WSIReader defaults and tensor conversion (#6058)

Fixes #6056 

### Description

This PR enable to instantiate `WSIReader` classes with default values
for `mode` and `dtype`. It also accepts `torch.dtype` as dtype and if
`torch.dtype` is provided, the output will be a `torch.Tensor` to avoid
additional step to convert the output for inference.

### Types of changes
<!--- Put an `x` in all the boxes that apply, and remove the not
applicable items -->
- [x] Non-breaking change (fix or new feature that would not break
existing functionality).
- [x] New tests added to cover the changes.
- [x] Integration tests passed locally by running `./runtests.sh -f -u
--net --coverage`.
- [x] Quick tests passed locally by running `./runtests.sh --quick
--unittests --disttests`.
- [x] In-line docstrings updated.

---------

Signed-off-by: Behrooz <[email protected]>

monai/data/wsi_reader.py

@@ -17,11 +17,19 @@
 from typing import Any
 
 import numpy as np
+import torch
 
-from monai.config import DtypeLike, PathLike
+from monai.config import DtypeLike, NdarrayOrTensor, PathLike
 from monai.data.image_reader import ImageReader, _stack_images
 from monai.data.utils import is_supported_format
-from monai.utils import WSIPatchKeys, ensure_tuple, optional_import, require_pkg
+from monai.utils import (
+    WSIPatchKeys,
+    dtype_numpy_to_torch,
+    dtype_torch_to_numpy,
+    ensure_tuple,
+    optional_import,
+    require_pkg,
+)
 
 OpenSlide, _ = optional_import("openslide", name="OpenSlide")
 TiffFile, _ = optional_import("tifffile", name="TiffFile")
@@ -33,12 +41,21 @@ class BaseWSIReader(ImageReader):
     """
     An abstract class that defines APIs to load patches from whole slide image files.
 
+    Args:
+        level: the whole slide image level at which the image is extracted.
+        channel_dim: the desired dimension for color channel.
+        dtype: the data type of output image.
+        device: target device to put the extracted patch. Note that if device is "cuda"",
+            the output will be converted to torch tenor and sent to the gpu even if the dtype is numpy.
+        mode: the output image color mode, e.g., "RGB" or "RGBA".
+        kwargs: additional args for the reader
+
     Typical usage of a concrete implementation of this class is:
 
     .. code-block:: python
 
         image_reader = MyWSIReader()
-        wsi = image_reader.read(, **kwargs)
+        wsi = image_reader.read(filepath, **kwargs)
         img_data, meta_data = image_reader.get_data(wsi)
 
     - The `read` call converts an image filename into whole slide image object,
@@ -58,13 +75,37 @@ class BaseWSIReader(ImageReader):
     supported_suffixes: list[str] = []
     backend = ""
 
-    def __init__(self, level: int = 0, channel_dim: int = 0, **kwargs):
+    def __init__(
+        self,
+        level: int,
+        channel_dim: int,
+        dtype: DtypeLike | torch.dtype,
+        device: torch.device | str | None,
+        mode: str,
+        **kwargs,
+    ):
         super().__init__()
         self.level = level
         self.channel_dim = channel_dim
+        self.set_dtype(dtype)
+        self.set_device(device)
+        self.mode = mode
         self.kwargs = kwargs
         self.metadata: dict[Any, Any] = {}
 
+    def set_dtype(self, dtype):
+        self.dtype: torch.dtype | np.dtype
+        if isinstance(dtype, torch.dtype):
+            self.dtype = dtype
+        else:
+            self.dtype = np.dtype(dtype)
+
+    def set_device(self, device):
+        if device is None or isinstance(device, (torch.device, str)):
+            self.device = device
+        else:
+            raise ValueError(f"`device` must be `torch.device`, `str` or `None` but {type(device)} is given.")
+
     @abstractmethod
     def get_size(self, wsi, level: int | None = None) -> tuple[int, int]:
         """
@@ -138,7 +179,7 @@ def _get_patch(
         raise NotImplementedError(f"Subclass {self.__class__.__name__} must implement this method.")
 
     def _get_metadata(
-        self, wsi, patch: np.ndarray, location: tuple[int, int], size: tuple[int, int], level: int
+        self, wsi, patch: NdarrayOrTensor, location: tuple[int, int], size: tuple[int, int], level: int
     ) -> dict:
         """
         Returns metadata of the extracted patch from the whole slide image.
@@ -175,8 +216,7 @@ def get_data(
         location: tuple[int, int] = (0, 0),
         size: tuple[int, int] | None = None,
         level: int | None = None,
-        dtype: DtypeLike = np.uint8,
-        mode: str = "RGB",
+        mode: str | None = None,
     ) -> tuple[np.ndarray, dict]:
         """
         Verifies inputs, extracts patches from WSI image and generates metadata, and return them.
@@ -185,15 +225,16 @@ def get_data(
             wsi: a whole slide image object loaded from a file or a list of such objects
             location: (top, left) tuple giving the top left pixel in the level 0 reference frame. Defaults to (0, 0).
             size: (height, width) tuple giving the patch size at the given level (`level`).
-                If None, it is set to the full image size at the given level.
+                If not provided or None, it is set to the full image size at the given level.
             level: the level number. Defaults to 0
-            dtype: the data type of output image
-            mode: the output image mode, 'RGB' or 'RGBA'
+            mode: the output image color mode, "RGB" or "RGBA". If not provided the default of "RGB" is used.
 
         Returns:
             a tuples, where the first element is an image patch [CxHxW] or stack of patches,
                 and second element is a dictionary of metadata
         """
+        if mode is None:
+            mode = self.mode
         patch_list: list = []
         metadata_list: list = []
         # CuImage object is iterable, so ensure_tuple won't work on single object
@@ -223,8 +264,25 @@ def get_data(
                 if size[0] <= 0 or size[1] <= 0:
                     raise ValueError(f"Patch size should be greater than zero, provided: patch size = {size}")
 
+            # Get numpy dtype if it is not already.
+            dtype_np = dtype_torch_to_numpy(self.dtype) if isinstance(self.dtype, torch.dtype) else self.dtype
             # Extract a patch or the entire image
-            patch = self._get_patch(each_wsi, location=location, size=size, level=level, dtype=dtype, mode=mode)
+            patch: NdarrayOrTensor
+            patch = self._get_patch(each_wsi, location=location, size=size, level=level, dtype=dtype_np, mode=mode)
+
+            # Convert the patch to torch.Tensor if dtype is torch
+            if isinstance(self.dtype, torch.dtype) or (
+                self.device is not None and torch.device(self.device).type == "cuda"
+            ):
+                # Ensure dtype is torch.dtype if the device is not "cpu"
+                dtype_torch = (
+                    dtype_numpy_to_torch(self.dtype) if not isinstance(self.dtype, torch.dtype) else self.dtype
+                )
+                # Copy the numpy array if it is not writable
+                if patch.flags["WRITEABLE"]:
+                    patch = torch.as_tensor(patch, dtype=dtype_torch, device=self.device)
+                else:
+                    patch = torch.tensor(patch, dtype=dtype_torch, device=self.device)
 
             # check if the image has three dimensions (2D + color)
             if patch.ndim != 3:
@@ -280,26 +338,53 @@ class WSIReader(BaseWSIReader):
         backend: the name of backend whole slide image reader library, the default is cuCIM.
         level: the level at which patches are extracted.
         channel_dim: the desired dimension for color channel. Default to 0 (channel first).
+        dtype: the data type of output image. Defaults to `np.uint8`.
+        mode: the output image color mode, "RGB" or "RGBA". Defaults to "RGB".
+        device: target device to put the extracted patch. Note that if device is "cuda"",
+            the output will be converted to torch tenor and sent to the gpu even if the dtype is numpy.
         num_workers: number of workers for multi-thread image loading (cucim backend only).
         kwargs: additional arguments to be passed to the backend library
 
     """
 
-    def __init__(self, backend="cucim", level: int = 0, channel_dim: int = 0, **kwargs):
-        super().__init__(level, channel_dim, **kwargs)
+    supported_backends = ["cucim", "openslide", "tifffile"]
+
+    def __init__(
+        self,
+        backend="cucim",
+        level: int = 0,
+        channel_dim: int = 0,
+        dtype: DtypeLike | torch.dtype = np.uint8,
+        device: torch.device | str | None = None,
+        mode: str = "RGB",
+        **kwargs,
+    ):
         self.backend = backend.lower()
         self.reader: CuCIMWSIReader | OpenSlideWSIReader | TiffFileWSIReader
         if self.backend == "cucim":
-            self.reader = CuCIMWSIReader(level=level, channel_dim=channel_dim, **kwargs)
+            self.reader = CuCIMWSIReader(
+                level=level, channel_dim=channel_dim, dtype=dtype, device=device, mode=mode, **kwargs
+            )
         elif self.backend == "openslide":
-            self.reader = OpenSlideWSIReader(level=level, channel_dim=channel_dim, **kwargs)
+            self.reader = OpenSlideWSIReader(
+                level=level, channel_dim=channel_dim, dtype=dtype, device=device, mode=mode, **kwargs
+            )
         elif self.backend == "tifffile":
-            self.reader = TiffFileWSIReader(level=level, channel_dim=channel_dim, **kwargs)
+            self.reader = TiffFileWSIReader(
+                level=level, channel_dim=channel_dim, dtype=dtype, device=device, mode=mode, **kwargs
+            )
         else:
             raise ValueError(
                 f"The supported backends are cucim, openslide, and tifffile but '{self.backend}' was given."
             )
         self.supported_suffixes = self.reader.supported_suffixes
+        self.level = self.reader.level
+        self.channel_dim = self.reader.channel_dim
+        self.dtype = self.reader.dtype
+        self.device = self.reader.device
+        self.mode = self.reader.mode
+        self.kwargs = self.reader.kwargs
+        self.metadata = self.reader.metadata
 
     def get_level_count(self, wsi) -> int:
         """
@@ -402,6 +487,10 @@ class CuCIMWSIReader(BaseWSIReader):
         level: the whole slide image level at which the image is extracted. (default=0)
             This is overridden if the level argument is provided in `get_data`.
         channel_dim: the desired dimension for color channel. Default to 0 (channel first).
+        dtype: the data type of output image. Defaults to `np.uint8`.
+        device: target device to put the extracted patch. Note that if device is "cuda"",
+            the output will be converted to torch tenor and sent to the gpu even if the dtype is numpy.
+        mode: the output image color mode, "RGB" or "RGBA". Defaults to "RGB".
         num_workers: number of workers for multi-thread image loading
         kwargs: additional args for `cucim.CuImage` module:
             https://github.com/rapidsai/cucim/blob/main/cpp/include/cucim/cuimage.h
@@ -411,8 +500,17 @@ class CuCIMWSIReader(BaseWSIReader):
     supported_suffixes = ["tif", "tiff", "svs"]
     backend = "cucim"
 
-    def __init__(self, level: int = 0, channel_dim: int = 0, num_workers: int = 0, **kwargs):
-        super().__init__(level, channel_dim, **kwargs)
+    def __init__(
+        self,
+        level: int = 0,
+        channel_dim: int = 0,
+        dtype: DtypeLike | torch.dtype = np.uint8,
+        device: torch.device | str | None = None,
+        mode: str = "RGB",
+        num_workers: int = 0,
+        **kwargs,
+    ):
+        super().__init__(level=level, channel_dim=channel_dim, dtype=dtype, device=device, mode=mode, **kwargs)
         self.num_workers = num_workers
 
     @staticmethod
@@ -551,13 +649,28 @@ class OpenSlideWSIReader(BaseWSIReader):
         level: the whole slide image level at which the image is extracted. (default=0)
             This is overridden if the level argument is provided in `get_data`.
         channel_dim: the desired dimension for color channel. Default to 0 (channel first).
+        dtype: the data type of output image. Defaults to `np.uint8`.
+        device: target device to put the extracted patch. Note that if device is "cuda"",
+            the output will be converted to torch tenor and sent to the gpu even if the dtype is numpy.
+        mode: the output image color mode, "RGB" or "RGBA". Defaults to "RGB".
         kwargs: additional args for `openslide.OpenSlide` module.
 
     """
 
     supported_suffixes = ["tif", "tiff", "svs"]
     backend = "openslide"
 
+    def __init__(
+        self,
+        level: int = 0,
+        channel_dim: int = 0,
+        dtype: DtypeLike | torch.dtype = np.uint8,
+        device: torch.device | str | None = None,
+        mode: str = "RGB",
+        **kwargs,
+    ):
+        super().__init__(level=level, channel_dim=channel_dim, dtype=dtype, device=device, mode=mode, **kwargs)
+
     @staticmethod
     def get_level_count(wsi) -> int:
         """
@@ -695,13 +808,28 @@ class TiffFileWSIReader(BaseWSIReader):
         level: the whole slide image level at which the image is extracted. (default=0)
             This is overridden if the level argument is provided in `get_data`.
         channel_dim: the desired dimension for color channel. Default to 0 (channel first).
+        dtype: the data type of output image. Defaults to `np.uint8`.
+        device: target device to put the extracted patch. Note that if device is "cuda"",
+            the output will be converted to torch tenor and sent to the gpu even if the dtype is numpy.
+        mode: the output image color mode, "RGB" or "RGBA". Defaults to "RGB".
         kwargs: additional args for `tifffile.TiffFile` module.
 
     """
 
     supported_suffixes = ["tif", "tiff", "svs"]
     backend = "tifffile"
 
+    def __init__(
+        self,
+        level: int = 0,
+        channel_dim: int = 0,
+        dtype: DtypeLike | torch.dtype = np.uint8,
+        device: torch.device | str | None = None,
+        mode: str = "RGB",
+        **kwargs,
+    ):
+        super().__init__(level=level, channel_dim=channel_dim, dtype=dtype, device=device, mode=mode, **kwargs)
+
     @staticmethod
     def get_level_count(wsi) -> int:
         """