RPJosh
/
wlsunset
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Explain the use of multiple locus better 

It was not entirely trivial to understand why the two locus were
implemented, and why there was a transition between them. Explain this
more explicitly.
master
Kenny Levinsen 2023-12-12 16:21:08 +01:00
parent b6cfe1761d
commit c7b622e8dc
1 changed files with 24 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

28
color_math.c
View File

@ -75,8 +75,13 @@ enum sun_condition calc_sun(struct tm *tm, double latitude, struct sun *sun) {
/*
* Illuminant D, or daylight locus, is is a "standard illuminant" used to
* describe natural daylight. It is on this locus that D65, the whitepoint used
* by most monitors and assumed by wlsunset, is defined.
* describe natural daylight as we perceive it, and as such is how we expect
* bright, cold white light sources to look. This is different from the
* planckian locus due to the effects of the atmosphere on sunlight travelling
* through it.
*
* It is on this locus that D65, the whitepoint used by most monitors and
* assumed by display servers, is defined.
*
* This approximation is strictly speaking only well-defined between 4000K and
* 25000K, but we stretch it a bit further down for transition purposes.
@ -103,9 +108,14 @@ static int illuminant_d(int temp, double *x, double *y) {
/*
* Planckian locus, or black body locus, describes the color of a black body at
* a certain temperatures. This is not entirely equivalent to daylight due to
* atmospheric effects.
* a certain temperatures directly at its source, rather than observed through
* a thick atmosphere.
*
* While we are used to bright light coming from afar and going through the
* atmosphere, we are used to seeing dim incandescent light sources from close
* enough for the atmosphere to not affect its perception, dictating how we
* expect dim, warm light sources to look.
*
* This approximation is only valid from 1667K to 25000K.
*/
static int planckian_locus(int temp, double *x, double *y) {
@ -182,6 +192,16 @@ struct rgb calc_whitepoint(int temp) {
return (struct rgb) {.r = 1.0, .g = 1.0, .b = 1.0};
}
// We are not trying to calculate the accurate whitepoint, but rather
// an expected observed whitepoint. We generally expect dim and warm
// light sources to follow the planckian locus, while we expect bright
// and cold light sources to follow the daylight locus. There is no
// "correct" way to transition between these two curves, and so the
// goal is purely to be subjectively pleasant/non-jarring.
//
// A smooth transition between the two in the range between 2500K and
// 4000K seems to do the trick for now.
struct xyz wp;
if (temp >= 25000) {
illuminant_d(25000, &wp.x, &wp.y);