PNG files and XMP metadata

[insanetesterftw]

XnViewMP writes XMP metadata in PNG files in the incorrect chunk, in the tEXt instead of iTXt, causing bad interaction with other applications which might lead to file corruption or loss of metadata.

EXAMPLE

I used two applications to write metadata to a PNG file: XnViewMP and Daminion.

The first example is from Daminion:

Code: Select all

iTXtXML:com.adobe.xmp     <?xpacket begin="" id="W5M0MpCehiHzreSzNTczkc9d"?>
<x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="XMP Core 5.4.0">
 <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
  <rdf:Description rdf:about=""
    xmlns:tiff="http://ns.adobe.com/tiff/1.0/"
    xmlns:photoshop="http://ns.adobe.com/photoshop/1.0/"
    xmlns:exif="http://ns.adobe.com/exif/1.0/"
    xmlns:dc="http://purl.org/dc/elements/1.1/"
    xmlns:xmp="http://ns.adobe.com/xap/1.0/"
   tiff:Orientation="1"
   photoshop:DateCreated="2015-02-23T02:09:39"
   exif:DateTimeOriginal="2015-02-23T02:09:39"
   xmp:MetadataDate="2015-02-26T12:45:18"
   xmp:ModifyDate="2015-02-26T12:45:18">
   <dc:description>
    <rdf:Alt>
     <rdf:li xml:lang="x-default">Daminion EXAMPLE DESCRIPTION</rdf:li>
    </rdf:Alt>
   </dc:description>
  </rdf:Description>
 </rdf:RDF>
</x:xmpmeta>
<?xpacket end="r"?>

The second example is from XnViewMP Version 0.72 x64 (Dec 19 2014):

Code: Select all

tEXtXML:com.adobe.xmp <?xpacket begin="" id="W5M0MpCehiHzreSzNTczkc9d"?>
<x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="XMP Core 5.1.2">
   <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
      <rdf:Description rdf:about=""
            xmlns:dc="http://purl.org/dc/elements/1.1/">
         <dc:description>XnViewMP EXAMPLE DESCRIPTION</dc:description>
      </rdf:Description>
   </rdf:RDF>
</x:xmpmeta>
<?xpacket end="w"?>

And this is how XnViewMP shows it:

Screen Capture

Screenshot - 26-02-2015 , 12_47_08.png (8.91 KiB) Viewed 14770 times

XnViewMP also appears to be using an old version Adobe's XMPCore. The most recent is 2014.12. http://www.adobe.com/devnet/xmp.html

Thank you.

[xnview]

could you send me an example of png with iTxt chunk?

[insanetesterftw]

I hope that posting here as an attachment is enough.

[xnview]

See Issue 621 for current status and details.

iTXt is better to save XMP??

[XnTriq]

PNG – inside an "iTXt" text block with the keyword "XML:com.adobe.xmp"

iTXt contains UTF-8 text, compressed or not, with an optional language tag. iTXt chunk with the keyword 'XML:com.adobe.xmp' can contain Extensible Metadata Platform (XMP).

An XMP packet is embedded in a PNG graphic file by adding a chunk of type iTXt. This chunk is semantically equivalent to the tEXt and zTXt chunks, but the textual data is in the UTF-8 encoding of the Unicode character set, instead of Latin-1.

The Chunk Data portion is the XMP packet. The packet must be marked as read-only. XMP software that is not aware of the file format must not be allowed to change the content of the XMP packet because of the CRC checksum following the chunk data.

There should be no more than one chunk containing XMP in each PNG file. Encoders are encouraged to place the chunk at the beginning of the file, but this is not required.

The PNG data format is shown in Table 9.