How to read LMDB with PNG images?

[joonjeon]

I see that your custom-implemented AnnotatedData function creates layers that read, parse, and automatically store data from LMDB.
But nowhere throughout the whole Internet was I able to find how to implement the procedure for this.

Seems like there's an internal implementation with C++-backend, and I have tried everything in Python to get the same functionality,
but there is always a problem with reading PNG-encoded image part of LMDB.

google protobuf's ParseFromString always returns an error saying that it cannot parse strings with non-utf8 characters.
This means there's got to be something within your C++-implementation that can parse the LMDB niftly, but despite close inspection of your code, I have NO IDEA how this works.

Is there a way to tackle this?