app+docs: 追查'官方更细腻'——定位到时域累积器(CAccumulator)；实测证明差异在参考帧(FFC baseline)而非显示侧平滑；累积器已实现但默认关闭

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

@@ -63,12 +63,24 @@ object OfficialTemp {
      * the official app's own wire parse (`UsbCommunication.parseCmd`,
      * D2P_SendParameter2), minus the leading magic word our reader consumes.
      *
+     * [baselineAcc] is the accumulator mode the SDK's `CAccumulator` runs with
+     * (`Reset(pixels, mode, 0)`, mode a power of two ≤ 0x40): the official
+     * pipeline pushes every raw frame through it before the NUC — a `>>log2(mode)`
+     * IIR that measurably removes ~2.3x of the noise/FPN the official phone app
+     * does not show (see docs/android_app/rendering_diff_phone_20261006.md §9).
+     *
      * Note on [fpaTempFix]: the SDK's compensation term `v50` was measured on a
      * reference capture as `dev+0x5C - dev+0x54` (0…89 mC, i.e. filtered vs
      * instantaneous FPA temperature), **not** as this field (the device reports
      * 1699 for it).  [fpaTempFix] is kept for completeness / future mapping.
      */
-    class AtPara(val atZeroErrorPoint: Int, val atErrorSlope: Float, val fpaTempFix: Int)
+    class AtPara(
+        val atZeroErrorPoint: Int,
+        val atErrorSlope: Float,
+        val fpaTempFix: Int,
+        /** CAccumulator mode (power of two; 1 = off). */
+        val baselineAcc: Int = 1,
+    )
 
     /**
      * Parse the radiance record from the DDT tail. Layout verified against the
@@ -110,7 +122,10 @@ object OfficialTemp {
         val atZero = MagProtocol.u32(payload, 40)
         val atSlope = Float.fromBits(MagProtocol.u32(payload, 44))
         if (atSlope == 0f || atSlope.isNaN() || kotlin.math.abs(atSlope) > 1f) return null
-        return AtPara(atZero, atSlope, fpaTempFix)
+        // baseLineAcc: CAccumulator mode, power of two <= 0x40 (SDK Reset() rejects others)
+        var acc = MagProtocol.u32(payload, 0)
+        if (acc < 1 || acc > 0x40 || (acc and (acc - 1)) != 0) acc = 1
+        return AtPara(atZero, atSlope, fpaTempFix, acc)
     }
 
     // ---------------------------------------------------------------- curve math

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

@@ -671,6 +671,7 @@ class RenderPipeline(
         val st = ffcStep(shutterValue)
         lastPhase = st
         if (st != 0) {
+            accReady = false          // SDK: accumulator Restart() at every FFC
             if (st == 2) {
                 // collect the reference in a SCRATCH buffer: decoding into `nuc`
                 // would leave raw (uncompensated) counts there, and the OSD
@@ -685,6 +686,7 @@ class RenderPipeline(
         val off = if (hasHdr) 0x1C else 0
         ByteReader.decodeU16(frame, off, npix, nuc)
         if (!hasRef) return false
+        accumulateInPlace()
 
         nucAndBlind(nuc, nuc)
         statsWindow()
@@ -810,11 +812,45 @@ class RenderPipeline(
     private var radRecord: OfficialTemp.RadRecord? = null
     private var atPara: OfficialTemp.AtPara? = null
 
+    // ---- official display accumulator (CAccumulator, mode = BasePara2.baseLineAcc) ----
+    // The SDK pushes every raw frame through it *before* the NUC
+    // (`CFunctions::Raw2Temperature`), restarts it at every FFC (`PushBaselineRaw`),
+    // and skips it while the baseline/shutter frames are collected.  With mode 4 it
+    // is a `>>2` IIR, which is what makes the official image ~2.3x smoother than an
+    // accumulator-less render (docs/android_app/rendering_diff_phone_20261006.md §9).
+    private var accumShift = 0                 // log2(mode); 0 = off
+    private val accBuf = IntArray(npix)
+    private var accReady = false
+
     /** Supply the official chain inputs once the session has parsed them. */
     fun setTempParams(rec: OfficialTemp.RadRecord?, at: OfficialTemp.AtPara?) {
         synchronized(lock) {
             radRecord = rec
             atPara = at
+            // Accumulator is implemented but stays OFF by default: measurements show the
+            // official receiver is not display-smoothed (its frame-to-frame noise equals
+            // ours, 4.12 vs 4.02) while its *spatial* noise is 2.3x lower -> the official
+            // difference comes from a cleaner FFC reference, not from temporal filtering
+            // (a strong temporal IIR here even *reveals* static banding; see
+            // docs/android_app/rendering_diff_phone_20261006.md §9).
+            accumShift = 0
+            accReady = false
+        }
+    }
+
+    /** In-place `buf = (buf*(M-1) + new) >> log2(M)`; first frame is copied verbatim. */
+    private fun accumulateInPlace() {
+        if (accumShift <= 0) return
+        if (!accReady) {
+            System.arraycopy(nuc, 0, accBuf, 0, npix)
+            accReady = true
+            return
+        }
+        val m1 = (1 shl accumShift) - 1
+        for (i in 0 until npix) {
+            val v = (accBuf[i] * m1 + nuc[i]) shr accumShift
+            accBuf[i] = v
+            nuc[i] = v
         }
     }