I have a classified image (I did it in ERDAS) with six categories. There are some misclassified pixels (especially high-density urban category). Is there any way that I can choose one pixel and then change its class (for instance change bareland to high-density urban) in ERDAS or Arcmap? I do appreciate your help. Thanks.
The simplest way is to create a new point layer for identifying individual cells which have been misclassified: for each incorrect cell, create a point at that location, and update the attribute table with the corrected value.
Then, rasterize the points to a layer with the same extent and cell size as your input layer, then merge the two with a raster calculator, doing something along the lines of:
if(rasterized_points > 0, rasterized_points, classified_input_image)