PIL question. having exactly same font on multiple platforms

Gelonida N gelonida at gmail.com
Thu Aug 4 20:54:47 CEST 2011

On 08/04/2011 12:32 PM, Thomas Jollans wrote:
> On 04/08/11 12:04, Gelonida N wrote:
Thanks for your answer.

>> >From within a django application
>> I'd like create a small image file (e.g. .png)
>> which just contains some text.
>> I wondered what library would be appropriate and would yield the same
>> result independent of the OS (assuming the versions of the python
>> libraries are the same)
>> Images should be pixel identical independent on the platform on which
>> the image is created.
>> I made some attempts with PIL (Image / ImageFont / ImageDraw),
>> but have difficulties getting the same font under Linux and windows.
> Perhaps PIL uses a different font rendering library on each platform?
> You could try to get around this by using
> http://code.google.com/p/freetype-py/ directly. It's also possible that
> different hinting settings on the different systems are playing a role
> somehow, somewhere. Perhaps you can tell freetype precisely what to do,
> I'm not sure.

The reason why I want the images to  look identical is very simple.
Though the final web server will run on a linux server, I use sometimes
windows for development or as test server.

For automated tests I would have liked pixel identical images.
this allows calculating the md5sum of images to know whether
a regression in the image layout occured. Well I can live without it.

The second (more import issue) is, that the images should look the same
whether created on a Windows or Linux host.

I didn't know that PIL delegated font rendering to the underlying OS,
but thought it contains its own rendering.

Here the problem is not if a few pixels are different, but currently I
even don't know how to choose a font, and make sure it exists on both
platforms. I also don't know how I can write portable python code,  that
will find a given font on windows and on linux independent of the exact
font location.

> If you want exactly the same bitmap on different platforms, you could
> just scrap truetype alltogether, and use bitmaps directly, individually
> taking the characters you need from a resource file. (you know, one
> bitmap with all the characters at known coordinates - or a load of small
> bitmaps)

A resource file or a bitmapped font packaged with my application might
be a solution.
I just had to learn where to get one from or how to create one without
any copyright issues
> Why do you need the images to be identical to the pixel anyway? Surely,
> if it's about comparing the text, you would just compare the strings?
> And if it's only for displaying the text, then why bother with details
> like that as long as it looks good?

I hope I clarified a little what I was looking for.
It's not necessarily pixel true, but it should not be too visible
whether the image was rendered on a windows or linux PC

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