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Thread: Fixes to PIL for handling XPM files.
Fixes to PIL for handling XPM files.
user name
 2006-10-24 15:07:24 

  


  

    


I recently downloaded the Python Imaging Library (PIL 1.1.5), and I
have been trying to use it to convert several hundred XPM files into
GIFs (I also tried converting into PNGs which may be useful in the
future).  During this process, I ran into various problems which appear
to be caused by bugs.



Most of the difficulties were related to XPMs -- not being able to load
XPM files which other applications were quite happy with. ; But there
were also a couple of minor issues with transparency in GIF and PNG
formats. 



Attached is a diff file containing the changes I had to make to the
code to fix these problems.  This fixes things for the vast majority of
the XPM files I have. ; There are still some XPMs that can't be loaded
(those which use more than one character per pixel for example), but
these are far less common.





Because I am not a regular contributer to this project I thought I
should include more information than just the diffs, so here is a list
of the bugs I found and what I changed as a result: 







Bug: PIL could not open some XPM files
because it failed to cope with some features of XPM syntax.



Fix: ; Various changes in XpmImagePlugin.py:




    
  
  • Changed the RE used to match the image
header to one that copes with leading spaces and multiple spaces
between words.
    • 



    
  
  • In XpmImageFile._open(), when reading the
image palette:
    • 




  
    
    
  • Ignore lines which are commented-out.
    • 
    
  • Strip leading and trailing whitespace
before processing.
    • 
    
  • Remove case sensitivity when looking for
"None".
    • 
    
  • Use ImageColor.getrgb() to interpret color
values.
    • 
    
  • Look ahead to detect colour names
consisting of multiple words
    • 
  




    
  
  • In XpmImageFile.load_read() (when reading
the pixels) ignore lines which are commented-out.
    • 










Bug: PIL could not open some XPM files,
because the color names were not recognized.



Fix: various changes to ImageColor.py:




    
  
  • Changed the colormap to the standard list of
X11 colours (as found on any Unix or Linux system).
    • 



Note: before this change, the
colormap apparently contained colours taken from CSS3 -- the comment
reads 'X11 colour table (from "CSS3 module: Color working draft")'. 
However some of the standard X11 colours clashed with existing colours
in the map.  In the end, I removed all the CSS3 colours and just
included the X11 colours.  The comment does say "X11 colour table"
after all.


    
  
  • getrgb(): Remove spaces from the color name
in order to find a match.  X11 has variations of some color names, such
as "light blue" and "LightBlue".   But the version with spaces was not
recognized.
    • 



    
  
  • getrgb(): Recognize colours specified as a
48-bit RGB string (e.g. #FFFF0000AAAA).  These are sometimes
encountered in XPMs. ; The 3 bytes of extra precision are ignored, and
the returned RGB value is a standard 24-bit RGB tuple.
    • 








Bug: PIL loaded all XPM files incorrectly, shifting the entire
image several pixels to the right (truncating it on the right, and
adding a a band of incorrect pixels on the left).



This is caused by trying to use memory mapping to read the file, which
prevents the proper XPM decoder from being used. ; Memory mapping does
not work because of the structure of XPM files -- the file includes
characters (such as the opening and closing quotes on each line) which
do not correspond to pixel values.



Fix: Changed load() in ImageFile.py to explicitly exclude XPM
files from the memory mapping. 



There may be a more elegent way to do this,
perhaps by changing the value of ImageFile.tile for XPMs. ; But I tried
the obvious thing -- changing the "raw" designation to something else,
and that seemed to break things even more. ;  Perhaps someone more
familiar with this code could do better.







Bug: Could not write GIFs with transparency.  The pixels which
should have been transparent were not.



Fix: Changed _save() in GifImagePlugin.py.   The code was
looking in the wrong dictionary for the transparency value.







Bug: Could not write PNGs with transparency.  The pixels which
should have been transparent were not.



Fix: Changed _save() in PngImagePlugin.py.  The code was looking
in the wrong dictionary for the transparency value.





-- 

Tom Heathcote


-- 
Tom Heathcote              Petris Technology
petris.com">tom.heathcotepetris.com   154 Brent Street
Tel +44 20 8202 2433       London  NW4 2DR
Fax +44 20 8202 2287       England



  

  
  
   
     
    

  

    Fixes to PIL for handling XPM files.
  


  

     user name

     2006-10-26 08:23:39
  


  

    
Tom Heathcote wrote:

> Attached is a diff file containing the changes I had to
make to the
 > code to fix these problems.  This fixes things for the
vast majority
 > of the XPM files I have.

thanks.  no time to comment on all these right now, but I
couldn't help 
noticing the following:

> *Fix Changed
_save() in GifImagePlugin.py.   The code was looking in 
> the wrong dictionary for the transparency value.

> *Fix Changed
_save() in PngImagePlugin.py.  The code was looking in 
> the wrong dictionary for the transparency value.

the "info" dictionary is a free-form dictionary
used to return in- 
formation from plugin loaders.  its content is not
standardized,
is dropped by most image operations, and is therefore not
used by "save".

instead, you have to use an explicit option when saving an
image:

     im.save(filename, transparency=value)

(that you had to change all plugins should have told you
that maybe you 
weren't using the API in the intended way, don't you think?


cheers /F

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