feat: add installation hints for missing image writers #7980

Author: aman0311x

monai/data/image_writer.py

@@ -116,7 +116,26 @@ def resolve_writer(ext_name, error_if_not_found=True) -> Sequence:
         except Exception:  # other writer init errors indicating it exists
             avail_writers.append(_writer)
     if not avail_writers and error_if_not_found:
-        raise OptionalImportError(f"No ImageWriter backend found for {fmt}.")
+        RECOMMENDED_PACKAGES = {
+            "png": "Pillow",
+            "jpg": "Pillow",
+            "jpeg": "Pillow",
+            "nii": "nibabel or SimpleITK",
+            "nii.gz": "nibabel or SimpleITK",
+            "nrrd": "pynrrd",
+            "tif": "Pillow or tifffile",
+            "tiff": "Pillow or tifffile",
+        }
+
+        fmt_clean = fmt.replace(".", "").lower()
+        package_hint = RECOMMENDED_PACKAGES.get(fmt_clean, "")
+
+        msg = f"No ImageWriter backend found for {fmt}."
+        if package_hint:
+            msg += f" Please install '{package_hint}' (e.g., pip install {package_hint})."
+        
+        raise OptionalImportError(msg)
+
     writer_tuple = ensure_tuple(avail_writers)
     SUPPORTED_WRITERS[fmt] = writer_tuple
     return writer_tuple