// assume k = -0.2 and R = 15x15
// needs 1 pixel width padding
public static Pixel Niblack(PNM image, int index, double k = -0.2, int length = 15, int padding = 7)
{
byte r, g, b;
float[] surrounding = new float[length * length];
int i = 0;
for (int m = 0; m < length; m++)
{
for (int n = 0; n < length; n++)
{
image.GetPixel(index - ((padding - m) * image.Width) - (padding - n), out r, out g, out b);
surrounding[i] = PNM.RGBToLuminosity(r, g, b);
i++;
}
}
float mean = surrounding.Average();
double threshold = mean + (k * (mean / surrounding.Length));
image.GetPixel(index, out r, out g, out b);
byte luminosity = PNM.RGBToLuminosity(r, g, b);
if (luminosity < threshold)
{
return(Pixel.Black);
}
return(Pixel.White);
}
// pixel_intensity >= threshold == white object
// pixel_intensity < threshold == black background
public static Pixel Plain(byte r, byte g, byte b, byte threshold)
{
byte lum = PNM.RGBToLuminosity(r, g, b);
if (lum >= threshold)
{
return(Pixel.White);
}
return(Pixel.Black);
}
public static Pixel ToGrayscale(byte r, byte g, byte b)
{
byte value = PNM.RGBToLuminosity(r, g, b);
return(new Pixel(value, value, value));
}