build.py: read blosc-compressed surface volumes

tools/build.py

@@ -65,7 +65,8 @@ def fetch_ct(w, src, shape_hw):
             break
     base = f"{root}/{lvl}"
     meta = json.loads(urllib.request.urlopen(f"{base}/.zarray").read())
-    assert meta.get("compressor") is None, f"compressed zarr not handled: {meta.get('compressor')}"
+    comp = meta.get("compressor")
+    assert comp is None or comp.get("id") == "blosc", f"compressed zarr not handled: {comp}"
     D, H, W = meta["shape"]
     cz, ch, cw = meta["chunks"]
     sep = meta.get("dimension_separator") or "."
@@ -81,6 +82,9 @@ def fetch_ct(w, src, shape_hw):
             body = r.stdout[:-3]
             if code in (b"403", b"404"):
                 return ij, None
+            if code == b"200" and comp:
+                import imagecodecs
+                body = imagecodecs.blosc_decode(body)
             if code == b"200" and len(body) == cz * ch * cw:
                 raw = body
                 break