The gap between scan lines is a function of image row (scan-line) pitch and spot profile.
If the spot profile is such that there is a significant gap between the intensity distributions of adjacent image rows (scan lines), then image structure will be visible to viewers closer than a certain distance. I have treated the image array as an array of pixels, without regard for the spatial distribution of light power across each pixel – the pixel's spot profile, or more technically, point spread function (PSF). The clean aperture excludes blanking transition samples, indicated here by black bands outside the left and right edges of the picture width, defined by the count of samples per picture width ( S PW). The Clean aperture should remain subjectively free from artifacts arising from filtering.
