[Elphel-support] stereo camera: resizing and combined frames mode problems

[Sebastian Pichelhofer]

Hi Philip

The issue you are describing is a general global issue with motion
picture cameras and fluorescent light.

The easiest fix is to change FPS and shutter speed to match the
flickering frequency or a multiple/division of it.

Try a shutter speed (exposure time) of 1/50 (25 or 50 fps), if you
need less motion blur try 1/100, 1/150...
If you still see lower frequency flickering (frequency of 1Hz or less)
then the power grid frequency is just a little bit off 50Hz and you
have to fine-tune your exposure time. Since the Elphel camera can use
any float value as exposure time you should be able to get perfectly
flicker free footage with a little bit of fine tuning.

Some more info on the internet:
http://ezinearticles.com/?All-About-Fluorescent-Light-Flicker-in-Cameras!&id=3193172

Regards Sebastian

On Mon, Dec 13, 2010 at 05:17, Oleg K Dzhimiev <oleg at elphel.com> wrote:
>
> ---------- Forwarded message ----------
> From: Philip Haynes <philip.haynes at mercurien.com>
> Date: 12 December 2010 17:46
> Subject: Re: stereo camera: resizing and combined frames mode problems
> To: Oleg K Dzhimiev <oleg at elphel.com>
>
>
> Hi Oleg,
>
> We tried what you suggested and we saw no notable difference.
>
> Just so we are clear this issue has to do with power frequency. Fluorescent lights
> (in Australia) operate at 50 hz and we are getting severe image strobing.
>
> Philip
> On 9/12/10 6:58 PM, "Oleg K Dzhimiev" <oleg at elphel.com> wrote:
>
> Hi Philip,
>
> We are working on fixing te correct resizing - it affects more areas in the UI... there are some problems with switching between the modes.
> But the phases in the firmware you've got should be fine. You can check that bye putting sensors in a triggered mode
>
> 10359_controls.html - has such button
> in telnet/ssh - "fpcf -i2cw16 48a0 41" - enable, "fpcf -i2cw16 48a0 0" - disable
>
> As a result you should see 5 clear colored vertical bars. If the image is not static - then let's try to trouble shoot this.
>
> Best regards,
> Oleg
>
> On 9 December 2010 00:24, Philip Haynes <philip.haynes at mercurien.com> wrote:
>
> Hi Oleg,
>
> I also sent through a note on phasing. Do you have a comment on this?
>
> Much thanks,
>
> Philip
>
>
> On 7/12/10 2:02 PM, "Oleg K Dzhimiev" <oleg at elphel.com <http://oleg@elphel.com> > wrote:
>
> Yes – but you lose half the image.
> Alternating means we get the full picture providing more data to start
> building up a 3D geometry. A 1600x(2*1200) image would be desirable, but I
> wasn’t aware possible.
>
> Yes 1600x(2*1200) is possible.
> Technically the only difference is that the vertical sync signal is interrupted for alternating and uninterrupted for combined.
> But doing 'alternating mode' is more complicated for autoexposure (analyzes the current frame to change exposure for the next one) and changing parameters for example - and it is not supported right now in the camera (but it is possible to enable it in the mux board so the camera will not know).
>
> Oleg
>
>
>
>
>
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