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diff --git a/man/blind-dual-key.1 b/man/blind-dual-key.1
new file mode 100644
index 0000000..6cfe7b8
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+++ b/man/blind-dual-key.1
@@ -0,0 +1,55 @@
+.TH BLIND-DUAL-KEY 1 blind
+.SH NAME
+blind-dual-key - Apply transparency to a video based on two videos and two key
+.SH SYNOPSIS
+.B blind-dual-key
+.I X
+.I Y
+.I Z
+.I dual-X
+.I dual-Y
+.I dual-Z
+.I dual-video
+.SH DESCRIPTION
+.B blind-dual-key
+reads a video from stdin and a video
+.IR dual-video .
+These two videos should be idential, except
+with two different background colours. The
+background colour used in the video from
+stdin should be specified in the arguments
+.IR X ,
+.IR Y ,
+and
+.IR Z ,
+using the CIE XYZ colour model. The
+background colour used in the video from
+.I dual-video
+should be specified in the arguments
+.IR dual-X ,
+.IR dual-Y ,
+and
+.IR dual-Z ,
+using the CIE XYZ colour model. Using this information,
+.B blind-dual-key
+reconstruct the alpha channel of the video
+and prints the video with its alpha channel to
+stdout.
+.SH NOTES
+.B blind-dual-key
+may be changed in the future to use some other colour model,
+therefore, it is recommended to also use
+.BR blind-colour-ciexyz (1)
+if you are specifying the colour in CIE XYZ.
+.P
+When making a video whose transparancy is recovered with
+.BR blind-dual-key ,
+select to opposite background colours, for
+example black and white or green and magenta.
+.SH SEE ALSO
+.BR blind (7),
+.BR blind-colour-ciexyz (1),
+.BR blind-colour-srgb (1)
+.SH AUTHORS
+Mattias Andrée
+.RI < maandree@kth.se >
diff --git a/man/blind.7 b/man/blind.7
index 79ac8eb..f8295fe 100644
--- a/man/blind.7
+++ b/man/blind.7
@@ -76,6 +76,9 @@ Calculate the dot product of colours in a video
 .BR blind-double-sine-wave (1)
 Apply double-sine-wave repetition to gradient
 .TP
+.BR blind-dual-key(1)
+Apply transparency to a video based on two videos and two key
+.TP
 .BR blind-extend (1)
 Add margins to a video
 .TP