It’s a 16-bit per channel TIFF in the ProPhotoRGB colorspace, using lossless zip compression.
If you want customize this, you can do that using a custom export preset.
From that link…
You may find that you want to have greater control over how and where the positive copies are made. This is possible to do now in Negative Lab Pro, but takes a little bit of setup.
- Select an image, and go to File > Export
- From the left pane, select the preset for “NLP - Positive Copy - TIFF”
- From here, you can customize all the export settings you want – both NLP metadata settings (which we’ll look at later) and regular export settings (like file naming, export location, color space, etc)
- IMPORTANT - now you need to SAVE your new export preset. Once your settings are how you want them, click “add” , then enter a preset name and folder.
- You can now access this anytime by right-clicking an image, selecting export , and then selecting your custom export preset.