internal ImageF(ImageF image)
: base(
image.Width,
image.Height,
image.BitsPerPixel,
image.HorizontalResolution,
image.VerticalResolution,
image.Transform)
{
}
/// <summary>
/// Calculates the histogram of oriented gradients (HOG) on the <see cref="Image"/>.
/// </summary>
/// <param name="cellSize">The cell size, in pixels.</param>
/// <param name="blockSize">The block size, in number of <paramref name="cellSize"/>.</param>
/// <param name="blockStride">The block stride size, in number of <paramref name="cellSize"/>.</param>
/// <param name="numberOfBins">The number of bins (orientations) in the histogram.</param>
/// <param name="threshold">
/// The threshold value to apply after normalization.
/// Bins that are less than the threshold, are set to zero.
/// </param>
/// <returns>
/// The <see cref="DenseVectorPackF"/> that contains packed points of interest.
/// </returns>
/// <exception cref="NotSupportedException">
/// The <see cref="Image{T}.BitsPerPixel"/> is not 1, 8, 24, or 32.
/// </exception>
public DenseVectorPackF HOG(
int cellSize,
int blockSize,
int blockStride,
int numberOfBins,
float threshold)
{
// convert image to float
ImageF srcf = PrepareImage();
int width = srcf.Width;
int height = srcf.Height;
int stride = srcf.Stride;
float[] bits = srcf.Bits;
/*if (NativeMethods.hog(
* srcf.BitsPerPixel,
* srcf.Width,
* srcf.Height,
* srcf.Stride,
* srcf.Bits) != 0)
* {
* throw new OutOfMemoryException();
* }*/
// calculate gradient vectors magnitude and direction using Prewitt operator (-1 0 1)
float[] mag = new float[bits.Length];
float[] ang = new float[bits.Length];
NativeMethods.gradientVectorPrewitt_f32(width, height, bits, stride, mag, stride, ang, stride);
// convert angles to bins
Mathematics.DivC(ang.Length, (float)(Math.PI / numberOfBins), ang, 0);
Vectors.Abs(ang.Length, ang, 0);
// calculate histograms
int cellCountX = width / cellSize;
int cellCountY = height / cellSize;
int blockCountX = ComputeBlockCount(cellCountX);
int blockCountY = ComputeBlockCount(cellCountY);
int blockCount = blockCountX * blockCountY;
int blockSizeInBins = blockSize * blockSize * numberOfBins;
float[] blocks = new float[blockCount * blockSizeInBins];
int offblock = 0; // running block offset
// to save memory we allocate histograms needed for one row of blocks only
// when we move throw the rows, the first histogram (not needed anymore) becomes last (working)
List <float[]> hist = CreateRotatingHist();
for (int iy = 0, offy = 0; iy < cellCountY; iy++, offy += stride * cellSize)
{
float[] h = hist[Core.MinMax.Min(iy, blockSize - 1)];
ComputeHistLine(offy, h);
if (iy + 1 >= blockSize)
{
// calculate blocks - we are at the last block line
if (((iy + 1 - blockSize) % blockStride) == 0)
{
ComputeBlockLine();
}
// rotate histograms
if (blockSize > 1 && iy + 1 < cellCountY)
{
RotateHist(hist);
}
}
}
Debug.Assert(offblock == blocks.Length, "We must have processed all blocks by now.");
// normalize blocks
const float Eps = 1e-10f;
for (int i = 0, off = 0; i < blockCount; i++, off += blockSizeInBins)
{
float norm = Vectors.L2Norm(blockSizeInBins, blocks, off);
Mathematics.DivC(blockSizeInBins, norm + Eps, blocks, off);
}
// apply threshold
if (threshold > 0.0f)
{
Vectors.ThresholdLT(blocks.Length, threshold, 0.0f, blocks, 0);
}
/*DenseVectorProxyF[] dense = new DenseVectorProxyF[blockCount];
* for (int i = 0, off = 0; i < blockCount; i++, off += blockSizeInBins)
* {
* dense[i] = new DenseVectorProxyF(blockSizeInBins, blocks, off);
* }*/
/*SparseVectorF[] sparse = new SparseVectorF[blockCount];
* for (int i = 0; i < blockCount; i++)
* {
* sparse[i] = SparseVectorF.FromDense(blockSizeInBins, vectors[i].X, 0);
* }*/
return(new DenseVectorPackF(blockCount, blockSizeInBins, blocks));
ImageF PrepareImage()
{
// convert image to 8bpp, then float
return(this
.ConvertTo(null, 8)
.Convert8To32f(
ComputeImageSize(this.Width),
ComputeImageSize(this.Height),
BorderType.BorderRepl,
0));
int ComputeImageSize(int size)
{
int kernelSize = cellSize * blockSize;
int kernelStride = cellSize * blockStride;
return(Core.MinMax.Max(size - kernelSize, 0).RoundUp(kernelStride) + kernelSize);
}
}
int ComputeBlockCount(int cellCount)
{
return((Core.MinMax.Max(cellCount - blockSize, 0) / blockStride) + 1);
}
List <float[]> CreateRotatingHist()
{
List <float[]> h = new List <float[]>(blockSize);
for (int i = 0; i < blockSize; i++)
{
h.Add(new float[cellCountX * numberOfBins]);
}
return(h);
}
void RotateHist(List <float[]> h)
{
float[] temp = h[0];
h.RemoveAt(0);
h.Add(temp);
Vectors.Set(temp.Length, 0, temp, 0);
}
void ComputeHistLine(int offy, float[] h)
{
for (int ix = 0, offx = offy, offh = 0; ix < cellCountX; ix++, offx += cellSize, offh += numberOfBins)
{
for (int iyc = 0, offyc = offx; iyc < cellSize; iyc++, offyc += stride)
{
for (int ixc = 0, offxc = offyc; ixc < cellSize; ixc++, offxc++)
{
float value = mag[offxc];
if (value != 0.0f)
{
////int bin = (int)ang[offxc] % numberOfBins;
////h[offh + bin] += mag[offxc];
float angle = ang[offxc];
int bin = (int)angle;
float value1 = value * (angle - bin);
h[offh + (bin % numberOfBins)] += value1;
h[offh + ((bin + 1) % numberOfBins)] += value - value1;
}
}
}
}
}
void ComputeBlockLine()
{
int blockLengthInBins = blockSize * numberOfBins;
int blockStrideInBins = blockStride * numberOfBins;
for (int ix = 0, offh = 0; ix < blockCountX; ix++, offh += blockStrideInBins)
{
for (int iyc = 0; iyc < blockSize; iyc++)
{
Vectors.Copy(blockLengthInBins, hist[iyc], offh, blocks, offblock);
offblock += blockLengthInBins;
}
}
}
}
