/// <summary>
/// Extracts corners from the gradient image. The method used here is one which uses the eigensystem at each
/// pixel (computed from the smoothed second moments) to determine whether a corner is present. A corner is
/// one in which both eigenvalues are above the threshold.
/// </summary>
/// <param name="grad">Gradient image of source</param>
/// <param name="threshold">Threshold used to determine corners</param>
/// <returns>A list of corners</returns>
public static unsafe Vector[] Extract(GradientImage grad, float threshold)
{
EigensystemImage eigen = EigensystemImage.Compute(SecondMomentImage.Compute(grad));
List <Vector> points = new List <Vector>();
int rows = eigen.Rows;
int columns = eigen.Columns;
fixed(float *src = eigen.RawArray)
{
float *srcPtr = src;
int channels = eigen.Channels;
for (int r = 0; r < rows; r++)
{
for (int c = 0; c < columns; c++, srcPtr += channels)
{
float lambda1 = srcPtr[0];
float lambda2 = srcPtr[1];
if (lambda1 > threshold && lambda2 > threshold)
{
points.Add(new DenseVector(new float[] { c, r }));
}
}
}
}
return(points.ToArray());
}
/// <summary>
/// Computes the second moments at each pixel based on the provided gradient image.
/// </summary>
/// <param name="grad">The gradient of the source image</param>
/// <returns>The second moment image</returns>
public static unsafe SecondMomentImage Compute(GradientImage grad)
{
int rows = grad.Rows;
int columns = grad.Columns;
float[, ,] data = new float[rows, columns, 3];
fixed(float *src = grad.RawArray, dst = data)
{
float *srcPtr = src;
float *dstPtr = dst;
int length = rows * columns;
for (int i = 0; i < length; i++, srcPtr += 4)
{
float ix = srcPtr[2];
float iy = srcPtr[3];
* dstPtr++ = ix * ix;
* dstPtr++ = iy * iy;
* dstPtr++ = ix * iy;
}
}
SecondMomentImage image = new SecondMomentImage();
image.SetData(data);
return(image);
}
/// <summary>
/// Computes DiscreteContours at the samples provided.
/// </summary>
/// <param name="samples">Samples to compute contours at</param>
/// <param name="pyramid">Image pyramid to use for samples</param>
/// <returns>DiscreteContours</returns>
public static List <Keypoint> Compute(List <ScaleSpaceSample> samples, ScaleSpacePyramid <GrayscaleImage> pyramid)
{
GradientImage[,] grads = new GradientImage[pyramid.Octaves, pyramid.Levels];
List <Keypoint> points = new List <Keypoint>();
foreach (ScaleSpaceSample sample in samples)
{
if (grads[sample.Octave, sample.Level] == null)
{
grads[sample.Octave, sample.Level] = GradientImage.Compute(pyramid[sample.Octave, sample.Level], false);
}
points.Add(Compute(sample, grads[sample.Octave, sample.Level], pyramid.ComputeSigma(sample.Octave, sample.Level)));
}
return(points);
}
/// <summary>
/// Compute the Discrete Contour descriptor from the provided patch. This match must be of gradients and
/// of the size specified by <see cref="RequiredPatchSize"/>. A raw image patch, or a patch of different
/// dimensions, will not work.
/// </summary>
/// <param name="sample">Sample to compute DiscreteContour at</param>
/// <param name="gradImage">Gradient image to use</param>
/// <param name="scale">The scale of the sample (the value returned by ComputeSigma() in ScaleSpacePyramid)</param>
/// <returns>Discrete Contour descriptor</returns>
public static unsafe Keypoint Compute(ScaleSpaceSample sample, GradientImage gradImage, float scale)
{
Keypoint point = new Keypoint(sample.X, sample.Y, sample.ImageScale, scale, 0);
float[] desc = new float[DESCRIPTOR_LENGTH];
int startR = sample.Row - SQUARE_SIZE / 2;
int startC = sample.Column - SQUARE_SIZE / 2;
int rows = gradImage.Rows;
int columns = gradImage.Columns;
int channels = gradImage.Channels;
int stride = columns * channels;
fixed(int *mask = MASK)
{
fixed(float *patch = gradImage.RawArray)
{
int *maskPtr = mask;
float *patchPtr;
if (startR < 0)
{
if (startC < 0)
{
patchPtr = patch;
}
else
{
patchPtr = patch + startC * channels;
}
}
else if (startC < 0)
{
patchPtr = patch + startR * stride;
}
else
{
patchPtr = patch + startR * stride + startC * channels;
}
for (int r = 0; r < SQUARE_SIZE; r++)
{
int rr = startR + r;
float *patchScan = patchPtr;
if (rr >= 0 && rr < rows - 1)
{
patchPtr += stride;
}
for (int c = 0; c < SQUARE_SIZE; c++, maskPtr++)
{
int bin = *maskPtr; //MASK[rr, cc];
float mag = patchScan[0]; //gradientPatch[rr, cc, 0];
float dir = patchScan[1]; //gradientPatch[rr, cc, 1];
int cc = startC + c;
if (cc >= 0 && cc < columns - 1)
{
patchScan += channels;
}
//if (mag != gradImage[Math.Max(0, Math.Min(rr, rows - 1)), Math.Max(0, Math.Min(cc, columns - 1)), 0])
// throw new Exception("testing");
if (bin < BINS)
{
addValue(bin, dir, mag * 2, desc);
}
else
{
bin -= BINS;
int bin1 = HALF[bin, 0];
int bin2 = HALF[bin, 1];
addValue(bin1, dir, mag, desc);
addValue(bin2, dir, mag, desc);
}
}
}
}
}
point.Descriptor = desc;
return(point);
}
/// <summary>
/// Extracts corners from the gradient image using the default threshold.
/// </summary>
/// <param name="grad">Gradient image of source</param>
/// <returns>A list of corners</returns>
public static Vector[] Extract(GradientImage grad)
{
return(Extract(grad, EigensystemImage.SENSITIVITY));
}
/// <summary>
/// Computes a gradient image from the source image.
/// </summary>
/// <param name="sigma">The sigma to use when blurring the source image.</param>
/// <param name="image">Source image</param>
/// <returns>Gradient image</returns>
public static unsafe GradientImage Compute(GrayscaleImage image, float sigma)
{
int rows = image.Rows;
int columns = image.Columns;
if (sigma > 0)
{
image = Convolution.ConvolveGaussian <GrayscaleImage>(image, sigma);
}
float[, ,] data = new float[rows, columns, 4];
fixed(float *src = image.RawArray, dst = data)
{
float *srcPtr = src;
float *srcPtrP = srcPtr + 1;
float *dstPtr = dst;
dstPtr += 2;
// X derivative
for (int r = 0; r < rows; r++)
{
*dstPtr = *srcPtrP - *srcPtr;
dstPtr += 4;
srcPtrP++;
for (int c = 1; c < columns - 1; c++, srcPtr++, srcPtrP++, dstPtr += 4)
{
*dstPtr = *srcPtrP - *srcPtr;
}
srcPtrP--;
*dstPtr = *srcPtrP - *srcPtr;
dstPtr += 4;
srcPtr += 2;
srcPtrP += 2;
}
srcPtr = src;
srcPtrP = srcPtr + columns;
dstPtr = dst;
dstPtr += 3;
int stride = 4 * columns;
for (int c = 0; c < columns; c++, srcPtr++, srcPtrP++, dstPtr += 4)
{
float *srcScan = srcPtr;
float *srcScanP = srcPtrP;
float *dstScan = dstPtr;
* dstScan = *srcScanP - *srcScan;
dstScan += stride;
srcScanP += columns;
for (int r = 1; r < rows - 1; r++, dstScan += stride, srcScan += columns, srcScanP += columns)
{
*dstScan = *srcScanP - *srcScan;
}
srcScanP -= columns;
*dstScan = *srcScanP - *srcScan;
}
dstPtr = dst;
int length = rows * columns;
for (int i = 0; i < length; i++, dstPtr += 4)
{
setData(dstPtr);
}
}
GradientImage result = new GradientImage();
result.SetData(data);
return(result);
}