Wrapping OpenCv C++ code for use in C#

I'm trying to wrap a C++ class which uses OpenCv so that I can use it in C#.

I have the C++ function:

void ImageBrightener::BrightenImage(const cv::Mat& sourceImage, cv::Mat& targetImage, int maxTarget)
{
    double scaleFactor;
    double shiftFactor = 0;
    double minVal = DBL_MAX, minValTemp;
    double maxVal = -DBL_MAX, maxValTemp;
    auto numPixels = 0;
    const auto RANGE_TOP_EXTEND = 10;
    const auto RANGE_BOTTOM_EXTEND = 7;

    assert(sourceImage.type() == CV_8UC1);
    assert(sourceImage.channels() == 1);

    cv::minMaxIdx(sourceImage, &minValTemp, &maxValTemp);
    if (minValTemp < minVal)
    minVal = minValTemp;
    if (maxValTemp>maxVal)
        maxVal = maxValTemp;

    numPixels += sourceImage.cols * sourceImage.rows;

    if (maxVal == minVal)
    {
        sourceImage.convertTo(targetImage, CV_8UC1, 1, shiftFactor);
        return;
    }

    // Account for prev/curr ROI differences - add a bit to the range
    maxVal += RANGE_TOP_EXTEND;
    minVal -= RANGE_BOTTOM_EXTEND;
    minVal = std::max(minVal, 0.);

    if ((maxVal - minVal) < maxTarget)
    {
        scaleFactor = maxTarget / (maxVal - minVal);
        shiftFactor = -1 * scaleFactor * minVal;

        sourceImage.convertTo(targetImage, CV_8UC1, scaleFactor, shiftFactor);
        return;
    }

    auto fltMinVal = static_cast<float>(minVal) - 1;
    auto fltMaxVal = static_cast<float>(maxVal) + 1;

    // Check histogram
    const unsigned int *currval;

    #define BINS   (100)
    #define CUTOFF (0.00003)
    #define RESCUTOFF (0.2)

    int hist[BINS] = { 0 };
    int bin;

    numPixels += sourceImage.cols * sourceImage.rows;
    for (auto rowIndex = 0; rowIndex < sourceImage.rows; rowIndex++)
    {
        currval = sourceImage.ptr<unsigned>(rowIndex, 0);
        for (auto colIndex = 0; colIndex < sourceImage.cols; colIndex++)
        {
            bin = static_cast<int>((BINS - 1) * ((*currval - fltMinVal) / (fltMaxVal - fltMinVal)));
            assert(bin >= 0 && bin < BINS);
            hist[bin]++;
            ++currval;
        }
    }

    double ratio;
    auto sum = 0;
    int i;
    for (i = BINS - 1; i >= 0; i--)
    {
        sum += hist[i];
        ratio = static_cast<double>(sum) / static_cast<double>(numPixels);
        if (ratio > CUTOFF)
            break;
    }
    if (static_cast<double>(BINS - i) / static_cast<double>(BINS) > RESCUTOFF)
        fltMaxVal = fltMinVal + ((i + 2)*(fltMaxVal - fltMinVal)) / BINS;

    // Account for prev/curr ROI differences - add a bit to the range
    fltMaxVal += RANGE_TOP_EXTEND;
    fltMinVal -= RANGE_BOTTOM_EXTEND;
    fltMinVal = std::max(fltMinVal, 0.f);

    scaleFactor = maxTarget / (fltMaxVal - fltMinVal);
    shiftFactor = -1 * scaleFactor * fltMinVal;

    sourceImage.convertTo(targetImage, CV_8UC1, scaleFactor, shiftFactor);
}

When I test this code using the following C++ code:

int main()
{
    auto* m_imageBrightener = new ImageBrightener();
    auto inputImage = cv::imread("E:\\ttt.png", CV_LOAD_IMAGE_UNCHANGED);

    cv::Mat outputImage;

    m_imageBrightener->BrightenImage(inputImage, outputImage, 2000);
    cv::imwrite("E:\\new_ttt.png", outputImage);
}

Everything works, the code does what it should, which is to get a dark 8bit image, and brighten it (I tried replacing 200 with 500 - it works fine). The new_ttt.png image is brightened as expected.

On the other hand, I have the following /Clr code, which wraps the C++ code and creates a DLL from it:

array<System::Byte>^ ImageProcessing::ImageBrightenerWrapper::BrightenImage(array<System::Byte>^ sourceImage, int imageWidth, int imageHeight, int maxTarget)
{
    array<System::Byte>^ targetImage = (array<System::Byte>^)sourceImage->Clone();

    pin_ptr<System::Byte> sourcePointer = &sourceImage[0];
    pin_ptr<System::Byte> targetPointer = &targetImage[0];

    cv::Mat sourceMat(imageHeight, imageWidth, CV_8UC1, (unsigned short*)sourcePointer);
    cv::Mat targetMat(imageHeight, imageWidth, CV_8UC1, (unsigned short*)targetPointer);

    targetMat.setTo(0);
    m_imageBrightener->BrightenImage(sourceMat, targetMat, maxTarget);

    uchar* tempPointer;
    for (auto rowIndex = 0; rowIndex < imageHeight; ++rowIndex)
    {
        tempPointer = targetMat.ptr<uchar>(rowIndex);
        for (auto colIndex = 0; colIndex < imageWidth; ++colIndex)
            targetImage[rowIndex + colIndex] = tempPointer[colIndex];
    }

    return targetImage;
}

With it, I also have a WPF application which has a slider which controls the maxTarget parameter.

This is what I'm facing:

1) On the one hand, any value between 0 and 960 for maxTarget brightens the row index which matches maxTarget / 2 - Meaning, that when I slide the slider to the right, for greater values, I get part of the image bright and the rest is as the original. (Example: if maxTarget is 300, then all of the rows between row #0 and row #150 will be brighter and the rest will be like the original).

2) On the other hand, if I cross the value if 960 for maxTarget then the application crashes with the following error (even though the code is surrounded with try/catch):

"An exception of type: 'System.AccessViolationException' occurred in ImageBrightenerWrapper.dll but was not handled in user code. Additional information: Attempted to read or write protected memory. This is pften an indication that other memory is corrupt."

What am I doing wrong here?