fix(nodes): read the real alpha channel in Mask from Alpha

invokeai/app/invocations/image.py

@@ -230,7 +230,7 @@ def invoke(self, context: InvocationContext) -> ImageOutput:
     title="Mask from Alpha",
     tags=["image", "mask"],
     category="mask",
-    version="1.2.2",
+    version="1.3.0",
 )
 class MaskFromAlphaInvocation(BaseInvocation, WithMetadata, WithBoard):
     """Extracts the alpha channel of an image as a mask."""
@@ -239,9 +239,11 @@ class MaskFromAlphaInvocation(BaseInvocation, WithMetadata, WithBoard):
     invert: bool = InputField(default=False, description="Whether or not to invert the mask")
 
     def invoke(self, context: InvocationContext) -> ImageOutput:
-        image = context.images.get_pil(self.image.image_name)
+        # Converting gives an image without an alpha channel a fully opaque one. Its last band is a color or
+        # palette channel, not alpha.
+        image = context.images.get_pil(self.image.image_name, mode="RGBA")
 
-        image_mask = image.split()[-1]
+        image_mask = image.getchannel("A")
         if self.invert:
             image_mask = ImageOps.invert(image_mask)
 

invokeai/frontend/api/openapi.json

@@ -85692,7 +85692,7 @@
         "tags": ["image", "mask"],
         "title": "Mask from Alpha",
         "type": "object",
-        "version": "1.2.2",
+        "version": "1.3.0",
         "output": {
           "$ref": "#/components/schemas/ImageOutput"
         }

tests/app/invocations/test_image.py

@@ -7,7 +7,12 @@
 import torch
 from PIL import Image, ImageFilter
 
-from invokeai.app.invocations.image import ImageField, OklabUnsharpMaskInvocation, OklchImageHueAdjustmentInvocation
+from invokeai.app.invocations.image import (
+    ImageField,
+    MaskFromAlphaInvocation,
+    OklabUnsharpMaskInvocation,
+    OklchImageHueAdjustmentInvocation,
+)
 from invokeai.app.invocations.primitives import ImageCollectionInvocation
 from invokeai.backend.image_util.color_conversion import (
     linear_srgb_from_oklab,
@@ -49,6 +54,51 @@ def _max_abs_diff_uint8(left: Image.Image, right: Image.Image) -> int:
     return int(numpy.abs(left_arr - right_arr).max())
 
 
+def _invoke_mask_from_alpha(input_image: Image.Image, invert: bool = False) -> list[int]:
+    context = MagicMock()
+    # Like the real context, convert to the requested mode.
+    context.images.get_pil.side_effect = lambda image_name, mode=None: (
+        input_image.convert(mode) if mode else input_image.copy()
+    )
+    context.images.save.side_effect = lambda image, image_category: SimpleNamespace(
+        image_name="out", width=image.width, height=image.height
+    )
+
+    MaskFromAlphaInvocation(image=ImageField(image_name="in"), invert=invert).invoke(context)
+    saved_image = context.images.save.call_args.kwargs["image"]
+
+    assert saved_image.mode == "L"
+    return numpy.asarray(saved_image).reshape(-1).tolist()
+
+
+def test_mask_from_alpha_uses_the_alpha_channel() -> None:
+    input_image = Image.new("RGBA", (3, 1))
+    input_image.putdata([(10, 20, 30, 0), (10, 20, 30, 128), (10, 20, 30, 255)])
+
+    assert _invoke_mask_from_alpha(input_image) == [0, 128, 255]
+    assert _invoke_mask_from_alpha(input_image, invert=True) == [255, 127, 0]
+
+
+def test_mask_from_alpha_treats_an_image_without_alpha_as_opaque() -> None:
+    rgb_image = Image.new("RGB", (3, 1))
+    rgb_image.putdata([(255, 0, 0), (0, 255, 0), (0, 0, 64)])
+    grayscale_image = Image.new("L", (3, 1))
+    grayscale_image.putdata([0, 64, 200])
+
+    assert _invoke_mask_from_alpha(rgb_image) == [255, 255, 255]
+    assert _invoke_mask_from_alpha(rgb_image, invert=True) == [0, 0, 0]
+    assert _invoke_mask_from_alpha(grayscale_image) == [255, 255, 255]
+
+
+def test_mask_from_alpha_uses_palette_transparency() -> None:
+    palette_image = Image.new("P", (3, 1))
+    palette_image.putpalette([0, 0, 0, 255, 255, 255])
+    palette_image.putdata([0, 1, 0])
+    palette_image.info["transparency"] = 0
+
+    assert _invoke_mask_from_alpha(palette_image) == [0, 255, 0]
+
+
 def test_image_collection_invocation_preserves_existing_collection_values() -> None:
     images = [ImageField(image_name="first"), ImageField(image_name="second")]