The present invention is related to an image scanner, and more particularly to an image scanner which includes means for determining a scan start point quickly and precisely.
Nowadays, an image scanner has gradually become a standard peripheral equipment of a personal computer. Therefore, scanner manufacturers have been trying their best to improve the scanning quality, for example, to compensate brightness, chrominance, etc., and/or correct scanning line errors. On the other hand, high scanning speed is also a criterion of an exquisite image scanner.
In order to enhance the scanning speed of an image scanner, several devices and methods have been proposed in prior art. For example, please refer to FIG. 1 which schematically shows home-sensor means for speeding up the movement of an image pickup module 11 from a standby line N to a scan start line M, i.e. a document reference line. In this case, it is assumed that the image pickup module 11 reaches the scan start line M after moving a distance D from the standby line N along the arrow direction. In other words, the image pickup module 11 directly moves a pre-determined distance, rather than moves pixel by pixel to detect the presence of a document, and then starts scanning. Therefore, the movement of the image pickup module 11 from the standby line N to the scan start line M is fast.
However, there likely to be defects resulting from errors of various parts and/or assembling inaccuracy in this home sensor means. For example, if the image pickup module 11 is inaccurately installed at a position lower than a predetermined one while assembling, i.e. the standby line is lowered, the actual scan start line M1 will be accordingly lower than the document reference line M after the same distance D of movement, referring to the dotted lines and the dotted arrow in FIG. 1. Therefore, the top portion 13 of the document 12 will be missed out in the scanning operation.
Another conventional means is proposed to avoid the missing of document data. Please refer to FIG. 2 which schematically shows means for precisely determining a scan start point in an image scanner. On the scanning platform of this image scanner, a black region 21 is provided in front of a scan start line R where a front edge of a document 22 to be scanned is positioned. In this case, the image pickup module (not shown) quickly moves toward the black region 21, and then slowly passes through the black region 21 after reaches the black region 21 to detect the disappearance of the black color. When the detected black color disappears, the image pickup module keeps on moving and begins to measure a distance Q along the arrow direction. It is assumed that the scan start line R is reached after the image pickup module moves the distance Q from the reference point P. By this way, the downshift error resulting from the downshift installation of the image pickup module, as shown in FIG. 1, can be avoided because the predetermined distance Q is measured from the lower edge of the black region, i.e. the reference point P, rather than from the standby line of the image pickup module. Nevertheless, there still exists a defect in this means. Generally, when the image pickup module reaches the scan start line R, the nth pixel unit of a CCD of the image pickup module is predetermined to serve as the start point of the same scanning line, and the nth pixel unit and the pixel units thereafter are used to simultaneously pick up the image of the document line by line. If the image pickup module slightly deflects from its pre-determined path owing to an assembling defect, the same distance Q of movement will make the image pickup module reach another deflective line rather than the pre-determined scan start line R so that the nth pixel unit of the CCD will be a little shifted, and the scanning of a left portion of the document might be missed out. In addition, the scanning lines will slant.
In the parent application bearing Ser. No. 09/152,152 and filed on Sep. 11, 1998, means for determining a scan start point quickly and precisely so as to enhance the overall scanning speed of an image scanner is disclosed. Referring to FIG. 3 which schematically show the operation of a preferred embodiment of the parent application, the above purpose can be achieved by providing on the platform 30 of the image scanner at least one pattern mark 31 between the home position H and the scan start S. The geometric shape of the pattern mark 31 is so specific that the coordinate of each of the points constituting the pattern mark 31 can be calculated under certain known conditions. For example, it can be designed that the linking of the points B, E and F constitutes an isosceles and right-angled triangle, i.e. ∠EBF=45xc2x0, ∠BFE=45xc2x0 and ∠BEF=90xc2x0, so that the coordinate of each of the points constituting the pattern mark 31 can be calculated under certain known conditions through triangular functions.
When a scanning operation starts, the CCD 32 of the image scanner moves a pre-determined distance L0 from the home position H quickly to reach a pre-scan position I, and reads coordinates of two reference points U and V of the pattern mark 31 at the pre-scan position I. According to the coordinates of the two reference points U and V, a further moving distance L1 of the CCD 32 from the pre-scan position I to an ultimate point B can be easily determined through a mathematical function, so the movement of the CCD in this stage can also be fast. Afterwards, the CCD 32 further quickly moves another pre-determined distance L2 from the ultimate point B to the scan start S, and then starts scanning. Accordingly, the scanning speed would be satisfactory. Furthermore, it can be understood that the distance L1 can be automatically adjusted to reach the same ultimate point B no matter if the CCD 32 starts moving accurately from the home position. Therefore, the determination of the scan start point would be relatively precise.
Although the image scanner of the parent application has been significantly improved in the precision and the speed of the determination of the scan start point, the means may suffer from the contamination spots on the platform. Generally, with reference to FIG. 3, the pattern mark 31 is printed on a white background region 33 with standard black. If the region 33 is contaminated and has spot(s) thereon, especially at the pre-scan position I, during the manufacturing process of the image scanner or after the scanner has been used for a period of time, the CCD 32 may erroneously reads the coordinates of the contamination spots instead of the two reference points U and V so that an error in the determination of the distance L1 according to the read coordinates and the pre-determined mathematical function may occur.
On the other hand, although the scanning speed of the image scanner of the parent application is satisfactory, there is still a demand for higher scanning speed.
Therefore, an object of the present invention is to provide for an image scanner a device for quickly and precisely determining a scan start point, in which the error resulting from the misreading of the coordinates of the contamination spots can be avoided.
Another object of the present invention is to provide a device for an image scanner for quickly and precisely determining a scan start point, in which the movement of the distance L0 from the home position to the pre-scan position as described above can be omitted so as to further enhance the overall scanning speed of the image scanner.
According to a first aspect of the present invention, an image scanner includes a photo-signal processing device moving along a specific direction from a home position for picking up an image of a scanned document, and converting the image into digital data to be further processed; and a scanning platform for placing thereon the document. The scanning platform has thereon a background region located in front of the scan start point along the specific direction, and a color block located within the background region, and having an interface with the background region. Coordinates of a first reference point and a second reference point located in the interface are read when the photo-signal processing device moves to a pre-scan position and performs a pre-scan operation, and the coordinates of the first and the second reference points correlate with a shift from the pre-scan position to a specified point of the color block along the specific direction through a correlating mathematical function, so that a scan start point of the photo-signal processing device for picking up the image of the scanned document is determined according to the coordinates of the first and the second reference points, the mathematical function, and a predetermined shift from the specified point to the scan start point along the specific direction.
Preferably, the background region is printed with standard white, and the color block is printed with standard black.
Preferably, the color block has a specific geometric shape whose circumference is consisted of sectional lines and/or curves of known mathematical functions, and the first and the second reference points are two intersectional points of the circumference of the color block and the pre-scan position of the photo-signal processing device.
In a preferred embodiment, the color block is an isosceles and right-angled triangular block, one of the orthogonal sides of which is parallel to the specific direction, and the other orthogonal side of which is located relatively upstream along the specific direction. Therefore, the correlating mathematical function will be
L1=[(x2xe2x88x92x1)2+(y2xe2x88x92y1)2]xc2xd cot 45xc2x0=[(x2xe2x88x92x1)2+(y2xe2x88x92y1)2]xc2xd
in which L1 indicates the shift from the pre-scan position to the specified point along the specific direction, (x1,y1) and (x2,y2) are the coordinates of the first and the second reference points, respectively, and
[(x2xe2x88x92x1)2+(y2xe2x88x92y1)2]xc2xd indicates a detected length between the two reference points. Therefore, the photo-signal processing device starts to perform a scanning operation after traveling a distance of (L1+L2) from the pre-scan position along the specific direction, in which L2 is the predetermined shift from the specified point to the scan start point along the specific direction.
Generally, the photo-signal processing device includes an image pickup device for performing the scanning operation, and detecting the coordinates of the first and the second reference points; and a driving device for moving the image pickup device from the home position along the specific direction.
In an embodiment, the background region and the color block are both located between the home position and the scan start point. Alternately and preferably, the background region and the color block are both located at the home position of the photo-signal processing device. In this case, the home position will serve as the pre-scan position to perform the pre-scan operation thereat, and the movement of the photo-signal processing device from the home position to the pre-scan position can be omitted.
According to a second aspect of the present invention, an image scanner includes a photo-signal processing device moving along a specific direction from a home position for picking up an image of a scanned document, and converting the image into digital data to be further processed; and a scanning platform for placing thereon the document. The scanning platform has thereon a background region located at the home position, and a color block located within the background region at the home position, and having an interface with the background region. The photo-signal processing device performs a pre-scan operation to read coordinates of a first reference point and a second reference point located in the interface at the home position, and the coordinates of the first and the second reference points correlate with a shift from the home position to a specified point of the color block along the specific direction through a correlating mathematical function, so that a scan start point of the photo-signal processing device for picking up the image of the scanned document is determined according to the coordinates of the first and the second reference points, the mathematical function, and a predetermined shift from the specified point to the scan start point along the specific direction.