When creating b/w photos I usually run thru the channels and pick 2 that I like to mix via Apply Image or Calculations. Sometimes I really like just one channel but noticed that when I apply image it doesn't look like the channel I'm previewing and adjustments are needed.

Is there a standard curve to replicate what one channel looks like if using apply image in RGB?

One is color managed while the other isn't?

Why not use the B&W adjustment layer, or the channel mixer set to monochrome?

You see a difference between Apply Image and just grabbing a channel because of the setting for your Gray Working Space under Color Settings. This is a little known and less discussed issue.

The RGB channels will vary depending on the Gray Working Space setting. Just about any channel operation will give different results depending on this setting. Every channel op expect Apply Image that is. Apply Image ignores the Gray Working Space setting and uses the value of "Gray Gamma 1.8" all the time.

Some demos to explain:

Load any image, go to the channels pallet and select any individual channel. With that channel displayed, go to Edit/Color Settings and cycle through the options for the Gray Working Space. Watch the display change.

With any option set, copy a channel and paste it back as a layer. Now cycle through the Gray Working Spaces again and see that the "gray" layer does NOT change. That's because it's now a full RGB layer and not subject to the Gray Working Space.

And for another test:

Set your Gray Working Space to "Gray Gamma 1.8".  Do an Apply Image comamnd of any channel to the image itself in normal blend mode. Compare that result to the actual channel you used. They should look the same. Set the Gray Working Space to some other value (Dot Gain 10%) and do the same Apply Image again. You should see the same results as the first Apply Image, proving that Apply Image does not care what the Gray Working Space is.

Cool, thanks for the explanation and examples.