diff --git a/htroot/api/snapshot.java b/htroot/api/snapshot.java
index 5ddf7cfba..b734d65b4 100644
--- a/htroot/api/snapshot.java
+++ b/htroot/api/snapshot.java
@@ -106,7 +106,7 @@ public class snapshot {
         final boolean xml = ext.equals("xml");
         final boolean pdf = ext.equals("pdf");
         if (pdf && !authenticated) return null;
-        final boolean pngjpg = ext.equals("png") || ext.equals("jpg");
+        final boolean pngjpg = ext.equals("png") || ext.equals(DEFAULT_EXT);
         String urlhash = post.get("urlhash", "");
         String url = post.get("url", "");
         DigestURL durl = null;
@@ -286,7 +286,7 @@ public class snapshot {
                 int width = Math.min(post.getInt("width", DEFAULT_WIDTH), DEFAULT_WIDTH);
                 int height = Math.min(post.getInt("height", DEFAULT_HEIGHT), DEFAULT_HEIGHT);
                 String imageFileStub = pdfFile.getAbsolutePath(); imageFileStub = imageFileStub.substring(0, imageFileStub.length() - 3); // cut off extension
-                File imageFile = new File(imageFileStub + DEFAULT_WIDTH + "." + DEFAULT_HEIGHT + "." + DEFAULT_EXT);
+                File imageFile = new File(imageFileStub + DEFAULT_WIDTH + "." + DEFAULT_HEIGHT + "." + ext);
                 if (!imageFile.exists() && authenticated) {
                     Html2Image.pdf2image(pdfFile, imageFile, DEFAULT_WIDTH, DEFAULT_HEIGHT, DEFAULT_DENSITY, DEFAULT_QUALITY);
                 }
diff --git a/source/net/yacy/cora/util/Html2Image.java b/source/net/yacy/cora/util/Html2Image.java
index d3de36ade..217817744 100644
--- a/source/net/yacy/cora/util/Html2Image.java
+++ b/source/net/yacy/cora/util/Html2Image.java
@@ -42,6 +42,7 @@ import javax.swing.text.html.HTMLDocument;
 import javax.swing.text.html.HTMLEditorKit;
 import javax.swing.text.html.ImageView;
 
+import net.yacy.cora.document.id.MultiProtocolURL;
 import net.yacy.document.ImageParser;
 import net.yacy.kelondro.util.FileUtils;
 import net.yacy.kelondro.util.OS;
@@ -140,17 +141,23 @@ public class Html2Image {
     }
     
     /**
-     * convert a pdf (first page) to an image. proper values are i.e. width = 1024, height = 1024, density = 300, quality = 75
+     * Convert a pdf (first page) to an image. Proper values are i.e. width = 1024, height = 1024, density = 300, quality = 75
      * using internal pdf library or external command line tool on linux or mac
-     * @param pdf input pdf file
-     * @param image output jpg file
-     * @param width
-     * @param height
+     * @param pdf input pdf file. Must not be null.
+     * @param image output image file. Must not be null, and should end with ".jpg" or ".png".
+     * @param width output width in pixels
+     * @param height output height in pixels
      * @param density (dpi)
-     * @param quality
-     * @return
+     * @param quality JPEG/PNG compression level
+     * @return true when the ouput image file was successfully written.
      */
-    public static boolean pdf2image(File pdf, File image, int width, int height, int density, int quality) {
+    public static boolean pdf2image(final File pdf, final File image, final int width, final int height, final int density, final int quality) {
+    	/* Deduce the ouput image format from the file extension */
+    	String imageFormat = MultiProtocolURL.getFileExtension(image.getName());
+    	if(imageFormat.isEmpty()) {
+    		/* Use JPEG as a default fallback */
+    		imageFormat = "jpg";
+    	}
         final File convert = convertMac1.exists() ? convertMac1 : convertMac2.exists() ? convertMac2 : convertDebian;
 
         // convert pdf to jpg using internal pdfbox capability
@@ -159,7 +166,7 @@ public class Html2Image {
                 PDDocument pdoc = PDDocument.load(pdf);
                 BufferedImage bi = new PDFRenderer(pdoc).renderImageWithDPI(0, density, ImageType.RGB);
 
-                return ImageIO.write(bi, "jpg", image);
+                return ImageIO.write(bi, imageFormat, image);
 
             } catch (IOException ex) { }
         }
@@ -188,7 +195,7 @@ public class Html2Image {
             //ConcurrentLog.warn("Html2Image", "failed to create image with command: " + commandx);
             message = OS.execSynchronous(commandx);
             for (String m: message) ConcurrentLog.warn("Html2Image", ">> " + m);
-            // now we must read and convert this file to a jpg with the target size 1024x1024
+            // now we must read and convert this file to the target format with the target size 1024x1024
             try {
                 File newPngFile = new File(pngFile.getAbsolutePath() + ".png");
                 pngFile.renameTo(newPngFile);
@@ -200,7 +207,7 @@ public class Html2Image {
                 // finally write the image
                 final BufferedImage bi = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
                 bi.createGraphics().drawImage(scaled, 0, 0, width, height, null);
-                ImageIO.write(bi, "jpg", image);
+                ImageIO.write(bi, imageFormat, image);
                 newPngFile.delete();
                 return image.exists();
             } catch (IOException e) {
diff --git a/test/java/net/yacy/cora/util/Html2ImageTest.java b/test/java/net/yacy/cora/util/Html2ImageTest.java
index 4274cd6df..2e92c2e23 100644
--- a/test/java/net/yacy/cora/util/Html2ImageTest.java
+++ b/test/java/net/yacy/cora/util/Html2ImageTest.java
@@ -1,3 +1,24 @@
+// Html2ImageTest.java
+// Copyright 2016,2017 by reger; https://github.com/reger24 luccioman; https://github.com/luccioman
+//
+// This is a part of YaCy, a peer-to-peer based web search engine
+//
+// LICENSE
+//
+// This program is free software; you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation; either version 2 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program; if not, write to the Free Software
+// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+
 package net.yacy.cora.util;
 
 import java.io.File;
@@ -38,8 +59,19 @@ public class Html2ImageTest {
             if (jpgfile.exists()) {
                 jpgfile.delete();
             }
-            Html2Image.pdf2image(pdffile, jpgfile, 1024, 1024, 300, 75);
+            assertTrue(Html2Image.pdf2image(pdffile, jpgfile, 1024, 1024, 300, 75));
             assertTrue(jpgfile.exists());
+            assertTrue(jpgfile.length() > 0);
+            System.out.println("Test image file successfully written : " + jpgfile.getAbsolutePath());
+            
+            final File pngFile = new File("test/DATA", pdffilename + ".png");
+            if (pngFile.exists()) {
+            	pngFile.delete();
+            }
+            assertTrue(Html2Image.pdf2image(pdffile, pngFile, 1024, 1024, 300, 75));
+            assertTrue(pngFile.exists());
+            assertTrue(pngFile.length() > 0);
+            System.out.println("Test image file successfully written : " + pngFile.getAbsolutePath());
         }
     }