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

diff --git a/extensions/CIE.c b/extensions/CIE.c
index a09ef06c55d0a2336b970838871c659705d4cabf..2e0aca2609d26ac2fccfa7e9cd92e5ec5f236ff9 100644 (file)
--- 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"),