linux v4l2 camera setting 'exposure_absolute' not restored correctly about reactivision

[s-light]

update:
with make debug the behavior is different for 3 and 4:
3. on next start value is read and set at camera correctly.
4. on exit it is saved correctly

[s-light]

update2:
with make debug and exposure at minimum value the behavior is different for 4 and 5:
4. on exit it is saved as min
5. on next start: minseems to be not recognized - exposure is switched to auto

[mkalten]

thanks for testing, I recently have been tweaking this particular setting, and although I managed to improve the actual functionality, there are still some apparent problems. I hope to have some time for that next week, your tests are definitely helping to resolve this I guess ...

[mkalten]

@s-light I just pushed another auto exposure fix which seems to work for me,
let me know if this also resolves your issue ...

[s-light]

@mkalten i think that partly fixed things -
now the behavior i see is the same for make alland make debug
i also found a bug in the Logitech HD Pro Webcam C920 firmware (tested only in combination with v4l2):
if i set absolute exposure with

v4l2-ctl  --device /dev/video19 --set-ctrl exposure_absolute=10

and directly after this read it again:

$ v4l2-ctl  --device /dev/video19 --get-ctrl exposure_absolute
exposure_absolute: 9

so it reports one lower than it is set..

with my other cam this set / get works as expected (it returns the same value as is set)

but the bug from update2 is still there: if i use the min value (in my case its 1) its read correctly and also set correctly. on exit it is saved as min. on restart of reacTIVision it seams that this min-value is recognized but for some reasons the cam is set to auto.
if i use some other text like xxx the cam is set to the minimum exposure in manual mode.
additionally i see two failed attempts to set uvc control messages in dmesg. - if it successfully sets the cam to absolute exposure i only see one failed attempt.
so i think the bug is because if the min setting is handle the cam is not first set to manual exposure mode.

[mkalten]

ad 1) I guess this may be your camera, which just selects the nearest value?
ad 2) I pushed another fix which hopefully resolves this issue

[s-light]

2. fixed :-) thanks for your great work!!!

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1. offtopic:
   tested some more - don't know if this is a bug in v4l2 or the cam firmware itself -

v4l2-ctl  --device /dev/video19 -l
exposure_absolute (int)    : min=3 max=2047 step=1 default=250 value=3

for all values below 500 it returns value one lower than set. i can see a difference in all steps down to 3. (3 also is darker than 4) so for me this does not make any sense. i also tested if this is different if the cam has a bright or dark picture - no difference found.