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I want to blend two DNG shots additively (emulating multiple exposure) and use RawTherapee to develop the result with its full spectrum of raw processing functionality.

What options for such DNG manipulation are available, if any?

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    \$\begingroup\$ If you do so you run the risk to alter data that RawTherapee would use for a correct result. What makes you think the result would be superior to editing images separately in RT (editing one and reusing the recipe on the others) and blending the result in a regular app (PS, Gimp...) ? \$\endgroup\$
    – xenoid
    Aug 2, 2020 at 10:00
  • \$\begingroup\$ The potential advantage of having more dynamic range in raw verses a developed JPG of only 8-bits per color can be matched by outputting 16-bit TIF instead. At that point you can merge first then edit, as is typically done with stacking. \$\endgroup\$ Aug 2, 2020 at 17:37
  • \$\begingroup\$ @user10216038 after the merging I want to be working with a scene-referred image still, I don't think it will be so if raw was bounced to TIF. \$\endgroup\$ Aug 2, 2020 at 19:47
  • \$\begingroup\$ Blending in add or screen mode should be a straightforward operation against raw pixels, all shots coming from the same camera, but I guess operating on raw image data is uncharted territory so far. \$\endgroup\$ Aug 2, 2020 at 19:48
  • \$\begingroup\$ not all of RawTherapee tools work on TIF files, too. Some require a DNG. \$\endgroup\$ Aug 2, 2020 at 19:50

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As far as I know, there is no publicly available program for blending sensor data of two shots before demosaicing and rastering it as a viewable picture.

While I could image this to be valuable in scientific fields, I cannot imagine any advantage apart from having to blend the data blindly vs seeing what I am doing after the base conversion.

So basically, there are no options for this unless you write your own raw data blender, which probably would take a lot of time and will not improve the image in any real way.

I can understand, that you want to skip the roundrtrip in a photo editing software and want to achieve something in your raw developer, that the program simply is not made for.

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  • \$\begingroup\$ It’s for creative effect—a prerequisite for achieving true film-like double exposure look, for example. This has to be applied to scene-referred image state, so the raw can be developed after that with full regular workflow. /// I know I can’t do this in my raw developer software and that’s fine, since that’s not what it’s for. “Roundrip to photo editing software” sounds kind of like it, but that software must be able to either destructively edit a given DNG, or write a new DNG that preserves everything and only performs one specific operation on each pixel obtained from the sensor. \$\endgroup\$ Aug 4, 2020 at 2:50
  • \$\begingroup\$ So far I believe this requires writing a new tool using Adobe’s DNG SDK. Sadly. \$\endgroup\$ Aug 4, 2020 at 2:51
  • \$\begingroup\$ I don’t see a problem with “blindly” (after all, that’s how photography worked for a long time). \$\endgroup\$ Aug 4, 2020 at 2:56

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