Jorick,
Yes binning/decimation is broken - we do not use it ourselves (for the reasons
I explained before) so I did not notice when I broke it - it did work
initially. I'll look into it, but it may take some time.
Andrey
---- On Tue, 13 Jun 2017 03:34:30 -0700 Jorick
Astrego<jor...@theidiotcompany.eu> wrote ----
On 05/31/2017 05:53 PM, Elphel Support wrote:
>
> 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.
Thanks for the explanation, the problem we have with post processing is that
for this phase of the project we are doing realtime image analytics with cuda
on a MJPEG stream.
We will be doing some raw capturing but we're looking to trigger this on
demand.
Maybe we could set the exposure parameters with an algorithm that does the
analytics , but I don't know if that will respond fast enough and this will
take up processing power. We will have to mess about with it some more ;-)
> 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.
Ok understood, we will do some more testing.
> 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, ...
For the realtime anlytics the resolution is too high, currently we scale it
down while processing. I was in the understanding that by binning you would
have all the light but half the resolution (I tried 1/2 binning)
So I just set horizontal and vertical to "1/2" and got the corrupted image.
When I set them back to the original setting the image remains corrupted. I
haven't had time to check if it stores the image uncorrupted yet.
This could be due to the outdated firmware, so we'll start with upgrading that.
I could probably also modify the streamer to output a lower resolution.
h264/h265 support would be even better. The idea is to run the analytics and
streaming and only grab the interesting frames in raw from the circular buffer.
How difficult would a color space conversion to YUV be on the elphel? We're
streaming so much the same color (green ;-) and this would save bandwith, it
would also be easier to change the brightness on parts of the image.
>
>
>
> 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.
We've received the latest firmware and we'll do some testing next week.
Thanks for the quick response!
Andrey
Regards,
Jorick Astrego
Met vriendelijke groet,
With kind regards,
Jorick Astrego
THE IDIOT COMPANY
Staalsteden 4-3A
7547 TA Enschede
The Netherlands +31 (0)53 20 30 275
i...@theidiotcompany.eu
WWW.THEIDIOTCOMPANY.EU
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