I get greyscale image successfully , but I have some query about pixel value classification, because concrete have cement,fine and coarse aggregate. How can I classify this material through greyscale? I need an unique identity pixel value for each material classification.or whether their are another method to get unique identity value for each concrete image.
I would recommend keeping the spectral data of the RGB bands. Run the classification with all the available spectral information. If you must use ArcGIS, try an image segmentation and classification rather than a pixel-based classifier. http://desktop.arcgis.com/en/arcmap/10.3/tools/spatial-analyst-toolbox/understanding-segmentation-and-classification.htm