Lazily load images from the tile iterator.
Lazily load images from the tile iterator.

When a tile is returned by the tile iterator, don't load the actual image until it is needed.

girder/large_image,DigitalSlideArchive/large_image,DigitalSlideArchive/large_image,girder/large_image,girder/large_image,DigitalSlideArchive/large_image