Adobe Camera Raw (ACR) 11.4 - Depth

[paulh51497126]

In ACR it is possible to set a depth for an image of either 8 or 16 bits per channel. The online help doesn't mention this option. What is the effect of applying 8 or 16 bits to an image?

(Moved to the ACR Forum and Merged with another ACR question by the same user by Moderator)

[paulh51497126]

I have been applying various profiles to my RAW files because it can produce some quite pleasing effects. But I'm not sure what these profiles are, and I can't see any explanation in the online help. For example, what is the difference between the Adobe Landscape and Camera Landscape profile? Where does ACR get this info from?

[elie_dinur]

A profile is first of all a collection of curves or LUTs that record the unique color rendering characteristics of a particular sensor/ camera model, so that the proper adjustments can be made to bring the colors to an agreed standard space. The maker creates a profile based on “insider” information they have – after all, they manufactured the micro-filters, sensor, etc. to certain known specs. Third party Raw converters have to use profiles that have been reverse-engineered. After obtaining a basic “standard” profile, additional curves are added on top of it to create “looks” or “styles” by altering tones and colors to what consumers supposedly want; a range of Adobe renderings that will theoretically be the same for any camera, or a range of Camera Matching styles imitating those done by the camera for jpg output.

[Per Berntsen]

Clicking the underlined text bottom center in the ACR window will open the Workflow options, where you among other things can set the the bit depth of the image. 

8-bit has 256 levels (shades of colors) per channel (red green and blue), a total of 16.7 million colors.

16-bit has 65,536 levels per channel, a total of 281 trillion colors.

Working in 16-bit gives you editing headroom. If you do heavy editing on an 8-bit image, you'll lose a lot of the original levels in the image, which will lead to banding - transitions between shades are no longer smooth - and the histogram will look like a comb because of the missing levels. Heavy editing on a 16-bit file, on the other hand, will not have any detrimental effect.
If you have finished editing in ACR and just want to use the image for printing, use 8-bit.

For example, what is the difference between the Adobe Landscape and Camera Landscape profile? Where does ACR get this info from?

I only use one profile - Adobe Color - but I think Camera landscape is an attempt by Adobe to mimic a corresponding profile in your camera (camera matching profile), whereas Adobe landscape is a more generic profile, not made for any particular camera.

All these profiles are part of the ACR installation.