PNG tEXt vs PNG iTXt

[dev.WsC]

Hello,

I am trying to write a title into a PNG file using the exiftool. That works well but it will end up in both PNG tEXt and PNG iTXt.

The Problem now is that if I try to modify the title with a different tool (iTag) this tool modifies only the PNG iTXt. When I now try to read the title using the exiftool again it will return only the unmodified title from PNG tEXt.

There are some ways around this problem but I did not manage to achieve one of them:

  1) Writing only to PNG iTXt
  2) Removing only PNG tEXt
  3) Reading only PNG iTXt and ignoring PNG tEXt

I tried already passing -charset UTF8 but with no success so far. Also accessing the group or tags directly did not work for me. Maybe I do not have the correct names for the group or tag?

I always end up with the following (only the relevant parts extracted with -v option):

Writing the title to the PNG with exiftool:

Code Select Expand


PNG iTXt (1652 bytes):
  + [XMP directory, 1630 bytes]
  | XMPToolkit = Image::ExifTool 10.63
  | Title = FirstTitle
...
PNG tEXt (16 bytes):
  | Title = FirstTitle
PNG IEND (end of image)


And after changing it with iTag:

Code Select Expand


PNG iTXt (1652 bytes):
  + [XMP directory, 1630 bytes]
  | XMPToolkit = XMP Core 4.4.0
  | Title = ChangedTitle
...
PNG tEXt (16 bytes):
  | Title = FirstTitle
PNG IEND (end of image)


Does anyone know how I can achive one of my three ways around this problem using exiftool or even has a better way to do it?

Any help is highly appreciated.

Andy

[Phil Harvey]

Hi Andy,

I now try to read the title using the exiftool again it will return only the unmodified title from PNG tEXt.

ExifTool will show both.  Add the -a option to see duplicate tags, and -G to see where they are stored.

From your verbose output, I see that the iTXt you are talking about is in fact XMP, accessed via XMP:Title.  The other one is PNG:Title.

It looks like iTag writes only XMP, not PNG tags.  To do this with ExifTool, write XMP:Title, not just "Title".

- Phil

[dev.WsC]

Hi Phil,

thanks a lot for answering this so fast.

That helped a lot.

With you your answer I can work around iTag in more than one way :-)

I chose to only write the XMP:Title in the first place and also to only read the XMP:Title after iTag changed it. I also was able to remove only the PNG:Title and keep the XMP:Title from the files already tagged and changed.

Thank you so much!

- Andy