95 lines
3.0 KiB
Dart
95 lines
3.0 KiB
Dart
import 'dart:math' as math;
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import 'dart:typed_data';
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import 'detection_result.dart';
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import 'motion_aggregator.dart';
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/// 静态场景背景建模：运行均值 + 方差，帧差高于自适应阈值的像素记为"新出现"，
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/// 分块聚合为新颖区域（novelty）。
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///
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/// 固定机位下，常驻物体（键盘/石头/文字）永远属于背景、不产生新颖区域；
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/// 走进画面的目标（动物移动/新出现）才会触发。比相邻帧差分更强的证据：
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/// 风吹草动是持续的背景更新，不会长期标记为新颖。
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class BackgroundModel {
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final int maxWidth;
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final int maxHeight;
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static const double learnRate = 0.05;
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static const double kSigma = 2.5;
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static const int minDiff = 15;
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static const int minPixels = 12;
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Float32List? _mean;
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Float32List? _var;
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int _tw = 0;
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BackgroundModel({this.maxWidth = 128, this.maxHeight = 128});
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/// 后台 isolate 用原始数据接口（与 MotionDetector 同源：直接取 planes[0]）。
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List<MotionRegion> updateRaw(
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Uint8List yPlane, int yStride, int width, int height) {
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final scale =
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maxWidth / width < maxHeight / height ? maxWidth / width : maxHeight / height;
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final tw = (width * scale).toInt().clamp(1, maxWidth);
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final th = (height * scale).toInt().clamp(1, maxHeight);
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if (tw == 0 || th == 0) return const [];
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final gray = Float32List(tw * th);
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for (var oy = 0; oy < th; oy++) {
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final sy = (oy / scale).toInt().clamp(0, height - 1);
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final idx = oy * tw;
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for (var ox = 0; ox < tw; ox++) {
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final sx = (ox / scale).toInt().clamp(0, width - 1);
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gray[idx + ox] = yPlane[sy * yStride + sx].toDouble();
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}
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}
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return update(gray, tw, th);
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}
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List<MotionRegion> update(Float32List gray, int tw, int th) {
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final n = gray.length;
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final mean = _mean;
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final variance = _var;
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if (mean == null || variance == null || mean.length != n || _tw != tw) {
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_mean = Float32List.fromList(gray);
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_var = Float32List(n);
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_tw = tw;
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return const [];
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}
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final diff = Uint8List(n);
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var fgCount = 0;
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for (var i = 0; i < n; i++) {
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final g = gray[i];
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final m = mean[i];
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final d = (g - m).abs();
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if (d > kSigma * math.sqrt(variance[i]) + minDiff) {
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diff[i] = 1;
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fgCount++;
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// 前景像素不更新背景，避免把移动目标吸收进背景
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} else {
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// 静态像素缓慢吸收进背景，适应光照漂移
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final nm = m + learnRate * (g - m);
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mean[i] = nm;
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variance[i] =
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variance[i] + learnRate * ((g - nm) * (g - nm) - variance[i]);
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}
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}
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// 全屏大变化 → 相机移动/场景切换，重建背景
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if (fgCount > n ~/ 2) {
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_mean = null;
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_var = null;
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return const [];
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}
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if (fgCount < minPixels) return const [];
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return MotionAggregator.aggregate(diff, tw, th);
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}
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/// 相机切换后重置，避免旧场景背景
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void reset() {
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_mean = null;
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_var = null;
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}
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}
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