private void histogramMatching(String inputHeader1, String inputHeader2, String outputHeader) {

    // check to see that the inputHeader and outputHeader are not null.
    if (inputHeader1.isEmpty() || outputHeader.isEmpty() || inputHeader2.isEmpty()) {
      showFeedback("One or more of the input parameters have not been set properly.");
      return;
    }

    try {
      int row, col;
      double z;
      int progress = 0;
      int numCells1 = 0;
      int numCells2 = 0;
      int i = 0;

      WhiteboxRasterInfo inputFile1 = new WhiteboxRasterInfo(inputHeader1);
      int rows1 = inputFile1.getNumberRows();
      int cols1 = inputFile1.getNumberColumns();
      double noData1 = inputFile1.getNoDataValue();

      WhiteboxRasterInfo inputFile2 = new WhiteboxRasterInfo(inputHeader2);
      int rows2 = inputFile2.getNumberRows();
      int cols2 = inputFile2.getNumberColumns();
      double noData2 = inputFile2.getNoDataValue();

      WhiteboxRaster outputFile =
          new WhiteboxRaster(
              outputHeader, "rw", inputHeader1, WhiteboxRaster.DataType.FLOAT, noData1);
      outputFile.setPreferredPalette(inputFile1.getPreferredPalette());

      double minValue1 = inputFile1.getMinimumValue();
      double maxValue1 = inputFile1.getMaximumValue();
      int numBins1 =
          Math.max(
              2 * (int) Math.ceil(maxValue1 - minValue1 + 1),
              (int) Math.ceil(Math.pow(rows1 * cols1, 1.0 / 3)));
      double binSize = (maxValue1 - minValue1) / numBins1;
      long[] histogram = new long[numBins1];
      int binNum;
      int numBinsLessOne1 = numBins1 - 1;
      double[] data;

      updateProgress("Histogram matching: ", 0);
      for (row = 0; row < rows1; row++) {
        data = inputFile1.getRowValues(row);
        for (col = 0; col < cols1; col++) {
          z = data[col];
          if (z != noData1) {
            numCells1++;
            binNum = (int) ((z - minValue1) / binSize);
            if (binNum > numBinsLessOne1) {
              binNum = numBinsLessOne1;
            }
            histogram[binNum]++;
          }
        }
        if (cancelOp) {
          cancelOperation();
          return;
        }
        progress = (int) (100f * row / (rows1 - 1));
        updateProgress("Histogram matching: ", progress);
      }

      updateProgress("Histogram matching: ", 0);

      double[] cdf = new double[numBins1];
      cdf[0] = histogram[0];
      for (i = 1; i < numBins1; i++) {
        cdf[i] = cdf[i - 1] + histogram[i];
      }

      for (i = 0; i < numBins1; i++) {
        cdf[i] = cdf[i] / numCells1;
      }

      double minValue2 = inputFile2.getMinimumValue();
      double maxValue2 = inputFile2.getMaximumValue();

      int numBins2 =
          Math.max(
              2 * (int) Math.ceil(maxValue2 - minValue2 + 1),
              (int) Math.ceil(Math.pow(rows2 * cols2, 1.0 / 3)));
      int numBinsLessOne2 = numBins2 - 1;
      long[] histogram2 = new long[numBins2];
      double[][] referenceCDF = new double[numBins2][2];

      for (row = 0; row < rows2; row++) {
        data = inputFile2.getRowValues(row);
        for (col = 0; col < cols2; col++) {
          z = data[col];
          if (z != noData2) {
            numCells2++;
            binNum = (int) ((z - minValue2) / binSize);
            if (binNum > numBinsLessOne2) {
              binNum = numBinsLessOne2;
            }
            histogram2[binNum]++;
          }
        }
        if (cancelOp) {
          cancelOperation();
          return;
        }
        progress = (int) (100f * row / (rows1 - 1));
        updateProgress("Histogram matching: ", progress);
      }

      // convert the reference histogram to a cdf.
      referenceCDF[0][1] = histogram2[0];
      for (i = 1; i < numBins2; i++) {
        referenceCDF[i][1] = referenceCDF[i - 1][1] + histogram2[i];
      }

      for (i = 0; i < numBins2; i++) {
        referenceCDF[i][0] = minValue2 + (i / (float) numBins2) * (maxValue2 - minValue2);
        referenceCDF[i][1] = referenceCDF[i][1] / numCells2;
      }

      int[] startingVals = new int[11];
      double pVal = 0;
      for (i = 0; i < numBins2; i++) {
        pVal = referenceCDF[i][1];
        if (pVal < 0.1) {
          startingVals[1] = i;
        }
        if (pVal < 0.2) {
          startingVals[2] = i;
        }
        if (pVal < 0.3) {
          startingVals[3] = i;
        }
        if (pVal < 0.4) {
          startingVals[4] = i;
        }
        if (pVal < 0.5) {
          startingVals[5] = i;
        }
        if (pVal < 0.6) {
          startingVals[6] = i;
        }
        if (pVal < 0.7) {
          startingVals[7] = i;
        }
        if (pVal < 0.8) {
          startingVals[8] = i;
        }
        if (pVal < 0.9) {
          startingVals[9] = i;
        }
        if (pVal <= 1) {
          startingVals[10] = i;
        }
      }

      updateProgress("Histogram matching: ", 0);
      int j = 0;
      double xVal = 0;
      double x1, x2, p1, p2;
      for (row = 0; row < rows1; row++) {
        data = inputFile1.getRowValues(row);
        for (col = 0; col < cols1; col++) {
          z = data[col];
          if (z != noData1) {
            binNum = (int) ((z - minValue1) / binSize);
            if (binNum > numBinsLessOne1) {
              binNum = numBinsLessOne1;
            }
            pVal = cdf[binNum];
            j = (int) (Math.floor(pVal * 10));
            for (i = startingVals[j]; i < numBins2; i++) {
              if (referenceCDF[i][1] > pVal) {
                if (i > 0) {
                  x1 = referenceCDF[i - 1][0];
                  x2 = referenceCDF[i][0];
                  p1 = referenceCDF[i - 1][1];
                  p2 = referenceCDF[i][1];
                  if (p1 != p2) {
                    xVal = x1 + ((x2 - x1) * ((pVal - p1) / (p2 - p1)));
                  } else {
                    xVal = x1;
                  }
                } else {
                  xVal = referenceCDF[i][0];
                }
                break;
              }
            }

            outputFile.setValue(row, col, xVal);
          }
        }

        if (cancelOp) {
          cancelOperation();
          return;
        }
        progress = (int) (100f * row / (rows1 - 1));
        updateProgress("Histogram matching: ", progress);
      }

      inputFile1.close();
      outputFile.close();

    } catch (OutOfMemoryError oe) {
      myHost.showFeedback("An out-of-memory error has occurred during operation.");
    } catch (Exception e) {
      myHost.showFeedback("An error has occurred during operation. See log file for details.");
      myHost.logException("Error in " + getDescriptiveName(), e);
    } finally {
      updateProgress("Progress: ", 0);
    }
  }
  /** Used to execute this plugin tool. */
  @Override
  public void run() {
    /*
     * This transformation has been taken from:
     * http://ij.ms3d.de/pdf/ihs_transforms.pdf
     * in reference to Haydn, Dalke, and Henkel (1982)
     * Note: 0 <= I <= 3, 0 <= H <= 3, 0 <= S <= 1
     */

    amIActive = true;

    String redHeader, greenHeader, blueHeader, intensityHeader, saturationHeader, hueHeader;

    if (args.length <= 0) {
      showFeedback("Plugin parameters have not been set.");
      return;
    }

    redHeader = args[0];
    greenHeader = args[1];
    blueHeader = args[2];
    intensityHeader = args[3];
    hueHeader = args[4];
    saturationHeader = args[5];

    // check to see that the inputHeader and outputHeader are not null.
    if (redHeader.isEmpty()
        || greenHeader.isEmpty()
        || blueHeader == null
        || intensityHeader.isEmpty()
        || hueHeader.isEmpty()
        || saturationHeader.isEmpty()) {
      showFeedback("One or more of the input parameters have not been set properly.");
      return;
    }

    try {
      int row, col;
      double redVal, greenVal, blueVal;
      //            double redRange, greenRange, blueRange;
      //            double redMin, greenMin, blueMin;
      double r, g, b;
      double i, s, h, m;
      float progress;

      WhiteboxRasterInfo red = new WhiteboxRasterInfo(redHeader);

      int rows = red.getNumberRows();
      int cols = red.getNumberColumns();

      WhiteboxRasterInfo green = new WhiteboxRasterInfo(greenHeader);
      if (green.getNumberRows() != rows || green.getNumberColumns() != cols) {
        showFeedback("All input images must have the same dimensions.");
        return;
      }
      WhiteboxRasterInfo blue = new WhiteboxRasterInfo(blueHeader);
      if (blue.getNumberRows() != rows || blue.getNumberColumns() != cols) {
        showFeedback("All input images must have the same dimensions.");
        return;
      }

      double redNoData = red.getNoDataValue();
      double greenNoData = green.getNoDataValue();
      double blueNoData = blue.getNoDataValue();

      WhiteboxRaster intensity =
          new WhiteboxRaster(
              intensityHeader, "rw", redHeader, WhiteboxRaster.DataType.FLOAT, redNoData);

      WhiteboxRaster hue =
          new WhiteboxRaster(hueHeader, "rw", redHeader, WhiteboxRaster.DataType.FLOAT, redNoData);

      WhiteboxRaster saturation =
          new WhiteboxRaster(
              saturationHeader, "rw", redHeader, WhiteboxRaster.DataType.FLOAT, redNoData);

      //            redMin = red.getDisplayMinimum();
      //            greenMin = green.getDisplayMinimum();
      //            blueMin = blue.getDisplayMinimum();
      //
      //            redRange = red.getDisplayMaximum() - redMin;
      //            greenRange = green.getDisplayMaximum() - greenMin;
      //            blueRange = blue.getDisplayMaximum() - blueMin;

      double overallMin =
          Math.min(
              Math.min(red.getDisplayMinimum(), green.getDisplayMinimum()),
              blue.getDisplayMinimum());

      double overallMax =
          Math.max(
              Math.max(red.getDisplayMaximum(), green.getDisplayMaximum()),
              blue.getDisplayMaximum());

      double range = overallMax - overallMin;

      double[] dataRed, dataGreen, dataBlue;
      for (row = 0; row < rows; row++) {
        dataRed = red.getRowValues(row);
        dataGreen = green.getRowValues(row);
        dataBlue = blue.getRowValues(row);
        for (col = 0; col < cols; col++) {
          redVal = dataRed[col];
          greenVal = dataGreen[col];
          blueVal = dataBlue[col];
          if ((redVal != redNoData) && (greenVal != greenNoData) && (blueVal != blueNoData)) {
            r = (redVal - overallMin) / range;
            if (r < 0) {
              r = 0;
            }
            if (r > 1) {
              r = 1;
            }
            g = (greenVal - overallMin) / range;
            if (g < 0) {
              g = 0;
            }
            if (g > 1) {
              g = 1;
            }
            b = (blueVal - overallMin) / range;
            if (b < 0) {
              b = 0;
            }
            if (b > 1) {
              b = 1;
            }

            m = Math.min(Math.min(r, g), b);

            i = r + g + b;

            if (i == 3) {
              h = 0;
            } else if (m == b) {
              h = (g - b) / (i - 3 * b);
            } else if (m == r) {
              h = (b - r) / (i - 3 * r) + 1;
            } else { // m == g
              h = (r - g) / (i - 3 * g) + 2;
            }

            if (h <= 1) {
              s = (i - 3 * b) / i;
            } else if (h <= 2) {
              s = (i - 3 * r) / i;
            } else { // H <= 3
              s = (i - 3 * g) / i;
            }

            intensity.setValue(row, col, i);
            hue.setValue(row, col, h);
            saturation.setValue(row, col, s);
          } else {
            intensity.setValue(row, col, redNoData);
            hue.setValue(row, col, redNoData);
            saturation.setValue(row, col, redNoData);
          }
        }
        if (cancelOp) {
          cancelOperation();
          return;
        }
        progress = (float) (100f * row / (rows - 1));
        updateProgress((int) progress);
      }

      intensity.addMetadataEntry("Created by the " + getDescriptiveName() + " tool.");
      intensity.addMetadataEntry("Created on " + new Date());
      intensity.close();

      hue.addMetadataEntry("Created by the " + getDescriptiveName() + " tool.");
      hue.addMetadataEntry("Created on " + new Date());
      hue.close();

      saturation.addMetadataEntry("Created by the " + getDescriptiveName() + " tool.");
      saturation.addMetadataEntry("Created on " + new Date());
      saturation.close();

      red.close();
      green.close();
      blue.close();

      // returning a header file string displays the image.
      returnData(intensityHeader);
      returnData(hueHeader);
      returnData(saturationHeader);

    } catch (OutOfMemoryError oe) {
      myHost.showFeedback("An out-of-memory error has occurred during operation.");
    } catch (Exception e) {
      myHost.showFeedback("An error has occurred during operation. See log file for details.");
      myHost.logException("Error in " + getDescriptiveName(), e);
    } finally {
      updateProgress("Progress: ", 0);
      // tells the main application that this process is completed.
      amIActive = false;
      myHost.pluginComplete();
    }
  }