Exposure mode problem

[anacierdem]

When "exposure_mode" is set to 'off', the output is black. pi firmware and python libraries are up to date.
The pi is a model B.

Will be further investigating the issue today. I'm suspecting that the problem may be in my code.

Figured it out, setting the exposure_mode to 'off' just after setting shutter_speed results in a black image but doing;

camera.shutter_speed = 30000

time.sleep(2);

camera.exposure_mode = 'off'

solves the problem. This should be further investigated.

[waveform80]

Hmm ... interesting stuff. It sounds like a firmware issue (I don't fully understand what exposure mode 'off' does under the covers), but either way it probably warrants some comment in the picamera docs as lots of people seem to be interested in this mode.

[waveform80]

While playing around with #182 another cause of this seems to be setting framerate (which resets the camera) after setting exposure_mode (given that framerate is frequently adjusted alongside shutter_speed this might explain why some people are seeing this issue). I'm going to add some warnings to the exposure_mode docs about this, but I think that's about all I can do on this for now.

[waveform80]

Looks like #171 and #182 are basically the same thing: the camera's analog gain starts off (just after init) as a really low value (1) which causes all frames to return black (there's probably some good reason for doing this, but I don't know enough about the firmware to know what). If you set exposure_mode to "off" (fixing the gains) before auto-gain control has had a chance to raise the gain up to a reasonable level (like 8) you'll just wind up with black frame after black frame.

I'll update the docs and recipes to include information about explicitly waiting for analog gain to reach a sensible level before setting exposure_mode to "off".