Why is the output of the Image Encoder here a tensor with the shape of (64, 64, 256) instead of a one-dimensional vector?

As far as I know, Image Encoder encodes an image into a one-dimensional vector.
Why is the output of the Image Encoder here a tensor with the shape of (64, 64, 256) instead of a one-dimensional vector ?
Does the output of the Image Encoder here represent the feature map of the input image ?

Review the repository's example notebooks and the Image Encoder usage related to the reported (64, 64, 256) output. Establish whether this output is a feature map and document the encoder output semantics; the issue names no specific file or test, so the appropriate documentation location and validation step still need to be identified.

Written by the indexing model from the issue text.