Image::read( ) - string encoding requirement?

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XtoF
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Image::read( ) - string encoding requirement?

Post by XtoF » 2012-04-18T08:20:52-07:00

Hi!

I'm writing a software generating web galleries (http://www.ezwebgallery.org), using Qt4 and Magick++. After having updated ImageMagick from 6.7.1-0 to 6.7.6-5, I couldn't read some photos using Magick::Image::read( const std::string &imageSpec_ ) anymore.

I found the cause, but I cannot determine if it is because of a former misuse of this function on my side or a regression. This occurred on Windows, I didn't try on Linux.

Code sample:

Code: Select all

string filenameLocal8( fileName.toLocal8Bit().constData() );
try{
     pic.read( filenameLocal8 );        
}
with fileName being a QString from Qt4 containing: "D:\Users\Chris\temp\sélection test\_PiqueNique&BBQ_011 Copie__.jpg"

As you can see this QString contains a character 'é', which is not part of the 128 character standard ASCII. It is "ISO 8859-1" encoded (via toLocal8Bit() )before being assigned to the std::string filenameLocal8. As I understand, a std::string contains no info about its encoding.

The data contained by filenameLocal8 is subsequently passed to OpenBlob then to fopen_utf8, in which the 'é' character is incorrectly decoded ; leading to call _wfopen with
"D:\Users\Chris\temp\slection test\_PiqueNique&BBQ_011 Copie__.jpg" as the path parameter ultimately failing.

Of course I understand this happened because the std::string I passed to Image::read was not UTF-8 encoded. Thus assigning it some proper UTF-8 data solved my problem. Anyway, as stated, 6.7.1-0 Image::read could use the ISO 8859-1 string and open the corresponding file with no trouble.
So,
  1. 1. If ImageMagick tries to determine if the filepath provided is "8bit ASCII" encoded or UTF-8 encoded, in this particular case 6.7.6-5 failed and 6.7.1-0 didn't.
  • 2. If there is a requirement to provide a string containing UTF-8 or plain 7bit "standard" ASCII, it should be mentioned somewhere in the Image::read documentation (I didn't find it). Of course I understand that UTF-8 is way better and fail proof than the various collection of "8bit ASCII" codecs.
What is your opinion on that matter?
Thanks! :)

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magick
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Re: Image::read( ) - string encoding requirement?

Post by magick » 2012-04-18T09:11:53-07:00

Retrofitting ImageMagick for internationalization has been quite challenging. After a number of attempts to satisfy both the Windows and Linux worlds, we settled on a consistent standard of utilizing UTF-8 encoding. If we coded ImageMagick from scratch we would of course use wide-characters but we do not have that luxury with the existing legacy code base. We will document the UTF-8 requirement in the source and documentation of ImageMagick.

michalfapso
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Re: Image::read( ) - string encoding requirement?

Post by michalfapso » 2014-06-23T01:44:28-07:00

Hi, I had also problems with using utf8 QString filenames with Magick++ compiled with MinGW. I posted the fix here: viewtopic.php?f=3&t=25785&p=112497#p112497

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