diff --git a/cpdfcommand.ml b/cpdfcommand.ml
index 08479ff..270c19e 100644
--- a/cpdfcommand.ml
+++ b/cpdfcommand.ml
@@ -4255,14 +4255,11 @@ let go () =
             Cpdfimage.extract_images ~raw:(args.encoding = Cpdfmetadata.Raw) ?path_to_p2p:(match args.path_to_p2p with "" -> None | x -> Some x) ?path_to_im:(match args.path_to_im with "" -> None | x -> Some x) args.encoding args.dedup args.dedup_per_page pdf range output_spec
   | Some (ImageResolution f) ->
       let pdf = get_single_pdf args.op true in
-        let range = parse_pagespec_allow_empty pdf (get_pagespec ()) in
-        let images = Cpdfimage.image_resolution pdf range f in
-          if args.format_json then
-            flprint
-              (Cpdfyojson.Safe.pretty_to_string
-                 (`List (map (fun (pagenum, xobject, w, h, wdpi, hdpi, objnum) ->
-                    `Assoc [("Object", `Int objnum); ("Page", `Int pagenum); ("XObject", `String xobject); ("W", `Int w); ("H", `Int h); ("Xdpi", `Float wdpi); ("Ydpi", `Float hdpi)]) images)))
-          else
+      let range = parse_pagespec_allow_empty pdf (get_pagespec ()) in
+        if args.format_json then
+          flprint (Pdfio.string_of_bytes (Cpdfimage.image_resolution_json pdf range f))
+        else
+          let images = Cpdfimage.image_resolution pdf range f in
             iter
               (function (pagenum, xobject, w, h, wdpi, hdpi, objnum) ->
                   if wdpi < f || hdpi < f then
diff --git a/cpdfimage.ml b/cpdfimage.ml
index f16376e..75d43ff 100644
--- a/cpdfimage.ml
+++ b/cpdfimage.ml
@@ -324,6 +324,14 @@ let image_resolution pdf range dpi =
   image_resolution pdf range dpi;
   rev !image_results
 
+let image_resolution_json pdf range dpi =
+  let images = image_resolution pdf range dpi in
+    Pdfio.bytes_of_string
+      (Cpdfyojson.Safe.pretty_to_string
+        (`List (map (fun (pagenum, xobject, w, h, wdpi, hdpi, objnum) ->
+           `Assoc [("Object", `Int objnum); ("Page", `Int pagenum); ("XObject", `String xobject);
+                   ("W", `Int w); ("H", `Int h); ("Xdpi", `Float wdpi); ("Ydpi", `Float hdpi)]) images)))
+
 (* All the images in file referenced at least once from the given range of pages. *)
 let images pdf range =
   let images = null_hash () in
diff --git a/cpdfimage.mli b/cpdfimage.mli
index 0e18936..85b32a6 100644
--- a/cpdfimage.mli
+++ b/cpdfimage.mli
@@ -11,6 +11,8 @@ val extract_images :
 (** Report image resolutions. *)        
 val image_resolution : Pdf.t -> int list -> float -> (int * string * int * int * float * float * int) list
 
+val image_resolution_json : Pdf.t -> int list -> float -> Pdfio.bytes
+
 (** List images in JSON format *)
 val images : Pdf.t -> int list -> Cpdfyojson.Safe.t