--- c/xpdf/pdftopng.cc	
+++ c/xpdf/pdftopng.cc	
@@ -21,6 +21,8 @@ 
 #include "SplashOutputDev.h"
 #include "config.h"
 
+#define INCHESPERMETER 39.37007874
+
 static int firstPage = 1;
 static int lastPage = 0;
 static int resolution = 150;
@@ -261,6 +263,9 @@ static void setupPNG(png_structp *png, png_infop *pngInfo, FILE *f,
   png_set_IHDR(*png, *pngInfo, bitmap->getWidth(), bitmap->getHeight(),
 	       bitDepth, colorType, PNG_INTERLACE_NONE,
 	       PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
+  png_set_pHYs(*png, *pngInfo, resolution*INCHESPERMETER, resolution*INCHESPERMETER,
+         PNG_RESOLUTION_METER);
+
   png_write_info(*png, *pngInfo);
 }