grayscale
=========

Goal:
-----
Convert the image to gray scale (i.e. no color). The image will retain its luminance and remove the chrominance.

Syntax:
-------
`grayscale`

Usage example:
--------------
`sic input.png output.png --apply-operations "grayscale;"`

See also:
---------
https://docs.rs/image/0.19.0/image/imageops/colorops/fn.grayscale.html