diff --git a/ImGuiToolkit.cpp b/ImGuiToolkit.cpp
index bb30748..40c33ff 100644
--- a/ImGuiToolkit.cpp
+++ b/ImGuiToolkit.cpp
@@ -778,3 +778,4 @@ void ToggleButton( const char* label, bool& toggle )
     if( ImGui::Button( label ) ) toggle = !toggle;
     if( active ) ImGui::PopStyleColor( 3 );
 }
+
diff --git a/ImGuiVisitor.cpp b/ImGuiVisitor.cpp
index 48181a0..adec9dd 100644
--- a/ImGuiVisitor.cpp
+++ b/ImGuiVisitor.cpp
@@ -47,7 +47,7 @@ void ImGuiVisitor::visit(Group &n)
         if (ImGuiToolkit::ButtonIcon(4, 15))
             n.rotation_.z = 0.f;
         ImGui::SameLine(0, 10);
-        ImGui::SliderAngle("slider angle", &(n.rotation_.z), -180.f, 180.f) ;
+        ImGui::SliderAngle("angle", &(n.rotation_.z), -180.f, 180.f) ;
 
         if (ImGuiToolkit::ButtonIcon(3, 15))  {
             n.scale_.x = 1.f;
@@ -114,6 +114,20 @@ void ImGuiVisitor::visit(Shader &n)
 
 void ImGuiVisitor::visit(ImageShader &n)
 {
+    ImGui::PushID(n.id());
+
+    if (ImGuiToolkit::ButtonIcon(2, 1)) {
+        n.brightness = 0.f;
+        n.contrast = 0.f;
+    }
+    ImGui::SameLine(0, 10);
+    float bc[2] = { n.brightness, n.contrast};
+    if ( ImGui::SliderFloat2("filter", bc, -1.0, 1.0) )
+    {
+        n.brightness = bc[0];
+        n.contrast = bc[1];
+    }
+    ImGui::PopID();
 }
 
 void ImGuiVisitor::visit(LineStrip &n)
diff --git a/Mesh.cpp b/Mesh.cpp
index 369fbf5..ac9425c 100644
--- a/Mesh.cpp
+++ b/Mesh.cpp
@@ -373,8 +373,3 @@ void Mesh::accept(Visitor& v)
     Primitive::accept(v);
     v.visit(*this);
 }
-
-//void Mesh::update( float dt )
-//{
-//    scale_.x = scale_.y;
-//}
diff --git a/Mesh.h b/Mesh.h
index 9559684..73b2b63 100644
--- a/Mesh.h
+++ b/Mesh.h
@@ -22,7 +22,6 @@ public:
     void init () override;
     void draw (glm::mat4 modelview, glm::mat4 projection) override;
     void accept (Visitor& v) override;
-//    void update (float dt) override;
 
     inline std::string getResource() const { return resource_; }
     inline std::string getTexture() const { return texturefilename_; }
diff --git a/Primitives.cpp b/Primitives.cpp
index f596b40..657c06b 100644
--- a/Primitives.cpp
+++ b/Primitives.cpp
@@ -98,9 +98,9 @@ void ImageSurface::accept(Visitor& v)
     v.visit(*this);
 }
 
-MediaSurface::MediaSurface(const std::string& path) : ImageSurface()
+MediaSurface::MediaSurface(const std::string& uri) : ImageSurface()
 {
-    resource_ = path;
+    resource_ = uri;
     mediaplayer_ = new MediaPlayer;
 }
 
@@ -140,12 +140,12 @@ void MediaSurface::update( float dt )
     if ( mediaplayer_->isOpen() ) {
         mediaplayer_->update();
 
-        if (parent_ != nullptr) {
-            parent_->transform_ = parent_->transform_ * glm::scale(glm::identity<glm::mat4>(), glm::vec3(mediaplayer_->aspectRatio(), 1.f, 1.f));
-            scale_.x = 1.0;
-        }
-        else
-            scale_.x = mediaplayer_->aspectRatio();
+//        if (parent_ != nullptr) {
+//            parent_->transform_ = parent_->transform_ * glm::scale(glm::identity<glm::mat4>(), glm::vec3(mediaplayer_->aspectRatio(), 1.f, 1.f));
+//            scale_.x = 1.0;
+//        }
+//        else
+        scale_.x = mediaplayer_->aspectRatio();
     }
 
     Primitive::update( dt );
diff --git a/Primitives.h b/Primitives.h
index f2e0fee..b1a6a49 100644
--- a/Primitives.h
+++ b/Primitives.h
@@ -4,8 +4,14 @@
 #include <string>
 
 #include "Scene.h"
+class MediaPlayer;
 
-// Draw a Rectangle (triangle strip) with a texture
+/**
+ * @brief The ImageSurface class is a Primitive to draw an image
+ *
+ * Image is read from the Ressouces (not an external file)
+ * Height = 1.0, Width is set by the aspect ratio of the image
+ */
 class ImageSurface : public Primitive {
 
     void deleteGLBuffers_() override {}
@@ -26,15 +32,18 @@ protected:
 };
 
 
-// Draw a Rectangle with a media as animated texture
-class MediaPlayer;
-
+/**
+ * @brief The MediaSurface class is an ImageSurface to draw a video
+ *
+ * URI is passed to a Media Player to handle the video playback
+ * Height = 1.0, Width is set by the aspect ratio of the image
+ */
 class MediaSurface : public ImageSurface {
 
     MediaPlayer *mediaplayer_;
 
 public:
-    MediaSurface(const std::string& path);
+    MediaSurface(const std::string& uri);
     ~MediaSurface();
 
     void init () override;
@@ -45,22 +54,10 @@ public:
     MediaPlayer *getMediaPlayer() { return mediaplayer_; }
 };
 
-//// Draw a Frame Buffer
-//class FrameBufferSurface : public Primitive {
 
-//    void deleteGLBuffers_() {}
-
-//public:
-//    FrameBufferSurface();
-
-//    void init () override;
-//    void draw(glm::mat4 modelview, glm::mat4 projection) override;
-//    void accept(Visitor& v) override;
-
-//};
-
-
-// Draw a Point
+/**
+ * @brief The Points class is a Primitive to draw Points
+ */
 class Points : public Primitive {
 
     uint pointsize_;
@@ -80,7 +77,10 @@ public:
     inline uint getPointSize() const { return pointsize_; }
 };
 
-// Draw a line strip
+
+/**
+ * @brief The LineStrip class is a Primitive to draw lines
+ */
 class LineStrip : public Primitive {
 
     uint linewidth_;
@@ -101,6 +101,9 @@ public:
 };
 
 
+/**
+ * @brief The LineSquare class is a square LineStrip (width & height = 1.0)
+ */
 class LineSquare : public LineStrip {
 
     void deleteGLBuffers_() override {}
@@ -113,6 +116,9 @@ public:
 };
 
 
+/**
+ * @brief The LineCircle class is a circular LineStrip (diameter = 1.0)
+ */
 class LineCircle : public LineStrip {
 
     void deleteGLBuffers_() override {}
diff --git a/Scene.cpp b/Scene.cpp
index 9d87ef9..47463da 100644
--- a/Scene.cpp
+++ b/Scene.cpp
@@ -164,6 +164,7 @@ void Primitive::deleteGLBuffers_()
         glDeleteVertexArrays ( 1, &vao_);
 }
 
+
 // Group
 
 Group::~Group()
diff --git a/Scene.h b/Scene.h
index 78de93d..cece07a 100644
--- a/Scene.h
+++ b/Scene.h
@@ -16,8 +16,27 @@ glm::mat4 transform(glm::vec3 translation, glm::vec3 rotation, glm::vec3 scale);
 class Shader;
 class Visitor;
 
-// Base virtual class for all Node types
-// Manages modelview transformations and culling
+
+/**
+ * @brief The Node class is the base virtual class for all Node types
+ *
+ * Every Node is given a unique id at instanciation
+ *
+ * Every Node has geometric operations for translation,
+ * scale and rotation. The update() function computes the
+ * transform_ matrix from these components.
+ *
+ * draw() shall be defined by the subclass.
+ * The visible flag can be used to show/hide a Node.
+ * To apply geometrical transformation, draw() can multiplying the
+ * modelview by the transform_ matrix.
+ *
+ * init() shall be called on the first call of draw():
+ *     if ( !initialized() )
+ *        init();
+ *
+ * accept() allows visitors to parse the graph.
+ */
 class Node {
 
     int       id_;
@@ -51,7 +70,22 @@ public:
     glm::vec3 scale_, rotation_, translation_;
 };
 
-// Leaf Nodes are primitives that can be rendered
+
+
+/**
+ * @brief The Primitive class is a leaf Node that can be rendered
+ *
+ * Primitive generates a STATIC vertex array object from
+ * a list of points, colors and texture coordinates.
+ * The vertex array is deleted in the Primitive destructor.
+ *
+ * Primitive class itself does not define any geometry: subclasses
+ * should fill the points, colors and texture coordinates
+ * in their constructor.
+ *
+ * Primitive can be given a shader that is used during draw.
+ *
+ */
 class Primitive : public Node {
 
 public:
@@ -75,8 +109,9 @@ protected:
     virtual void deleteGLBuffers_();
 };
 
-// Other Nodes establish hierarchy with a group of nodes
-
+//
+// Other Nodes establish hierarchy with a set of nodes
+//
 struct z_comparator
 {
     inline bool operator () (const Node *a, const Node *b) const
@@ -97,7 +132,19 @@ private:
 };
 typedef std::multiset<Node*, z_comparator> NodeSet;
 
-
+/**
+ * @brief The Group class contains a list of pointers to Nodes.
+ *
+ * A Group defines the hierarchy in the scene graph.
+ *
+ * The list of Nodes* is a NodeSet, a depth-sorted set
+ * accepting multiple nodes at the same depth (multiset)
+ *
+ * update() will update all children
+ * draw() will draw all children
+ *
+ * When a group is deleted, the children are NOT deleted.
+ */
 class Group : public Node {
 
 public:
@@ -119,6 +166,13 @@ protected:
     NodeSet children_;
 };
 
+/**
+ * @brief The Switch class is a Group to selectively update & draw ONE selected child
+ *
+ * update() will update only the active child
+ * draw() will draw only the active child
+ *
+ */
 class Switch : public Group {
 
 public:
@@ -142,7 +196,13 @@ protected:
     NodeSet::iterator active_;
 };
 
-// Animation Nodes
+/**
+ * @brief The Animation class is a Group with an update() function
+ *
+ * The update() computes a transformation of the Group to apply a movement
+ * which is applied to all children.
+ *
+ */
 class Animation : public Group {
 
 public:
diff --git a/main.cpp b/main.cpp
index 1bfc384..44faa04 100644
--- a/main.cpp
+++ b/main.cpp
@@ -280,7 +280,7 @@ int main(int, char**)
 //    Points P(pts, pink);
 //    P.setPointSize(60);
     Mesh P("mesh/target.ply");
-    P.scale_ = glm::vec3(0.5f);
+    P.scale_ = glm::vec3(0.15f);
 
     Mesh meshicon("mesh/icon_video.ply");