Available with Spatial Analyst license.
Reclassify an image after classification
After you classify an image, you will probably encounter small errors in the classification result. To address these it is often easier to simply edit the final classified image rather than recreate training sites and do the process again. Here, you can make edits to individual features or objects. You can select a feature and reclassify it as any other class that you want. This is a postprocessing step designed to account for errors in the classification process. All changes that you make are displayed in the Edits Log section of this page. You have the option to check on or off any of the edits that you have made. If you uncheck an edit, this means that it will not be used in the reclassifier. As you are fixing errors, you will want to see the underlying imagery to verify that the new class make sense. Press the L key to toggle the transparency of the classified image on and off.
Use the Reclassify an object tool to draw a circle on the classified image. The segment from which the circle originates will be changed to the new class. If the circle encompasses all of the segment, the entire segment will change to the new class. If the circle only encompasses part of the segment, only that part of the circle will change.
Use the Reclassify within a region tool to draw a polygon on the classified image. The current class within this polygon will be changed to the new class. You can use the Any class to change all the pixels within the region to the new class.