diff --git a/colmap_input.py b/colmap_input.py
index 4ac54cc..1fef01f 100644
--- a/colmap_input.py
+++ b/colmap_input.py
@@ -160,7 +160,7 @@ def read_images_binary(path: str) -> List[Image]:
             qvec = binary_image_properties[1:5]
             tvec = binary_image_properties[5:8]
             cam_id = binary_image_properties[8]
-            image_name = ''
+            image_name = ""
             current_char = read_next_bytes(fid, 1, "c")[0]
             while current_char != b"\x00":  # look for the ASCII 0 entry
                 image_name += current_char.decode("utf-8")
@@ -249,7 +249,7 @@ def quaternion_to_rotation_matrix(qvec: List[float]) -> np.ndarray:
     parser = argparse.ArgumentParser(description="Convert colmap results into input for PatchmatchNet")
 
     parser.add_argument("--input_folder", type=str, help="Project input dir.")
-    parser.add_argument("--output_folder", type=str, default='', help="Project output dir.")
+    parser.add_argument("--output_folder", type=str, default="", help="Project output dir.")
     parser.add_argument("--num_src_images", type=int, default=-1, help="Related images")
     parser.add_argument("--theta0", type=float, default=5)
     parser.add_argument("--sigma1", type=float, default=1)
@@ -262,6 +262,12 @@ def quaternion_to_rotation_matrix(qvec: List[float]) -> np.ndarray:
     if not args.output_folder:
         args.output_folder = args.input_folder
 
+    if args.input_folder is None or not os.path.isdir(args.input_folder):
+        raise Exception("Invalid input folder")
+
+    if args.output_folder is None or not os.path.isdir(args.output_folder):
+        raise Exception("Invalid output folder")
+
     image_dir = os.path.join(args.input_folder, "images")
     model_dir = os.path.join(args.input_folder, "sparse")
     cam_dir = os.path.join(args.output_folder, "cams")
diff --git a/colmap_output.py b/colmap_output.py
index eaee118..4737c8e 100644
--- a/colmap_output.py
+++ b/colmap_output.py
@@ -125,8 +125,8 @@ def write_points_3d(path: str):
     parser = argparse.ArgumentParser(description="Convert colmap results into input for PatchMatchNet")
 
     parser.add_argument("--input_folder", type=str, help="Input PatchMatchNet reconstruction dir")
-    parser.add_argument("--results_folder", type=str, help="Input PatchMatchNet results dir")
-    parser.add_argument("--output_folder", type=str, default='', help="Output ColMap MVS workspace")
+    parser.add_argument("--results_folder", type=str, default="", help="Input PatchMatchNet results dir")
+    parser.add_argument("--output_folder", type=str, default="", help="Output ColMap MVS workspace")
 
     args = parser.parse_args()
 
@@ -136,6 +136,15 @@ def write_points_3d(path: str):
     if not args.output_folder:
         args.output_folder = args.input_folder
 
+    if args.input_folder is None or not os.path.isdir(args.input_folder):
+        raise Exception("Invalid input folder")
+
+    if args.results_folder is None or not os.path.isdir(args.results_folder):
+        raise Exception("Invalid results folder")
+
+    if args.output_folder is None or not os.path.isdir(args.output_folder):
+        raise Exception("Invalid output folder")
+
     create_output_dirs(args.output_folder)
     copy_maps(args.input_folder, args.results_folder, args.output_folder)
     cams, ims, im_pairs = read_reconstruction(args.input_folder)
diff --git a/convert_eth3d_dataset.py b/convert_eth3d_dataset.py
index 1e7eaf1..ecdbaab 100644
--- a/convert_eth3d_dataset.py
+++ b/convert_eth3d_dataset.py
@@ -1,5 +1,4 @@
 import argparse
-import numpy as np
 import os
 import shutil
 from datasets.data_io import read_image_dictionary
@@ -61,7 +60,7 @@
 
             # Copy GT depth map
             depth_gt_filename = os.path.join(args.input_folder, scan, "depths", image_index[view_id])
-            depth_gt_filename = os.path.splitext(depth_gt_filename.replace('_undistorted', ''))[0] + '.pfm'
+            depth_gt_filename = os.path.splitext(depth_gt_filename.replace("_undistorted", ""))[0] + ".pfm"
             shutil.copy(depth_gt_filename, os.path.join(depth_path, "{:0>8}.pfm".format(view_id)))
 
             # Create mask from GT depth map and save in output