The process of image processing is the method by which image signal is converted to physical image by using a photographic software.

(A) The process of Image processing is the method by which image signal is converted to physical image
(B) The process of image processing is the way that image signal is converted to physical image
(C) Image processing is the process by which image signal is converted to physical image
(D) Image processing occurs when image signal is converted to physical image
(E) Image processing, the process by which image signal is converted to physical image

OA is C
What is the perfecr modifier here. An Expert contribution pls. Thanks