Change black as material and white as empty space

README.md

@@ -27,6 +27,7 @@ Then open the local Gradio URL in your browser, upload an STL file, and generate
 - Shows an interactive 3D viewer for rotating the model
 - Lets you choose layer height and XY pixel size
 - Produces one `.tif` image per slice
+- Encodes material as black (`0`) and empty space as white (`255`) in each TIFF slice
 - Lets you step through the slice stack in the browser
 - Exports a ZIP containing the generated TIFF images
 

stl_slicer.py

@@ -129,7 +129,7 @@ def _render_slice(
     image_size: tuple[int, int],
     pixel_size: float,
 ) -> Image.Image:
-    image = Image.new("L", image_size, 0)
+    image = Image.new("L", image_size, 255)
 
     if section is None:
         return image
@@ -142,12 +142,12 @@ def _render_slice(
     for exterior, holes in polygons:
         draw.polygon(
             _to_pixel_ring(exterior, x_min, y_min, pixel_size, image.height),
-            fill=255,
+            fill=0,
         )
         for hole in holes:
             draw.polygon(
                 _to_pixel_ring(hole, x_min, y_min, pixel_size, image.height),
-                fill=0,
+                fill=255,
             )
 
     return image

tests/test_stl_slicer.py

@@ -34,8 +34,7 @@ def test_slice_stl_to_tiffs_creates_non_empty_tiffs(tmp_path) -> None:
     with Image.open(stack.tiff_paths[0]) as first_image:
         pixels = np.array(first_image)
 
-    assert pixels.max() == 255
-    assert pixels.sum() > 0
+    assert np.any(pixels == 0)
 
 
 def test_compose_even_odd_polygons_preserves_holes() -> None: