QImageWriter and EXIF

[SGaist]

Might be, I can't confirm, I don't have images containing such data to test.

[samdol]

@Pablo-J.-Rogina
Thank you, I used it before. but it only reads exif information. Because I want to preserve EXIF after save image, I need a method to read/write exif.

[samdol]

@SGaist
I found that Reading Gps information should be like this,

  qDebug()<<"laa: "<< QString::number(value_GpsLatitude.toRationalVector().at(0).first)+"/"+QString::number(value_GpsLatitude.toRationalVector().at(0).second);
  qDebug()<<"laa: "<< QString::number(value_GpsLatitude.toRationalVector().at(1).first)+"/"+QString::number(value_GpsLatitude.toRationalVector().at(1).second);
  qDebug()<<"laa: "<< QString::number(value_GpsLatitude.toRationalVector().at(2).first)+"/"+QString::number(value_GpsLatitude.toRationalVector().at(2).second);

But I still don't understand why it changes Gps value after

header.saveToJpeg("C:/myfile.jpg");  

It changes even without

header.setValue(QExifImageHeader::GpsLatitude, value_GpsLatitude);

It seems a bug.
You may get test jpg file with gps_tag from here

[Luisa]

@samdol I have the same problem.

If I load metadata and then I save without changing anything I read incorrect value.
Have you find a solution?

QExifImageHeader * source = new QExifImageHeader();
QExifValue *vale;
source->loadFromJpeg(filedest);
source->saveToJpeg(filedest);
QExifImageHeader * dest = new QExifImageHeader();
dest->loadFromJpeg(filedest);

Thanke you for your help

Luisa

[SGaist]

IIRC, when I took a look at it, there was an issue with handling some of the tags. I can't remember exactly what it was.

[Luisa]

@SGaist Do you know a library that I could use to read / write exif files? I need to cross compile it for a system embedded. I tried exiv2 with poor results

[jsulm]

@Luisa https://github.com/libexif/libexif

[Luisa]

@jsulm I try to use this library but I have some problem with GPSAltitude and so on...

Have you some example to write GPS param into file jpg?
and Usercomment field?

Thank you so much

[jsulm]

@Luisa Sorry, I don't have any examples

[Luisa]

@jsulm :-(

[mrjj]

@Luisa
Hi
I was wondering if the sample
https://github.com/libexif/libexif/blob/master/contrib/examples/write-exif.c
combined with the info from
https://libexif.github.io/internals/exif-entry_8c-source.html

EXIF_TAG_USER_COMMENT
EXIF_TAG_GPS_VERSION_ID
EXIF_TAG_GPS_ALTITUDE_REF:

might work ?

[Pablo J. Rogina]

@Luisa said in QImageWriter and EXIF:

I try to use this library but I have some problem with GPSAltitude and so on...

Could you please show the issue?