/// <summary>
/// Differences the current image with the previous one and computes the number of pixels
/// above the set difference threshold in the selected ROI
/// </summary>
/// <param name="imCurrent">The current frame to difference with the previous</param>
/// <param name="roi">The ROI in which to perform the compuation</param>
/// <returns>Number of pixels above threshold in the delta frame</returns>
public int ComputeNumDeltaPixels(Image8 imCurrent, IppiROI roi)
{
double nPixels = 0;
if (!_isFirst)
{
//form difference image
cv.ippiAbsDiff_8u_C1R(imCurrent[roi.TopLeft], imCurrent.Stride, _imPrevious[roi.TopLeft], _imPrevious.Stride, _imDelta[roi.TopLeft], _imDelta.Stride, roi.Size);
//threshold image
BWImageProcessor.Im2Bw(_imDelta, _imThresh, roi, _threshold);
//count pixels
ip.ippiSum_8u_C1R(_imThresh[roi.TopLeft], _imThresh.Stride, roi.Size, &nPixels);
}
else
{
_isFirst = false;
}
//copy current image to previous image buffer
ip.ippiCopy_8u_C1R(imCurrent[roi.TopLeft], imCurrent.Stride, _imPrevious[roi.TopLeft], _imPrevious.Stride, roi.Size);
//return pixel count - divide sum by 255 since threshold sets al values to 255
return((int)nPixels / 255);
}
/// <summary>
/// Tracks the tailsegments on the supplied image and returns
/// the angles and distances of each segment from the tailstart
/// </summary>
/// <param name="image">The image on which to id the tail</param>
/// <returns>NSegments number of TailPoints</returns>
public TailSegment[] TrackTail(Image8 image)
{
lock (_regionLock)
{
//CURRENTLY ONLY DOWNWARD FACING TAILS ARE PROPERLY VERIFIED!!!
//Generate background by morphology operation - 10 times a second or whenever our coordinates changed
//in the default case where the tail is darker than the background, using closing operation otherwise opening
if (_frameNumber % (_frameRate / 10) == 0 || !_bgValid)
{
if (!_bgValid)
{
//if our regions changed, reblank our images!
ip.ippiSet_8u_C1R(0, _background.Image, _background.Stride, _background.Size);
ip.ippiSet_8u_C1R(0, _foreground.Image, _foreground.Stride, _foreground.Size);
ip.ippiSet_8u_C1R(0, _thresholded.Image, _thresholded.Stride, _thresholded.Size);
}
if (_lightOnDark)
{
BWImageProcessor.Open(image, _background, _calc1, _strel, _trackRegionOuter);
}
else
{
BWImageProcessor.Close(image, _background, _calc1, _strel, _trackRegionOuter);
}
_bgValid = true;
}
//Compute foreground
IppHelper.IppCheckCall(cv.ippiAbsDiff_8u_C1R(_background[_trackRegionInner.TopLeft], _background.Stride, image[_trackRegionInner.TopLeft], image.Stride, _foreground[_trackRegionInner.TopLeft], _foreground.Stride, _trackRegionInner.Size));
//Threshold
BWImageProcessor.Im2Bw(_foreground, _thresholded, _trackRegionInner, _threshold);
//Fill small holes
BWImageProcessor.Close3x3(_thresholded, _thresholded, _calc1, _trackRegionOuter);
}
//Tracking concept: We track the angle of each segment end (TailStart+SegmentLength:TailEnd)
//as the angular displacement from the previous segment end
//To do this we define one full-circle with radius SegmentLength and an angle step corresponding
//to ~1 Pixel. Then for each angle we pre-compute in InitializeScanPoints the corresponding x
//and y offsets. From the full circle set we track -90 to +90 degrees around the angle of the
//previous segment - for the initial segment that angle will be 0. For each segment we will return
//the segment angle and its associated end-point coordinate
var retval = new TailSegment[_nSegments];
lock (_scanPointLock)
{
//The index of the absolute angle of the previous segment in our angle sweep array
//determines which angles we sweep over for the next segment
int prevAngleIndex = _scanAngles.Length / 2;
int nAnglesPerHalfPi = prevAngleIndex / 2;//this is the number of entries in the array that we have to walk to cover 90 degrees
//we scan beginning with one segment length away from tail start and then walk
//down the tail rather than using circles fixed arount the tailstart
IppiPoint prevSegmentEnd = TailStart;
//loop over tail segments
for (int i = 0; i < _nSegments; i++)
{
//loop over scan-points from -pi/2 to +pi/2 (i.e. nAnglesPerHalfPi) around previous segment angle
//interpreting the scan points as offsets around the previous tail segment
//end point
//then find tail angle of this segment
int pointsFound = 0;//the number of non-zero pixels identified
for (int j = -1 * nAnglesPerHalfPi; j < nAnglesPerHalfPi + 1; j++)
{
//Determine the index to scan - usually this will simply be "prevAngleIndex+j" however we
//have to loop around our angle array properly in case we screen more extreme angles
int currIndex = prevAngleIndex + j;
if (currIndex >= _scanAngles.Length)
{
currIndex = currIndex % _scanAngles.Length;
}
else if (currIndex < 0)
{
currIndex = currIndex + _scanAngles.Length;
}
//If current point is outside of the image, ignore it
IppiPoint pt = new IppiPoint(_coordinateOffsets[currIndex].x + prevSegmentEnd.x, _coordinateOffsets[currIndex].y + prevSegmentEnd.y);
if (pt.x < 0 || pt.y < 0 || pt.x >= _imageSize.width || pt.y >= _imageSize.height)
{
continue;
}
//if the value at the current point >0 we mark that angle as valid
//by storing the index in our anglestore
if (*_thresholded[pt] > 0)
{
_angleStore[pointsFound] = currIndex;
pointsFound++;
}
}
//find the median point in our angle store if we have more than 2 points stored
//the value in our angle store will directly give us the absolute screen angle of the segment
//as well as the coordinate offset which we can used together with the previous segment endpoint
//to compute the tail segment end coordinate - to get the delta angle we need to get the difference
//between the stored index and the previously stored index, prevAngleIndex
//after computing the appropriate return values we update prevAngleIndex with the index from the angle store
//and prevSegmentEnd with the returned coordinate of the current tail segment
double deltaTailAngle;
IppiPoint coordinate;
int pos; //the index in the angle store that we determine to be the tail-center
if (pointsFound == 0) //we have lost the tail - no reason to keep tracking - fill remaining positions in array with NaNs for their angle
{
for (int k = i; k < _nSegments; k++)
{
deltaTailAngle = double.NaN;
coordinate = new IppiPoint();
retval[k] = new TailSegment(deltaTailAngle, coordinate);
}
break;
}
else if (pointsFound < 3)
{
pos = _angleStore[0];
}
else
{
//we want the angle at the median position of valid points
//we don't compute intermediate positions however (we should be able to afford this since our angle step is so small), so in case
//of an even number of points, the top of the lower half currently
//wins - since array indexing is zero based, we have to subtract 1
//from the computed median position
pos = _angleStore[(int)(Math.Ceiling(pointsFound / 2.0) - 1)];
}
coordinate = new IppiPoint(prevSegmentEnd.x + _coordinateOffsets[pos].x, prevSegmentEnd.y + _coordinateOffsets[pos].y);
deltaTailAngle = (pos - prevAngleIndex) * _angleStep;
//the condition above of wrapping around the "angle circle":if (currIndex >= _scanAngles.Length)....
//results in one very large (close to +360 or -360) angle of opposite sign at the switch point
//however, since we usually only scan over offsets from +90 to -90 this case is easy to spot
//and remedy:
if (deltaTailAngle > 90)
{
deltaTailAngle = deltaTailAngle - 360;//this should create the appropriate tail angle btw. 0 and -90
}
else if (deltaTailAngle < -90)
{
deltaTailAngle = 360 + deltaTailAngle;//this should create the appropriate tail angle btw. 0 and +90
}
prevAngleIndex = pos;
prevSegmentEnd = coordinate;
retval[i] = new TailSegment(deltaTailAngle, coordinate);
}//loop over tail segments
}
_frameNumber++;
return(retval);
}