This one is complicated and brief. It may make more questions come my way, but here goes.
You can convert 8bit color images into 16bit color images that act (a bit) like 16bit images if the original has grain texture (aka it’s a raw film scan in 8bit Lab or RGB).
1. Open your raw film scan, covert to 16bit, then convert to Adobe RGB.
2. Upscale at least more than 10% using preserve details in photoshop (no noise reduction yet). This will do an initial interpolation into 16bit.
3. Open Camera Raw Filter and reduce the color noise by 20 to 40 percent.
4. At this point you can also reduce the luminance noise a bit (if you want to).
This effectively uses a 4th channel of data (aside from R, G, and B channels) to register a near 16bit image. That is the location data of the film grain!
The luminance bit depth in an 8bit RGB is immense. When you separate the luminance out in 16bit space and then wash the chroma (colors) together (in 16bit space at a higher resolution) the image is actually interpolated into 16bit.
best and happy Wednesday!