search

chiahaoliu / xpdAcquireFuncs

helper functions to XPD computer
0 stars 0 forks source link

dark correction method needs to be robust #24

Closed chiahaoliu closed 8 years ago

chiahaoliu commented 8 years ago

For now, dark substraction in save_tif() function only works perfectly when exposure time of light images is equal to exposure time of dark images. Possible issue might come from

ratio = int(scan_cnt_time / dark_cnt_time) correct_img = light_img - dark_imag*ratio

Need more tests to figure out what reason.

chiahaoliu commented 8 years ago

maybe essientially exposure time of dark frames needs to be the same exposure time of light images, like how QXRD operates. Uneqaul exposure time between dark/light frames always leads to over correction, create negative intensities and those negative intensities will be set to 0 in SrXplanar, which results in a flat back ground in I(q)

Real reason for this is unclear yet, electronic signal could be the issue

sbillinge commented 8 years ago

I see. Make sure we get a library of darks with all different exposure times in that case.....

Good detective work!

On Tue, Nov 10, 2015 at 5:54 AM, Timothy Liu notifications@github.com wrote:

maybe essientially exposure time of dark frames needs to be the same exposure time of light images, like how QXRD operates. Uneqaul exposure time between dark/light frames always leads to over correction, create negative intensities and those negative intensities will be set to 0 in SrXplanar, which results in a flat back ground in I(q)

Real reason for this is unclear yet, electronic signal could be the issue

— Reply to this email directly or view it on GitHub https://github.com/chiahaoliu/xpdAcquireFuncs/issues/24#issuecomment-155388116 .

Prof. Simon Billinge

Applied Physics & Applied Mathematics Columbia University 500 West 120th Street Room 200 Mudd, MC 4701 New York, NY 10027 Tel: (212)-854-2918 (o) 851-7428 (lab)

Condensed Matter Physics and Materials Science Dept. Brookhaven National Laboratory P.O. Box 5000 Upton, NY 11973-5000 (631)-344-5661

email: sb2896 at columbia dot edu home: http://thebillingegroup.com

sbillinge commented 8 years ago

So this is almost certainly due to the instability of the detector electronics. It means that an exposure of 0.4 seconds is not the same as two exposures of 0.2 seconds.

The proper fix for this I think is to go to continuous acquisition and when bluesky requests an "acquire" it merely saves those frames.