TIFF and PCD files have the ability to store different resolutions of the same image. For TIFF, these files appear to be Sequences (multi-frame images), until further investigation shows each frame to be of a different size. Such sequences are not allowed and so the user must choose which one of the resolutions to open out of the file. These types of TIFF files are named Multiple Resolution TIFF's.
To get a list of the sizes of each frame, check the ResolutionSizes property.
This library does not support writing of Multiple Resolution files, so this is a read-only property.