/// <summary>
/// Adaptive Histogram Equalization
/// </summary>
/// <param name="bitplane">bitplane of current image</param>
/// <param name="windowSize">size of window</param>
private static void AHE(ref MyBitplane bitplane, int windowSize)
{
// Prepare data
MyBitplane newBitplane = new MyBitplane(bitplane.Width, bitplane.Height);
MyBitplane window = new MyBitplane(windowSize, windowSize);
int x;
int y;
for (y = 0; y < bitplane.Height; ++y)
{
for (x = 0; x < bitplane.Width; ++x)
{
// Create window
CreateWindow(ref bitplane, windowSize, ref window, y, x);
// Histogram equalization on window
HE(ref window);
// Replace pixel from windowHE
newBitplane.SetPixel(x, y, window.GetPixel(windowSize / 2, windowSize / 2));
}
}
// Copy
for (y = 0; y < bitplane.Height; ++y)
{
for (x = 0; x < bitplane.Width; ++x)
{
bitplane.SetPixel(x, y, newBitplane.GetPixel(x, y));
}
}
}
/// <summary>
/// Histogram Equalization
/// </summary>
/// <param name="bitplane">bitplane of current image</param>
private static void HE(ref MyBitplane bitplane)
{
// Histogram
double[] histogram = calculateHistogram(bitplane);
// Probability
double totalElements = bitplane.Width * bitplane.Height;
double[] probability = new double[256];
int i;
for (i = 0; i < 256; i++)
{
probability[i] = histogram[i] / totalElements;
}
// Comulative probability
double[] comulativeProbability = calculateComulativeFrequency(probability);
// Multiply comulative probability by 256
int[] floorProbability = new int[256];
for (i = 0; i < 256; i++)
{
floorProbability[i] = (int)Math.Floor(comulativeProbability[i] * 255);
}
// Transform old value to new value
int x;
for (int y = 0; y < bitplane.Height; y++)
{
for (x = 0; x < bitplane.Width; x++)
{
bitplane.SetPixel(x, y, (byte)floorProbability[bitplane.GetPixel(x, y)]);
}
}
}
/// <summary>
/// Create window on current bitplane
/// Edges are mirrored
/// </summary>
/// <param name="bitplane">bitplane of current image</param>
/// <param name="windowSize">size of window</param>
/// <param name="window">window reference filled from bitmap</param>
/// <param name="y">current y position on bitplane</param>
/// <param name="x">current x position on bitplane</param>
private static void CreateWindow(ref MyBitplane bitplane, int windowSize, ref MyBitplane window, int y, int x)
{
int jIndex = 0;
int iIndex;
int i;
for (int j = 0 - (windowSize / 2); j < (windowSize / 2); ++j)
{
iIndex = 0;
for (i = 0 - (windowSize / 2); i < (windowSize / 2); ++i)
{
int xx = x + i;
if (xx < 0)
{
xx = Math.Abs(xx);
}
if (xx >= bitplane.Width)
{
xx = (bitplane.Width - 1) + ((bitplane.Width) - (xx + windowSize));
}
int yy = y + j;
if (yy < 0)
{
yy = Math.Abs(yy);
}
if (yy >= bitplane.Height)
{
yy = (bitplane.Height - 1) + ((bitplane.Height) - (yy + windowSize));
}
window.SetPixel(iIndex, jIndex, bitplane.GetPixel(xx, yy));
++iIndex;
}
++jIndex;
}
}
/// <summary>
/// Contrast Limited Histogram Equalization implementation
/// </summary>
/// <param name="bitplane"></param>
/// <param name="contrastLimit"></param>
private static void CLHE(ref MyBitplane bitplane, double contrastLimit)
{
double cl = (contrastLimit * (bitplane.Width * bitplane.Height)) / 256;
double top = cl;
double bottom = 0;
double SUM = 0;
int i;
// Histogram
double[] histogram = calculateHistogram(bitplane);
while (top - bottom > 1)
{
double middle = (top + bottom) / 2;
SUM = 0;
foreach (double value in histogram)
{
if (value > middle)
{
SUM += value - middle;
}
}
if (SUM > (cl - middle) * 256)
{
top = middle;
}
else
{
bottom = middle;
}
}
double clipLevel = Math.Round(bottom + (SUM / 256));
double L = cl - clipLevel;
for (i = 0; i < 256; i++)
{
if (histogram[i] >= clipLevel)
{
histogram[i] = clipLevel;
}
else
{
histogram[i] += L;
}
}
double perBin = SUM / 256;
for (i = 0; i < 256; i++)
{
histogram[i] += perBin;
}
histogram = calculateComulativeFrequency(histogram);
int[] finalFreq = new int[256];
double min = Utils.findMin(histogram);
for (i = 0; i < 256; i++)
{
finalFreq[i] = (int)((histogram[i] - min) / ((bitplane.Width * bitplane.Height) - 2) * 255);
}
int x;
for (int y = 0; y < bitplane.Height; ++y)
{
for (x = 0; x < bitplane.Width; ++x)
{
bitplane.SetPixel(x, y, (byte)finalFreq[bitplane.GetPixel(x, y)]);
}
}
}