diff --git a/src/ppclock/client.py b/src/ppclock/client.py
index 923681d..4260103 100644
--- a/src/ppclock/client.py
+++ b/src/ppclock/client.py
@@ -19,6 +19,7 @@ from pathlib import Path
 
 from . import commands as C
 from . import image_pipeline as IP
+from . import protocol as P
 from .transports import bridge as _bridge_mod
 from .transports import local as _local_mod
 from .transports.base import TransportError  # noqa: F401  (SDK 公开异常)
@@ -117,6 +118,11 @@ class PPClient:
         img = IP.Image.open(source) if isinstance(source, (str, Path)) else source
         bw, red = IP.process_image(img, size=size, algorithm=algo,
                                    tricolor=not mono, **adjust)
+        if red is None and P.requires_complete_image_planes(
+                getattr(self._t, "firmware_revision", None)):
+            # HM42 stores the two 400x300 planes as one sequential image.  Its
+            # Web-BLE client sends an empty red plane even for monochrome input.
+            red = bytes(len(bw))
         small = len(bw) in (3500, 9000)
         await C.upload_image(self._t, bw, red, small=small, slot=slot)
         return {"bytes_bw": len(bw), "bytes_red": len(red) if red else 0,
diff --git a/src/ppclock/protocol.py b/src/ppclock/protocol.py
index d15f2d5..2781857 100644
--- a/src/ppclock/protocol.py
+++ b/src/ppclock/protocol.py
@@ -29,6 +29,17 @@ def select_rxtx_uuid(firmware_revision: str | None) -> str:
         return RXTX_CHAR_UUID_LEGACY
     return RXTX_CHAR_UUID
 
+
+def requires_complete_image_planes(firmware_revision: str | None) -> bool:
+    """Whether a nominally mono full-screen upload still needs both planes.
+
+    The HM42 Web-BLE implementation always sends the 400x300 black/white plane
+    followed by a red plane before opcode 01.  Omitting the second plane leaves
+    HM42 rendering stale/uninitialised red data (observed as a red noisy screen).
+    """
+    revision = (firmware_revision or "").strip().upper()
+    return revision.startswith("HM42_AIO")
+
 MODES = {
     **{f"image{i}": bytes([0xE1, 0x00, 0x00 + i]) for i in range(4)},
     "calendar1": bytes.fromhex("e10103"),
diff --git a/tests/test_client.py b/tests/test_client.py
index 22e311d..4d95c0d 100644
--- a/tests/test_client.py
+++ b/tests/test_client.py
@@ -7,10 +7,11 @@ from ppclock.client import PPClient
 
 
 class FakeTransport:
-    def __init__(self):
+    def __init__(self, firmware_revision=None):
         self.epd_writes = []
         self.rxtx_writes = []
         self.address = "AA:BB:CC:DD:EE:FF"
+        self.firmware_revision = firmware_revision
 
     async def __aenter__(self):
         return self
@@ -78,6 +79,33 @@ class TestCommands:
         assert client._t.rxtx_writes[0] == bytes([0xEA, 0x00])
         assert len(client._t.epd_writes) == 63 + 63 + 1
 
+    @pytest.mark.asyncio
+    async def test_upload_mono_non_hm42_sends_one_plane(self):
+        from PIL import Image
+        client = PPClient(FakeTransport("PP_da14585_4.2"))
+        result = await client.upload_image(
+            Image.new("RGB", (400, 300), "white"), slot=1,
+            algo="none", mono=True,
+        )
+        assert result["bytes_bw"] == 15000
+        assert result["bytes_red"] == 0
+        assert len(client._t.epd_writes) == 63 + 1
+
+    @pytest.mark.asyncio
+    async def test_upload_mono_hm42_appends_empty_red_plane(self):
+        from PIL import Image
+        client = PPClient(FakeTransport("HM42_AIO_V1.0.9"))
+        result = await client.upload_image(
+            Image.new("RGB", (400, 300), "white"), slot=1,
+            algo="none", mono=True,
+        )
+        assert result["bytes_bw"] == 15000
+        assert result["bytes_red"] == 15000
+        assert len(client._t.epd_writes) == 63 + 63 + 1
+        first_red = client._t.epd_writes[63]
+        assert first_red[:4] == bytes.fromhex("03000000")
+        assert set(first_red[4:]) == {0}
+
     @pytest.mark.asyncio
     async def test_render_template(self, client):
         result = await client.render_template("custom", {"text": "你好"})
diff --git a/tests/test_protocol.py b/tests/test_protocol.py
index 811dfca..4fb52eb 100644
--- a/tests/test_protocol.py
+++ b/tests/test_protocol.py
@@ -67,6 +67,12 @@ class TestCommandFrames:
         assert P.select_rxtx_uuid("PP_da14585_4.2") == P.RXTX_CHAR_UUID
         assert P.select_rxtx_uuid(None) == P.RXTX_CHAR_UUID
 
+    def test_complete_image_planes_by_firmware_family(self):
+        assert P.requires_complete_image_planes("HM42_AIO_V1.0.9") is True
+        assert P.requires_complete_image_planes("hm42_aio_v2") is True
+        assert P.requires_complete_image_planes("PP_da14585_4.2") is False
+        assert P.requires_complete_image_planes(None) is False
+
     def test_parking(self):
         """停车牌 "12" → EF1122（向量#4）"""
         assert P.parking_frame("12") == bytes([0xEF, 0x11, 0x22])