uploaded image width

I have the following to upload an image. I need the width and height of the image. How do I get?

if (FileUpload1.PostedFile != null && FileUpload1.PostedFile.FileName != "")
{
byte[] imageSize = new byte[FileUpload1.PostedFile.ContentLength];
HttpPostedFile uploadedImage = FileUpload1.PostedFile;
uploadedImage.InputStream.Read(imageSize, 0, (int)FileUpload1.PostedFile.ContentLength);

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}