.TH BLIND-SET-ALPHA 1 blind
.SH NAME
blind-set-alpha - Multiply the alpha channel of a video
.SH SYNOPSIS
.B blind-set-alpha
[-i]
.I alpha-stream
.SH DESCRIPTION
.B blind-set-alpha
reads a video from stdin and a mask video from
.IR alpha-stream .
The video is printed to stdout, with each alpha value
multiplied by the product of the luminosity and the
alpha value of the corresponding pixel and frame in
the mask video.
.P
If stdin is longer than
.IR alpha-stream ,
the remainder of stdin is printed without any changes.
If stdin is shorter than
.IR alpha-stream ,
the remainder of
.I alpha-stream
is ignored but may be partially read.
.SH OPTIONS
.TP
.B -i
Use the inverse luminosity of the mask video instead
of the luminosity. It is still multiplied by the
alpha value.
.SH SEE ALSO
.BR blind (7),
.BR blind-single-colour (1),
.BR blind-dissolve (1),
.BR blind-transition (1),
.BR blind-arithm (1),
.BR blind-set-luma (1),
.BR blind-invert-luma (1),
.BR blind-set-saturation (1),
.BR blind-extract-alpha (1)
.SH AUTHORS
Mattias Andrée
.RI < maandree@kth.se >