W
W. eWatson
- Jan 1, 1970
- 0
I'm trying to determine how the algorithm described below works. Perhaps
it's a common simple method. It's for a b/w video camera and a mask is
used to block areas that are not of interest.
-----------------
When performing frame-to-frame differencing, the video motion detection
box counts the number of pixels that increase in brightness by more than
the corresponding threshold value in the image mask. When this number of
above-threshold pixels exceeds the number in the Trigger Threshold field
for two frames in a row, an event occurs. Once an event occurs, the
event is not complete until the number of above-threshold pixels falls
below the number in the Untrigger Threshold field for two frames in a row.
------------------
The description more or less sounds good, but interplay between the two
image frames and the mask is not clear to me. Is a difference made
between the two images, and then against the mask values or is the mask
applied against each image and the two results compared against one
another?
In this case, a mask is produced by assigning a value from 0 to 255 to
each pixel. For a pixel to be considered as a motion the imaged value
for the pixel must be greater than the mask value. A simple flat mask is
to assign a value of, say, 50 to all pixels and consider only pixels in
the image that exceed 50 in brightness.
P.S.
I happened to find an old text on this, Digital Image Processing, by
Gonzael and Wintz, and noticed they discuss such matters in a chapter
titled Image Segmentation.
it's a common simple method. It's for a b/w video camera and a mask is
used to block areas that are not of interest.
-----------------
When performing frame-to-frame differencing, the video motion detection
box counts the number of pixels that increase in brightness by more than
the corresponding threshold value in the image mask. When this number of
above-threshold pixels exceeds the number in the Trigger Threshold field
for two frames in a row, an event occurs. Once an event occurs, the
event is not complete until the number of above-threshold pixels falls
below the number in the Untrigger Threshold field for two frames in a row.
------------------
The description more or less sounds good, but interplay between the two
image frames and the mask is not clear to me. Is a difference made
between the two images, and then against the mask values or is the mask
applied against each image and the two results compared against one
another?
In this case, a mask is produced by assigning a value from 0 to 255 to
each pixel. For a pixel to be considered as a motion the imaged value
for the pixel must be greater than the mask value. A simple flat mask is
to assign a value of, say, 50 to all pixels and consider only pixels in
the image that exceed 50 in brightness.
P.S.
I happened to find an old text on this, Digital Image Processing, by
Gonzael and Wintz, and noticed they discuss such matters in a chapter
titled Image Segmentation.