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diff --git a/libred_get_temperature.3 b/libred_get_temperature.3 new file mode 100644 index 0000000..f5e8883 --- /dev/null +++ b/libred_get_temperature.3 @@ -0,0 +1,89 @@ +.TH LIBRED_GET_TEMPERATURE 3 LIBRED +.SH NAME +libred_get_temperature \- Calculate the temperature of a colour +.SH SYNOPSIS +.nf +#include <libred.h> + +double \fBlibred_get_temperature\fP(double \fIr\fP, double \fIg\fP, double \fIb\fP, double *\fIY\fP, + double *\fIr_error\fP, double *\fIg_error\fP, double *\fIb_error\fP); +double \fBlibred_get_temperature_xy\fP(double \fIx\fP, double \fIy\fP, double *\fIx_error\fP, double *\fIy_error\fP); +.fi +.PP +Link with +.I -lred +.IR -lm . +.SH DESCRIPTION +The +.BR libred_get_temperature () +function parses +.RI ( r , +.IR g , +.IR b ) +as a colour encoded in sRGB with values between 0 and 1 +and with the sRGB transfer function applied. From that +it calculates the CIE Y (luminosity) of the colour and +stores it in +.I *Y +and then normalises the the colour to have Y = 1 and +calculates the closest matching colour temperature, +which is returned. +.PP +The calculated temperature may not line perfectly with +the colour so the difference between the colour of the +returned temperature and the input colour (after +normalisation to Y = 1) is returned in sRGB as +.RI ( *r_error ", " *g_error ", " *b_error ), +interpreted the same way as +.IR r , +.IR g , +and +.IR b . +.PP +The +.BR libred_get_temperature_xy () +function is a variant of the +.BR libred_get_temperature () +function that uses the CIE xy colour space +(CIE xyY with Y = 1). Unlike sRGB, CIE xy +does not have a transfer function, so the values +are linear, and the values also do not have any +limits and does have a natural interpretation. +.PP +Any of +.IR Y , +.IR r_error , +.IR g_error , +.IR b_error , +.IR x_error , +and +.IR y_error +that is +.I NULL +is ignored. +.SH RETURN VALUE +The +.BR libred_get_temperature () +and +.BR libred_get_temperature_xy () +functions return the colour temperature in Kelvins. +.SH ERRORS +None. +.SH NOTES +The sRGB transfer function is applied to +.IR *r_error , +.IR *g_error , +and +.IR *b_error . +One cannoy simply subtract them from +.IR r , +.IR g , +and +.IR b , +without first undoing the transfer function, +to get the colour or the calculated temperature. +.SH SEE ALSO +.BR libred.h (0), +.BR libred (7), +.BR libred_get_temperature (3), +.BR libred_solar_elevation (3) |