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From Joakim Knudsen <joakim.gr...@gmail.com>
Subject Re: Creating EXIF tags (TiffOutputField) the right way
Date Sat, 28 May 2016 19:10:26 GMT
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)?

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);



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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