diff --git a/README.md b/README.md
index a60a9db..e1452a5 100644
--- a/README.md
+++ b/README.md
@@ -77,6 +77,7 @@ Load shows the request error (for example `HTTP 500`) when the store cannot be r
 
 - Verify the `guid` output from the builder is connected to Preview BG Update's `guid` input
 - Check the ComfyUI console for a line starting with `[ByAE Ideogram BG]`. A failed save names the reason: no image, an empty or invalid guid, an image that could not be converted, or a disk write error
+- RGBA frames are composited onto black, and single-channel frames are expanded to RGB, before the file is written. The conversion warning is for a tensor that still cannot be turned into an image
 - The temp directory must be writable (usually `ComfyUI/temp`)
 
 ### Saved workflows break after updating
diff --git a/nodes/ideogram4_nodes.py b/nodes/ideogram4_nodes.py
index ca3b647..7d14886 100644
--- a/nodes/ideogram4_nodes.py
+++ b/nodes/ideogram4_nodes.py
@@ -167,11 +167,54 @@ def _coerce_opacity(value, default=0.5):
         return default
 
 
+def _uint8_frame_kind(shape):
+    """How to open one HWC frame. Unknown shapes stay on the RGB path.
+
+    ComfyUI documents IMAGE as [B,H,W,C] with three channels. Pillow still
+    rejects mode RGB for [H,W], [H,W,1], and [H,W,4], which is what a mask
+    or an image that kept its alpha looks like.
+    """
+    if (
+        not isinstance(shape, tuple)
+        or not shape
+        or not all(
+            isinstance(n, int) and not isinstance(n, bool) and n > 0 for n in shape
+        )
+    ):
+        return "rgb"
+    if len(shape) == 2:
+        return "gray"
+    if len(shape) == 3 and shape[-1] == 4:
+        return "rgba"
+    if len(shape) == 3 and shape[-1] == 1:
+        return "gray1"
+    return "rgb"
+
+
+def _rgb_image_from_uint8(arr):
+    """RGB image for the temp PNG. Alpha is composited onto black.
+
+    The editor draws that PNG over a black canvas, so a transparent pixel
+    should become black rather than keep an unrelated RGB value.
+    """
+    kind = _uint8_frame_kind(getattr(arr, "shape", None))
+    if kind == "rgba":
+        rgba = Image.fromarray(arr, mode="RGBA")
+        black = Image.new("RGBA", rgba.size, (0, 0, 0, 255))
+        return Image.alpha_composite(black, rgba).convert("RGB")
+    if kind == "gray":
+        return Image.fromarray(arr, mode="L").convert("RGB")
+    if kind == "gray1":
+        flat = arr.reshape(arr.shape[0], arr.shape[1])
+        return Image.fromarray(flat, mode="L").convert("RGB")
+    return Image.fromarray(arr, mode="RGB")
+
+
 def _tensor_to_pil(image):
     if image is None:
         return None
     arr = (image[0].detach().cpu().numpy() * 255.0).clip(0, 255).astype(np.uint8)
-    return Image.fromarray(arr, mode="RGB")
+    return _rgb_image_from_uint8(arr)
 
 
 def _load_bg_from_temp(guid):
diff --git a/tests/test_nodes.py b/tests/test_nodes.py
index e7169d8..2723845 100644
--- a/tests/test_nodes.py
+++ b/tests/test_nodes.py
@@ -9,10 +9,20 @@ from nodes.ideogram4_nodes import (
     sanitize_bg_guid, _norm_bbox, _palette, _hex_rgb, _dumps, _parse_json_list,
     _caption_to_boxes, _coerce_layout_int, _coerce_opacity,
     _elements_from_boxes, _preview_edges, _render_preview, ImageDraw,
-    save_bg_image_to_temp,
+    save_bg_image_to_temp, _uint8_frame_kind, _rgb_image_from_uint8, Image,
 )
 
 
+class _FakeFrame:
+    def __init__(self, shape):
+        self.shape = shape
+        self.reshaped = None
+
+    def reshape(self, *args):
+        self.reshaped = args
+        return ("flat", args)
+
+
 class TestPromptHelpers(unittest.TestCase):
     def test_sanitize_bg_guid_valid(self):
         valid_guid = "12345678-1234-4abc-8abc-123456789012"
@@ -401,6 +411,47 @@ class TestPromptHelpers(unittest.TestCase):
         self.assertIsNone(result)
         self.assertTrue(any("invalid background guid" in line.lower() for line in cm.output))
 
+    def test_uint8_frame_kind_matches_channel_count(self):
+        self.assertEqual(_uint8_frame_kind((8, 8, 3)), "rgb")
+        self.assertEqual(_uint8_frame_kind((8, 8, 4)), "rgba")
+        self.assertEqual(_uint8_frame_kind((8, 8, 1)), "gray1")
+        self.assertEqual(_uint8_frame_kind((8, 8)), "gray")
+        # Anything else keeps the RGB attempt, which reports a conversion failure.
+        self.assertEqual(_uint8_frame_kind((8, 8, 2)), "rgb")
+        self.assertEqual(_uint8_frame_kind((0, 8, 3)), "rgb")
+        self.assertEqual(_uint8_frame_kind(None), "rgb")
+        # bool is an int, and True == 1, so a boolean channel count must not
+        # take the single-channel path.
+        self.assertEqual(_uint8_frame_kind((8, 8, True)), "rgb")
+
+    def test_rgba_frame_is_composited_onto_black(self):
+        arr = _FakeFrame((2, 3, 4))
+        Image.fromarray.reset_mock()
+        Image.new.reset_mock()
+        Image.alpha_composite.reset_mock()
+        _rgb_image_from_uint8(arr)
+        Image.fromarray.assert_called_once_with(arr, mode="RGBA")
+        Image.new.assert_called_once()
+        args, _kwargs = Image.new.call_args
+        self.assertEqual(args[0], "RGBA")
+        self.assertEqual(args[2], (0, 0, 0, 255))
+        Image.alpha_composite.assert_called_once()
+        Image.alpha_composite.return_value.convert.assert_called_once_with("RGB")
+
+    def test_single_channel_frame_is_opened_as_grayscale(self):
+        gray = _FakeFrame((4, 5))
+        Image.fromarray.reset_mock()
+        _rgb_image_from_uint8(gray)
+        Image.fromarray.assert_called_once_with(gray, mode="L")
+        Image.fromarray.return_value.convert.assert_called_once_with("RGB")
+
+        column = _FakeFrame((4, 5, 1))
+        Image.fromarray.reset_mock()
+        _rgb_image_from_uint8(column)
+        self.assertEqual(column.reshaped, (4, 5))
+        Image.fromarray.assert_called_once_with(("flat", (4, 5)), mode="L")
+        Image.fromarray.return_value.convert.assert_called_once_with("RGB")
+
     def test_save_bg_image_warns_when_conversion_fails(self):
         guid = "12345678-1234-4abc-8abc-123456789012"
         image_mod = save_bg_image_to_temp.__globals__["Image"]