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diff --git a/sci_gateway/cpp/opencv_imhistmatch.cpp b/sci_gateway/cpp/opencv_imhistmatch.cpp
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+/*
+ * imhistmatch
+ *
+ * histogram matching in scilab
+ *
+ */
+
+// Created by Samiran Roy, mail: samiranroy@cse.iitb.ac.in
+// An implementation of imhistmatch method
+// Usage:
+// 1) imhistmatch(image,referenceimage)
+// 2) imhistmatch(image,referenceimage,outputbins)
+
+// Known Changes from Matlab:
+/*
+ * Default number of bins is 256 - for both input and output
+ */
+
+#include <numeric>
+#include "opencv2/core/core.hpp"
+#include "opencv2/highgui/highgui.hpp"
+#include "opencv2/opencv.hpp"
+#include <iostream>
+using namespace cv;
+using namespace std;
+extern "C" {
+#include "api_scilab.h"
+#include "Scierror.h"
+#include "BOOL.h"
+#include <localization.h>
+#include "sciprint.h"
+#include "../common.h"
+
+// Matches the input image histogram with the reference image histogram,
+// returning the output in n bins
+
+Mat match(Mat image, Mat ref, int bins) {
+  Mat dst, hist;
+  Mat input_image = Mat::zeros(image.size(), CV_8U);
+  Mat refhist;
+
+  int inputbins = 256;
+
+  Mat cdf = Mat(inputbins, 1, CV_8U, cvScalar(0));
+
+  Mat refcdf = Mat(bins, 1, CV_8U, cvScalar(0));
+
+  // Calculating histogram of image
+  image.convertTo(dst, CV_8U, 1, 0);
+
+  calcHist(&dst, 1, 0, Mat(), hist, 1, &inputbins, 0);
+
+  // Calculating histogram of reference image
+
+  ref.convertTo(dst, CV_8U, 1, 0);
+  calcHist(&dst, 1, 0, Mat(), refhist, 1, &bins, 0);
+
+  hist.copyTo(cdf);
+  refhist.copyTo(refcdf);
+
+  // calculate cdf
+  for (int h = 1; h < inputbins; h++) {
+    float binVal = hist.at<float>(h, 0);
+
+    cdf.at<float>(h, 0) = cdf.at<float>(h, 0) + cdf.at<float>(h - 1, 0);
+  }
+
+  // normalize histogram
+  for (int h = 0; h < inputbins; h++) {
+    cdf.at<float>(h, 0) = cdf.at<float>(h, 0) / cdf.at<float>(inputbins - 1, 0);
+  }
+
+  // for reference image
+
+  // calculate cdf
+  for (int h = 1; h < bins; h++) {
+    float binVal = refhist.at<float>(h, 0);
+
+    refcdf.at<float>(h, 0) =
+        refcdf.at<float>(h, 0) + refcdf.at<float>(h - 1, 0);
+  }
+
+  // normalize histogram
+  for (int h = 0; h < bins; h++) {
+    refcdf.at<float>(h, 0) =
+        refcdf.at<float>(h, 0) / refcdf.at<float>(bins - 1, 0);
+  }
+
+  // for( int h = 0; h < bins; h++ )
+  //          {
+  //            sciprint("%f\n",refcdf.at<float>(h,0));
+
+  //          }
+
+  //          sciprint("\n");
+
+  // for( int h = 0; h < bins; h++ )
+  //          {
+  //            sciprint("%f\n",cdf.at<float>(h,0));
+
+  //          }
+
+  float observed_cdf, minval;
+  float minindex;
+
+  for (int i = 0; i < input_image.rows; i++)
+    for (int j = 0; j < input_image.cols; j++) {
+      observed_cdf = cdf.at<float>(image.at<uchar>(i, j), 0);
+
+      minval = 1000;  // will be overwritten
+
+      for (int h = 0; h < bins; h++) {
+        if ((abs(refcdf.at<float>(h, 0) - observed_cdf)) < minval) {
+          minval = abs(refcdf.at<float>(h, 0) - observed_cdf);
+          minindex = h;
+        }
+        // sciprint("%d\n",minindex);
+      }
+
+      input_image.at<uchar>(i, j) = minindex;
+    }
+  transpose(input_image, input_image);
+
+  return input_image;
+}
+
+int opencv_imhistmatch(char *fname, unsigned long fname_len) {
+  SciErr sciErr;
+  int intErr = 0;
+
+  int *piAddr = NULL;
+  int *piAddrNew = NULL;
+  int *piAddr2 = NULL;
+  int *piAddr3 = NULL;
+
+  double num_bins = 256;  // default number of bins for histogram calculation
+
+  // checking input argument
+  CheckInputArgument(pvApiCtx, 2, 3);
+  CheckOutputArgument(pvApiCtx, 1, 1);
+
+  // Get the number of input arguments
+  int inputarg = *getNbInputArgument(pvApiCtx);
+
+  // get input matrix
+
+  Mat image, new_image, r, g, b;
+  retrieveImage(image, 1);
+
+  Mat ref;
+  retrieveImage(ref, 2);
+
+  int case1 = 0;
+  if (image.channels() == 1)
+
+  {
+    if (ref.channels() != 1) {
+      sciprint(
+          "If A is a grayscale image, the ref image must also be grayscale\n");
+      return 0;
+
+    } else {
+      case1 = 1;
+    }
+  }
+
+  else if (image.channels() == 3)
+
+  {
+    if (ref.channels() == 1) {
+      case1 = 2;
+    }
+    if (ref.channels() == 3) {
+      case1 = 3;
+    }
+  }
+
+  else {
+    sciprint("Invalid Image\n");
+    return 0;
+  }
+
+  if (!((image.channels() == 3) || (image.channels() == 1))) {
+    sciprint("Invalid Image\n");
+    return 0;
+  }
+
+  if (!((ref.channels() == 3) || (ref.channels() == 1))) {
+    sciprint("Invalid Reference Image\n");
+    return 0;
+  }
+
+  if (inputarg == 3) {
+    // Get the number of bins for histogram calculation
+    sciErr = getVarAddressFromPosition(pvApiCtx, 3, &piAddr3);
+    if (sciErr.iErr) {
+      printError(&sciErr, 0);
+      return 0;
+    }
+
+    intErr = getScalarDouble(pvApiCtx, piAddr3, &num_bins);
+    if (sciErr.iErr) {
+      return intErr;
+    }
+
+    if (num_bins < 1) {
+      sciprint("Invalid number of histogram bins\n");
+      return 0;
+    }
+  }
+
+  int bins = (int)num_bins;
+
+  if (case1 == 1) {
+    new_image = match(image, ref, bins);
+
+  }
+
+  else if (case1 == 2) {
+    Mat rgb[3];
+
+    split(image, rgb);
+
+    r = match(rgb[0], ref, bins);
+
+    g = match(rgb[1], ref, bins);
+
+    b = match(rgb[2], ref, bins);
+
+    vector<Mat> channels;
+
+    channels.push_back(r);
+    channels.push_back(g);
+    channels.push_back(b);
+
+    merge(channels, new_image);
+
+    transpose(new_image, new_image);
+
+  }
+
+  else if (case1 == 3) {
+    Mat rgb[3];
+    Mat rgbref[3];
+
+    split(ref, rgbref);
+    split(image, rgb);
+
+    r = match(rgb[0], rgbref[0], bins);
+
+    g = match(rgb[1], rgbref[1], bins);
+
+    b = match(rgb[2], rgbref[2], bins);
+
+    vector<Mat> channels;
+
+    channels.push_back(r);
+    channels.push_back(g);
+    channels.push_back(b);
+
+    merge(channels, new_image);
+
+    transpose(new_image, new_image);
+  }
+
+  // Normalizing the final image
+  cv::normalize(new_image, new_image, 0, 255, NORM_MINMAX, CV_8U);
+
+  // sciprint("\n");
+
+  //  for (int i = 0; i < new_image.rows; i++) {
+  //    for (int j = 0; j < new_image.cols; j++) {
+  //      sciprint(" %i ", new_image.at<uchar>(i,j));
+
+  //    }
+
+  // sciprint("\n");
+  //  }
+
+  int temp = nbInputArgument(pvApiCtx) + 1;
+  string tempstring = type2str(new_image.type());
+  char *checker;
+  checker = (char *)malloc(tempstring.size() + 1);
+  memcpy(checker, tempstring.c_str(), tempstring.size() + 1);
+  returnImage(checker, new_image, 1);
+  free(checker);
+
+  // Assigning the list as the Output Variable
+  AssignOutputVariable(pvApiCtx, 1) = nbInputArgument(pvApiCtx) + 1;
+  // Returning the Output Variables as arguments to the Scilab environment
+  ReturnArguments(pvApiCtx);
+  return 0;
+}
+/* ==================================================================== */
+}
+