Camera register fiddling

[JohannesTaelman]

I explored to possibility to write the camera registers during video capture. After setting the exposure mode to off, MMAL does not touch the i2c bus anymore, so it can be taken over. Starting the capture with exposure mode off results in a black image, and I haven't figured out which register writes are needed to fix this, so capturing still needs to start with a normal exposure setting.

This patch is working on a raspi B+, with bcm2835 compiled for V1 pinmapping.
Changing the exposure register 3501 clearly works.
http://pastebin.com/h2mz4fSd
This is proof-of-concept code, only intended for hacking around!

[6by9]

As our datasheets are under NDA, I can't say too much. What I will say is that there are other registers that interact with exposure.

The sensor only sees commands for analogue gain and exposure time. Digital gain (and AWB etc) is done within the GPU, so setting the exposure mode to off before allowing any frames through will result in digital gain still being at x0.0 and hence black images.

[JohannesTaelman]

Any workaround to force this digital gain to unity? Any particular exposure mode that sets it to unity?

thanks!

[6by9]

Any workaround to force this digital gain to unity? Any particular exposure mode that sets it to unity?

Not currently. As I currently understand it, the first frame has to go through to actually set the digital gain, and if AGC is OFF at that point then it will not get set.
I will look into it though.