app+docs: 第三十九轮结案——官方条纹更不明显真因是我们开着官方从不开启的 7×7 细节增强（GPU 画布/Skia 预放大/合成截屏逐环 A/B 全部排除，暗区 ROW 0.31-0.46→0.14-0.23≈官方 0.15，设置页去掉误导推荐并注明代价，设备增强已恢复 0，123 单测全绿）

android/app/src/main/kotlin/com/mag160c/thermal/ui/live/LiveRenderer.kt

@@ -62,6 +62,18 @@ class LiveRenderer(
     private var bitmap = Bitmap.createBitmap(320, 240, Bitmap.Config.ARGB_8888)
     private var bufW = 320
     private var bufH = 240
+
+    // Round 39 verdict (docs/android_app/rendering_diff_phone_20261006.md §17.7):
+    // the "official background stripes are less visible" gap was NOT the display
+    // chain at all. A/B on the device: hardware vs software canvas — identical
+    // dark-region ROW; a Skia 6x pre-scale stage — identical; in-app bitmap dump
+    // vs screenshot — identical, i.e. nothing between the pipeline output and the
+    // screen adds alternation. The whole gap was the 7x7 detail enhancement
+    // running at level 4 on this device (official app NEVER calls
+    // SetDetailEnhancement — jadx, and round 22 already measured "level 2 makes
+    // noise larger"). With enhancement off the dark-region ROW drops from
+    // 0.31-0.46 to 0.14-0.21 x1e-2 arc ≈ the official 0.15. The renderer keeps
+    // the round-38 single-stage nativeOut draw below.
     private val textPaint = Paint(Paint.ANTI_ALIAS_FLAG).apply {
         color = Color.WHITE
         typeface = Typeface.SANS_SERIF
@@ -234,13 +246,12 @@ class LiveRenderer(
             fit.cx - size[0] / 2f, fit.cy - size[1] / 2f,
             fit.cx + size[0] / 2f, fit.cy + size[1] / 2f,
         )
-        // Single filtered scale buffer -> screen. The official viewer's 640x480
-        // offscreen stage was tried (round 38) and REVERTED: in our portrait
-        // fitRect the second stage lands on a 2.25x non-integer scale, and the
-        // GPU's rendering of it measurably WORSENED the column-direction
-        // alternation on the device (0.33 -> 0.55 x1e-2 arc) — an artifact the
-        // official (landscape, integer 3x second stage) doesn't have. The 160x120
-        // -> 1440x1920 single scale is 9x/16x integer, artifact-free.
+        // Single filtered scale buffer -> screen. Round 39 additionally tried a
+        // Skia 6x pre-scale stage (second stage an exact integer 2x, unlike the
+        // round-38 640x480 attempt): the device A/B showed NO display-quality
+        // gain over this single-stage draw, so it was reverted — the stripe gap
+        // was the detail enhancement, not any scaling stage (see the class
+        // comment above).
         if (src != null) canvas.drawBitmap(bitmap, src, dstRect, paint)
         else canvas.drawBitmap(bitmap, null, dstRect, paint)
         canvas.restore()

android/app/src/main/kotlin/com/mag160c/thermal/ui/settings/SettingsScreen.kt

@@ -249,8 +249,10 @@ fun SettingsScreen(
                     Text(
                         "加强局部细节（官方同款 7×7 局部映射）。档位越高：①对比度门槛越高，" +
                             "只有更强的细节会被增强，弱对比区域（噪声所在处）被排除；" +
-                            "②强边缘的增强幅度更大。所以高档位是「更锐但更挑」，" +
-                            "而不是「连噪声一起放大」。",
+                            "②强边缘的增强幅度更大。\n\n" +
+                            "注意：实测开启增强会放大暗场（低温背景）的固定条纹。官方 App 的" +
+                            "实时画面从不开启增强（逆向 jadx 全量搜索无 SetDetailEnhancement 调用），" +
+                            "想要与官方一致的背景观感请选「关闭」。",
                         style = MaterialTheme.typography.bodySmall,
                         color = MaterialTheme.colorScheme.onSurfaceVariant,
                         modifier = Modifier.padding(bottom = 8.dp),
@@ -262,6 +264,10 @@ fun SettingsScreen(
                     // local contrast dominates the divisor). On flat, noisy areas the
                     // divisor floor holds the amplitude at 128/gain regardless of
                     // level, which is why cranking it up sharpens instead of boiling.
+                    // Round 39: the official app NEVER calls SetDetailEnhancement
+                    // (jadx), and on-device A/B showed level 4 is what inflated the
+                    // dark-region row stripes (0.31-0.46 -> 0.14-0.21 when off) —
+                    // hence no "recommended" tag on any level and the notice above.
                     Column(
                         modifier = Modifier
                             .heightIn(max = 320.dp)
@@ -272,7 +278,7 @@ fun SettingsScreen(
                             1 to "1 级（轻微）",
                             2 to "2 级",
                             3 to "3 级",
-                            4 to "4 级（推荐）",
+                            4 to "4 级",
                             6 to "6 级",
                             8 to "8 级（强）",
                         ).forEach { (lvl, label) ->