.TH IM_LINTRA 3 "24 April 1991"
.SH NAME
im_lintra, im_lintra_vec \- performs a linear transformation on an image
.SH SYNOPSIS
.B #include <vips/vips.h>

.B int im_lintra_vec(n, a, in, b, out)
.br
.B int n;
.br
.B double *a, *b;
.br
.B IMAGE *in, *out;

.B int im_lintra(a, in, b, out)
.br
.B double a, b;
.br
.B IMAGE *in, *out;

.SH DESCRIPTION
.B im_lintra_vec(3)
performs a linear transform on image in, that is, it calculates

  out = a * in + b

.B a
and 
.B b
are vectors, ie. arrays of constants of length
.B n.
If 
.B in
has one band, then the vectors may be any length and the output image will
have the same number of bands as the length of the vector. If 
.B in
has many bands, then the vector must be length 1, or have the same length as
the number of bands in the image. 

If the input format is one of the integer types
then output is float.  In all other cases the
output is the same as the input.

.B im_lintra(3)
is a convenience function which calls
.B im_lintra_vec(3)
with a vector of length 1.

.SH RETURN VALUE
The function returns 0 on success and -1 on error.
.SH BUGS
The function does not check for under/overflow
.SH SEE\ ALSO
im_exptra(3), im_logtra(3)
.SH AUTHOR
N. Dessipris \- 24/04/1991
.br
J. Cupitt (rewrite) \- 21/7/93