termcol: 16-colour palettes for msx and c64

[sheet.git] / Shiar_Sheet / Colour.pm

diff --git a/Shiar_Sheet/Colour.pm b/Shiar_Sheet/Colour.pm
index 1812789aae3b5288774987d12bbb69df5003f60d..7ea68e9dcf63bd3874facf8e8a89f068d52ba213 100644 (file)
--- a/Shiar_Sheet/Colour.pm
+++ b/Shiar_Sheet/Colour.pm
@@ -2,9 +2,14 @@ package Shiar_Sheet::Colour;
 
 use strict;
 use warnings;
-use List::Util 'min';
+use List::Util qw( min max );
 
-our $VERSION = '1.00';
+our $VERSION = '1.01';
+
+# ITU-R recommendation 601 luma co-efficients
+our $kr = .299;
+our $kb = .114;
+our $kg = 1 - $kb - $kr;
 
 sub new {
        my $class = shift;
@@ -12,10 +17,26 @@ 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*.299 + $g*.587 + $b*.114;
+       return $r*$kr + $g*$kg + $b*$kb;
 }
 
 sub rgb24 {