Re: Webcam video to external storage device

From: Anthony Ayiomamitis (anthony_at_perseus.no2spam.gr)
Date: 11/10/04 

Date: Wed, 10 Nov 2004 20:54:27 +0200

matt wrote:

>Anthony Ayiomamitis wrote in message ...
>
>
>>Carsten A. Arnholm wrote:
>>
>>
>>
>>>Anthony Ayiomamitis wrote:
>>>
>>>
>>>
>>>
>>>>Okay, I will go back and check to confirm that the Phillips ToUCam Pro
>>>>740k can accomodate USB2.0 ... thanks for the heads-up.
>>>>
>>>>
>>>>
>>>>
>>Hi Carsten,
>>
>>
>>
>>>There is no need to check. The ToUCam 740k is USB1.1 only. Of course, it
>>>
>>>
>is
>
>
>>>compatible with a USB2.0 PCMCIA card (I use one such card with my 740k),
>>>
>>>
>but
>
>
>>>don't expect USB2 speeds.
>>>
>>>
>>>
>>I am somewhat puzzled. I cannot go past 10 fps without dropping frames.
>>In fact, at 10 fps I am also dropping frames whereas there is no problem
>>at 5 fps. With a maximum possible fps rate of 60, what was their
>>thinking? Or is it just for screen refresh purposes only and whereas
>>they expect you to use 5 or 10 fps for image capture?
>>
>>
>>
>>>The reason I am using the PCMCIA card is that the USB1.1 port of my laptop
>>>does not deliver enough power, causing problems. Via the PCMCIA it works
>>>
>>>
>ok.
>
>
>>Okay. My sole interest was to supposedly increase the capture rate.
>>
>>Anthony.
>>
>>
>>
>>>Clear skies
>>>Carsten A. Arnholm
>>>http://arnholm.org/
>>>
>>>
>>>
>>>
>>>
>>>
>
>Anthony,
>
Hi Matt,

>What is the ultimate goal you're trying to achieve ? For what reason do you
>want to increase the frame rate in other words ?
>
>- If it is to increase the number of captured frames, just capture for a few
>more minutes. 10 minutes of avi recording at 5fps gets you 3000 frames , and
>10 minutes is nothing compared to the time it takes to set up the equipment
>for an iimaging session , boot the computer, focus, wait to reach thermal
>balance etc .
>
Agreed with the exception that for Mars and Jupiter and, to a lesser
extent, Saturn, we are also bound by rotation effects. For the moon and
Venus, for example, it is a non-issue. As a result, my only solution is
to increase the frame rate within the same time window.

>- If you want faster frame rate to freeze the seeing, you need to actually
>reduce the exposure time not the frame transfer duration in order to freeze
>what's inside each frame .
>
Agreed and I do exposure for the quickest possible exposure.

>There's a catch 22 here, because the only way to reduce exposure time is by
>having a more sensitive camera (you may consider the color ccd replacement
>with a b&w ccd that is a direct pin compatible replacement), or a larger
>scope.
>
I do have a large scope (Celestron's 14" SCT) and as such I am gathering
quite a few photos already .... I just need to capture and save as many
of those as possible. :-)

>The b&w ccd is easy if you can handle the elec tronics rework, you may get
>one in Europe from Framos .
>
>A larger scope would bring more light and a brighter image but that comes at
>the expense of reduced possibility of lucky exposures .
>
Lucky exposures are something I can deal with ... I am fortunate to have
good transparency as well as good seeing and I am simply looking to get
as many good frames for stacking as possible.

>See the original Fried paper regarding the lucky exposure probability :
>http://www.astrosurf.com/cavadore/optique/turbulence/Probability_of_getting_
>a_lucky_.pdf
>or a lay explanation of it with some clear pictures and graphs :
>http://www.astrosurf.com/cavadore/optique/turbulence/
>The bottom line being that a larger scope will bring crisper frames with
>better s/n than a smaller scope but at much larger time intervals if the ccd
>is maintained constant .
>
Thanks for the above links ... I will take a look very shortly!

> One other thing that you may consider if you haven't already is to use the
>raw hack for your webcam to increase quality , this being a purely (free)
>software operation is the least costly improvement .
>
I will look into this as well, for I do recall seeing something about
this hack at one time. I have also specified uncompressed mode in
K3CCDTools in order to minimize any further image degradation.
Nevertheless, I will check into this raw mode as well.

Your input and feedback is very much appreciated!

Anthony.

>best regards,
>matt tudor
>
>
>
>

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