diff --git a/rtengine/guidedfilter.cc b/rtengine/guidedfilter.cc
index e64ef4e3e..e7fe9b8af 100644
--- a/rtengine/guidedfilter.cc
+++ b/rtengine/guidedfilter.cc
@@ -154,6 +154,9 @@ void guidedFilter(const array2D<float> &guide, const array2D<float> &src, array2
             rad = LIM(rad, 0, (min(s.width(), s.height()) - 1) / 2 - 1);
             float **src = s;
             float **dst = d;
+#ifdef _OPENMP
+            #pragma omp parallel if (multithread)
+#endif
             boxblur<float, float>(src, dst, blur_buf.data, rad, rad, s.width(), s.height());
         };
 
diff --git a/rtengine/improcfun.cc b/rtengine/improcfun.cc
index e34415c1e..a58362596 100644
--- a/rtengine/improcfun.cc
+++ b/rtengine/improcfun.cc
@@ -4348,17 +4348,8 @@ void ImProcFunctions::chromiLuminanceCurve(PipetteBuffer *pipetteBuffer, int pW,
     }
 
 
-    LUTu hist16Clad;
-    LUTu hist16Llad;
-
-    //preparate for histograms CIECAM
-    if (pW != 1) { //only with improccoordinator
-        hist16Clad(65536);
-        hist16Clad.clear();
-        hist16Llad(65536);
-        hist16Llad.clear();
-
-    }
+    const float histLFactor = pW != 1 ? histLCurve.getSize() / 100.f : 1.f;
+    const float histCFactor = pW != 1 ? histCCurve.getSize() / 48000.f : 1.f;
 
 #ifdef _DEBUG
     MyTime t1e, t2e;
@@ -4863,8 +4854,7 @@ void ImProcFunctions::chromiLuminanceCurve(PipetteBuffer *pipetteBuffer, int pW,
 
                 //update histogram C
                 if (pW != 1) { //only with improccoordinator
-                    int posp = (int)sqrt(atmp * atmp + btmp * btmp);
-                    hist16Clad[posp]++;
+                    histCCurve[histCFactor * sqrt(atmp * atmp + btmp * btmp)]++;
                 }
 
                 if (editPipette && editID == EUID_Lab_LCCurve) {
@@ -4919,8 +4909,7 @@ void ImProcFunctions::chromiLuminanceCurve(PipetteBuffer *pipetteBuffer, int pW,
 
                 //update histo LC
                 if (pW != 1) { //only with improccoordinator
-                    int posl = Lprov1 * 327.68f;
-                    hist16Llad[posl]++;
+                    histLCurve[Lprov1 * histLFactor]++;
                 }
 
                 Chprov1 = sqrt(SQR(atmp) + SQR(btmp)) / 327.68f;
@@ -5007,13 +4996,6 @@ void ImProcFunctions::chromiLuminanceCurve(PipetteBuffer *pipetteBuffer, int pW,
         }
     } // end of parallelization
 
-    if (pW != 1) { //only with improccoordinator
-        //update histogram C  with data chromaticity and not with CC curve
-        hist16Clad.compressTo(histCCurve);
-        //update histogram L with data luminance
-        hist16Llad.compressTo(histLCurve);
-    }
-
 #ifdef _DEBUG
 
     if (settings->verbose) {