imagedata: report if file is DNG

rtengine/imagedata.cc

@@ -565,6 +565,8 @@ FramesData::FramesData(const Glib::ustring &fname, time_t ts) :
 
         meta.getDimensions(w_, h_);
 
+        isDNG = find_exif_tag("Exif.Image.DNGVersion");
+
         // -----------------------
         // Special file type detection (HDR, PixelShift)
         // ------------------------
@@ -778,6 +780,11 @@ bool FramesData::getHDR() const
     return isHDR;
 }
 
+bool FramesData::getDNG() const
+{
+    return isDNG;
+}
+
 std::string FramesData::getImageType() const
 {
     return isPixelShift ? "PS" : isHDR ? "HDR" : "STD";