From b99ec63306e697c1c148f888a0890da3390d60fa Mon Sep 17 00:00:00 2001
From: sinvo <admin@mcraft.cn>
Date: Thu, 19 Mar 2026 17:25:43 +0800
Subject: [PATCH] =?UTF-8?q?=E4=BF=AE=E5=A4=8D=E6=96=87=E5=AD=97=E7=B3=8A?=
 =?UTF-8?q?=E6=88=90=E4=B8=80=E5=9B=A2=EF=BC=9A=E7=94=A8gamma=E6=9B=B2?=
 =?UTF-8?q?=E7=BA=BF=E4=BB=A3=E6=9B=BF=E7=BA=BF=E6=80=A7=E5=88=86=E6=AE=B5?=
 =?UTF-8?q?LUT?=
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线性分段把0-210全压到0-30，笔画间灰度差异丢失导致糊成墨团。
改用gamma=2.5的幂曲线，文字整体变黑但保留笔画间的灰度渐变，
文字清晰可辨。

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
---
 CamScanner.cs | 20 +++++++-------------
 1 file changed, 7 insertions(+), 13 deletions(-)

diff --git a/CamScanner.cs b/CamScanner.cs
index 122174e..6542917 100644
--- a/CamScanner.cs
+++ b/CamScanner.cs
@@ -366,22 +366,16 @@ public static class DocumentScanner
         Mat normU8 = new Mat(h, w, MatType.CV_8U);
         Marshal.Copy(resultData, 0, normU8.Data, resultData.Length);
 
-        // --- d: 非线性对比度增强（让文字更黑）---
-        // 用 LUT 做分段映射：
-        //   0-210: 线性映射到 0-30（文字区域强力压暗）
-        //   210-255: 线性映射到 30-255（背景区域拉亮）
+        // --- d: 非线性对比度增强 ---
+        // 用 gamma 曲线代替线性分段，保留文字笔画间的灰度层次
+        // gamma > 1：中间调压暗（文字变黑），但保留灰度渐变不糊成一团
         byte[] lut = new byte[256];
         for (int i = 0; i < 256; i++)
         {
-            if (i <= 210)
-            {
-                lut[i] = (byte)(i * 30 / 210);
-            }
-            else
-            {
-                lut[i] = (byte)(30 + (i - 210) * 225 / 45);
-            }
-            if (lut[i] > 255) lut[i] = 255;
+            double x = i / 255.0;
+            // gamma=2.5 让文字明显变黑，但笔画间灰度差异保留
+            double y = Math.Pow(x, 2.5);
+            lut[i] = (byte)Math.Min(255, Math.Max(0, (int)(y * 255.0)));
         }
         Mat lutMat = new Mat(1, 256, MatType.CV_8U, lut);
         Mat contrasted = new Mat();