On Fri, 17 May 2024 08:27:02 -0700, James Holton <jmhol...@lbl.gov> wrote:

...
>
>With a bit of a caveat on how many photons/pixel you need for stable
>background subtraction. XDS starts having issues around 1 photon/pixel
>or less, and DIALS claims to be able to get to 0.01 photons/pixel, but I
>have not personally pushed it that far.  Not yet.
>

Hi James,

I fully agree with your recommendations in general, but want to comment on this 
specific one, reporting the values that I wrote into the relevant XDSwiki 
article ( https://wiki.uni-konstanz.de/xds/index.php/Low_dose_data ; check out 
its history):
- until 2015, the lowest average background count per pixel for XDS was 0.5
- in 2017 I changed that value to 0.05, after revision of the code in XDS 
(BUILT=20161101) 

To improve the estimate for very low background, one can use the RELRAD and 
RELBET keywords in XDS.INP .

Best wishes,
Kay

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