commit 9af1c69b745399f6225c8a55219371c7dca1855b
Author: cpu <cpu@virtonline.eu>
Date:   Thu Jun 11 18:30:03 2026 +0200

    initial

diff --git a/.gitignore b/.gitignore
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+++ b/.gitignore
@@ -0,0 +1,3 @@
+__pycache__/
+output/
+.venv/
diff --git a/Dummy.pm4n b/Dummy.pm4n
new file mode 100644
index 0000000..e54b8b4
Binary files /dev/null and b/Dummy.pm4n differ
diff --git a/Readme.md b/Readme.md
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+++ b/Readme.md
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+TODO: Add table of content
+# MSLA PCB Exposure: KiCad → Photon Mono 4
+Using an MSLA (Masked Stereolithography Apparatus) resin printer for creating PCBs is a technique known as "Direct UV Exposure." Instead of printing a plastic part, you use the printer's LCD screen as a dynamic digital mask to cure photosensitive materials (etch resist, solder resist and silkscreen) on a copper board.
+
+KiCad PCB layers need to be converted to `.pm4n` files for direct UV exposure on an **Anycubic Photon Mono 4** (9024×5120 px, 17 µm/px, 1494.12 DPI) on the screen size of 153.408 x 87.040 mm.
+
+---
+
+## Setup
+
+### 1. KiCad: Set your design grid
+In KiCad's PCB editor, go to `Preferences → Preferences → PCB Editor → Grids` and add a custom grid of 0.017 mm. This ensures trace edges land on pixel boundaries and avoids the sub-pixel rounding that causes the ±1px size error people see with arbitrary grids.
+
+### 2. Create the `Dummy.pm4n` file
+
+
+Open **CHITUBOX Basic** slicer (or any other slicer that works for your resin printer), select printer **Anycubic Photon Mono 4**, slice any tiny STL (e.g.: 1×1×0.05 mm box), and save as `Dummy.pm4n` in the same directory as `export.sh`.
+
+This file is reused for every job — it carries the correct LCD resolution metadata.
+
+### 3. Install dependencies
+
+```bash
+python3 -m venv .venv
+source .venv/bin/activate
+pip install pygerber Pillow numpy
+```
+
+Or activate the `venv` once and put `source .venv/bin/activate` in your shell profile.
+
+### 4. Export multiple layers (e.g. copper + soldermask + silkscreen)
+
+```bash
+./export.sh \
+    --layers Front,Back,F.Mask,B.Mask,F.SilkS,B.SilkS \
+    --invert Front,Back,F.Mask,B.Mask,F.SilkS,B.SilkS \
+    --mirror Front,F.Mask,F.SilkS \
+    --exposure 60 \
+    ../kicad2panel/panel/Flow_Controller_Panel.kicad_pcb
+```
+It should output:
+```bash
+Plotted to './output/gerbers/Flow_Controller_Panel-Front.gbr'.
+Plotted to './output/gerbers/Flow_Controller_Panel-Back.gbr'.
+Plotted to './output/gerbers/Flow_Controller_Panel-F_Silkscreen.gbr'.
+Plotted to './output/gerbers/Flow_Controller_Panel-B_Silkscreen.gbr'.
+Plotted to './output/gerbers/Flow_Controller_Panel-F_Mask.gbr'.
+Plotted to './output/gerbers/Flow_Controller_Panel-B_Mask.gbr'.
+output/pm4n/Flow_Controller_Panel-Front.pm4n
+output/pm4n/Flow_Controller_Panel-Front.preview.png
+output/pm4n/Flow_Controller_Panel-Back.pm4n
+output/pm4n/Flow_Controller_Panel-Back.preview.png
+output/pm4n/Flow_Controller_Panel-F_Mask.pm4n
+output/pm4n/Flow_Controller_Panel-F_Mask.preview.png
+output/pm4n/Flow_Controller_Panel-B_Mask.pm4n
+output/pm4n/Flow_Controller_Panel-B_Mask.preview.png
+output/pm4n/Flow_Controller_Panel-F_Silkscreen.pm4n
+output/pm4n/Flow_Controller_Panel-F_Silkscreen.preview.png
+output/pm4n/Flow_Controller_Panel-B_Silkscreen.pm4n
+output/pm4n/Flow_Controller_Panel-B_Silkscreen.preview.png
+```
+#### 4.1. Check the layer preview
+Check the `output/pm4n/Flow_Controller_Panel-*.preview.png` — traces should appear black on white background.
+- background = UV exposed = resist removed = etched away
+- traces = dark = resist kept = copper stays
+
+#### 4.2. Check the printer exposure
+Open the `.pm4n` in `Chitubox Basic` slicer to visually verify before printing.
+
+#### 4.3. Adjust exposure
+Start with `--exposure 60` and bracket from there — Bungard presensitized at 405nm typically lands between 30–120s depending on board vintage and storage.
+
+
+#### Export single layer (e.g. copper)
+
+Export the front layer as gerber
+```bash
+kicad-cli pcb export gerbers -o output/gerbers -l F.Cu ../kicad2panel/panel/Flow_Controller_Panel.kicad_pcb
+```
+It should output
+```bash
+Plotted to 'output/gerbers/Flow_Controller_Panel-Front.gtl'.
+```
+
+Convert the gerber to pm4n and preview
+```bash
+python3 gerber_to_pm4n.py Dummy.pm4n output/gerbers/Flow_Controller_Panel-Front.gtl \
+    --invert --mirror --exposure 120
+It should output
+```bash
+output/gerbers/Flow_Controller_Panel-Front.pm4n
+output/gerbers/Flow_Controller_Panel-Front.preview.png
+```
+
+Open the preview image
+```bash
+xdg-open output/gerbers/Flow_Controller_Panel-Front.preview.png
+```
+
+Open the `Flow_Controller_Panel-Front.pm4n` in `Chitubox Basic` slicer to visually verify before printing.
+
+---
+
+## Troubleshooting
+
+**`kicad-cli: command not found`** — add KiCad to PATH:
+```bash
+export PATH="/usr/lib/kicad/bin:$PATH"
+```
+Or on Flatpak:
+```bash
+alias kicad-cli='flatpak run --command=kicad-cli org.kicad.KiCad'
+```
+
+**Expected Gerber not found** — KiCad's layer→filename mapping:
+
+| Layer | Filename stem |
+|---|---|
+| `F.Cu` | `Front` |
+| `B.Cu` | `Back` |
+| `F.Mask` | `F_Mask` |
+| `B.Mask` | `B_Mask` |
+| `F.SilkS` | `F_Silkscreen` |
+
+---
+
diff --git a/diagnose_pm4n.py b/diagnose_pm4n.py
new file mode 100644
index 0000000..71ee2ec
--- /dev/null
+++ b/diagnose_pm4n.py
@@ -0,0 +1,62 @@
+#!/usr/bin/env python3
+"""Run this on your machine: python3 diagnose_pm4n.py Dummy.pm4n"""
+import struct, sys
+
+path = sys.argv[1] if len(sys.argv) > 1 else 'Dummy.pm4n'
+data = open(path, 'rb').read()
+fsize = len(data)
+print(f"File: {path}  ({fsize} bytes)")
+print()
+
+# Parse ANYCUBIC header
+magic        = data[0:8]
+version      = struct.unpack_from('<I', data, 8)[0]
+n_sections   = struct.unpack_from('<I', data, 12)[0]
+header_size  = struct.unpack_from('<I', data, 16)[0]
+print(f"Magic:         {magic}")
+print(f"Bytes 8-11:    {data[8:12].hex()}  (={version})")
+print(f"Section count: {n_sections}")
+print(f"Header size:   {header_size}  (0x{header_size:X})")
+print()
+
+# Section table: n_sections entries of (offset:u32, length:u32) starting at byte 20
+print(f"Section table ({n_sections} entries from offset 20):")
+sections = []
+for i in range(n_sections):
+    base = 20 + i * 8
+    if base + 8 > fsize:
+        break
+    off = struct.unpack_from('<I', data, base)[0]
+    ln  = struct.unpack_from('<I', data, base+4)[0]
+    sections.append((off, ln))
+
+for idx, (off, ln) in enumerate(sections):
+    tag = data[off:off+4] if off + 4 <= fsize else b'????'
+    tag_str = tag.decode('ascii', errors='replace')
+    print(f"  [{idx:2d}]  offset=0x{off:06X} ({off:7d})  length={ln:7d}  tag@offset={tag_str!r}")
+
+print()
+# Also peek at each section start for tag-like content
+print("Content at each section offset (first 32 bytes):")
+for idx, (off, ln) in enumerate(sections):
+    if off + 16 <= fsize:
+        chunk = data[off:off+32]
+        # Try to find sub-tags
+        for sub_off in range(0, min(32, len(chunk))-3):
+            sub_tag = chunk[sub_off:sub_off+4]
+            if all(32 <= b < 127 for b in sub_tag):
+                sub_len = struct.unpack_from('<I', chunk, sub_off+4)[0] if sub_off+8 <= len(chunk) else 0
+                print(f"  section[{idx}]+0x{sub_off:02X}  tag={sub_tag.decode()!r}  next_u32={sub_len}")
+                break
+        else:
+            print(f"  section[{idx}]  hex: {chunk[:16].hex()}")
+
+print()
+# Look for exposure-like floats (1.0 to 600.0) across the whole file
+print("Float values in range [1.0 .. 600.0] across whole file:")
+for off in range(0, fsize - 3, 4):
+    v = struct.unpack_from('<f', data, off)[0]
+    if 1.0 <= v <= 600.0 and v == round(v, 1):
+        # Show context
+        section_hint = next((f"sec[{i}]+{off-s:d}" for i,(s,l) in enumerate(sections) if s <= off < s+l), "outside")
+        print(f"  0x{off:06X}  {v:.1f}  ({section_hint})")
diff --git a/export.sh b/export.sh
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+++ b/export.sh
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+#!/usr/bin/env bash
+# export_for_msla.sh — KiCad Gerber export + pm4n generation for Anycubic Photon Mono 4
+#
+# Usage:
+#   ./export_for_msla.sh [OPTIONS] <path/to/board.kicad_pcb>
+#
+# Options:
+#   --layers  LAYER,LAYER,...  KiCad layer names to export (default: F.Cu)
+#   --invert  LAYER,LAYER,...  Layers to invert  (comma-separated)
+#   --mirror  LAYER,LAYER,...  Layers to mirror  (comma-separated)
+#   --exposure SECONDS         Exposure time in seconds (default: 60)
+#   --dummy   FILE             Dummy .pm4n template (default: Dummy.pm4n beside this script)
+#   --out     DIR              Output directory (default: ./output)
+#   --dpmm    N                Render resolution in dots/mm (default: native 58.824)
+#   --pos     X,Y              Board position on LCD in mm (default: centred)
+#   --preview-scale N          Downsample preview PNG by N (default: 1 = full resolution)
+#   --verbose                  Print detailed progress
+#   -h, --help                 Show this help
+#
+# Normal output: one output filepath per layer.
+# Verbose output: full progress from KiCad and the converter.
+#
+# Example:
+#   ./export_for_msla.sh --invert F.Cu,B.Mask --mirror F.Cu,F.Mask panel/board.kicad_pcb
+#
+# KiCad layer name → Gerber filename stem:
+#   F.Cu    → F_Cu          B.Cu    → B_Cu
+#   F.Mask  → F_Mask        B.Mask  → B_Mask
+#   F.SilkS → F_Silkscreen  B.SilkS → B_Silkscreen
+#   F.Paste → F_Paste       B.Paste → B_Paste
+#   Edge.Cuts → Edge_Cuts
+#   Front   → Front         Back    → Back
+
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+PYTHON="${PYTHON:-python3}"
+CONVERTER="$SCRIPT_DIR/gerber_to_pm4n.py"
+
+# ---- defaults ----
+LAYERS="F.Cu"
+INVERT_LAYERS=""
+MIRROR_LAYERS=""
+EXPOSURE="60"
+DUMMY="$SCRIPT_DIR/Dummy.pm4n"
+OUT_DIR="./output"
+DPMM=""
+POS=""
+VERBOSE=0
+PREVIEW_SCALE=""
+
+# ---- helpers ----
+usage() {
+    grep '^#' "$0" | sed 's/^# \{0,1\}//'
+    exit 0
+}
+
+log() { [[ $VERBOSE -eq 1 ]] && echo "$@" || true; }
+
+contains() {
+    local list="$1" item="$2"
+    echo "$list" | tr ',' '\n' | grep -qx "$item"
+}
+
+layer_to_filename() {
+    case "$1" in
+        F.Cu)      echo "Front" ;;
+        B.Cu)      echo "Back" ;;
+        F.SilkS)   echo "F_Silkscreen" ;;
+        B.SilkS)   echo "B_Silkscreen" ;;
+        Edge.Cuts) echo "Edge_Cuts" ;;
+        *)         echo "${1//./_}" ;;
+    esac
+}
+
+# ---- parse arguments ----
+PCB_FILE=""
+while [[ $# -gt 0 ]]; do
+    case "$1" in
+        --layers)   LAYERS="$2";         shift 2 ;;
+        --invert)   INVERT_LAYERS="$2";  shift 2 ;;
+        --mirror)   MIRROR_LAYERS="$2";  shift 2 ;;
+        --exposure) EXPOSURE="$2";       shift 2 ;;
+        --dummy)    DUMMY="$2";          shift 2 ;;
+        --out)      OUT_DIR="$2";        shift 2 ;;
+        --dpmm)     DPMM="$2";           shift 2 ;;
+        --pos)           POS="$2";            shift 2 ;;
+        --preview-scale) PREVIEW_SCALE="$2";  shift 2 ;;
+        --verbose)  VERBOSE=1;           shift ;;
+        -h|--help)  usage ;;
+        -*)         echo "ERROR: unknown option: $1" >&2; exit 1 ;;
+        *)          PCB_FILE="$1";       shift ;;
+    esac
+done
+
+[[ -z "$PCB_FILE" ]] && { echo "ERROR: no .kicad_pcb file specified" >&2; exit 1; }
+[[ ! -f "$PCB_FILE" ]] && { echo "ERROR: file not found: $PCB_FILE" >&2; exit 1; }
+[[ ! -f "$DUMMY"    ]] && { echo "ERROR: Dummy.pm4n not found: $DUMMY" >&2; exit 1; }
+
+BOARD_NAME="$(basename "$PCB_FILE" .kicad_pcb)"
+GERBERS_DIR="$OUT_DIR/gerbers"
+PM4N_DIR="$OUT_DIR/pm4n"
+mkdir -p "$GERBERS_DIR" "$PM4N_DIR"
+
+# ---- Step 1: export Gerbers ----
+log "=== Exporting Gerbers ==="
+log "  Board:  $PCB_FILE"
+log "  Layers: $LAYERS"
+
+kicad-cli pcb export gerbers \
+    --output "$GERBERS_DIR" \
+    --layers "$LAYERS" \
+    --no-protel-ext \
+    --subtract-soldermask \
+    --no-netlist \
+    "$PCB_FILE" \
+    2>/dev/null
+
+log ""
+
+# ---- Step 2: convert to pm4n ----
+log "=== Converting to .pm4n ==="
+
+IFS=',' read -ra LAYER_LIST <<< "$LAYERS"
+for LAYER in "${LAYER_LIST[@]}"; do
+    LAYER_STEM="$(layer_to_filename "$LAYER")"
+    GBR_FILE="$GERBERS_DIR/${BOARD_NAME}-${LAYER_STEM}.gbr"
+
+    if [[ ! -f "$GBR_FILE" ]]; then
+        echo "WARNING: Gerber not found for layer $LAYER (expected: $GBR_FILE)" >&2
+        continue
+    fi
+
+    OUT_PM4N="$PM4N_DIR/${BOARD_NAME}-${LAYER_STEM}.pm4n"
+
+    FLAGS=()
+    contains "$INVERT_LAYERS" "$LAYER" && FLAGS+=(--invert)
+    contains "$MIRROR_LAYERS" "$LAYER" && FLAGS+=(--mirror)
+    [[ -n "$DPMM" ]] && FLAGS+=(--dpmm "$DPMM")
+    [[ -n "$POS"  ]] && FLAGS+=(--pos "$POS")
+    [[ -n "$PREVIEW_SCALE" ]] && FLAGS+=(--preview-scale "$PREVIEW_SCALE")
+    [[ $VERBOSE -eq 1 ]] && FLAGS+=(--verbose)
+
+    log "  $LAYER  →  $OUT_PM4N  [${FLAGS[*]:-} exposure=${EXPOSURE}s]"
+
+    "$PYTHON" "$CONVERTER" \
+        "$DUMMY" \
+        "$GBR_FILE" \
+        --output "$OUT_PM4N" \
+        --exposure "$EXPOSURE" \
+        "${FLAGS[@]}"
+done
+
+log "=== Done ==="
\ No newline at end of file
diff --git a/gerber_to_pm4n.py b/gerber_to_pm4n.py
new file mode 100755
index 0000000..b1f947d
--- /dev/null
+++ b/gerber_to_pm4n.py
@@ -0,0 +1,279 @@
+#!/usr/bin/env python3
+"""
+gerber_to_pm4n.py  –  Anycubic Photon Mono 4 PCB exposure file generator
+
+Usage:
+    python3 gerber_to_pm4n.py <dummy.pm4n> <board.gbr> [options]
+
+Options:
+    -o OUTPUT       Output file path  [default: <board>.pm4n]
+    --invert        Invert the image (for positive-working resist like Bungard standard)
+    --mirror        Mirror X axis (for copper-side-down placement on FEP)
+    --exposure SEC  Exposure time in seconds  [default: 60]
+    --dpmm N        Render resolution in dots/mm  [default: 58.824, native 17µm/px]
+    --pos X,Y       Board position mm from top-left (default: centred)
+    --verbose       Print detailed progress
+
+Photon Mono 4 specs:  9024 × 5120 px  |  153.408 × 87.040 mm  |  17.001 µm/px
+"""
+
+import argparse
+import struct
+import sys
+import io
+from pathlib import Path
+from PIL import Image, ImageOps
+
+# ---------------------------------------------------------------------------
+# Printer constants
+# ---------------------------------------------------------------------------
+LCD_W_PX    = 9024
+LCD_H_PX    = 5120
+LCD_W_MM    = 153.408
+LCD_H_MM    = 87.040
+NATIVE_DPMM = LCD_W_PX / LCD_W_MM   # 58.824 dpmm  (1 px ≈ 17.001 µm)
+
+# ---------------------------------------------------------------------------
+# pm4n format constants  (reverse-engineered from Dummy.pm4n)
+# ---------------------------------------------------------------------------
+LAYE_TAG     = b'LAYE'
+MODE_TAG     = b'Mode'
+ENTRY_STRIDE = 0x20   # 32 bytes per layer entry
+LAYE_HDR_SIZE = 0x1C  # bytes before first entry within LAYE section
+
+
+def find_tag(data: bytes, tag: bytes, start: int = 0) -> int:
+    """Return file offset of first occurrence of tag aligned to 4 bytes."""
+    i = (start + 3) & ~3
+    while i + 4 <= len(data):
+        if data[i:i+4] == tag:
+            return i
+        i += 4
+    pos = data.find(tag, start)
+    if pos < 0:
+        raise ValueError(f"Tag {tag!r} not found in file")
+    return pos
+
+
+def count_laye_entries(data: bytes, laye_off: int) -> int:
+    """Count layer entries by scanning until EXTR tag or implausible float."""
+    entry_start = laye_off + LAYE_HDR_SIZE
+    n = 0
+    while True:
+        pos = entry_start + n * ENTRY_STRIDE
+        if pos + 4 > len(data):
+            break
+        word = data[pos:pos+4]
+        if word in (b'EXTR', b'MACH', b'Mode', b'HEAD', b'PREV', b'LAYE'):
+            break
+        v = struct.unpack_from('<f', data, pos)[0]
+        if not (0.0 < v < 1000.0):
+            break
+        n += 1
+    return n
+
+
+def unpack_u32(data: bytes, off: int) -> int:
+    return struct.unpack_from('<I', data, off)[0]
+
+
+# ---------------------------------------------------------------------------
+# Photon Workshop RLE  (BW — 2 bytes per run)
+#   Byte0 [7:4] colour nibble: 0x0=black, 0xF=white
+#   Byte0 [3:0] + Byte1: run length − 1  (12-bit, max run=4096)
+# ---------------------------------------------------------------------------
+MAX_RUN = 4096
+
+def encode_rle(pixels: bytes) -> bytes:
+    out = bytearray()
+    i, n = 0, len(pixels)
+    while i < n:
+        colour = pixels[i]
+        nibble = 0xF if colour >= 0x80 else 0x0
+        j = i + 1
+        while j < n and pixels[j] == colour and (j - i) < MAX_RUN:
+            j += 1
+        run = j - i
+        enc = run - 1
+        out.append((nibble << 4) | ((enc >> 8) & 0x0F))
+        out.append(enc & 0xFF)
+        i = j
+    return bytes(out)
+
+
+# ---------------------------------------------------------------------------
+# Gerber → PIL Image at LCD resolution
+# ---------------------------------------------------------------------------
+
+def render_gerber(gbr_path: Path, dpmm: float,
+                  invert: bool, mirror: bool,
+                  pos_mm: tuple | None,
+                  verbose: bool = False) -> Image.Image:
+    try:
+        from pygerber.gerberx3.api.v2 import (
+            GerberFile, ColorScheme, PixelFormatEnum, ImageFormatEnum
+        )
+    except ImportError:
+        sys.exit(
+            "ERROR: pygerber not found.\n"
+            "Activate the venv:  source .venv/bin/activate\n"
+            "Or install:         pip install pygerber Pillow"
+        )
+
+    buf = io.BytesIO()
+    GerberFile.from_file(str(gbr_path)).parse().render_raster(
+        buf,
+        dpmm=int(round(dpmm)),
+        color_scheme=ColorScheme.DEFAULT_GRAYSCALE,
+        pixel_format=PixelFormatEnum.RGB,
+        image_format=ImageFormatEnum.PNG,
+    )
+    buf.seek(0)
+    layer_img = Image.open(buf).convert('L')
+
+    cw, ch = layer_img.size
+    canvas  = Image.new('L', (LCD_W_PX, LCD_H_PX), 0)
+
+    if pos_mm is not None:
+        px = max(0, int(round(pos_mm[0] * dpmm)))
+        py = max(0, int(round(pos_mm[1] * dpmm)))
+    else:
+        px = (LCD_W_PX - cw) // 2
+        py = (LCD_H_PX - ch) // 2
+
+    canvas.paste(layer_img, (px, py))
+
+    if mirror:
+        canvas = ImageOps.mirror(canvas)
+    if invert:
+        canvas = ImageOps.invert(canvas)
+
+    canvas = canvas.point(lambda v: 255 if v >= 128 else 0)
+
+    if verbose:
+        print(f"  Gerber rendered: {layer_img.size[0]}×{layer_img.size[1]} px"
+              f"  placed at ({px},{py})  invert={invert}  mirror={mirror}")
+
+    return canvas
+
+
+# ---------------------------------------------------------------------------
+# pm4n surgery
+# ---------------------------------------------------------------------------
+
+def patch_pm4n(dummy_path: Path, image: Image.Image,
+               exposure_sec: float, output_path: Path,
+               verbose: bool = False):
+
+    def log(*a):
+        if verbose:
+            print(*a)
+
+    raw = bytearray(dummy_path.read_bytes())
+
+    new_rle      = encode_rle(image.convert('L').tobytes())
+    new_rle_size = len(new_rle)
+
+    laye_off   = find_tag(raw, LAYE_TAG)
+    n_entries  = count_laye_entries(raw, laye_off)
+    log(f"  LAYE at 0x{laye_off:06X}, {n_entries} layer entries")
+
+    composite_off  = unpack_u32(raw, laye_off + 0x14)
+    old_block_size = unpack_u32(raw, laye_off + 0x18)
+    log(f"  Image blocks: first=0x{composite_off:06X}, "
+        f"old_size={old_block_size}, new_size={new_rle_size}")
+
+    # Patch exposure in all entries
+    for i in range(n_entries):
+        base = laye_off + LAYE_HDR_SIZE + i * ENTRY_STRIDE
+        struct.pack_into('<f', raw, base + 0x04, exposure_sec)
+    log(f"  Exposure patched to {exposure_sec}s in {n_entries} entries")
+
+    # Update block size in LAYE header and Mode header
+    struct.pack_into('<I', raw, laye_off + 0x18, new_rle_size)
+    mode_off = find_tag(raw, MODE_TAG)
+    struct.pack_into('<I', raw, mode_off + 0x48, new_rle_size)
+    log(f"  Mode at 0x{mode_off:06X}")
+
+    # Update image offsets and sizes in all entries
+    for i in range(n_entries):
+        base = laye_off + LAYE_HDR_SIZE + i * ENTRY_STRIDE
+        struct.pack_into('<I', raw, base + 0x18, composite_off + (i + 1) * new_rle_size)
+        struct.pack_into('<I', raw, base + 0x1C, new_rle_size)
+
+    # Splice new image data (composite block + one block per layer, all identical)
+    n_blocks      = n_entries + 1
+    old_end       = composite_off + n_blocks * old_block_size
+    raw[composite_off:old_end] = new_rle * n_blocks
+
+    output_path.write_bytes(raw)
+    log(f"  Written: {output_path}  ({len(raw):,} bytes)")
+
+
+# ---------------------------------------------------------------------------
+# CLI
+# ---------------------------------------------------------------------------
+
+def parse_args():
+    p = argparse.ArgumentParser(
+        description='Convert Gerber → Anycubic Photon Mono 4 .pm4n PCB exposure file',
+    )
+    p.add_argument('dummy',          help='Dummy .pm4n template')
+    p.add_argument('gerber',         help='Input Gerber file')
+    p.add_argument('-o', '--output', default=None)
+    p.add_argument('--invert',       action='store_true')
+    p.add_argument('--mirror',       action='store_true')
+    p.add_argument('--exposure',     type=float, default=60.0)
+    p.add_argument('--dpmm',         type=float, default=NATIVE_DPMM)
+    p.add_argument('--pos',          default=None)
+    p.add_argument('--verbose',      action='store_true')
+    p.add_argument('--preview-scale', type=int, default=1, metavar='N',
+                   help='Downsample preview PNG by factor N (default: 1 = full resolution)')
+    return p.parse_args()
+
+
+def main():
+    args  = parse_args()
+    dummy = Path(args.dummy)
+    gbr   = Path(args.gerber)
+    v     = args.verbose
+
+    for p, label in [(dummy, 'dummy'), (gbr, 'gerber')]:
+        if not p.exists():
+            sys.exit(f"ERROR: {label} file not found: {p}")
+
+    out    = Path(args.output) if args.output else gbr.with_suffix('.pm4n')
+    pos_mm = None
+    if args.pos:
+        try:
+            x, y   = map(float, args.pos.split(','))
+            pos_mm = (x, y)
+        except Exception:
+            sys.exit("ERROR: --pos must be X,Y  e.g.  --pos 10.5,8.0")
+
+    if v:
+        print(f"Gerber:   {gbr}")
+        print(f"Dummy:    {dummy}")
+        print(f"Output:   {out}")
+        print(f"Invert:   {args.invert}  Mirror: {args.mirror}"
+              f"  Exposure: {args.exposure}s  dpmm: {args.dpmm:.3f}")
+
+    img = render_gerber(gbr, dpmm=args.dpmm, invert=args.invert,
+                        mirror=args.mirror, pos_mm=pos_mm, verbose=v)
+
+    preview = out.with_suffix('.preview.png')
+    scale = args.preview_scale
+    if scale <= 1:
+        img.save(preview)
+    else:
+        img.resize((img.size[0] // scale, img.size[1] // scale), Image.NEAREST).save(preview)
+
+    patch_pm4n(dummy, img, args.exposure, out, verbose=v)
+
+    # Always print the output path (quiet mode only output)
+    print(out)
+    print(preview)
+
+
+if __name__ == '__main__':
+    main()
\ No newline at end of file