From b4535d6efc205c790c8263ba3f9568f9b442027d Mon Sep 17 00:00:00 2001
From: Debarshi Ray <debarshir@gnome.org>
Date: Sat, 9 Jan 2016 19:41:29 +0100
Subject: [PATCH] CIE: Add conversion from "RGB float" to "CIE Lab float" and
 vice versa

Conversions from "RGB float" to "CIE Lab float" are 10 times slower
without this. One use case is passing a "RGB float" buffer to a
saturation operation that works in the "CIE Lab" colour space.

https://bugzilla.gnome.org/show_bug.cgi?id=760310
---
 extensions/CIE.c | 84 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 84 insertions(+)

diff --git a/extensions/CIE.c b/extensions/CIE.c
index a09ef06..2e0aca2 100644
--- a/extensions/CIE.c
+++ b/extensions/CIE.c
@@ -467,6 +467,42 @@ Yaf_to_Laf (float *src,
   return samples;
 }
 
+static long
+rgbf_to_Labf (float *src,
+              float *dst,
+              long   samples)
+{
+  long n = samples;
+
+  while (n--)
+    {
+      float r = src[0];
+      float g = src[1];
+      float b = src[2];
+
+      float xr = 0.43603516f / D50_WHITE_REF_X * r + 0.38511658f / D50_WHITE_REF_X * g + 0.14305115f / D50_WHITE_REF_X * b;
+      float yr = 0.22248840f / D50_WHITE_REF_Y * r + 0.71690369f / D50_WHITE_REF_Y * g + 0.06060791f / D50_WHITE_REF_Y * b;
+      float zr = 0.01391602f / D50_WHITE_REF_Z * r + 0.09706116f / D50_WHITE_REF_Z * g + 0.71392822f / D50_WHITE_REF_Z * b;
+
+      float fx = xr > LAB_EPSILON ? cbrtf (xr) : (LAB_KAPPA * xr + 16.0f) / 116.0f;
+      float fy = yr > LAB_EPSILON ? cbrtf (yr) : (LAB_KAPPA * yr + 16.0f) / 116.0f;
+      float fz = zr > LAB_EPSILON ? cbrtf (zr) : (LAB_KAPPA * zr + 16.0f) / 116.0f;
+
+      float L = 116.0f * fy - 16.0f;
+      float A = 500.0f * (fx - fy);
+      float B = 200.0f * (fy - fz);
+
+      dst[0] = L;
+      dst[1] = A;
+      dst[2] = B;
+
+      src += 3;
+      dst += 3;
+    }
+
+  return samples;
+}
+
 static long
 rgbaf_to_Labaf (float *src,
                 float *dst,
@@ -505,6 +541,42 @@ rgbaf_to_Labaf (float *src,
   return samples;
 }
 
+static long
+Labf_to_rgbf (float *src,
+                float *dst,
+                long   samples)
+{
+  long n = samples;
+
+  while (n--)
+    {
+      float L = src[0];
+      float A = src[1];
+      float B = src[2];
+
+      float fy = (L + 16.0f) / 116.0f;
+      float fx = fy + A / 500.0f;
+      float fz = fy - B / 200.0f;
+
+      float yr = L > LAB_KAPPA * LAB_EPSILON ? cubef (fy) : L / LAB_KAPPA;
+      float xr = cubef (fx) > LAB_EPSILON ? cubef (fx) : (fx * 116.0f - 16.0f) / LAB_KAPPA;
+      float zr = cubef (fz) > LAB_EPSILON ? cubef (fz) : (fz * 116.0f - 16.0f) / LAB_KAPPA;
+
+      float r =  3.134274799724f * D50_WHITE_REF_X * xr -1.617275708956f * D50_WHITE_REF_Y * yr -0.490724283042f * D50_WHITE_REF_Z * zr;
+      float g = -0.978795575994f * D50_WHITE_REF_X * xr +1.916161689117f * D50_WHITE_REF_Y * yr +0.033453331711f * D50_WHITE_REF_Z * zr;
+      float b =  0.071976988401f * D50_WHITE_REF_X * xr -0.228984974402f * D50_WHITE_REF_Y * yr +1.405718224383f * D50_WHITE_REF_Z * zr;
+
+      dst[0] = r;
+      dst[1] = g;
+      dst[2] = b;
+
+      src += 3;
+      dst += 3;
+    }
+
+  return samples;
+}
+
 static long
 Labaf_to_rgbaf (float *src,
                 float *dst,
@@ -570,6 +642,18 @@ conversions (void)
     "linear", laba_to_rgba,
     NULL
   );
+  babl_conversion_new (
+    babl_format ("RGB float"),
+    babl_format ("CIE Lab float"),
+    "linear", rgbf_to_Labf,
+    NULL
+  );
+  babl_conversion_new (
+    babl_format ("CIE Lab float"),
+    babl_format ("RGB float"),
+    "linear", Labf_to_rgbf,
+    NULL
+  );
   babl_conversion_new (
     babl_format ("RGBA float"),
     babl_format ("CIE Lab alpha float"),
-- 
2.30.2