Screen E-Book (.PDF) - MacDermid Autotype

Where does moiré come from?The human eye has evolved to be sensitiveto patterns. It’s rather important to knowthat a set of stripes is heading in your directionif you want to avoid being eatenby a tiger. Moiré is seen when two regularpatterns combine to form a third pattern.A typical example is seen when you passbeneath a bridge. To your eyes, the railingsat the front of the bridge are at a slightlydifferent spacing from those at the backand you get a pattern such as:Figure i. Moiréwhen two similarline patterns areoverlayed.The top two squares are the same patternof vertical lines, the one on the rightis spaced slightly further apart. When youcombine the two as in the bottom left,sometimes the lines are on top of eachother, making the line the same as theoriginal, and sometimes the line of onefalls in the spacing of the other, makingthe whole thing much darker. The imagein the bottom right is the calculated moiré,showing a good match between theoryand the human eye. If I show you the combinedimage in colour, you see where theproblem comes from.95