> I did it roughly correct.
> There should, again, be no functional change between V1 and V2 and v3
> 
>   src/py/cam/cam.py                |  22 +++
>   src/py/cam/cam_metadata_graph.py | 236 +++++++++++++++++++++++++++++++
>   2 files changed, 258 insertions(+)
>   create mode 100644 src/py/cam/cam_metadata_graph.py

What HW and OS did you use to test this?

I tried with RPi OS, and after installing lots of stuff and finally getting libcamera compiling on the device, I got:

Traceback (most recent call last):
   File "/home/tomba/nfs/libcamera/./src/py/cam/cam.py", line 253, in event_handler
     self.__request_handler(ctx, req)
   File "/home/tomba/nfs/libcamera/./src/py/cam/cam.py", line 284, in __request_handler
     ctx.graph_drawer.update_graph(ts, req.metadata)
   File "/home/tomba/nfs/libcamera/src/py/cam/cam_metadata_graph.py", line 81, in update_graph
     self.__animate()
   File "/home/tomba/nfs/libcamera/src/py/cam/cam_metadata_graph.py", line 169, in __animate
     self.blit_manager.update()
   File "/home/tomba/nfs/libcamera/src/py/cam/cam_metadata_graph.py", line 206, in update
     self.on_draw(None)
   File "/home/tomba/nfs/libcamera/src/py/cam/cam_metadata_graph.py", line 189, in on_draw
     self._draw_animated()
   File "/home/tomba/nfs/libcamera/src/py/cam/cam_metadata_graph.py", line 200, in _draw_animated
     fig.draw_artist(a)
   File "/usr/lib/python3/dist-packages/matplotlib/figure.py", line 1879, in draw_artist
     raise AttributeError("draw_artist can only be used after an "
AttributeError: draw_artist can only be used after an initial draw which caches the renderer

I'm still trying to get pyqt and matplotlib working on my buildroot...

While I don't yet quite know how this behaves and looks like, I do wonder if this
is something that would be better done with a separate script. We already have
--save-frames option, we could add --save-metadata. And use matplotlib to show that
data, possibly on a separate device (I'm thinking of showing it on my PC, as the dirs
are shared via NFS).

  Tomi