Abstract:
A color image reading device, an output controller and a method of controlling an output from a color image reading device provide for an improved signal-noise ratio for the scanning of two-dimensional objects, as in document scanners. In the present invention, the position of a color image reading device with respect to an object to be read is oriented in order to optimize illumination in, for example, the blue wavelength. Pixel data for each line is read, generated in reverse order and/or re-phased so as to compensate for offset linear sensors on the color image reading device.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a color image reading device, an output controller for an image capture system, and a method of controlling an output from a color image reading device. More specifically, the invention relates to the optimization of the positioning of multiple-array linear charge-coupled devices (CCD) to provide improved signal to noise ratio for the scanning of two-dimensional objects, as in document scanners. 
     BACKGROUND OF THE INVENTION 
     A color image reading device such as a linear color charge-coupled device (CCD) may be comprised of an array of linear sensors. Each of the linear sensors are optimized to receive a different portion of a spectral emission from an object imaged on the device. In conventional color CCD devices, each of the linear sensors may include a different color filter and each sensor is separated from an adjacent sensor by a distance of N lines. This results in each array capturing a different line of the document during one raster scan. In conventional arrangements, one of the linear sensors of the array of sensors may be less sensitive to spectral emission. As an example, the signal-to-noise ratio (S/N) for the blue channel or filter in CCD devices may be lower than desired due to the lower sensitivity of the CCD to blue light, and/or lower object illumination levels in the blue portion of the spectrum. Also, because of the CCD line offset as noted above, a single raster from the CCD will contain information from three separate lines. To properly register and display an image, the data of the image must be re-phased to place data from a single line of the image into the same raster of image data. 
     SUMMARY OF THE INVENTION 
     The present invention provides for an arrangement which overcomes the drawbacks noted above. A first feature of the present invention relates to the reversal of the orientation of the color image reading device relative to an object to be imaged upon it, in order to optimize illumination in blue wavelengths. Because the individual line sensors of the color image reading device are physically offset from one another, that offset results in each sensor capturing a different segment of the object during each raster. When it is desirable to reverse the orientation of the color image reading device relative to the object to be scanned in order to optimize illumination and signal-to-noise ratio, pixel data for each line is then generated in reverse order. In a further feature of the present invention, the altered data from the offset linear sensors are phased based on the reversed orientation noted above. 
     The present invention provides for a method and means by which to compensate order and phasing of the output from a color image reading device, such as a color image scanning system, that arises from the relative orientation of multiple linear sensor arrays, which involves orienting the color image reading device relative to an object to be scanned by means of a line controller. 
     The present invention relates to a color image reading device which comprises an array of linear sensors, with each of the linear sensors receiving a different portion of a spectral emission from an object to be imaged. One of the linear sensors of the array of linear sensors being least sensitive to spectral emission and being positioned closest to an illumination source for the object. 
     The present invention further relates to a color image reading device which comprises an array of linear sensors, with each of the linear sensors receiving a different portion of a spectral emission from an object to be imaged. One of the linear sensors of the array of linear sensors receiving a portion of a spectral emission that is weakest and being positioned closest to an illumination source for the object. 
     The present invention further relates to an output controller for an image capture system which comprises a color image reading device having an array of linear sensors that receive a different portion of a spectral emission from an object to be. An orientation of the linear sensors resulting in a reversal of pixel data within a raster. The controller of the present invention further comprises a line controller that receives the pixel data from the color image reading device and reverses the pixel data. 
     The present invention further relates to an output controller for an image capture system which comprises a color image reading device having an array of linear sensors which receive a different portion of a spectral emission from an object to be imaged and provides an image signal indicative thereof. The image signal comprises a raster of pixel data from different points on the object. The controller further comprises a line controller which receives the image signal from the color image reading device and re-phases color pixel values of the raster of pixel data to refer to the same point on the object. 
     The present invention further relates to a method of controlling an output from a color image reading device which comprises the steps of passing an object to be read relative to a color image reading device having an array of linear sensors, so as to provide for a raster of pixel data representative of different points on the object; and providing the raster of pixel data to a line controller which reverses the raster of pixel data. 
     The present invention further relates to a method of controlling an output from a color image reading device which comprises the steps of passing an object to be read relative to a color image reading device having an array of linear sensors, so as to provide for a raster of pixel data representative of different points on the object; and providing the raster of pixel data to a line controller which re-phases color pixel values of the raster of pixel data to refer to the same point on the object. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 a - 1   c  illustrate the scanning of an object via a color image reading device such as a CCD; 
     FIG. 2 illustrates an image capture system including a line controller, an image reading device such as a CCD, and a memory device such as a SRAM; 
     FIG. 3 illustrates a schematic illustration of the elements of the line controller; 
     FIG. 4 illustrates a state machine illustration of the selection process with respect to the line controller of FIG. 3; and 
     FIG. 5 illustrates a raster stream transformation with respect to the line controller of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, wherein like reference numerals represent identical or corresponding parts throughout the several views, FIGS. 1 a - 1   c  illustrate a scanning and orientation of an object  7  to be scanned or read with respect to a color image reading device  9  in accordance with the present invention. As shown in FIGS. 1 a - 1   c , object  7  is a sheet of paper, while color image reading device  9  is a CCD (charge-coupled device). As shown in FIG. 1 a , CCD  9  of the present invention includes, in sequential order, a blue sensor  9   a , a green sensor  9   b  and a red sensor  9   c . As further shown in FIGS. 1 a - 1   c , time is illustrated on the X-axis of the page and is measured relative to the start of a valid page reading. In accordance with the present invention, the orientation of the sensors are set so that blue sensor  9   a  of CCD  9  is closest to an illumination source  50 , such as a lamp, and sees object  7  first and, therefore, in FIG. 1 a  blue sensor  9   a  is at line  0 , green sensor  9   b  is off the page, and red sensor  9   c  is off the page. 
     FIG. 1 b  represents N lines after a valid page reading. As shown in FIG. 1 b , blue sensor  9   a  is at line N, green sensor  9   b  is at line  0  and red sensor  9   c  is off the page. 
     FIG. 1 c  represents  2 N lines after a valid page. As illustrated in FIG. 1 c , blue sensor  9   a  is at line  2 N, green sensor  9   b  is at line N and red sensor  9   c  is at line  0 . Therefore, red sensor  9   c  sees the document last. 
     FIG. 2 illustrates an image capture system which includes a line controller  11  and a memory (SRAM) (static random access memory)  14  associated with CCD  9 . In the arrangement of the present invention, line controller  11  accepts a raster of pixel data (RGB) (red, green, blue) that was composed of three different points on object  7  from CCD  9 , and produces a raster of pixel data (RGB) with the color values re-phased and/or reversed to refer to the same point on a document. 
     As shown in FIG. 2, line controller  11  receives 3 color data values from CCD  9 , a valid line signal to confirm valid data from CCD  9 , a pixel clock to signal a valid pixel, and data from SRAM  14  which temporarily stores data. 
     SRAM  14  is organized as rows of raster data. Each row contains a raster of color pixels (RGB). The number of rows required, N+2, is determined by the number of rasters N between the furthest two color sensors on CCD  9 . 
     In a preferred embodiment of the present invention, the furthest two color sensors are 16 rasters apart. Therefore, 17 rows are required to store the rasters plus an extra row for the incoming raster. To permit access to the temporarily stored data, the address of SRAM  14  is partitioned as follows: 
     SRAM address=&lt;ROW Address&gt;&lt;Pixel Number&gt;where: 
     Row Address represents a raster stored; and 
     Pixel Number represents a specific RGB pixel value in the raster. 
     FIG. 3 shows a schematic view of the specifics of line controller  11 . In the present invention, counters  17 ,  19 ,  21  as shown in FIG. 3 are used to generate the row address and pixel number. Counter  17  is an up-pixel counter, counter  19  is a down pixel counter and counter  21  is a row counter. Row counter  21  includes a store row counter  21   a , a red loadable counter  21   b , a green loadable counter  21   c  and a blue loadable counter  21   d . At the end of a valid line, row counter  21  is incremented, pixel counter  17  is reset to 0 and pixel counter  19  is set to the maximum number of pixels per raster. Line controller  11  stores incoming pixel data in the current row specified by row counter  21 . Pixel counter  17  increments for each RGB pixel value. Line controller  11  thereafter performs re-phasing on a previous row so three counters are required to specify the source of the data value for the re-phased color channel. Counter  21  is loadable to allow the controller to handle any CCD re-phasing offset. Since line controller  11  performs re-phasing on a current pixel number before the next pixel value, line controller  11  must be clocked at a higher rate than a CCD pixel clock which runs the image reading device. 
     As further shown in FIG. 3, a pixel counter Mux  23  receives a select signal with respect to counter  17  or counter  19  to provide for a pixel address to SRAM  14 . The specifics of the selection signal is illustrated as a state machine in FIG.  4 . As shown in FIG. 4, during selection, after idle  100  and CCD pixel ready status  101 , a CCD pixel is stored in row N ( 103 ) and up pixel counter  17  is selected. As also shown, a reading of a red pixel from row N- 1  ( 105 ) selects down pixel counter  19 , a reading of a green pixel from row N- 1 -phase offset ( 107 ) selects down pixel counter  19 , and a reading of a blue pixel from row N- 1 - 2 *(phase-phase offset) ( 109 ) selects down pixel counter  19 . The system repeats for the next CCD pixel. 
     As further shown in FIG. 3, a Row Select Mux  25  receives a select signal with respect to row counters ( 21   a ,  21   b ,  21   c  and  21   d ) to provide for a row address to SRAM  14 . The specifics of the selection signal is illustrated as a state machine in FIG.  4 . As shown in FIG. 4, during selection, after idle  100  and CCD pixel ready status  101 , a CCD pixel is stored in row N ( 103 ) and store row counter  21   a  is selected. As also shown, a reading of a red pixel from row N- 1  ( 105 ) selects red loadable counter  21   b , a reading of a green pixel from row N- 1 -phase offset ( 107 ) selects green loadable counter  21   c , and a reaidng of a blue pixel from row N- 1 - 2 *(phase-phase offset) ( 109 ) selects down blue loadable counter  21   d . The system repeats for the next CCD pixel. 
     FIG. 5 illustrates a raster stream transformation. As shown in FIG. 5, incoming data from CCD  9  is reversed and/or re-phased by line controller  11 . For example, data from CCD  9  can enter line controller  11  (Row) (Pixel) as R 0,0  G 8,0  B 16,0  and exit line controller  11  as R 0,0  G 0,0  B 0,0 . In a preferred embodiment of the present invention, red sensor  9   a  of the CCD  9  sees the object  7  last, so that reversing and/or re-phasing is referenced to red sensor  9   a . Red (loadable) counter  21   b  stores the row number for the previously captured rasters. Green (loadable) counter  21   c  stores the number of rasters between the green and red sensors. Blue (loadable) counter  21   d  likewise stores the number of rasters between the blue and red sensors. To provide line reversal, another pixel counter  19  (FIG. 3) is used. Counter  19  starts at the maximum number of pixels per raster and counts down. When writing to SRAM  14 , counter  17  which is an up-pixel counter is used. When reading from SRAM  14 , counter  19  which is a down-pixel counter is used. Row counter  21  rolls over when it reaches the maximum number of rows specified. In the present invention, compensation for the reversal is accomplished utilizing the same hardware that is used for line rephasing. 
     Therefore, the present invention provides for an arrangement that optimizes a positioning of multiple-array linear color CCD devices so as to improve the signal-to-noise ratio for the scanning of two-dimensional objects as in document scanners. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.