[tools 2/3] winetest/build-patterns: Use the Luv colorspace for interpolating colors.
Francois Gouget
fgouget at codeweavers.com
Tue Aug 31 08:40:02 CDT 2021
Interpolation works best in a colorspace where the distance between
colors is representative of their perceptual difference. That's
roughly the case in the Luv colorspace and much less so in the RGB
one.
Signed-off-by: Francois Gouget <fgouget at codeweavers.com>
---
This introduces a dependency on the Graphics::ColorObject perl module
which is provided by the libgraphics-colorobject-perl Debian package.
Note that on Debian 11 this package is missing a dependency on
libgraphics-colornames-www-perl.
---
winetest/build-patterns | 23 +++++++++++++++--------
1 file changed, 15 insertions(+), 8 deletions(-)
diff --git a/winetest/build-patterns b/winetest/build-patterns
index ff72516f6..72291401e 100755
--- a/winetest/build-patterns
+++ b/winetest/build-patterns
@@ -22,6 +22,7 @@ use open ':utf8';
use CGI qw(:standard);
use POSIX; # ceil()
+use Graphics::ColorObject;
use Text::CSV::Encoded;
use Time::Piece;
@@ -860,15 +861,15 @@ if (open(my $fh, "-|", $cmd))
sub color2html($)
{
my ($c) = @_;
- return sprintf "#%02x%02x%02x", $c->[0], $c->[1], $c->[2];
+ return "#". $c->as_RGBhex();
}
-sub blend($$$)
+sub interpolate($$$)
{
my ($p, $start, $end) = @_;
- my $r = [int($start->[0] * (1 - $p) + $end->[0] * $p + 0.5),
- int($start->[1] * (1 - $p) + $end->[1] * $p + 0.5),
- int($start->[2] * (1 - $p) + $end->[2] * $p + 0.5)];
+ my $r = [$start->[0] * (1 - $p) + $end->[0] * $p,
+ $start->[1] * (1 - $p) + $end->[1] * $p,
+ $start->[2] * (1 - $p) + $end->[2] * $p];
return $r;
}
@@ -896,7 +897,7 @@ sub compute_set_colors($)
my $count = @values;
if ($count == 1)
{
- $set->{$values[0]} = color2html($keycolors[0]);
+ $set->{$values[0]} = color2html(Graphics::ColorObject->new_RGB255($keycolors[0]));
}
else
{
@@ -904,6 +905,12 @@ sub compute_set_colors($)
# when many colors are needed.
$keycolors[0] = [0, 179, 179] if ($count > 10);
+ # Convert the key colors to the Luv colorspace where the distance
+ # between colors is roughly representative of the perceptual difference
+ # between them. This allows linear interpolation to produce relatively
+ # uniform gradients (which is not the case in the RGB colorspace).
+ map { $_ = Graphics::ColorObject->new_RGB255($_)->as_Luv() } @keycolors;
+
# Compute the total length of the path traced by the key colors through
# the colorspace. This is necessary so the gradient remains uniform
# even if two key colors are close to each other. This does assume that
@@ -929,8 +936,8 @@ sub compute_set_colors($)
}
# And blend
- my $Rgb = blend(($pos - $keypos[$k]) / ($keypos[$k+1] - $keypos[$k]), $keycolors[$k], $keycolors[$k+1]);
- $set->{$values[$_]} = color2html($Rgb);
+ my $Luv = interpolate(($pos - $keypos[$k]) / ($keypos[$k+1] - $keypos[$k]), $keycolors[$k], $keycolors[$k+1]);
+ $set->{$values[$_]} = color2html(Graphics::ColorObject->new_Luv($Luv));
}
}
}
--
2.30.2
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