Re: Compressed image without NDPluginCodec

[Érico Nogueira Rolim via Tech-talk <tech-talk at aps.anl.gov>]

On 2/14/26 01:57, Michael Davidsaver via Tech-talk wrote:

On 2/13/26 12:29 PM, Nariyoshi, Pedro via Tech-talk wrote:

Hello all,

I have been trying to create a records to display an image on a CS-Studio Phoebus screen. The problem is that transmitting the waveforms directly is quite bandwidth intensive. For our cameras, we tend to use NDPluginCodec with NDPluginPva, which works fairly well, but I would like to avoid having to write some glue code to send the waveforms to a dummy asynNDArrayDriver. I have been trying (without much success) to do it. I have tried creating a json to load via dbLoadGroup and via p4p, but as soon as I set the codec to jpeg and try to send compressed data, everything stops working:

Mark Rivers has recently done some work with the new NDPluginPvx and compression, which may be relevant.

 nt.wrap doesn't like the compressed data,

Correct, so far.  I would be interested if someone had time to look at adding support to P4P.  Identifying python libraries implementing the various compression algorithms would be step one.

For P4P, would the library then be able to handle compression transparently (à la libhdf5)?

Do you think PVXS would ever support such a mechanism, or would it remain a lower level tool and simply forward already compressed buffers and compression metadata?

 and I am having trouble getting the json to have a structure that Phoebus will recognize.

The best I can point to now is this example from PVXS

https ://github.com/epics-base/pvxs/blob/master/test/image.db

the equivalent for dbLoadGroup

https ://github.com/epics-base/pvxs/blob/master/test/image.json

The dummy "QSRV2_image_demo" pixels array used by this example comes from

https ://github.com/epics-base/pvxs/blob/master/ioc/imagedemo.c

 Does anyone have experience with this? Or maybe a suggestion on how to get compressed data to display on Phoebus screens?

Best regards,

Pedro Nariyoshi Software Controls Engineer Facility for Rare Isotope Beams Michigan State University 640 South Shaw Lane East Lansing, MI 48824, USA Tel. 517-908-7352 Email: nariyosh at frib.msu.edu

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