pdfimages: Account for rotation in PPI calculation

Closes: poppler/poppler#3

utils/ImageOutputDev.cc

@@ -227,10 +227,10 @@ void ImageOutputDev::listImage(GfxState *state, Object *ref, Stream *str, int wi
     }
 
     const double *mat = state->getCTM();
-    double width2 = mat[0] + mat[2];
-    double height2 = mat[1] + mat[3];
-    double xppi = fabs(width * 72.0 / width2) + 0.5;
-    double yppi = fabs(height * 72.0 / height2) + 0.5;
+    double width2 = sqrt(mat[0] * mat[0] + mat[1] * mat[1]);
+    double height2 = sqrt(mat[2] * mat[2] + mat[3] * mat[3]);
+    double xppi = fabs(width * 72.0 / width2);
+    double yppi = fabs(height * 72.0 / height2);
     if (xppi < 1.0)
         printf("%5.3f ", xppi);
     else