| 摘要 |
<p>Apparatus for ascertaining the fitness of a document having some printed regions and some unprinted regions, by determining its degree of soiling. A sensor (16) provides reflectance signals representing the intensity of light reflected from a number of sensed elements on the face of the document. A signal processing circuit responsive to the reflectance signals includes means (26) for determining for each of a number of areas of the document, the number of elements in the area which result in a signal level exceeding a first threshold, representing the upper limit of brightness for printed areas on the document; and means (24, 34, 36) for determining whether the number of elements exceeding the first threshold reaches a given proportion of the total number of sensed elements for that area. Each area is then given a brightness value dependent on the relationship between a second threshold, representing the upper limit of brightness for unprinted areas having an excessive degree of soiling, and those signal levels of the elements of the area which exceed the first threshold. The fitness or unfitness of the document is judged from the brightness values of all such areas. In another form of apparatus embodying the invention, a first comparator compares the level of the signal from the sensor with a first threshold and the signal is integrated only over periods in which its level exceeds this first threshold. The resulting signal represents the total reflectance of the brighter areas of the face of the document. A further signal is obtained representing the total time that the reflectance signal level exceeds the first threshold and this duration signal and the total reflectance signal are used in combination to provide the "fit" or "unfit" output signal for the document.</p> |
