I cannot get hold of the XMP standard at the moment, all linked pages seem to be down. I would like to know how it defines the region of interest, e.g. to mark a face. As far as I remember, I should specify the centre of RoI and its width and height, with relative coordinates. But which corners do (0, 0) and (1, 1) correspond to?

1 Answer 1


The XMP files created by Lightroom seems to follow the MWG description (website currently down), as it contains this link to describe its content :


I took a random XMP file from one of my picture containing a recognized person : the part mwg-rs:Region is structured as follows :

<mwg-rs:Regions rdf:parseType="Resource">
        mwg-rs:Name="The name part"

You can see that for this image, the region is specified by an "Area" structure, containing 4 values, which appear to be percentages relative to the whole image :

  • stArea:x and stArea:y are the coordinates of the center of the area, relative to the upper left corner of the image
  • stArea:h and stArea:w are the height and the width

So to answer your question, (0,0) is the upper left corner of the pictures and (1,1) is the lower right corner.

As a side note, I don't know how the "Rotation" parameter of the mwg-rs Description part comes to play: at your place, I would make some tests :)

  • Thanks for answering about the coordinate system. However: are you sure stArea:x, y refer to the corner of the area? I would expect (and also vaguely remember) that it's the centre.
    – texnic
    Apr 9, 2019 at 12:36
  • I found my own old question where the exampl shows that (x, y) probably define the centre of the region (x+w and y+h are both >1).
    – texnic
    Apr 9, 2019 at 12:39
  • You are right regarding the area:x and area:y parameters, I edited my answer.
    – Olivier
    Apr 9, 2019 at 16:19

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