Deleting tags in: XMP XMP-*
Sorry, XMP-x:XMPToolkit is unsafe for writing
  Writing new tags after deleting groups: XMP XMP-*
Writing XMP-dc:Subject
  Editing tags in: PNG XMP 
  Creating tags in: PNG XMP 
  FileType = PNG
  FileTypeExtension = PNG
  MIMEType = image/png
PNG IHDR (13 bytes):
PNG bKGD (2 bytes):
Creating XMP iTXt chunk:
  Creating XMP
    + XMP-dc:Subject = 'test'
PNG IDAT (1 chunk, total 14 bytes)
PNG iTXt (437 bytes):
  Deleting XMP
PNG IEND (end of image)