[Nexus] pixel_mask documentation

Tobias.Richter at diamond.ac.uk Tobias.Richter at diamond.ac.uk
Wed Jul 10 10:04:39 BST 2013

Hi Michael,

Thanks for that clarification. I will add that to the documentation of NXdetector.

The only slight problem I have is that bit 7 is special in that for the 95% (more 99% I would guess) of the users that is a good pixel and hence it should not be "masked". I mean that's why you Dectris guys go through all the effort of manufacturing them like that, right?

If other vendors create detectors with other types of special pixels you would have to mask out a strange combination of bits of that bit mask to get a useful detector mask.

How would everyone feel about:

* moving this corner information to a separate field?
* using (for example) bits 31 downwards in the pixel_mask for usable non non-perfect pixels, so that software would normally use (mask & 0x0000FFFF) and will in all likelihood never need to change even when new types of pixels come up?

Or is it too late for any changes?

Kind regards,


From: Michael Rissi [michael.rissi at dectris.com]
Sent: 10 July 2013 06:48
To: Richter, Tobias (DLSLtd,RAL,DIA); Marcus Mueller
Cc: Herbert J. Bernstein; nexus at nexusformat.org
Subject: Re: [Nexus] pixel_mask documentation

Hey Tobias,

We intend also to mark the invalid pixels in the images themselves with -1. So only if you want to know what is wrong with a marked pixel, you can check the pixel mask.

Is 6 or 7 targeted for corner pixels on Eiger/Pilatus?

7 is for corner pixels. Bit 6 is for pixels that lie in a cluster of bad pixels.

To make it easy for consuming software I would not want any bits to be set for a usable pixel value. 95% would not care about a reason for not using the pixel. Flagging up these special pixels somewhere is useful but maybe not in a "mask". Maybe I am wrong anyway.

What's "5 non uniform" exactly?  Just that I can make the documentation most meaningful.

I am sorry, that was still there for historical reasons... We can remove this flag, as we do not really need it anymore.

Bits do come in handy though. It allows us to add:

8 user specified
For pixels that are masked out by the user although they have a physically "correct" reading but for example represent artefacts in the measurement like beamstops. Agreed?

Yes, definitely!

Best regards,

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