How can I use emgucv to convert a rgb image to gray image?

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C#

Emgu-CV

Image<Bgr, Byte> srcimage = new Image<Bgr, byte>("201221230019.JPG");

Image<Gray, float> btt = srcimage.Convert<Gray, float>();

it can't work ,shows the problem:"

Convertion from Image<Emgu.CV.Structure.Bgr, System.Single> to Image<Emgu.CV.Structure.Gray, System.Single> is not supported by OpenCV

" ,is it because the new version doesn't support the operating? and the

opencv_highgui220.dll

,

opencv_imgproc220.dll

,

opencv_legacy245.dll

is was correctly referenced.

What I have tried:

I also tried:

Bitmap bt = new Bitmap(path);

Image<Bgr, float> img11 = new Image<Bgr,float>(bt);

Image<Gray, float> img2 = new Image<Gray, float>(bt1);

it also doesn't work,the same problem appeared.