fixed paths

Readme.md

@@ -60,7 +60,7 @@ 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.
+Check the `output/pm4n/Flow_Controller_Panel-*.preview.png` images — traces should appear black on white background.
 - background = UV exposed = resist removed = etched away
 - traces = dark = resist kept = copper stays
 
@@ -86,18 +86,19 @@ 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
+output/pm4n/Flow_Controller_Panel-Front.pm4n
+output/pm4n/Flow_Controller_Panel-Front.preview.png
 ```
 
 Open the preview image
 ```bash
-xdg-open output/gerbers/Flow_Controller_Panel-Front.preview.png
+xdg-open output/pm4n/Flow_Controller_Panel-Front.preview.png
 ```
 
-Open the `Flow_Controller_Panel-Front.pm4n` in `Chitubox Basic` slicer to visually verify before printing.
+Open the `output/pm4n/Flow_Controller_Panel-Front.pm4n` in `Chitubox Basic` slicer to visually verify before printing.
 
 ---
 

gerber_to_pm4n.py

@@ -242,7 +242,16 @@ def main():
         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')
+    if args.output:
+        out = Path(args.output)
+    else:
+        # If in 'output/gerbers/', default to 'output/pm4n/'
+        parent = gbr.parent
+        if parent.name == 'gerbers' and parent.parent.name == 'output':
+            out = parent.parent / 'pm4n' / gbr.with_suffix('.pm4n').name
+        else:
+            out = gbr.with_suffix('.pm4n')
+
     pos_mm = None
     if args.pos:
         try: