From d71977b4dd65ded24dff77339751c77e498a84e5 Mon Sep 17 00:00:00 2001
From: Gregor Mittag <4136328+ghellwig@users.noreply.github.com>
Date: Sat, 16 Feb 2019 15:05:31 +0100
Subject: [PATCH] Add JPEG2000 compression flag.

---
 .../imgcodecs/include/opencv2/imgcodecs.hpp   |  3 ++-
 modules/imgcodecs/src/grfmt_jpeg2000.cpp      | 20 +++++++++++++++++--
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/modules/imgcodecs/include/opencv2/imgcodecs.hpp b/modules/imgcodecs/include/opencv2/imgcodecs.hpp
index b326001882..dd70d16da4 100644
--- a/modules/imgcodecs/include/opencv2/imgcodecs.hpp
+++ b/modules/imgcodecs/include/opencv2/imgcodecs.hpp
@@ -94,7 +94,8 @@ enum ImwriteFlags {
        IMWRITE_PAM_TUPLETYPE       = 128,//!< For PAM, sets the TUPLETYPE field to the corresponding string value that is defined for the format
        IMWRITE_TIFF_RESUNIT = 256,//!< For TIFF, use to specify which DPI resolution unit to set; see libtiff documentation for valid values
        IMWRITE_TIFF_XDPI = 257,//!< For TIFF, use to specify the X direction DPI
-       IMWRITE_TIFF_YDPI = 258 //!< For TIFF, use to specify the Y direction DPI
+       IMWRITE_TIFF_YDPI = 258, //!< For TIFF, use to specify the Y direction DPI
+       IMWRITE_JPEG2000_COMPRESSION_X1000 = 272 //!< For JPEG2000, use to specify the target compression rate (multiplied by 1000). The value can be from 0 to 1000. Default is 1000.
      };
 
 enum ImwriteEXRTypeFlags {
diff --git a/modules/imgcodecs/src/grfmt_jpeg2000.cpp b/modules/imgcodecs/src/grfmt_jpeg2000.cpp
index be280e285a..18d8904aa9 100644
--- a/modules/imgcodecs/src/grfmt_jpeg2000.cpp
+++ b/modules/imgcodecs/src/grfmt_jpeg2000.cpp
@@ -43,6 +43,7 @@
 #include "precomp.hpp"
 
 #ifdef HAVE_JASPER
+#include <sstream>
 
 #include "grfmt_jpeg2000.hpp"
 #include "opencv2/imgproc.hpp"
@@ -467,7 +468,7 @@ bool  Jpeg2KEncoder::isFormatSupported( int depth ) const
 }
 
 
-bool  Jpeg2KEncoder::write( const Mat& _img, const std::vector<int>& )
+bool  Jpeg2KEncoder::write( const Mat& _img, const std::vector<int>& params )
 {
     int width = _img.cols, height = _img.rows;
     int depth = _img.depth(), channels = _img.channels();
@@ -476,6 +477,18 @@ bool  Jpeg2KEncoder::write( const Mat& _img, const std::vector<int>& )
     if( channels > 3 || channels < 1 )
         return false;
 
+    CV_Assert(params.size() % 2 == 0);
+    double target_compression_rate = 1.0;
+    for( size_t i = 0; i < params.size(); i += 2 )
+    {
+        switch(params[i])
+        {
+        case cv::IMWRITE_JPEG2000_COMPRESSION_X1000:
+            target_compression_rate = std::min(std::max(params[i+1], 0), 1000) / 1000.0;
+            break;
+        }
+    }
+
     jas_image_cmptparm_t component_info[3];
     for( int i = 0; i < channels; i++ )
     {
@@ -511,7 +524,10 @@ bool  Jpeg2KEncoder::write( const Mat& _img, const std::vector<int>& )
         jas_stream_t *stream = jas_stream_fopen( m_filename.c_str(), "wb" );
         if( stream )
         {
-            result = !jas_image_encode( img, stream, jas_image_strtofmt( (char*)"jp2" ), (char*)"" );
+            std::stringstream options;
+            options << "rate=" << target_compression_rate;
+
+            result = !jas_image_encode( img, stream, jas_image_strtofmt( (char*)"jp2" ), (char*)options.str().c_str() );
 
             jas_stream_close( stream );
         }