Image scanner systems

Abstract: A scanner system for detecting images on a surface (8) and generating an electronic representation thereof for transmission to an image processing system, including at least three rows (100, 102, 104) of n sensors generating charges representative of detected light of preselected wavelengths during an integration period of a selected duration. Each row of sensors is comprised of substantially similar construction, and suitable for detection of a preselected wavelength. Sensors may be chosen from a sensor type which facilitates transfer of charges through the sensor. The sensor rows are provided with discharge paths interconnecting each sensor in a row in charge-passing relationship with a sensor in a successive row, and a storage device (106), whereby sensors in a first row are discharged to a storage device through sensors in the second and third rows; sensors in a second row are discharged to a storage device through corresponding sensors in a third row; and sensors in a third row are discharged into a storage device prior to transmission of the charges as output information. The charges are passed to the storage device between integration periods. A new integration period may be started as soon as data from the first row sensors reach a storage device.

Description: The present invention relates primarily to a raster input scanning device, and more particularly to raster input scanners having color sensor arrays for deriving color information from a scanned image. For the purpose of background information on scanned image technology, US-A-4,506,301 is relevant. US-A-4,396,950 discloses a CCD camera incorporating a row of photosites using a clocked transfer gate to transfer output signals in parallel to a shift register, from which they are fed in series. US-A-4,264,921 discloses the parallel transfer of output signals from one row of sensors to an adjacent row. Raster input scanning devices generally include an array of photoelectric sensors or detectors or photosites arranged across an image-scanning field for detecting light from an image; a data transmission and processing system for taking the image data derived from the photoelectric detectors and passing the image information to a data processing system, such as a microprocessor; and a transport for relative movement of the image to be scanned across the scanning field so that photoelectric sensors extending transversely across the image field direction of motion are able to detect, on a line-by-line basis, the images on the scanned surface. Of particular interest is the processing of color images. In color image scanning, the scanned image must be broken into component colors, each of which is processed separately for later assimilation to produce the entire image. This may be done in a variety of ways. In the past, the entire image was scanned, for example three times, each time with a different color filter superimposed over the scanned image. Thus, each scanning operation produced selected color information based on the filter over the image. In such a system, the detectors are able to detect only the difference between a light and dark image, and may use detectors similar to those detecting only black and white information. With the development of color filter sensors, which provide photosites with color filters, and the ability to make longer arrays of photosites, it has become possible to provide scanning systems requiring only a single pass of the image. In these systems, a large amount of data is created by the photosites, requiring fast handling of the data by image-processing systems, and, particularly, within the array itself. The speed at which the document can be read is dependent on the time in which data derived by the photosites can be transmitted to the processing system. For example, if it is desired to move the image surface in a Y-direction at a speed of 25 mm/s, and a resolution of 12 scan lines/mm is desired, it becomes necessary to move data from 300 scan lines of data per second from the photosites to the processor. Since the arrays may range along the X-direction in length from 3500 to in excess of 5100 photosites, it will be appreciated that a large amount of information must be handled to achieve the required processing speed. A commercial product by Toshiba Corporation, Model No. TCD 112, provides a sensor arrangement including a plurality of arrays in offset and overlapping relationship to cover the X-direction of an image field. This product splits each individual photosite into three sites, each with a color filter. Color image information may be derived from the sensors, and is passed in sequential fashion to a data processor. It would be preferable, however, to provide an array with larger photosites since a larger photosite is more sensitive to the light focused thereon and allows the document to be scanned at a higher rate. Additionally, the overlapping and offset arrangement of the TCD 112 makes it difficult to align the segments. Thus, extensive processing of the signal is required to compensate for the offset alignment of the arrays. The primary object of the present invention is to provide a photosite sensor array arrangement suitable for use in a color image raster input scanning system. Accordingly, the present invention provides a scanner system which is claimed in the appended claims. The invention provides for an array extending across the entire field in the X-direction of an image to be scanned so that no alignment of the arrays is required in this respect. Large photosites may be used in each row, as a single row of photosites detects only a particular light wavelength, while succeeding similar rows detect other wavelengths. Thus, the available array space does not need to be divided for the purpose of providing color photosites on a single array. This arrangement maintains the sensitivity of the array at a high level, and allows shorter integration times to be utilized, thereby increasing the speed of image reading. The present invention will now be described, by way of example with reference to the accompanying drawings, in which: FIGURE 1 is a schematic view of an optical assembly in a preferred embodiment of the invention; FIGURE 2 is a schematic view of a sensor array of the invention; FIGURE 2A is a diagram demonstrating the operation of the sensor array of FIGURE 2 with time, and FIGURE 3 is a schematic view of another embodiment of a sensor array of the invention. Referring now to the drawings, FIGURE 1 shows, somewhat schematically, an arrangement for an optical system of a raster input scanner of the present invention, and providing an image from an original document 8 supported on platen 9 to be scanned by an imaging sensor array A. The optical system of raster input scanner 10 comprises lamp 12 and adjustable reflector 14 for illuminating document 8. Mirrors 16, 18, 20 and 22 direct light reflected from the document 8 to a lens 24 to focus and direct the image on the sensor array A. Information derived from the sensors will be directed to a conventional information or data-processing system (not shown). The acquired data will be manipulated as desired for display, storage, etc. It will be appreciated that the present invention is readily applicable to other arrangements. Fiber optic assemblies, or other arrangements of mirrors and lenses, may be used to direct an image to the array. Additionally, it will be appreciated that while the described embodiment scans reflected light, the invention is equally applicable to other optical storage media such as slides, transparencies, aperture cards, etc. Also not shown is a carriage means for moving the document 8 in a longitudinal (Y) direction (left-to-right as viewed in FIGURE 1) to provide scan lines moving successively along the document 8 to be scanned by the sensor array. The elements comprising the mechanical and optical systems in a raster input scanner are widely varying and well known in the art, and do not form a part of the present invention. In accordance with the invention, sensor array A is comprised of three parallel rows of sensors comprising photosites 100, 102, 104, best shown in FIGURE 2. As will be appreciated, an increase in the number of photosites results in improved image resolution. In a preferred embodiment of the present invention, a photosite row may include upwards of 3500 individual photosites. For the purpose of illustration, however, a limited number of photosites, labeled 1, 2, 3, 4 and n, is shown as an example. FIGURE 2 shows an arrangement including photosite rows 100, 102, 104 arranged to pass information derived from the image to storage means comprising storage registers 106, 108, and from the storage registers 106, 108 to shift registers 110, 112, from which information may be passed to a data-processing system (not shown). All three photosite rows 100, 102, 104, as well as the storage registers 106, 108 and shift registers 110, 112, may be provided on a single monolithic chip to form sensor array A. The rows are arranged perpendicularly to the fast scan (Y-axis) direction of image scanning, which is indicated as the vertical direction in FIGURE 2. Photosite rows 100, 102, 104 may be comprised of either photodiodes or charge-coupled devices (CCD's). Color filters selected to filter undesired wavelengths of light are arranged over each row of photosites or each photosite. In the present embodiment, photosite rows 102, 104 may be comprised of CCD's,and provided with filters for passing green and red light. Photodiodes often have a better spectral response in the blue light region than CCD's, but do not allow image information to be easily passed through the photosite. Accordingly, photosite row 100 may be comprised of photodiodes and located in the array A furthest away from shift registers 110, 112, so that there will be no requirement that image information pass through such sites, thereby allowing the superior response characteristics of the photodiodes for shorter wavelength to be utilized. It will be appreciated that while these colors have been selected for a preferred embodiment, other color combinations of sensors are possible, and within the scope of the present invention. It is also within the scope of the invention to provide that all of the photosites be comprised of CCD's, rather than mixing types. Each photosite in photosite rows 100, 102 is connected to a corresponding photosite in a succeeding row, while each photosite in photosite row 104 is connected to a bit in storage register 106 in information-transferring relationship, which is in turn connected to storage register 108. In a preferred embodiment of the invention, storage register 108 passes data from alternating bits to either shift register 110, or through shift register 110 to shift register 112 for transmission of the data to the data processor. The transmission of data by two shift registers serves to increase toe rate at which image information may be passed to the data processor. Charges are transferred between adjacent photosite rows, storage or shift registers through transfer gates TR n , indicated by toe lines across the path of charge travel between the successive rows in FIGURE 2. Thus, photosite row 100 is connected to photosite row 102 through transfer gates TR₁, photosite row 102 is connected to photosite row 104 through transfer gates TR₂, photosite row 104 is connected to storage register 106 through transfer gates TR₃, storage register 106 is connected to storage register 108 transfer gate TR₄, storage register 108 is connected to shift register 110 through TR₅ and shift register 110 is connected to shift register 112 through TR₆. Charge passes between the rows, through the gates, when a positive-going voltage signal triggers the gates TR n to a charge-passing condition. FIGURE 2A shows the operation of array A in FIGURE 2 with respect to time (t). The line labeled INTEGRATE represents successive integration periods or scan times S n of the scanning device over time (t), or the period between times of data transfer. In the present embodiment, a desirable scan time S₁ may be approximately 1/300 sec. or approximately the reciprocal of the desired number of scan lines per second. During scan time S₁, photosites in array A are exposed to a selected scan line and store image information or data therefrom as a charge developed at the photosite. As described above, on completion of data acquisition, after a predetermined time, data derived at each photosite in each photosite row will be passed to a corresponding photosite in a succeeding row. Figure 2A shows approximate relative times for transferring or shifting data from photosite row to photosite row, from photosite row to storage register, from the storage register to storage register, from storage register to shift register, or from shift register to shift register by indicating the relative times at which transfer gates TR₁, TR₂, TR₃, TR₄, TR₅ and TR₆ are opened. As shown in Figure 2A, data are passed through successive positions in the array, until the data derived thereby have been moved to the storage and shift registers, whereupon a new scan time S₂ is commenced, and the process repeated. With each successive shift, color image data derived from a particular row are moved to succeeding rows until the photosite rows are empty and a new integration period started. It will be appreciated that the sensors may continuously sense light reflected from the image to be sensed, but the amount of light received between integration periods, or during data shifting, is relatively small in comparison to the light detected during the defined integration periods, and has little effect on the output image. As shown in FIGURE 2A, at the end of scan time S₁, beginning at some time prior to the period demonstrated on the graph, image data derived at each photosite are transferred or shifted to a corresponding photosite in a succeeding photosite row or bit in a storage register. A voltage signal is directed to transfer gates TR₆, TR₅, TR₄, and TR₃ at a time t₀ as indicated by the substantially simultaneous signals indicated for each in the graphs TR₆, TR₅, TR₄, and TR₃ in FIGURE 2A. The signal to each of the transfer gates between red-detecting photosite row 104 and the shift registers 110 and 112 allows charge data derived at photosites in red-detecting photosite row 104 to pass to shift registers 110 and 112. In order to avoid the possibility of the charge flowing back to the photosites after passing to a successive position, transfer gates of the set are successively closed, or a non-charge passing condition is created, as data pass therethrough, beginning with transfer gate TR₃ and moving in the charge- passing direction towards transfer gate TR₆. Thus, the set of gates TR₆, TR₅, TR₄, and TR₃ are simultaneously opened to allow the flow of information derived at red-detecting photosites in row 104 to shift registers 110 and 112. After a selected time, gate TR₃ is closed to prevent the back flow of charge thereto, trapping charge in the storage registers and shift registers. Subsequently, TR₄ is closed and the charge remains in only storage register 108 and the two shift registers. With the simultaneous closing of gates TR₅ and TR₆, the red image data derived at photosite row 104 remain in the shift registers 110 and 112 for passage out of the array A. Immediately following the arrival of the red-image information at the shift registers, with the photosite row 104 and the storage registers empty, the green-image information derived at photosite row 102 may be moved in a similar manner to storage register. At time t₁, a signal is directed to the set of transfer gates TR₄, TR₃ and TR₂ to open those gates for passage of the green-image information derived at photosite row 102 to storage register 108. Again, to prevent the return of the charge to photosite row 102 or storage register 108, the gates are sequentially closed. Thus, after a selected period, gate TR₂ is closed to prevent the back flow of charge thereto, trapping charge in the photosite row 104 and the storage registers. Subsequently, TR₃ is closed and the charge remains in only storage register 108. Similarly, charge is moved from blue-detecting photosite row 100. At time t₂, a pulse is directed to the set of transfer gates TR₃, TR₂ and TR₁ to open those gates for passage of the blue-image information derived at photosite row 100 to storage register 106. Transfer gates TR₁, TR₂, and TR₃ are also sequentially closed to prevent the backflow of charge information. Thus, at time t₃, information has been passed to successive locations, emptying each of photosite rows 100, 102, and 104 in succession. The period of shifting data from each photosite row to another position in the array is expected to be, for example, approximately on the order of 1 µsecond, with the transfer of all the photosite rows to the storage and shift registers taking on the order of 3 µseconds. With the completion of the transfer of the data in row 100 to storage register 106, photosite rows 100, 102, and 104 are empty and scanner array A is ready for the next integration period S₂ during which it will derive more image information from subsequent scan lines. Subsequent to transferring image information from the photosite rows to the storage and shift registers, and while new data are being acquired at the photosite rows, image information must be shifted out to the data-processing section. Immediately upon completion of the transfer of image data derived at blue-detecting photosite row 100 to storage register 106, data originally derived at red-detecting photosite row 104 are passed from shift registers 110 and 112, as indicated on the SHIFT REGISTER line of FIGURE 2A to the data processing system within the time described RED SHIFT. The shift operation takes a relatively long period, for example, on the order of 1000 µseconds and comprises the longest period during the data movement operation. Subsequent to shifting data originally derived at red light detecting photosite row 104 out from the array, and with the shift registers 110, 112 now empty, the data originally derived at green light detecting photosite row 102, which at this time are in storage register 108, are moved to the shift registers 110 and 112. To accomplish this a voltage signal is applied to TR₅ and TR₆ at t₄ to open these transfer gates and allow the transfer of the data from storage register 108 to the shift registers 110 and 112. After a predetermined time, the gates are closed to prevent the backflow of the charge from the shift registers to the storage registers. On completion of the transfer of data from storage register 108 to shift registers 110 and 112, storage register 108 is empty, and data from storage register 106, originally derived at blue light detecting photosite row 100, are transferred to storage register 108. Accordingly, at t₅, transfer gate TR₄ is opened for a predetermined period to allow the transfer of data to storage register 108. At t₆ the data in shift registers 110 and 112 are transferred out from the array. At a subsequent t₆, the data originally derived at blue light detecting photosite row 100 are transferred from storage register 108 to shift registers 110 and 112, in the same manner as previously described, whereby a voltage signal is applied to TR₅ and TR₆ at t₇ to open these transfer gates and allow the transfer of the data from storage register 108 to the shift registers 110 and 112. The gates are closed after a predetermined time to prevent the backflow of the charge from the shift registers to the storage registers. On completion of the transfer, at a time t 8, the data in shift registers 110 and 112 are moved out from the array to, for example, a data-processing stage of the device. With the completion of the transfer of data from the storage and shift registers out of the array, the charge data derived at the photosites since the commencement of scan time S₂ may now begin to be transferred out from the photosite rows to the storage and shift registers. Accordingly, at t₉, the transfer process may begin again, with the transfer of data derived at red light detecting photosite row 104 to shift registers 110 and 112. Referring now to FIGURE 3, an array A′ includes the array A as shown in FIGURE 2, and a mirror image of that array offset by half-pixel width. The increased number of photosites increases resolution since it provides more photosites per unit of area, and allows a shorter integration period because the period required for integration is dependent on the amount of light detected. To this end, photosite rows 200, 202, 204, 206, 208, 210 are provided in two groups I and II of three rows each. Photosite rows 200, 202, 204 are provided with associated storage registers 212, 214, and shift registers 216, 218, while photosite rows 206, 208, 210 are provided with associated storage registers 220, 222, and shift registers 224, 226. The photosite rows are arranged generally as discussed for the arrangement in FIGURE 2. Each group of three rows of photosites, includes photosite rows suitable for detection of blue, red and green light. The blue photosite rows may be comprised of photodiodes. When a row of photodiodes is used for the blue photosites, they are located in the respective groups furthest from the storage registers so that data are not passed through them, but rather are passed only out from them. Each corresponding row of photosites, e.g. the two blue rows of photosites, are offset from each other about approximately half photosite width to provide the corresponding photosites in an overlapping arrangement, whereby the image area is covered by two photosites.

Claims: A system for scanning an object and generating an electronic representation thereof, the system including an image-scanning stage including a row of sensors for generating output signals in response to incidence on the sensors of radiation from the object at wavelengths to which the sensors are sensitive, each sensor being connected through a transfer gate to a data store adapted to shift the output signals to a downstream signal processor, characterised in that: the system is adapted to respond to coloured objects; there are three parallel rows of sensors (100, 102, 104), the sensors in any row being sensitive to radiation of a wavelength which is significantly different from the wavelengths to which the other two rows of sensors are sensitive, each sensor in the first row being connected in cascade to a sensor in the other two rows, of which the third row is connected to the data stores (106, 108), and there are transfer gates (TRn) in each output path between the respective rows for controlling the timing of the transfer of output signals from the first row to the second row; from the second row to the third row; from the third row to the data stores, and from the data stores to associated data-processing apparatus. A system as claimed in claim 1, in which the sensors (100) of the first row are photodiodes, and in which the sensors (102, 104) of the other rows are charge-coupled devices. A system as claimed in claim 1 or 2, in which the data store includes at least two storage registers (106, 108), in which the first storage register (106) receives charges representing data from the third row of sensors (104), and the second storage register receives charges from the first storage register and passes them to means (110, 112) for shifting them to data-processing means. A system as claimed in claim 3, in which the shift means includes at least two shift registers (110, 112), and in which the second storage register passes charges derived from each of the sensor rows alternately to the two shift registers. A system as claimed in any preceding claim, in which each row of sensors is made up of a pair of rows of sensors, with the rows of each pair being offset from each other by a distance of about half the width of a sensor. A method for scanning an object to generate an electronic representation thereof, by using an image-scanning stage including a row of sensors for generating output signals in response to incidence on the sensors of radiation from the object at wavelengths to which the sensors are sensitive, each sensor being connected through a transfer gate to a data store adapted to shift the output signals to a downstream signal processor, characterised by the steps of: (a) using a sensor array having three parallel rows of sensors (100, 102, 104), the sensors in any row being sensitive to radiation of a wavelength which is significantly different from the wavelengths to which the other two rows of sensors are sensitive, each sensor in the first row being connected in cascade to a sensor in the other two rows, of which the third row is connected to the data stores (106, 108); (b) providing an integration period during which the sensors are in a radiation-detecting condition; (c) passing output signals produced by the sensors, in the periods between successive integration periods, to the immediately-following sensors or data store; (d) passing output signals from the data store to means (110, 112) for shifting them onwards, and (e) repeating step (b) after the output signals from the sensor rows reach the data store. A method as claimed in claim 6, including the steps of: (f) using transfer gates (TRn) between the adjacent rows of sensors (100, 102, 104) and data store (106, 108), and using two parallel data stores connected to a shift register (110, 112); (g) producing a signal-passing condition in a first set of transfer gates connecting together the first row of sensors, the data store and the shift register, for a second period, during which the output signals are transferred from the first row to the shift register; (h) producing a signal-passing condition in a second set of transfer gates connecting together the second row of sensors and the data store, for a third period, during which the output signals are transferred from the second row to the second store; (i) producing a signal-passing condition in a third set of transfer gates connecting together the third row of sensors and the data store, for a fourth period, during which the output signals are transferred from the third row to the first store; (j) transferring output signals from the shift register as output image data; (k) producing a signal-passing condition in a fourth set of transfer gates connecting together the second store and the shift register, for a fifth period, during which the output signals are transferred from the second store to the shift register; (l) producing a signal-passing condition in a fifth set of transfer gates connecting together the first store and the second store, for a sixth period, during which the output signals are transferred from the first store to the second store; (m) repeating step (j); (n) repeating step (k), and (o) repeating step (j). A method as claimed in claim 7, in which producing the signal-passing condition in the transfer gates includes producing a signal-passing condition substantially simultaneously in each gate of the set and, after a chosen period has elapsed from production of the signal-passing condition, inhibiting further passing of signals in the signal-passing direction.

Inventors: MATTESON RONALD GRANT, TANDON JAGDISH CHAND, MATTESON, RONALD GRANT, TANDON, JAGDISH  CHAND, TANDON, JAGDISH CHAND
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1987
Main classification: H04N1
IPC codes: H04N1, H04N9