OpenCV Histogram Mat to Bitmap for Picturebox - c++

Question

I use a FLIR Camera (Grasshopper3) and the SDK (Spinnaker) to take an image (Mono8). After converting the image, I wuold like to compute the Histogram and display it in my GUI in a picturebox (C++ CLR/CLI .net environment). For this, I need to convert it, but I guess there is a mistake in the color conversion or the BitMap creation.
Here is the code:
Spinnaker::ImagePtr convertedImage_MONO = Grasshopper3.pResultImage_MONO->Convert(Spinnaker::PixelFormat_Mono8, Spinnaker::NO_COLOR_PROCESSING); // Raw image is converted to Mono8
unsigned int XPadding = convertedImage_MONO->GetXPadding();
unsigned int YPadding = convertedImage_MONO->GetYPadding();
unsigned int rowsize = convertedImage_MONO->GetWidth();
unsigned int colsize = convertedImage_MONO->GetHeight();
//image data contains padding. When allocating Mat container size, you need to account for the X,Y image data padding.
cv::Mat cvimg_Mono = cv::Mat(colsize + YPadding, rowsize + XPadding, CV_8UC1, convertedImage_MONO->GetData(), convertedImage_MONO->GetStride());
cvtColor(cvimg_Mono, cvimg_Mono, cv::COLOR_BGR2BGRA);
// Histogram
int bins = 256;
int histSize[] = { bins };
// Set ranges for histogram bins
float lranges[] = { 0, 256 };
const float* ranges[] = { lranges };
// create matrix for histogram
cv::Mat hist;
int channels[] = { 0 };
// create matrix for histogram visualization
int const hist_height = 256;
cv::Mat3b hist_image = cv::Mat3b::zeros(hist_height, bins);
cv::calcHist(&cvimg_Mono, 1, channels, cv::Mat(), hist, 1, histSize, ranges, true, false);
double max_val = 0;
minMaxLoc(hist, 0, &max_val);
// visualize each bin
for (int b = 0; b < bins; b++)
{
float const binVal = hist.at<float>(b);
int const height = cvRound(binVal*hist_height / max_val);
cv::line(hist_image, cv::Point(b, hist_height - height), cv::Point(b, hist_height), cv::Scalar::all(255));
}
cv::Mat Histogram_Mono = hist_image;
cv::resize(Histogram_Mono, Histogram_Mono, cv::Size(pictureBox_Mono->Width, pictureBox_Mono->Height), cv::INTER_AREA);
hBit_Mono = CreateBitmap(Histogram_Mono.cols, Histogram_Mono.rows, 1, 32, Histogram_Mono.data); // hBit_Mono was created global
bmp_Mono = Bitmap::FromHbitmap((IntPtr)hBit_Mono); // bmp_Mono was created as a global Bitmap
pictureBox_Mono->Image = bmp_Mono;