System::Drawing::Bitmap to unsigned char *

Question

I have a C# .NET library that grabs frames from a camera. I need to send those frames to a native application that takes images from an unsigned char*.

I initially take the frames as System::Drawing::Bitmap.

So far I can retrieve a byte[] from the Bitmap. My test is done with an image of resolution 400*234, I should be getting 400*234*3 bytes to get to the 24bpp a RGB image requires.

However, I'm getting a byte[] of size 11948.

This is how I convert from Bitmap to byte[]:

private static byte[] ImageToByte(Bitmap img)
{
    ImageConverter converter = new ImageConverter();
    return (byte[])converter.ConvertTo(img, typeof(byte[]));
}

What is the proper way to convert from System::Drawing::Bitmap to RGB unsigned char*?

Answer 1

This has to be done using the lockBits method, here is a code example:

    Rectangle rect = new Rectangle(0, 0, m_bitmap.Width, m_bitmap.Height);
    BitmapData bmpData = m_bitmap.LockBits(rect, ImageLockMode.ReadOnly,
        m_bitmap.PixelFormat);

    IntPtr ptr = bmpData.Scan0;
    int bytes = Math.Abs(bmpData.Stride) * m_bitmap.Height;
    byte[] rgbValues = new byte[bytes];
    Marshal.Copy(ptr, rgbValues, 0, bytes);
    m_bitmap.UnlockBits(bmpData);
    GCHandle handle = GCHandle::Alloc(rgbValues, GCHandleType::Pinned);
    unsigned char * data = (unsigned char*) (void*) handle.AddrOfPinnedObject();
    //do whatever with data