From cd2153f4543468eebfc04031f2cd1c979d9a6962 Mon Sep 17 00:00:00 2001
From: Stephan Loyd <stephanloyd9@gmail.com>
Date: Fri, 6 Jan 2023 21:27:48 +0800
Subject: [PATCH] Fix f_lab accuracy. This fixes GH-6

---
 lib/PDL/Transform/Color.pm |  2 +-
 t/color.t                  | 10 +++++++++-
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/lib/PDL/Transform/Color.pm b/lib/PDL/Transform/Color.pm
index 5dfa066..2bb1346 100644
--- a/lib/PDL/Transform/Color.pm
+++ b/lib/PDL/Transform/Color.pm
@@ -1493,7 +1493,7 @@ sub f_lab {
     my $delta = 6/29;
     my $delta3 = $delta * $delta * $delta;
     return ( 
-	($in >  $delta3) * ( $in * (($in->abs+($in==0)) ** (0.333-1)) ) +
+	($in >  $delta3) * ( $in * (($in->abs+($in==0)) ** (1/3-1)) ) +
 	($in <= $delta3) * ( $in / (3 * $delta * $delta) + 4/29 )
 	);
 }
diff --git a/t/color.t b/t/color.t
index 297efa3..1527dcc 100644
--- a/t/color.t
+++ b/t/color.t
@@ -178,6 +178,14 @@ eval {$t = t_xyz2lab();};
 is $@, '', "t_xyz2lab ran OK";
 eval {$b=pdl(1,1,1)->apply($t);};
 is $@, '', "t_xyz2lab applied OK";
-ok all(approx $b, pdl(100, 8.5859237, 5.5509345)), 't_xyz2lab right values' or diag "got=$b";
+ok all(approx $b, pdl(100, 8.5945916, 5.5564131)), 't_xyz2lab right values' or diag "got=$b";
+
+
+for my $rgb (pdl(255, 0, 0), pdl(0, 255, 0), pdl(0, 0, 255)) {
+    my $t = t_lab() x !t_srgb();
+    my $lab = $rgb->apply($t);
+    my $rgb2 = $lab->invert($t);
+    ok(all(approx $rgb2, $rgb), "t_lab loop $rgb") or diag "got=$b";
+}
 
 done_testing;