Photo curves adjustment grey colour space.

[GeoffM33]

Whilst experimenting with alternate ways to make a black & white version of an image I tried the live curves adjustment layer and chose the grey colour space in the curves drop-down. Adjust the curve in the usual way and the image becomes mono (but we knew that). It can then be saved out as a mono pic. Good. I then looked in the Master curves drop down and found options for "intensity" and "alpha". Alpha does not seem to be relevant for this exercise, but "intensity" has some dramatic effects. You can get some really crackling old style black & white results by juggling Master and Intensity settings. Put a selective colour adjustment (or similar) layer under the curves layer and you can further modify/target the curves results.

So why am I posting this? 1. To share it, and 2. to ask what "intensity" is and why it behaves as described above. What is its official purpose?

Yours, intrigued, GM

[R C-R]

Maybe I'm being too simplistic about it but in this context isn't "intensity" just greyness?

[loukash]

8 hours ago, GeoffM33 said:

alternate ways to make a black & white version of an image

Turning the Levels adjustment into Gray mode will have exactly the same effect as the 30/89/59/70/11/41% "true BW" setting in the Black&White adjustment.

Oddly enough, not so in the Curves adjustment, unless you move one of the curve nodes by at least 0.001, or add a third node somewhere.

[GeoffM33]

Loukash. Thanks for your comments and the useful b/w settings values. I have made a preset of that. Also for your insight into Levels Gray and Curves behaviour. Best wishes. Stay safe.