imgproc: update cornerSubPix documentation

modules/imgproc/include/opencv2/imgproc.hpp

@@ -1861,7 +1861,7 @@ gradient term \f$G\f$ and the second gradient term \f$b\f$ gives:
 The algorithm sets the center of the neighborhood window at this new center \f$q\f$ and then iterates
 until the center stays within a set threshold.
 
-@param image Input image.
+@param image Input single-channel, 8-bit or float image.
 @param corners Initial coordinates of the input corners and refined coordinates provided for
 output.
 @param winSize Half of the side length of the search window. For example, if winSize=Size(5,5) ,