If the motion that is occurring is too small to be distinguished from
'noise'--(delta on the difference)--then I'm not sure
how any amount of averaging or other tricks of math elan will help. It sounds
like you need to enhance the capture.
A zoom lens or a carefully arranged set of mirrors might help. The mirrors
might allow some
redundant cross-feed to both cameras, which for sure would help you detect the
signal from the noise. Sometimes getting
a new (or additional) perspective on a problem can be illuminating and
enlightening. ILLUMINATING--gee, if you can
control the lighting this might help in a really big way!
On Monday, July 07, 2008, at 07:21PM, "Memo Akten" <[EMAIL PROTECTED]> wrote:
>
>If the amount of motion you are waiting for is quite small, it might
>be hard to look at the motion via frame difference on the whole frame
>and compare to a threshold. If thats the case, I would suggest one of
>two options:
>
>- do a frame difference as mentioned, but instead of summing the total
>difference in the whole frame and comparing to a threshold, divide the
>screen into a grid, and sum the difference in each grid. If any grid
>has more motion than a threshold, switch to that feed.
>- similar to the above, (but more complex - but easier to do as one of
>the samples has something very similar), do an optical flow motion
>estimation on the feeds, then check to see if any velocity vector is
>greater than a threshold.
>
>Normally if developing from scratch the first option is much easier.
>But there is already a QC optical flow implementation in the samples
>(developer/examples/Quartz Composer/Plugins/Optical Flow). There you
>will find 2 QTZ files, any one of those will do but the
>OpticalFlow.qtz is probably easier to start with, you just need the
>branch upto and including the CI Optical Flow. This core image kernel
>takes two frames (current and prev) and outputs a new image containing
>velocity vectors (R is horizontal speed, G is vertical speed).What you
>want to do is loop through this image and check to see if any velocity
>(i.e. any pixel) is greater than a threshold (you DONT want to average
>all velocities and compare to a threshold because you will have the
>same problem as the whole image frame differencing in that the subtle
>movements will be absorbed by the noise).
>
>P.S. in those optical flow QTZ samples, it will give an error about
>missing plugin. The OpticalFlowDownloader QCPlugin is not that
>important, all it does is take the RG vector field image, and convert
>it into an array of numbers. If its easier you could just compile the
>plugin and iterate through the array instead of the image... or better
>still just modify the QCPlugin to do the looping (as it already does
>do that) and just return the maximum velocity instead of (or as well
>as) the array of numbers....
>
>hope this helps,
>
>
>Memo (Mehmet S. Akten)
>
>www.memo.tv
>
>[EMAIL PROTECTED]
>
>
>
>On 7 Jul 2008, at 20:13, Jeffrey Weekley wrote:
>
>> Thanks to Chris W. for his reply using a QC Histogram approach, but
>> since neither screen capture nor speaker video source changes all
>> that much, we weren't able to generate a delta that was wide enough
>> to elicit a switch from one source to another.
>>
>> I _know_ I saw such a composition at the WWCD last year ('07), but I
>> can't find that example online or in the developer directory with
>> XCode.
>>
>> Does anyone have this, because I think it's just what we're looking
>> for.
>>
>> In a nutshell, here's the problem again:
>>
>> One Video Screen Capture + One Camera Video (plus audio). We want to
>> be able to post both videos to a directory, bring them into QC and
>> switch between the video sources, based on whether or not something
>> is happening on the screen capture. Most of the time, it's subtle,
>> like a mouse move. The audio from the camera plays through out. We
>> then want a Quicktime movie from the QC.
>>
>> Any ideas?
>>
>> Thanks in advance.
>>
>> -Jeff W.
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