NAME

diff_segment -- create unit to segment image

PROTOTYPE

unitptr diff_segment( int iDx, int iDy, unitptr uHost)

ARGUMENTS

int iDx
width of image rectangle
int iDy
height of image rectangle
unitptr uHost
host unit

RETURN VALUE:

A pointer to the created unit or NULL in the case of an error.

INTERFACE OF CREATED UNIT:

X_in[iDx*iDy]:
(packed input field 0) Input image
EPS_in[3]:
adaptation rates for reference background (pins 0 and 1 for masked and unmasked pixels), and update threshold (pin 2, default = 0.8).
CTL_in[5]:
(control field) pos. and neg. deviation thresholds (pins 0,1, default is 10) for marking a pixel, output value (pin 2, default is 0, i.e. transmit input pixel intensity) and number of hole filling iterations (pin 3, default=0) and min. number of masked neighbors for hole filling (pin 4, default=5).
X_out[iDx*iDy]:
(packed output field 0) Output image. Zero at all unmarked pixel locations, input intensity or CTL_in[2] at the remaining marked locations.

EXECUTION OF CREATED UNIT:

This unit compares the current input image on a pixel by pixel basis with an internally stored reference image. Those pixel locations of the input image for which the intensity is by more than CTL_in[0] larger or by more than CTL_in[1] smaller than the intensity at the corresponding reference image location are marked (i.e., marked are all pixels with intensity outside the closed interval [ref-CTL_in[1],ref+CTL_in[0]] ). The output image is zero at all unmarked pixel locations, while all marked locations have the pixel value of the corresponding input pixel if CTL_in[2]=0 (the default), or the constant value CTL_in[2] otherwise.

ADAPTATION OF CREATED UNIT:

During an adapt-call, the unit adapts its internal reference image according to one of two modes: a) if the fraction of marked pixels from the previous exec - call exceeds the update threshold ( EPS_in[2] ), the reference image is replaced by the current input image. This feature can be used for an automatic recalibration after, e.g., camere moves or very large image changes. The default value for the update threshold is EPS_in[2]=0.8. b) if a) does not apply, an adapt - call will make for all pixels in the reference image the following gradual intensity change: 

     New[i] = (1-eps)*Old[i] + eps*X_in[i]
Here, the value eps=EPS_in[0] will be used for all pixels that occupy unmarked pixel locations, and eps=EPS_in[1] for all pixels that occupy marked pixel locations. This can be used to automatically adapt to slow changes in lighting.

CONTROL MODES:

The following control modes are defined:

NST_INIT:
replace current reference image by input image.

SPECIAL FEATURES:

If CTL_in[3]>0, the output image will be constructed only after the set of marked pixels has been CTL_in[3] times iteratively enlarged according to the following procedure: add to the set of marked pixels all those unmarked pixels that have at least CTL_in[4] marked nearest neighbors in their 8-neighborhood. The default setting is CTL_in[3]=0 (i.e., no iterations) and CTL_in[4]=5. This has the effect to close small `holes'' in the transmitted pixel set. NOTE: in the current implementation, hole filling is restricted to the subrectangle that is surrounded by a 1-pixel wide margin from the image border, and the iterations are (for efficiency reasons) computed unbuffered, i.e., holes are filled while scanning the image line wise during each iteration.

STATUS:

Preliminary.

DEFAULTS:

EPS_in[0]=0
adaptation rate for unmarked part of reference image
EPS_in[1]=0
adaptation rate for marked part of reference image
EPS_in[2]=0.8
threshold for full update of reference image by input image
CTL_in[0]=10
required pos. deviation from reference image for marking
CTL_in[1]=10
required neg. deviation from reference image for marking
CTL_in[2]=0
at marked locations: 0=transmit image intensity, the constant value CTL_in[2] otherwise.
CTL_in[3]=0
number of `hole filling''-iterations
CTL_in[4]=5
min. number of marked neighbors for hole filling.

FILE

/homes/jontrup/nst5/man/../o.sol2//../foldersrc/nst_filter.c