public static CompressedImage CompressWithDCT(this double[,] channelPixels, Options options,
int compressionLevel = 4)
{
var frequencesPerBlock = -1;
var DCTSize = options.DCTSize;
var height = channelPixels.GetLength(0);
var width = channelPixels.GetLength(1);
var result = new List <double>();
for (var y = 0; y < height; y += DCTSize)
{
for (var x = 0; x < width; x += DCTSize)
{
var subMatrix = channelPixels.GetSubMatrix(y, DCTSize, x, DCTSize, DCTSize);
subMatrix.ShiftMatrixValues(-128);
var channelFreqs = DCTHelper.DCT2D(subMatrix);
frequencesPerBlock = DCTSize * DCTSize;
for (var i = 0; i < DCTSize; i++)
{
for (var j = 0; j < DCTSize; j++)
{
if (i + j < compressionLevel)
{
result.Add(channelFreqs[i, j]);
continue;
}
channelFreqs[i, j] = 0;
frequencesPerBlock--;
}
}
}
}
return(new CompressedImage
{
CompressionLevel = compressionLevel,
FrequencesPerBlock = frequencesPerBlock,
Frequences = result,
Height = height,
Width = width
});
}
private static List <double> GetFrequencesFromSubmatrix(double[,] channelPixels, int DCTSize, int compressionLevel, int y,
int x)
{
var subMatrix = channelPixels.GetSubMatrix(y, DCTSize, x, DCTSize, DCTSize);
subMatrix.ShiftMatrixValues(-128);
var localResult = new List <double>();
var channelFreqs = DCTHelper.DCT2D(subMatrix);
for (var i = 0; i < DCTSize; i++)
{
for (var j = 0; j < DCTSize; j++)
{
if (i + j < compressionLevel)
{
localResult.Add(channelFreqs[i, j]);
continue;
}
channelFreqs[i, j] = 0;
}
}
return(localResult);
}
