Patent Abstract:
An image reading device that detects the edge of the image to be read and masks the areas outside the edge during the read. The image reading device includes a light transmittance modification device in the optical path between the image illumination source and the photoelectric conversion device. During a pre-scan of the image, the position of the edge of the image is stored in a memory unit. During the actual scan of the image to be read, the edge data is fed to the modification device for each position of the scanner. The modification device blocks out those portions of the area being scanned that are outside the image. In this manner, the image is read while the border area is masked.

Full Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image reading device that converts light passed through an original image into electrical signals using a photoelectric conversion element, such as a CCD (Charged Coupled Device) camera, and, more particularly, to such an image reading device capable of masking a specified range of the original image. 
     2. Description of the Related Art 
     In the aforementioned field, it is known to use devices such as shading sheets to block out unwanted portions of image light being projected from a translucent original, such as a negative or a transparency. Borders and excess image areas are typically blocked out in this manner. Conventionally, such as shown in FIG. 10, several shading sheets are cut so as to block out these unwanted areas when placed on and around the original. The user would then stack the shading sheets on the original before transmitting light therethrough. 
     Most image reading devices use an original cassette glass for holding the image. An original holding glass is typically placed over top of the original to secure it in place. Light is transmitted through the original and recorded as electrical signals by a photoelectric conversion element, such as a CCD output. Currently, equipment designed to digitize originals must rely on shading sheets to eliminate excess areas. The shading sheets are held between the cassette glass and the holding glass with the image. As the light cannot pass through the shielding, the camera only sees those regions of the image which the user wishes to be recorded. 
     Each image to be processed in the aforementioned manner requires a different set of shields to achieve the desired results. Even if only the clear borders of each image are masked, there is still a need for multiple shading sheets, one for each size of original to be processed. There is a practical limit to the different types of sheets that can be prepared, thus limiting the user to a defined number of formats and shading schemes. It is also difficult to maintain the full set of shielding sheets due to the inevitable damage and loss of such sheets. As such, there exists a need for an apparatus and a method for masking an area of an original without using light shielding sheets. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a light shielding device capable of shielding a variable area of an original image. 
     It is another object of the present invention to provide a light shielding device capable of shielding a portion of an original image based upon pre-defined values. 
     It is yet another object of the present invention to provide an image reading device having a light shading device capable of shielding areas of an original image based upon pre-defined values. 
     It is yet a further object of the invention to provide an image reading device capable of determining which areas of an image are to be shielded. 
     It is yet a further object of the invention to provide an image reading device capable of determining which areas of an original image are to be shielded and then causing those images to be so shielded during the actual scanning of the original image. 
     Additional objects and advantages of the invention will be set forth in part in the description that follows, and in part, will be obvious from the description, or may be learned by practice of the invention. 
     The foregoing objects of the present invention are achieved by providing an image reading device that includes a light modification unit that masks regions of an original image based upon values inputted before or during the actual scanning of the image. The above objects of the present invention may also be achieved with an image reading device that includes a light modification unit able to shield regions of an original image based upon values derived by the image reading device during a pre-scan sequence of the original image. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and advantages of the invention will become apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which: 
     FIG. 1 is an isometric diagram of the light modification apparatus and image holding device for an image reading device according to a preferred embodiment of the invention. 
     FIG. 2 is a cross-sectional view of an image reading device in accordance with a preferred embodiment of the present invention. 
     FIG. 3 is a block diagram of the image reading device in accordance with the preferred embodiment of the present invention. 
     FIG. 4 is a flow chart showing an example of the operation of the image reading device according to the preferred embodiment of the present invention. 
     FIG. 5 is a flow chart showing an example of the pre-scan routine performed by the image reading device according to the preferred embodiment of the present invention. 
     FIG. 6A is a top view of the original image holding apparatus and light modification apparatus of the image reading device according to an embodiment of the present invention. 
     FIGS. 6B and 6C are graphs showing an example output of a CCD in accordance with an embodiment of the present invention. 
     FIG. 7A is a top view of the image holding apparatus and light modification apparatus of an image reading device in accordance with an embodiment of the present invention. 
     FIGS. 7B and 7C are graphs showing an example of the output of the CCD in accordance with an embodiment of the present invention. 
     FIG. 8 is a top view of the original image holding apparatus and light shielding apparatus of an image reading device according to another embodiment of the prese invention. 
     FIG. 9 is a block diagram of an image reading device in accordance with the alternative embodiment of the present invention, as shown in FIG.  9 . 
     FIG. 10 is an isometric view of a conventional original image holding device and light shielding sheets. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
     Referring now to FIGS. 1 and 2, wherein shown is a configuration of a first embodiment of an image reading device according to the present invention. As used herein, the term “original” shall refer to the translucent image carrier to be read. Referring to FIG. 2, an original cassette  13 , attached to the upper surface of main unit  11 , holds the original  12 . Original cassette  13  is connected to motor  35  which causes the cassette to move in the direction of the sub-scan indicated by the arrow A—A. The original  12  is held between an original cassette glass  14  and an original holding glass  15 . A light source  16  is secured to the main unit  11  above the path of the sub-scan. The light emitted by source  16  is transmitted through original  12 , reflected by three reflecting mirrors  17 , 18 , 19 , and travels through lens system  20  onto CCD  21 . CCD  21  receives the image and converts it into electrical signals. 
     Between light source  16  and cassette  13 , on the optical axis  22  uniting light source  16  and reflecting mirror  17 , a narrow transparent plate  23  is positioned which spans cassette  13  in a direction perpendicular to the direction of the sub-scan. The narrow transparent plate  23  has two glass plates holding light transmittance element  24  therebetween. Light transmittance element  24  comprises components, such as LCDs and/or electrochromatic elements, in a linear matrix form. The light transmittance of specified portions of transmittance element  24  is controlled by applying a specified voltage to the LCDs or electrochromatic elements. Light is shaded if the transmittance of the elements approaches zero percent. 
     Referring now to FIG. 3, wherein shown is a block diagram of an image reading device according to the preferred embodiment of the present invention, as shown in FIGS. 1 and 2. A CPU  32  controls the various elements of the image reading device according to a program stored in ROM  33 . Control includes executing the image reading operation stored in ROM  33 . The data necessary for executing the various processing operations is stored, as necessary, in a RAM  34 . Input section  31  operates to receive specific commands. 
     An interface (I/F)  36  outputs signals corresponding to the operation of an input section  31  to CPU  32  through a bus. The data outputted by the CCD  21  is supplied to the CPU  32  through the bus. CPU  32  then typically supplies this data to RAM  34  where it is stored for future operations. In addition, CPU  32  controls the light source  16  through interface  36 , causing light to be emitted. Similarly, CPU  32  controls light transmittance element  24  and sets specific elements therein to the desired light transmittance levels. Moreover, CPU  32  drives motor  35  through interface  36  to transport original cassette  13  during the scanning operation. 
     Referring now to FIGS. 4 and 5, therein depicted are flow charts explaining the operation of the image reading device according to the preferred embodiment. First, in step  101 , original  12  is set at the desired position on original cassette  13 . Next, in step  102 , the preliminary scan (“pre-scan”) is performed to determine which areas of the image should be masked during the actual scan. The pre-scan is started when input section  31  is operated and a read-start command is given. The CPU  32  then activates light source  16 , causing original cassette  13  to be illuminated. 
     CPU  32  subsequently drives motor  35  to transfer the original cassette in the direction of the sub-scan, as shown by arrow A—A in FIG.  2 . Thus, the light emanating from the light source  16  illuminates the original cassette  13 , passing through the original  12 , and is reflected by reflecting mirrors  17 ,  18 , 19  towards lens system  20 . Lens system  20  focuses the light and directs it to the CCD  21  for processing. 
     The details of pre-scan step  102  are shown in FIG.  5 . For exemplary purposes, the pre-scan process described below is for the purpose of masking the border of an original. It can be recognized by one skilled in the art that other areas can be selected and masked by changing the selection criteria. First, in step  301 , the original cassette is transported such that the first pixel line of the cassette is placed into the read position, i.e., in optical path  22 . Next, the variable n, used to indicate the read position, is set to 1. Thereafter, in step  302 , the first pixel line is read by CCD  21 . The pixel line is read perpendicular to the direction of the sub-scan, in the direction of the main scan. Once the pixel line has been read, the mask range of that line is determined in step  303 . 
     To determine the mask range of the pixel line, the CPU  32  stores the data gathered by the CCD  21  into RAM  34 . This stored data is compared with a reference value, set in advance, to obtain the position of the edge of the main scan of original  12 . Typically the light that passes through original cassette  13  outside the region occupied by the original  12  is greater in quantity than the light which must also pass through the original  12 . Thus, when the reference value is set to a light quantity value between these two, the position of the edge of the original can be detected. The area to be masked can be determined from this edge position. 
     The position to be masked as determined in step  303  is placed into RAM  34  in step  304 . 
     In the subsequent step  305 , the current read line, as indicated by the variable n, is compared to a value m that indicates the last line of the original cassette  13 . If n is less than m, n is incremented and the cassette is transported to the next pixel line in step  306 . Thereafter, the process repeats from step  302 . The image reading device will continue to read subsequent pixel lines and to determine the masking range for each pixel line until the last line is reached, at which point the determination, in step  305 , will fail and the pre-scan will end. Through this process, the position of the edge of the original  12  on the original cassette  13  is attained for each pixel line and stored in RAM  34 . 
     After the pre-scan sequence has been completed, the actual scan is initiated in step  103 . In preparation for the actual scan, original cassette  13  is returned to the initial position. This time as the cassette is being driven during the actual scan, the light transmittance element  24 , attached to transparent plate  23 , is driven as a mask according to the data stored in RAM  34 . The areas that were determined in step  303  to be masked can be blocked by modifying the transmittance of the elements in light transmittance element  24  to zero percent (or some sufficiently small value). Conversely, those areas that do not need to be masked are controlled such that their light transmittance becomes 100 percent (or sufficiently large value). In this way, the light of the border of original  12  is, in effect, shaded. 
     Referring again to FIG. 1, along with transporting the original cassette in the direction indicated by arrow A, voltage is imparted to the elements of the light transmittance element  24  in the mask area determined in step  303 . By performing this light shielding for each pixel line lying on the direction of main-scan, along the sub-scan direction, according to the data stored in RAM  34  the specified area of the image of original  12  can be masked. Thus, only the specified area of the image is extracted by CCD  21 . FIGS. 6A-C and  7 A-C show conceptual examples of CCD&#39;s  21  output intensity in relationship to various positions of the original  12  upon the original cassette  13 . As shown in FIGS. 6A-C, when the two sides of the original  12  are at right angles to the direction of the sub-scan (see FIG.  6 A), the output of the CCD  21  varies during the pre-scan (FIG.  6 B). As can be seen, the outside areas of original cassette  13  that are not obstructed by the image of original  12  display a high transmittance of light. In contrast, those areas obscured by the image of original  12  display lesser transmittance values. Area  37  indicates the portion of the image of the original that is to be read by CCD  21 . FIG. 6C is representative of the desired output of CCD  21  during the actual scan while light transmittance element  24  is in use. Those areas determined to be outside the image are masked and thus display low transmittance. 
     Referring now to FIG. 7A, this figure portrays a situation where an original  12  is skewered on original cassette  13 . In this case, the output of the CCD during the pre-scan, FIG. 6B, and actual scan, FIG. 7C, are appropriately skewered to the right. 
     Where LCDs and other electrochromatic elements are used as the light transmittance element  24 , there are instances in which the light emanating from the light source  16  cannot be completely shaded, but if the light can be shaded to a certain extent, the dynamic range of CCD  21  can be concentrated in the read range of the original  12 . 
     Although the first embodiment of the present invention has been described with respect to specific components for the image reading device, it will be recognized that the first embodiment is not limited to those specific components. For example, although the first embodiment has been described with respect to a CCD, it will be recognized that other kinds of image reading devices can be employed. Further, it will be recognized that, while in the above embodiment the optical system (light source  16 , light transmittance element  24 , reflecting mirror  17 ,  18 ,  19 , lens system  20  and CCD  21 ) is stationary while the original cassette  13  is transported through optical axis  22 , the optical system could be transported instead of the original cassette. In fact, it is only necessary that the optical system and the original cassette move in relationship to one another. 
     It will also be recognized by one of ordinary skill in the art that the light transmittance element  24  need not be positioned between original cassette  13  and the light source  16 , but rather must only be on the optical path from light source  16  to the CCD  21 . It has been found that the position between original cassette  13  and light source  16  offers little deterioration in image quality, but requires that the length of transmittance element  24  be as wide as original cassette  13 . On the other hand, if light transmittance element  24  is positioned between the original cassette  13  and the lens system  20 , it must only be a length that corresponds to the aperture of lens system  20 . While this enables cost reductions, the light from original  12  is typically dampened by the glass plate that forms transparent plate  23 , thus deteriorating the quality of the image of original  12 . 
     Referring now to FIG. 8, this figure shows a top view of an image reading device according to a second embodiment of the present invention, wherein the light transmittance is controlled by a mechanically operated light shielding plate. Like elements in the figures of the first and second embodiments are referred to by like reference numerals, and a description of the like elements will not be repeated in detail here. 
     According to the second embodiment of the present invention, the image reading device has light shielding plates  42 L and  42 R which are positioned to one side of original cassette  13 . Nuts  43 R and  43 L are attached to light shielding plates  42 R and  42 L, respectively. Nuts  43 R and  43 L are threaded onto screws  44 R and  44 L, respectively. The position of light shielding plates  42 R and  42 L, with respect to original cassette  13  and the pixel line to be scanned, shown by line  22 , is controlled respectively by motors  41 R and  41 L, which rotate corresponding screws  44 R and  44 L. 
     FIG. 9 is a block diagram of the electrical configuration for the image reading device according to the second embodiment of the present invention. As can be seen, motors  41 L and  41 R are connected to interface  36  for control by CPU  32 . The rest of the electrical configuration is similar to that of the first embodiment. 
     When motors  41 L and  41 R are driven by CPU  32 , the screws  44 L and  44 R are rotated. This rotation acts to lever nuts  43 L and  43 R in the direction of the sub-scan. Light shielding plates  42 L and  42 R are formed such that their inner sides  42 La and  42 Ra are angled with respect to the sub-scan direction. Therefore, the position at which the light from light source  16  is shaded changes as the plates are moved in relationship to pixel scanning line  22 . As will be readily apparent, the specified areas of the image of original  12  can be masked in the same way as the case in which light transmittance element  24  was used. 
     In operation, the main difference between the first embodiment and the second embodiment is that, in the first embodiment, multiple originals can be placed across scan line  22  and still be correctly masked. Due to the mechanical limitations of the second embodiment, only one original can be placed across scan line  22 . 
     Although the second embodiment of the present invention has been described with respect to specific components for the image reading device, it will be recognized that the second embodiment is not limited to those specific components. For example, although the second embodiment has been described with respect to triangular shielding plates, it will be recognized that other shapes may be used. Further, it will be recognized that other mechanisms for driving the shields can be employed. 
     Although a few preferred embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalence.

Technology Classification (CPC): 7