termcol: globally define luma coefficients

Prepare for reuse in other YUVish conversions.

diff --git a/Shiar_Sheet/Colour.pm b/Shiar_Sheet/Colour.pm
index 1812789aae3b5288774987d12bbb69df5003f60d..303e37556c5825d2712652378e5a4f694023a203 100644 (file)
--- a/Shiar_Sheet/Colour.pm
+++ b/Shiar_Sheet/Colour.pm
@@ -6,6 +6,11 @@ use List::Util 'min';
 
 our $VERSION = '1.00';
 
 
 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);
 sub new {
        my $class = shift;
        my @rgb = @_ >= 3 ? @_ : (map {hex} $_[0] =~ /(..)/g);


@@ -13,9 +18,9 @@ sub new {
 }
 
 sub luminance {
 }
 
 sub luminance {

-       # perceived brightness (using ITU-R recommendation 601 luma co-efficients)
+       # perceived brightness

        my ($r, $g, $b) = @{ $_[0] };
        my ($r, $g, $b) = @{ $_[0] };

-       return $r*.299 + $g*.587 + $b*.114;
+       return $r*$kr + $g*$kg + $b*$kb;

 }
 
 sub rgb24 {
 }
 
 sub rgb24 {