I'm trying to do the exact same thing as How can I map the colors in a greyscale image to a specific color "gradient"?, but am failing for unknown reasons. I think the real problem is that I don't understand what gradient map actually does.
To try to figure out why I wasn't getting the result I was expecting, I created a linear black and white gradient as my test image. I then used the same gradient for my map. My expectation was that my gradient would either remain the same or be reversed. The actual result was quite different, though.
What the heck is happening? How can I get the results I expect?