diff --git a/4-seasons.sh b/4-seasons.sh
index e4c9a6f..484ac2f 100755
--- a/4-seasons.sh
+++ b/4-seasons.sh
@@ -92,6 +92,7 @@ mapfile -t all_images < <(find "$image_dir" -type f -name "*.jpg" | sort)
 # SEASONS_GREY_STDDEV_MIN=0 (default) disables the grey filter.
 # Set to e.g. 5 in sky-cam.conf to drop uniform grey frames (bad-signal captures).
 GREY_MIN="${SEASONS_GREY_STDDEV_MIN:-0}"
+GREY_DARK_FLOOR="${SEASONS_GREY_DARK_FLOOR:-30}"  # frames darker than this are never skipped
 images=(); bad=0; grey=0
 for img in "${all_images[@]}"; do
     # Empty or unreadable
@@ -106,10 +107,14 @@ for img in "${all_images[@]}"; do
         echo "WARNING: skipping corrupt frame: $(basename "$img")"
         ((bad++)) || true; continue
     fi
-    # Optional: skip uniform-grey bad-signal frames (low pixel standard deviation)
+    # 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.
     if [ "$GREY_MIN" != "0" ] && command -v convert &>/dev/null; then
-        stddev=$(convert "$img" -colorspace Gray -format "%[fx:int(standard_deviation*255)]" info: 2>/dev/null || echo "255")
-        if [ "${stddev:-255}" -lt "$GREY_MIN" ]; then
+        read -r stddev mean < <(convert "$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
diff --git a/sky-cam.conf b/sky-cam.conf
index 04d3b2c..ed9d92b 100644
--- a/sky-cam.conf
+++ b/sky-cam.conf
@@ -257,13 +257,17 @@ AUDIO_BITRATE=192k       # montage-mvt.sh           — music track on movement
 
 # ── Frame validation (4-seasons.sh) ──────────────────────────────────────────
 # Corrupt or empty frames (e.g. first frame after a camera reconnect) are always
-# skipped automatically via ffprobe.
+# skipped automatically via ffprobe.  No config needed.
 #
-# SEASONS_GREY_STDDEV_MIN: also skip uniform-grey frames caused by a bad RTSP
-# signal.  These are valid JPEGs but contain a near-solid grey image.
-# Value is the minimum pixel standard deviation on a 0–255 scale.
-# 0 = disabled (default).  Try 5–10 if your camera produces grey frames on reconnect.
-SEASONS_GREY_STDDEV_MIN=0
+# SEASONS_GREY_STDDEV_MIN / SEASONS_GREY_DARK_FLOOR — optional bad-signal filter.
+# 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).
+# Requires ImageMagick (convert).  Start with these values and tune from there:
+#SEASONS_GREY_STDDEV_MIN=5    # skip if stdev < 5 (very uniform)
+#SEASONS_GREY_DARK_FLOOR=30   # …but only if mean brightness > 30 (not a night frame)
 
 # ── Montage attribution overlay ───────────────────────────────────────────────
 # A translucent bar across the top of each movement montage, naming the