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From Joakim Knudsen <joakim.gr...@gmail.com>
Subject Re: Creating EXIF tags (TiffOutputField) the right way
Date Tue, 31 May 2016 17:20:25 GMT
Following a post on the User-Commons-Apache log (from 2012), I ended up
with the following code which seems to work.
It writes proper Unicode, which I can read back successfully using
ExifTool. I also see the comment nicely in Windows Explorer, and under File
> Properties.
Note I changed the field type from ASCII to FIELD_TYPE_UNDEFINED, otherwise
(with ASCII) it did not work. At least Windows couldn't make sense of the
EXIF data.

// http://osdir.com/ml/user-commons-apache/2012-03/msg00046.html
byte[] unicodeMarker = new byte[]{ 0x55, 0x4E, 0x49, 0x43, 0x4F, 0x44,
        0x45, 0x00 };
byte[] comment = textToSet.getBytes(ENCODING_UTF16); // OR UTF-16BE if
the file is big-endian!
byte[] bytesComment = new byte[unicodeMarker.length + comment.length];
System.arraycopy(unicodeMarker, 0, bytesComment, 0, unicodeMarker.length);
System.arraycopy(comment, 0, bytesComment, unicodeMarker.length,
comment.length);

TiffOutputField exif_comment = new
TiffOutputField(TiffConstants.EXIF_TAG_USER_COMMENT,
        TiffFieldTypeConstants.FIELD_TYPE_UNDEFINED,
bytesComment.length, bytesComment);


I can now write UserComment: "æøå" without problems :)



- Joakim


On 31 May 2016 at 17:39, Benedikt Ritter <britter@apache.org> wrote:

> Hello Joachim,
>
> Joakim Knudsen <joakim.grahl@gmail.com> schrieb am Sa., 28. Mai 2016 um
> 21:10 Uhr:
>
> > Hi Benedikt, and thanks for replying!
> >
> > So, if FieldType is unused, maybe the alternative, simpler constructor is
> > more appropriate/correct to use?
> >
> > // try using the approach given in the example (modified from the GPS
> tag):
> > TiffOutputField exif_comment = TiffOutputField.create(
> >         TiffConstants.EXIF_TAG_USER_COMMENT,
> >         outputSet.byteOrder, textToSet);
> >
> > However, now Sanselan throws an ImageWriteException:
> > org.apache.sanselan.ImageWriteException: Tag has unexpected data type.
> >
> > So are you 100% sure field type should not be set (to ASCII)?
> >
>
> No, I'm just saying that it uses a hard coded encoding anyway :-)
>
>
> >
> > Next, you're saying the string to set (textToSet) is converted internally
> > to byte array, using US-ASCII encoding.
> > If I try writing "æøåæøå" to a file, I get "쎦쎸쎥쎦쎸쎥" when I copy
the JPEG
> > out and check Properties in Windows Explorer.
> > If I write only ASCII characters, e.g. "Test", then that comes through
> just
> > fine.
> >
> > In summary, here is the code that works for me (except non-ASCII
> > characters):
> >
> >
> > *//
> >
> >
> http://mail-archives.apache.org/mod_mbox/commons-user/201203.mbox/%3CCAJm2B-mYCXYKuyu=Hs8UAZCpw-B=KWuZ4gsZFUOBvZWUN0LUfA@mail.gmail.com%3E
> > <
> >
> http://mail-archives.apache.org/mod_mbox/commons-user/201203.mbox/%3CCAJm2B-mYCXYKuyu=Hs8UAZCpw-B=KWuZ4gsZFUOBvZWUN0LUfA@mail.gmail.com%3E
> > >*byte
> > b[] = ExifTagConstants.EXIF_TAG_USER_COMMENT.encodeValue(
> >         TiffFieldTypeConstants.FIELD_TYPE_ASCII,
> >         textToSet, outputSet.
> > *byteOrder*);
> >
> > // constructor arguments: taginfo tag fieldtype count bytes
> > TiffOutputField exif_comment = new
> > TiffOutputField(TiffConstants.EXIF_TAG_USER_COMMENT.tag,
> >         TiffConstants.EXIF_TAG_USER_COMMENT,
> > TiffFieldTypeConstants.FIELD_TYPE_UNDEFINED,
> >         b.length, b);
> >
>
> The provided links indicate to me, that it is possible to write non ASCII
> characters. Are you sure your code looks like what Damjan suggested?
>
> Benedikt
>
>
> >
> >
> >
> > Joakim
> >
> >
> >
> > On 22 May 2016 at 15:29, Benedikt Ritter <britter@apache.org> wrote:
> >
> > > Hello Joakim
> > >
> > > Joakim Knudsen <joakim.grahl@gmail.com> schrieb am Sa., 21. Mai 2016
> um
> > > 19:29 Uhr:
> > >
> > > > Hi List!
> > > >
> > > > I'm working on an Android app, where I want to read and write "EXIF
> > tags"
> > > > to JPEG files on the device. Sanselan 0.97 seems to work perfectly,
> > > > although it's a bit complicated to work with EXIF tags/directories.
> > > >
> > > > The specific tags I'm interested in, is EXIF_TAG_USER_COMMENT and
> > > > EXIF_TAG_IMAGE_DESCRIPTION.
> > > > According to the documentation I could find, UserComment is of field
> > type
> > > > "undefined", whereas ImageDescription is of field type ASCII.
> > > >
> > > >
> > >
> >
> http://www.awaresystems.be/imaging/tiff/tifftags/privateifd/exif/usercomment.html
> > > >
> http://www.awaresystems.be/imaging/tiff/tifftags/imagedescription.html
> > > >
> > > > What's the proper way of creating those tags, wrt. charset etc? I
> want
> > as
> > > > wide as possible character support (æøå etc).
> > > >
> > > > I find different discussions online, with different advice. Seems two
> > > > constructors are going around, where the simpler one does not deal
> with
> > > > charset/encoding at all. This one uses the .create method:
> > > >
> > > > String textToSet = "Some Text æøå";
> > > >
> > > > TiffOutputField exif_comment = TiffOutputField.create(
> > > >                 TiffConstants.EXIF_TAG_USER_COMMENT,
> > > >                 outputSet.byteOrder, textToSet);
> > > >
> > > >
> > > > while this one uses the standard constructor:
> > > >
> > > > byte b[] = ExifTagConstants.EXIF_TAG_USER_COMMENT.encodeValue(
> > > >         TiffFieldTypeConstants.FIELD_TYPE_ASCII,
> > > >         textToSet, outputSet.byteOrder
> > > > );
> > > >
> > > > // constructor arguments: taginfo tag fieldtype count bytes
> > > > TiffOutputField exif_comment2 = new
> > > > TiffOutputField(TiffConstants.EXIF_TAG_USER_COMMENT.tag,
> > > >         TiffConstants.EXIF_TAG_USER_COMMENT,
> > > > TiffFieldTypeConstants.FIELD_TYPE_UNDEFINED,
> > > >         b.length, b);
> > > >
> > > > In this last one, the string to set has been converted to a byte
> array
> > > > first. But can/should I set the encoding anywhere?
> > > >
> > > > Is the field type even ASCII? This information seems to indicate it's
> > > > not ASCII...
> > > >
> > > >
> > >
> >
> http://www.awaresystems.be/imaging/tiff/tifftags/privateifd/exif/usercomment.html
> > > >
> > > >
> > > > Need some help here, as you can see, to get this right. The second
> > > > approach above does seem to work in my app, but I'd like to be sure
> > > > I'm not somehow messing up the JPEGs on the deviced.
> > > >
> > >
> > > I've looked at the code of
> > > org.apache.commons.imaging.formats.tiff.taginfos.TagInfoGpsText
> > > (ExifTagConstants.EXIF_TAG_USER_COMMENT is an instance of
> > TagInfoGpsText).
> > > Here are my observations:
> > >
> > > - The FieldType parameter, which you have set to
> > > TiffFieldTypeConstants.FIELD_TYPE_ASCII is never used in the
> > implemenation
> > > of encodeValue(FieldType, Object, ByteOrder)
> > > - When converting the input String to byte array,
> String.getBytes(String
> > > charsetName) is used
> > > - For charsetName "US-ASCII" is always used (it can not be configured
> by
> > > the user)
> > >
> > > So my guess is, that the code will not handle characters not in the
> > > US-ASCII charset correctly.
> > >
> > > Benedikt
> > >
> > >
> > > >
> > > >
> > > >
> > > > Joakim
> > > >
> > >
> >
>

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