From e67da429ddd4333537b07f8810dfc658ccd7922e Mon Sep 17 00:00:00 2001
From: Mendel Mobach <mendel@mobach.nl>
Date: Fri, 16 Oct 2026 18:57:15 +0200
Subject: [PATCH] Print all non-white logo colors as solid black

---
 README.md                       |  4 +++-
 load_printer_logo.py            |  8 +++++---
 tests/test_load_printer_logo.py | 20 ++++++++++++++++++++
 3 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/README.md b/README.md
index 8636feb..775f6af 100644
--- a/README.md
+++ b/README.md
@@ -47,7 +47,9 @@ uploading. Restart the backend afterwards.
 The default stored width is 192 dots; `LOGO` prints at twice the stored width
 and height, so the printed width is at most 384 dots. `--width` changes the
 stored width. Images retain their aspect ratio; transparent pixels and padding
-become white. Stored logos persist after power-off; receipt generation does not
+become white. Only near-white pixels (all RGB channels at least 245) remain
+white; every other color becomes solid black, without dithering.
+Stored logos persist after power-off; receipt generation does not
 upload the image again.
 
 Epson's [FS q command](https://download4.epson.biz/sec_pubs/pos/reference_en/escpos/fs_lq.html)
diff --git a/load_printer_logo.py b/load_printer_logo.py
index 7c4154d..2017ca9 100644
--- a/load_printer_logo.py
+++ b/load_printer_logo.py
@@ -5,7 +5,7 @@
 import struct
 import time
 
-from PIL import Image, ImageOps
+from PIL import Image, ImageChops, ImageOps
 import serial
 
 from config import load_config
@@ -20,8 +20,10 @@ def encode_logo(path, width=192):
         image = source.convert("RGBA")
     image.thumbnail((width, 512), Image.Resampling.LANCZOS)
     white = Image.new("RGBA", image.size, "white")
-    gray = Image.alpha_composite(white, image).convert("L")
-    ink = ImageOps.invert(gray.point(lambda value: 255 if value >= 128 else 0))
+    red, green, blue = Image.alpha_composite(white, image).convert("RGB").split()
+    # Keep only near-white pixels white, including bright saturated colors as ink.
+    darkest = ImageChops.darker(ImageChops.darker(red, green), blue)
+    ink = ImageOps.invert(darkest.point(lambda value: 255 if value >= 245 else 0))
     x_bytes, y_bytes = (image.width + 7) // 8, (image.height + 7) // 8
     padded = Image.new("1", (x_bytes * 8, y_bytes * 8), 0)
     padded.paste(ink.convert("1"), (0, 0))
diff --git a/tests/test_load_printer_logo.py b/tests/test_load_printer_logo.py
index b6a3974..5fd4b20 100644
--- a/tests/test_load_printer_logo.py
+++ b/tests/test_load_printer_logo.py
@@ -33,6 +33,26 @@ def test_logo_scales_proportionally(tmp_path):
     )
 
 
+def test_only_near_white_pixels_remain_white(tmp_path):
+    path = tmp_path / "colors.png"
+    image = Image.new("RGB", (8, 1))
+    image.putdata(
+        [
+            (255, 255, 255),
+            (245, 245, 245),
+            (244, 244, 244),
+            (180, 180, 180),
+            (255, 255, 0),
+            (255, 255, 200),
+            (244, 255, 255),
+            (0, 0, 0),
+        ]
+    )
+    image.save(path)
+
+    assert loader.encode_logo(path)[7:] == b"\x00\x00" + b"\x80" * 6
+
+
 @pytest.mark.parametrize("width", [0, 513])
 def test_invalid_width_does_not_load_or_upload(width):
     with pytest.raises(ValueError):