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?
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.
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.