In Capture One, you have two choices, essentially, when you right-click on an image:
Edit with...
and
Open with ...
If you choose "Edit with...," Capture One will render your raw file to an RGB file and then pass that image file to the application you have chosen. If you choose "Open with....," Capture One will pass the raw file to the selected application - what you do with the raw file once in the that application is up to you.
The other thing to consider is that the DNG specification permits different types of DNG file variants. DxO, for example, has always produced a "linear" DNG as its output - this means that pixel operations like PRIME denoising can be exported from DxO as a DNG because that DNG is a "linear" - meaning demosaic'ed - DNG.
The workflow you are probably trying to achieve is:
1) Import your raw files into Capture One.
2) Choose the raw file you want to pass to DxO for PRIME noise reduction, lens corrections, etc.
3) Right-click on that file and choose "Open with..." (or, from the menus: Image > Open with...) and select DxO PhotoLab 3. This should launch PL3 and open the raw file in PL3.
4) Do your corrections to the raw file in PL3 (PRIME NR, lens corrections, anything you want, really).
5) Once you are satisfied, in PL3 choose: "Export to Application" (there should be a button in the lower right of the interface, otherwise: Image > Export > Export to Application) and choose Capture One 20. See the attached screenshot - in this dialog, you can specify DNG as the exported file type. This DNG will be a linear DNG that has already been demosaic'ed to include all of the adjustments you applied in PL3. But, it will still be a DNG, so you can use a DNG workflow with it.
6) Once you hit OK, the resulting (new) DNG file will be passed back to Capture One as: <filename>_openWith.dng.
There you go. Now you can continue editing your DNG in Capture One, with the PRIME corrections applied in DxO. If you really want to use Capture One for all of the actual tonal and color edits, then don't do them in DxO, just apply NR and lens corrections there, for example.
I hope this is what you were looking to do.
Good luck!
kirk
PS - When I select a raw file in Capture One and then use the "Edit with..." option, I can only export a TIFF or JPEG to the external application of my choosing. That is, DNG is not a choice. Are you sure that it is when you are following the steps you describe in your original post? See second screenshot. Maybe it is a Mac v PC thing.

Image hosted by forum (
1025468)
© kirkt [SHARE LINK] THIS IS A LOW QUALITY PREVIEW. Please log in to see the good quality stuff. Image hosted by forum (
1025470)
© kirkt [SHARE LINK] THIS IS A LOW QUALITY PREVIEW. Please log in to see the good quality stuff.