private void OnePointOperation(string operation)
 {
     if (operation == "ThreshHoldGraySave")
     {
         mainImage.ThresholdLevelSave(startThLevel, endThLevel);
         InvalidateImage();
     }
     else if (operation == "StretchGrayLevel")
     {
         mainImage.StretchGrayLevel(startThLevel, endThLevel);
         InvalidateImage();
     }
     else
     {
         mainImage.OnePointOperation(operation);
         InvalidateImage();
     }
 }