[Image-SIG] PIL: FAST images from C-Extension?

Fri, 19 Mar 1999 21:58:38 +0100

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fredrik_lundh@ivab.se is invalid??
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Date: Fri, 19 Mar 1999 21:55:26 +0100
From: Sven Havemann <s.havemann@tu-bs.de>
Organization: Institut fuer Computergrafik
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To: Fredrik Lundh <fredrik_lundh@ivab.se>, n.schenk@tu-bs.de
Subject: PIL: FAST images from C-Extension? 
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Hi!
===

We're producing animated bitmaps in a C-extension module to Python and
would like to display them FAST using Python/Tkinter/PIL. How can I
transfer images from C to Python? I've written a demo extension doing
so, you can find THE SOURCE (just 10 kB) in

ftp://ftp.cg.cs.tu-bs.de/pub/cg/people/havemann/pildirect/pildirect.zip

The problem is: IT IS TOO SLOW!

My idea was to have an update function for a Tk Canvas doing the
following (in Python): 

=============================================
im=Image.new("RGB",(800,800))
canvas=Canvas(root,width=802,height=802)
imtk = ImageTk.PhotoImage(im)
canvas.create_image(0,0,image=imtk,anchor=NW)
canvas.pack()

def update():
   global im,imtk
   test(im)           # updating the image from our extension module
   imtk.paste(im)     # updating the PhotoImage
   tkroot.after(5,update)  # loop
=============================================

test(im) extracts the bitmap info from the Image.Image data structure
and works quite nicely and fast. But the imtk.paste(im) obviously
performs a FLOYD-STEINBERG DITHERING IN EVERY STEP resulting in an
unacceptable O(m*n) complexity for bitmap size (m x n). 

Questions: Why is there dithering at all? Isn't the Tk PhotoImage a
Truecolor image? How can I tell Tk to allocate a truecolor visual (by
default)? 

The next idea was to use indexed color PhotoImages. But then I didn't
manage to set the image palette and found some inconsistencies in
ImagePalette.py from PIL ('raw' attribute not found in image.load()) and
fixed it in a copied version... 

I've discovered that there's a new version of PIL, so I will retry using
Imaging-1.0b1.tar.gz instead of Imaging-0.3b2.tgz monday... But maybe
someone can tell me whether I run in the WRONG DIRECTION AT ALL and
maybe there's obviously a BETTER SOLUTION!!!

TIA for any hint,
regards, Sven.

-- 
__________________________________________________________________
 dipl-inform. Sven Havemann        Institut fuer ComputerGraphik
 Odastrasse 6                      Rebenring 18
 38122 Braunschweig - Germany      38106 Braunschweig - Germany
 Tel. 0531/2808955                 Tel. 0531/391-2108, Fax: -2103
 s.havemann@tu-bs.de               http://www.cg.cs.tu-bs.de

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