Logo: keep the drawing as the source, generate every variant with ffmpeg

README.md

@@ -138,4 +138,7 @@ produces. `./build.sh maxmsp` reports this and exits rather than failing inside
 ./build.sh jack
 ```
 
-<img src="./zerr_logo.png" alt="zerr_logo" />
+<picture>
+  <source media="(prefers-color-scheme: dark)" srcset="./assets/logo/zerr-logo-white-transparent.png">
+  <img src="./assets/logo/zerr-logo-black-transparent.png" alt="Zerr logo" width="320">
+</picture>

assets/logo/README.md

@@ -0,0 +1,19 @@
+# Zerr* logo
+
+`zerr-logo-paper.png` is the original drawing (charcoal on paper, 1024 px). Everything else in
+this folder is generated from it by `tools/make-logo-variants.sh` with ffmpeg only; do not edit
+the generated files by hand, rerun the script instead.
+
+| File | Use |
+| --- | --- |
+| `zerr-logo-black-transparent.png` | default on light surfaces (README, docs) |
+| `zerr-logo-white-transparent.png` | dark surfaces; the README switches to it in dark mode |
+| `zerr-logo-black-on-white.png`, `zerr-logo-white-on-black.png` | opaque versions for places that cannot composite alpha |
+| `zerr-logo-grey-transparent.png` | neutral ink for watermarks or surfaces of unknown brightness |
+| `zerr-logo-avatar-*.png` | disc-masked, padded 1216 px, for GitHub or chat avatars |
+| `zerr-logo.ico` | favicon, 16 to 256 px |
+| `sizes/` | 512 to 32 px copies of the two transparent variants |
+| `trimmed/` | cropped to the ink bounding box plus a 24 px margin |
+
+`maxmsp/media/zerr_logo.png` is the 256 px black-on-transparent copy the Max help patches load;
+the script overwrites it too.

tools/make-logo-variants.sh

@@ -0,0 +1,101 @@
+#!/usr/bin/env bash
+# Derive every Zerr* logo variant from the original drawing with ffmpeg only.
+#
+# The source is charcoal ink on textured paper. One luminance stretch turns it into an
+# ink-coverage mask (paper -> 0, solid ink -> 255, charcoal grain in between); every variant
+# is that mask composited over a colour. The drawing itself is never edited.
+#
+#   tools/make-logo-variants.sh            # regenerate assets/logo/ and maxmsp/media/zerr_logo.png
+#   W=0.83 B=0.14 tools/make-logo-variants.sh   # retune the levels
+#
+# Tunables (measured on the 1024 px source with ffmpeg's histogram filter, 2026-10-15):
+# paper sits at luminance 208-239, solid ink at 0-63, charcoal grain in between.
+set -euo pipefail
+cd "$(dirname "$0")/.."
+
+SRC=${SRC:-assets/logo/zerr-logo-paper.png}
+OUT=${OUT:-assets/logo}
+W=${W:-0.81}  # white point: luminance at or above W*255 is background
+B=${B:-0.16}  # black point: luminance at or below B*255 is solid ink
+# Ink bounding box plus a 24 px margin (alpha > 128, at least 3 px per row/column).
+TRIM=${TRIM:-crop=877:873:84:83}
+SIZES=${SIZES:-"512 256 128 64 32"}
+ICO_SIZES="16 32 48 64 128 256"
+AVATAR_PAD=96  # px added on each side before the disc so the outer nodes are not clipped
+MAX_MEDIA=maxmsp/media/zerr_logo.png
+
+for tool in ffmpeg ffprobe; do
+    command -v "$tool" >/dev/null || { echo "$tool not found" >&2; exit 1; }
+done
+[ -f "$SRC" ] || { echo "source not found: $SRC" >&2; exit 1; }
+
+IFS=, read -r WIDTH HEIGHT < <(ffprobe -v error -select_streams v:0 -show_entries stream=width,height \
+    -of csv=p=0 "$SRC")
+SIZE="${WIDTH}x${HEIGHT}"
+
+# Ink coverage. LEVELS leaves ink dark on a white background; MASK (negated) is the alpha plane.
+LEVELS="format=gray,colorlevels=rimin=${B}:rimax=${W}:gimin=${B}:gimax=${W}:bimin=${B}:bimax=${W}"
+MASK="${LEVELS},negate"
+
+ff() { ffmpeg -v error -y "$@"; }
+
+# ink_on_transparent <colour> <out.png>: solid colour under the mask, transparent elsewhere.
+ink_on_transparent() {
+    ff -i "$SRC" -f lavfi -i "color=c=$1:s=$SIZE" \
+        -filter_complex "[0:v]${MASK}[a];[1:v][a]alphamerge" -frames:v 1 -pix_fmt rgba "$2"
+}
+
+mkdir -p "$OUT/sizes" "$OUT/trimmed"
+
+echo "mask: W=$W B=$B on $SRC ($SIZE)"
+
+# The four main variants.
+ff -i "$SRC" -vf "${LEVELS},format=rgb24" "$OUT/zerr-logo-black-on-white.png"
+ff -i "$SRC" -vf "${MASK},format=rgb24"   "$OUT/zerr-logo-white-on-black.png"
+ink_on_transparent black "$OUT/zerr-logo-black-transparent.png"
+ink_on_transparent white "$OUT/zerr-logo-white-transparent.png"
+
+# Neutral grey ink for watermarks and surfaces of unknown brightness.
+ink_on_transparent 0x808080 "$OUT/zerr-logo-grey-transparent.png"
+
+# Size set of the transparent variants. The colour plane is uniform, so Lanczos on rgba
+# cannot produce colour fringes; only the alpha is resampled.
+for name in black-transparent white-transparent; do
+    for s in $SIZES; do
+        ff -i "$OUT/zerr-logo-$name.png" -vf "scale=${s}:${s}:flags=lanczos" \
+            "$OUT/sizes/zerr-logo-$name-$s.png"
+    done
+done
+
+# Multi-size favicon, PNG-compressed entries.
+ico_inputs=()
+ico_maps=()
+i=0
+for s in $ICO_SIZES; do
+    tmp="$OUT/sizes/.ico-$s.png"
+    ff -i "$OUT/zerr-logo-black-transparent.png" -vf "scale=${s}:${s}:flags=lanczos" "$tmp"
+    ico_inputs+=(-i "$tmp")
+    ico_maps+=(-map "$i")
+    i=$((i + 1))
+done
+ff "${ico_inputs[@]}" "${ico_maps[@]}" -c:v png -f ico "$OUT/zerr-logo.ico"
+rm -f "$OUT"/sizes/.ico-*.png
+
+# Trimmed to the ink bounding box.
+for name in black-on-white white-on-black black-transparent white-transparent grey-transparent; do
+    ff -i "$OUT/zerr-logo-$name.png" -vf "$TRIM" "$OUT/trimmed/zerr-logo-$name.png"
+done
+
+# Circle avatars: pad so the outer nodes fit inside the disc, then multiply the alpha by a
+# disc with a one-pixel anti-aliased rim.
+disc="format=rgba,geq=r='r(X,Y)':g='g(X,Y)':b='b(X,Y)':a='alpha(X,Y)*clip(W/2-hypot(X+0.5-W/2,Y+0.5-H/2),0,1)'"
+pad="pad=iw+2*${AVATAR_PAD}:ih+2*${AVATAR_PAD}:${AVATAR_PAD}:${AVATAR_PAD}:color=0x00000000"
+for name in black-transparent white-transparent; do
+    ff -i "$OUT/zerr-logo-$name.png" -vf "${pad},${disc}" "$OUT/zerr-logo-avatar-$name.png"
+done
+
+# The Max package ships a 256 px copy under this fixed name (the .maxhelp files reference it).
+ff -i "$OUT/zerr-logo-black-transparent.png" -vf "scale=256:256:flags=lanczos" "$MAX_MEDIA"
+
+echo "written:"
+find "$OUT" "$MAX_MEDIA" -type f \( -name '*.png' -o -name '*.ico' \) | sort