Unloading an image removes the image data from working memory without erasing the image objects from the drawing.
To improve application performance, you can unload images you no longer need. An unloaded image cannot be displayed or plotted. The unload operation is just one of several image removal methods. For temporary removal, consider the hide operation. For more complete removal, consider the erase and detach operations.
Reloading puts the image back into working memory and redisplays it.