Where does format = gray go for -vf format = gray in python

[kt-lowen]

Hello! I am wondering how to implement for format = gray in the filter for ffmpeg. I am trying to do the equivalent of -vf format="gray" in python and stuck on how to get this working.

When I do:

(
            ffmpeg.input(img_seq_template, framerate=framerate, **input_options)
           .filter(format="gray")
            .output(filename=output_path, **output_options)
            .run(overwrite_output=override_existing)
  )

I don't have any issues, but I am hoping to also have a dictionary for my filter parameter. When I try to put in format into a dictionary and pass it into .filter(), I either get an error to specify the filter name and an error saying format is not a valid filter. I am wondering what filter name I need to pass for this, and also why format="gray".

Thanks!