Investigate, and potentially implement using -grayscale instead of -colorspace Gray

[DrWhoCares]

-grayscale is OpenCL accelerated. https://imagemagick.org/script/opencl.php
Equivalent command would be -grayscale Rec709Luma. As per https://www.imagemagick.org/script/command-line-options.php#grayscale

[DrWhoCares]

In my tests, it was not using my GPU for whatever reason. RTX 2070. Ended up being slower since it wasn't using any of the optimizations. If there's a method to detect if it will use the optimizations, adding in a conditional would be nice.