diff --git a/rtengine/curves.cc b/rtengine/curves.cc
index a4f85a878..4d00d361a 100644
--- a/rtengine/curves.cc
+++ b/rtengine/curves.cc
@@ -291,7 +291,7 @@ void CurveFactory::curveLightBrightColor (
 void CurveFactory::curveBW (
 		procparams::ChannelMixerbwParams::eTCModeId curveModeb, const std::vector<double>& curvePointsbw,
 		procparams::ChannelMixerbwParams::eTCModeId curveModeb2, const std::vector<double>& curvePointsbw2,
-		LUTu & histogram, LUTu & histogramCropped, LUTu & outBeforeCCurveHistogram,//for Luminance  
+		LUTu & histogrambw, LUTu & histogramCropped, LUTu & outBeforeCCurveHistogrambw,//for Luminance  
 		ChMixerbw & customToneCurvebw1,
 		ChMixerbw & customToneCurvebw2,
 		int skip)
@@ -304,7 +304,7 @@ void CurveFactory::curveBW (
 			dcurve[i] = CLIPD(val);
 		}
 
-	outBeforeCCurveHistogram.clear();
+	outBeforeCCurveHistogrambw.clear();
 	bool histNeeded = false;
 	
 	DiagonalCurve* tcurve = NULL;
@@ -312,7 +312,7 @@ void CurveFactory::curveBW (
 
 	if (!curvePointsbw2.empty() && curvePointsbw2[0]>DCT_Linear && curvePointsbw2[0]<DCT_Unchanged) {
 		tcurve = new DiagonalCurve (curvePointsbw2, CURVES_MIN_POLY_POINTS/skip);
-		if (outBeforeCCurveHistogram /*&& histogramCropped*/)
+		if (outBeforeCCurveHistogrambw /*&& histogramCropped*/)
 				histNeeded = true;
 		
 	}
@@ -331,7 +331,7 @@ void CurveFactory::curveBW (
 
 	if (!curvePointsbw.empty() && curvePointsbw[0]>DCT_Linear && curvePointsbw[0]<DCT_Unchanged) {
 		tcurve = new DiagonalCurve (curvePointsbw, CURVES_MIN_POLY_POINTS/skip);
-		if (outBeforeCCurveHistogram /*&& histogramCropped*/)
+		if (outBeforeCCurveHistogrambw /*&& histogramCropped*/)
 				histNeeded = true;
 		
 	}
@@ -353,7 +353,7 @@ void CurveFactory::curveBW (
 			if (histNeeded) {
 				float hval = dcurve[i];
 				int hi = (int)(255.0*CLIPD(hval));
-				outBeforeCCurveHistogram[hi] += histogram[i] ;
+				outBeforeCCurveHistogrambw[hi] += histogrambw[i] ;
 			}
 	}
 	
diff --git a/rtengine/curves.h b/rtengine/curves.h
index 9157e2c6b..59dbe2e2e 100644
--- a/rtengine/curves.h
+++ b/rtengine/curves.h
@@ -190,7 +190,7 @@ class CurveFactory {
 	static void curveBW (
 		procparams::ChannelMixerbwParams::eTCModeId curveModeb, const std::vector<double>& curvePointsbw,
 		procparams::ChannelMixerbwParams::eTCModeId curveModeb2, const std::vector<double>& curvePointsbw2,
-		LUTu & histogram, LUTu & histogramCropped, LUTu & outBeforeCCurveHistogram, 
+		LUTu & histogrambw, LUTu & histogramCropped, LUTu & outBeforeCCurveHistogrambw, 
 		ChMixerbw & customToneCurvebw1,
 		ChMixerbw & customToneCurvebw2,
 		int skip);
diff --git a/rtengine/improccoordinator.cc b/rtengine/improccoordinator.cc
index 0590432e3..19d5cd7f2 100644
--- a/rtengine/improccoordinator.cc
+++ b/rtengine/improccoordinator.cc
@@ -44,7 +44,7 @@ ImProcCoordinator::ImProcCoordinator ()
       lhskcurve(65536,0),
       clcurve(65536,0),
 
-      vhist16(65536),
+      vhist16(65536),vhist16bw(65536),
       lhist16(65536), lhist16Cropped(65536),
       lhist16CAM(65536), lhist16CroppedCAM(65536),
       lhist16CCAM(65536), lhist16CroppedCCAM(65536),
@@ -57,6 +57,7 @@ ImProcCoordinator::ImProcCoordinator ()
       histBlue(256), histBlueRaw(256),
       histLuma(256), histChroma(256),
       histToneCurve(256),
+      histToneCurveBW(256),
       histLCurve(256),
       histCCurve(256),
       histCLurve(256),
@@ -298,7 +299,7 @@ void ImProcCoordinator::updatePreviewImage (int todo, Crop* cropCall) {
         CurveFactory::RGBCurve (params.rgbCurves.bcurve, bCurve, scale==1 ? 1 : 1);
 
        CurveFactory::curveBW (params.chmixerbw.curveMode, params.chmixerbw.curve, params.chmixerbw.curveMode2, params.chmixerbw.curve2,
-									vhist16, histCropped, histToneCurve, customToneCurvebw1, customToneCurvebw2,scale==1 ? 1 : 1);
+									vhist16bw, histCropped, histToneCurveBW, customToneCurvebw1, customToneCurvebw2,scale==1 ? 1 : 1);
 		
 		//initialize rrm bbm ggm different from zero to avoid black screen in somme cases
 		double rrm=33.; 
diff --git a/rtengine/improccoordinator.h b/rtengine/improccoordinator.h
index 04e89d92b..c8a290639 100644
--- a/rtengine/improccoordinator.h
+++ b/rtengine/improccoordinator.h
@@ -88,7 +88,7 @@ class ImProcCoordinator : public StagedImageProcessor {
         LUTf lhskcurve;
         LUTf clcurve;
 
-        LUTu vhist16;
+        LUTu vhist16,vhist16bw;
         LUTu lhist16,lhist16Cropped;
         LUTu lhist16CAM,lhist16CroppedCAM;
         LUTu lhist16CCAM,lhist16CroppedCCAM;
@@ -99,7 +99,7 @@ class ImProcCoordinator : public StagedImageProcessor {
         LUTu histRed, histRedRaw;
         LUTu histGreen, histGreenRaw;
         LUTu histBlue, histBlueRaw;
-        LUTu histLuma, histToneCurve, histLCurve, histCCurve, histCLurve,  histLLCurve, histLCAM, histCCAM, histClad, bcabhist, histChroma;
+        LUTu histLuma, histToneCurve, histToneCurveBW, histLCurve, histCCurve, histCLurve,  histLLCurve, histLCAM, histCCAM, histClad, bcabhist, histChroma;
 
         LUTf rCurve;
         LUTf gCurve;
diff --git a/rtengine/improcfun.cc b/rtengine/improcfun.cc
index 057567965..48d329747 100644
--- a/rtengine/improcfun.cc
+++ b/rtengine/improcfun.cc
@@ -2847,9 +2847,10 @@ void ImProcFunctions::chromiLuminanceCurve (int pW, LabImage* lold, LabImage* ln
 				val = (double)i / 47999.0;
 				dCcurve[i] = CLIPD(val);
 			}
-		for (int i=0; i<65535; i++) {  //# 32768*1.414  approximation maxi for chroma
+		for (int i=0; i<65535; i++) {  //  a
 				val = (double)i / 65534.0;
 				dLcurve[i] = CLIPD(val);
+				
 			}
 			
 		hist16Clad.clear();