help debugging noob code - converting binary data to images...

Lie Lie.1296 at
Sun Jun 29 11:47:36 CEST 2008

On Jun 29, 11:18 am, la... at wrote:
> Ok I'm a Python noob, been doing OK so far, working on a data
> conversion program and want to create some character image files from
> an 8-bit ROM file.
> Creating the image I've got down, I open the file and use TK to draw
> the images... but
> 1)  It does not seem to end (running in IDLE), I have to kill the
> process to retry it seems tkinter does not close(?)
> 2) Once I added the Image module open won't open my binary file
> (complains its not an image file, which is isnt.)  I am sure I need to
> prefix open with something but I can't seem to find an example of how
> to word it,
> Below is the code (if it is lousy its because I've mainly been
> borrowing by examples as I go...) Any suggestions are gretly
> appreciated.
> #!/usr/local/bin/python
> from Tkinter import *
> from string import *
> from Image import *


You're importing everything to the current namespace and this corrupts
the current namespace, specifically the 'open' function inside would shadow the built-in 'open' function.

import Tkinter
import string
import Image

There are use cases where doing 'from blah import *' is useful, such
as importing constants, but in general try to avoid importing
everything to current namespace.

> root = Tk()
> root.title('Canvas')

If you used 'import Tkinter', you'd have to change that code to:
root = Tkinter.Tk()

> #open commodore Cset rom
> cset  = open("chargen","r")

Because you shadowed the built-in 'open' with the 'from Image import
*', this would call instead of the built-in open.

> canvas = Canvas(width=16, height=16, bg='white')

If you used 'import Tkinter', you'd have to change that code to:
canvas = Tkinter.Canvas(...)

> canvas.pack(expand=YES, fill=BOTH)
> # character size factor
> size = 2
> # read all 512 characters from ROM
> for cchar in range(0, 511, 1):

You can use this instead:
for cchar in range(511):

but beware, this creates range with length 511 (so do the original
range), which means you're lacking on space for the last char.
You probably wanted this instead:
for cchar in range(512):

But again, python can loop directly over string/list/file, etc, so
this might be best:
for char in

>     #draw line
>     while charline < 8:
>         position = 0
>         x =
>         ch = ord(x)
>         # draw pixels
>         while position < 8:
>             if ch & ( 2 ** position ):
>                 xp = 1+(7-position)*size
>                 yp = 1+charline*size
>                 canvas.create_rectangle(xp,yp,xp+size,yp+size,
> fill='black', width=0)
>             position += 1

Since you're planning to use Image module (from PIL/Python Imaging
Library) why not use functions from Image instead to create the image.
The format of the file you're using seems to be RAW format (i.e.
simple uncompressed bitmap, without any kinds of header). That means
Image.fromstring() should work.

>         charline += 1
>     #save character image
>     outfile = "/home/mydir/work/char"+zfill(cchar,3)+".png"
>     #clear canvas for next char...
>     canvas.create_rectangle(1,1,size*8,size*8, fill='white', width=0)
> root.mainloop()

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