[app][dxfile2nx] allow to provide pixel size as a single value

close #66

nxtomomill/app/dxfile2nx.py

@@ -64,6 +64,24 @@ def convert_2elmts__tuple_to_float(input_str) -> tuple:
         return float(v1), float(v2)
 
 
+def _get_pixel_size(input_str) -> tuple:
+    try:
+        values = convert_2elmts__tuple_to_float(input_str)
+    except ValueError:
+        try:
+            value = float(input_str)
+        except Exception:
+            raise ValueError(
+                f"Unable to convert {input_str} to pixel size."
+                f"Should be provided as a tuple (x_pixel_size, y_pixel_size) "
+                f"or as a single value pixel_size"
+            )
+        else:
+            return value, value
+    else:
+        return values
+
+
 def main(argv):
     """ """
     parser = argparse.ArgumentParser(
@@ -103,7 +121,7 @@ def main(argv):
     parser.add_argument(
         "--pixel-size",
         default=(None, None),
-        help="pixel size in meter as (x pixel size, y pixel size)",
+        help="pixel size in meter as (x pixel size, y pixel size) or as a single value",
     )
     parser.add_argument(
         "--fov",
@@ -167,7 +185,7 @@ def main(argv):
         input_entry=options.input_entry,
         output_entry=options.output_entry,
         scan_range=convert_2elmts__tuple_to_float(options.scan_range),
-        pixel_size=convert_2elmts__tuple_to_float(options.pixel_size),
+        pixel_size=_get_pixel_size(options.pixel_size),
         field_of_view=options.field_of_view,
         distance=distance,
         overwrite=options.overwrite,