[FEA] Quick Hash of WSI

[bhashemian]

Often times MONAI users need to collate the patches extracted from the same WSI. Currently, we are relying on the file path to perform such operation but similar to OpenSlide it would great if cuCIM can compute a quick hash of the image (or part of the image) and provide it in CuImage metadata. A SHA-1 hash would be good enough since we don't care about security of the hash function here.

openslide.quickhash-1
A non-cryptographic hash of a subset of the slide data. It can be used to uniquely identify a particular virtual slide, but cannot be used to detect file corruption or modification.

[kaczmarj]

i am also interested in getting a hash for whole slide images, and i found openslide's C implementation for this:

https://github.com/openslide/openslide/blob/549e81b6662efe2b2285f11a5bcb31ccd7b95655/src/openslide-decode-tifflike.c#L996-L1143

[kaczmarj]

fwiw i implemented a small version of openslide's quickhash. it doesn't do everything openslide's implementation does.

it works by getting an md5 hash of the commend and vendor name in the tiff metadata, along with the hash of the lowest resolution image in the pyramid.

"""Hash parts of a whole slide image.

This implementation is heavily inspired by OpenSlide's quickhash1:
https://github.com/openslide/openslide/blob/549e81b6662efe2b2285f11a5bcb31ccd7b95655/src/openslide-decode-tifflike.c#L996-L1143
"""

from __future__ import annotations

import hashlib

import tiffslide
from PIL import Image
from tiffslide.tiffslide import PROPERTY_NAME_COMMENT
from tiffslide.tiffslide import PROPERTY_NAME_VENDOR


def _read_smallest_level(tslide: tiffslide.TiffSlide) -> Image.Image:
    smallest_level = tslide.level_count - 1
    size = tslide.level_dimensions[smallest_level]
    return tslide.read_region((0, 0), level=smallest_level, size=size)


def _hash_str_and_property(
    hasher: hashlib._Hash, tslide: tiffslide.TiffSlide, name: str
) -> None:
    value = tslide.properties.get(name)
    if value is not None:
        hasher.update(name.encode())
        hasher.update(str(value).encode())


def quickhash(tslide: tiffslide.TiffSlide) -> str:
    """Return a quick MD5 hash of a whole slide image."""
    m = hashlib.md5()
    _hash_str_and_property(m, tslide, PROPERTY_NAME_COMMENT)
    _hash_str_and_property(m, tslide, PROPERTY_NAME_VENDOR)
    smallest_level_bytes = _read_smallest_level(tslide).tobytes()
    m.update(smallest_level_bytes)
    return m.hexdigest()