With students new to digital photography and who are capturing in jpeg out of fear for the difficulties they assume go with RAW, I have found it useful to have them open some of their jpeg files in Adobe Camera RAW. They become familiar with the tools there and are willing to switch to RAW capture.
My question is this: What happens to that jpeg image if they set ACR to 16 bits and they continue to open their jpeg image into Photoshop (or Elements) with ACR set to 16 bits. Since that data isn't contained in the jpeg file, what does ACR do? Does it "manufacture" extra data?
With either 8-bits or 16-bits black is 0 and white is the highest possible number, so adding bits just adds precision to the numbers, not extra data. With 16-bits you get 256 colors between each of the original 256-colors of the 8-bit JPG so it’s like having fractional colors compared to the original 8-bit colors.
An analogous situation using decimal numbers might be: if the JPG starts with 3 decimal digits of precision then the numbers could range from 000 to 999 with 000 being black to 999 being white, but if you doubled the number of digits to 6 then the color numbers would range from 000.000 to 999.000. These are exactly the same values as we started with, but if we choose to manipulate the colors, which is the point of using ACR in the first place, then we don’t lose information.