Hi,
Currently we are testing a panoramic NC393 camera and are having problems
with the auto exposure on multiple image sensors.
When there is half shadow, half bright light in the collective images.
The image is dark on the shadow part. Does autoexposure apply globally or
should every sensor apply it's own autoexposure settings?
Jorick, with the limited dynamic range of the small format sensors it is a
challenge to capture maximal data from the image, and there is no universal
fits-all set of autoexposure parameters. We probably need to create some
tutorial about it.
The overall strategy is to keep maximal data from each channel - EXIF data in
each image contains acquisition settings so it is possible to match individual
channels after acquisition - that just may require more than 8-bit of the
intensity for the intermediate data.
Each channel operates it autoexposure independently, so the output may not
match in raw form - it needs post-processing. For example channels can be
combined in a single 16-bit per color panorama and then high-pass filter (with
low cutoff frequency ~ 1/2000 pix) applied to reduce difference between bright
and dark parts of the panorama.
What would be a way to get a more balanced exposure?
There are multiple parameters that control autoexposure, the main are window,
level and fraction. The daemons (1 per each of the 4 channels) builds
histograms for all pixels inside the selected rectangular area, and then
calculates required exposure so the specified fraction of all pixels have
values below the specified level.
Default settings are for images where there are no very bright objects (like
the Sun) in the field of view, so if the camera is pointed there the picture
will become all dark. If you change the fraction to say 95%, then up to 5% of
the pixels are allowed to be above the level - that level does not have to be
very high, so exceeding it do not mean necessarily overexposure. Camvc program
allows you to adjust this pair (fraction/level) graphically. You can turn off
autoexposure, set it manually to the desired level and then move slider for the
fraction - level value will be adjusted to match it.
Second question, is binning supported and do we have to do any aditional
steps for this? We'd like to reduce the resolution while still using the whole
sensor. When I set it to 1/2 Horizontally and 1/2 Vertically, the output gets
corrupted.
Binning is supported, it should all be the same as in the 353 camera. Can you
please describe precisely how you've got corrupted images, we will try to
reproduce (and address) the problem.
On the other hand, binning and decimation are not r3eally good in any of the
color mosaic sensors as these modes reduce resolution more than twice. Because
of the Bayer mosaic (1 row):
R1 G1 R2 G2 R3 G3 R4 G4
R1 will be merged with R2, R3 - with R4 and similar G1 with G2:
R1+R2, G1+G2, R3+R4, G3+G4, ...
Also we have a problem in the Camogm recording application, we use fast
recording (without partition).
When I press record, I get a warning about a buffer underrun. If click
away the message, recording starts and the buffers stay full.
When I forget to OK the warning, the elphel becomes unresponsive on the
http interface after a while and it looks if the recording task hangs.
A reboot doesn't work as it never reboots, we had to power off the camera
to get it going again. After reboot the recording is lost from what I see.
What firmware version do you have ? There were many changes in camogm earlier
this year.
Andrey
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