Use a predictable RNG when adding noise to low-bitrate images.

[dcpomatic.git] / src / lib / dcp_video.cc

diff --git a/src/lib/dcp_video.cc b/src/lib/dcp_video.cc
index cb151772700a62e661ea4dcb1f50adabf67527bb..1f9f76771c3282c96fa2437765e22eba2d652a9d 100644 (file)
--- a/src/lib/dcp_video.cc
+++ b/src/lib/dcp_video.cc
@@ -1,5 +1,5 @@
 /*
-    Copyright (C) 2012-2016 Carl Hetherington <cth@carlh.net>
+    Copyright (C) 2012-2021 Carl Hetherington <cth@carlh.net>
 
     This file is part of DCP-o-matic.
 
@@ -18,6 +18,7 @@
 
 */
 
+
 /** @file  src/dcp_video_frame.cc
  *  @brief A single frame of video destined for a DCP.
  *
@@ -28,17 +29,19 @@
  *  of images that require encoding.
  */
 
-#include "dcp_video.h"
+
+#include "compose.hpp"
 #include "config.h"
-#include "exceptions.h"
-#include "encode_server_description.h"
+#include "cross.h"
+#include "dcp_video.h"
+#include "dcpomatic_log.h"
 #include "dcpomatic_socket.h"
+#include "encode_server_description.h"
+#include "exceptions.h"
 #include "image.h"
 #include "log.h"
-#include "dcpomatic_log.h"
-#include "cross.h"
 #include "player_video.h"
-#include "compose.hpp"
+#include "rng.h"
 #include "warnings.h"
 #include <libcxml/cxml.h>
 #include <dcp/raw_convert.h>
@@ -128,6 +131,7 @@ DCPVideo::encode_locally ()
        int constexpr minimum_size = 65536;
 
        auto xyz = convert_to_xyz (_frame, boost::bind(&Log::dcp_log, dcpomatic_log.get(), _1, _2));
+       int noise_amount = 2;
        while (true) {
                enc = dcp::compress_j2k (
                        xyz,
@@ -142,6 +146,8 @@ DCPVideo::encode_locally ()
                        break;
                }
 
+               LOG_GENERAL (N_("Frame %1 encoded size was small (%2); adding noise at level %3"), _index, enc.size(), noise_amount);
+
                /* The JPEG2000 is too low-bitrate for some decoders <cough>DSS200</cough> so add some noise
                 * and try again.  This is slow but hopefully won't happen too often.  We have to do
                 * convert_to_xyz() again because compress_j2k() corrupts its xyz parameter.
@@ -150,13 +156,18 @@ DCPVideo::encode_locally ()
                xyz = convert_to_xyz (_frame, boost::bind(&Log::dcp_log, dcpomatic_log.get(), _1, _2));
                auto size = xyz->size ();
                auto pixels = size.width * size.height;
+               dcpomatic::RNG rng(42);
                for (auto c = 0; c < 3; ++c) {
                        auto p = xyz->data(c);
                        for (auto i = 0; i < pixels; ++i) {
-                               *p = std::min(4095, std::max(0, *p + rand() % 2));
+                               *p = std::min(4095, std::max(0, *p + (rng.get() % noise_amount)));
                                ++p;
                        }
                }
+
+               ++noise_amount;
+               /* Something's gone badly wrong if this much noise doesn't help */
+               DCPOMATIC_ASSERT (noise_amount < 16);
        }
 
        switch (_frame->eyes()) {