Bas-relief manual

Let's take this sea landscape:

Select the sea using Pen Tool. Choose Gradient Tool, take the foreground colour as white, background colour as black. Make the gradient filling down-top. Then select the sky, desaturate it, make Auto Contrast. Then use the semi-transparent gradient filling with 80% opacity. Make Auto Contrast again. Draw the seashore with a black colour. This is our depth map:

gradient filling the sea semi-transparent gradient filling the sky with 80% opacity drawing the seeshore with a black

This is the anaglyphic image:

This is the animated image: