First stab at dpi_threshold

cpdfimage.ml

@@ -723,13 +723,28 @@ let process
     | `List l -> hashset_of_list (map (function `Assoc (("Object", `Int i)::_) -> i | _ -> assert false) l)
     | _ -> assert false
   in
+  let highdpi =
+    let objnums =
+      if dpi_threshold = 0 then [] else
+        let results = image_resolution pdf range max_float in
+          let cmp (_, _, _, _, _, _, a) (_, _, _, _, _, _, b) = compare a b in
+          (* Get each obj number associated with its *lowest* resolution *)
+          let sets = collate cmp (sort cmp results) in
+          let heads = map hd (map (sort (fun (_, _, _, _, a, b, _) (_, _, _, _, c, d, _) -> compare (fmin a b) (fmin c d))) sets) in
+          (* Choose only those where this figure is more than the dpi_threshold *)
+          (*iter (fun (_, _, _, _, wdpi, hdpi, objnum) -> Printf.printf "%f %f %i\n" wdpi hdpi objnum) heads;*)
+          let needed = keep (fun (_, _, _, _, wdpi, hdpi, objnum) -> fmin wdpi hdpi > float_of_int dpi_threshold) heads in
+            map (fun (_, _, _, _, _, _, objnum) -> objnum) needed
+    in
+      hashset_of_list objnums
+  in
   let nobjects = Pdf.objcard pdf in
   let ndone = ref 0 in
   let process_obj objnum s =
     match s with
     | Pdf.Stream ({contents = dict, _} as reference) ->
         ndone += 1;
-        if Hashtbl.mem inrange objnum then begin match
+        if Hashtbl.mem inrange objnum && (dpi_threshold = 0 || Hashtbl.mem highdpi objnum) then begin match
           Pdf.lookup_direct pdf "/Subtype" dict,
           Pdf.lookup_direct pdf "/Filter" dict,
           Pdf.lookup_direct pdf "/BitsPerComponent" dict,