Answer Pablo 2nd

            UnmanagedImage img = UnmanagedImage.FromManagedImage(AForge.Imaging.Image.FromFile(@"C:\Users\admin\Pictures\img008.jpg"));
            ImageStatistics stat = new ImageStatistics(img);
            AForge.Math.Histogram hist = stat.Gray; //or .GrayWithoutBlack, .Blue, .Green, .Red
            int[] histBins = hist.Values;
            int pixelCount = 0;
            for (int i = 5; i < 128; i++)
                pixelCount += histBins[i];
            Console.WriteLine("numbers of pixels in the gray range: " + pixelCount);