.TH LIBCOLOUR_CIELCHUV 7 libcolour
.SH NAME
LIBCOLOUR_CIELCHUV - CIE LChuv
.SH DESCRIPTION
CIE LCh_uv [\(aq_\(aq denotes subscript of
subsequent characters] (also known as CIE HLC_uv)
colours are presented with either of
.nf

	typedef struct libcolour_cielchuv_f libcolour_cielchuv_f_t;
	typedef struct libcolour_cielchuv_lf libcolour_cielchuv_lf_t;
	typedef struct libcolour_cielchuv_llf libcolour_cielchuv_llf_t;

.fi
These
.BR struct s
use
.BR float ,
.BR double ,
and
.BR long\ double ,
respecitively, for the values stored in them,
and are otherwise identical.
.B struct libcolour_cielchuv_f
is defined as
.nf

	struct libcolour_cielchuv_f {
		enum libcolour_model \fImodel\fP;
		float \fIL\fP;
		float \fIC\fP;
		float \fIh\fP;
		struct libcolour_ciexyz \fIwhite\fP;
		double \fIone_revolution\fP;
	};

.fi
.I .model
shall be set to
.BR LIBCOLOUR_CIELCHUV .
In
.BR union\ libcolour_colour_f ,
.BR union\ libcolour_colour_lf ,
and
.BR union\ libcolour_colour_llf ,
.I .cielchuv
is used for CIE LChuv colours.
.P
.IR .L ,
.IR .C ,
and
.I .h
hold the L* (luma), C*_uv (chroma), and
h_uv (hue) values, respectively,
.I .white
is the white point, and
.I .one_revolution
the The value lowest positive values of
.I .h
that is equivalent to 0. 360 if the hue is measured
in degrees, 400 if the hue is measured in gon, and
2 pi if the hue is measured radian. Any value can
be used.
.I .white
and
.I .one_revolution
are not part of the colour, but rather part of
the colour space.
.P
L* is 0 in black and 100 in white.
.P
The call
.BI libcolour_proper(& c )
on a
.B struct libcolour_cielchuv_t
.I c
sets
.I c.white.model
to
.BR LIBCOLOUR_CIEXYZ ,
and if
.I c.one_revolution
is 0, it is set to 360.
Zero is always returned in this case.
.P
CIE LCh_uv approximates uniform human colour
perception using cylindrical representation.
.P
CIE LCh_uv is not additive. It is a cylindrical
representation of CIE 1976 (L*, u*, v*).
.SH SEE ALSO
.BR libcolour (7)
.SH AUTHORS
Mattias Andrée
.RI < maandree@kth.se >