/// <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)
{
var img = image.Convolve(new FloatImage(7, 7, 1));
var resized = img.Resize(32, 32);
var C = CreateDctMatrix(32);
var Ctransp = C.Transpose();
var dctImage = C.Multiply(resized).Multiply(Ctransp);
var sum = 0f;
for (var y = 0; y < 8; y++)
{
for (var x = 0; x < 8; x++)
{
sum += dctImage[x, y];
}
}
var median = sum / 64f;
var r = 0ul;
for (var y = 0; y < 8; y++)
{
for (var x = 0; x < 8; x++)
{
r |= dctImage[x, y] > median ? (1ul << (x + 8 * y)) : 0;
}
}
return(r);
}
/// <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)
{
var img = image.Convolve(new FloatImage(7, 7, 1));
var resized = img.Resize(32, 32);
var coeff = _DctMatrix ?? (_DctMatrix = CreateDctMatrix(32));
var dctImage = coeff.MatrixMultiply(resized).MatrixMultiply(coeff, isTransposed: true);
var median = GetMedianOf64(dctImage);
var r = 0ul;
for (var y = 0; y < 8; y++)
{
for (var x = 0; x < 8; x++)
{
r |= dctImage[x + 1, y + 1] > median ? (1ul << (x + 8 * y)) : 0;
}
}
return(r);
}
public static FloatImage Blur(this IByteImage image, float sigma) => image.Convolve(FloatImage.CreateGaussian(3, sigma));
