Automated/timelapse illuminance script

  • 3 Replies
  • 927 Views
Automated/timelapse illuminance script
« on: 09 / January / 2015, 13:45:19 »
Advertisements
Hey gang, sorry if this isn't the correct way to go about it, but I'm looking for an automated method to capture moonlight illuminance for a research project I've undertaken - trying to see if nocturnal behaviour of some birds changes with lunar illuminance.

Searching around keeps pointing me in the direction of the fantastic CDHK, and it seems like it would have everything I need. I'm no photography buff, but while I assume I could extract the data from timelapse photos, it would be much less time consuming if I could rig a camera (or 3) to record the value directly. I'll be attempting to do this consecutively for 3 months in three different locations, so any efficiency gains I can make will make a big difference.

Thanks for the help, keep up your great work!

*

Offline reyalp

  • ******
  • 11091
Re: Automated/timelapse illuminance script
« Reply #1 on: 09 / January / 2015, 17:33:20 »
I'm no photography buff, but while I assume I could extract the data from timelapse photos, it would be much less time consuming if I could rig a camera (or 3) to record the value directly.
There are several distinct parts to this
1) A timelapse script that runs for months on end with minimal intervention
2) Supplying power to the cameras, and perhaps turning them on and off at specific times.
3) Analyzing image data to determine an absolute illuminance value.

Doing this with CHDK will require some hacking on your part, most likely both with hardware and scripting.

For #1, you might start with Waterwingz "ultimate" script http://chdk.setepontos.com/index.php?topic=9969.0

For #2, you'll find some useful discussion in the hardware hacking sub-forum, particularly http://chdk.setepontos.com/index.php?topic=10284.0

For #3, I am working on code for CHDK 1.4 which gets you the average value of a specified region of the frame buffer. Combined with exposure settings this can give you an absolute illumance value, subject to some caveats. This value could easily be logged to a file. Development thread: http://chdk.setepontos.com/index.php?topic=11081.msg119265#msg119265

Caveats:
* You can measure R, G, B separately or average them, but the color response of your cameras particular CFA is not taken into account.
* The units are unspecified. In other words, a value of X represents some specific amount of light landing on the sensor, but you would need external calibration to turn that into some particular units. You can turn it into something approximating a Canon Bv value.
* If you want to use an existing script for timelapse, you would need to add code to allow it to use this feature. Or if you used the scripts I've developed for this feature, you'd need to adapt them to your application.

This is in the unstable development branch. The feature should be useable, but the interfaces may change from version to version, and you might run into unrelated bugs.
Don't forget what the H stands for.

Re: Automated/timelapse illuminance script
« Reply #2 on: 12 / January / 2015, 15:13:38 »
Wow, thanks for the reply. You've given me plenty to read.

the color response of your cameras particular CFA is not taken into account.

In theory, will there be much difference between CFAs of cameras of the same model?

I'm all for a little hacking, but if I get stuck adapting your scripts can I shoot you a message?
Thanks!

*

Offline reyalp

  • ******
  • 11091
Re: Automated/timelapse illuminance script
« Reply #3 on: 12 / January / 2015, 15:51:21 »
In theory, will there be much difference between CFAs of cameras of the same model?
I would expect no practical difference between cameras of the same model.

My point was that without knowing the response of the filters on a particular model of CCD, the relationship between reported values and absolute real world values (x photons in y frequency range) is not known. There is a color matrix which attempts reproduce colors similar to the Canon jpeg, but the quality of that varies between ports and it certainly isn't calibrated in any rigorous way. This may well not matter for your project.
Quote
I'm all for a little hacking, but if I get stuck adapting your scripts can I shoot you a message?
I'd prefer to have questions in the forum, so others can contribute and befit from the answers. I'd suggest posting any questions related to your project in this thread.
Don't forget what the H stands for.


 

Related Topics