Think of it this way: The Trinitrons have two visible horizontal lines, but shadow mask monitors effectively have 1023 (for 1280x1024 res)lines, one between each row of pixels. Shadow mask monitors have empty space on all 4 sides of each pixel, whereas aperture grille monitors, like Trinitrons, only have empty space on the left and right of the pixel. This results in MUCH better image quality, because more phosphor is exposed to the user.