The MipImage format is used for storing textures and UI elements in Amulets & Armor. Each MipImage is built up of one or more sub-images. If there are multiple sub-images, they are used to store smaller copies of the main image in descending size.
Sub-image format notes
Note: Width & Height are always the size of the first/largest image. Each sub-image size is half as wide and half as tall as the previous sub-image (rounded down). Textures and UI elements are actually stored slightly differently: UI elements are stored as displayed, while textures are rotated 90-degrees counterclockwise. There is no information in the image file to indicate this however, so it must be known by the context in which the image is used.
Sub-image format details