How to compute the composition of all predicted flow fields

microsoft / Recursive-Cascaded-Networks

[ICCV 2019] Recursive Cascaded Networks for Unsupervised Medical Image Registration

https://arxiv.org/abs/1907.12353

MIT License

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How to compute the composition of all predicted flow fields #12

Closed Algolzw closed 4 years ago

Algolzw commented 4 years ago

Hello, I have a question that how to compute the composition of all predicted flow fields. Can I just use "SpatialTransformer(field1, field2)" to reconstruct the final displacement field? Thanks.

zsyzzsoft commented 4 years ago

Suppose we have two displacement fields A and B, to compute A compose B, one should call SpatialTransformer(B, A) + A (see recursive_cascaded_networks.py, line 98-99).

Algolzw commented 4 years ago

May I ask why "+ A"? I'm really confused.

zsyzzsoft commented 4 years ago

It's because they are displacement fields. A detailed formula can be found in the VTN paper, section III.A.