// Source - https://jivp-eurasipjournals.springeropen.com/articles/10.1186/s13640-016-0138-1
public static Image <Bgr, Byte> Adaptive(Image <Bgr, Byte> image, bool showWindows = false)
{
Image <Hsv, Byte> hsvImage;
Image <Gray, Byte> grayImage;
Image <Gray, double> grayImageNormilized;
Image <Gray, Byte> grayImageEnhanced;
Image <Gray, double> grayImageEnhancedNormilized;
Image <Hsv, Byte> hsvImageEnhanced;
Image <Bgr, Byte> result;
// Color image?
// FOR NOW CONSIDER ONLY COLOR IMAGES
bool isColorImage = true;
// RGB to HSV and take V
hsvImage = ImageHelper.ToHsv(image);
var hsvChannels = hsvImage.Split();
grayImage = hsvChannels.ElementAt(2);
// Normalize image
grayImageNormilized = ImageHelper.NormalizeImage(grayImage);
// Low contrast image?
bool isLowContrastImage;
bool isDarkImage;
double[] pixelValues = ImageHelper.GetImagePixels(grayImageNormilized);
double[] positivePixelValues = pixelValues.Where(x => x > 0).ToArray(); // filter 0 values to retrieve more accurate results (according to article)
double mu = StatisticsHelper.Average(positivePixelValues); // mean of the image intensity
double sigma = StatisticsHelper.StandartDeviation(positivePixelValues); // standard deviation
Func <List <string> > g = () =>
{
string Q1 = "Q1"; // low-contrast class
string Q2 = "Q2"; // high (or moderate) contrast class
string QSubclassDark = "Dark";
string QSubclassBright = "Bright";
string Q;
string QSubclass;
// D=diff((μ+2σ),(μ−2σ))
//double D = (mu + 2.0 * sigma) - (mu - 2.0 * sigma);
double D = 4.0 * sigma; // seci=ond criteria
// τ is a parameter used for defining the contrast of an image
double tao = 3.0; // τ=3 is a suitable choice for characterizing the contrasts of different images.
if (D <= (1.0 / tao))
{
Q = Q1;
}
else
{
Q = Q2;
}
if (mu >= 0.5)
{
QSubclass = QSubclassBright;
}
else
{
QSubclass = QSubclassDark;
}
return(new List <string>()
{
Q,
QSubclass
});
};
List <string> imageClasses = g();
isLowContrastImage = imageClasses[0] == "Q1" ? true : false;
isDarkImage = imageClasses[1] == "Dark" ? true : false;
// Intensity transformation
// c and γ are two parameters that control the shape of the transformation curve
// In contrast to traditional gamma correction, AGC sets the values of γ and c automatically using image information, making it an adaptive method
double c = default(double);
double gamma = default(double);
Func <double, double> Heaviside = (x) =>
{
if (x <= 0)
{
return(0);
}
else // (x > 0)
{
return(1);
}
};
grayImageEnhancedNormilized = new Image <Gray, double>(grayImage.Size);
for (int m = 0; m < grayImageNormilized.Rows; m++)
{
for (int n = 0; n < grayImageNormilized.Cols; n++)
{
Gray pixel = grayImageNormilized[m, n];
double I_in = pixel.Intensity;
//// Enhancement of low-contrast image
if (isLowContrastImage)
{
// calc gamma
gamma = -Math.Log(sigma, newBase: 2);
// calc k
double I_gamma = Math.Pow(I_in, gamma);
double k = I_gamma + (1 - I_gamma) * Math.Pow(mu, gamma);
// calc c
c = 1.0 / (1.0 + Heaviside(0.5 - mu) * (k - 1.0));
// Bright image in Q1
if (isDarkImage == false)
{
// mu >= 0.5 => c = 1
//c = 1;
}
// Dark image in Q1
if (isDarkImage == true)
{
// mu < 0.5 => c = 1/k
//c = 1.0 / k;
}
}
//// Enhancement of high- or moderate-contrast image
if (isLowContrastImage == false)
{
// calc gamma
gamma = Math.Exp((1.0 - (mu + sigma)) / 2.0);
// calc k
double I_gamma = Math.Pow(I_in, gamma);
double k = I_gamma + (1.0 - I_gamma) * Math.Pow(mu, gamma);
// calc c
c = 1.0 / (1.0 + Heaviside(0.5 - mu) * (k - 1.0));
// Dark image in Q2
if (isDarkImage == true)
{
// For images with μ<0.5, (μ+σ)≤1, since both μ and σ are less than (or equal to) 0.5 which implies γ≥1
}
// Bright image in ϱ 2
if (isDarkImage == false)
{
}
}
// apply final formula
// I_out = c * I_in
double val = c * Math.Pow(I_in, gamma);
grayImageEnhancedNormilized[m, n] = new Gray(val);
}
}
// DeNormalize image
grayImage = ImageHelper.DeNormalizeImage(grayImageNormilized);
grayImageEnhanced = ImageHelper.DeNormalizeImage(grayImageEnhancedNormilized);
// get enhanced hsv image
hsvImageEnhanced = new Image <Hsv, byte>(new Image <Gray, Byte>[] { hsvChannels[0], hsvChannels[1], grayImageEnhanced });
// convert hsv to rgb
result = ImageHelper.ToBgr(hsvImageEnhanced);
if (showWindows)
{
EmguCvWindowManager.Display(image, "AGC_V2_1 image");
EmguCvWindowManager.Display(hsvImage, "AGC_V2_2 hsvImage");
EmguCvWindowManager.Display(grayImage, "AGC_V2_3 grayImage");
EmguCvWindowManager.Display(grayImageEnhanced, "AGC_V2_4 grayImageEnhanced");
EmguCvWindowManager.Display(hsvImageEnhanced, "AGC_V2_5 hsvImageEnhanced");
EmguCvWindowManager.Display(result, "AGC_V2_6 result");
}
return(result);
}