diff --git a/convert_img.py b/convert_img.py
index f26787d..41d815e 100644
--- a/convert_img.py
+++ b/convert_img.py
@@ -70,13 +70,13 @@ def image_to_tspl_commands(image_path):
         for x in range(target_width):
             pixel = img.getpixel((x, y))
             
-            should_print = False
-            # 修正逻辑：用户反馈打印出来是负片（黑底白字），说明原有的判断反了。
-            # 我们现在采用完全相反的逻辑。
-            # 之前的逻辑: if pixel != 0: should_print = True (导致背景被打印)
-            # 现在的逻辑: if pixel == 0: should_print = True (即 0(黑)打印，255(白)不打印)
+            # 逻辑修正:
+            # 我们希望 黑色像素(0) -> 打印(1)
+            # 白色像素(255) -> 不打印(0)
+            # 使用 < 128 判定，增加容错性，防止像素值偏移
             
-            if pixel == 0: 
+            should_print = False
+            if pixel < 128: # Black or Dark Gray
                 should_print = True
             
             if should_print:
diff --git a/debug_dither.py b/debug_dither.py
new file mode 100644
index 0000000..69f14cf
--- /dev/null
+++ b/debug_dither.py
@@ -0,0 +1,27 @@
+from PIL import Image, ImageDraw
+
+# Create a test image with gray lines
+img = Image.new('L', (100, 100), color=255)
+d = ImageDraw.Draw(img)
+d.line([10, 10, 90, 90], fill=128, width=2) # Gray line
+d.line([10, 90, 90, 10], fill=0, width=2)   # Black line
+
+# Convert with default dithering
+img1 = img.convert('1')
+zeros1 = 0
+for y in range(100):
+    for x in range(100):
+        if img1.getpixel((x, y)) == 0: zeros1 += 1
+print(f"Default dither zeros: {zeros1}")
+
+# Convert with NO dithering (Threshold)
+# Note: convert('1', dither=Image.Dither.NONE) might still do dithering in some versions?
+# The reliable way to threshold is point operation or custom threshold.
+# But let's check convert('1', dither=0)
+img2 = img.convert('1', dither=Image.Dither.NONE)
+zeros2 = 0
+for y in range(100):
+    for x in range(100):
+        if img2.getpixel((x, y)) == 0: zeros2 += 1
+print(f"No dither zeros: {zeros2}")
+
diff --git a/debug_img.py b/debug_img.py
new file mode 100644
index 0000000..9422239
--- /dev/null
+++ b/debug_img.py
@@ -0,0 +1,69 @@
+from PIL import Image
+import os
+
+def debug_image(image_path):
+    if not os.path.exists(image_path):
+        print(f"Error: {image_path} not found")
+        return
+
+    img = Image.open(image_path)
+    print(f"Original mode: {img.mode}")
+    
+    # 模拟 convert_img.py 的处理流程
+    if img.mode in ('RGBA', 'LA') or (img.mode == 'P' and 'transparency' in img.info):
+        alpha = img.convert('RGBA').split()[-1]
+        bg = Image.new("RGBA", img.size, (255, 255, 255, 255))
+        bg.paste(img, mask=alpha)
+        img = bg
+    
+    img = img.convert('L')
+    img = img.convert('1')
+    print(f"Converted mode: {img.mode}")
+    
+    width, height = img.size
+    print(f"Size: {width}x{height}")
+    
+    zeros = 0
+    non_zeros = 0
+    values = {}
+    
+    # 采样一些像素
+    for y in range(min(height, 10)):
+        row_vals = []
+        for x in range(min(width, 10)):
+            val = img.getpixel((x, y))
+            row_vals.append(str(val))
+        print(f"Row {y} first 10 pixels: {', '.join(row_vals)}")
+        
+    # 统计所有像素
+    for y in range(height):
+        for x in range(width):
+            val = img.getpixel((x, y))
+            if val == 0:
+                zeros += 1
+            else:
+                non_zeros += 1
+                if val not in values:
+                    values[val] = 0
+                values[val] += 1
+                
+    print(f"Total pixels: {width*height}")
+    print(f"Zeros (Black?): {zeros}")
+    print(f"Non-zeros (White?): {non_zeros}")
+    print(f"Non-zero values distribution: {values}")
+
+if __name__ == "__main__":
+    # 尝试找一个存在的图片，或者创建一个
+    img_path = "test_image.png"
+    if not os.path.exists(img_path):
+        # 创建一个简单的测试图片
+        img = Image.new('RGB', (100, 100), color = 'white')
+        # 画个黑框
+        from PIL import ImageDraw
+        d = ImageDraw.Draw(img)
+        d.rectangle([10, 10, 90, 90], outline='black', fill='black')
+        img.save("debug_test.png")
+        img_path = "debug_test.png"
+        print("Created debug_test.png")
+        
+    debug_image(img_path)
diff --git a/websocket_server/convert_img.py b/websocket_server/convert_img.py
index 71c6694..470d7cb 100644
--- a/websocket_server/convert_img.py
+++ b/websocket_server/convert_img.py
@@ -57,9 +57,10 @@ def image_to_tspl_commands(image_path):
             # 逻辑修正:
             # 我们希望 黑色像素(0) -> 打印(1)
             # 白色像素(255) -> 不打印(0)
+            # 使用 < 128 判定，增加容错性，防止像素值偏移
             
             should_print = False
-            if pixel == 0: # Black
+            if pixel < 128: # Black or Dark Gray
                 should_print = True
             
             if should_print:
diff --git a/websocket_server/server.py b/websocket_server/server.py
index 82b171f..2b6333c 100644
--- a/websocket_server/server.py
+++ b/websocket_server/server.py
@@ -569,8 +569,8 @@ def optimize_prompt(asr_text, progress_callback=None):
 1. 风格必须是：简单的黑白线稿、简笔画、图标风格 (Line art, Sketch, Icon style)。
 2. 画面必须清晰、线条粗壮，适合低分辨率热敏打印机打印。
 3. 绝对不要有复杂的阴影、渐变、黑白线条描述。
-4. 背景必须是纯白 (White background)。
-5. 提示词内容请使用英文描述，因为绘图模型对英文理解更好，但在描述中强调 "black and white line art", "simple lines", "vector style"。
+4. 背景必须是纯白 (White background)，线条要粗方便打印。
+5. 提示词内容请使用英文描述，因为绘图模型对英文理解更好，但在描述中强调 "black and white line art", "bold simple lines", "vector style"。
 6. 尺寸比例遵循宽48mm:高30mm (约 1.6:1)。
 7. 直接输出优化后的提示词，不要包含任何解释。"""
 
@@ -1025,4 +1025,5 @@ if __name__ == "__main__":
     local_ip = socket.gethostbyname(hostname)
     print(f"Server running on ws://{local_ip}:8000/ws/audio")
     
-    uvicorn.run(app, host="0.0.0.0", port=8000)
+    # 禁用自动Ping以避免并发写入冲突 (ws_ping_interval=None)
+    uvicorn.run(app, host="0.0.0.0", port=8000, ws_ping_interval=None, ws_ping_timeout=None)