Using the AutoCAD imaging commands, you can modify image display values such as brightness and contrast, and you can clip an image so that only part of the image is displayed in the drawing. However, these adjustments affect only how the image appears in your drawing. You cannot use AutoCAD by itself to permanently edit the image pixels.
AutoCAD Raster Design toolset was designed to work with AutoCAD so that you can permanently edit your images. For example, if you make adjustments to the brightness and contrast of an image using the AutoCAD Raster Design toolset Histogram (iHistogram) command, you can save the edits to the image file itself. Then, whenever you open a drawing that contains that image file, the image appears with the correct brightness and contrast values.
If, on the other hand, you use the AutoCAD IMAGEADJUST command to edit the Image Adjust color map and you have the same image inserted into other drawings, you must repeat the same changes to each insertion of the image in all drawings.