diff --git a/src/Mod/Image/App/ImageBase.cpp b/src/Mod/Image/App/ImageBase.cpp
index f96ab4fcb5..10471c82bf 100644
--- a/src/Mod/Image/App/ImageBase.cpp
+++ b/src/Mod/Image/App/ImageBase.cpp
@@ -26,7 +26,7 @@ using namespace Image;
 // Constructor (constructs an empty image)
 ImageBase::ImageBase()
 {
-    _pPixelData = NULL;
+    _pPixelData = nullptr;
     _owner = true;
     _width = 0;
     _height = 0;
@@ -50,7 +50,7 @@ ImageBase::ImageBase(const ImageBase &rhs)
     if (rhs._owner == true)
     {
         // rhs is the owner - do a deep copy
-        _pPixelData = NULL;
+        _pPixelData = nullptr;
         _owner = false; // avoids a superfluous delete
         if (createCopy((void *)(rhs._pPixelData), rhs._width, rhs._height, rhs._format, rhs._numSigBitsPerSample) != 0)
             throw Base::RuntimeError("ImageBase::ImageBase. Error creating copy of image");
@@ -105,12 +105,12 @@ void ImageBase::clear()
     if (_owner == true)
     {
         delete [] _pPixelData;
-        _pPixelData = NULL;
+        _pPixelData = nullptr;
     }
     // Else just reset the pointer (the owner of the pixel data must be responsible for deleting it)
     else
     {
-        _pPixelData = NULL;
+        _pPixelData = nullptr;
     }
 
     // Re-initialise the other variables
@@ -201,7 +201,7 @@ int ImageBase::_setColorFormat(int format, unsigned short numSigBitsPerSample)
 int ImageBase::_allocate()
 {
     // Check that pixel data pointer is null
-    if (_pPixelData != NULL)
+    if (_pPixelData != nullptr)
         return -1;
 
     // Allocate the space needed to store the pixel data
@@ -296,7 +296,7 @@ int ImageBase::pointTo(void* pSrcPixelData, unsigned long width, unsigned long h
 // if there is no image data
 int ImageBase::getSample(int x, int y, unsigned short sampleIndex, double &value)
 {
-    if ((_pPixelData == NULL) || 
+    if ((_pPixelData == nullptr) || 
         (sampleIndex >= _numSamples) ||
         (x < 0) || (x >= (int)_width) || 
         (y < 0) || (y >= (int)_height))
diff --git a/src/Mod/Image/App/ImageBase.h b/src/Mod/Image/App/ImageBase.h
index bb013316be..0c8d1a5889 100644
--- a/src/Mod/Image/App/ImageBase.h
+++ b/src/Mod/Image/App/ImageBase.h
@@ -44,7 +44,7 @@ public:
     ImageBase(const ImageBase &rhs);
     ImageBase & operator=(const ImageBase &rhs);
 
-    bool hasValidData() const { return (_pPixelData != 0); }
+    bool hasValidData() const { return (_pPixelData != nullptr); }
     void* getPixelDataPtr() { return (void *)_pPixelData; }
     bool isOwner() const { return _owner; }
     unsigned long getWidth() const { return _width; }
diff --git a/src/Mod/Image/Gui/AppImageGuiPy.cpp b/src/Mod/Image/Gui/AppImageGuiPy.cpp
index f60fd706d5..0b67532756 100644
--- a/src/Mod/Image/Gui/AppImageGuiPy.cpp
+++ b/src/Mod/Image/Gui/AppImageGuiPy.cpp
@@ -74,7 +74,7 @@ private:
 
         // Extract image into a general RGB format recognised by the ImageView class
         int format = IB_CF_RGB24;
-        unsigned char *pPixelData = NULL;
+        unsigned char *pPixelData = nullptr;
         if (imageq.isNull() == false) {
             pPixelData = new unsigned char[3 * (unsigned long)imageq.width() * (unsigned long)imageq.height()];
             unsigned char *pPix = pPixelData;
diff --git a/src/Mod/Image/Gui/OpenGLImageBox.cpp b/src/Mod/Image/Gui/OpenGLImageBox.cpp
index aa1484e70c..7ee2e0c045 100644
--- a/src/Mod/Image/Gui/OpenGLImageBox.cpp
+++ b/src/Mod/Image/Gui/OpenGLImageBox.cpp
@@ -101,7 +101,7 @@ GLImageBox::GLImageBox(QWidget * parent, Qt::WindowFlags f)
     _zoomFactor = 1.0;
     _base_x0 = 0;
     _base_y0 = 0;
-    _pColorMap = 0;
+    _pColorMap = nullptr;
     _numMapEntries = 0;
 
 #if defined(_DEBUG) && 0
@@ -243,7 +243,7 @@ void GLImageBox::drawImage()
         glPixelTransferf(GL_BLUE_SCALE, (float)scale);
 
         // Load the color map if present
-        if (_pColorMap != 0)
+        if (_pColorMap != nullptr)
         {
             if (!haveMesa) glPixelTransferf(GL_MAP_COLOR, 1.0);
             glPixelMapfv(GL_PIXEL_MAP_R_TO_R, _numMapEntries, _pColorMap);
@@ -254,10 +254,10 @@ void GLImageBox::drawImage()
         else
         {
             glPixelTransferf(GL_MAP_COLOR, 0.0);
-            glPixelMapfv(GL_PIXEL_MAP_R_TO_R, 0, NULL);
-            glPixelMapfv(GL_PIXEL_MAP_G_TO_G, 0, NULL);
-            glPixelMapfv(GL_PIXEL_MAP_B_TO_B, 0, NULL);
-            glPixelMapfv(GL_PIXEL_MAP_A_TO_A, 0, NULL);
+            glPixelMapfv(GL_PIXEL_MAP_R_TO_R, 0, nullptr);
+            glPixelMapfv(GL_PIXEL_MAP_G_TO_G, 0, nullptr);
+            glPixelMapfv(GL_PIXEL_MAP_B_TO_B, 0, nullptr);
+            glPixelMapfv(GL_PIXEL_MAP_A_TO_A, 0, nullptr);
         }
 
         // Get the pixel format
@@ -698,7 +698,7 @@ void GLImageBox::resetDisplay()
 void GLImageBox::clearColorMap()
 {
     delete [] _pColorMap;
-    _pColorMap = 0;
+    _pColorMap = nullptr;
     _numMapEntries = 0;
 }
 
@@ -851,7 +851,7 @@ int GLImageBox::setColorMapAlphaValue(int index, float value)
 // Helper function to convert a pixel's value (of a sample) to the color map index (i.e. the map index that will be used for that pixel value)
 unsigned int GLImageBox::pixValToMapIndex(double PixVal)
 {
-    if (_pColorMap != NULL)
+    if (_pColorMap != nullptr)
     {
         double MaxVal = pow(2.0, _image.getNumBitsPerSample()) - 1.0;
         double Scale = (pow(2.0, _image.getNumBitsPerSample()) - 1.0) / (pow(2.0, _image.getNumSigBitsPerSample()) - 1.0);
diff --git a/src/Mod/Image/Gui/OpenGLImageBox.h b/src/Mod/Image/Gui/OpenGLImageBox.h
index 7959b36300..d9a38d98a7 100644
--- a/src/Mod/Image/Gui/OpenGLImageBox.h
+++ b/src/Mod/Image/Gui/OpenGLImageBox.h
@@ -37,7 +37,7 @@ class ImageGuiExport GLImageBox : public QOpenGLWidget
 
 public:
 
-    GLImageBox(QWidget * parent = 0, Qt::WindowFlags f = Qt::WindowFlags());
+    GLImageBox(QWidget * parent = nullptr, Qt::WindowFlags f = Qt::WindowFlags());
     ~GLImageBox();
 
     Image::ImageBase *getImageBasePtr() { return &_image; }