From 6e19e617482820b7d6894d11adbb65064ad49836 Mon Sep 17 00:00:00 2001
From: Mischa POSLAWSKY <perl@shiar.org>
Date: Mon, 26 Oct 2015 13:05:41 +0100
Subject: [PATCH] termcol: globally define luma coefficients

Prepare for reuse in other YUVish conversions.
---
 Shiar_Sheet/Colour.pm | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/Shiar_Sheet/Colour.pm b/Shiar_Sheet/Colour.pm
index 1812789..303e375 100644
--- a/Shiar_Sheet/Colour.pm
+++ b/Shiar_Sheet/Colour.pm
@@ -6,6 +6,11 @@ use List::Util 'min';
 
 our $VERSION = '1.00';
 
+# ITU-R recommendation 601 luma co-efficients
+our $kr = .299;
+our $kb = .114;
+our $kg = 1 - $kb - $kr;
+
 sub new {
 	my $class = shift;
 	my @rgb = @_ >= 3 ? @_ : (map {hex} $_[0] =~ /(..)/g);
@@ -13,9 +18,9 @@ sub new {
 }
 
 sub luminance {
-	# perceived brightness (using ITU-R recommendation 601 luma co-efficients)
+	# perceived brightness
 	my ($r, $g, $b) = @{ $_[0] };
-	return $r*.299 + $g*.587 + $b*.114;
+	return $r*$kr + $g*$kg + $b*$kb;
 }
 
 sub rgb24 {
-- 
2.30.0