What is an .XMP file?

Discussion in 'Beyond the Basics' started by kkamin, Oct 11, 2009.

  1. kkamin
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    kkamin New Member

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    I'm new to RAW files, so I see an .XMP file that accompanies it. I believe it is the metadata collected by the camera right?

    1. Why isn't this information embedded directly into the RAW file somewhere?

    2. If I change the metadata of a RAW file within Bridge, will it write to that .XMP file? What happens when I write to the metadata of a JPEG, it writes inside the actual JPEG right?

    3. After I convert the RAW file into a TIFF or whatever, does that .XMP file data get put into the TIFF or whatever?

    Thanks!
  2. Derrel
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    Derrel Mr. Rain Cloud

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    No, the .xmp file is a "sidecar file" that is written only after the RAW file has been handled by software at the computer stage. Adobe's sidecar files carry the .xmp file type--other RAW software creates sidecar files with a different file extension.

    SilkyPix RAW developer software for example uses the file type .spd when correcting a JPEG, but the sidecar files are still written and stored separately from the edited JPEG files.

    I don't think it's correct to call the .xmp file EXIF information, since it's more of a list of editing parameters that have been/should be applied to a RAW image to make it open and look the way the photographer has adjusted the raw files.

    These .xmp files do not have to reside in the same folders as the Nikon .NEF or the Canon .CR2 or the Fuji .RAF RAW files--that is a preference that you can change; if you like, the .xmp information can be stored in a central database, but the default is to create sidecar files that "ride with" the motorcycle, err, with the RAW file...
  3. Josh66
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    Josh66 Well-Known Member

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    Think of them as a 'history' of what you did to the RAW in PP.

    The software can't actually alter the RAW, so it has to save the changes to a separate file.
  4. kkamin
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    kkamin New Member

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    I think I get it.

    1. The metadata in other file formats, jpeg for example is embedded in the file?

    2. Since the .XMP is created after I touch the file with Adobe, what happens if I delete it? Why do I need it?

    3. The metadata will be embedded once I save the file as a TIFF or whatever, right?

    4. If I centralize the .XMP files to a database, how will the RAW know where to find it?

    Thanks, I'm confundito
  5. Derrel
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    Derrel Mr. Rain Cloud

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    The .xmp file is the "recipe" that has a record of the changes and parameter assignments given to the RAW file in an Adobe product. If you discard the .xmp sidecar files, the next time the RAW images are opened, the software will display the images in the default mode.

    So, let's say you import 10 virtually identical portrait images, all raw files, into Adobe Bridge, and you open one and perfect it, and apply a new white balance, boost the saturation a small amount, and set a custom tone curve, and apply a heavy vignette. You then select all the files, and in terms of the raw image development, you click the "Same as Previous Conversion" box. The software will take note of each file's number and the list of changes and tweaks you elected to create, and it will write all that info into a .xmp file for each individual raw image. As long as those sidecar files reside in the same folder as the raw images, the raw files will be opened again with the changes applied. If you ditch the .xmp files, the raws will be opened in their As-Shot form,using the Adobe Camera RAW profile you have set to open say, Canon 5D files with.

    If the database is stored on your computer....the .xmp files do not travel with the database; consequently, I have never elected to have the sidecar files reside in the database, but have always gone with the default and allowed the .xmp files to be placed in the same folder as the raw images.
  6. Garbz
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    Garbz New Member

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    kkamin you're missing a fundamental concept:

    A RAW image is not saved, and not changed on a pixel level. You make changes to a RAW image and the "recipe" (that's a good word for it Derrel) is either saved along side it or in a database. If you delete the database or the XMP file and open the RAW again you will be back to square one. These settings are also not transferable. The RAW doesn't know where to find it's XMP file or where in the database it is located. The CameraRAW or Lightroom databases know which settings are associated with the RAW file. If you go making changes to that RAW in Lightroom then open the RAW file CaptureNX or Aperture you will again be at square one since they have no record of the changes.

    A TIFF or JPEG on the other hand is not metadata and not a recipe. It represents the image on a pixel by pixel basis. Once you save it you overwrite all the pixels in the file as you save. You can't get the original back unless you made a copy or didn't overwrite it when you saved.

    So:
    1. Metadata is saved in JPEG files but these are things like camera settings, and not a recipe for modifications.
    2. When you delete an XMP file after you edit it you will lose all the edits to the RAW file since they are not saved over the RAW file.
    3. Once converted to any format other than RAW the changes are rasterised to whatever the local format permits. Some permit layers and transparencies, some like JPEG just permit the pixel per pixel data.
    4. If you centralise it all, like say Lightroom does, the question is how does Lightroom know where to find the RAW file. That's what will really go wrong, move the RAW and Lightroom is likely to get confused, not the other way around.
  7. musicaleCA
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    musicaleCA New Member

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    And this is why I switched to DNG. Such a headache saver. (I recently asked a Canon rep why their cameras didn't support DNG yet. His response was "Because it's not the right way to do it" and continued on to make an argument for proprietary control of their particular RAW files. What a bloody mess.)

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