added reference png export

.gitignore

@@ -224,3 +224,6 @@ __marimo__/
 .streamlit/secrets.toml
 python_app/runtime
 SHARE_INTERNET_TO_PI.md
+
+CLAUDE.md
+./docs

python_app/gui/controllers/app_window_preprocess_mixin.py

@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 from python_app.gui.preprocess_dialog import PreprocessDialog
+from python_app.gui.trace_png_export import export_trace_png
 from python_app.orchestration.preprocess_assets import (
     PREPROCESS_ASSET_SPECS,
     VISIBLE_PREPROCESS_ASSET_KEYS,
@@ -701,6 +702,12 @@ class AppWindowPreprocessMixin:
                     f"{display_name} sequence completed and saved: set={set_name}, "
                     f"radar_variants={len(saved_sets)} [{saved_summary}]"
                 )
+                self._export_multi_radar_preview_pngs(
+                    session=session,
+                    saved_sets=saved_sets,
+                    kind=kind,
+                    set_name=set_name,
+                )
             else:
                 dialog.set_status(f"{display_name} set saved: {set_name} ({len(collection.traces)} traces)")
                 self._log(f"{display_name} sequence completed and saved: set={set_name}, key={radar_key}")
@@ -708,6 +715,50 @@ class AppWindowPreprocessMixin:
         except Exception as exc:  # noqa: BLE001
             self._show_exception("Failed to save preprocess set", exc)
 
+    def _export_multi_radar_preview_pngs(
+        self,
+        *,
+        session: MultiRadarSequentialCaptureSession,
+        saved_sets: list,
+        kind: str,
+        set_name: str,
+    ) -> None:
+        """Save amplitude/phase PNGs for every captured combo across all radar configs.
+
+        The live preview only shows the last config of each combo, so this persists a
+        graph for the other configs too, under the store's ``preview_png/`` tree. The
+        set is already saved by the time we get here, so any rendering failure is
+        logged but never aborts the save.
+        """
+        channel = preprocess_asset_channel(kind)
+        display_name = preprocess_asset_display_name(kind)
+        # batch.traces and saved_sets are both ordered by the session's radar
+        # variants, so index i refers to the same config in both.
+        saved_count = 0
+        for batch in session.captured_batches():
+            for trace, saved in zip(batch.traces, saved_sets):
+                combo_label = f"input={trace.combo.input} output={trace.combo.output}"
+                try:
+                    png_path = self._store.preview_png_dir(kind, set_name, saved.radar_key) / (
+                        f"i{trace.combo.input}_o{trace.combo.output}.png"
+                    )
+                    export_trace_png(
+                        trace,
+                        png_path,
+                        channel=channel,
+                        title=f"{display_name} | {saved.display_name} | {combo_label}",
+                    )
+                    saved_count += 1
+                except Exception as exc:  # noqa: BLE001
+                    self._log(
+                        f"Failed to save preview PNG for {saved.display_name} ({combo_label}): {exc}"
+                    )
+        if saved_count and saved_sets:
+            png_root = self._store.preview_png_dir(kind, set_name, saved_sets[0].radar_key).parent
+            self._log(
+                f"Saved {saved_count} preview PNG(s) for {len(saved_sets)} radar config(s) under {png_root}"
+            )
+
     def _abort_capture_sequence(self, *, resume_pipeline: bool = True) -> None:
         """Abort active capture session and optionally resume pipeline."""
         if self._capture_session is None:

python_app/gui/trace_png_export.py

@@ -0,0 +1,77 @@
+"""Render captured traces (amplitude + phase) to standalone PNG files.
+
+The preprocess preview pane only shows the *last* radar variant of each combo,
+so during a multi-config reference capture the operator never sees the other
+variants. This helper renders the same amplitude/phase plot pair used in the
+preview into off-screen PNG files, letting us persist a graph for every config.
+"""
+
+from __future__ import annotations
+
+import logging
+from pathlib import Path
+
+import numpy as np
+import pyqtgraph as pg
+from PyQt6.QtCore import QRectF
+from pyqtgraph.exporters import ImageExporter
+
+from python_app.models.dataset_model import TraceData
+
+logger = logging.getLogger(__name__)
+
+# Matches the preview pane styling in preprocess_dialog so saved PNGs and the
+# on-screen preview look the same.
+_BACKGROUND = "#101418"
+_MAGNITUDE_PEN = pg.mkPen("#4cc9f0", width=1.8)
+_PHASE_PEN = pg.mkPen("#f48c06", width=1.8)
+_EXPORT_SIZE = (1400, 520)
+
+
+def export_trace_png(
+    trace: TraceData,
+    output_path: Path,
+    *,
+    channel: str,
+    title: str,
+) -> None:
+    """Render one trace's amplitude (dB) and wrapped phase (deg) panes to a PNG.
+
+    Builds an off-screen ``GraphicsLayoutWidget`` (never shown), plots the same
+    curves as the live preview, and exports the scene as a PNG. Requires a
+    running ``QApplication`` (always true inside the GUI).
+    """
+    samples = trace.s11 if channel == "s11" else trace.s21
+    magnitude_db = 20.0 * np.log10(np.maximum(np.abs(samples), 1e-12))
+    phase_deg = np.degrees(np.angle(samples))
+
+    layout = pg.GraphicsLayoutWidget(show=False, size=_EXPORT_SIZE)
+    layout.setBackground(_BACKGROUND)
+    try:
+        layout.addLabel(title, row=0, col=0, colspan=2)
+
+        magnitude_plot = layout.addPlot(row=1, col=0)
+        magnitude_plot.showGrid(x=True, y=True, alpha=0.2)
+        magnitude_plot.setLabel("bottom", "Frequency", units="Hz")
+        magnitude_plot.setLabel("left", "Magnitude", units="dB")
+        magnitude_plot.plot(trace.frequency_hz, magnitude_db, pen=_MAGNITUDE_PEN)
+
+        phase_plot = layout.addPlot(row=1, col=1)
+        phase_plot.showGrid(x=True, y=True, alpha=0.2)
+        phase_plot.setLabel("bottom", "Frequency", units="Hz")
+        phase_plot.setLabel("left", "Phase", units="deg")
+        phase_plot.plot(trace.frequency_hz, phase_deg, pen=_PHASE_PEN)
+
+        # An off-screen widget never receives a resizeEvent, so its central
+        # GraphicsLayout keeps its small preferred size and both plots would be
+        # squeezed into the left edge of the image. Force the layout geometry to
+        # the target size, doing manually what a resizeEvent normally triggers.
+        layout.ci.setGeometry(QRectF(0, 0, _EXPORT_SIZE[0], _EXPORT_SIZE[1]))
+
+        output_path.parent.mkdir(parents=True, exist_ok=True)
+        exporter = ImageExporter(layout.scene())
+        exporter.parameters()["width"] = _EXPORT_SIZE[0]
+        exporter.export(str(output_path))
+    finally:
+        layout.close()
+        layout.deleteLater()

python_app/storage/npz/store.py

@@ -411,5 +411,15 @@ class NpzStore(StoreApi):
         """Return directory for set kind and radar key."""
         return self._root_dir / kind / radar_key
 
+    def preview_png_dir(self, kind: str, set_name: str, radar_key: str) -> Path:
+        """Return directory for preview PNGs of one set/radar variant.
+
+        Lives under ``preview_png/`` inside the store so saved graphs sit next to
+        the data they describe, grouped by set name then radar variant. The set
+        name is operator-supplied, so it is sanitized; ``radar_key`` is already
+        filesystem-safe by construction.
+        """
+        return self._root_dir / "preview_png" / kind / sanitize_path_component(set_name) / radar_key
+
 
 __all__ = ["NpzStore", "radar_key_from_config"]