what does get_img_output_length() means?

[sunshuofeng]

this is your code:
def get_img_output_length(width, height):
def get_output_length(input_length):
# filter_sizes = [3, 3, 3, 3, 3, 3, 3]
# strides = [2, 1, 2, 1, 2, 2, 2]
filter_sizes = [3, 3, 3, 3, 3, 3]
strides = [2, 1, 2, 1, 2, 2]

    assert len(filter_sizes) == len(strides)

    for i in range(len(filter_sizes)):
        input_length = (input_length - filter_sizes[i]) // strides[i] + 1

    return input_length

return get_output_length(width), get_output_length(height)

what does it means?
slides the 3*3 window on feature map?