fix Could not parse bool from flag (#2359)

src/training/tesstrain_utils.py

@@ -174,7 +174,7 @@ def check_file_readable(*filenames):
 )
 
 parser.add_argument(
-    "--distort_image", dest="distort_image", help="set --distort_image=true."
+    "--distort_image", dest="distort_image", action="store_true"
 )
 
 tessdata_group = parser.add_argument_group(
@@ -315,9 +315,11 @@ def generate_font_image(ctx, font, exposure, char_spacing):
         f"--exposure={exposure}",
         f"--outputbase={outbase}",
         f"--max_pages={ctx.max_pages}",
-        f"--distort_image={ctx.distort_image}",
     ]
 
+    if ctx.distort_image:
+        common_args.append("--distort_image")
+
     # add --writing_mode=vertical-upright to common_args if the font is
     # specified to be rendered vertically.
     if font in VERTICAL_FONTS: