diff --git a/rtengine/previewimage.cc b/rtengine/previewimage.cc
index f9f6c12a1..9de5c81cb 100644
--- a/rtengine/previewimage.cc
+++ b/rtengine/previewimage.cc
@@ -84,26 +84,16 @@ PreviewImage::PreviewImage (const Glib::ustring &fname, const Glib::ustring &ext
                     unsigned char *dst;
                     #pragma omp for schedule(static,10)
 
-                    for (unsigned int i = 0; i < (unsigned int)(h); i++) {
+                    for (unsigned int i = 0; i < (unsigned int)(h); ++i) {
                         src = data + i * w * 3;
                         dst = previewImage->get_data() + i * w * 4;
 
-                        for (unsigned int j = 0; j < (unsigned int)(w); j++) {
+                        for (unsigned int j = 0; j < (unsigned int)(w); ++j) {
                             unsigned char r = *(src++);
                             unsigned char g = *(src++);
                             unsigned char b = *(src++);
 
-#if __BYTE_ORDER__==__ORDER_LITTLE_ENDIAN__
-                            *(dst++) = b;
-                            *(dst++) = g;
-                            *(dst++) = r;
-                            *(dst++) = 0;
-#else
-                            *(dst++) = 0;
-                            *(dst++) = r;
-                            *(dst++) = g;
-                            *(dst++) = b;
-#endif
+                            poke255_uc(dst, r, g, b);
                         }
                     }
                 }
@@ -178,17 +168,8 @@ PreviewImage::PreviewImage (const Glib::ustring &fname, const Glib::ustring &ext
                             unsigned char r = *(src++);
                             unsigned char g = *(src++);
                             unsigned char b = *(src++);
-#if __BYTE_ORDER__==__ORDER_LITTLE_ENDIAN__
-                            *(dst++) = b;
-                            *(dst++) = g;
-                            *(dst++) = r;
-                            *(dst++) = 0;
-#else
-                            *(dst++) = 0;
-                            *(dst++) = r;
-                            *(dst++) = g;
-                            *(dst++) = b;
-#endif
+
+                            poke255_uc(dst, r, g, b);
                         }
                     }
                 }
diff --git a/rtengine/previewimage.h b/rtengine/previewimage.h
index 5135ddd9a..26b9a85d2 100644
--- a/rtengine/previewimage.h
+++ b/rtengine/previewimage.h
@@ -20,7 +20,7 @@
 #define _PREVIEWIMAGE_
 
 #include <gtkmm.h>
-#include "cairomm/cairomm.h"
+#include <cairomm/cairomm.h>
 
 namespace rtengine
 {
diff --git a/rtengine/utils.cc b/rtengine/utils.cc
index b45e4b436..2366f3a0c 100644
--- a/rtengine/utils.cc
+++ b/rtengine/utils.cc
@@ -29,6 +29,51 @@ using namespace std;
 namespace rtengine
 {
 
+void poke255_uc(unsigned char* &dest, unsigned char r, unsigned char g, unsigned char b)
+{
+#if __BYTE_ORDER__==__ORDER_LITTLE_ENDIAN__
+    *(dest++) = b;
+    *(dest++) = g;
+    *(dest++) = r;
+    *(dest++) = 0;
+#else
+    *(dest++) = 0;
+    *(dest++) = r;
+    *(dest++) = g;
+    *(dest++) = b;
+#endif
+}
+
+void poke01_d(unsigned char* &dest, double r, double g, double b)
+{
+#if __BYTE_ORDER__==__ORDER_LITTLE_ENDIAN__
+    *(dest++) = (unsigned char)(b * 255.);
+    *(dest++) = (unsigned char)(g * 255.);
+    *(dest++) = (unsigned char)(r * 255.);
+    *(dest++) = 0;
+#else
+    *(dest++) = 0;
+    *(dest++) = (unsigned char)(r * 255.);
+    *(dest++) = (unsigned char)(g * 255.);
+    *(dest++) = (unsigned char)(b * 255.);
+#endif
+}
+
+void poke01_f(unsigned char* &dest, float r, float g, float b)
+{
+#if __BYTE_ORDER__==__ORDER_LITTLE_ENDIAN__
+    *(dest++) = (unsigned char)(b * 255.f);
+    *(dest++) = (unsigned char)(g * 255.f);
+    *(dest++) = (unsigned char)(r * 255.f);
+    *(dest++) = 0;
+#else
+    *(dest++) = 0;
+    *(dest++) = (unsigned char)(r * 255.f);
+    *(dest++) = (unsigned char)(g * 255.f);
+    *(dest++) = (unsigned char)(b * 255.f);
+#endif
+}
+
 void bilinearInterp (const unsigned char* src, int sw, int sh, unsigned char* dst, int dw, int dh)
 {
 
diff --git a/rtengine/utils.h b/rtengine/utils.h
index 3040e39b9..1e742ffb3 100644
--- a/rtengine/utils.h
+++ b/rtengine/utils.h
@@ -22,6 +22,13 @@
 namespace rtengine
 {
 
+// update a point of a Cairo::Surface by accessing the raw data
+void poke255_uc(unsigned char* &dest, unsigned char r, unsigned char g, unsigned char b);
+// update a point of a Cairo::Surface by accessing the raw data
+void poke01_d(unsigned char* &dest, double r, double g, double b);
+// update a point of a Cairo::Surface by accessing the raw data
+void poke01_f(unsigned char* &dest, float r, float g, float b);
+
 void bilinearInterp (const unsigned char* src, int sw, int sh, unsigned char* dst, int dw, int dh);
 void nearestInterp (const unsigned char* src, int sw, int sh, unsigned char* dst, int dw, int dh);
 void rotate (unsigned char* img, int& w, int& h, int deg);