diff --git a/src/BackgroundRenderer/BackgroundRenderer.cc b/src/BackgroundRenderer/BackgroundRenderer.cc
index ba1e832..a5dda2f 100644
--- a/src/BackgroundRenderer/BackgroundRenderer.cc
+++ b/src/BackgroundRenderer/BackgroundRenderer.cc
@@ -49,23 +49,12 @@ BackgroundRenderer * BackgroundRenderer::getFallbackBackgroundRenderer(HTMLRende
     return nullptr;
 }
 
-BackgroundRenderer::~BackgroundRenderer()
+void BackgroundRenderer::proof_begin_string(GfxState *state, OutputDev * dev)
 {
-    //delete proof_state
-    if (proof_state)
-        delete proof_state;
-}
-
-void BackgroundRenderer::proof_begin_string(GfxState *state)
-{
-    auto dev = (OutputDev*) dynamic_cast<SplashBackgroundRenderer*>(this);
-    if (!dev)
-        dev = (OutputDev*) dynamic_cast<CairoBackgroundRenderer*>(this);
-
     if (!proof_state)
     {
         PDFRectangle rect(0, 0, state->getPageWidth(), state->getPageHeight());
-        proof_state = new GfxState(state->getHDPI(), state->getVDPI(), &rect, state->getRotate(), dev->upsideDown());
+        proof_state.reset(new GfxState(state->getHDPI(), state->getVDPI(), &rect, state->getRotate(), dev->upsideDown()));
         proof_state->setFillColorSpace(new GfxDeviceRGBColorSpace());
         proof_state->setStrokeColorSpace(new GfxDeviceRGBColorSpace());
     }
@@ -78,24 +67,20 @@ void BackgroundRenderer::proof_begin_string(GfxState *state)
     sc = sc.distance(blue) >  0.4 ? blue : yellow;
 
     if (state->getFillColorSpace()->getMode() != csDeviceRGB)
-        dev->updateFillColorSpace(proof_state);
+        dev->updateFillColorSpace(proof_state.get());
     if (state->getStrokeColorSpace()->getMode() != csDeviceRGB)
-        dev->updateStrokeColorSpace(proof_state);
+        dev->updateStrokeColorSpace(proof_state.get());
     GfxColor gfc, gsc;
     fc.get_gfx_color(gfc);
     sc.get_gfx_color(gsc);
     proof_state->setFillColor(&gfc);
     proof_state->setStrokeColor(&gsc);
-    dev->updateFillColor(proof_state);
-    dev->updateStrokeColor(proof_state);
+    dev->updateFillColor(proof_state.get());
+    dev->updateStrokeColor(proof_state.get());
 }
 
-void BackgroundRenderer::proof_end_text_object(GfxState *state)
+void BackgroundRenderer::proof_end_text_object(GfxState *state, OutputDev * dev)
 {
-    auto dev = (OutputDev*) dynamic_cast<SplashBackgroundRenderer*>(this);
-    if (!dev)
-        dev = (OutputDev*) dynamic_cast<CairoBackgroundRenderer*>(this);
-
     dev->updateFillColorSpace(state);
     dev->updateStrokeColorSpace(state);
     dev->updateFillColor(state);
diff --git a/src/BackgroundRenderer/BackgroundRenderer.h b/src/BackgroundRenderer/BackgroundRenderer.h
index e1c6179..6ae9bf5 100644
--- a/src/BackgroundRenderer/BackgroundRenderer.h
+++ b/src/BackgroundRenderer/BackgroundRenderer.h
@@ -10,9 +10,11 @@
 #define BACKGROUND_RENDERER_H__
 
 #include <string>
+#include <memory>
 
 class PDFDoc;
 class GfxState;
+class OutputDev;
 
 namespace pdf2htmlEX {
 
@@ -27,8 +29,8 @@ public:
     // Currently only svg bg format might need a bitmap fallback.
     static BackgroundRenderer * getFallbackBackgroundRenderer(HTMLRenderer * html_renderer, const Param & param);
 
-    BackgroundRenderer(): proof_state(nullptr) {}
-    virtual ~BackgroundRenderer();
+    BackgroundRenderer() {}
+    virtual ~BackgroundRenderer() {}
 
     virtual void init(PDFDoc * doc) = 0;
     //return true on success, false otherwise (e.g. need a fallback)
@@ -37,10 +39,10 @@ public:
 
     // for proof output
 protected:
-    void proof_begin_string(GfxState *state);
-    void proof_end_text_object(GfxState *state);
+    void proof_begin_string(GfxState * state, OutputDev * dev);
+    void proof_end_text_object(GfxState * state, OutputDev * dev);
 private:
-    GfxState * proof_state;
+    std::unique_ptr<GfxState> proof_state;
 };
 
 } // namespace pdf2htmlEX
diff --git a/src/BackgroundRenderer/CairoBackgroundRenderer.cc b/src/BackgroundRenderer/CairoBackgroundRenderer.cc
index 1e9eabd..e5371b6 100644
--- a/src/BackgroundRenderer/CairoBackgroundRenderer.cc
+++ b/src/BackgroundRenderer/CairoBackgroundRenderer.cc
@@ -68,14 +68,14 @@ void CairoBackgroundRenderer::drawChar(GfxState *state, double x, double y,
 void CairoBackgroundRenderer::beginString(GfxState *state, GooString * str)
 {
     if (param.proof == 2)
-        proof_begin_string(state);
+        proof_begin_string(state, this);
     CairoOutputDev::beginString(state, str);
 }
 
 void CairoBackgroundRenderer::endTextObject(GfxState *state)
 {
     if (param.proof == 2)
-        proof_end_text_object(state);
+        proof_end_text_object(state, this);
     CairoOutputDev::endTextObject(state);
 }
 
diff --git a/src/BackgroundRenderer/SplashBackgroundRenderer.cc b/src/BackgroundRenderer/SplashBackgroundRenderer.cc
index 7feb043..b4cfc01 100644
--- a/src/BackgroundRenderer/SplashBackgroundRenderer.cc
+++ b/src/BackgroundRenderer/SplashBackgroundRenderer.cc
@@ -93,14 +93,14 @@ void SplashBackgroundRenderer::drawChar(GfxState *state, double x, double y,
 void SplashBackgroundRenderer::beginString(GfxState *state, GooString * str)
 {
     if (param.proof == 2)
-        proof_begin_string(state);
+        proof_begin_string(state, this);
     SplashOutputDev::beginString(state, str);
 }
 
 void SplashBackgroundRenderer::endTextObject(GfxState *state)
 {
     if (param.proof == 2)
-        proof_end_text_object(state);
+        proof_end_text_object(state, this);
     SplashOutputDev::endTextObject(state);
 }