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Are there any applications (Windows or Linux) that support the .nar format that is used by Windows Phones to store HDR images? In particular I am wondering if there are programs that allow to change the HDR exposure of the image in the same way as can be done on the phone when I download the .nar container (which can be opened as a zip archive) to a computer.

In the .nar container I find the following files:

  • EV0.jpg, ArtisticHDR.jpg, NaturalHDR.jpg
  • content.xml
  • richsettings.xml

content.xml basically contains a listing of the files:

<image properties="Natural">NaturalHDR.jpg</image>
<image properties="Artistic">ArtisticHDR.jpg</image>
<image properties="Original">EV0.jpg</image>

richsettings.xml contains a "blend value":

<BlendValue>0.57000000000000006</BlendValue>

and some tags that seem to be references to the images but they are integers and so I am not sure which jpegs they refer to (e.g. <Reference>0</Reference>).

As the archive contains the "original" image but none with higher / lower exposure (only *HDR.jpg that are already processed) I am tempted to assume that the photo app (when you re-adjust the exposure) only interpolates between two of the files in this archive? This would be easy to do in any image editing software.

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First off, note that HDR is actually a bit of a misnomer. The feature, originally named "Rich Capture", handles more than just scenes with high contrast, which HDR was originally intended for. Depending on the amount of ambient light and whether or not flash is enabled it can also take multiple exposures with and without flash (Dynamic Flash) or with a shorter and longer shutter speed (Dynamic Exposure). See this article at AAWP for more information on how the different modes are triggered.

As far as actual HDR (i.e. capturing the scene at multiple exposure levels) is concerned, you're right in that in such a case the .NAR file only contains three pre-processed versions of the scene, with varying levels of "HDR-ness" (from none to a lot), that you can simply blend between. If you want the actual exposures so you can do your own compositing on a PC, you'll have to enable RAW capture (choose the JPG+DNG option in Camera settings), if your phone supports it, though this will of course use a lot of storage (the Lumia 950's .DNG files for example, are about 25 MB in size, and you'll get three per shot).

As for editing HDR photos on a PC, in Windows 10 you can simply use the Photos app in the same way as on your phone - click on the "Choose the best lighting" option at the top right. The only catch is that you'll have to manually copy over the .NAR file to the same folder where the .JPG is, because it doesn't get uploaded to OneDrive automatically.

Alternatively, you can use pretty much any photo editing software you have that supports layers. Simply extract the three .JPG files from the .NAR file, copy them to the image editor and play with layer opacity until you've achieved the blend you want. You can ask for specific recommendations for software that can do that at http://softwarerecs.stackexchange.com.

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As a matter of fact there is one application. You change the HDR exposure in the Photos app when you are running Windows 10 Mobile, and one the desktop, guess which application you can use to do the same thing:

enter image description here

Yes, the Photos app again.

The trick is in importing the photos and the .nar packages into the same folder, rather than importing just the pictures (the basic type of import done by most media import tools like Windows Media Player, Adobe Bridge etc). I would ideally recommend File Explorer to do that task. Try it

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