Abstract
In CRT-PC monitors or dot-matrix type displays such as LCDs and PDPs, moire fringes often appear when converting resolution or size of displayed images which have signal frequencies at or near the sampling frequency. An optimization of the spatial frequency filter response for eliminating the frequency components, which are responsible for the moire fringes, has been performed. For an example of reducing XGA images by 80%, a combined band eliminate and low pass spatial frequency filters should be employed. The band eliminate filter is used to reduce moire patterns caused by low frequency components and has a Gaussian profile with the central frequency at 0.23 line/pixel, attenuation of 0.74∼0.87, and a half-width at a half-maximum of 0.08∼0.12 line/pixel. The low pass filter is used to reduce moire patterns caused by high frequency components and eliminates signal exceeding 0.36 line/pixel. Filtering is applied only to the area in which moire is expected to appear. As a result, moire contrast is reduced to 0.02 and improvement of picture quality can be attained.
