Remember, the settings of lit color and shadow color are supposed to come from your photo. You're supposed to find and area of an existing real shadow, and sample the color outside and inside the shadow. The shader will then reproduce those same colors.

You haven't shown me what you're using, nor an example of a real shadow in the photo, so I'm only guessing here.

Nor have you shown me the calibration image, so I can't tell if you really got black and white or not. If you did not get black and white, in particular if the calibration white isn't white, the shadow strength will never reach its maximum.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)