Update thumbnail gen

Author: cb341

CLAUDE.md

@@ -0,0 +1,62 @@
+# Gallery image workflow
+
+Source images go in `webp-gallery/` (big) and `webp-gallery/thumbs/` (220x220 square thumb). Convention: `snake_case.webp`, big ~850px wide preserving aspect, thumb 220x220 cropped square. Front matter `image:` in `_gallery/<slug>.md` points to the big webp.
+
+## Tools available locally
+- `sips` (built-in macOS) — resize, crop with `--cropOffset Y X`
+- `cwebp` at `/opt/local/bin/cwebp` — encode webp (use `-q 85`)
+- `dwebp` — decode webp to png/jpg when re-cropping an already-converted file
+- No `magick`/ImageMagick `convert`, no `ffmpeg`, no Python PIL. Don't reach for them.
+
+## Convert a new gallery image
+
+```bash
+SRC=path/to/source.jpg                 # original from camera/phone
+SLUG=keyboard                          # snake_case
+TMP=$(mktemp -d)
+sips -s format jpeg --resampleWidth 850 "$SRC" --out "$TMP/big.jpg" >/dev/null
+sips -c 220 220 "$SRC" --out "$TMP/thumb.jpg" >/dev/null   # default center crop — often bad
+cwebp -q 85 "$TMP/big.jpg"   -o "webp-gallery/${SLUG}.webp"
+cwebp -q 85 "$TMP/thumb.jpg" -o "webp-gallery/thumbs/${SLUG}.webp"
+```
+
+## Picking a thumbnail crop (do this — center crop is usually wrong)
+
+`sips -c H W` crops from center by default and produces bad thumbs for off-center subjects. Generate a matrix of candidates and let the user pick:
+
+```bash
+SRC=webp-gallery/keyboard.webp        # or original jpg
+OUT=webp-gallery/thumbs/_picks
+mkdir -p "$OUT"; TMP=$(mktemp -d)
+dwebp "$SRC" -o "$TMP/src.png" >/dev/null 2>&1   # skip if already png/jpg
+# read W H from `sips -g pixelWidth -g pixelHeight`
+# pick 3 square sizes (full short-edge, medium, tight) × 3 horizontal positions (left/center/right)
+# vary vertical position too if image is tall
+for s in 637 500 380; do                          # square sizes in px
+  for xp in left center right; do
+    xmax=$((W - s)); ymax=$((H - s)); y=$((ymax/2))
+    case $xp in left) x=0;; center) x=$((xmax/2));; right) x=$xmax;; esac
+    sips -c $s $s --cropOffset $y $x "$TMP/src.png" --out "$TMP/c.png" >/dev/null
+    sips -z 220 220 "$TMP/c.png" --out "$TMP/r.png" >/dev/null
+    cwebp -quiet -q 85 "$TMP/r.png" -o "$OUT/${SLUG}_${s}_${xp}.webp"
+  done
+done
+open "$OUT"                                       # let user pick in Finder
+```
+
+After user picks, copy chosen file to `webp-gallery/thumbs/${SLUG}.webp` and delete `_picks/`.
+
+Note `sips --cropOffset` argument order is **Y X**, not X Y.
+
+## Front matter
+Existing convention from `_gallery/*.md`:
+```yaml
+---
+layout: gallery
+title: "..."
+order: <int>
+category: "..."
+image: "/webp-gallery/<slug>.webp"
+alt: "..."
+---
+```