I'm interested in learning how to create gradient maps to emulate a specific toned monochrome print. I understand how a GM can tone a photo.
But is there a technique to extract or match the tones of an existing image? Then I can apply my custom GM to other images.
I think this task does not lend itself to automation well, creating the gradient Map manually seems preferable to me.
Moreover the luminance and contrast of the target image may make manual corrections necessary.
Have you checked out the Color Lookup Adjustment yet?