Add 64-bit imshow behavior in the documentation.

modules/highgui/include/opencv2/highgui.hpp

@@ -361,7 +361,7 @@ Otherwise, the image is scaled to fit the window. The function may scale the ima
 -   If the image is 8-bit unsigned, it is displayed as is.
 -   If the image is 16-bit unsigned or 32-bit integer, the pixels are divided by 256. That is, the
     value range [0,255\*256] is mapped to [0,255].
--   If the image is 32-bit floating-point, the pixel values are multiplied by 255. That is, the
+-   If the image is 32-bit or 64-bit floating-point, the pixel values are multiplied by 255. That is, the
     value range [0,1] is mapped to [0,255].
 
 If window was created with OpenGL support, cv::imshow also support ogl::Buffer , ogl::Texture2D and