What is ideal line (white or black or greyscale) in fspecial, motion filter?

I played with the tool for a while but I cannot understand the formula used to prepare the motion filter.

I found this in the documentation: Motion filter information

Few simple questions. What is the ideal line (white or black or greyscale)?

When line was specified as 1: the filter was 1.

When line was specified as 2: the filter was [.25 .25 .25].

When line was specified as 3: the filter was [.33 .33 .33].

I kept motion angle as constant 90 degrees for the above values.

I think the filter is a Gaussian distribution line where in the middle pixel is white or whiter and going towards either ends, pixels become darker or black.

The documentation says the nearest distance between location and ideal line segment. How does it find the nearest distance?

I did not find the formula helpful. Can anyone explain me? Thank you.