I have a thematic raster image containing 18 land use classes (like built-up, water bodies, plantations, forest, etc.). When I display this image in a GIS application (Arcmap/Erdas IMAGINE), the map is displayed with all the classes in the attribute table. The attribute table has the histogram/count column for each class and the area of each class that I have computed. But when I enquire a pixel, its value is zero. When I try to run an algorithm on this image, the output is a blank image (all zeros), because the pixel values in my original image are zeros.
The original values were present to begin with, because I had worked with the image in the past. Only now, the image with the colors I had assigned to different classes is visible and the attribute table has the original data, but the pixel values are all zeros.
What could be the problem? And is there a way to restore this raster image?