protected override void InitializeDecoding(string src, int passHash, int lsbIndicator)
{
base.InitializeDecoding(src, passHash, lsbIndicator);
var filter = new Laplace(Bitmap, LsbIndicator, 8);
IDictionary<Pixel, int> filtered = new Dictionary<Pixel, int>();
for (var x = 0; x < Bitmap.Width; x++)
{
for (var y = 0; y < Bitmap.Height; y++)
{
filtered.Add(new Pixel(x, y), filter.GetValue(x, y));
}
}
mLaplaceValues = filtered.OrderByDescending(key => key.Value);
}
protected override double Calculation(LockBitmap originalBmp, LockBitmap steganoBmp)
{
var origFiltered = new Laplace(originalBmp, 0, 8);
var stegoFiltered = new Laplace(steganoBmp, 0, 8);
var originalDiff = 0.0;
var totalDiff = 0.0;
for (var y = 0; y < originalBmp.Height; y++)
{
for (var x = 0; x < originalBmp.Width; x++)
{
//TODO Shouldnt that be the other direction? First TOTAL and second ORIGINAL?
originalDiff += Math.Pow(origFiltered.GetValue(x, y) - stegoFiltered.GetValue(x, y), 2);
totalDiff += Math.Pow(origFiltered.GetValue(x, y), 2);
}
}
return originalDiff/totalDiff;
}
/**
* Gets the laplace graph of an image. The image
* is assumed to be colour, no negative values will
* result.
*
* @param image The image to get the graph of.
* @return The graph of the image.
*/
public static double[][] GetGraph(LockBitmap image)
{
var filter = new Laplace(image, 0, 8);
//filter the image
var fparray =
new FilteredPixel[image.Width*image.Height];
for (var i = 0; i < image.Width; i++)
{
for (var j = 0; j < image.Height; j++)
{
fparray[i*image.Height + j] =
new FilteredPixel(i, j,
Math.Abs(filter.GetValue(i, j)));
}
}
//sort the filter results
//is in ascending order - low at start, high at end
Array.Sort(fparray, new FpComparator());
//now for each individual filter result, we count how many we have
//first find out how many different values we have
var numdistinct = 1;
for (var i = 1; i < fparray.Length; i++)
{
if (fparray[i].FilterValue != fparray[i - 1].FilterValue)
{
numdistinct++;
}
}
//now we create an array to hold the filter values and their counts
//var results = new double[numdistinct][2];
var results = new double[numdistinct][];
for (var i = 0; i < results.Length; i++)
{
results[i] = new double[2];
}
results[0][0] = fparray[0].FilterValue;
results[0][1] = 1;
var k = 0;
//now we fill up the array
foreach (var t in fparray)
{
if (results[k][0] != t.FilterValue)
{
k++;
results[k][0] = t.FilterValue;
results[k][1] = 1;
}
else
{
results[k][1]++;
}
}
//now normalise the graph
foreach (var t in results)
{
t[1] = t[1]/fparray.Length;
}
//graph produced, return results
return results;
}
private void GenerateShips()
{
var filter = new Laplace(Bitmap, LsbIndicator, 8);
IDictionary<Pixel, int> filtered = new Dictionary<Pixel, int>();
for (var x = 0; x < Bitmap.Width; x++)
{
for (var y = 0; y < Bitmap.Height; y++)
{
filtered.Add(new Pixel(x, y), filter.GetValue(x, y));
}
}
var ordered = filtered.OrderByDescending(key => key.Value);
//TODO: dynamic maybe? Top 100
mShips = new HashSet<Pixel>(ordered.Select((x, y) => x.Key).Take(50));
}
