X-Git-Url: http://git.shiar.nl/sheet.git/blobdiff_plain/83596eca2ea1782932a4af42727ece9af8067f13..1f3b44e51107dc97ce2bded07b93325e96835744:/Shiar_Sheet/Colour.pm

diff --git a/Shiar_Sheet/Colour.pm b/Shiar_Sheet/Colour.pm
index 1812789..cedfdfb 100644
--- a/Shiar_Sheet/Colour.pm
+++ b/Shiar_Sheet/Colour.pm
@@ -2,9 +2,16 @@ package Shiar_Sheet::Colour;
 
 use strict;
 use warnings;
-use List::Util 'min';
+use List::Util qw( min max );
 
-our $VERSION = '1.00';
+our $VERSION = '1.02';
+
+# ITU-R recommendation 601 luma co-efficients
+our $kr = .299;
+our $kb = .114;
+our $kg = 1 - $kb - $kr;
+
+my $PI = 2 * atan2 1, 0;
 
 sub new {
 	my $class = shift;
@@ -12,10 +19,32 @@ sub new {
 	bless \@rgb, $class;
 }
 
+sub newyuv {
+	# convert from YPbPr values 0..255 (or hex string)
+	my $class = shift;
+	my ($y, $cb, $cr) = @_ >= 3 ? @_ : (map {hex} $_[0] =~ /(..)/g);
+
+	$_ -= 128 for $cb, $cr;
+	$_ /= 255 for $y, $cb, $cr;
+
+	my @rgb = map { max(0, min(255, $_ * 255)) } (
+		$y                             + $cr,
+		$y - $cb * (1 - $kb) * $kb/$kg - $cr * $kr/$kg,
+		$y + $cb * (1 - $kb)           ,
+	);
+	bless \@rgb, $class;
+}
+
 sub luminance {
-	# perceived brightness (using ITU-R recommendation 601 luma co-efficients)
+	# perceived brightness
+	my ($r, $g, $b) = @{ $_[0] };
+	return $r*$kr + $g*$kg + $b*$kb;
+}
+
+sub hue {
 	my ($r, $g, $b) = @{ $_[0] };
-	return $r*.299 + $g*.587 + $b*.114;
+	my $hue = atan2 sqrt(3) * ($g - $b), $r*2 - $g - $b;
+	return ($hue + $PI) / $PI / 2; # 0 .. 1
 }
 
 sub rgb24 {