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A friend who was part of the team that developed the D5 firmware said it was a nightmare trying to satisfy demands from customers expecting their old lenses to work like modern lenses with with no weird colour casts, aberrations, softness. In the end, they had to draw the line somewhere.
I still say the approach is do what you can in camera but use an out of camera application. Trying to do it inside the camera is like trying to fit 10 kilos of ramen in a saki glass.
One approach might be to make a cloud application. You control everything then (e.g. OS, Processing Power). Figure out a tier pricing for 500, 1000, etc. adjustments per month. I'd like to say 100 free every month, 500 starts at $5.00 USD, $10 for 1,000, and give a discount to NPS members.
Once you get the math down you could move it to iOS, as it's the most controlled platform of the major mobile ones. This would be a killer iPad Pro app. I'm sure Apple would help you folks port it. Sell it for $5.00 for your first 10 lenses for one year of use. $5.00 for each additional 5 lenses. Just keep rolling updates out, charge $5.00 per major release, no more or less, micro payments and trust the volume of loyal Nikon-aholics to make it happen.
Ignore Android, you will be pulling your hair out. Then if you have the demand Mac, Linux and Windows. You might look into plug-ins to different post processing software (e.g. Adobe).
Don't try to do too much, just adjust for the classic glass, no cropping, no dodging, no burning, output the same RAW format and/or JPEG, nothing more. Lots of other software out there that your customers already have to do post processing. Getting them to change will dramatically increase the .
Cloud based apps are the perfect platform as you control all aspects of it and you dial up the memory/processor as you need.
While I haven't done any firmware work, I did a LOT of development in early computers what have less power and space than cameras do today.
B2 (;->