/// <summary>
/// compute dct robust image hash
/// </summary>
/// <param name="image">An image to compute DCT hash.</param>
/// <returns>hash of type ulong</returns>
public static ulong ComputeDctHash(IByteImage image)
{
FloatImage img = image.Convolve(new FloatImage(7, 7, 1));
FloatImage resized = img.Resize(32, 32);
FloatImage coeff = _DctMatrix ?? (_DctMatrix = CreateDctMatrix(32));
FloatImage dctImage = coeff.MatrixMultiply(resized).MatrixMultiply(coeff, isTransposed: true);
float median = GetMedianOf64(dctImage);
ulong r = 0ul;
for (int y = 0; y < 8; y++)
{
for (int x = 0; x < 8; x++)
{
r |= dctImage[x + 1, y + 1] > median ? (1ul << (x + 8 * y)) : 0;
}
}
return(r);
}
