What do "filter width" and "filter height&quo

[jonatha]

I am a newbie, and so far I can only seem to get Modect to operate in one of two modes - either the camera stays in a permanent state of alarm, or it stays in a permanet state of idle. I clearly do not understand what all the knobs really do...

I am experimenting with a single DCS-900 between 6 and 7 fps, which either because of the lighting conditions or because it's not a very good camera seems to create a rather noisy picture.

In describing filter width and height, the doc says the feature "removes any pixels that do not participate in a contiguous block of pixels above a certain size." I do not understand what this sentence is trying to say - I can think of two possible meanings, but I haven't been able to figure out which (if either) is correct.

Both of the meanings require that a pixel have 8 "contiguous" neighbors (up/down/left/right/4 diagonals) rather than 4 (up/down/left/right)...

Suppose I have a 3x3 filter. The doc could mean

1) Look at the 3x3 block of pixels centered on the alarmed pixel. If there are no other alarmed pixels in the block, ignore the alarmed pixel.

This would account for the recommendation that filter sizes be kept small, since the larger the block the more likely it will be to contain alarmed pixels created by noise, so larger blocks wouldn't tend to eliminate noise, they'd tend to retain it. But it would also imply a 1x1 filter should eliminate all alarmed pixels, which doesn't seem to be the case.

2) If the alarmed pixel is not part of a block of alarmed pixels that is at least 3x3 in size, ignore the alarmed pixel.

This would also account for the recommendation that filter sizes be kept small, since the larger the filter the more likely "real" alarmed pixels would be to be tossed. And the maximum filter size allowed (15x15) seems to greatly eliminate noise-created alarms.

[zoneminder]

Your second explanation is correct! I am revamping the zone and filter views as we speak as I know they can be a bit confusing. If you stick to a default of 3x3 for now you should be ok. If you are in a constant state of alarm then I suspect something else is wrong. What are your other settings? You could also switch on RECORD_STATS (beware you may also need to switch on CREATE_ANALYSIS_IMAGES due to a bug) and see what the actual values generated are.

Phil

[jonatha]

I have all the other settings as relaxed as possible (e.g., minpixel=0, maxpixel=255, min alarmed area=0%, max alarmed area=100%) in order to be able to determine the effect of the filter settings by themselves. I understand this is not the way things should be done in reality.

Thanks for your post; I will be bothering you with more newbie questions in the near future I am sure...

[zoneminder]

No problem. Setting the minima to 0 is disallowed from the next version by the way!

Phil