private string HistoGramValues(string _imageName)
                            {
                                // Get your image in a bitmap; this is how to get it from a picturebox
                                Bitmap bmOriginal = new Bitmap("D:\\inetpub\\webs\\francescobelloniit\\universita\\eimmagini\\images\\" + _imageName);

                                // Get your image in greyscale
                                Bitmap bm = MakeGrayscale3(bmOriginal);
        
                                int h = bm.Height;
                                int l = bm.Width;
                                CheckValueTest = "immagine alta:" + h + ", larga: " + l + "("+h+"x"+l+" = "+(h*l).ToString()+")";

                                // Store the histogram in a dictionary (grigio | valore di grigio)          
                                Dictionary<int, int> histo = new Dictionary<int, int>();

                                for (int x = 0; x < bm.Width; x++)
                                {
                                    for (int y = 0; y < bm.Height; y++)
                                    {
                                        // Get pixel color 
                                        Color c = bm.GetPixel(x, y);
                                        int grey = (int)(c.R * 0.3 + c.G * 0.59 + c.B * 0.11);

                                        // If it exists in our 'histogram' increment the corresponding value, or add new
                                        if (histo.ContainsKey(grey))
                                            histo[grey] = histo[grey] + 1;
                                        else
                                            histo.Add(grey, 1);
                                    }
                                }

                                int nPx=0;

                                // This outputs the histogram in an output window
                                StringBuilder sb = new StringBuilder();
                                for (int i = 0; i < 256; i++)
                                {
                                    if (histo.ContainsKey(i))
                                    {
                                        sb.Append("{ x: '" + i + "', y: " + histo[i] + " }," + "\r\n");  
                                        nPx+=histo[i];
                                    }
                                }

                                CheckValueTest += "--> ho contato " + nPx + "px"; 

                                string temp = sb.ToString();
                                temp=RemoveLast(temp,",");
                                showValues += temp.Replace("\r\n","<br />");

                                return getHistogramScript(temp);

                            }