add strided patches

fixes #202

This adds a command line option '--patch-overlap-ratio' that controls
the level of overlap between adjacent patches. Negative values create
space between patches, and values closer to 1 makes patches overlap
more.

wsinfer/cli/infer.py

@@ -303,6 +303,16 @@ def get_stdout(args: list[str]) -> str:
     " area, it is filled with foreground. The default is 190um x 190um. The units of"
     " this argument are microns squared.",
 )
+@click.option(
+    "--patch-overlap-ratio",
+    default=0.0,
+    type=click.FloatRange(min=None, max=1, max_open=True),
+    help="The ratio of overlap among patches. The default value of 0 produces"
+    " non-overlapping patches. A value in (0, 1) will produce overlapping patches."
+    " Negative values will add space between patches. A value of -1 would skip"
+    " every other patch. A value of 0.5 will provide 50%% of overlap between patches."
+    " Values must be in (-inf, 1).",
+)
 def run(
     ctx: click.Context,
     *,
@@ -321,6 +331,7 @@ def run(
     seg_closing_kernel_size: int,
     seg_min_object_size_um2: float,
     seg_min_hole_size_um2: float,
+    patch_overlap_ratio: float = 0.0,
 ) -> None:
     """Run model inference on a directory of whole slide images.
 
@@ -398,6 +409,7 @@ def run(
         closing_kernel_size=seg_closing_kernel_size,
         min_object_size_um2=seg_min_object_size_um2,
         min_hole_size_um2=seg_min_hole_size_um2,
+        overlap=patch_overlap_ratio,
     )
 
     if not results_dir.joinpath("patches").exists():

wsinfer/patchlib/__init__.py

@@ -14,7 +14,7 @@
 from ..wsi import _validate_wsi_directory
 from ..wsi import get_avg_mpp
 from .patch import get_multipolygon_from_binary_arr
-from .patch import get_nonoverlapping_patch_coordinates_within_polygon
+from .patch import get_patch_coordinates_within_polygon
 from .segment import segment_tissue
 
 logger = logging.getLogger(__name__)
@@ -34,6 +34,7 @@ def segment_and_patch_one_slide(
     closing_kernel_size: int = 6,
     min_object_size_um2: float = 200**2,
     min_hole_size_um2: float = 190**2,
+    overlap: float = 0.0,
 ) -> None:
     """Get non-overlapping patch coordinates in tissue regions of a whole slide image.
 
@@ -171,12 +172,13 @@ def segment_and_patch_one_slide(
     half_patch_size = round(patch_size / 2)
 
     # Nx4 --> N x (minx, miny, width, height)
-    coords = get_nonoverlapping_patch_coordinates_within_polygon(
+    coords = get_patch_coordinates_within_polygon(
         slide_width=slide_width,
         slide_height=slide_height,
         patch_size=patch_size,
         half_patch_size=half_patch_size,
         polygon=polygon,
+        overlap=overlap,
     )
     logger.info(f"Found {len(coords)} patches within tissue")
 
@@ -299,6 +301,7 @@ def segment_and_patch_directory_of_slides(
     closing_kernel_size: int = 6,
     min_object_size_um2: float = 200**2,
     min_hole_size_um2: float = 190**2,
+    overlap: float = 0.0,
 ) -> None:
     """Get non-overlapping patch coordinates in tissue regions for a directory of whole
     slide images.
@@ -373,6 +376,7 @@ def segment_and_patch_directory_of_slides(
                 closing_kernel_size=closing_kernel_size,
                 min_object_size_um2=min_object_size_um2,
                 min_hole_size_um2=min_hole_size_um2,
+                overlap=overlap,
             )
         except Exception as e:
             logger.error(f"Failed to segment and patch slide\n{slide_path}", exc_info=e)

wsinfer/patchlib/patch.py

@@ -128,12 +128,13 @@ def merge_polygons(polygon: MultiPolygon, idx: int, add: bool) -> MultiPolygon:
     return polygon, contours_unscaled, hierarchy[np.newaxis]
 
 
-def get_nonoverlapping_patch_coordinates_within_polygon(
+def get_patch_coordinates_within_polygon(
     slide_width: int,
     slide_height: int,
     patch_size: int,
     half_patch_size: int,
     polygon: Polygon,
+    overlap: float = 0.0,
 ) -> npt.NDArray[np.int_]:
     """Get coordinates of patches within a polygon.
 
@@ -149,6 +150,12 @@ def get_nonoverlapping_patch_coordinates_within_polygon(
         Half of the length of a patch in pixels.
     polygon : Polygon
         A shapely Polygon representing the presence of tissue.
+    overlap : float
+        The proportion of the patch_size to overlap. A value of 0.5
+        would have an overlap of 50%. A value of 0.2 would have an
+        overlap of 20%. Negative values will add space between patches.
+        A value of -1 would skip every other patch. Value must be in (-inf, 1).
+        The default value of 0.0 produces non-overlapping patches.
 
     Returns
     -------
@@ -157,12 +164,19 @@ def get_nonoverlapping_patch_coordinates_within_polygon(
         contains the coordinates of the top-left of a tile: (minx, miny).
     """
 
+    if overlap >= 1:
+        raise ValueError(f"overlap must be in (-inf, 1) but got {overlap}")
+
+    # Handle potentially overlapping slides.
+    step_size = round((1 - overlap) * patch_size)
+    logger.info(f"Patches are {patch_size} px, with step size of {step_size} px.")
+
     # Make an array of Nx2, where each row is (x, y) centroid of the patch.
     tile_centroids_arr: npt.NDArray[np.int_] = np.array(
         list(
             itertools.product(
-                range(0 + half_patch_size, slide_width, patch_size),
-                range(0 + half_patch_size, slide_height, patch_size),
+                range(0 + half_patch_size, slide_width, step_size),
+                range(0 + half_patch_size, slide_height, step_size),
             )
         )
     )