diff --git a/rtengine/iimage.h b/rtengine/iimage.h
index af2969581..2def35e06 100644
--- a/rtengine/iimage.h
+++ b/rtengine/iimage.h
@@ -82,22 +82,18 @@ public:
     // Read the raw dump of the data
     void readData  (FILE *fh) {}
     // Write a raw dump of the data
-    void writeData (FILE *fh) {}
+    void writeData (FILE *fh) const {}
 
     virtual void normalizeInt (int srcMinVal, int srcMaxVal) {};
     virtual void normalizeFloat (float srcMinVal, float srcMaxVal) {};
-    virtual void computeHistogramAutoWB (double &avg_r, double &avg_g, double &avg_b, int &n, LUTu &histogram, int compression) {}
+    virtual void computeHistogramAutoWB (double &avg_r, double &avg_g, double &avg_b, int &n, LUTu &histogram, int compression) const {}
     virtual void getSpotWBData (double &reds, double &greens, double &blues, int &rn, int &gn, int &bn,
                                 std::vector<Coord2D> &red, std::vector<Coord2D> &green, std::vector<Coord2D> &blue,
-                                int tran) {}
-    virtual void getAutoWBMultipliers (double &rm, double &gm, double &bm)
+                                int tran) const {}
+    virtual void getAutoWBMultipliers (double &rm, double &gm, double &bm) const
     {
         rm = gm = bm = 1.0;
     }
-    virtual const char* getType () const
-    {
-        return "unknown";
-    }
 
 };
 
@@ -232,7 +228,7 @@ public:
     }
 
     // Send back the row stride. WARNING: unit = byte, not element!
-    int getRowStride ()
+    int getRowStride () const
     {
         return rowstride;
     }
@@ -316,7 +312,7 @@ public:
     }
 
     /** Copy the data to another PlanarWhateverData */
-    void copyData(PlanarWhateverData<T> *dest)
+    void copyData(PlanarWhateverData<T> *dest) const
     {
         assert (dest != NULL);
         // Make sure that the size is the same, reallocate if necessary
@@ -389,7 +385,7 @@ public:
     }
 
     template <class IC>
-    void resizeImgTo (int nw, int nh, TypeInterpolation interp, PlanarWhateverData<IC> *imgPtr)
+    void resizeImgTo (int nw, int nh, TypeInterpolation interp, PlanarWhateverData<IC> *imgPtr) const
     {
         //printf("resizeImgTo: resizing %s image data (%d x %d) to %s (%d x %d)\n", getType(), width, height, imgPtr->getType(), imgPtr->width, imgPtr->height);
         if (width == nw && height == nh) {
@@ -499,17 +495,7 @@ public:
 #endif
     }
 
-    void calcHist(unsigned int *hist16)
-    {
-        for (int row = 0; row < height; row++)
-            for (int col = 0; col < width; col++) {
-                unsigned short idx;
-                convertTo(v(row, col), idx);
-                hist16[idx]++;
-            }
-    }
-
-    void transformPixel (int x, int y, int tran, int& tx, int& ty)
+    void transformPixel (int x, int y, int tran, int& tx, int& ty) const
     {
 
         if (!tran) {
@@ -552,7 +538,7 @@ public:
         }
     }
 
-    void getPipetteData (T &value, int posX, int posY, int squareSize, int tran)
+    void getPipetteData (T &value, int posX, int posY, int squareSize, int tran) const
     {
         int x;
         int y;
@@ -573,14 +559,14 @@ public:
         value = n ? T(accumulator / float(n)) : T(0);
     }
 
-    void readData   (FILE *f)
+    void readData (FILE *f)
     {
         for (int i = 0; i < height; i++) {
             fread (v(i), sizeof(T), width, f);
         }
     }
 
-    void writeData  (FILE *f)
+    void writeData (FILE *f) const
     {
         for (int i = 0; i < height; i++) {
             fwrite (v(i), sizeof(T), width, f);
@@ -622,12 +608,12 @@ public:
     }
 
     // Send back the row stride. WARNING: unit = byte, not element!
-    int getRowStride ()
+    int getRowStride () const
     {
         return rowstride;
     }
     // Send back the plane stride. WARNING: unit = byte, not element!
-    int getPlaneStride ()
+    int getPlaneStride () const
     {
         return planestride;
     }
@@ -732,7 +718,7 @@ public:
     }
 
     /** Copy the data to another PlanarRGBData */
-    void copyData(PlanarRGBData<T> *dest)
+    void copyData(PlanarRGBData<T> *dest) const
     {
         assert (dest != nullptr);
         // Make sure that the size is the same, reallocate if necessary
@@ -820,7 +806,7 @@ public:
     }
 
     template <class IC>
-    void resizeImgTo (int nw, int nh, TypeInterpolation interp, IC *imgPtr)
+    void resizeImgTo (int nw, int nh, TypeInterpolation interp, IC *imgPtr) const
     {
         //printf("resizeImgTo: resizing %s image data (%d x %d) to %s (%d x %d)\n", getType(), width, height, imgPtr->getType(), imgPtr->width, imgPtr->height);
         if (width == nw && height == nh) {
@@ -869,9 +855,9 @@ public:
             // This case should never occur!
             for (int i = 0; i < nh; i++) {
                 for (int j = 0; j < nw; j++) {
-                    r(i, j) = 0;
-                    g(i, j) = 0;
-                    b(i, j) = 0;
+                    imgPtr->r(i, j) = 0;
+                    imgPtr->g(i, j) = 0;
+                    imgPtr->b(i, j) = 0;
                 }
             }
         }
@@ -942,7 +928,7 @@ public:
 #endif
     }
 
-    void calcGrayscaleHist(unsigned int *hist16)
+    void calcGrayscaleHist(unsigned int *hist16) const
     {
         for (int row = 0; row < height; row++)
             for (int col = 0; col < width; col++) {
@@ -956,7 +942,7 @@ public:
             }
     }
 
-    void computeAutoHistogram (LUTu & histogram, int& histcompr)
+    void computeAutoHistogram (LUTu & histogram, int& histcompr) const
     {
         histcompr = 3;
 
@@ -975,7 +961,7 @@ public:
             }
     }
 
-    void computeHistogramAutoWB (double &avg_r, double &avg_g, double &avg_b, int &n, LUTu &histogram, const int compression)
+    void computeHistogramAutoWB (double &avg_r, double &avg_g, double &avg_b, int &n, LUTu &histogram, const int compression) const
     {
         histogram.clear();
         avg_r = avg_g = avg_b = 0.;
@@ -1007,7 +993,7 @@ public:
             }
     }
 
-    void getAutoWBMultipliers (double &rm, double &gm, double &bm)
+    void getAutoWBMultipliers (double &rm, double &gm, double &bm) const
     {
 
         double avg_r = 0.;
@@ -1038,7 +1024,7 @@ public:
         bm = avg_b / double(n);
     }
 
-    void transformPixel (int x, int y, int tran, int& tx, int& ty)
+    void transformPixel (int x, int y, int tran, int& tx, int& ty) const
     {
 
         if (!tran) {
@@ -1083,7 +1069,7 @@ public:
 
     virtual void getSpotWBData (double &reds, double &greens, double &blues, int &rn, int &gn, int &bn,
                                 std::vector<Coord2D> &red, std::vector<Coord2D> &green, std::vector<Coord2D> &blue,
-                                int tran)
+                                int tran) const
     {
         int x;
         int y;
@@ -1120,7 +1106,7 @@ public:
         }
     }
 
-    void getPipetteData (T &valueR, T &valueG, T &valueB, int posX, int posY, int squareSize, int tran)
+    void getPipetteData (T &valueR, T &valueG, T &valueB, int posX, int posY, int squareSize, int tran) const
     {
         int x;
         int y;
@@ -1147,7 +1133,7 @@ public:
         valueB = n ? T(accumulatorB / float(n)) : T(0);
     }
 
-    void readData   (FILE *f)
+    void readData (FILE *f)
     {
         for (int i = 0; i < height; i++) {
             fread (r(i), sizeof(T), width, f);
@@ -1162,7 +1148,7 @@ public:
         }
     }
 
-    void writeData  (FILE *f)
+    void writeData (FILE *f) const
     {
         for (int i = 0; i < height; i++) {
             fwrite (r(i), sizeof(T), width, f);
@@ -1345,7 +1331,7 @@ public:
     }
 
     /** Copy the data to another ChunkyRGBData */
-    void copyData(ChunkyRGBData<T> *dest)
+    void copyData(ChunkyRGBData<T> *dest) const
     {
         assert (dest != nullptr);
         // Make sure that the size is the same, reallocate if necessary
@@ -1421,7 +1407,7 @@ public:
     }
 
     template <class IC>
-    void resizeImgTo (int nw, int nh, TypeInterpolation interp, IC *imgPtr)
+    void resizeImgTo (int nw, int nh, TypeInterpolation interp, IC *imgPtr) const
     {
         //printf("resizeImgTo: resizing %s image data (%d x %d) to %s (%d x %d)\n", getType(), width, height, imgPtr->getType(), imgPtr->width, imgPtr->height);
         if (width == nw && height == nh) {
@@ -1485,9 +1471,9 @@ public:
             // This case should never occur!
             for (int i = 0; i < nh; i++) {
                 for (int j = 0; j < nw; j++) {
-                    r(i, j) = 0;
-                    g(i, j) = 0;
-                    b(i, j) = 0;
+                    imgPtr->r(i, j) = 0;
+                    imgPtr->g(i, j) = 0;
+                    imgPtr->b(i, j) = 0;
                 }
             }
         }
@@ -1545,7 +1531,7 @@ public:
         }
     }
 
-    void calcGrayscaleHist(unsigned int *hist16)
+    void calcGrayscaleHist(unsigned int *hist16) const
     {
         for (int row = 0; row < height; row++)
             for (int col = 0; col < width; col++) {
@@ -1559,7 +1545,7 @@ public:
             }
     }
 
-    void computeAutoHistogram (LUTu & histogram, int& histcompr)
+    void computeAutoHistogram (LUTu & histogram, int& histcompr) const
     {
         histcompr = 3;
 
@@ -1578,7 +1564,7 @@ public:
             }
     }
 
-    void computeHistogramAutoWB (double &avg_r, double &avg_g, double &avg_b, int &n, LUTu &histogram, const int compression)
+    void computeHistogramAutoWB (double &avg_r, double &avg_g, double &avg_b, int &n, LUTu &histogram, const int compression) const
     {
         histogram.clear();
         avg_r = avg_g = avg_b = 0.;
@@ -1610,7 +1596,7 @@ public:
             }
     }
 
-    void getAutoWBMultipliers (double &rm, double &gm, double &bm)
+    void getAutoWBMultipliers (double &rm, double &gm, double &bm) const
     {
 
         double avg_r = 0.;
@@ -1641,7 +1627,7 @@ public:
         bm = avg_b / double(n);
     }
 
-    void transformPixel (int x, int y, int tran, int& tx, int& ty)
+    void transformPixel (int x, int y, int tran, int& tx, int& ty) const
     {
 
         if (!tran) {
@@ -1686,7 +1672,7 @@ public:
 
     virtual void getSpotWBData (double &reds, double &greens, double &blues, int &rn, int &gn, int &bn,
                                 std::vector<Coord2D> &red, std::vector<Coord2D> &green, std::vector<Coord2D> &blue,
-                                int tran)
+                                int tran) const
     {
         int x;
         int y;
@@ -1723,14 +1709,14 @@ public:
         }
     }
 
-    void readData   (FILE *f)
+    void readData (FILE *f)
     {
         for (int i = 0; i < height; i++) {
             fread (r(i), sizeof(T), 3 * width, f);
         }
     }
 
-    void writeData  (FILE *f)
+    void writeData (FILE *f) const
     {
         for (int i = 0; i < height; i++) {
             fwrite (r(i), sizeof(T), 3 * width, f);
@@ -1751,31 +1737,31 @@ public:
     /** @brief Returns a mutex that can is useful in many situations. No image operations shuold be performed without locking this mutex.
       * @return The mutex */
     virtual MyMutex& getMutex () = 0;
-    virtual cmsHPROFILE getProfile () = 0;
+    virtual cmsHPROFILE getProfile () const = 0;
     /** @brief Returns the bits per pixel of the image.
       * @return The bits per pixel of the image */
-    virtual int getBitsPerPixel () = 0;
+    virtual int getBitsPerPixel () const = 0;
     /** @brief Saves the image to file. It autodetects the format (jpg, tif, png are supported).
       * @param fname is the name of the file
         @return the error code, 0 if none */
-    virtual int saveToFile (Glib::ustring fname) = 0;
+    virtual int saveToFile (const Glib::ustring &fname) const = 0;
     /** @brief Saves the image to file in a png format.
       * @param fname is the name of the file
       * @param compression is the amount of compression (0-6), -1 corresponds to the default
       * @param bps can be 8 or 16 depending on the bits per pixels the output file will have
         @return the error code, 0 if none */
-    virtual int saveAsPNG  (Glib::ustring fname, int bps = -1) = 0;
+    virtual int saveAsPNG (const Glib::ustring &fname, int bps = -1) const = 0;
     /** @brief Saves the image to file in a jpg format.
       * @param fname is the name of the file
       * @param quality is the quality of the jpeg (0...100), set it to -1 to use default
         @return the error code, 0 if none */
-    virtual int saveAsJPEG (Glib::ustring fname, int quality = 100, int subSamp = 3 ) = 0;
+    virtual int saveAsJPEG (const Glib::ustring &fname, int quality = 100, int subSamp = 3 ) const = 0;
     /** @brief Saves the image to file in a tif format.
       * @param fname is the name of the file
       * @param bps can be 8 or 16 depending on the bits per pixels the output file will have
       * @param isFloat is true for saving float images. Will be ignored by file format not supporting float data
         @return the error code, 0 if none */
-    virtual int saveAsTIFF (Glib::ustring fname, int bps = -1, float isFloat = false, bool uncompressed = false) = 0;
+    virtual int saveAsTIFF (const Glib::ustring &fname, int bps = -1, bool isFloat = false, bool uncompressed = false) const = 0;
     /** @brief Sets the progress listener if you want to follow the progress of the image saving operations (optional).
       * @param pl is the pointer to the class implementing the ProgressListener interface */
     virtual void setSaveProgressListener (ProgressListener* pl) = 0;
diff --git a/rtengine/image16.cc b/rtengine/image16.cc
index 5ceb4f804..618d31641 100644
--- a/rtengine/image16.cc
+++ b/rtengine/image16.cc
@@ -60,7 +60,7 @@ Image16::~Image16()
 {
 }
 
-void Image16::getScanline(int row, unsigned char* buffer, int bps, bool isFloat)
+void Image16::getScanline(int row, unsigned char* buffer, int bps, bool isFloat) const
 {
 
     if (data == nullptr) {
@@ -124,7 +124,7 @@ void Image16::setScanline(int row, unsigned char* buffer, int bps, unsigned int
      */
 }
 
-Image16* Image16::copy()
+Image16* Image16::copy() const
 {
 
     Image16* cp = new Image16(width, height);
@@ -132,7 +132,7 @@ Image16* Image16::copy()
     return cp;
 }
 
-void Image16::getStdImage(ColorTemp ctemp, int tran, Imagefloat* image, PreviewProps pp)
+void Image16::getStdImage(const ColorTemp &ctemp, int tran, Imagefloat* image, PreviewProps pp) const
 {
 
     // compute channel multipliers
@@ -295,8 +295,7 @@ void Image16::getStdImage(ColorTemp ctemp, int tran, Imagefloat* image, PreviewP
 #undef GCLIP
 }
 
-Image8*
-Image16::to8()
+Image8* Image16::to8() const
 {
     Image8* img8 = new Image8(width, height);
 
@@ -311,8 +310,7 @@ Image16::to8()
     return img8;
 }
 
-Imagefloat*
-Image16::tofloat()
+Imagefloat* Image16::tofloat() const
 {
     Imagefloat* imgfloat = new Imagefloat(width, height);
 
diff --git a/rtengine/image16.h b/rtengine/image16.h
index 804f8cc72..3431d8afd 100644
--- a/rtengine/image16.h
+++ b/rtengine/image16.h
@@ -40,62 +40,71 @@ public:
     Image16(int width, int height);
     ~Image16();
 
-    Image16*             copy();
+    Image16* copy() const;
 
-    Image8*              to8();
-    Imagefloat*          tofloat();
+    Image8* to8() const;
+    Imagefloat* tofloat() const;
 
-    virtual void         getStdImage(ColorTemp ctemp, int tran, Imagefloat* image, PreviewProps pp);
+    void getStdImage(const ColorTemp &ctemp, int tran, Imagefloat* image, PreviewProps pp) const override;
 
-    virtual const char*  getType() const
+    const char* getType() const override
     {
         return sImage16;
     }
-    virtual int          getBPS()
+    int getBPS() const override
     {
         return 8 * sizeof(unsigned short);
     }
-    virtual void         getScanline(int row, unsigned char* buffer, int bps, bool isFloat = false);
-    virtual void         setScanline(int row, unsigned char* buffer, int bps, unsigned int numSamples);
+
+    void getScanline(int row, unsigned char* buffer, int bps, bool isFloat = false) const override;
+    void setScanline(int row, unsigned char* buffer, int bps, unsigned int numSamples) override;
 
     // functions inherited from IImage16:
-    virtual MyMutex&     getMutex()
+    MyMutex& getMutex() override
     {
         return mutex();
     }
-    virtual cmsHPROFILE  getProfile()
+
+    cmsHPROFILE getProfile() const override
     {
         return getEmbeddedProfile();
     }
-    virtual int          getBitsPerPixel()
+
+    int getBitsPerPixel() const override
     {
         return 8 * sizeof(unsigned short);
     }
-    virtual int          saveToFile(Glib::ustring fname)
+
+    int saveToFile(const Glib::ustring &fname) const override
     {
         return save(fname);
     }
-    virtual int          saveAsPNG(Glib::ustring fname, int bps = -1)
+
+    saveAsPNG(const Glib::ustring &fname, int bps = -1) const override
     {
         return savePNG(fname, bps);
     }
-    virtual int          saveAsJPEG(Glib::ustring fname, int quality = 100, int subSamp = 3)
+
+    int saveAsJPEG(const Glib::ustring &fname, int quality = 100, int subSamp = 3) const override
     {
         return saveJPEG(fname, quality, subSamp);
     }
-    virtual int          saveAsTIFF(Glib::ustring fname, int bps = -1, float isFloat = false, bool uncompressed = false)
+
+    int saveAsTIFF(const Glib::ustring &fname, int bps = -1, bool isFloat = false, bool uncompressed = false) const override
     {
         return saveTIFF(fname, bps, isFloat, uncompressed);
     }
-    virtual void         setSaveProgressListener(ProgressListener* pl)
+
+    void setSaveProgressListener(ProgressListener* pl) override
     {
         setProgressListener(pl);
     }
-    virtual void         free()
+
+    void free() override
     {
         delete this;
     }
-    void                 ExecCMSTransform(cmsHTRANSFORM hTransform);
+    void ExecCMSTransform(cmsHTRANSFORM hTransform);
 
     /* void                 ExecCMSTransform(cmsHTRANSFORM hTransform, const LabImage &labImage, int cx, int cy); */
 };
diff --git a/rtengine/image8.cc b/rtengine/image8.cc
index 15a6d9acc..edced2fe5 100644
--- a/rtengine/image8.cc
+++ b/rtengine/image8.cc
@@ -37,7 +37,7 @@ Image8::~Image8 ()
 {
 }
 
-void Image8::getScanline (int row, unsigned char* buffer, int bps, bool isFloat)
+void Image8::getScanline (int row, unsigned char* buffer, int bps, bool isFloat) const
 {
 
     if (data == nullptr) {
@@ -89,7 +89,7 @@ void Image8::setScanline (int row, unsigned char* buffer, int bps, unsigned int
     }
 }
 
-Image8* Image8::copy ()
+Image8* Image8::copy () const
 {
 
     Image8* cp = new Image8 (width, height);
@@ -97,7 +97,7 @@ Image8* Image8::copy ()
     return cp;
 }
 
-void Image8::getStdImage (ColorTemp ctemp, int tran, Imagefloat* image, PreviewProps pp)
+void Image8::getStdImage (const ColorTemp &ctemp, int tran, Imagefloat* image, PreviewProps pp) const
 {
     // compute channel multipliers
     float rm = 1.f, gm = 1.f, bm = 1.f;
diff --git a/rtengine/image8.h b/rtengine/image8.h
index 9bb5d51e3..2cc670a4a 100644
--- a/rtengine/image8.h
+++ b/rtengine/image8.h
@@ -38,55 +38,65 @@ public:
     Image8 (int width, int height);
     ~Image8 ();
 
-    Image8*              copy ();
+    Image8* copy () const;
 
-    virtual void         getStdImage (ColorTemp ctemp, int tran, Imagefloat* image, PreviewProps pp);
+    void getStdImage (const ColorTemp &ctemp, int tran, Imagefloat* image, PreviewProps pp) const override;
 
-    virtual const char*  getType     () const
+    const char* getType () const override
     {
         return sImage8;
     }
-    virtual int          getBPS      ()
+
+    int getBPS () const override
     {
         return 8 * sizeof(unsigned char);
     }
-    virtual void         getScanline (int row, unsigned char* buffer, int bps, bool isFloat = false);
-    virtual void         setScanline (int row, unsigned char* buffer, int bps, unsigned int numSamples);
+
+    void getScanline (int row, unsigned char* buffer, int bps, bool isFloat = false) const override;
+    void setScanline (int row, unsigned char* buffer, int bps, unsigned int numSamples) override;
 
     // functions inherited from IImage*:
-    virtual MyMutex&     getMutex ()
+    MyMutex& getMutex () override
     {
         return mutex ();
     }
-    virtual cmsHPROFILE  getProfile ()
+
+    cmsHPROFILE getProfile () const override
     {
         return getEmbeddedProfile ();
     }
-    virtual int          getBitsPerPixel ()
+
+    int getBitsPerPixel () const override
     {
         return 8 * sizeof(unsigned char);
     }
-    virtual int          saveToFile (Glib::ustring fname)
+
+    int saveToFile (const Glib::ustring &fname) const override
     {
         return save (fname);
     }
-    virtual int          saveAsPNG  (Glib::ustring fname, int bps = -1)
+
+    int saveAsPNG (const Glib::ustring &fname, int bps = -1) const override
     {
         return savePNG (fname, bps);
     }
-    virtual int          saveAsJPEG (Glib::ustring fname, int quality = 100, int subSamp = 3)
+
+    int saveAsJPEG (const Glib::ustring &fname, int quality = 100, int subSamp = 3) const override
     {
         return saveJPEG (fname, quality, subSamp);
     }
-    virtual int          saveAsTIFF (Glib::ustring fname, int bps = -1, float isFloat = false, bool uncompressed = false)
+
+    int saveAsTIFF (const Glib::ustring &fname, int bps = -1, bool isFloat = false, bool uncompressed = false) const override
     {
         return saveTIFF (fname, bps, isFloat, uncompressed);
     }
-    virtual void         setSaveProgressListener (ProgressListener* pl)
+
+    void setSaveProgressListener (ProgressListener* pl) override
     {
         setProgressListener (pl);
     }
-    virtual void         free ()
+
+    void free () override
     {
         delete this;
     }
diff --git a/rtengine/imagefloat.cc b/rtengine/imagefloat.cc
index fd6bc1c75..63c521040 100644
--- a/rtengine/imagefloat.cc
+++ b/rtengine/imagefloat.cc
@@ -110,7 +110,7 @@ void Imagefloat::setScanline (int row, unsigned char* buffer, int bps, unsigned
 
 namespace rtengine { extern void filmlike_clip(float *r, float *g, float *b); }
 
-void Imagefloat::getScanline (int row, unsigned char* buffer, int bps, bool isFloat)
+void Imagefloat::getScanline (int row, unsigned char* buffer, int bps, bool isFloat) const
 {
 
     if (data == nullptr) {
@@ -159,7 +159,7 @@ void Imagefloat::getScanline (int row, unsigned char* buffer, int bps, bool isFl
     }
 }
 
-Imagefloat* Imagefloat::copy ()
+Imagefloat* Imagefloat::copy () const
 {
 
     Imagefloat* cp = new Imagefloat (width, height);
@@ -168,7 +168,7 @@ Imagefloat* Imagefloat::copy ()
 }
 
 // This is called by the StdImageSource class. We assume that fp images from StdImageSource don't have to deal with gamma
-void Imagefloat::getStdImage (ColorTemp ctemp, int tran, Imagefloat* image, PreviewProps pp)
+void Imagefloat::getStdImage (const ColorTemp &ctemp, int tran, Imagefloat* image, PreviewProps pp) const
 {
 
     // compute channel multipliers
@@ -330,7 +330,7 @@ void Imagefloat::getStdImage (ColorTemp ctemp, int tran, Imagefloat* image, Prev
 }
 
 Image8*
-Imagefloat::to8()
+Imagefloat::to8() const
 {
     Image8* img8 = new Image8(width, height);
 #ifdef _OPENMP
@@ -349,7 +349,7 @@ Imagefloat::to8()
 }
 
 Image16*
-Imagefloat::to16()
+Imagefloat::to16() const
 {
     Image16* img16 = new Image16(width, height);
 #ifdef _OPENMP
diff --git a/rtengine/imagefloat.h b/rtengine/imagefloat.h
index d84e742ce..bd7ae2a46 100644
--- a/rtengine/imagefloat.h
+++ b/rtengine/imagefloat.h
@@ -44,63 +44,65 @@ public:
     Imagefloat (int width, int height);
     ~Imagefloat ();
 
-    Imagefloat*          copy ();
+    Imagefloat* copy () const;
 
-    Image8*              to8();
-    Image16*             to16();
+    Image8* to8() const;
+    Image16* to16() const;
 
-    virtual void         getStdImage (ColorTemp ctemp, int tran, Imagefloat* image, PreviewProps pp);
+    void getStdImage (const ColorTemp &ctemp, int tran, Imagefloat* image, PreviewProps pp) const override;
 
-    virtual const char*  getType     () const
+    const char* getType () const override
     {
         return sImagefloat;
     }
-    virtual int          getBPS      ()
+
+    int getBPS () const override
     {
         return 8 * sizeof(float);
     }
-    virtual void         getScanline (int row, unsigned char* buffer, int bps, bool isFloat = false);
-    virtual void         setScanline (int row, unsigned char* buffer, int bps, unsigned int numSamples);
+
+    void getScanline (int row, unsigned char* buffer, int bps, bool isFloat = false) const override;
+    void setScanline (int row, unsigned char* buffer, int bps, unsigned int numSamples) override;
 
     // functions inherited from IImagefloat:
-    virtual MyMutex&     getMutex ()
+    MyMutex& getMutex () override
     {
         return mutex ();
     }
-    virtual cmsHPROFILE  getProfile ()
+    cmsHPROFILE getProfile () const override
     {
         return getEmbeddedProfile ();
     }
-    virtual int          getBitsPerPixel ()
+    int getBitsPerPixel () const override
     {
         return 8 * sizeof(float);
     }
-    virtual int          saveToFile (Glib::ustring fname)
+    int saveToFile (const Glib::ustring &fname) const override
     {
         return save (fname);
     }
-    virtual int          saveAsPNG  (Glib::ustring fname, int bps = -1)
+    int saveAsPNG  (const Glib::ustring &fname, int bps = -1) const override
     {
         return savePNG (fname, bps);
     }
-    virtual int          saveAsJPEG (Glib::ustring fname, int quality = 100, int subSamp = 3)
+    int saveAsJPEG (const Glib::ustring &fname, int quality = 100, int subSamp = 3) const override
     {
         return saveJPEG (fname, quality, subSamp);
     }
-    virtual int          saveAsTIFF (Glib::ustring fname, int bps = -1, float isFloat = false, bool uncompressed = false)
+    int saveAsTIFF (const Glib::ustring &fname, int bps = -1, bool isFloat = false, bool uncompressed = false) const override
     {
         return saveTIFF (fname, bps, isFloat, uncompressed);
     }
-    virtual void         setSaveProgressListener (ProgressListener* pl)
+    void setSaveProgressListener (ProgressListener* pl) override
     {
         setProgressListener (pl);
     }
-    virtual void         free ()
+    void free () override
     {
         delete this;
     }
 
-    inline uint16_t      DNG_FloatToHalf(float f)
+    inline uint16_t DNG_FloatToHalf(float f) const
     {
         union {
             float f;
diff --git a/rtengine/imageio.cc b/rtengine/imageio.cc
index 9ac72be58..76a6417ff 100644
--- a/rtengine/imageio.cc
+++ b/rtengine/imageio.cc
@@ -201,7 +201,7 @@ void png_read_data(png_struct_def  *png_ptr, unsigned char *data, size_t length)
 void png_write_data(png_struct_def *png_ptr, unsigned char *data, size_t length);
 void png_flush(png_struct_def *png_ptr);
 
-int ImageIO::getPNGSampleFormat (Glib::ustring fname, IIOSampleFormat &sFormat, IIOSampleArrangement &sArrangement)
+int ImageIO::getPNGSampleFormat (const Glib::ustring &fname, IIOSampleFormat &sFormat, IIOSampleArrangement &sArrangement)
 {
     FILE *file = g_fopen (fname.c_str (), "rb");
 
@@ -273,7 +273,7 @@ int ImageIO::getPNGSampleFormat (Glib::ustring fname, IIOSampleFormat &sFormat,
     }
 }
 
-int ImageIO::loadPNG  (Glib::ustring fname)
+int ImageIO::loadPNG  (const Glib::ustring &fname)
 {
 
     FILE *file = g_fopen (fname.c_str (), "rb");
@@ -543,7 +543,7 @@ int ImageIO::loadJPEGFromMemory (const char* buffer, int bufsize)
     return IMIO_SUCCESS;
 }
 
-int ImageIO::loadJPEG (Glib::ustring fname)
+int ImageIO::loadJPEG (const Glib::ustring &fname)
 {
     FILE *file = g_fopen(fname.c_str (), "rb");
 
@@ -629,7 +629,7 @@ int ImageIO::loadJPEG (Glib::ustring fname)
     }
 }
 
-int ImageIO::getTIFFSampleFormat (Glib::ustring fname, IIOSampleFormat &sFormat, IIOSampleArrangement &sArrangement)
+int ImageIO::getTIFFSampleFormat (const Glib::ustring &fname, IIOSampleFormat &sFormat, IIOSampleArrangement &sArrangement)
 {
 #ifdef WIN32
     wchar_t *wfilename = (wchar_t*)g_utf8_to_utf16 (fname.c_str(), -1, NULL, NULL, NULL);
@@ -731,7 +731,7 @@ int ImageIO::getTIFFSampleFormat (Glib::ustring fname, IIOSampleFormat &sFormat,
     return IMIO_VARIANTNOTSUPPORTED;
 }
 
-int ImageIO::loadTIFF (Glib::ustring fname)
+int ImageIO::loadTIFF (const Glib::ustring &fname)
 {
 
     static MyMutex thumbMutex;
@@ -972,7 +972,7 @@ void PNGwriteRawProfile(png_struct *ping, png_info *ping_info, const char *profi
 
 } // namespace
 
-int ImageIO::savePNG  (Glib::ustring fname, volatile int bps)
+int ImageIO::savePNG  (const Glib::ustring &fname, int bps) const
 {
     if (getWidth() < 1 || getHeight() < 1) {
         return IMIO_HEADERERROR;
@@ -1111,7 +1111,7 @@ int ImageIO::savePNG  (Glib::ustring fname, volatile int bps)
 
 
 // Quality 0..100, subsampling: 1=low quality, 2=medium, 3=high
-int ImageIO::saveJPEG (Glib::ustring fname, int quality, int subSamp)
+int ImageIO::saveJPEG (const Glib::ustring &fname, int quality, int subSamp) const
 {
     if (getWidth() < 1 || getHeight() < 1) {
         return IMIO_HEADERERROR;
@@ -1301,7 +1301,7 @@ int ImageIO::saveJPEG (Glib::ustring fname, int quality, int subSamp)
     return IMIO_SUCCESS;
 }
 
-int ImageIO::saveTIFF (Glib::ustring fname, int bps, float isFloat, bool uncompressed)
+int ImageIO::saveTIFF (const Glib::ustring &fname, int bps, bool isFloat, bool uncompressed) const
 {
     if (getWidth() < 1 || getHeight() < 1) {
         return IMIO_HEADERERROR;
@@ -1595,7 +1595,7 @@ void png_flush(png_structp png_ptr)
     }
 }
 
-int ImageIO::load (Glib::ustring fname)
+int ImageIO::load (const Glib::ustring &fname)
 {
 
     if (hasPngExtension(fname)) {
@@ -1609,7 +1609,7 @@ int ImageIO::load (Glib::ustring fname)
     }
 }
 
-int ImageIO::save (Glib::ustring fname)
+int ImageIO::save (const Glib::ustring &fname) const
 {
     if (hasPngExtension(fname)) {
         return savePNG (fname);
@@ -1621,3 +1621,57 @@ int ImageIO::save (Glib::ustring fname)
         return IMIO_FILETYPENOTSUPPORTED;
     }
 }
+
+void ImageIO::setProgressListener (ProgressListener* l)
+{
+    pl = l;
+}
+
+void ImageIO::setSampleFormat(IIOSampleFormat sFormat)
+{
+    sampleFormat = sFormat;
+}
+
+IIOSampleFormat ImageIO::getSampleFormat() const
+{
+    return sampleFormat;
+}
+
+void ImageIO::setSampleArrangement(IIOSampleArrangement sArrangement)
+{
+    sampleArrangement = sArrangement;
+}
+
+IIOSampleArrangement ImageIO::getSampleArrangement() const
+{
+    return sampleArrangement;
+}
+
+cmsHPROFILE ImageIO::getEmbeddedProfile () const
+{
+    return embProfile;
+}
+
+void ImageIO::getEmbeddedProfileData (int& length, unsigned char*& pdata) const
+{
+    length = loadedProfileLength;
+    pdata = (unsigned char*)loadedProfileData;
+}
+
+MyMutex& ImageIO::mutex ()
+{
+    return imutex;
+}
+
+void ImageIO::deleteLoadedProfileData( )
+{
+    if(loadedProfileData) {
+        if(loadedProfileDataJpg) {
+            free(loadedProfileData);
+        } else {
+            delete[] loadedProfileData;
+        }
+    }
+
+    loadedProfileData = nullptr;
+}
diff --git a/rtengine/imageio.h b/rtengine/imageio.h
index bb9fbc5f4..5970866f0 100644
--- a/rtengine/imageio.h
+++ b/rtengine/imageio.h
@@ -28,11 +28,11 @@
 #define IMIO_FILETYPENOTSUPPORTED  6
 #define IMIO_CANNOTWRITEFILE       7
 
+#include <glibmm.h>
+#include <libiptcdata/iptc-data.h>
 #include "rtengine.h"
 #include "imageformat.h"
-#include <glibmm.h>
 #include "procparams.h"
-#include <libiptcdata/iptc-data.h>
 #include "../rtexif/rtexif.h"
 #include "imagedimensions.h"
 #include "iimage.h"
@@ -63,18 +63,8 @@ protected:
     IIOSampleArrangement sampleArrangement;
 
 private:
-    void deleteLoadedProfileData( )
-    {
-        if(loadedProfileData) {
-            if(loadedProfileDataJpg) {
-                free(loadedProfileData);
-            } else {
-                delete[] loadedProfileData;
-            }
-        }
+    void deleteLoadedProfileData( );
 
-        loadedProfileData = nullptr;
-    }
 public:
     static Glib::ustring errorMsg[6];
 
@@ -84,75 +74,42 @@ public:
 
     virtual ~ImageIO ();
 
-    void setProgressListener (ProgressListener* l)
-    {
-        pl = l;
-    }
+    void setProgressListener (ProgressListener* l);
+    void setSampleFormat(IIOSampleFormat sFormat);
+    IIOSampleFormat getSampleFormat() const;
+    void setSampleArrangement(IIOSampleArrangement sArrangement);
+    IIOSampleArrangement getSampleArrangement() const;
 
-    void                 setSampleFormat(IIOSampleFormat sFormat)
-    {
-        sampleFormat = sFormat;
-    }
-    IIOSampleFormat      getSampleFormat()
-    {
-        return sampleFormat;
-    }
-    void                 setSampleArrangement(IIOSampleArrangement sArrangement)
-    {
-        sampleArrangement = sArrangement;
-    }
-    IIOSampleArrangement getSampleArrangement()
-    {
-        return sampleArrangement;
-    }
+    virtual void getStdImage (const ColorTemp &ctemp, int tran, Imagefloat* image, PreviewProps pp) const = 0;
+    virtual int getBPS () const = 0;
+    virtual void getScanline (int row, unsigned char* buffer, int bps, bool isFloat = false) const = 0;
+    virtual void setScanline (int row, unsigned char* buffer, int bps, unsigned int numSamples = 3) = 0;
+    virtual const char* getType () const = 0;
 
-    virtual void    getStdImage (ColorTemp ctemp, int tran, Imagefloat* image, PreviewProps pp) = 0;
-    virtual int     getBPS      () = 0;
-    virtual void    getScanline (int row, unsigned char* buffer, int bps, bool isFloat = false) {}
-    virtual void    setScanline (int row, unsigned char* buffer, int bps, unsigned int numSamples = 3) {}
+    int load (const Glib::ustring &fname);
+    int save (const Glib::ustring &fname) const;
 
-    virtual bool    readImage   (Glib::ustring &fname, FILE *fh)
-    {
-        return false;
-    };
-    virtual bool    writeImage  (Glib::ustring &fname, FILE *fh)
-    {
-        return false;
-    };
-
-    int load (Glib::ustring fname);
-    int save (Glib::ustring fname);
-
-    int loadPNG  (Glib::ustring fname);
-    int loadJPEG (Glib::ustring fname);
-    int loadTIFF (Glib::ustring fname);
-    static int getPNGSampleFormat  (Glib::ustring fname, IIOSampleFormat &sFormat, IIOSampleArrangement &sArrangement);
-    static int getTIFFSampleFormat (Glib::ustring fname, IIOSampleFormat &sFormat, IIOSampleArrangement &sArrangement);
+    int loadPNG (const Glib::ustring &fname);
+    int loadJPEG (const Glib::ustring &fname);
+    int loadTIFF (const Glib::ustring &fname);
+    static int getPNGSampleFormat (const Glib::ustring &fname, IIOSampleFormat &sFormat, IIOSampleArrangement &sArrangement);
+    static int getTIFFSampleFormat (const Glib::ustring &fname, IIOSampleFormat &sFormat, IIOSampleArrangement &sArrangement);
 
     int loadJPEGFromMemory (const char* buffer, int bufsize);
     int loadPPMFromMemory(const char* buffer, int width, int height, bool swap, int bps);
 
-    int savePNG  (Glib::ustring fname, volatile int bps = -1);
-    int saveJPEG (Glib::ustring fname, int quality = 100, int subSamp = 3);
-    int saveTIFF (Glib::ustring fname, int bps = -1, float isFloat = false, bool uncompressed = false);
+    int savePNG (const Glib::ustring &fname, int bps = -1) const;
+    int saveJPEG (const Glib::ustring &fname, int quality = 100, int subSamp = 3) const;
+    int saveTIFF (const Glib::ustring &fname, int bps = -1, bool isFloat = false, bool uncompressed = false) const;
 
-    cmsHPROFILE getEmbeddedProfile ()
-    {
-        return embProfile;
-    }
-    void        getEmbeddedProfileData (int& length, unsigned char*& pdata)
-    {
-        length = loadedProfileLength;
-        pdata = (unsigned char*)loadedProfileData;
-    }
+    cmsHPROFILE getEmbeddedProfile () const;
+    void getEmbeddedProfileData (int& length, unsigned char*& pdata) const;
 
     void setMetadata (const rtexif::TagDirectory* eroot);
     void setMetadata (const rtexif::TagDirectory* eroot, const rtengine::procparams::ExifPairs& exif, const rtengine::procparams::IPTCPairs& iptcc);
-    void setOutputProfile  (const char* pdata, int plen);
-    MyMutex& mutex ()
-    {
-        return imutex;
-    }
+    void setOutputProfile (const char* pdata, int plen);
+
+    MyMutex& mutex ();
 };
 
 }