| 摘要 |
A document I containing lines 2 printed at an interference scanning frequency which causes conventional scanning and copying devices to introduce distortions in a copy of the document and prevents color separating copies of the document. The document bears an image 21 which has lines printed at a line frequency which is an interfering scanning frequency. A document I I containing an image 12 which has several layers, each of which has lines printed at an angle and color which may be different from the other layers. At least one of the layers in document I I may be printed at an interfering scanning frequency. Also, the intersection between the lines of the layers may form a white space which has an interference scanning frequency by selecting appropriate angles between the lines. Interference scanning frequencies of a scanner may be determined by a document bearing a plurality of line frequencies, each line frequency being in a row and being printed at a variety of densities. An apparatus may be used to deten-nine interference scanning frequencies of a scanning device by scanning a document with a plurality of images with a plurality of line frequencies and then determining which line frequencies create a scanned image with significant distortions, moiré patterns or density gains.
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