fix(webpage): downscale large full-size ptycho PNGs before upload

omny.psi.ch/upload.php rejected the full-size probe/spectrum PNGs of
stitched reconstructions with HTTP 413. Full-size copies above 900 kB are
now saved as downscaled PNGs until they fit.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ALDnH16dC6iyHjhe5Ey4w9

csaxs_bec/bec_ipython_client/plugins/OMNY_shared/webpage_generator_base.py

@@ -136,6 +136,10 @@ _MISMATCH_LOCAL_PORT    = 8081
 # Subfolders follow the pattern dset_NNNNN and contain S#####_*_phase.png etc.
 _PTYCHO_ONLINE_DIR = "~/data/raw/analysis/online/ptycho"
 _PTYCHO_THUMB_PX   = 200   # longest edge of generated thumbnail in pixels
+# The upload server (omny.psi.ch/upload.php) rejects large POSTs with HTTP 413;
+# stitched reconstructions produce full-size PNGs above that. Full-size copies
+# larger than this are downscaled until they fit.
+_PTYCHO_FULL_MAX_BYTES = 900_000
 
 VERBOSITY_SILENT  = 0
 VERBOSITY_NORMAL  = 1
@@ -1324,7 +1328,7 @@ class WebpageGeneratorBase:
                     img.save(thumb_path, "JPEG", quality=85)
                 else:
                     shutil.copy2(src, thumb_path)
-                shutil.copy2(src, full_path)
+                self._copy_full_capped(src, full_path)
                 images.append({
                     "role":    role,
                     "thumb":   thumb_name,
@@ -1339,6 +1343,26 @@ class WebpageGeneratorBase:
         self._last_ptycho_scan = scan_id
         return {"scan_id": scan_id, "images": images, "folder": str(latest_dir)}
 
+    @staticmethod
+    def _copy_full_capped(src: Path, dst: Path, max_bytes: int = _PTYCHO_FULL_MAX_BYTES) -> None:
+        """Copy src to dst; if src is larger than max_bytes, save a downscaled
+        PNG instead (halving the pixel area each step) so the upload server
+        accepts it. Without Pillow, or if it can't get small enough, the
+        plain/smallest copy is kept."""
+        if src.stat().st_size <= max_bytes or not _PIL_AVAILABLE:
+            shutil.copy2(src, dst)
+            return
+        img = _PILImage.open(src)
+        img.load()
+        w, h = img.size
+        scale = 1.0
+        while True:
+            scale *= 0.7071
+            size = (max(1, int(w * scale)), max(1, int(h * scale)))
+            img.resize(size, _PILImage.LANCZOS).save(dst, "PNG", optimize=True)
+            if dst.stat().st_size <= max_bytes or min(size) <= 64:
+                return
+
     # ------------------------------------------------------------------
     # Subclass hooks
     # ------------------------------------------------------------------

tests/tests_bec_ipython_client/test_webpage_ptycho_full_size_cap.py

@@ -0,0 +1,32 @@
+"""Full-size ptycho PNGs copied for upload are capped in size: the upload
+server rejected large (stitched) probe/spectrum images with HTTP 413."""
+
+import numpy as np
+import pytest
+
+PIL = pytest.importorskip("PIL.Image")
+
+from csaxs_bec.bec_ipython_client.plugins.OMNY_shared.webpage_generator_base import (
+    WebpageGeneratorBase,
+)
+
+
+def test_large_png_is_downscaled_below_cap(tmp_path):
+    src, dst = tmp_path / "S00085-S00093_probe.png", tmp_path / "out.png"
+    PIL.fromarray((np.random.default_rng(0).random((800, 1200, 3)) * 255).astype("uint8")).save(src)
+    cap = 300_000
+    assert src.stat().st_size > cap
+
+    WebpageGeneratorBase._copy_full_capped(src, dst, max_bytes=cap)
+
+    assert dst.stat().st_size <= cap
+    assert PIL.open(dst).size[0] < 1200
+
+
+def test_small_png_is_copied_unchanged(tmp_path):
+    src, dst = tmp_path / "S00001_phase.png", tmp_path / "out.png"
+    PIL.new("RGB", (50, 50)).save(src)
+
+    WebpageGeneratorBase._copy_full_capped(src, dst, max_bytes=300_000)
+
+    assert dst.read_bytes() == src.read_bytes()