pre merge cleanup

sras_compute.py

@@ -18,7 +18,9 @@ import numpy as np
 import scipy.fft as scipy_fft
 import scipy.ndimage as scipy_ndimage
 
-from sras_format import CH1_IDX, CH3_IDX, CH4_IDX, SrasFile, adc_to_mv
+from sras_format import (
+    CH1_IDX, CH3_IDX, CH4_IDX, PAD_FACTOR_MAX, SrasFile, adc_to_mv,
+)
 
 # ---------------------------------------------------------------------------
 # FFT backend
@@ -420,6 +422,56 @@ def dc_image_mv(sras: SrasFile, angle_idx: int, ch_idx: int,
         *sras.cal(ch_idx))
 
 
+def cached_rf_image(sras: SrasFile, angle_idx: int,
+                    dc_threshold_mv: float | None,
+                    apply_bg_sub: bool = True,
+                    n_fft: int | None = None,
+                    dc4_mv: np.ndarray | None = None,
+                    allow_dc_recompute: bool = True) -> np.ndarray | None:
+    """The stored peak-frequency image for one angle (v5 PREC or v7 CACH),
+    masked and ready to display — or None if no stored image can serve these
+    settings and a real FFT is needed.
+
+    Stored images are unmasked, so they serve any threshold — but they carry
+    one bg-sub state and one zero-padding, and a view asking for either of the
+    others is asking for different numbers, not a different rendering of the
+    same ones. Padding is the sharp edge: a pad-10 view resolves peaks on a
+    10x finer bin grid, so handing back a pad-1 image would quietly undo the
+    setting. v5 PREC and CACH v1 tails record no pad and are natural
+    resolution by construction.
+
+    Cheap enough to call on the GUI thread — a copy plus a comparison —
+    *except* when the CH4 mask has to be read from disk to build it. Pass
+    *allow_dc_recompute* False to return None in that case instead, and leave
+    the whole-channel read to a worker.
+    """
+    cached_freq = sras.precomputed_freq_mhz[angle_idx]
+    # n_fft None means "no padding", i.e. exactly samples_per_frame points.
+    want_n_fft = n_fft if n_fft is not None else sras.samples_per_frame
+    if (cached_freq is None
+            or want_n_fft != sras.precomputed_pad_factor * sras.samples_per_frame
+            or sras.precomputed_bg_sub != (apply_bg_sub and sras.background is not None)):
+        return None
+
+    if dc_threshold_mv is None:
+        return cached_freq.copy()
+
+    # DC4 mask, in priority order: stored DC block, caller-supplied image,
+    # or a fresh (cheap — no FFT) recompute.
+    dc4_img = sras.cached_dc_mv(angle_idx, CH4_IDX)
+    if dc4_img is None:
+        dc4_img = dc4_mv
+    if dc4_img is None:
+        if not allow_dc_recompute:
+            return None
+        dc4_img = adc_to_mv(compute_dc_image(sras, angle_idx, CH4_IDX),
+                            *sras.cal(CH4_IDX))
+
+    freq_img = cached_freq.copy()
+    freq_img[dc4_img < dc_threshold_mv] = 0.0
+    return freq_img
+
+
 def compute_rf_image(sras: SrasFile, angle_idx: int,
                      dc_threshold_mv: float | None,
                      apply_bg_sub: bool = True,
@@ -455,28 +507,20 @@ def compute_rf_image(sras: SrasFile, angle_idx: int,
 
     Fast path: if the file has a precomputed peak-frequency image for this
     angle (v5 PREC or v7 CACH), zero-padding is off, and the bg-sub flag
-    matches, the stored image is used directly — no FFT is run.
+    matches, the stored image is used directly — no FFT is run. That test is
+    cached_rf_image, which the viewer also applies before it ever dispatches
+    a compute at all.
     """
-    n_rows, n_frames = sras.image_shape(angle_idx)
-    data = sras.data[angle_idx]
-
     # ---- Fast path: precomputed image (v5 PREC or v7 CACH) ----------------
-    cached_freq = sras.precomputed_freq_mhz[angle_idx]
+    cached = cached_rf_image(sras, angle_idx, dc_threshold_mv,
-    if (cached_freq is not None
+                             apply_bg_sub=apply_bg_sub, n_fft=n_fft,
-            and n_fft is None                     # no custom zero-padding
+                             dc4_mv=dc4_mv)
-            and sras.precomputed_bg_sub == (apply_bg_sub and sras.background is not None)):
+    if cached is not None:
-        freq_img = cached_freq.copy()
+        return cached
-        if dc_threshold_mv is not None:
-            # DC4 mask, in priority order: already-cached DC block, caller-
-            # supplied image, or a fresh (cheap — no FFT) recompute.
-            dc4_img = sras.cached_dc_mv(angle_idx, CH4_IDX)
-            if dc4_img is None:
-                dc4_img = dc4_mv if dc4_mv is not None else adc_to_mv(
-                    compute_dc_image(sras, angle_idx, CH4_IDX), *sras.cal(CH4_IDX))
-            freq_img[dc4_img < dc_threshold_mv] = 0.0
-        return freq_img
 
     # ---- Chunked FFT path --------------------------------------------------
+    n_rows, n_frames = sras.image_shape(angle_idx)
+    data = sras.data[angle_idx]
     exact = exact or _FFT_EXACT_ENV
     spf = sras.samples_per_frame
     n_len = n_fft if n_fft is not None else spf
@@ -589,17 +633,19 @@ def compute_rf_image(sras: SrasFile, angle_idx: int,
 # ---------------------------------------------------------------------------
 
 def cache_file(path: str, mode: str, apply_bg_sub: bool,
-               fft_backend: str = "scipy", max_workers: int = 0) -> str:
+               fft_backend: str = "scipy", max_workers: int = 0,
+               pad_factor: int = 1) -> str:
     """Compute and store DC or FFT images for every angle of one file,
     converting v6 → v7 in place. Returns "" on success or an error message.
 
     Module-level and picklable so it can run in a ProcessPoolExecutor. The
-    FFT backend and worker cap are passed explicitly because module globals
+    FFT backend, worker cap and pad factor are passed explicitly because
-    do not survive a spawn.
+    module globals do not survive a spawn.
 
-    The stored FFT cache is always natural-resolution (pad 1): the v7 SFFT
+    *pad_factor* is stored alongside the images: a cache is only usable by a
-    block records no pad factor, and padded views compute live fast enough
+    view asking for the same padding, so caching at the viewer's own setting
-    (see _peak_bins_zoom) that caching them is not worth a format change.
+    is the difference between a batch that pays off and one that can never be
+    read back (see cached_rf_image).
     """
     global _MAX_WORKERS
     try:
@@ -630,15 +676,18 @@ def cache_file(path: str, mode: str, apply_bg_sub: bool,
             sras.write_v7_cache(new_dc3_mv=dc3, new_dc4_mv=dc4)
         else:
             effective_bg = apply_bg_sub and sras.background is not None
+            pad = max(1, min(PAD_FACTOR_MAX, int(pad_factor)))
+            n_fft = None if pad <= 1 else sras.samples_per_frame * pad
             # dc_threshold_mv=None: store unmasked images and mask at display
             # time (same convention as v5's PREC block). Skipping the mask
             # also skips reading CH4 entirely. The FFT path parallelises
             # internally over blocks, so angles run one at a time with the
             # full budget.
             freq = [compute_rf_image(sras, a, dc_threshold_mv=None,
-                                     apply_bg_sub=effective_bg)
+                                     apply_bg_sub=effective_bg, n_fft=n_fft)
                     for a in range(n)]
-            sras.write_v7_cache(new_freq_mhz=freq, new_bg_sub=effective_bg)
+            sras.write_v7_cache(new_freq_mhz=freq, new_bg_sub=effective_bg,
+                                new_pad_factor=pad)
         return ""
     except Exception as exc:
         return str(exc)

sras_format.py

@@ -60,7 +60,12 @@ PREC_FLAG_BG_SUB = 0x01
 CACH_MAGIC = b"CACH"
 CACH_HDR_FMT = ">4sBB"                        # magic, cach_version, block_flags
 CACH_HDR_SIZE = struct.calcsize(CACH_HDR_FMT)
-CACH_VERSION = 1
+# v2 added the SFFT pad factor. Writers always emit v2; readers still accept
+# v1, whose FFT block is natural-resolution by construction. An older reader
+# meeting a v2 tail rejects the whole section on the version check and
+# recomputes — no cache, but no misreading either.
+CACH_VERSION = 2
+CACH_VERSION_MIN = 1
 CACH_FLAG_DC = 0x01
 CACH_FLAG_FFT = 0x02
 
@@ -69,9 +74,12 @@ SDCB_HDR_FMT = ">4sBH"                        # magic, reserved, n_stored
 SDCB_HDR_SIZE = struct.calcsize(SDCB_HDR_FMT)
 
 SFFT_MAGIC = b"SFFT"
-SFFT_HDR_FMT = ">4sBH"                        # magic, flags, n_stored
+SFFT_HDR_FMT_V1 = ">4sBH"                     # magic, flags, n_stored
+SFFT_HDR_FMT = ">4sBHH"                       # magic, flags, n_stored, pad_factor
 SFFT_HDR_SIZE = struct.calcsize(SFFT_HDR_FMT)
 SFFT_FLAG_BG_SUB = 0x01
+# The viewer clamps its pad factor to this, and the field is a uint16.
+PAD_FACTOR_MAX = 256
 
 # Fixed channel indices into the .sras data array (CH1=RF, CH3/CH4=Bias DC)
 CH1_IDX, CH3_IDX, CH4_IDX = 0, 1, 2
@@ -169,7 +177,9 @@ class SrasFile:
     ``precomputed_dc3_mv`` / ``precomputed_dc4_mv`` / ``precomputed_freq_mhz``,
     always as ragged per-angle lists (``list[np.ndarray | None]``, one entry
     per angle, ``None`` where that angle was never stored) regardless of
-    source version.
+    source version. The settings the FFT images were computed under travel
+    with them as ``precomputed_bg_sub`` / ``precomputed_pad_factor``, since a
+    stored image is only usable by a view asking for the same two.
     """
 
     def __init__(self, path: str):
@@ -226,6 +236,9 @@ class SrasFile:
         self.precomputed_dc4_mv: list[np.ndarray | None] = [None] * n_angles
         self.precomputed_dc3_mv: list[np.ndarray | None] = [None] * n_angles
         self.precomputed_bg_sub: bool = False
+        # Zero-padding the stored FFT images were computed at; 1 = natural
+        # resolution, which is all a v5 PREC or CACH v1 tail can hold.
+        self.precomputed_pad_factor: int = 1
 
     def cached_dc_mv(self, angle_idx: int, ch_idx: int) -> np.ndarray | None:
         """A stored DC image (already in mV) for (angle, channel), or None."""
@@ -496,16 +509,18 @@ class SrasFile:
         return end
 
     def _read_cache_block(self, f, hdr_fmt: str, magic: bytes,
-                          stores: list[list]) -> int | None:
+                          stores: list[list]) -> tuple | None:
         """Read one CACH sub-block header, then its per-angle image entries
         into *stores* (one list per image the block stores per angle).
 
-        Returns the header's flags byte, or None if the block is malformed.
+        Every sub-block header is (magic, flags, n_stored, *extras). Returns
+        everything after the magic, so a caller that has extras knows how to
+        read them, or None if the block is malformed.
         """
         raw = f.read(struct.calcsize(hdr_fmt))
         if len(raw) < struct.calcsize(hdr_fmt):
             return None
-        block_magic, flags, n_stored = struct.unpack(hdr_fmt, raw)
+        block_magic, flags, n_stored, *extras = struct.unpack(hdr_fmt, raw)
         if block_magic != magic:
             return None
         for _ in range(n_stored):
@@ -515,7 +530,7 @@ class SrasFile:
             shape = self.image_shape(angle_idx)
             for store in stores:
                 store[angle_idx] = _read_f32_image(f, shape)
-        return flags
+        return (flags, *extras)
 
     def _parse_cach_section(self, offset: int):
         """Parse the v7 CACH tail that holds precomputed DC/FFT images."""
@@ -525,7 +540,8 @@ class SrasFile:
             if len(header_raw) < CACH_HDR_SIZE:
                 return
             magic, cach_version, block_flags = struct.unpack(CACH_HDR_FMT, header_raw)
-            if magic != CACH_MAGIC or cach_version != CACH_VERSION:
+            if (magic != CACH_MAGIC
+                    or not CACH_VERSION_MIN <= cach_version <= CACH_VERSION):
                 return
 
             if block_flags & CACH_FLAG_DC:
@@ -535,17 +551,23 @@ class SrasFile:
                     return
 
             if block_flags & CACH_FLAG_FFT:
-                flags = self._read_cache_block(
+                # v1 has no pad field: those images are natural-resolution.
-                    f, SFFT_HDR_FMT, SFFT_MAGIC, [self.precomputed_freq_mhz])
+                hdr_fmt = SFFT_HDR_FMT if cach_version >= 2 else SFFT_HDR_FMT_V1
-                if flags is None:
+                header = self._read_cache_block(
+                    f, hdr_fmt, SFFT_MAGIC, [self.precomputed_freq_mhz])
+                if header is None:
                     return
+                flags, *extras = header
                 self.precomputed_bg_sub = bool(flags & SFFT_FLAG_BG_SUB)
+                self.precomputed_pad_factor = (
+                    min(max(1, extras[0]), PAD_FACTOR_MAX) if extras else 1)
 
     def write_v7_cache(self, *,
                        new_dc3_mv: list[np.ndarray | None] | None = None,
                        new_dc4_mv: list[np.ndarray | None] | None = None,
                        new_freq_mhz: list[np.ndarray | None] | None = None,
-                       new_bg_sub: bool | None = None):
+                       new_bg_sub: bool | None = None,
+                       new_pad_factor: int | None = None):
         """Store computed DC and/or FFT images into this file's CACH tail,
         in place, converting a v6 source to v7 (or updating an existing v7
         file). Only the block(s) passed in are recomputed; whichever block
@@ -565,6 +587,11 @@ class SrasFile:
         final_dc4 = new_dc4_mv if new_dc4_mv is not None else self.precomputed_dc4_mv
         final_freq = new_freq_mhz if new_freq_mhz is not None else self.precomputed_freq_mhz
         final_bg_sub = new_bg_sub if new_bg_sub is not None else self.precomputed_bg_sub
+        final_pad = (new_pad_factor if new_pad_factor is not None
+                     else self.precomputed_pad_factor)
+        if not 1 <= final_pad <= PAD_FACTOR_MAX:
+            raise ValueError(
+                f"pad factor {final_pad} outside 1..{PAD_FACTOR_MAX}")
 
         dc_entries = [a for a in range(self.n_angles) if final_dc3[a] is not None]
         fft_entries = [a for a in range(self.n_angles) if final_freq[a] is not None]
@@ -584,7 +611,8 @@ class SrasFile:
 
         if fft_entries:
             fft_flags = SFFT_FLAG_BG_SUB if final_bg_sub else 0
-            payload += struct.pack(SFFT_HDR_FMT, SFFT_MAGIC, fft_flags, len(fft_entries))
+            payload += struct.pack(SFFT_HDR_FMT, SFFT_MAGIC, fft_flags,
+                                   len(fft_entries), final_pad)
             for a in fft_entries:
                 payload += struct.pack(">H", a)
                 payload += final_freq[a].astype(">f4").tobytes()
@@ -612,6 +640,7 @@ class SrasFile:
         self.precomputed_dc4_mv = final_dc4
         self.precomputed_freq_mhz = final_freq
         self.precomputed_bg_sub = final_bg_sub
+        self.precomputed_pad_factor = final_pad
 
     # ------------------------------------------------------------------
     # Axes helpers

sras_viewer/dialogs.py

@@ -48,7 +48,8 @@ class FftOptionsDialog(QDialog):
                  current_pad_factor: int,
                  samples_per_frame: int | None,
                  sample_rate_hz: float | None,
-                 grating_um: float):
+                 grating_um: float,
+                 cached_pad_factor: int | None = None):
         super().__init__(parent)
         self.setWindowTitle("FFT Options")
         self.setModal(True)
@@ -57,6 +58,10 @@ class FftOptionsDialog(QDialog):
         self._samples_per_frame = samples_per_frame
         self._sample_rate_hz = sample_rate_hz
         self._grating_um = grating_um
+        # The pad the open file's stored FFT cache was computed at, if it has
+        # one — picking anything else here makes that cache unreadable, which
+        # is worth saying before Apply rather than after.
+        self._cached_pad_factor = cached_pad_factor
 
         layout = QVBoxLayout(self)
 
@@ -109,6 +114,11 @@ class FftOptionsDialog(QDialog):
             lbl.setStyleSheet(_CSS_HINT)
             zl.addWidget(lbl)
 
+        self._lbl_cache = QLabel()
+        self._lbl_cache.setWordWrap(True)
+        self._lbl_cache.setStyleSheet(_CSS_WARN)
+        zl.addWidget(self._lbl_cache)
+
         layout.addWidget(grp_zp)
 
         # ---- Buttons ---------------------------------------------------
@@ -126,6 +136,13 @@ class FftOptionsDialog(QDialog):
         sr = self._sample_rate_hz
         pad = self._spin_pad.value()
 
+        self._lbl_cache.setText(
+            "" if self._cached_pad_factor in (None, pad) else
+            f"! This file's stored FFT cache was computed at pad "
+            f"{self._cached_pad_factor}x, so at {pad}x it can't be used and "
+            f"CH1/Velocity will recompute. Re-run Convert -> Batch Compute FFT "
+            f"to cache at {pad}x.")
+
         if spf is None or sr is None:
             self._lbl_nfft.setText("Load a file to preview FFT parameters.")
             self._lbl_freq_res.setText("")

sras_viewer/main_window.py

@@ -79,11 +79,15 @@ class SrasViewerWindow(QMainWindow):
 
         # Display-only settings (colormap, grating) never trigger a
         # recompute — they're applied to cached data on redraw. DC images
-        # (CH3/CH4) are cheap and precomputed for every angle in the
+        # (CH3/CH4) are cheap: they come straight from the file's stored
-        # background right after load. CH1/Velocity FFT images are
+        # cache when Batch Compute DC has been run for it (see
-        # computed lazily (with a progress popup) the first time an
+        # _stored_dc_image), and are otherwise precomputed for every angle
-        # angle/threshold combination is viewed — using the cached DC4
+        # in the background right after load. CH1/Velocity FFT images come
-        # image to skip the FFT entirely for masked-out pixels — and
+        # from the file's own stored cache when Batch Compute FFT has been
+        # run for it (see _stored_fft_image), and are otherwise computed
+        # lazily (with a progress popup) the first time an angle/threshold
+        # combination is viewed — using the cached DC4 image to skip the
+        # FFT entirely for masked-out pixels. Either way the result is
         # cached per (angle, bg_sub, n_fft, threshold) so revisiting the
         # same combination is free.
         self._dc_cache: dict[tuple[int, int], np.ndarray] = {}
@@ -219,7 +223,14 @@ class SrasViewerWindow(QMainWindow):
         self.spin_angle.setRange(0, 0)
         self.spin_angle.setEnabled(False)
         self.spin_angle.setMinimumWidth(64)
-        self.spin_angle.editingFinished.connect(self._on_view_changed)
+        # Keyboard tracking off is what makes valueChanged safe to act on: it
+        # stops the signal firing per keystroke, so typing "12" is one change
+        # to angle 12 (on Return or focus-out) rather than a trip to angle 1
+        # first. Arrow clicks and the wheel still emit immediately, which
+        # editingFinished alone did not — that is why stepping the angle used
+        # to leave the plot on the previous one until the box lost focus.
+        self.spin_angle.setKeyboardTracking(False)
+        self.spin_angle.valueChanged.connect(self._on_view_changed)
         self.lbl_angle_deg = QLabel("—")
         angle_field = QWidget()
         ar = QHBoxLayout(angle_field)
@@ -598,12 +609,32 @@ class SrasViewerWindow(QMainWindow):
         n_fft = sum(1 for x in s.precomputed_freq_mhz if x is not None)
         if n_dc or n_fft:
             bg_note = " (bg-sub)" if s.precomputed_bg_sub else " (no bg-sub)"
+            pad_note = (f", pad {s.precomputed_pad_factor}x"
+                        if n_fft and s.precomputed_pad_factor > 1 else "")
             notes.append(
                 f"Cached images: DC {n_dc}/{s.n_angles} angles, "
-                f"FFT {n_fft}/{s.n_angles} angles{bg_note if n_fft else ''} "
+                f"FFT {n_fft}/{s.n_angles} angles"
+                f"{bg_note + pad_note if n_fft else ''} "
                 "— display is instant for cached angles")
         elif s.version == 7:
             notes.append("v7 format: no cache blocks stored yet")
+
+        # A stored FFT cache the current settings can't read back is the one
+        # failure here with no other symptom: the images are right there in
+        # the file and every angle still recomputes. Say why.
+        if n_fft:
+            reasons = []
+            if s.precomputed_pad_factor != self._fft_pad_factor:
+                reasons.append(f"stored at pad {s.precomputed_pad_factor}x, "
+                               f"FFT Options is set to {self._fft_pad_factor}x")
+            if s.precomputed_bg_sub != (self.chk_bg_sub.isChecked()
+                                        and s.background is not None):
+                reasons.append("stored with bg-sub "
+                               f"{'on' if s.precomputed_bg_sub else 'off'}")
+            if reasons:
+                notes.append(f"! Cached FFT unusable as configured ({'; '.join(reasons)})"
+                             " — CH1/Velocity will recompute. Re-run Convert -> "
+                             "Batch Compute FFT to cache at the current settings.")
         self.lbl_frame_warn.setText("\n".join(notes))
 
     # ------------------------------------------------------------------
@@ -656,6 +687,9 @@ class SrasViewerWindow(QMainWindow):
         # Background subtraction changes the FFT input, so it genuinely
         # invalidates the cached raw FFT (the cache key includes it) —
         # _refresh_display() recomputes only on a miss for the new state.
+        # It can also decide whether the file's stored cache is readable, so
+        # the info panel's verdict on that has to be redrawn with it.
+        self._update_scan_info_labels()
         if self._is_fft_mode():
             self._refresh_display()
 
@@ -838,6 +872,14 @@ class SrasViewerWindow(QMainWindow):
             return None
         return self._sras.samples_per_frame * self._fft_pad_factor
 
+    def _cached_fft_pad_factor(self) -> int | None:
+        """The pad factor the open file's stored FFT images were computed at,
+        or None if it has none stored."""
+        if self._sras is None or not any(x is not None
+                                         for x in self._sras.precomputed_freq_mhz):
+            return None
+        return self._sras.precomputed_pad_factor
+
     def _is_fft_mode(self) -> bool:
         """Is the selected channel an FFT-derived (CH1/Velocity) mode?"""
         return (self._sras is not None
@@ -877,6 +919,45 @@ class SrasViewerWindow(QMainWindow):
             self._aligned_cache[key] = cached
         return cached
 
+    def _stored_fft_image(self, angle_idx: int) -> np.ndarray | None:
+        """The file's own batch-computed FFT image for this angle, masked for
+        the current threshold — or None if it can't serve the current settings.
+
+        Batch Compute FFT stores a peak-frequency image per angle in the file
+        itself, and the whole point of paying for that once is that display is
+        then instant. Without this check the viewer only ever found the stored
+        image deep inside ComputeWorker, so every angle change after a batch
+        still dispatched a background job behind a "Computing FFT…" popup for
+        an image that was already sitting on disk.
+        """
+        img = compute.cached_rf_image(
+            self._sras, angle_idx,
+            dc_threshold_mv=self.spin_threshold_mv.value(),
+            apply_bg_sub=self.chk_bg_sub.isChecked(),
+            n_fft=self._current_n_fft(),
+            dc4_mv=self._dc_cache.get((angle_idx, CH4_IDX)),
+            # Masking is a copy plus a comparison, but *reading* CH4 to build
+            # the mask is a whole-channel read — that case belongs on a worker,
+            # so it returns None here and falls through to _start_compute.
+            allow_dc_recompute=False)
+        if img is not None:
+            self._fft_cache[self._fft_cache_key(angle_idx)] = img
+        return img
+
+    def _stored_dc_image(self, angle_idx: int, ch_idx: int) -> np.ndarray | None:
+        """The file's own batch-computed DC image for (angle, channel), if it
+        has one — the CH3/CH4 half of _stored_fft_image.
+
+        The worker this saves would have handed back the very same stored
+        array (dc_image_mv prefers it over recomputing), so all it ever cost
+        was a thread and a progress popup — but that is exactly what made
+        "Batch Compute DC and Store" look like it had done nothing.
+        """
+        img = self._sras.cached_dc_mv(angle_idx, ch_idx)
+        if img is not None:
+            self._dc_cache[(angle_idx, ch_idx)] = img
+        return img
+
     def _refresh_display(self):
         """Show the image for the current angle/channel/threshold, using
         cached data whenever possible and only falling back to a background
@@ -888,12 +969,16 @@ class SrasViewerWindow(QMainWindow):
 
         if ch_idx in CH1_DERIVED_MODES:
             raw = self._fft_cache.get(self._fft_cache_key(angle_idx))
+            if raw is None:
+                raw = self._stored_fft_image(angle_idx)
             if raw is not None:
                 self._show_image_now(self._scale_for_display(raw, ch_idx),
                                      angle_idx, ch_idx)
                 return
         else:
             cached = self._dc_cache.get((angle_idx, ch_idx))
+            if cached is None:
+                cached = self._stored_dc_image(angle_idx, ch_idx)
             if cached is not None:
                 self._show_image_now(cached, angle_idx, ch_idx)
                 return
@@ -1163,7 +1248,11 @@ class SrasViewerWindow(QMainWindow):
             return
 
         self._batch_errors = []
-        worker = BatchCacheWorker(paths, mode, self.chk_bg_sub.isChecked())
+        # Cache at the pad factor currently configured, not a fixed pad 1 —
+        # a cache stored at any other padding is one this viewer can never
+        # read back (see _stored_fft_image).
+        worker = BatchCacheWorker(paths, mode, self.chk_bg_sub.isChecked(),
+                                  self._fft_pad_factor)
         started = self._run_worker(
             Jobs.BATCH, worker,
             connect=(
@@ -1338,6 +1427,7 @@ class SrasViewerWindow(QMainWindow):
             samples_per_frame=self._sras.samples_per_frame if self._sras else None,
             sample_rate_hz=self._sras.sample_rate_hz if self._sras else None,
             grating_um=self.spin_grating_um.value(),
+            cached_pad_factor=self._cached_fft_pad_factor(),
         )
         if dlg.exec() != QDialog.DialogCode.Accepted:
             return
@@ -1347,7 +1437,9 @@ class SrasViewerWindow(QMainWindow):
         self._settings.setValue("fft/pad_factor", self._fft_pad_factor)
         # Pad factor changes the FFT bin count, so it genuinely invalidates
         # the cached raw FFT (part of the cache key) — _refresh_display()
-        # recomputes only on a cache miss.
+        # recomputes only on a cache miss. It also decides whether the file's
+        # stored cache can be read back at all, which the info panel reports.
+        self._update_scan_info_labels()
         if self._is_fft_mode():
             self._refresh_display()
 

sras_workers.py

@@ -189,7 +189,10 @@ class BatchCacheWorker(QObject):
 
     *mode* is ``"dc"`` (CH3/CH4 mean images) or ``"fft"`` (CH1 peak-frequency
     images, unmasked — masking is applied at display time, same as v5's PREC
-    convention).
+    convention). FFT images are computed and stored at *pad_factor*, the
+    viewer's own zero-padding setting: a stored image only serves a view
+    asking for the same padding, so caching at any other one produces a file
+    the viewer will never read back.
 
     Files are processed one per subprocess: they are fully independent, each
     opens its own memmap and writes only its own bytes, and only path strings
@@ -201,11 +204,13 @@ class BatchCacheWorker(QObject):
     file_done = pyqtSignal(str, str)
     finished = pyqtSignal()
 
-    def __init__(self, paths: list[str], mode: str, apply_bg_sub: bool):
+    def __init__(self, paths: list[str], mode: str, apply_bg_sub: bool,
+                 pad_factor: int = 1):
         super().__init__()
         self._paths = paths
         self._mode = mode
         self._apply_bg_sub = apply_bg_sub
+        self._pad_factor = pad_factor
 
     def _report(self, path: str, err: str, done: int, total: int):
         self.file_done.emit(path, err)
@@ -230,7 +235,8 @@ class BatchCacheWorker(QObject):
         with ProcessPoolExecutor(max_workers=n_procs) as executor:
             futures = {
                 executor.submit(cache_file, p, self._mode, self._apply_bg_sub,
-                                compute.get_fft_backend(), per_proc_workers): p
+                                compute.get_fft_backend(), per_proc_workers,
+                                self._pad_factor): p
                 for p in paths
             }
             for fut in as_completed(futures):
@@ -254,7 +260,8 @@ class BatchCacheWorker(QObject):
             try:
                 err = cache_file(path, self._mode, self._apply_bg_sub,
                                  compute.get_fft_backend(),
-                                 compute.default_max_workers())
+                                 compute.default_max_workers(),
+                                 self._pad_factor)
             except Exception as exc:
                 err = str(exc)
             done += 1

tests/test_gui.py

@@ -94,11 +94,18 @@ def test_dc_precompute_all_angles(ctx):
 
 
 def test_angle_switching_from_cache(ctx):
+    """Setting the angle must redraw on its own — no nudge from the test.
+
+    The spinbox used to be wired to editingFinished alone, so stepping it with
+    the arrows changed the number and left the plot on the previous angle until
+    the box happened to lose focus.
+    """
     win, s = ctx.win, ctx.s
     for a in range(s.n_angles):
         win.spin_angle.setValue(a)
-        win._on_view_changed()
         pump(60)
+        assert win._current_angle == a, \
+            f"angle {a} redrawn from the spinbox alone, showing {win._current_angle}"
         expected = win._sras.image_shape(a)
         assert win._current_image.shape == expected, \
             f"angle {a} shows its own geometry {expected}, got {win._current_image.shape}"
@@ -106,6 +113,44 @@ def test_angle_switching_from_cache(ctx):
         "no compute job needed for cached DC angles"
 
 
+def test_angle_steps_and_typing(ctx):
+    """The arrows step and redraw one angle at a time; typing commits once,
+    without a stop at every intermediate value."""
+    win, s = ctx.win, ctx.s
+    assert s.n_angles > 2, "fixture needs several angles"
+    win.spin_angle.setValue(0)
+    pump(60)
+
+    seen = []
+    win.spin_angle.valueChanged.connect(seen.append)
+    try:
+        win.spin_angle.stepUp()
+        pump(60)
+        assert win._current_angle == 1, f"arrow stepped to 1, showing {win._current_angle}"
+        win.spin_angle.stepDown()
+        pump(60)
+        assert win._current_angle == 0, f"arrow stepped to 0, showing {win._current_angle}"
+
+        # Typing must not redraw per keystroke — that is what editingFinished
+        # bought and what keyboard tracking has to keep buying.
+        seen.clear()
+        last = s.n_angles - 1
+        win.spin_angle.lineEdit().selectAll()
+        QTest.keyClicks(win.spin_angle.lineEdit(), str(last))
+        pump(30)
+        assert seen == [] and win._current_angle == 0, \
+            f"half-typed text must not redraw ({seen}, showing {win._current_angle})"
+        QTest.keyClick(win.spin_angle, Qt.Key.Key_Return)
+        pump(60)
+        assert seen == [last], f"committed exactly once on Return: {seen}"
+        assert win._current_angle == last
+    finally:
+        win.spin_angle.valueChanged.disconnect(seen.append)
+        win.spin_angle.clearFocus()
+        win.spin_angle.setValue(0)
+        pump(60)
+
+
 def test_channel_switching(ctx):
     win = ctx.win
     win.spin_angle.setValue(0)