Add CAM02 JCh and CAM02-UCS J'a'b' conversions

* src/lcms.c (rad2deg, parse_jch_list, parse_jab_list, xyz_to_jch):
(jch_to_xyz, jch_to_jab, jab_to_jch): New functions.
(lcms-jch->xyz, lcms-jch->xyz, lcms-jch->jab, lcms-jab->jch): New Lisp
functions.
(lcms-cam02-ucs): Refactor.
(syms_of_lcms2): Declare new functions.
* test/src/lcms-tests.el (lcms-roundtrip, lcms-ciecam02-gold):
(lcms-jmh->cam02-ucs-silver): New tests.
* etc/NEWS: Mention new functions.

etc/NEWS

@@ -76,7 +76,8 @@ If the lcms2 library is installed, Emacs will enable features built on
 top of that library.  The new configure option '--without-lcms2' can
 be used to build without lcms2 support even if it is installed.  Emacs
 linked to Little CMS exposes color management functions in Lisp: the
-color metrics 'lcms-cie-de2000' and 'lcms-cam02-ucs'.
+color metrics 'lcms-cie-de2000' and 'lcms-cam02-ucs', as well as
+functions for conversion to and from CIE CAM02 and CAM02-UCS.
 
 ** The configure option '--with-gameuser' now defaults to 'no',
 as this appears to be the most common configuration in practice.

src/lcms.c

@@ -25,6 +25,13 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 
 #include "lisp.h"
 
+typedef struct
+{
+  double J;
+  double a;
+  double b;
+} lcmsJab_t;
+
 #ifdef WINDOWSNT
 # include <windows.h>
 # include "w32.h"
@@ -36,6 +43,8 @@ DEF_DLL_FN (cmsHANDLE, cmsCIECAM02Init,
 	    (cmsContext ContextID, const cmsViewingConditions* pVC));
 DEF_DLL_FN (void, cmsCIECAM02Forward,
 	    (cmsHANDLE hModel, const cmsCIEXYZ* pIn, cmsJCh* pOut));
+DEF_DLL_FN (void, cmsCIECAM02Reverse,
+	    (cmsHANDLE hModel, const cmsJCh* pIn, cmsCIEXYZ* pOut));
 DEF_DLL_FN (void, cmsCIECAM02Done, (cmsHANDLE hModel));
 DEF_DLL_FN (cmsBool, cmsWhitePointFromTemp,
 	    (cmsCIExyY* WhitePoint, cmsFloat64Number TempK));
@@ -54,6 +63,7 @@ init_lcms_functions (void)
   LOAD_DLL_FN (library, cmsCIE2000DeltaE);
   LOAD_DLL_FN (library, cmsCIECAM02Init);
   LOAD_DLL_FN (library, cmsCIECAM02Forward);
+  LOAD_DLL_FN (library, cmsCIECAM02Reverse);
   LOAD_DLL_FN (library, cmsCIECAM02Done);
   LOAD_DLL_FN (library, cmsWhitePointFromTemp);
   LOAD_DLL_FN (library, cmsxyY2XYZ);
@@ -63,6 +73,7 @@ init_lcms_functions (void)
 # undef cmsCIE2000DeltaE
 # undef cmsCIECAM02Init
 # undef cmsCIECAM02Forward
+# undef cmsCIECAM02Reverse
 # undef cmsCIECAM02Done
 # undef cmsWhitePointFromTemp
 # undef cmsxyY2XYZ
@@ -70,6 +81,7 @@ init_lcms_functions (void)
 # define cmsCIE2000DeltaE      fn_cmsCIE2000DeltaE
 # define cmsCIECAM02Init       fn_cmsCIECAM02Init
 # define cmsCIECAM02Forward    fn_cmsCIECAM02Forward
+# define cmsCIECAM02Reverse    fn_cmsCIECAM02Reverse
 # define cmsCIECAM02Done       fn_cmsCIECAM02Done
 # define cmsWhitePointFromTemp fn_cmsWhitePointFromTemp
 # define cmsxyY2XYZ            fn_cmsxyY2XYZ
@@ -145,6 +157,12 @@ deg2rad (double degrees)
   return M_PI * degrees / 180.0;
 }
 
+static double
+rad2deg (double radians)
+{
+  return 180.0 * radians / M_PI;
+}
+
 static cmsCIEXYZ illuminant_d65 = { .X = 95.0455, .Y = 100.0, .Z = 108.8753 };
 
 static void
@@ -180,6 +198,46 @@ parse_xyz_list (Lisp_Object xyz_list, cmsCIEXYZ *color)
   return true;
 }
 
+static bool
+parse_jch_list (Lisp_Object jch_list, cmsJCh *color)
+{
+#define PARSE_JCH_LIST_FIELD(field)					\
+  if (CONSP (jch_list) && NUMBERP (XCAR (jch_list)))			\
+    {									\
+      color->field = XFLOATINT (XCAR (jch_list));			\
+      jch_list = XCDR (jch_list);					\
+    }									\
+  else									\
+    return false;
+
+  PARSE_JCH_LIST_FIELD (J);
+  PARSE_JCH_LIST_FIELD (C);
+  PARSE_JCH_LIST_FIELD (h);
+
+  if (! NILP (jch_list))
+    return false;
+  return true;
+}
+
+static bool
+parse_jab_list (Lisp_Object jab_list, lcmsJab_t *color)
+{
+#define PARSE_JAB_LIST_FIELD(field)					\
+  if (CONSP (jab_list) && NUMBERP (XCAR (jab_list)))			\
+    {									\
+      color->field = XFLOATINT (XCAR (jab_list));			\
+      jab_list = XCDR (jab_list);					\
+    }									\
+  else									\
+    return false;
+
+  PARSE_JAB_LIST_FIELD (J);
+  PARSE_JAB_LIST_FIELD (a);
+  PARSE_JAB_LIST_FIELD (b);
+
+  return true;
+}
+
 static bool
 parse_viewing_conditions (Lisp_Object view, const cmsCIEXYZ *wp,
                           cmsViewingConditions *vc)
@@ -216,6 +274,204 @@ parse_viewing_conditions (Lisp_Object view, const cmsCIEXYZ *wp,
   return true;
 }
 
+static void
+xyz_to_jch (const cmsCIEXYZ *xyz, cmsJCh *jch, const cmsViewingConditions *vc)
+{
+  cmsHANDLE h;
+
+  h = cmsCIECAM02Init (0, vc);
+  cmsCIECAM02Forward (h, xyz, jch);
+  cmsCIECAM02Done (h);
+}
+
+static void
+jch_to_xyz (const cmsJCh *jch, cmsCIEXYZ *xyz, const cmsViewingConditions *vc)
+{
+  cmsHANDLE h;
+
+  h = cmsCIECAM02Init (0, vc);
+  cmsCIECAM02Reverse (h, jch, xyz);
+  cmsCIECAM02Done (h);
+}
+
+static void
+jch_to_jab (const cmsJCh *jch, lcmsJab_t *jab, double FL, double c1, double c2)
+{
+  double Mp = 43.86 * log (1.0 + c2 * (jch->C * sqrt (sqrt (FL))));
+  jab->J = 1.7 * jch->J / (1.0 + (c1 * jch->J));
+  jab->a = Mp * cos (deg2rad (jch->h));
+  jab->b = Mp * sin (deg2rad (jch->h));
+}
+
+static void
+jab_to_jch (const lcmsJab_t *jab, cmsJCh *jch, double FL, double c1, double c2)
+{
+  jch->J = jab->J / (1.0 + c1 * (100.0 - jab->J));
+  jch->h = atan2 (jab->b, jab->a);
+  double Mp = hypot (jab->a, jab->b);
+  jch->h = rad2deg (jch->h);
+  if (jch->h < 0.0)
+    jch->h += 360.0;
+  jch->C = (exp (c2 * Mp) - 1.0) / (c2 * sqrt (sqrt (FL)));
+}
+
+DEFUN ("lcms-xyz->jch", Flcms_xyz_to_jch, Slcms_xyz_to_jch, 1, 3, 0,
+       doc: /* Convert CIE CAM02 JCh to CIE XYZ.
+COLOR is a list (X Y Z), with Y scaled about unity.
+Optional arguments WHITEPOINT and VIEW are the same as in `lcms-cam02-ucs',
+which see.  */)
+  (Lisp_Object color, Lisp_Object whitepoint, Lisp_Object view)
+{
+  cmsViewingConditions vc;
+  cmsJCh jch;
+  cmsCIEXYZ xyz, xyzw;
+
+#ifdef WINDOWSNT
+  if (!lcms_initialized)
+    lcms_initialized = init_lcms_functions ();
+  if (!lcms_initialized)
+    {
+      message1 ("lcms2 library not found");
+      return Qnil;
+    }
+#endif
+
+  if (!(CONSP (color) && parse_xyz_list (color, &xyz)))
+    signal_error ("Invalid color", color);
+  if (NILP (whitepoint))
+    xyzw = illuminant_d65;
+  else if (!(CONSP (whitepoint) && parse_xyz_list (whitepoint, &xyzw)))
+    signal_error ("Invalid white point", whitepoint);
+  if (NILP (view))
+    default_viewing_conditions (&xyzw, &vc);
+  else if (!(CONSP (view) && parse_viewing_conditions (view, &xyzw, &vc)))
+    signal_error ("Invalid viewing conditions", view);
+
+  xyz_to_jch(&xyz, &jch, &vc);
+  return list3 (make_float (jch.J), make_float (jch.C), make_float (jch.h));
+}
+
+DEFUN ("lcms-jch->xyz", Flcms_jch_to_xyz, Slcms_jch_to_xyz, 1, 3, 0,
+       doc: /* Convert CIE XYZ to CIE CAM02 JCh.
+COLOR is a list (J C h), where lightness of white is equal to 100, and hue
+is given in degrees.
+Optional arguments WHITEPOINT and VIEW are the same as in `lcms-cam02-ucs',
+which see.  */)
+  (Lisp_Object color, Lisp_Object whitepoint, Lisp_Object view)
+{
+  cmsViewingConditions vc;
+  cmsJCh jch;
+  cmsCIEXYZ xyz, xyzw;
+
+#ifdef WINDOWSNT
+  if (!lcms_initialized)
+    lcms_initialized = init_lcms_functions ();
+  if (!lcms_initialized)
+    {
+      message1 ("lcms2 library not found");
+      return Qnil;
+    }
+#endif
+
+  if (!(CONSP (color) && parse_jch_list (color, &jch)))
+    signal_error ("Invalid color", color);
+  if (NILP (whitepoint))
+    xyzw = illuminant_d65;
+  else if (!(CONSP (whitepoint) && parse_xyz_list (whitepoint, &xyzw)))
+    signal_error ("Invalid white point", whitepoint);
+  if (NILP (view))
+    default_viewing_conditions (&xyzw, &vc);
+  else if (!(CONSP (view) && parse_viewing_conditions (view, &xyzw, &vc)))
+    signal_error ("Invalid viewing conditions", view);
+
+  jch_to_xyz(&jch, &xyz, &vc);
+  return list3 (make_float (xyz.X / 100.0),
+                make_float (xyz.Y / 100.0),
+                make_float (xyz.Z / 100.0));
+}
+
+DEFUN ("lcms-jch->jab", Flcms_jch_to_jab, Slcms_jch_to_jab, 1, 3, 0,
+       doc: /* Convert CIE CAM02 JCh to CAM02-UCS J'a'b'.
+COLOR is a list (J C h) as described in `lcms-jch->xyz', which see.
+Optional arguments WHITEPOINT and VIEW are the same as in `lcms-cam02-ucs',
+which see.  */)
+  (Lisp_Object color, Lisp_Object whitepoint, Lisp_Object view)
+{
+  cmsViewingConditions vc;
+  lcmsJab_t jab;
+  cmsJCh jch;
+  cmsCIEXYZ xyzw;
+  double FL, k, k4;
+
+#ifdef WINDOWSNT
+  if (!lcms_initialized)
+    lcms_initialized = init_lcms_functions ();
+  if (!lcms_initialized)
+    {
+      message1 ("lcms2 library not found");
+      return Qnil;
+    }
+#endif
+
+  if (!(CONSP (color) && parse_jch_list (color, &jch)))
+    signal_error ("Invalid color", color);
+  if (NILP (whitepoint))
+    xyzw = illuminant_d65;
+  else if (!(CONSP (whitepoint) && parse_xyz_list (whitepoint, &xyzw)))
+    signal_error ("Invalid white point", whitepoint);
+  if (NILP (view))
+    default_viewing_conditions (&xyzw, &vc);
+  else if (!(CONSP (view) && parse_viewing_conditions (view, &xyzw, &vc)))
+    signal_error ("Invalid viewing conditions", view);
+
+  k = 1.0 / (1.0 + (5.0 * vc.La));
+  k4 = k * k * k * k;
+  FL = vc.La * k4 + 0.1 * (1 - k4) * (1 - k4) * cbrt (5.0 * vc.La);
+  jch_to_jab (&jch, &jab, FL, 0.007, 0.0228);
+  return list3 (make_float (jab.J), make_float (jab.a), make_float (jab.b));
+}
+
+DEFUN ("lcms-jab->jch", Flcms_jab_to_jch, Slcms_jab_to_jch, 1, 3, 0,
+       doc: /* Convert CAM02-UCS J'a'b' to CIE CAM02 JCh.
+COLOR is a list (J' a' b'), where white corresponds to lightness J equal to 100.
+Optional arguments WHITEPOINT and VIEW are the same as in `lcms-cam02-ucs',
+which see.  */)
+  (Lisp_Object color, Lisp_Object whitepoint, Lisp_Object view)
+{
+  cmsViewingConditions vc;
+  cmsJCh jch;
+  lcmsJab_t jab;
+  cmsCIEXYZ xyzw;
+  double FL, k, k4;
+
+#ifdef WINDOWSNT
+  if (!lcms_initialized)
+    lcms_initialized = init_lcms_functions ();
+  if (!lcms_initialized)
+    {
+      message1 ("lcms2 library not found");
+      return Qnil;
+    }
+#endif
+
+  if (!(CONSP (color) && parse_jab_list (color, &jab)))
+    signal_error ("Invalid color", color);
+  if (NILP (whitepoint))
+    xyzw = illuminant_d65;
+  else if (!(CONSP (whitepoint) && parse_xyz_list (whitepoint, &xyzw)))
+    signal_error ("Invalid white point", whitepoint);
+  if (NILP (view))
+    default_viewing_conditions (&xyzw, &vc);
+  else if (!(CONSP (view) && parse_viewing_conditions (view, &xyzw, &vc)))
+    signal_error ("Invalid viewing conditions", view);
+
+  k = 1.0 / (1.0 + (5.0 * vc.La));
+  k4 = k * k * k * k;
+  FL = vc.La * k4 + 0.1 * (1 - k4) * (1 - k4) * cbrt (5.0 * vc.La);
+  jab_to_jch (&jab, &jch, FL, 0.007, 0.0228);
+  return list3 (make_float (jch.J), make_float (jch.C), make_float (jch.h));
+}
+
 /* References:
    Li, Luo et al. "The CRI-CAM02UCS colour rendering index." COLOR research
    and application, 37 No.3, 2012.
@@ -239,10 +495,9 @@ The default viewing conditions are (20 100 1 1).  */)
 {
   cmsViewingConditions vc;
   cmsJCh jch1, jch2;
-  cmsHANDLE h1, h2;
   cmsCIEXYZ xyz1, xyz2, xyzw;
-  double Jp1, ap1, bp1, Jp2, ap2, bp2;
+  lcmsJab_t jab1, jab2;
-  double Mp1, Mp2, FL, k, k4;
+  double FL, k, k4;
 
 #ifdef WINDOWSNT
   if (!lcms_initialized)
@@ -267,41 +522,17 @@ The default viewing conditions are (20 100 1 1).  */)
   else if (!(CONSP (view) && parse_viewing_conditions (view, &xyzw, &vc)))
     signal_error ("Invalid view conditions", view);
 
-  h1 = cmsCIECAM02Init (0, &vc);
+  xyz_to_jch (&xyz1, &jch1, &vc);
-  h2 = cmsCIECAM02Init (0, &vc);
+  xyz_to_jch (&xyz2, &jch2, &vc);
-  cmsCIECAM02Forward (h1, &xyz1, &jch1);
-  cmsCIECAM02Forward (h2, &xyz2, &jch2);
-  cmsCIECAM02Done (h1);
-  cmsCIECAM02Done (h2);
 
-  /* Now have colors in JCh, need to calculate J'a'b'
-
-     M = C * F_L^0.25
-     J' = 1.7 J / (1 + 0.007 J)
-     M' = 43.86 ln(1 + 0.0228 M)
-     a' = M' cos(h)
-     b' = M' sin(h)
-
-     where
-
-     F_L = 0.2 k^4 (5 L_A) + 0.1 (1 - k^4)^2 (5 L_A)^(1/3),
-     k = 1/(5 L_A + 1)
-  */
   k = 1.0 / (1.0 + (5.0 * vc.La));
   k4 = k * k * k * k;
   FL = vc.La * k4 + 0.1 * (1 - k4) * (1 - k4) * cbrt (5.0 * vc.La);
-  Mp1 = 43.86 * log (1.0 + 0.0228 * (jch1.C * sqrt (sqrt (FL))));
+  jch_to_jab (&jch1, &jab1, FL, 0.007, 0.0228);
-  Mp2 = 43.86 * log (1.0 + 0.0228 * (jch2.C * sqrt (sqrt (FL))));
+  jch_to_jab (&jch2, &jab2, FL, 0.007, 0.0228);
-  Jp1 = 1.7 * jch1.J / (1.0 + (0.007 * jch1.J));
-  Jp2 = 1.7 * jch2.J / (1.0 + (0.007 * jch2.J));
-  ap1 = Mp1 * cos (deg2rad (jch1.h));
-  ap2 = Mp2 * cos (deg2rad (jch2.h));
-  bp1 = Mp1 * sin (deg2rad (jch1.h));
-  bp2 = Mp2 * sin (deg2rad (jch2.h));
 
-  return make_float (sqrt ((Jp2 - Jp1) * (Jp2 - Jp1) +
+  return make_float (hypot (jab2.J - jab1.J,
-                           (ap2 - ap1) * (ap2 - ap1) +
+                            hypot (jab2.a - jab1.a, jab2.b - jab1.b)));
-                           (bp2 - bp1) * (bp2 - bp1)));
 }
 
 DEFUN ("lcms-temp->white-point", Flcms_temp_to_white_point, Slcms_temp_to_white_point, 1, 1, 0,
@@ -359,6 +590,10 @@ void
 syms_of_lcms2 (void)
 {
   defsubr (&Slcms_cie_de2000);
+  defsubr (&Slcms_xyz_to_jch);
+  defsubr (&Slcms_jch_to_xyz);
+  defsubr (&Slcms_jch_to_jab);
+  defsubr (&Slcms_jab_to_jch);
   defsubr (&Slcms_cam02_ucs);
   defsubr (&Slcms2_available_p);
   defsubr (&Slcms_temp_to_white_point);

test/src/lcms-tests.el

@@ -94,6 +94,38 @@ B is considered the exact value."
     (apply #'color-xyz-to-xyy (lcms-temp->white-point 7504))
     '(0.29902 0.31485 1.0))))
 
+(ert-deftest lcms-roundtrip ()
+  "Test accuracy of converting to and from different color spaces"
+  (skip-unless (featurep 'lcms2))
+  (should
+   (let ((color '(.5 .3 .7)))
+     (lcms-triple-approx-p (lcms-jch->xyz (lcms-xyz->jch color))
+                           color
+                           0.0001)))
+  (should
+   (let ((color '(.8 -.2 .2)))
+     (lcms-triple-approx-p (lcms-jch->jab (lcms-jab->jch color))
+                           color
+                           0.0001))))
+
+(ert-deftest lcms-ciecam02-gold ()
+  "Test CIE CAM02 JCh gold values"
+  (skip-unless (featurep 'lcms2))
+  (should
+   (lcms-triple-approx-p
+    (lcms-xyz->jch '(0.1931 0.2393 0.1014)
+                   '(0.9888 0.900 0.3203)
+                   '(18 200 1 1.0))
+    '(48.0314 38.7789 191.0452)
+    0.02))
+  (should
+   (lcms-triple-approx-p
+    (lcms-xyz->jch '(0.1931 0.2393 0.1014)
+                   '(0.9888 0.90 0.3203)
+                   '(18 20 1 1.0))
+    '(47.6856 36.0527 185.3445)
+    0.09)))
+
 (ert-deftest lcms-dE-cam02-ucs-silver ()
   "Test CRI-CAM02-UCS deltaE metric values from colorspacious."
   (skip-unless (featurep 'lcms2))
@@ -114,4 +146,16 @@ B is considered the exact value."
     8.503323264883667
     0.04)))
 
+(ert-deftest lcms-jmh->cam02-ucs-silver ()
+  "Compare JCh conversion to CAM02-UCS to values from colorspacious."
+  (skip-unless (featurep 'lcms2))
+  (should
+   (lcms-triple-approx-p (lcms-jch->jab '(50 20 10))
+                         '(62.96296296 16.22742674 2.86133316)
+                         0.05))
+  (should
+   (lcms-triple-approx-p (lcms-jch->jab '(10 60 100))
+                         '(15.88785047 -6.56546789 37.23461867)
+                         0.04)))
+
 ;;; lcms-tests.el ends here