More on using the SPC900

[JamesF]

I've posted a few times recently on what I've discovered about the way the SPC900 works based on my reading of the Linux drivers. I've now pulled all of that information together here:

Notes on Using the SPC900NC for Planetary Imaging | www.tanstaafl.co.uk

I hope it's of some use.

James

[StuW]

When using an LX modified version at say 1sec exposure, does the firmware compress the image if it's at 640x480? It is after all it is running at 1fps.

[JamesF]

I don't have a modded camera so I can't be sure, but I believe that whilst you're only actually getting 1fps and the configured setting is ignored, the negotiated data rates and compression still apply for the configured setting. So, if you select 10fps and run the LX mod with an exposure time of one second the compression level for 10fps still applies.

It would therefore seem sensible to select 5fps if you're using the LX mod to get the least possible compression.

The thought occurs to me that because under Linux we can UTSL ("Use The Source, Luke") it may be possible to modify the driver offer frame rates of 1fps and longer and to attempt to negotiate a 640x480 size frame with no compression in those cases. It looks like it's the driver that controls what compression is chosen, so that may be possible. I'm getting towards out of my depth in terms of the driver implementation at this point however

James

[NickK]

It's a pity that the camera isn't attached via 2.0 (full or high speed) to give you non-compressed bandwidth.

Another option is to use a run length compression when the value is below a certain amount - this would say 'is the pixel value below a certain value? If so call it 0 and then run-length compress it (non-lossy)'.

[JamesF]

It would be excellent with a USB2.0 interface I think. I reckon you'd at least be able to get 640x480 @ 15fps uncompressed which is perhaps all you'd ever need.

James