Fix rear camera default and robust cap color correction workflow

lib/main.dart

@@ -150,6 +150,7 @@ class _MosaicHomePageState extends State<MosaicHomePage> {
   Future<void> _captureCapPhoto() async {
     final XFile? captured = await _picker.pickImage(
       source: ImageSource.camera,
+      preferredCameraDevice: CameraDevice.rear,
       imageQuality: 95,
       maxWidth: 1800,
     );
@@ -159,10 +160,17 @@ class _MosaicHomePageState extends State<MosaicHomePage> {
     final detected = await compute(_extractCapFromPhotoIsolate, bytes);
     if (!mounted) return;
 
-    final dominantColor = Color(detected['dominantColor'] as int);
-    final averageColor = Color(detected['averageColor'] as int);
-    final previewBytes = detected['previewPng'] as Uint8List;
+    Color dominantColor = Color(detected['dominantColor'] as int);
+    Color averageColor = Color(detected['averageColor'] as int);
+    Uint8List previewBytes = detected['previewPng'] as Uint8List;
     final bool usedFallback = detected['usedFallback'] as bool? ?? false;
+    final imageW = (detected['imageW'] as num).toDouble();
+    final imageH = (detected['imageH'] as num).toDouble();
+    double circleX = (detected['circleX'] as num).toDouble() / imageW;
+    double circleY = (detected['circleY'] as num).toDouble() / imageH;
+    double circleR =
+        (detected['circleR'] as num).toDouble() / math.min(imageW, imageH);
+
     ColorExtractionMode mode = _colorExtractionMode;
     Color selected =
         mode == ColorExtractionMode.dominant ? dominantColor : averageColor;
@@ -174,6 +182,26 @@ class _MosaicHomePageState extends State<MosaicHomePage> {
       builder: (ctx) {
         return StatefulBuilder(
           builder: (ctx, setDialogState) {
+            Future<void> recalculate() async {
+              final adjusted = await compute(
+                _extractCapFromAdjustedCircleIsolate,
+                <String, dynamic>{
+                  'sourceBytes': bytes,
+                  'circleX': circleX,
+                  'circleY': circleY,
+                  'circleR': circleR,
+                },
+              );
+              dominantColor = Color(adjusted['dominantColor'] as int);
+              averageColor = Color(adjusted['averageColor'] as int);
+              previewBytes = adjusted['previewPng'] as Uint8List;
+              selected = mode == ColorExtractionMode.dominant
+                  ? dominantColor
+                  : averageColor;
+              _photoCapHexCtrl.text = _colorToHex(selected);
+              setDialogState(() {});
+            }
+
             return AlertDialog(
               title: const Text('Deckel fotografieren'),
               content: SingleChildScrollView(
@@ -189,8 +217,8 @@ class _MosaicHomePageState extends State<MosaicHomePage> {
                     const SizedBox(height: 8),
                     Text(
                       usedFallback
-                          ? 'Kreis wurde per Kanten-Fallback erkannt.'
-                          : 'Kreis wurde automatisch auf dem Deckel erkannt.',
+                          ? 'Kreiserkennung per Fallback. Bei Bedarf Kreis manuell korrigieren.'
+                          : 'Kreis automatisch erkannt. Optional unten feinjustieren.',
                       style: Theme.of(context).textTheme.bodySmall,
                     ),
                     const SizedBox(height: 8),
@@ -198,11 +226,11 @@ class _MosaicHomePageState extends State<MosaicHomePage> {
                       segments: const [
                         ButtonSegment(
                           value: ColorExtractionMode.dominant,
-                          label: Text('Dominante Farbe'),
+                          label: Text('Dominant (robust)'),
                         ),
                         ButtonSegment(
                           value: ColorExtractionMode.average,
-                          label: Text('Durchschnitt'),
+                          label: Text('Gewichteter Mittelwert'),
                         ),
                       ],
                       selected: {mode},
@@ -217,10 +245,42 @@ class _MosaicHomePageState extends State<MosaicHomePage> {
                     ),
                     const SizedBox(height: 8),
                     Text(
-                      'Nur Pixel innerhalb des erkannten Kreisinneren werden ausgewertet.',
+                      'Robuste Analyse: Schatten/Outlier werden reduziert, nur geeignete Pixel im Kreis werden gewichtet.',
                       style: Theme.of(context).textTheme.bodySmall,
                     ),
-                    const SizedBox(height: 12),
+                    const SizedBox(height: 8),
+                    const Text('Manuelle Kreis-Korrektur',
+                        style: TextStyle(fontWeight: FontWeight.w600)),
+                    Slider(
+                      value: circleX.clamp(0.15, 0.85),
+                      min: 0.15,
+                      max: 0.85,
+                      label: 'X',
+                      onChanged: (v) => setDialogState(() => circleX = v),
+                    ),
+                    Slider(
+                      value: circleY.clamp(0.15, 0.85),
+                      min: 0.15,
+                      max: 0.85,
+                      label: 'Y',
+                      onChanged: (v) => setDialogState(() => circleY = v),
+                    ),
+                    Slider(
+                      value: circleR.clamp(0.12, 0.48),
+                      min: 0.12,
+                      max: 0.48,
+                      label: 'Radius',
+                      onChanged: (v) => setDialogState(() => circleR = v),
+                    ),
+                    Align(
+                      alignment: Alignment.centerRight,
+                      child: OutlinedButton.icon(
+                        onPressed: recalculate,
+                        icon: const Icon(Icons.tune),
+                        label: const Text('Kreis anwenden & neu berechnen'),
+                      ),
+                    ),
+                    const SizedBox(height: 8),
                     Row(
                       children: [
                         Container(
@@ -1243,6 +1303,11 @@ Map<String, dynamic> _extractCapFromPhotoIsolate(Uint8List sourceBytes) {
       'dominantColor': Colors.orange.toARGB32(),
       'averageColor': Colors.orange.toARGB32(),
       'usedFallback': true,
+      'circleX': 0.5,
+      'circleY': 0.5,
+      'circleR': 0.3,
+      'imageW': 1,
+      'imageH': 1,
       'previewPng': Uint8List.fromList(
           img.encodePng(img.Image(width: 1, height: 1), level: 1)),
     };
@@ -1276,7 +1341,74 @@ Map<String, dynamic> _extractCapFromPhotoIsolate(Uint8List sourceBytes) {
   );
 
   final stats = _sampleCapColors(decoded, upscaledCircle);
+  final preview = _buildCirclePreview(analysis, detected);
 
+  return {
+    'dominantColor': stats.dominantArgb,
+    'averageColor': stats.averageArgb,
+    'usedFallback': usedFallback,
+    'circleX': upscaledCircle.cx,
+    'circleY': upscaledCircle.cy,
+    'circleR': upscaledCircle.r,
+    'imageW': decoded.width,
+    'imageH': decoded.height,
+    'previewPng': Uint8List.fromList(img.encodePng(preview, level: 1)),
+  };
+}
+
+Map<String, dynamic> _extractCapFromAdjustedCircleIsolate(
+    Map<String, dynamic> request) {
+  final sourceBytes = request['sourceBytes'] as Uint8List;
+  final decoded = img.decodeImage(sourceBytes);
+  if (decoded == null) {
+    return {
+      'dominantColor': Colors.orange.toARGB32(),
+      'averageColor': Colors.orange.toARGB32(),
+      'previewPng': Uint8List.fromList(
+          img.encodePng(img.Image(width: 1, height: 1), level: 1)),
+    };
+  }
+
+  final cx = ((request['circleX'] as num).toDouble() * decoded.width)
+      .clamp(0.0, decoded.width.toDouble());
+  final cy = ((request['circleY'] as num).toDouble() * decoded.height)
+      .clamp(0.0, decoded.height.toDouble());
+  final r = ((request['circleR'] as num).toDouble() *
+          math.min(decoded.width, decoded.height))
+      .clamp(8.0, math.min(decoded.width, decoded.height) * 0.49);
+
+  final circle = _DetectedCircle(cx: cx, cy: cy, r: r);
+  final stats = _sampleCapColors(decoded, circle);
+
+  const int analysisMaxSize = 480;
+  final scale = decoded.width >= decoded.height
+      ? (decoded.width > analysisMaxSize
+          ? analysisMaxSize / decoded.width
+          : 1.0)
+      : (decoded.height > analysisMaxSize
+          ? analysisMaxSize / decoded.height
+          : 1.0);
+  final analysis = scale < 1.0
+      ? img.copyResize(decoded,
+          width: (decoded.width * scale).round(),
+          height: (decoded.height * scale).round(),
+          interpolation: img.Interpolation.average)
+      : decoded;
+
+  final preview = _buildCirclePreview(
+    analysis,
+    _DetectedCircle(
+        cx: circle.cx * scale, cy: circle.cy * scale, r: circle.r * scale),
+  );
+
+  return {
+    'dominantColor': stats.dominantArgb,
+    'averageColor': stats.averageArgb,
+    'previewPng': Uint8List.fromList(img.encodePng(preview, level: 1)),
+  };
+}
+
+img.Image _buildCirclePreview(img.Image analysis, _DetectedCircle detected) {
   final preview = img.copyResize(analysis,
       width: math.min(analysis.width, 320),
       height: (math.min(analysis.width, 320) * analysis.height / analysis.width)
@@ -1284,13 +1416,7 @@ Map<String, dynamic> _extractCapFromPhotoIsolate(Uint8List sourceBytes) {
   final previewScale = preview.width / analysis.width;
   _drawCircle(preview, detected.cx * previewScale, detected.cy * previewScale,
       detected.r * previewScale);
-
-  return {
-    'dominantColor': stats.dominantArgb,
-    'averageColor': stats.averageArgb,
-    'usedFallback': usedFallback,
-    'previewPng': Uint8List.fromList(img.encodePng(preview, level: 1)),
-  };
+  return preview;
 }
 
 _DetectedCircle? _detectCapCircle(img.Image image) {
@@ -1371,13 +1497,9 @@ _DetectedCircle _fallbackCapCircle(int width, int height) {
 }
 
 _CapColorStats _sampleCapColors(img.Image image, _DetectedCircle circle) {
-  final buckets = <int, _RgbBucket>{};
-  double sumR = 0;
-  double sumG = 0;
-  double sumB = 0;
-  int included = 0;
+  final samples = <_ColorSample>[];
 
-  final insetRadius = circle.r * 0.78;
+  final insetRadius = circle.r * 0.76;
   final r2 = insetRadius * insetRadius;
   final minX = math.max(0, (circle.cx - insetRadius).floor());
   final maxX = math.min(image.width - 1, (circle.cx + insetRadius).ceil());
@@ -1388,47 +1510,50 @@ _CapColorStats _sampleCapColors(img.Image image, _DetectedCircle circle) {
     final dy = y - circle.cy;
     for (int x = minX; x <= maxX; x++) {
       final dx = x - circle.cx;
-      if ((dx * dx) + (dy * dy) > r2) continue;
+      final dist2 = (dx * dx) + (dy * dy);
+      if (dist2 > r2) continue;
 
       final p = image.getPixel(x, y);
       final r = p.r.toInt();
       final g = p.g.toInt();
       final b = p.b.toInt();
+      final hsv = _rgbToHsv(r, g, b);
+      final lum = 0.2126 * r + 0.7152 * g + 0.0722 * b;
+      final radial = 1.0 - math.sqrt(dist2) / insetRadius;
 
-      sumR += r;
-      sumG += g;
-      sumB += b;
-      included++;
-
-      final bucketKey = ((r ~/ 16) << 8) | ((g ~/ 16) << 4) | (b ~/ 16);
-      final bucket = buckets.putIfAbsent(bucketKey, () => _RgbBucket());
-      bucket.add(r, g, b);
+      samples.add(_ColorSample(
+        r: r,
+        g: g,
+        b: b,
+        saturation: hsv[1],
+        value: hsv[2],
+        luminance: lum,
+        radialWeight: radial.clamp(0.1, 1.0),
+      ));
     }
   }
 
-  if (included == 0) {
+  if (samples.isEmpty) {
     final fallback = const Color(0xFFFF9800).toARGB32();
     return _CapColorStats(averageArgb: fallback, dominantArgb: fallback);
   }
 
-  final average = Color.fromARGB(255, (sumR / included).round(),
-          (sumG / included).round(), (sumB / included).round())
-      .toARGB32();
+  final lumValues = samples.map((s) => s.luminance).toList()..sort();
+  final lowLum = _percentile(lumValues, 0.18);
+  final highLum = _percentile(lumValues, 0.98);
 
-  _RgbBucket? dominant;
-  for (final bucket in buckets.values) {
-    if (dominant == null || bucket.count > dominant.count) dominant = bucket;
-  }
-  final dominantArgb = dominant == null
-      ? average
-      : Color.fromARGB(
-              255,
-              (dominant.r / dominant.count).round(),
-              (dominant.g / dominant.count).round(),
-              (dominant.b / dominant.count).round())
-          .toARGB32();
+  final filtered = samples.where((s) {
+    if (s.luminance < lowLum || s.luminance > highLum) return false;
+    if (s.value < 0.18) return false;
+    return true;
+  }).toList();
 
-  return _CapColorStats(averageArgb: average, dominantArgb: dominantArgb);
+  final usable = filtered.isEmpty ? samples : filtered;
+
+  final avg = _weightedAverage(usable);
+  final dominant = _weightedDominant(usable);
+
+  return _CapColorStats(averageArgb: avg, dominantArgb: dominant);
 }
 
 void _drawCircle(img.Image image, double cx, double cy, double r) {
@@ -1468,17 +1593,39 @@ class _CapColorStats {
   const _CapColorStats({required this.averageArgb, required this.dominantArgb});
 }
 
-class _RgbBucket {
-  int count = 0;
-  int r = 0;
-  int g = 0;
-  int b = 0;
+class _ColorSample {
+  final int r;
+  final int g;
+  final int b;
+  final double saturation;
+  final double value;
+  final double luminance;
+  final double radialWeight;
 
-  void add(int nr, int ng, int nb) {
-    count++;
-    r += nr;
-    g += ng;
-    b += nb;
+  const _ColorSample({
+    required this.r,
+    required this.g,
+    required this.b,
+    required this.saturation,
+    required this.value,
+    required this.luminance,
+    required this.radialWeight,
+  });
+
+  double get weight => radialWeight * (0.55 + saturation * 0.75);
+}
+
+class _WeightedRgb {
+  double weight = 0;
+  double r = 0;
+  double g = 0;
+  double b = 0;
+
+  void add(_ColorSample s, double w) {
+    weight += w;
+    r += s.r * w;
+    g += s.g * w;
+    b += s.b * w;
   }
 }
 
@@ -1489,6 +1636,82 @@ class _Candidate {
   const _Candidate({required this.index, required this.distance});
 }
 
+int _weightedAverage(List<_ColorSample> samples) {
+  final acc = _WeightedRgb();
+  for (final s in samples) {
+    final w = s.weight;
+    acc.add(s, w);
+  }
+  if (acc.weight <= 0) return const Color(0xFFFF9800).toARGB32();
+  return Color.fromARGB(
+    255,
+    (acc.r / acc.weight).round().clamp(0, 255),
+    (acc.g / acc.weight).round().clamp(0, 255),
+    (acc.b / acc.weight).round().clamp(0, 255),
+  ).toARGB32();
+}
+
+int _weightedDominant(List<_ColorSample> samples) {
+  final bins = <int, _WeightedRgb>{};
+  for (final s in samples) {
+    final hsv = _rgbToHsv(s.r, s.g, s.b);
+    final hBin = (hsv[0] / 20).floor().clamp(0, 17);
+    final sBin = (hsv[1] * 4).floor().clamp(0, 3);
+    final vBin = (hsv[2] * 4).floor().clamp(0, 3);
+    final key = (hBin << 6) | (sBin << 3) | vBin;
+    final bucket = bins.putIfAbsent(key, () => _WeightedRgb());
+    bucket.add(s, s.weight);
+  }
+
+  _WeightedRgb? best;
+  for (final b in bins.values) {
+    if (best == null || b.weight > best.weight) best = b;
+  }
+  if (best == null || best.weight <= 0) return _weightedAverage(samples);
+
+  return Color.fromARGB(
+    255,
+    (best.r / best.weight).round().clamp(0, 255),
+    (best.g / best.weight).round().clamp(0, 255),
+    (best.b / best.weight).round().clamp(0, 255),
+  ).toARGB32();
+}
+
+List<double> _rgbToHsv(int r, int g, int b) {
+  final rf = r / 255.0;
+  final gf = g / 255.0;
+  final bf = b / 255.0;
+  final maxC = math.max(rf, math.max(gf, bf));
+  final minC = math.min(rf, math.min(gf, bf));
+  final delta = maxC - minC;
+
+  double h;
+  if (delta == 0) {
+    h = 0;
+  } else if (maxC == rf) {
+    h = 60 * (((gf - bf) / delta) % 6);
+  } else if (maxC == gf) {
+    h = 60 * (((bf - rf) / delta) + 2);
+  } else {
+    h = 60 * (((rf - gf) / delta) + 4);
+  }
+  if (h < 0) h += 360;
+
+  final s = maxC == 0 ? 0.0 : delta / maxC;
+  final v = maxC;
+  return [h, s, v];
+}
+
+double _percentile(List<double> sorted, double p) {
+  if (sorted.isEmpty) return 0;
+  final pos = (sorted.length - 1) * p.clamp(0.0, 1.0);
+  final lo = pos.floor();
+  final hi = pos.ceil();
+  if (lo == hi) return sorted[lo];
+  final t = pos - lo;
+  return sorted[lo] * (1 - t) + sorted[hi] * t;
+}
+
 double _mix(double a, double b, double t) => a + (b - a) * t;
 
 List<double> _argbToLab(int argb) {