访问冲突-为什么在c#中调用AForge库函数会导致AccessViolationException

下面的代码导致访问冲突异常-为什么?我可以从unsafe块内部调用AForge过滤器吗?

unsafe
{
    BitmapData bmd = ThresholdedImage.LockBits(boundingR, ImageLockMode.ReadWrite, ThresholdedImage.PixelFormat);
    BitmapData bmda = intersectResult.LockBits(
        new Rectangle(0, 0, intersectResult.Width, intersectResult.Height),  
        ImageLockMode.ReadWrite,  
        intersectResult.PixelFormat);

    intersectResult = intersectFilter.Apply(bmd); //causes exception here
    ImageStatistics st = new ImageStatistics(intersectResult);
    area = st.PixelsCountWithoutBlack;
    intersectResult.UnlockBits(bmda);
    ThresholdedImage.UnlockBits(bmd);
}