Image processing is often used for photography or movie. As we know, the scanner plays an indispensable role in this field. Higher resolution is required to obtain more clear images, but the image files also occupy a larger space in the disk. An image of A4-size may be converted into a file of few megabytes when it is scanned with resolution of 600 dpi (dot per inch). Sometimes, an image with lower resolution is allowable so the size of the image file can be reduced significantly. The required resolution is various according to circumstances. For example, scanning a usual document requires a lower resolution, but scanning a beautiful photograph needs a higher resolution. Accordingly, the conventional scanner with single resolution is not suitable for all different kinds of images. Recently, the concept of a scanner with multiple resolutions has been proposed. It is conceivable that some additional elements are needed for "switching" among resolutions to achieve this concept.
A driving element is usually adopted to perform the "switching" function. The word "switching" means that some optical elements is driven by the driving element to be move along with the light path according to the desired resolution of the scanning operation. It is possible but not commercially practicable because any moving action is unfavorable to the precision of the scanner. Precise locations of the optical elements are very important. IF the optical elements are moved, no one can assure that they would be moved to the right positions. A slight error occurred in moving the optical element will cause a serious error in the resulting image file. In other to improve the above-described defects, it is necessary to make efforts for manufacturing the conventional scanner with multiple resolutions.
Please refer to FIG. 1 which shows the operational process of a conventional scanner. The piece of paper 11 is put on the scanning window to be scanned. As shown in FIG. 1A, if a lower resolution is acceptable, the low-magnifying powered lens 121 of the lens set 12 is moved to be located within the light path so that an image received by a charge coupled device 13 can be magnified to a smaller size. On the other hand, if a higher resolution is required, the high-magnifying powered lens 122 of the lens set 12 is moved to be located within the light path and an image received by the charge coupled device 13 is magnified to a larger size, as shown in FIG. 1B. The most serious disadvantage of this method is its unsatisfied precision resulting from the movement of the lens set 12. The method also has other disadvantages. To perform this moving function, an additional space is needed for locating the driving device and moving the optical elements. It is a tendency for modem machine to have a minimum size.
Many improved devices or methods have been disclosed. For instance, Taiwanese Patent Publication No. 281851 disclosed a method used for scanner, fax machine, copy machine or the like with optional resolutions. It teaches that both the zoom lens and the charge coupled device are movable, both of which are driven by a driving motor. In order to keep the precision of the machines, a calibrating unit is required. Besides, Taiwanese Patent Publication Nos. 286850 disclosed that the charge coupled device is moved by a ball screw. Other relevant patents, Taiwanese Patents Publication No. 232398, 235112, and 280480, teach that lenses are moved by their respective featured driving elements. The improvement of these prior publications seem nothing in comparison of their large volume, high production cost, and unsatisfied precision.