diff --git a/mspconvert.py b/mspconvert.py
index 34a74a3..788ea41 100755
--- a/mspconvert.py
+++ b/mspconvert.py
@@ -6,15 +6,17 @@
 # one at https://mozilla.org/MPL/2.0/.
 
 import sys
+import re
 
 print("MS Paint file converter utility v0.1")
 print("Written by A.M. Rowsell, MPL Version 2.0 license\n")
 if len(sys.argv) < 2:
-    print("Please provide filename (without extension)!")
-    print("Example usage:\n./mspconvert.py DONUT")
+    print("Please provide filename!")
+    print("Example usage:\n./mspconvert.py DONUT.MSP")
     sys.exit(255)
 
 filename = sys.argv[1]
+filename_ne = re.split(r"\.", filename)[0]
 width = 0
 height = 0
 # The output file follows the very simple XBM format
@@ -29,19 +31,19 @@ static unsigned char {0}_bits [] =
 outputData = b''
 
 try:
-    with open(filename + ".MSP", 'rb') as f:
-        versionString = f.read(4)
-        if versionString == b'\x4c\x69\x6e\x53':
+    with open(filename, 'rb') as f:
+        versionString = f.read(4)                # check for the magic bytes
+        if versionString == b'\x4c\x69\x6e\x53': # this represents the string "LinS"
             version = 2
-        elif versionString == b'\x44\x61\x6e\x4d':
+        elif versionString == b'\x44\x61\x6e\x4d': # this represents the string "DanM"
             version = 1
         else:
-            print("The given file {0}.MSP is not a valid Microsoft Paint file!".format(filename))
-            sys.exit(255)
+            print("The given file {0} is not a valid Microsoft Paint file!".format(filename))
+            sys.exit(255)       # exit with -1
 
         if version == 2:
             print("Version 2 Paint file detected...")
-            width = int.from_bytes(f.read(2), "little")
+            Width = int.from_bytes(f.read(2), "little") 
             height = int.from_bytes(f.read(2), "little")
             size = int((width * height) / 8)
             f.seek((height * 2) + 32) # seek to the start of image data
@@ -52,7 +54,7 @@ try:
                     for i in range(0,rllLen):
                         outputData += rllValue
                         size -= 1
-                else:
+                else:           # read the following number of bytes verbatim
                     rllLen = int.from_bytes(byte, "little")
                     for i in range(0,rllLen):
                         outputData += f.read(1)
@@ -61,7 +63,7 @@ try:
             for i in range(0, size):
                 outputData += b'\xff'
 
-            with open(filename + "_converted.xbm", 'w') as f:
+            with open(filename_ne + "_converted.xbm", 'w') as f:
                 print("Writing output file...")
                 f.write(outputString.format(filename, width, height))
                 f.write(" {\n")
@@ -93,17 +95,17 @@ try:
                     q = 0
             outputString += " };"
 
-            with open(filename + "_converted.xbm", 'w') as f:
+            with open(filename_ne + "_converted.xbm", 'w') as f:
                 print("Writing output file...")
                 f.write(outputString)
             print("Done!")
             sys.exit(0)
 
 except FileNotFoundError:
-    print("{0}.MSP does not exist! Quitting...".format(filename))
+    print("{0} does not exist! Quitting...".format(filename))
     sys.exit(255)
 except PermissionError:
-    print("Unable to open {0}.MSP -- insufficient permissions! Quitting...".format(filename))
+    print("Unable to open {0} -- insufficient permissions! Quitting...".format(filename))
     sys.exit(255)
 except Exception:
     print("Something went wrong! Quitting...")