P: Ability to invert negative scans to positives (color and black-and-white)

Anthony,

With all the help above, there should be some hints of what to do, but I will say again:  To invert a negative you can do this in LR or Elements too. 

Once you have the negative, click Filer>Adjustments>Invert. 

This will reverse the negative to a positive.  Your positive should respond to any other adjustments in Photoshop (later on that).   Likewise, refer to my answer above and to Todd Shane's answer too. Both of us utilize the Epson v850 scanner.  This scanner gives positives in crisp color and not much needs to be adjusted and all of them will be right-side-up and frontward (label in front).  It takes 12 at a time which is a little work but worth our time. 

Also, I use a 50 slide scanner (3X more expensive) which takes twice as long to scan all 50 but is easier, all 50 slides are negatives, then I invert them to positives.  It's become a routine with a quick zap of the color or fade adjustments, takes less than 2 seconds in a routine.  The 50 slide scanner has a "fog" on each slide as it doesn't scan the best but this can be eliminated and sharpness comes back to a crisp positive with a few quick clicks.  The 50 slide scanner has its faults as it can break down some after 2 years.  It can be fixed for 1/3 of its sale price which is still a little expensive. I am using my old 50 slide scanner for the 5th year as I am getting it refurbished (one time) this year to use for another 3 to 5 years.  We use it for customers at work and its been used for 2000 slides at a time, maybe 3 times now, otherwise, small batches.  Over that scanner, I will recommend the Espon v850 for the best in scans.    

This might be why Adobe has not responded to you.  Elements and LR and Photoshop have always had Filter>Adjustments>Invert for negatives to positives.   When you get used to Photoshop, you will see that the adjustments of the image is fast and easy.  Have a good eye for it so that when its enough quit your adjustments, otherwise, it could run ya stir crazy, don't need to be that perfect.   

Remember all slides are set for a 2X3 foot screens (in the old days) which were in 3000 resolution for the big screen.  Their size will convert to a 4X6 or 5X7 easily.  I scan my photos at only 1000 so they will fit onto a disc better.  The positives converted to a 4X6 at 300 dpi, as follows:  Slides at actual size (1.34" X 0,83") at 1000 dpi, are the SAME SIZE as 4x6 at 300 dpi - they are exactly equal.  Your Photoshop does batch conversions for this.  Look in elements under File>ProcessMutilplePhotos.  In that dialog box, you can convert to 4X6 size AND to 300 dpi size at the same time, AND keep at TIFF (RAW) for photo prints, OR convert from TIFF to JPEG if you want a slide show.  For a slide show, be sure to make them 4X6 size JPEG (at 300 dpi) so the screen will show them big enough.  AND, don't use a slide show software which only sets them to a show and  nothing else.  Instead, just put them info a folder, and in Windows Media Player select the folder and it'll run your photos as a show on screen.  Also, your TV might have a USB port which will run the photos automatically the same way, no slide show software needed and you don't need Windows media player.  The TV has all you need to run it from a flash drive on the TV.  

I have the experience since I have done this for my customers a lot.   
I hope all of this has helped some of you.   

Steve Lehman, mcse   

I've encountered no issues with color or B&W negative film. Noise Reduction works well to reduce grain visibility. Sharpening typically requires higher settings, but also works well. Fine-grain 35mm film shot with a good lens looks a live camera shot. The biggest issue in LR is dust spot and scratch removal. The Spot Removal tool is pretty crude and slow compared to PS's Spot Healing Brush with Content-Aware Type selected.

Event though, all the other sliders are then « inverted ».
I’m not sure how the sharpness and noise reduction algos cope with such images...

Did you remember to make a preset for that curve? That is almost as quick as a button.

Thank you all for the comments on my parallel comment, which was merged to this one.
To address a few points:
1. I use a self-made negative/slide scanner made out of wood, lighting and a canon 7d. Once I upload to the computer, I transfer to my mobile via network drive;
2. Yes, you are able to use the curve to invert the negative into positive. However it would be great to have a quick button (function) to make the process faster. Imagine, I have over 500 negatives. To do this into all via mobile is not smart.
Thanks again.
Regards
Rodnei

Feature to invert negatives. Can do in desktop but not in mobile app.

Since Adobe is the developer and owner of the DNG specification it shouldn't be too difficult for them to implement a raw data invert function that doesn't also invert the LR controls. The primary issue is how to implement this capability AND maintain compatibility. Some more info here: http://dcptool.sourceforge.net/DCPFIles.html

The processing pipe
So, this is how, in vastly simplified form, you process your raw data in context of a DNG Camera Profile, assuming the Forward and Reduction Matrixes are not present (see the specification for more detail😞

    
    1.Linearize, rescale, do black level compensation, clip, etc.
    2.Derive interpolated ColorMatrix and HueSatDelta matrixes based on the color temperature.
    3.Get to an XYZ (absolute color space) via the interpolated ColorMatrix.
    4.Convert to HSV.
    5.Apply the interpolated HueSatDelta mapping table to get new colors.
    6.Convert back to XYZ.
    7.Do your exposure compensation, fill light, etc in whatever color space you want
    8.Convert to HSV, apply the LookTable and ToneCurve, convert back. Or, if I read the spec right, use the LookTable and the ToneCurve as the basis for your adjustment settings

"Also, you cannot auto white balance on the inverted negative. It seems like it should work, but the Adobe SDK on profiles said that the profiles are applied at the end of the image rendering process, so the white balance tool is still seeing the non-inverted image."

What if you did the inversion with the profile's HSV look table rather than the RGB LUT?  The SDK documentation says that the HSV look table is applied earlier in the image pipeline, so maybe it's applied before any of the Develop settings.  If so, then you could do white balancing and the sliders wouldn't be inverted?

I only have a fuzzy understanding of how one might create such HSV look tables in this instance, though.

Also, you cannot auto white balance on the inverted negative. It seems like it should work, but the Adobe SDK on profiles said that the profiles are applied at the end of the image rendering process, so the white balance tool is still seeing the non-inverted image.

Yet another reason for Adobe to do some additional work and fix both.