4-seasons: replace size-rejection with 1MB fast-skip for grey filter

File size can't reliably reject bad frames (200KB can be good or bad).
Remove SEASONS_MIN_FRAME_BYTES.  Instead, the grey/green uniform-colour
filter (SEASONS_GREY_STDDEV_MIN) now skips the expensive ImageMagick
check for files above SEASONS_LARGE_FRAME_BYTES (default 1 MB) since
those are always good.  Only sub-1MB files get the content check, making
the filter practical on days with 40k+ images.

https://claude.ai/code/session_01C4jbd3waXG3eKZYbGUjLUQ

4-seasons.sh

@@ -95,11 +95,14 @@ trap cleanup EXIT
 
 mapfile -t all_images < <(find "$image_dir" -type f -name "*.jpg" | sort)
 
-# Validate each frame: skip empty files, corrupt JPEGs, and optionally grey/uniform frames.
-# SEASONS_GREY_STDDEV_MIN=0 (default) disables the grey filter.
-# Set to e.g. 5 in sky-cam.conf to drop uniform grey frames (bad-signal captures).
+# Validate each frame: skip empty files and optionally uniform-colour bad-signal frames.
+# SEASONS_GREY_STDDEV_MIN=0 (default) disables the content check entirely.
+# When enabled, large files (> SEASONS_LARGE_FRAME_BYTES, default 1 MB) are trusted
+# as good without running the expensive ImageMagick check — only sub-1MB frames
+# are inspected.  This keeps the filter fast even on days with 40k+ images.
 GREY_MIN="${SEASONS_GREY_STDDEV_MIN:-0}"
-GREY_DARK_FLOOR="${SEASONS_GREY_DARK_FLOOR:-30}"  # frames darker than this are never skipped
+GREY_DARK_FLOOR="${SEASONS_GREY_DARK_FLOOR:-30}"
+LARGE_BYTES="${SEASONS_LARGE_FRAME_BYTES:-1048576}"  # files above this skip content check
 images=(); bad=0; grey=0
 for img in "${all_images[@]}"; do
     # Skip empty or unreadable files (0-byte writes from camera reconnects)
@@ -107,15 +110,18 @@ for img in "${all_images[@]}"; do
         echo "WARNING: skipping empty/missing frame: $(basename "$img")"
         ((bad++)) || true; continue
     fi
-    # Optional: skip uniform-grey bad-signal frames.
-    # A frame is bad-signal if it is BOTH uniform (low stddev) AND not dark.
-    # Night frames are dark so they pass even with low stddev.
+    # Optional: skip uniform-colour bad-signal frames (green, grey, etc.).
+    # Only runs ImageMagick on files below SEASONS_LARGE_FRAME_BYTES — large files
+    # are always good and skip the check entirely.
     if [ "$GREY_MIN" != "0" ] && command -v convert &>/dev/null; then
-        read -r stddev mean < <(convert "$img" -colorspace Gray \
-            -format "%[fx:int(standard_deviation*255)] %[fx:int(mean*255)]" \
-            info: 2>/dev/null || echo "255 128")
-        if [ "${stddev:-255}" -lt "$GREY_MIN" ] && [ "${mean:-0}" -gt "$GREY_DARK_FLOOR" ]; then
-            ((grey++)) || true; continue
+        fsize=$(stat -c%s "$img" 2>/dev/null || echo 0)
+        if [ "$fsize" -lt "$LARGE_BYTES" ]; then
+            read -r stddev mean < <(convert "$img" -colorspace Gray \
+                -format "%[fx:int(standard_deviation*255)] %[fx:int(mean*255)]" \
+                info: 2>/dev/null || echo "255 128")
+            if [ "${stddev:-255}" -lt "$GREY_MIN" ] && [ "${mean:-0}" -gt "$GREY_DARK_FLOOR" ]; then
+                ((grey++)) || true; continue
+            fi
         fi
     fi
     images+=("$img")

sky-cam.conf

@@ -256,18 +256,23 @@ ENCODE_PRESET=slow       # ffmpeg preset for all encodes (slow/medium/fast)
 AUDIO_BITRATE=192k       # montage-mvt.sh           — music track on movement montages
 
 # ── Frame validation (4-seasons.sh) ──────────────────────────────────────────
-# Corrupt or empty frames (e.g. first frame after a camera reconnect) are always
-# skipped automatically via ffprobe.  No config needed.
+# Empty (0-byte) frames are always skipped.  No config needed for that.
 #
 # SEASONS_GREY_STDDEV_MIN / SEASONS_GREY_DARK_FLOOR — optional bad-signal filter.
+# Catches uniform-colour frames caused by a bad RTSP signal: solid green, grey, etc.
+# These are valid JPEGs but contain no real image content.
 # Uncomment both lines to enable.  A frame is dropped only when BOTH are true:
 #   1. pixel standard deviation (0–255) < SEASONS_GREY_STDDEV_MIN  (frame is uniform)
 #   2. mean brightness (0–255)          > SEASONS_GREY_DARK_FLOOR  (frame is not dark)
-# This keeps genuine night frames (dark + low variation) while dropping
-# solid-grey bad-signal frames (mid-bright + no variation).
+# Night frames are dark so they always pass even if stddev is low.
 # Requires ImageMagick (convert).  Start with these values and tune from there:
-#SEASONS_GREY_STDDEV_MIN=5    # skip if stdev < 5 (very uniform)
+#SEASONS_GREY_STDDEV_MIN=5    # skip if stdev < 5 (very uniform colour)
 #SEASONS_GREY_DARK_FLOOR=30   # …but only if mean brightness > 30 (not a night frame)
+#
+# Performance: ImageMagick is only called on files below SEASONS_LARGE_FRAME_BYTES.
+# Files above that threshold are always good and skip the check entirely.
+# Default 1 MB — adjust if your camera produces larger bad-signal frames.
+#SEASONS_LARGE_FRAME_BYTES=1048576
 
 # ── Montage attribution overlay ───────────────────────────────────────────────
 # A translucent bar across the top of each movement montage, naming the