utmanga is the cli app that provides various tools to grayscale manga pages.
utmanga [command] --help to get help of the app and commands.
go 1.21.5 or higher is required.
When install just run go build in root directory of the project.
No additional tools are required.
You can download executables from release page.
If you want build it yourself then read build section.
If you want to run it from any directory, put it in one of the $PATH directories.