private static unsafe BinaryImage Hysteresis(GradientImage grad, IArrayHandler <byte> nms, float tlow, float thigh)
{
int r, c, pos, numedges, highcount;
int[] hist = new int[short.MaxValue];
float maximum_mag, lowthreshold, highthreshold;
maximum_mag = 0;
float[,] magChannel = grad.ExtractChannel(0);
short[] mag = new short[magChannel.Length];
fixed(short *dst = mag)
{
fixed(float *src = magChannel)
{
float *srcPtr = src;
short *dstPtr = dst;
for (int i = 0; i < mag.Length; i++, srcPtr++, dstPtr++)
{
*dstPtr = (short)(*srcPtr * 255);
}
}
}
int rows = grad.Rows;
int cols = grad.Columns;
byte[] edge = new byte[rows * cols];
fixed(byte *src = nms.RawArray)
{
byte *srcPtr = src;
int length = rows * cols;
for (pos = 0; pos < length; pos++)
{
if (*srcPtr++ == POSSIBLE_EDGE)
{
edge[pos] = POSSIBLE_EDGE;
}
else
{
edge[pos] = NOEDGE;
}
}
}
for (r = 0, pos = 0; r < rows; r++, pos += cols)
{
edge[pos] = NOEDGE;
edge[pos + cols - 1] = NOEDGE;
}
pos = (rows - 1) * cols;
for (c = 0; c < cols; c++, pos++)
{
edge[c] = NOEDGE;
edge[pos] = NOEDGE;
}
for (r = 0; r < short.MaxValue; r++)
{
hist[r] = 0;
}
for (r = 0, pos = 0; r < rows; r++)
{
for (c = 0; c < cols; c++, pos++)
{
if (edge[pos] == POSSIBLE_EDGE)
{
hist[mag[pos]]++;
}
}
}
for (r = 1, numedges = 0; r < short.MaxValue; r++)
{
if (hist[r] != 0)
{
maximum_mag = (short)r;
}
numedges += hist[r];
}
highcount = (int)(numedges * thigh + 0.5);
r = 1;
numedges = hist[1];
while ((r < (maximum_mag - 1)) && (numedges < highcount))
{
r++;
numedges += hist[r];
}
highthreshold = (short)r;
lowthreshold = (short)(highthreshold * tlow + 0.5);
for (r = 0, pos = 0; r < rows; r++)
{
for (c = 0; c < cols; c++, pos++)
{
if ((edge[pos] == POSSIBLE_EDGE) && (mag[pos] >= highthreshold))
{
edge[pos] = EDGE;
follow_edges(edge, mag, pos, lowthreshold, cols);
}
}
}
for (r = 0, pos = 0; r < rows; r++)
{
for (c = 0; c < cols; c++, pos++)
{
if (edge[pos] != EDGE)
{
edge[pos] = NOEDGE;
}
}
}
BinaryImage edgeImage = new BinaryImage(rows, cols);
fixed(bool *dst = edgeImage.RawArray)
{
bool *dstPtr = dst;
int length = rows * cols;
for (pos = 0; pos < length; pos++)
{
*dstPtr++ = edge[pos] == EDGE;
}
}
return(edgeImage);
}
private static unsafe IArrayHandler <byte> NonMaximalSuppression(GradientImage magImage)
{
int nrows = magImage.Rows;
int ncols = magImage.Columns;
int rowcount, colcount, count;
float[,] magVals = magImage.ExtractChannel(0);
float[,] gradxVals = magImage.ExtractChannel(2);
float[,] gradyVals = magImage.ExtractChannel(3);
byte[] data = new byte[nrows * ncols];
fixed(byte *result = data)
{
fixed(float *mag = magVals, gradx = gradxVals, grady = gradyVals)
{
float *magrowptr, magptr;
float *gxrowptr, gxptr;
float *gyrowptr, gyptr;
float z1, z2;
float m00, gx, gy;
float mag1, mag2, xperp, yperp;
byte * resultrowptr, resultptr;
/****************************************************************************
* Zero the edges of the result image.
****************************************************************************/
for (count = 0, resultrowptr = result, resultptr = result + ncols * (nrows - 1);
count < ncols; resultptr++, resultrowptr++, count++)
{
*resultrowptr = *resultptr = 0;
}
for (count = 0, resultptr = result, resultrowptr = result + ncols - 1;
count < nrows; count++, resultptr += ncols, resultrowptr += ncols)
{
*resultptr = *resultrowptr = 0;
}
/****************************************************************************
* Suppress non-maximum points.
****************************************************************************/
for (rowcount = 1, magrowptr = mag + ncols + 1, gxrowptr = gradx + ncols + 1,
gyrowptr = grady + ncols + 1, resultrowptr = result + ncols + 1;
rowcount < nrows - 2;
rowcount++, magrowptr += ncols, gyrowptr += ncols, gxrowptr += ncols,
resultrowptr += ncols)
{
for (colcount = 1, magptr = magrowptr, gxptr = gxrowptr, gyptr = gyrowptr,
resultptr = resultrowptr; colcount < ncols - 2;
colcount++, magptr++, gxptr++, gyptr++, resultptr++)
{
m00 = *magptr;
gx = *gxptr;
gy = *gyptr;
if (m00 == 0)
{
*resultptr = NOEDGE;
continue;
}
else
{
xperp = -(gx = *gxptr) / ((float)m00);
yperp = (gy = *gyptr) / ((float)m00);
}
if (gx >= 0)
{
if (gy >= 0)
{
if (gx >= gy)
{
/* 111 */
/* Left point */
z1 = *(magptr - 1);
z2 = *(magptr - ncols - 1);
mag1 = (m00 - z1) * xperp + (z2 - z1) * yperp;
/* Right point */
z1 = *(magptr + 1);
z2 = *(magptr + ncols + 1);
mag2 = (m00 - z1) * xperp + (z2 - z1) * yperp;
}
else
{
/* 110 */
/* Left point */
z1 = *(magptr - ncols);
z2 = *(magptr - ncols - 1);
mag1 = (z1 - z2) * xperp + (z1 - m00) * yperp;
/* Right point */
z1 = *(magptr + ncols);
z2 = *(magptr + ncols + 1);
mag2 = (z1 - z2) * xperp + (z1 - m00) * yperp;
}
}
else
{
if (gx >= -gy)
{
/* 101 */
/* Left point */
z1 = *(magptr - 1);
z2 = *(magptr + ncols - 1);
mag1 = (m00 - z1) * xperp + (z1 - z2) * yperp;
/* Right point */
z1 = *(magptr + 1);
z2 = *(magptr - ncols + 1);
mag2 = (m00 - z1) * xperp + (z1 - z2) * yperp;
}
else
{
/* 100 */
/* Left point */
z1 = *(magptr + ncols);
z2 = *(magptr + ncols - 1);
mag1 = (z1 - z2) * xperp + (m00 - z1) * yperp;
/* Right point */
z1 = *(magptr - ncols);
z2 = *(magptr - ncols + 1);
mag2 = (z1 - z2) * xperp + (m00 - z1) * yperp;
}
}
}
else
{
if ((gy = *gyptr) >= 0)
{
if (-gx >= gy)
{
/* 011 */
/* Left point */
z1 = *(magptr + 1);
z2 = *(magptr - ncols + 1);
mag1 = (z1 - m00) * xperp + (z2 - z1) * yperp;
/* Right point */
z1 = *(magptr - 1);
z2 = *(magptr + ncols - 1);
mag2 = (z1 - m00) * xperp + (z2 - z1) * yperp;
}
else
{
/* 010 */
/* Left point */
z1 = *(magptr - ncols);
z2 = *(magptr - ncols + 1);
mag1 = (z2 - z1) * xperp + (z1 - m00) * yperp;
/* Right point */
z1 = *(magptr + ncols);
z2 = *(magptr + ncols - 1);
mag2 = (z2 - z1) * xperp + (z1 - m00) * yperp;
}
}
else
{
if (-gx > -gy)
{
/* 001 */
/* Left point */
z1 = *(magptr + 1);
z2 = *(magptr + ncols + 1);
mag1 = (z1 - m00) * xperp + (z1 - z2) * yperp;
/* Right point */
z1 = *(magptr - 1);
z2 = *(magptr - ncols - 1);
mag2 = (z1 - m00) * xperp + (z1 - z2) * yperp;
}
else
{
/* 000 */
/* Left point */
z1 = *(magptr + ncols);
z2 = *(magptr + ncols + 1);
mag1 = (z2 - z1) * xperp + (m00 - z1) * yperp;
/* Right point */
z1 = *(magptr - ncols);
z2 = *(magptr - ncols - 1);
mag2 = (z2 - z1) * xperp + (m00 - z1) * yperp;
}
}
}
/* Now determine if the current point is a maximum point */
if ((mag1 > 0.0) || (mag2 > 0.0))
{
*resultptr = NOEDGE;
}
else
{
if (mag2 == 0.0)
{
*resultptr = NOEDGE;
}
else
{
*resultptr = POSSIBLE_EDGE;
}
}
}
}
}
}
ByteArrayHandler handler = new ByteArrayHandler(nrows, ncols, 1);
fixed(byte *dst = handler.RawArray)
{
byte *dstPtr = dst;
int length = nrows * ncols;
for (int pos = 0; pos < length; pos++)
{
*dstPtr++ = data[pos];
}
}
//MonochromeImage mono = new MonochromeImage(nrows, ncols);
//for (int r = 0; r < nrows; r++)
// for (int c = 0; c < ncols; c++)
// mono[r, c] = handler[r, c, 0];
//mono.ToRGB().Save("cannyNMS.bmp");
return(handler);
}