Thank you @wong . With --metering set to “matrix” it works better now. Default value for the metering the is spot detection as it seems, like you mentioned with area in the center.
I will do the cropping the area of interest now after the image has been taken because using --roi seem to break something with the metering for the exposure / focus.
Even with the ND4 fitted on a cloudy day the AEC/AGC algorithms seem to do well here. This image is taken all by default values, except “–autofocus on” and “–metering matrix” being set.
Instead of the --timelapse function I will use a script for taking sequences of images every x seconds. By doing so I can trigger a new calculation of exposure and refocusing the lens every 5 to ten minutes or so. Im unsure if the --timelapse function would do recalculations until the timeout got reached or if it just does calculation and focus setting just on the first image taken.
@picamfan
I’ve been running my timelapse setup with part of an ND graduated filter, just something I had at hand. I’d guess it amounts to ~ -1.5 EV. That turned out to be sufficient to achieve properly exposed clouds but still stay within reasonable exposure times at night. Resonable being 15s exposure with a gain of 5.0 that is
I’ve also been playing around with HDR processing as described in the document that @wong linked above. Tuning everything I was able to achieve quite nice results, but it turned out to be not very stable in the long run. Also, I was only able to use 50% resolution because of memory limitations on the Pi 3b+.
I ended up (for now with gamma-correcting the images with a gamma of ~1.4 and a subsequent contrast-stretch, both done with imagemagick. I’ll revisit that when I find time to tune the Raspi a bit with regard to memory consumption…
I also tried tuning the auto exposure process (again as mentioned in the pdf above) in the hopes of achieving good auto exposure even at night. Automatic white balance evaluation by libcamera is also “a bit” hit and miss in low light situations. See also libcamera-still long exposures ? - Page 2 - Raspberry Pi Forums regarding this issue, it’s an interesting read.
For now, I ran out of steam and reverted to manual settings at night. I’m working on a Python wrapper for libcamera-still to achieve exposure and WB fading over the course of the day. If I achieve something presentable I’ll report back here
Yes, the timelapse function is not reliable. I noticed at night it takes a first image that’s underexposed, but all subsequent images are well exposed.
BTW, did you find (or is there at all…?) a way to get feedback from libcamera about the settings it determines with its auto exposure and white balance algorithms?
All in all the libcamera apps are a bit of a black box, and the settings are not very coherent, if you are a photography nerd like I am…
you nailed it @frx , I would love to have a bit more man page or -h output for each of the parameters and min / max values and so on. It is a lot of try and error here with libcamera. of course that’s not arducam’s fault. But I hope that maybe aducam developers can do a writeup or wiki article with their lib camera know how, do’s and don’ts.
Today I noticed those kind of scratches / stripes in the upper middle sky part. It was there with the ND8 filter attached aswell as now with the ND4. the protective glass on the outdoor case was removed so I think since those stripes must come from the camera lens or the sensor itself.
with gamma-correcting the images with a gamma of ~1.4 and a subsequent contrast-stretch, both done with imagemagick. I’ll revisit that when I find time to tune the Raspi a bit with regard to memory consumption…
