diff --git a/conv/CMakeLists.txt b/conv/CMakeLists.txt
index 5bbce77..6601db0 100644
--- a/conv/CMakeLists.txt
+++ b/conv/CMakeLists.txt
@@ -1,12 +1,18 @@
 add_executable(dcode_fcode common.hh dcode_fcode.cc)
 target_link_libraries(dcode_fcode PRIVATE args)
 
+add_executable(fcode_fidx common.hh fcode_fidx.cc)
+target_link_libraries(fcode_fidx PRIVATE args)
+
 add_executable(fidx_stego common.hh fidx_stego.cc)
 target_link_libraries(fidx_stego PRIVATE args minimp4 openh264)
 
 add_executable(stego_fprob common.hh stego_fprob.cc)
 target_link_libraries(stego_fprob PRIVATE args minimp4 openh264)
 
+add_executable(fprob_fcprob common.hh fprob_fcprob.cc)
+target_link_libraries(fprob_fcprob PRIVATE args)
+
 add_executable(fcprob_fcode common.hh fcprob_fcode.cc)
 target_link_libraries(fcprob_fcode PRIVATE args)
 
diff --git a/conv/fcode_fidx.cc b/conv/fcode_fidx.cc
new file mode 100644
index 0000000..c1bd540
--- /dev/null
+++ b/conv/fcode_fidx.cc
@@ -0,0 +1,58 @@
+#include <fstream>
+#include <iostream>
+#include <string>
+
+#include <args.hxx>
+
+#include "common.hh"
+
+
+namespace param {
+using namespace ::args;
+
+ArgumentParser parser {
+  "converter: feature codes -> feature indices"
+};
+HelpFlag help {
+  parser, "help", "display this menu", {'h', "help"},
+};
+
+ValueFlag<std::string> fcmap {
+  parser, "path", "feature code map", {"fc-map"},
+};
+
+}  // namespace param
+
+
+static void Exec() {
+  std::ifstream fcmap_st {args::get(param::fcmap)};
+  Enforce(!!fcmap_st, "fcmap path is invalid");
+  const auto fcmap = ReadMatrix<uint32_t>(fcmap_st);
+  Enforce(fcmap.size() > 0, "empty fcmap");
+  for (auto& idxs : fcmap) {
+    Enforce(idxs.size() > 0, "fcmap has empty item");
+  }
+
+  size_t fcode;
+  while (std::cin >> fcode) {
+    Enforce(fcode < fcmap.size(), "fcode overflow");
+
+    for (const auto idx : fcmap[fcode]) {
+      std::cout << idx << ' ';
+    }
+    std::cout << '\n';
+  }
+}
+
+int main(int argc, char** argv)
+try {
+  param::parser.ParseCLI(argc, argv);
+  Exec();
+  return EXIT_SUCCESS;
+} catch (const args::Help&) {
+  std::cout << param::parser << std::endl;
+  return EXIT_SUCCESS;
+} catch (const std::exception& e) {
+  std::cerr << e.what() << std::endl;
+  return EXIT_FAILURE;
+}
diff --git a/conv/fcprob_fcode.cc b/conv/fcprob_fcode.cc
index f344405..924b59b 100644
--- a/conv/fcprob_fcode.cc
+++ b/conv/fcprob_fcode.cc
@@ -36,11 +36,11 @@ Flag output_prob {
 
 
 static void Exec() {
-  const auto cprobs = ReadMatrix<double>(std::cin);
-  Enforce(cprobs.size() > 0 && cprobs[0].size() > 0, "empty matrix");
+  const auto fprobs = ReadMatrix<double>(std::cin);
+  Enforce(fprobs.size() > 0 && fprobs[0].size() > 0, "empty matrix");
 
-  const auto dur = cprobs.size();
-  const auto n   = cprobs[0].size();
+  const auto dur = fprobs.size();
+  const auto n   = fprobs[0].size();
 
   std::ifstream smap_st {args::get(param::smap)};
   Enforce(!!smap_st, "smap path is invalid");
@@ -53,16 +53,16 @@ static void Exec() {
   };
   std::vector<Step> steps((dur+1)*n);
   for (size_t i = 0; i < n; ++i) {
-    steps[i].prob = cprobs[0][i];
+    steps[i].prob = fprobs[0][i];
   }
   for (size_t t = 1; t < dur; ++t) {
-    Enforce(cprobs[t].size() == n, "ill-formed matrix");
+    Enforce(fprobs[t].size() == n, "ill-formed matrix");
     for (size_t i = 0; i < n; ++i) {
       const auto& cur = steps[(t-1)*n + i];
       for (auto j : smap[(t-1)*n+i]) {
         auto& next = steps[t*n + j];
 
-        const auto sum = cur.prob + cprobs[t][j];
+        const auto sum = cur.prob + fprobs[t][j];
         if (next.prob < sum) {
           next.prob = sum;
           next.from = i;
diff --git a/conv/fprob_fcprob.cc b/conv/fprob_fcprob.cc
new file mode 100644
index 0000000..3e4320a
--- /dev/null
+++ b/conv/fprob_fcprob.cc
@@ -0,0 +1,66 @@
+#include <fstream>
+#include <iostream>
+#include <string>
+
+#include <args.hxx>
+
+#include "common.hh"
+
+
+namespace param {
+using namespace ::args;
+
+ArgumentParser parser {
+  "converter: feature codes -> feature indices"
+};
+HelpFlag help {
+  parser, "help", "display this menu", {'h', "help"},
+};
+
+ValueFlag<std::string> smap {
+  parser, "path", "step map file path", {"smap"},
+};
+ValueFlag<std::string> fcmap {
+  parser, "path", "feature code map", {"fc-map"},
+};
+
+}  // namespace param
+
+
+static void Exec() {
+  const auto fprobs = ReadMatrix<double>(std::cin);
+  Enforce(fprobs.size() > 0 && fprobs[0].size() > 0, "empty matrix");
+
+  std::ifstream fcmap_st {args::get(param::fcmap)};
+  Enforce(!!fcmap_st, "fcmap path is invalid");
+  const auto fcmap = ReadMatrix<uint32_t>(fcmap_st);
+  Enforce(fcmap.size() > 0, "empty fcmap");
+  for (auto& idxs : fcmap) {
+    Enforce(idxs.size() > 0, "fcmap has empty item");
+  }
+
+  for (size_t t = 0; t < fprobs.size(); ++t) {
+    Enforce(fprobs[t].size() <= fcmap.size(), "unmatched fprobs and fcmap");
+    for (size_t c = 0; c < fcmap.size(); ++c) {
+      double sum = 0;
+      for (auto i : fcmap[c]) {
+        sum += fprobs[t][i];
+      }
+      std::cout << sum / fcmap[c].size() << ' ';
+    }
+    std::cout << '\n';
+  }
+}
+
+int main(int argc, char** argv)
+try {
+  param::parser.ParseCLI(argc, argv);
+  Exec();
+  return EXIT_SUCCESS;
+} catch (const args::Help&) {
+  std::cout << param::parser << std::endl;
+  return EXIT_SUCCESS;
+} catch (const std::exception& e) {
+  std::cerr << e.what() << std::endl;
+  return EXIT_FAILURE;
+}