diff --git a/.DS_Store b/.DS_Store
index 3df77a9..b1ad57d 100644
Binary files a/.DS_Store and b/.DS_Store differ
diff --git a/.gitignore b/.gitignore
index 496ee2c..3ab7c79 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,4 @@
-.DS_Store
\ No newline at end of file
+.DS_Store
+*/.DS_Store
+
+.DS_Store
diff --git a/DSK Image/BLANK-PRODOS.dsk.png b/DSK Image/BLANK-PRODOS.dsk.png
deleted file mode 100644
index fd800af..0000000
Binary files a/DSK Image/BLANK-PRODOS.dsk.png and /dev/null differ
diff --git a/DSK Image/DSK-Image.py b/DSK Image/DSK-Image.py
index cd26935..6b9881b 100644
--- a/DSK Image/DSK-Image.py	
+++ b/DSK Image/DSK-Image.py	
@@ -7,14 +7,16 @@
 	@RetroConnector
 
 	requires ImageMagick: http://www.imagemagick.org/
-	 and python PNG module: https://pypi.python.org/pypi/pypng 
+	 and python PNG module: https://pypi.python.org/pypi/pypng
 """
 
 
 import os,sys				# filesystem functions
+import subprocess
+
 
 try:
-    import png				# PNG image library
+	import png # PNG image library
 except:
     print("\n\n" + sys.argv[0] + " requires the Python PNG module\n\n   Download from https://pypi.python.org/pypi/pypng \n   Or type in shell: pip install pypng\n\n")
     sys.exit(1)				# exit on exception - no library installed
@@ -26,12 +28,25 @@ except:
     print("\n\nUsage: python "+ sys.argv[0] +" [filename]\n\n [filename] should be a .DSK file of 143kb.\n")
     sys.exit(1)				# exit on exception - no file chosen
 
-TEMPFILENAME = "DiskImageTEMP.png"
-PNG = open(TEMPFILENAME, "wb")	# open a PNG for writing
+
+print("Checking " + INPUTFILE + "...\n")
+
+# to do: check for 140k 5.25'' disks vs 400k/800k 3.5''	and adjust accordingly
+
+if (os.path.getsize(INPUTFILE)) != 143360:		# check file size. for 5.25'', it needs to be 143k
+	print("\n\nOops. Is " + INPUTFILE + " a DSK file of 143kb?\n\n")
+	sys.exit(1)				# exit on exception - file is empty, etc
 
 					# The point: Make a PNG image from the data on a floppy disk image.
-					# 35 tracks, each with 16 sectors of 256 bytes each, for a total of 143,360 bytes
+					# 5.15'' disks have 35 tracks, each with 16 sectors of 256 bytes each, for a total of 143,360 bytes
 					# so 35 lines of 4096 px.
+TRACKS = 35
+SECTORS = 16
+BYTESPERSECTOR = 256
+
+TEMPFILENAME = "DiskImageTEMP.png"
+PNG = open("DiskImageTEMP.png", "wb")	# open a PNG for writing
+
 
 					# new, empty arrays
 BYTES  = []
@@ -40,7 +55,7 @@ PIXELS = []
 try:
     byte = DSK.read(1) 			# read a byte
     while byte != "":			# while the file still has bytes in it
-        byte = DSK.read(1)	
+        byte = DSK.read(1)
         if len(byte) > 0: 		# the last byte, for whatever reason, is length 0. Bah.
             BYTES.append(ord(byte))	# append the number representing the byte (0-255) to the BYTES array
 except:
@@ -50,23 +65,23 @@ except:
 
 print("\n Starting.\n")
 
-for TRACK in range(0,35,1):		# for each of the 35 tracks
-    LINE=[]						# start a new line of pixels
-    for SECTOR in range(0,4096,1):	# write the bytes for the sectors in that track to the line array
-        offset = (SECTOR * TRACK) + SECTOR
-        LINE.append(BYTES[(SECTOR * TRACK) + SECTOR])
+for TRACK in range(0,TRACKS,1):		# for each of the 35 tracks
+	LINE=[]				# start a new line of pixels
+	for SECTOR in range(0,SECTORS*BYTESPERSECTOR,1):	# write the bytes for the sectors in that track to the line array
+		offset = (SECTOR * TRACK) + SECTOR
+		LINE.append(BYTES[(SECTOR * TRACK) + SECTOR])
 
-    print(" Track: " + str(TRACK))
-    PIXELS.append(LINE)		# add the array of pixels to the array of arrays
+	print(" Track: " + str(TRACK))
+	PIXELS.append(LINE)		# add the array of pixels to the array of arrays
 
 print("\n Done.\n")
- 
-					# write to the PNG file 
-w = png.Writer(4096,35, greyscale=True, bitdepth=8) 
+
+					# write to the PNG file
+w = png.Writer(SECTORS*BYTESPERSECTOR,TRACKS, greyscale=True, bitdepth=8)
 w.write(PNG, PIXELS)			# each number in the array becomes a pixel in the image. each array becomes a line.
 
-print(" Writing to disk. Chunka-chunk-cka. Whirr...\n")
-
+sys.stdout.write("\n\n\r Writing bytes to disk. Chunka-chunka-chunk. Whirr.\n\n")
+sys.stdout.flush()
 
 DSK.close()				# done with these files. close them.
 PNG.close()
@@ -75,19 +90,24 @@ PNG.close()
 OUTPUTFILE = os.path.join(INPUTFILE + ".png")
 					# set a destination file same as DSK, but with PNG extension
 
-os.system('convert '+TEMPFILENAME+' -matte -virtual-pixel transparent -resize 1024x1024! -rotate 90 -distort Polar "512 110 512,512 -180,180" "'+OUTPUTFILE+'"')
-					# Using ImageMagick, convert the 4096x35px image to a square, rotate, then rotate around an axis.
-					# NOTE: Windows command line needs to have Polar coordinates enquoted with " not '
-					# NOTE: Windows has a native command called convert which does something very different 
-					#       from ImageMagick's convert command, so obviously this will fail if IM is not installed
+
+
+try:
+	subprocess.call(['convert', 'DiskImageTEMP.png', '-matte', '-virtual-pixel', 'transparent', '-resize', '1024x1024!', '-rotate', '90', '-distort', 'Polar', '512 110 512,512 -180,180', OUTPUTFILE])
+					# convert the 4096x35px image to a square, rotate, then rotate around an axis.
+except OSError:
+    print("\n\nOops. This script requires ImageMagick: http://www.imagemagick.org/")
+    sys.exit(1)				# exit on exception - needs imagemagick installed
+
+
 
 if 'win32' in sys.platform:
-	# Because the Windows "start" commandline command cannot take an enquoted file or pathname, 
-	# which is necessary if the path has spaces, we have to obtain the "short" version of 
+	# Because the Windows "start" commandline command cannot take an enquoted file or pathname,
+	# which is necessary if the path has spaces, we have to obtain the "short" version of
 	# the file/path in the 8.3 format. There is no Python library to do this for us.
-	# Said another way: Windows is broken in that enquoting a file argument after their start 
-	# command causes it to open a blank terminal. Boo! 
-	# But we do this *after* the ImageMagick convert process above, because that will take an 
+	# Said another way: Windows is broken in that enquoting a file argument after their start
+	# command causes it to open a blank terminal. Boo!
+	# But we do this *after* the ImageMagick convert process above, because that will take an
 	# enquoted file just fine.
     from ctypes import windll, create_unicode_buffer, sizeof
     buf = create_unicode_buffer( 512 )
@@ -96,7 +116,7 @@ if 'win32' in sys.platform:
 else:
 	# Otherwise we enquote the output file becuase it may have spaces
     OUTPUTFILE = '"' + OUTPUTFILE + '"'
-	
+
 platform_commands = {
 					'darwin' : 'open', 			# opens the resulting image in the default Mac image viewer (Preview.app)
 					'linux'  : 'xdg-open', 		# opens the resulting image in the default Linux image viewer (mime-determined); Python 2: 'linux2', Python 3: 'linux'