app+docs: 参考帧窗口参数化(baselineFrames, 默认4)——实测延长到8会把开快门帧收进参考导致不稳定；结论：需快门感知的参考收集

android/app/src/main/kotlin/com/mag160c/thermal/core/RenderPipeline.kt

@@ -20,6 +20,16 @@ class RenderPipeline(
     private val ffcPeriod: Int = 1800,
     private val ffcDrift: Int = 250,
     private val warmFrames: Int = 20,
+    /**
+     * Number of *settled* shutter frames averaged into the FFC reference.
+     *
+     * The official core feeds every frame of the shutter window into
+     * `CAccumulator` (`CFunctions::PushBaselineRaw`), so its reference is much
+     * cleaner than a short 4-frame average — which is why the official image
+     * shows less residual FPN (fewer stripes) at the same frame-to-frame noise.
+     * Default 4 keeps the byte-exact C reference behaviour (tests).
+     */
+    private val baselineFrames: Int = 4,
     private val cdfPivot75: Boolean = true,
     private val force75: Boolean = true,
     /** FFC command callback: param 0 = FFC(0), 1 = FFC(1). */
@@ -224,8 +234,9 @@ class RenderPipeline(
             for (i in 0 until npix) refAcc[i] += frame[i]
         }
         refCnt++
-        if (refCnt >= 4) {
-            for (i in 0 until npix) ref[i] = refAcc[i] shr 2
+        if (refCnt >= baselineFrames.coerceIn(1, 64)) {
+            val n = refCnt
+            for (i in 0 until npix) ref[i] = refAcc[i] / n
             refCnt = 0
             hasRef = true
         }
@@ -609,15 +620,16 @@ class RenderPipeline(
             if (idx == 1) rebuildTables(shutterAtFfc)
             return 1
         }
-        if (idx <= 9) {
-            if (idx == 9) onFfc?.invoke(1)
+        val refEnd = 5 + baselineFrames.coerceIn(1, 64)
+        if (idx <= refEnd) {
+            if (idx == refEnd) onFfc?.invoke(1)
             if (idx == 6) {
                 refCnt = 0
                 hasRef = false
             }
             return 2 // ref collection window
         }
-        if (idx <= 13) return 1
+        if (idx <= refEnd + 4) return 1
         // normal frame: FFC condition
         var drift = shutterIn - shutterAtFfc
         if (drift < 0) drift = -drift

android/app/src/main/kotlin/com/mag160c/thermal/usb/IrSession.kt

@@ -324,6 +324,11 @@ class IrSession(context: Context) {
             // off the two distributions coincide (median 50 vs 61, mean 80 vs 82).
             // See docs/android_app/rendering_diff_phone_20261006.md §8.
             cdfPivot75 = false,
+            // baselineFrames stays at the verified 4: extending the window to 8 made
+            // the output *unstable* (frame-to-frame gray noise 3.95 -> 8.8), i.e. the
+            // device re-opens the shutter earlier than our schedule assumes, so the
+            // extra frames poison the reference.  A shutter-aware reference
+            // collection is the follow-up (docs/android_app/rendering_diff_phone_20261006.md §9.4).
             onFfc = { param ->
                 sendCmd(
                     MagProtocol.cmd8(MagProtocol.CMD_SET_SHUTTER_STATE, param),