[0001]     This application claims the benefit of Taiwan application Serial No. 94112636, filed Apr. 20, 2005, the subject matter of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The invention relates in general to a method of adjusting an image parameter and a scanning apparatus using this method, and more particularly to a method and an apparatus of adjusting a mechanical parameter to compensate for an image parameter.  
         [0004]     1. Description of the Related Art  
         [0005]     In scanning apparatuses, such as a scanner, a multi-function printer, and the like, an adjusting operation (calibration) has to be performed before each scanning process in order to ensure the scanned quality. For example, the gain and the offset of the analog front end (AFE) have to be adjusted, and the photo response non-uniformity (PRNU) and the dark signal non-uniformity (DSNU) of the charge coupled device (CCD) have to be compensated.  
         [0006]     However, the adjusting procedure mentioned hereinabove only can adjust the factor of influencing the image quality in the aspect of the deviations of the electric elements of the scanning system. However, no adjusting procedure has been proposed to adjust the variation in the transmission mechanism after a long term of usage, wherein the variation in the transmission mechanism may influence the precision of a leading edge of the document, the precision of the image magnification in the scanning direction, and the precision of the color registration.  
         [0007]     In general, the image of the to-be-scanned picture is acquired by a chassis of a scanning apparatus moving relatively the to-be-scanned picture. A motor, such as a stepping motor, in the scanning apparatus controls the movement of the chassis. The moving distance of the chassis is determined according to the step number of encoder pulses generated when the stepping motor moves the chassis. The relationships between the number of encoder pulses and the moving distance of the chassis may be obtained according to  FIGS. 5A  to  5 C.  FIG. 5A  is a graph showing a relationship between a moving distance of a chassis and a step pulse in an ideal condition. As shown in  FIG. 5A , a chassis in a scanning apparatus having a resolution of 600 DPI (Dots Per Inch) is moved by 1/600 inches in an ideal step when a step pulse is generated. If no transmission error is caused, the chassis is moved by 8/600 inches precisely after 8 step pulses are generated.  
         [0008]     When the mechanism has variations, the moving distance of the chassis is not equal to 1/600 inches when the motor generates one step pulse.  FIG. 5B  is a graph showing a relationship between the moving distance of the chassis and the step pulse when the moving distance of the chassis is shortened. As shown in  FIG. 5B , when 8 step pulses are generated, the chassis is not moved by 8/600 inches precisely, and its moving distance is only about 5.3/600 inches. However, the scanning apparatus still regards that the chassis has been moved by 8/600 inches.  FIG. 5C  is a graph showing a relationship between the moving distance of the chassis and the step pulse when the moving distance of the chassis is lengthened. As shown in  FIG. 5C , the chassis is not moved by 8/600 inches precisely after 8 step pulses of the pulse signal P are generated, and the moving distance of the chassis is about 10.7/600 inches. However, the scanning apparatus still regards that the chassis is moved by 8/600 inches.  
         [0009]     In summary, the scanning apparatus misjudges the moving distance of the chassis under the conditions of  FIGS. 5B and 5C . Thus, the scanned image under the condition of  FIG. 5B  is enlarged on the vertical axis, and the scanned image under the condition of  FIG. 5C  is reduced on the vertical axis. Both of the conditions may cause errors of finding the leading edge of the document, of the image magnification in the scanning direction, and of the parameters such as the color registration. Thus, the scanned image quality is deteriorated and is quite different from that of the to-be-scanned picture.  
       SUMMARY OF THE INVENTION  
       [0010]     It is therefore an object of the invention to provide a method of adjusting an image parameter and a scanning apparatus using the method.  
         [0011]     The invention achieves the above-identified object by providing a method of adjusting an image parameter. The method includes the steps of: scanning a standard picture and moving the standard picture by an actual distance; generating a pulse signal corresponding to the actual distance; getting a standard distance corresponding to the pulse signal; and comparing the actual distance with the standard distance and adjusting a default pulse frequency. The default pulse frequency is increased when the actual distance is shorter than the standard distance, and decreased when the actual distance is longer than the standard distance.  
         [0012]     The invention also achieves the above-identified object by providing a scanning apparatus including a chassis, a motor and a processor. The chassis scans a standard picture to generate an image signal. The motor moves at least one of the chassis and the standard picture relative to each other by an actual distance. The motor has an encoder for generating a pulse signal when the motor operates to move the chassis or the standard picture relative to each other by the actual distance. The processor receives the pulse signal and the image signal, computes the actual distance according to the image signal, compares the actual distance with a standard distance corresponding to the pulse signal, and adjusts a default pulse frequency. The default pulse frequency is increased when the actual distance is shorter than the standard distance, and decreased when the actual distance is longer than the standard distance.  
         [0013]     Other objects, features, and advantages of the invention will become apparent from the following detailed description of the preferred but non-limiting embodiment. The following description is made with reference to the accompanying drawings.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a schematic illustration showing a scanning apparatus according to a preferred embodiment of the invention.  
         [0015]      FIG. 2  is a flow chart showing a method of adjusting an image parameter according to the preferred embodiment of the invention.  
         [0016]      FIG. 3  is a schematic illustration showing a standard picture, which is a to-be-scanned document.  
         [0017]      FIG. 4  is a schematic illustration showing a standard picture fixed in the scanning apparatus.  
         [0018]      FIG. 5A  is a graph showing a relationship between a moving distance of a chassis and a step pulse in an ideal condition.  
         [0019]      FIG. 5B  is a graph showing a relationship between the moving distance of the chassis and the step pulse when the moving distance of the chassis is shortened.  
         [0020]      FIG. 5C  is a graph showing a relationship between the moving distance of the chassis and the step pulse when the moving distance of the chassis is lengthened.  
         [0021]      FIG. 6A  is a schematic illustration showing a result obtained after the scanning apparatus scans the standard picture when the actual distance is equal to the standard distance.  
         [0022]      FIG. 6B  is a schematic illustration showing a result obtained after the scanning apparatus scans the standard picture when the actual distance is longer than the standard distance.  
         [0023]      FIG. 6C  is a schematic illustration showing a result obtained after the scanning apparatus scans the standard picture when the actual distance is shorter than the standard distance. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]      FIG. 1  is a schematic illustration showing a scanning apparatus according to a preferred embodiment of the invention. The scanning apparatus  100  includes a chassis  110 , a motor  120  and a processor  150 . The chassis  110  includes optical and electric elements, such as a light source, reflecting mirrors, a lens and a charge coupled device (CCD), to acquire an image of a to-be-scanned picture.  
         [0025]     The motor  120  is, for example, a DC motor for producing a relative displacement between the chassis  110  and the to-be-scanned picture. The motor  120  has an encoder  140  and a code wheel  130 . When the motor  120  moves the chassis  110  relative to the to-be-scanned picture or moves the to-be-scanned picture relative to the chassis  110 , the code wheel  130  is also rotated. The encoder  140  obtains a rotation state of the motor  120  according to a rotation state of the code wheel  130 . The encoder  140  generates a pulse signal P according to the rotation of the motor  120 .  
         [0026]     The processor  150  obtains a forwarding distance of the chassis  110  relative to the to-be-scanned picture according to a pulse signal P and a default pulse frequency (default pulse per DPI), and thus determines the image parameters of the to-be-scanned picture, such as a leading edge of a document, an image magnification in the scanning direction, a color registration, and/or the like. The pulse signal P is the number of encoder pulses outputted by the encoder  140  when a relative movement between the chassis  110  and the to-be-scanned picture is produced. The default pulse is frequency is a default value, which defines the number of encoder pulses outputted by the encoder  140  when the relative movement between the chassis  110  and the to-be-scanned picture equals a distance between two adjacent scan lines.  
         [0027]     When an image parameter adjusting procedure is performed, the chassis  110  scans a standard picture to generate a corresponding image signal, and the motor  120  moves the chassis  110  and the standard picture to produce an actual distance between the chassis  110  and the standard picture. The encoder  140  generates the pulse signal P according to the rotation of the motor  120  corresponding to the actual distance. The processor  150  calculates the actual distance according to the image signal, which is acquired by the chassis  110  and corresponds to the standard picture, and compares the actual distance with the standard distance corresponding to the pulse signal P so as to adjust the default pulse frequency. When the actual distance is shorter than the standard distance, the processor  150  increases the default pulse frequency. When the actual distance is longer than the standard distance, the processor  150  decreases the default pulse frequency.  
         [0028]     The standard picture has multiple straight lines or calibration lines, and the actual distance is obtained according to a gap between the straight lines or the calibration lines. The standard picture may be implemented in two ways. In the first way, the standard picture is a to-be-scanned document. In the second way, the standard picture is fixed in the scanning apparatus  100 .  FIG. 3  is a schematic illustration showing a standard picture, which is a to-be-scanned document. The standard picture  300  is a to-be-scanned document having a plurality of straight lines, such as straight lines L 1  and L 2 . The actual distance is the distance between the straight lines L 1  and L 2 .  FIG. 4  is a schematic illustration showing a standard picture fixed in the scanning apparatus  100 . As shown in  FIG. 4 , the standard picture is directly scanned by the scanning apparatus  100  without a scanning document. The scanning apparatus  100  gets the actual distance according to the gap between the calibration lines P 1  and P 2 , or between the calibration lines P 3  and P 4 .  
         [0029]      FIG. 2  is a flow chart showing a method of adjusting an image parameter according to the preferred embodiment of the invention. First, the chassis  110  scans the standard picture and the standard picture is moved the actual distance relatively, as shown in step  21 . Next, the encoder  140  generates the pulse signal P corresponding to the actual distance, as shown in step  22 . Then, the processor  150  gets the standard distance corresponding to the pulse signal P, as shown in step  23 . Finally, the processor  150  compares the actual distance with the standard distance and adjusts the default pulse frequency, as shown in step  24 .  
         [0030]     In step  23 , the standard distance is obtained by calculation according to the default pulse frequency and the pulse signal P. Alternatively, the scanning apparatus  100  may further include a recording unit  160 , and the processor  150  may get the standard distance from the recording unit  160 . In step  24 , when the actual distance is shorter than the standard distance, the processor  150  increases the default pulse frequency. When the actual distance is longer than the standard distance, the processor  150  decreases the default pulse frequency.  
         [0031]     For example, in a scanning apparatus having the optical resolution of 600 DPI, it is assumed that the standard distance corresponding to the pulse signal P is 1/600 inches when 128 pulses are generated in the pulse signal P, and the default pulse frequency is 128 pulses. Because of the uncertain variation factors in the mechanism, the actual distance between the chassis and the standard picture may be smaller than or greater than 1/600 inches when 128 pulses are generated in the pulse signal P. As shown in step  24 , if the actual distance is greater than 1/600 inches, the units of the 128 pulses are reduced or the default pulse frequency is reduced. If the actual distance is smaller than 1/600 inches, the units of the 128 pulses are enlarged or the default pulse frequency is increased.  
         [0032]     The distortion state on the vertical axis of the scanned image will be described below. With reference to the scanning apparatus  100  having the resolution of 600 DPI, wherein the default pulse frequency is 128 pulses per DPI. When the encoder  140  generates a pulse signal P having 128 pulses, it means that the forwarding pixel distance of the chassis  110  is 1/600 inches, and the processor  150  calculates the forwarding distance of the chassis and the associated image parameters according to the pulse signal P.  FIG. 6A  is a schematic illustration showing a result obtained after the scanning apparatus scans the standard picture  300  of  FIG. 3 . The straight line L 7  in an image  610  of the standard picture corresponds to the straight line L 1 , and the straight line L 8  corresponds to the straight line L 2 . The distance between the straight line L 1  and the straight line L 2  is 1 inch. In an ideal condition when no error is caused in the transmission of the gear set, the gap between the straight line L 7  and the straight line L 8  is defined by pixels P 1  to P 600 , each of which represents 1/600 inches in the standard picture  300 .  
         [0033]      FIG. 6B  is a schematic illustration showing a result obtained after the scanning apparatus scans the standard picture when the actual distance is longer than the standard distance. In this case, the gear transmission error enlarges the moving distance of the chassis  110 . For example, the chassis  110  can acquire the straight lines L 7  and L 8  when it is moved by the distance of 300 pixels. That is, the actual moving distance of the chassis  110  is 1/300 inches every 128 pulses. Thus, it is observed that only 300 pixels P 1 ′ to P 300 ′ exist between the straight lines L 7  and L 8  rather than the original 600 pixels, as shown in  FIG. 6B , and the image corresponding to pixels P 301 ′ to P 600 ′ is additionally acquired. When the encoder  140  generates 128 pulses, the moving distance of the chassis is no longer 1/600 inches. Thus, the default pulse frequency (or Default Pulse per DPI, DPD) has to be reduced to obtain a corrected pulse frequency (or Corrected Pulse per DPI, CPD) as: 
 CPD=(300/600)*128=64   (1)  
         [0034]      FIG. 6C  is a schematic illustration showing a result obtained after the scanning apparatus scans the standard picture when the actual distance is shorter than the standard distance. In this case, the actual moving distance per pixel unit of the chassis  110  is shortened. For example, if the chassis  110  can acquire the image of straight lines L 1  and L 2  as it is moved by the distance of 600 pixels in the ideal state, then the chassis  110  has to be moved by the distance of 1200 pixels such that the straight lines L 1  and L 2  may be acquired. That is, the moving distance of the chassis  110  is 1/1200 inches after 128 pulses are generated. In the ideal state, 600 pixels should exist between the straight lines L 7  and L 8 . In  FIG. 6C , however, pixels P 1 ″ to P 600 ″ cannot be extended from the straight line L 8  to the straight lines L 8 . Because the pixels P 1 ″ to P 600 ″ only correspond to one half of the original image ranging from the straight line L 1  to the straight line L 2 . The default pulse frequency (DPD) should be increased as: 
 CPD=(1200/600)*128=256   (2).  
         [0035]     According to Equations (1) and (2), it is obtained that: 
 
CP2D=(P/T)*DPD   (3), 
 
 wherein T is the theoretical number of pixels per unit distance, 600 pixels represent 1 inch in this embodiment, and P is the practical number of pixels per unit distance. In the example of  FIG. 6B , P is 300. In the example of  FIG. 6C , P is 1200. 
 
         [0036]     In order to simplify the system design, the values of DPD and CPD are integers without fractions. In other words, the minimum difference |ΔP| between DPD and CPD before or after been adjusted has to be “ 1 ”. So, the precision compensating limit (the difference |ΔP|) of this adjusting principle may be calculated according to Equation (3) as: 
 
|CPD−DPD|≧1. 
 
         [0037]     Substitute CPD=(P/T)*DPD into the former equation, it is obtained that: 
 
|(P/T)*DPD−DPD|≧1. 
 
         [0038]     Remove the signs for absolute value, it is obtained that: 
 
(P/T)*DPD−DPD≧1   (4) 
 
or 
 
(P/T)*DPD−DPD≦−1   (5). 
 
         [0039]     It is obtained, from Equation (4), that: 
 
P*DPD−T*DPD≧T, and 
 
P≧(DPD+1)*T/DPD   (6). 
 
         [0040]     It is obtained, from Equation (5), that: 
 
P*DPD−T*DPD)≦T, and 
 
P≦(DPD+1)*T/DPD   (7). 
 
         [0041]     It is obtained, from Equations (6) and (7), that: 
 
|ΔP|≧{[(DPD+1)/DPD]*T−T}/T*100%, and 
 
|ΔP|≧(100/DPD)*100%   (8). 
 
         [0042]     Calculating the difference |ΔP| according to Equation (8) means that the adjustment may be made according to Equation (3) as long as the position error caused by the gear set when the chassis or the sheet is moved is greater that the difference |ΔP|.  
         [0043]     The methods of performing the image parameter adjusting procedure in the scanning apparatus  100  will be described in the following. In a first method, the scanning apparatus  100  may include a user interface (not shown), and the user can enable the image parameter adjusting procedure through the user interface, such as an adjust-enable button (not shown) of the scanning apparatus  100 , or through a computer host electrically connected to the scanning apparatus  100 . In the second method, the recording unit  160  also records the usage state of the scanning apparatus  100 , and the processor  150  automatically enables the image parameter adjusting procedure according to the usage state of the scanning apparatus  100 .  
         [0044]     The method of adjusting image parameters and the scanning apparatus according to the embodiment of the invention can adjust the errors of the mechanical parameters, which are caused by the deteriorated transmission precision and are neglected in the conventional adjusting method. The method may further analyze the associated parameters and adjust the associated compensation parameters, such that the associated parameters are free from being influenced by the variation of the transmission precision, and the image quality may be ensured. The invention can be applied to a production line to finely adjust the scanning apparatuses before they are shipped out. After the scanning apparatus has been used for a period of time at the user end, the user can make the adjustment or the scanning apparatus can make the adjustment automatically so as to keep the scan magnification on the desired precision level after a long term of usage.  
         [0045]     While the invention has been described by way of example and in terms of a preferred embodiment, it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.
A method of adjusting an image parameter and a scanning apparatus are provided. The method includes the steps of: scanning a standard picture and moving the standard picture by an actual distance; generating a pulse signal corresponding to the actual distance; getting a standard distance corresponding to the pulse signal; and comparing the actual distance with the standard distance and adjusting a default pulse frequency. When the actual distance is shorter than the standard distance, the default pulse frequency is increased. When the actual distance is longer than the standard distance, the default pulse frequency is decreased.