Image segmentation using the histogram

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C#

histogram

image-processing

I am trying to do an image segmentation which depends on the histogram values, first I did k-mean, then I convert the image to grey and taken the histogram value from it. Finally, I using the threshold to get the requested part.

What I have tried:

private void button2_Click(object sender, EventArgs e)
        {
            int width = image.Width;
            int height = image.Height;
            
            Color p;

            //Grayscale
            for (int y = 0; y < height; y++)
            {
                for (int x = 0; x < width; x++)
                {
                    p = image.GetPixel(x, y);
                    int a = p.A;
                    int r = p.R;
                    int g = p.G;
                    int b = p.B;
                    double someDouble = ((r * 0.3) + (g * 0.59) + (b * 0.11));
                    int avg = Convert.ToInt32(someDouble);
                    //int avg = (r + g + b) / 3;
                    avg = (avg < 100) && (avg > 80) ? 0 : 255;     // Converting 

                                     gray pixels to either pure black or pure white
                    
                    bmp1.SetPixel(x, y, Color.FromArgb(a,avg, avg, avg));
                }
            }
            pictureBox2.Image = bmp1;
        }

my question? I didn't get good segmentation...can someone give me advice, and what does the command "

avg = (avg < 100) && (avg > 80) ? 0 : 255;

" give me when become true? white "1" or black"0"?