What does the title of the movie "A Scanner Darkly" mean?

In a comment, our seasonally named Cascabel wrote:

The makers of the movie are playing on the phrase "a mirror (glass), darkly" It seems to originate in 1 Corinthians 13:12.

Also in a comment, StoneyB also wrote:

Cascabel's got it. The verse (AV) is "For now we see through a glass, darkly; but then face to face: now I know in part; but then shall I know even as also I am known."

jlovegren says in a comment:

The significance of the title is revealed in Chapter 13 of the book, in a conversation between the protagonist and two psychologists, as they discuss his impaired brain function. He has difficulty recognizing himself in video recordings (made with a scanner), and the psychologists explain that his brain is processing input in a mirrored fashion. The protagonist then reflects on St. Paul's letter to the Corinthians.