Patent Publication Number: US-8988740-B2

Title: Scanning method and apparatus

Description:
RELATED APPLICATION 
     The present application is a national stage application under 35 U.S.C. §371 of International Application No. PCT/SG2011/000003, filed Jan. 4, 2011, which is incorporated by reference herein in its entirety. 
     FIELD OF INVENTION 
     The invention broadly relates to a method of scanning and an apparatus thereof. In particular, the invention pertains to a method of scanning using an area sensor. 
     BACKGROUND 
     The digitizing of analog information that is printed on paper or any other medium (hereinafter termed as ‘scanning’) while on-the-move is somewhat cumbersome due to the considerable size and weight of scanners available today. Mobile scanning solutions available today generally use linear image sensors which scan a document line by line. However, they typically require either motorized paper feeding (sheet-feed scanners) or a moving carriage (flatbed scanners) which results in significant weight and bulk. An additional limitation of sheet-feed scanners is their inability to directly scan bounded materials such as passports, magazine pages or multi-paged documents. 
     Instead of utilizing linear image sensors, an alternative method of mobile scanning involves taking a digital photograph with digital image capturing devices such as digital cameras. These digital image capturing devices typically comprise an area image sensor. Area image sensors can capture the entire scan area on its sensing surface rather than capturing the image line-by-line as with linear sensors. Without the need for paper feeding, such digital image capturing devices have the ability to scan bounded and multi-paged materials. Also, such image capturing devices are usually lighter and smaller than conventional scanners because they do not require any motor or moving mechanism (gear, belt, pulley, carriage, plate, etc). Although this can result in a relatively more portable scanning solution, disadvantages include image distortion due to ambient light. For example, a bright spot from an overhead light source can be seen on the captured image. Shadows can also appear when there is blockage of light, for instance, when a user&#39;s hand is positioned above the target object when taking a digital photo. 
     Furthermore, images may be blurred if the user&#39;s hand is not steady and/or the flash is not used. If a flash is used, a flash spot usually appears on the digital image, especially if the document to be scanned is of the glossy/specular reflectable type. The conventional way to solve this is by moving the light source far away or/and to the bottom side of the photo sensor. In this way, the flash spot will appear outside of the document scan area. However, a lot of light power is wasted and the light output is very low. Furthermore, the size of the scanner cannot be made small if the photo sensor and light source were to be in the same housing. 
     In addition, if the image is not aimed directly to the paper plane, there can be a perspective distortion. 
     A need therefore exists to provide, a method of scanning and an apparatus thereof that seeks to address at least one of the abovementioned problems. 
     SUMMARY 
     According to the first aspect of the present invention, there is provided a scanner device comprising: an area sensor; a light source; and a processor means; wherein the scanner device is configured such that the area sensor, under the control of the processor means, measures an ambient video level; and the processor means calculates a gain and/or a exposure time and/or light source power for an actual flash video level using a stored reference video level and the measured ambient video level such that a summation of the actual flash video level and the ambient video level yields a desired video level in a scan image of the document using the calculated gain and/or exposure time and/or light source power. 
     The desired video level may be associated with a brightest video level having a threshold pixel count in the measured ambient video level. 
     The scanner device may be configured such that the processor means performs image processing on the scan image of the document for uniformity correction and ambient light removal. 
     The image processing may comprise using a stored reference uniformity profile for the uniformity correction. 
     The area sensor, under the control of the processor means, may take an ambient video level image of the document in a first frame of a scanning mode or a frame obtained from a low resolution video mode during preview, and may take the scan image of the document using the calculated gain and/or exposure time and/or light source power in a second frame, and the image processing may comprise subtracting the ambient video level image from the scan image for the ambient light removal. 
     The scanner may further comprise a plurality of light sources and a shutter for the area sensor, the shutter may be configured such that the area sensor captures different portions of a single frame during the exposure to different ones of the light sources such that flash spots may be removed from the scan image. 
     The light source may comprise a lens configured to provide substantially uniform light luminance at different scan distances and perspectives. 
     The processor means may apply rotational alignment, perspective alignment, automatic cropping, and/or automatic orientation. 
     The scanner may further comprise a user interface for providing a blank canvas for positioning different portions of the scan image into a single image file. 
     The scanner may further comprise means for detecting corners of a document by image processing in a live preview mode, and a user interface for displaying the detected corners in a live view image. 
     The scanner may further comprise means for real-time user assignment of scan boundaries, and a user interface for displaying the scan boundaries in a live view image. 
     The scanner may further comprise means for assigning adjustable marquee scan areas for data picking for the scanning. 
     The scanner may further comprise means for projecting one or more markers indicative of a scan area. 
     The scanner may further comprise attachment means for attaching the scanner to an external device. 
     The attachment means may be configured for releasably attaching the scanner to the external device. 
     The attachment means may comprise a support member disposed between two or more attachment elements, wherein the support member support a main body of the scanner and the attachment elements may be configured to attaching to different portions of the external device. 
     One of the attachment elements may comprise a hook portion for connecting to an edge of the external device, and the other attachment element may comprise a first velcro-based element for co-operating with a second velcro-based element disposed on the external device. 
     The scanner may further comprise a plurality of light sources, each light source having an associated blocking means, the blocking means may be configured to block the associated light source in a direction of a flash spot, such that flash spots may be removed from the scan image. 
     The area sensor may be tilted relative to a scanner body such that a minimum distance between the area sensor and a light source of the scanner for removing a flash spot from the scan image may be reduced compared to an un-tilted configuration. 
     According to a second aspect of the present invention, there is provided a method of scanning, comprising the steps of: measuring an ambient video level using an area sensor under the control of a processor means; and calculating a gain and/or a exposure time and/or light source power for an actual flash video level using a stored reference flash video level and the measured ambient video level such that a summation of the actual flash video level and the ambient video level yields a desired video level in a scan image of the document using the calculated gain and/or exposure time and/or light source power. 
     The desired video level may be associated with a brightest video level having a threshold pixel count in the measured ambient video level. 
     The method may further comprise the step of performing image processing on the scan image of the document for uniformity correction and ambient light removal. 
     The step of image processing may comprise using a stored reference uniformity profile for the uniformity correction. 
     The method may further comprise the steps of: taking an ambient video level image of the document in a first frame of a scanning mode or a frame obtained from a low resolution video mode during preview; taking the scan image of the document using the calculated gain and/or exposure time and/or light source power in a second frame; and subtracting the ambient video level image from the scan image for the ambient light removal. 
     The method may further comprise using a plurality of light sources and a shutter for the area sensor such that the area sensor captures different portions of a single frame during the exposure to different ones of the light sources such that flash spots may be removed from the scan image. 
     The area sensor may comprise a lens configured to provide substantially uniform light luminance at different scan distances and perspectives. 
     The method may further comprise the step(s) of applying rotational alignment, perspective alignment, automatic cropping and/or automatic orientation. 
     The method may further comprise the step of positioning different portions of the scan image into a single image file on a blank canvas. 
     The method may further comprise the step of projecting one or more markers indicative of a scan area. 
     The method may further comprise using a plurality of light sources, each light source having an associated blocking means, and using the blocking means to block the associated light source in a direction of a flash spot, such that flash spots may be removed from the scan image. 
     The method may further comprise disposing the area sensor such that it captures the scan image at an off-normal angle with respect to the document such that flash spots may be removed from the scan image. 
     The method may further comprise tilting the area sensor relative to a scanner body such that a minimum distance between the area sensor and a light source of the scanner for removing a flash spot from the scan image may be reduced compared to an un-tilted configuration. 
     The method may further comprise applying a perspective correction algorithm to the scan image. 
     The method may further comprise automatically detecting a glossy document intended for scanning for changing between a glossy mode and a normal mode of scanning. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Example embodiments of the invention will be better understood and readily apparent to one of ordinary skill in the art from the following written description, by way of example only, and in conjunction with the drawings, in which: 
         FIG. 1  is a histogram indicating video level V oa , according to an embodiment of the present invention. 
         FIG. 2  is a chart illustrating the video level V oa +V o1  being adjusted to a video level of about 250, according to an embodiment of the present invention. 
         FIG. 3  is a flow chart illustrating a method of adjusting the Gain (G), according to an embodiment of the present invention. 
         FIG. 4  is a flow chart illustrating a method of adjusting the exposure time, t e , according to an embodiment of the present invention. 
         FIG. 5  is a flow chart illustrating a method of adjusting the flash power, L f , according to an embodiment of the present invention. 
         FIG. 6  is a graph depicting various video levels. 
         FIG. 7  is a schematic illustrating a set-up incorporating light sources and an area sensor, according to an embodiment of the present invention. 
         FIG. 8   a  is an example of a weightage distribution graph. 
         FIG. 8   b  is a schematic illustrating a set-up incorporating light sources and an area sensor, according to an embodiment of the present invention. 
         FIG. 8   c  is a schematic illustrating a set-up comprising an untilted light source and an area sensor, according to an embodiment of the present invention. 
         FIG. 8   d  is a schematic illustrating a set-up comprising a tilted light source and area sensor, according to an embodiment of the present invention. 
         FIG. 8   e  is a schematic illustrating a set-up comprising a tilted light source and area sensor, according to an embodiment of the present invention. 
         FIG. 8   f  is a schematic illustrating visual indicators, according to an embodiment of the present invention. 
         FIG. 8   g  is a schematic illustrating a set-up comprising light sources and an area sensor, according to the present embodiment. 
         FIG. 8   h  is a schematic illustrating a set-up comprising a light blocking means according to an embodiment of the invention. 
         FIG. 8   i  is a schematic illustrating a light blocking means, according to an embodiment of the invention. 
         FIG. 8   j  is a schematic illustrating a light blocking means, according to an embodiment of the invention. 
         FIG. 8   k  is a schematic illustrating a set-up comprising means for partially blocking a light source, according to another embodiment of the invention. 
         FIG. 8   l  is a schematic illustrating an alternative set-up comprising means for partially blocking a light source, according to an embodiment of the invention. 
         FIG. 8   m  is a schematic illustrating a set-up for adjusting the position of a light source, according to an embodiment of the invention. 
         FIGS. 9   a  and  b  are schematic diagrams illustrating light source angles before and after a lens is placed after the light source. 
         FIG. 10   a  is a diagram depicting the light luminance profile on a scan area. 
         FIG. 10   b  is graph illustrating a typical light intensity distribution as angular displacement varies. 
         FIG. 10   c  is a screen capture of a graphical user interface, according to an embodiment of the present invention. 
         FIG. 10   d  is a screen capture of a graphical user interface, according to an embodiment of the present invention, showing disturbances within a scan boundary. 
         FIG. 11  is a screen capture of a document with three marquees indicating three selected regions. 
         FIG. 12  is a schematic illustrating various forms of guiding lights, according to an embodiment of the invention. 
         FIG. 13  is a schematic illustrating a set-up comprising a guiding light and an area sensor, according to an example embodiment. 
         FIG. 14  is a schematic drawing of a cling-on structure, according to an embodiment of the invention. 
         FIG. 15  is a schematic drawing of a cling-on structure, according to an embodiment of the invention. 
         FIG. 16  is a schematic drawing of a cling-on structure, according to an embodiment of the invention. 
         FIG. 17  is a schematic drawing of a cling-on structure, according to an embodiment of the invention. 
         FIG. 18  is a schematic of a computer system for implementing the method and system for scanning. 
         FIG. 19  is a flow chart illustrating a method of scanning, according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     In an example embodiment of the present invention, there is provided a method of scanning a document with an area sensor wherein ambient light disturbance can be advantageously minimized. In addition to the area sensor, a bright light source (e.g. LED or Xenon) and a global (electronic or mechanical) shutter are provided to advantageously minimize sensor integration time. In this example embodiment, a global shutter (such as used in high end cameras, for example DSLR cameras) is preferred to a rolling shutter (typically found in mobile phone cameras) as relatively shorter exposure times can be achieved. An algorithm to determine a suitable exposure time (t e ), gain (G) and flash power (L f ) is also provided. 
     When capturing an image, the area sensor is exposed to ambient light (L a ) and a flash light (L f ) for t e  seconds. The area sensor converts the image to an electric signal. The electric signal can be a voltage signal, which can be subsequently amplified by a suitable gain (G). The amplified voltage signal, which may be in the range of 0 to 2V, is fed to an analog-to-digital converter (ADC). The ADC outputs digital data, for example, in 8 bit format (0-255 video levels). 
     A video level (V o ) can be obtained from the ADC and is defined as follows:
 
 V   o   =K   1   ·K   2 ( L   f   +L   a )· t   e   (1),
 
K 1  is a constant depending on characteristics of the area sensor (e.g. pixel size), lens (e.g f number) and the size of the area being scanned (e.g sensor-document distance and view angle), and K 2  is equal to {255/ADC input range} for 8 bit data.
 
     In particular, a reference flash video level (V o1 ) can be measured, for example, during manufacturing, and is defined as follows:
 
 V   o1   =K ( L   f1 +0)· t   e1   ·G   1   (2),
 
K=K 1 . K 2  (as above).
 
     The reference flash video level (V o1 ) is measured at a given exposure time (t e1 ) and gain (G 1 ), using a blank white piece of paper as the reference object. The measured reference flash video level V o1  and the settings used (L f1 , t e1 , G 1 ) can be stored in the scanner memory for future reference. 
     Thereafter, during use, and before every scan, an ambient video level (V oa ) of the scanning condition is determined, wherein:
 
 V   oa   =K (0 +L   a )· t   e1   ·G   1   (3),
 
     The ambient video level (V oa ) can also be obtained from a low resolution video mode during a live preview (on a graphical user interface) of a scan image. 
       FIG. 1  is a histogram of an example image, designated generally as reference numeral  100 , according to an embodiment of the present invention, indicating video level V oa , which is the brightest video level whereby there is substantial pixel count equal or brighter than it, in this example, 10% of the total number of pixels. However, it will be appreciated that in different embodiments, V oa  can be set to different values. 
     In the example embodiment, the aim is to determine an actual flash video level V′ o1  such that the sum of V oa  and V′ o1  yields a desired video level, e.g. 250, as illustrated in  FIG. 2 . i.e.:
 
 V   oa   +V′   o1 =250  (4)
 
     The variables t e , G and L f  (see equation (3)) are adjusted accordingly such that (V oa +V′ o1 ) is at a video level of about 250. 
     It will be appreciated that in different embodiments, the desired video level can be set to different values than 250. 
     To obtain the desired video level based on the stored reference level (see equation (2)), one can either (i) adjust the Gain (G) while keeping the flash power (L f ) and the exposure time (t e ) fixed; (ii) adjust the t e , keeping L f  and G fixed; or (iii) L f  by fixing the ratio of L f  to L a , then adjust either t e  or G. 
       FIG. 3  is a flow chart, designated generally as reference numeral  300 , illustrating a method of adjusting the Gain (G), according to an embodiment of the present invention. At step  302 , a reference flash video level (V o1 ) is obtained (as described above). At step  304 , before every scan, an ambient video level (V oa ) of the scanning condition is determined (as described above). At step  306 , the Gain, G, is calculated using the formulae: 
     
       
         
           
             
               
                 
                   
                     
                       
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     In this instance, V tgt  can be the 250 video level. At step  308 , scanning is performed using the calculated Gain, G, together with t e1  and L f1 . 
       FIG. 4  is a flow chart, designated generally as reference numeral  400 , illustrating a method of adjusting the exposure time, t e , according to an embodiment of the present invention. At step  402 , a reference flash video level (V o1 ) is obtained (as described above). At step  404 , before every scan, an ambient video level (V oa ) of the scanning condition is determined (as described above). At step  406 , the exposure time, t e , is calculated using the formulae: 
     
       
         
           
             
               
                 
                   
                     
                       
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     In this instance, V tgt  can be the 250 video level. At step  408 , scanning is performed using the calculated exposure time, t e , together with G 1  and L f1 . 
       FIG. 5  is a flow chart, designated generally as reference numeral  500 , illustrating a method of adjusting the flash power, L f , according to an embodiment of the present invention. At step  502 , a reference flash video level (V o1 ) is obtained (as described above). At step  504 , before every scan, an ambient video level (V oa ) of the scanning condition is determined (as described above). At step  506 , the Gain, G, is calculated via the formula: 
     
       
         
           
             
               
                 
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     In this instance, V tgt  can be the 250 video level. Alternatively to step  506 , at step  508 , the exposure time, t e , is calculated via the formula: 
                     t   e     =       t     e   ⁢           ⁢   1       ×         V   tgt         V   oa     +     (       K   f     ·     V   oa       )         .               (   8   )               
Similarly, V tgt  can be the 250 video level.
 
     After either step  506  or  508 , at step  510 , the light source power (P f ) that is required can be calculated as follows: 
                   P   f       P     f   ⁢           ⁢   1         =       V   f       V     o   ⁢           ⁢   1           ,         
where P f1  is the flash power used during the initial referencing which gives V o1 .
 
                   P   f       P     f   ⁢           ⁢   1         =         K   f     ·     V   oa         V     o   ⁢           ⁢   1           ,         
where K f =V f /V oa , the desired flash over ambient light ratio.
 
     
       
         
           
             
               
                 
                   
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     The light source power (P f ) of a LED light source can be adjusted by varying its forward current. At step  512 , scanning is performed using the calculated Gain (G) and light source power (P f ) values. Alternatively to step  512 , at step  514 , scanning is performed using the calculated exposure time (t e ) and source power (P f ) values. The global shutter as described above advantageously facilitates the use of a fast exposure time (t e ) and a flash with high source power (P f ). 
     Combinations of the gain (G), exposure time (t e ) and source power (P f ) can be calculated analytically. Accordingly, it will be appreciated that in other example embodiments, scanning can be performed using an analytically determined combination of one or more of the calculated gain (G), exposure time (t e ) and source power (P f ). 
     A hierarchy can be established wherein a particular variable is calculated in preference to others. For example, depending on product priority:
         i. Gain adjustment can be carried out first if product cost/simplicity is desired, sacrificing on image noise and ambient light disturbance   ii. Exposure time adjustment can be carried out first if the lowest image noise is desired, sacrificing on image sharpness if there is scanner/document motion while scanning (e.g. when the exposure time is longer than 10 ms)   iii. Source power adjustment can be carried out first if lowest ambient light disturbance is desired, sacrificing on product size (as a bigger capacitance may be required)       

     In another embodiment of the invention, there is provided a method of scanning a document with an area sensor, advantageously with uniformity correction and ambient light removal. In this embodiment, 2 frames are preferably taken during scanning.  FIG. 6  is a graph, designated generally as reference number  600 , depicting various video levels. With reference to  FIG. 6 , Ambient light data (or ambient video level) (A) is obtained in the first frame. In the second frame, data (P in ) comprising both ambient light and flash light is obtained. Uniformity correction with ambient light removal can be applied to the image of the second frame using Ambient light data (A) from the first frame and a reference white paper data (or reference flash video level) (W) that is obtained, for example, during manufacturing. 
     A corrected video level (P 0 ) can be obtained as follows: 
                     P   o     =           P   in     -   A       W   -   A       ×   255.             (   10   )               
(P in −A) is denoted as X in  FIG. 6 , which is the contribution from the flash light only. In other words, the ambient component is substantially removed. (W−A) denotes the uniformity correction. Assuming 8 bits, the 255 video level is the white-most point. The target document to be scanned is preferably not moved and P in  is not saturated.
 
     According to another embodiment of the present invention, there is provided a method of scanning a document with an area sensor, advantageously with removal of a spot of flash light.  FIG. 7  is a schematic, designated generally as reference numeral  700 , illustrating a set-up incorporating light sources and an area sensor, according to the embodiment. In particular, there are two light sources  702   a/b  disposed at each side of an area photo sensor  704 . The two light sources  702   a/b  are preferably at substantially the same height level with the area photo sensor  704 . A plurality of frames, preferably 3 frames, are taken. For the first frame, both light sources  702   a/b  are off and ambient light data is obtained. For the second frame, the light source  702   a  is switched on while the light source  702   b  is switched off and image data is captured by the area photo sensor  704 . A first flash spot  706   a  appears on a document  708  that is to be scanned. For the third frame, the light source  702   b  is switched on while the light source  702   a  is switched off and image data is captured by the area photo sensor  704 . A second flash spot  706   b  appears on the document  708  that is to be scanned. To advantageously remove the first flash spot  706   a , section B  710   b  of frame  2  is used. Similarly, to remove the second flash spot  706   b , section A  710   a  of frame  3  is used. Finally, the second (with section B  710   b ) and third (with section A  710   a ) frames are integrated by any currently known methods to remove the glossy flash spot. The integrated image advantageously has no flash spots. The first frame can be used to correct the uniformity and remove the ambient light of the integrated frame (as described above). 
     The first flash spot  706   a  from frame  2  is designated a near to zero weightage, thus substantially eliminating it from the integrated image. Similarly, the second flash spot  706   b  from frame  3  is designated a near to zero weightage, thus substantially eliminating it from the integrated image.  FIG. 8   a  is an example of a weightage distribution graph, designated generally as reference numeral  800 , that can be used for this embodiment of the present invention. 
     A second method of scanning a document with an area sensor, advantageously with removal of a spot of flash light involves using mechanical or electronics means to block the light path of the flash spots by taking one frame. In other words, different portions of a single frame are captured during exposure of different ones of a plurality of light sources. In comparison, in the first method described above, multiple frames are taken and the frames are subsequently integrated to form a single frame. 
     With reference to  FIG. 7 , in the first half of a particular frame exposure time, mechanical means (e.g.: a mechanical shutter) or electronic means, can be used to block the light path of the area photo sensor  704  looking at section B  710   b  while the light source  702   b  is switched on and light source  702   a  is off. In effect, the image in section A  710   a  is advantageously captured during the first half of the frame while flash spot  706   b  is not captured. 
     In the second half of the frame exposure time, the light path of the area photo sensor  704  looking at section A  710   a  is blocked while the light source  702   a  is switched on and light source  702   a  is off. In effect, the image in section B  710   b  is advantageously captured during the second half of the frame while flash spot  706   a  is not captured. This method advantageously enables the entire document to be captured by the area photo sensor  704  in one frame without any flash spots. 
     A third method of scanning a document with an area sensor, advantageously with removal of a spot of flash light involves using different light sources for different rows of the frame during the exposure time.  FIG. 8   b  is a schematic, designated generally as reference numeral  801 , illustrating a set-up incorporating light sources and an area sensor, according to the present embodiment. With reference to  FIG. 8   b , when the area sensor (not shown) is capturing Section A  810   a  (i.e. rows 1 to N/2−1), light source  802   b  is switched on (light source  802   a  is off). When the area sensor (not shown) is capturing Section B  810   b  (i.e. rows N/2−1 to N), light source  802   a  is switched on (light source  802   b  is off). This method advantageously enables the entire document to be captured by the area photo sensor in one frame without any flash spots. 
     A fourth method of scanning a document with an area sensor, advantageously with removal of a spot of flash light involves tilting the area sensor such that the flash spot appears outside the area sensor&#39;s view. Perspective correction (described below) is preferably performed on the scanned image when the area sensor is tilted. In other words, the area sensor is disposed such that it captures the scan image at an off-normal angle with respect to a document such that flash spots are removed from the scan image. 
       FIG. 8   c  is a schematic, designated generally as reference numeral  812 , illustrating a set-up comprising an untilted light source and an area sensor, according to an embodiment of the present invention. The area sensor  814  and the light source  816  are disposed above and parallel to a document  818  which is to be scanned. In other words, a centre light path  820  of the area sensor  814  is orthogonal to the document  818 . The light source  816  produces a flash spot  822  on the document  818  within the area sensor&#39;s  814  view (indicated by boundary light paths  821   a  and  821   b ), consequently causing the flash spot  822  to appear on a scanned image. 
       FIG. 8   d  is a schematic, designated generally as reference numeral  813 , illustrating a set-up comprising a tilted light source and area sensor, according to an embodiment of the present invention. In contrast to  FIG. 8   c , in  FIG. 8   d , the area sensor  814  and the light source  816  are tilted such that they are no longer disposed parallel to the document  818  which is to be scanned. The tilting can be performed, for example, manually by the user or by the area sensor being mechanically tilted at an angle within the scanner body. The centre light path  820  of the area sensor  814  is not orthogonal to the document  818  but at an acute angle θ. The light source  816  produces a flash spot  822  on the document  818 , but is not within the area sensor&#39;s  814  view (indicated by boundary light paths  821   a  and  821   b ). Consequently, the flash spot  822  does not appear on a scanned image. 
       FIG. 8   e  is a schematic, designated generally as reference numeral  824 , illustrating a set-up comprising a tilted light source and area sensor, according to an embodiment of the present invention. The area sensor  814  and the light source  816  are tilted at an angle “μ” within the scanner body. To facilitate a compact scanner body, the distance “d1” between the area sensor  814  and the light source  816  is preferably made as short as possible as follows: 
     μ: area sensor to scanner body angle 
     α: area sensor half view angle 
     θ: pre-determined camera tilt angle
 
β=180°−θ−α  (10a) and;
 
ε=90°−(180°−2β)  (10b)
 
     Accordingly,
 
ε=90°−(180°−2(180°−θ−α))
 
ε=90°−(180°−360°+2θ+2α)
 
ε=90°−(−180°+2θ+2α)
 
ε=90°+180°−2θ−2α
 
ε=270°−2θ−2α  (10c)
 
     Also,
 
μ=ε+α  (10d)
 
     Accordingly,
 
μ=270°−2θ−2α+α
 
μ=270°−2θ−α  (10e)
 
Therefore, when “μ” is equal to (270°−2θ−α), d1 (scanner body length) is the shortest.
 
     It will be appreciated by a person skilled in the art that a flash spot typically appears on glossy documents. For non-glossy documents, flash spots usually do not appear. Accordingly, in another embodiment of the present invention, there is provided a “dual scan angle” such that for the scanning of non-glossy documents, the area sensor can be disposed parallel (at a “first angle”) to the document which is to be scanned to achieve full resolution. In other words, the centre light path of the area sensor is orthogonal to the document (similar to  FIG. 8   c ). For the scanning of glossy documents, the area sensor is tilted at a predetermined angle (“second angle”) such that it is no longer disposed parallel to the document which is to be scanned. The centre light path of the area sensor is at an acute angle with respect to the document (similar to  FIG. 8   d/e ). 
     A user-selectable “normal mode” and a “glossy mode” can be implemented depending on the type of document to be scanned. An indicator can be used to warn the user if the area sensor is not in a tilted position in the “glossy” mode, or if the area sensor is in a tilted position in the “normal” mode. Such indicators can be in the form as illustrated in  FIG. 8   f , which is designated generally as reference numeral  826 . When a user selects the “glossy mode”, the indicator for “glossy mode” is turned on. If the area sensor is not in a tilted position, the indicator is in the form of a rhombus  827  which is an indication to the user that the scanner (area sensor) is to be tilted. Once the area sensor is tilted to a sufficient angle, the indicator changes to a square  828 , indicating that the area sensor is sufficiently tilted. Similarly, in the “normal mode” (scanning of non-glossy documents), if the area sensor is not in a tilted position, the indicator is in the form of a square  829 . Once the area sensor is tilted, the indicator changes to a rhombus  830 , indicating that the area sensor is tilted. It will be appreciated by a person skilled in the art that other types of indicators, including audio and visual indicators (e.g. lines, dots, etc) may also be used. 
     In a further embodiment of the present invention, detection of a flash spot on a glossy document can be performed to provide an automatic switching between the “glossy” and “normal” mode.  FIG. 8   g  is a schematic, designated generally as reference numeral  831 , illustrating a set-up comprising light sources and an area sensor, according to embodiments of the present invention. In addition to the area sensor  814  and scanning light source  816 , an extra light source  832  is disposed proximate to the area sensor  814 . In order to detect a flash spot, the scanning light source  816  is turned off. A low exposure time is set and the extra light source  832  is turned on. If the document  818  is of a glossy type, a flash spot  834  appears and the area sensor  814  detects a video level of 255. Accordingly, the “glossy mode” can automatically be switched on for the scanning of a glossy document. 
     A fifth method of scanning a document with an area sensor, advantageously with removal of a spot of flash light involves a plurality of light sources, each having an associated blocking means, wherein the blocking means blocks the associated light source in a direction of a flash spot, such that flash spots are removed from the scan image. 
       FIG. 8   h  is a schematic, generally designated as reference numeral  835 , illustrating a set-up comprising a light blocking means, according to an embodiment of the invention. The light blocking means  837  is disposed below the light source  816  to advantageously block light rays  836  from reaching a glossy document so that flash spots  822  do not appear on the document surface during scanning by an area sensor  814 . 
     In addition to blocking light from the light source  816 , the light blocking means  837  can block secondary diffused light from the scanner housing, PCB board, LED lens/glass and the like. 
       FIG. 8   i  is a schematic, generally designated as reference numeral  839 , illustrating a light blocking means, according to an embodiment of the invention. The light source  816  can be surrounded by a light blocking means, here in the form of a barrier  840  of length b to substantially prevent light from reaching plane  838   a , but allowing light to reach plane  838   b.    
     The light blocking means can also be in the form of a housing  840 , surrounding a light source  816 , an example of which is shown in  FIG. 8   j . The left schematic  841  is a cross sectional view of such a housing while the right schematic  842  is a perspective front view of such a housing. The housing  840  acts as an aperture to reduce the size of the light source (from a to a′) while substantially maintaining the same level of luminance. As the size of the light source  816  (denoted as “a”) decreases, the distance “d” between the light source and the blocking means is reduced, and vice versa. A smaller light source is desirable so that the distance “d” can be reduced to facilitate the construction of a smaller and more compact scanner. 
       FIG. 8   k  is a schematic, generally designated as reference numeral  850 , illustrating a set-up comprising means for partially blocking a light source, according to another embodiment of the invention. The blocking means comprises transparent windows  854   a/b  that can allow light to pass through and barriers  852   a/b  that substantially prevent light from passing through. The barriers  852   a/b  are similar to those described above. The blocking means is disposed below the light sources  816  and can be pivoted upwards to enable storage within the scanner body when not in use (as shown in the lower portion of  FIG. 8   k ). 
       FIG. 8   m  is a schematic, generally designated as reference numeral  851 , illustrating an alternative set-up comprising means for partially blocking a light source, according to an embodiment of the invention. The blocking means comprises transparent windows  854   a/b  and barriers  852   a/b/c/d . The barriers  852   a/b/c/d  are similar to those described above. The blocking means can be pivoted upwards to enable storage with the scanner body. Further, during storage, the barriers  852   a/b  can be configured to move to alternate positions so that the light source  816  is not obstructed when stored within the scanner body (as shown in the lower portion of  FIG. 8   m ). 
     A sixth method of scanning a document with an area sensor, advantageously with removal of a spot of flash light involves moving a light source to a position wherein the resulting flash spot is out of the viewing angle of the area sensor.  FIG. 8   n  is a schematic, generally designated as reference numeral  860 , illustrating a set-up for varying the position of a light source, according to an embodiment of the invention. During the scanning of non-glossy documents, a light source can be at a position  816   a  which is proximate to the area sensor  814 . During the scanning of glossy documents, the light source can be extended horizontally to position  816   b  which is at a position further away from the area sensor  814  compared to position  816   a . At position  816   b , the light source produces a flash spot outside the viewing angle (denoted by light paths  861   a/b ) of the area sensor  814  such that flash spots advantageously do not appear on the scanned image. 
     According to another embodiment of the present invention, there is provided a method of scanning a document with an area sensor, advantageously with perspective correction, rotation correction, automatic cropping and/or automatic orientation. 
     Some area sensors are handheld and there may be difficulties in rotational and perspective alignment, for example, when the device comprising the area sensor is not held directly above and parallel to the document to be scanned. Applying perspective and rotation correction can produce scanned images similar to those of a flatbed scanner. 
     An auto cropping algorithm can determine the edges of the scanned document and crop it out from the background. An automatic orientation algorithm can determine whether the document is in portrait or landscape orientation and adjust the scanned imaged into the same orientation. 
     Commercially available LED flashes typically provide a 120 degree light source angle, as shown in  FIG. 9   a . During scanning, this relatively large light source angle results in wasted light energy. Moreover, given a fixed light luminosity, as the area to be illuminated gets bigger, luminance drops. 
     Accordingly, in another embodiment of the present invention, there is provided a light source lens  904  that can provide substantially uniform light luminance at different scan distances and perspectives. The light source lens is disposed after the light source and can also concentrate the light power into a smaller scan area, as shown in  FIG. 9   b.    
       FIG. 10   a  is a diagram depicting the light luminance profile on a scan area. The scan area is divided into 6 circular zones, each with an area denoted as L1, L2 . . . L6 and a corresponding radius r1, r2 . . . r6.  FIG. 10   b  is graph illustrating a typical light intensity distribution as angular displacement varies. Superimposed on  FIG. 10   b  is bar chart indicating the intensity corresponding to the 6 zones of  FIG. 10   a . The lens is designed such that the light luminance at the 6 zones are substantially uniform as indicated in  FIG. 10   b.    
     With reference to  FIG. 10   a , if the radius of the innermost circle r1 is fixed, the value of the radius of the second innermost circle r2 can be determined using the equation:
 
 L 1 /L 2=(π· r 1 2 )/(π· r 2 2   −π·r 1 2 )= r 1 2 /( r 2 2   −r 1 2 )
 
 L 1( r 2 2   −r 1 2 )= L 2 ·r 1 2  
 
 L 1 ·r 2 2   =L 1 ·r 1 2   +L 2 ·r 1 2  
 
 L 1 ·r 2 2 =( L 1 +L 2) r 1 2  
 
 r 2 /r 1=√(( L 1 +L 2))/ L 1
 
∴ r 2=(√(( L 1 +L 2))/ L 1)· r 1  (11)
 
Similarly, if the radius of the innermost circle r1 is fixed, the radius of the third innermost circle r3, can be determined using the equation:
 
 L 1 /L 3=(π· r 1 2 )/(π· r 3 2   −π·r 2 2 )= r 1 2 /( r 3 2   −r 2 2 )
 
 L 1( r 3 2   −r 2 2 )= L 3 ·r 1 2  
 
 L 1 ·r 3 2   =L 1 ·r 2 2   +L 3 ·r 1 2  
 
 L 1 ·r 3 2   =L 1(( L 1 +L 2)/ L 1)· r 1 2   +L 3 ·r 1 2  
 
 L 1 ·r 3 2 =( L 1 +L 2) r 1 2   +L 3 ·r 1 2  
 
 L 1 ·r 3 2 =( L 1 +L 2 +L 3) r 1 2  
 
 r 3 /r 1=√(( L 1 +L 2 +L 3))/ L 1
 
∴ r 3=(√(( L 1 +L 2 +L 3))/ L 1)· r 1  (12)
 
Similarly, if the radius of the innermost circle r1 is fixed, the radius of the fourth innermost circle r4, can be determined using the equation:
 
 L 1 /L 4=(π· r 1 2 )/(π· r 4 2   −π·r 3 2 )
 
 L 1 /L 4 =r 1 2 /( r 4 2   −r 3 2 )
 
 L 1( r 4 2   −r 3 2 )= L 4 ·r 1 2  
 
 L 1 ·r 4 2   =L 1 ·r 3 2   +L 4 ·r 1 2  
 
 L 1 ·r 4 2   =L 1(( L 1 +L 2 +L 3)/ L 1)· r 1 2   +L 4 ·r 1 2  
 
 L 1 ·r 4 2 =( L 1 +L 2 +L 3) r 1 2   +L 4 ·r 1 2  
 
 L 1 ·r 4 2 =( L 1 +L 2 +L 3 +L 4) r 1 2  
 
 r 4 /r 1=√(( L 1 +L 2 +L 3 +L 4))/ L 1
 
∴ r 4=(√(( L 1 +L 2 +L 3 +L 4))/ L 1)· r 1  (13)
 
     By determining the values of the radii r2, r3, r4, etc, a custom-made aspherical lens can be manufactured, for example, by plastic-molding. 
     According to a further embodiment of the present invention, there is provided a method of scanning a document with an area sensor, advantageously with automatic multi-cropping. For a single document, automatic-cropping can be performed by first determining the border of the document by edge detection or corner detection. Once the borders are detected, it can be automatically cropped. When there is more than one document in the scan area, it is relatively more difficult to automatically crop all the documents. For example, the number of documents present and their respective orientations are not known. Cropping and rotation for single documents as described above are extended to multiple documents as follows: 
     A document (A) is first introduced into the scan area. A user interface can provide a live display of the scan area, for example in the form of an LCD display screen, so that a user can know the position of the document(s) in relation to the scan area. When the document A enters the scan area and is in a fixed position, an algorithm detects, in real time, the four corners of the document A, and a scan boundary is assigned to the document A. 
     When a second document (B) is introduced into the scan area, the algorithm processes the scan boundary for document B (in a similar manner as described above for document A), while ignoring the scan boundary for document A. If document B enters document A&#39;s boundary, the user interface can alert the user that it is not allowed. For example, the alert can be in the form of flashing lines indicating the boundary of document A that is displayed on the LCD display screen. When the document B is in a fixed position, the algorithm detects, in real time, the four corners of the document B, and a scan boundary is assigned to the document B. These steps are repeated for subsequent documents, if any. In other words, for every new document that enters the scan area, the algorithm applies single edge detection. 
     In another embodiment of the present invention, after the algorithm detects, in real time, the four corners of the document (as described above), visual markers, for example in the form of dots  1052 ,  1054 ,  1056  and  1058  as shown in  FIG. 10   c , can be displayed on the user interface to demarcate the four corners of the document  1059 . After the four corners are detected, a scan boundary  1060  for the document  1059  is assigned (as described above). 
     For some corner detection algorithms, some corners may not be detected correctly (i.e. not all the detected “corners” correspond to the actual corners of a document  1059 ) if there are other objects (disturbances) within the scan boundary, as illustrated in  FIG. 10   d . In  FIG. 10   d , a pen  1062  causes the corner detection algorithm to incorrectly detect a corner, a shown by the dots  1056  and  1058 . In another example in  FIG. 10   d , a user&#39;s hand  1064  causes the corner detection algorithm to incorrectly detect a corner, a shown by the dot  1058 . 
     With a live preview of the scan area, a user can check whether the corners of a document have been correctly detected. If not, the user can remove the disturbance(s) so that the algorithm can advantageously correctly detect the corners of the document to facilitate further processing steps such as automatic cropping. In known methods, a user usually can only see whether the right cropping is performed after the scan is complete. In this embodiment, the user can advantageously make changes using the live preview before scanning, thus saving unnecessary repeat of the scan. 
     Users may want to highlight and/or select specific portions of a document (data picking) rather than the entire document. The saved file size is thus reduced as only the selected portions are saved. Accordingly, there is provided a user interface for enabling distributed data in a document to be scanned and consolidated with an area sensor, according to another embodiment of the present invention. A LCD display screen is preferably incorporated so that a user can view the document to be scanned. 
     The user interface comprises a marquee which is a virtual boundary displayed on the LCD display screen to indicate to the user the effective area that is being selected. The aspect ratio of the marquee can be dynamically controlled and adjusted so as to allow the user to select the required portions of the document to be scanned. The scanner advantageously comprises means for assigning the adjustable marquee scan areas for data picking for the scanning. 
     Prior to scanning, a selection of required data is performed. For example, with reference to  FIG. 11 , a user only wants the portions within the three marquees (boxes). The aspect ratios (heights and widths) of the marquees are different. The user can control the different aspect ratios dynamically, for example, with button(s) on the scanner unit or keyboard, which allows users to determine the width and height of the marquees. For instance, if a user presses the “left” button of a keyboard, the width of the marquee decreases, and when the “right” button is pressed, the width increases. Similarly, if a user presses the “up” button of a keyboard, the length of the marquee increases, and when the “down” button is pressed, the length decreases. Alternatively, touch screens or joysticks can be used to vary the aspect ratio of the marquees. 
     Alternatively, the boundary of the marquee can be configured to automatically ‘grow’. An indicator such as a cross or dot is superimposed at the centre of the LCD display for a user to align to the centre of the desired data to be picked. Upon a suitable command from the user, the marquee automatically ‘grows’ until it detects the next high frequency content in the image (either at the sides top or bottom). High frequency content can be text, lines, or the boundary of images. In the event that the marquee grows to exceed what the user wants, the user can manually ‘shrink’ the marquee width or height. 
     After the required data is selected, the selected data is saved in a temporary clipboard. A new blank canvas is provided for the selected data to be sequentially dumped onto it. The selected data can be dumped onto the canvas at a fixed location (e.g. centre) or at the nearest empty space available. A user may also manually re-position each dumped data onto the canvas at any time. Once the first canvas is filled, a second and subsequent blank canvas can be made available for further data to be dumped into it. This process continues until the user saves the data. The application may then generate a single or multi-page document, for example in Portable Document Format (PDF), containing the canvas(es) with selected data. 
     Post-image processing methods known in the art such as colour correction, background removal, optical character recognition (OCR) and automatic file naming can be made available to the user after scanning is completed. For automatic file naming, OCR is carried out and different text can be append together to make up the file name of the saved document. In this way, a user does not need to manually key in the file name during saving the file. 
     In stark contrast, in conventional manual ‘cropping’ (e.g. in a mobile phone camera edit mode), after the cropped image is selected, the original scanned document is closed. To crop another image from the document, the document is re-opened. For example, with reference to  FIG. 11 , if a user selects the data in the 3 boxes, the original file is opened 3 times and cropped 3 times. Furthermore, the cropped image results in 3 separate files, unlike the single consolidated page of selected data according to example embodiments. 
     When a conventional digital camera is used to capture the image of the document, a display means, usually in the form of LCD screen is typically provided so that a user is able to know the boundaries of the scan area. However, if a display means is not present, the user is unable to know whether or not the document is within the effective scan area. Accordingly, in another embodiment of the present invention, there is provided a method of scanning a document with an area sensor, advantageously with a visual guide, here in the form of a guiding light (e.g. a laser pointer or LED) superimposed on the scan area. The guiding light can be in the form of a lighted area  1202 , borders  1204 , or dots  1206  as illustrated in  FIG. 12 . In other words, the guiding light projects one or more markers indicative of a scan area. 
       FIG. 13  is a schematic, designated generally as reference numeral  1300 , illustrating a set-up comprising a guiding light and an area sensor, according to the above mentioned example embodiment. A guiding light  1302  is preferably placed approximately near the centre of the area photo sensor  1304 . The guiding light angle (β) and photo sensor view angle (α) are preferably approximately equal so that the guiding light and photo sensor light path can substantially coincide irrespective of distances, perspective or rotation. 
     Some portions of the description above are explicitly or implicitly presented in terms of algorithms and functional or symbolic representations of operations on data within a computer memory. These algorithmic descriptions and functional or symbolic representations are the means used by those skilled in the data processing arts to convey most effectively the substance of their work to others skilled in the art. An algorithm is here, and generally, conceived to be a self-consistent sequence of steps leading to a desired result. The steps are those requiring physical manipulations of physical quantities, such as electrical, magnetic or optical signals capable of being stored, transferred, combined, compared, and otherwise manipulated. 
     Unless specifically stated otherwise, and as apparent from the above description, it will be appreciated that throughout the present specification, discussions utilizing terms such as “calculating”, “determining”, “replacing”, “generating”, “initializing”, “outputting”, or the like, refer to the action and processes of a computer system, or similar electronic device, that manipulates and transforms data represented as physical quantities within the computer system into other data similarly represented as physical quantities within the computer system or other information storage, transmission or display devices. 
     The present specification also discloses apparatus for performing the operations of the methods. Such apparatus may be specially constructed for the required purposes, or may comprise a general purpose computer or other device selectively activated or reconfigured by a computer program stored in the computer. The algorithms and displays presented herein are not inherently related to any particular computer or other apparatus. Various general purpose machines may be used with programs in accordance with the teachings herein. Alternatively, the construction of more specialized apparatus to perform the required method steps may be appropriate. The structure of a conventional general purpose computer will appear from the description below. 
     In addition, the present specification also implicitly discloses a computer program, in that it would be apparent to the person skilled in the art that the individual steps of the method described herein may be put into effect by computer code. The computer program is not intended to be limited to any particular programming language and implementation thereof. It will be appreciated that a variety of programming languages and coding thereof may be used to implement the teachings of the disclosure contained herein. Moreover, the computer program is not intended to be limited to any particular control flow. There are many other variants of the computer program, which can use different control flows without departing from the spirit or scope of the invention. 
     Furthermore, one or more of the steps of the computer program may be performed in parallel rather than sequentially. Such a computer program may be stored on any computer readable medium. The computer readable medium may include storage devices such as magnetic or optical disks, memory chips, or other storage devices suitable for interfacing with a general purpose computer. The computer readable medium may also include a hard-wired medium such as exemplified in the Internet system, or wireless medium such as exemplified in the GSM mobile telephone system. The computer program when loaded and executed on such a general-purpose computer effectively results in an apparatus that implements the steps of the preferred method. 
     The invention may also be implemented as hardware modules. More particular, in the hardware sense, a module is a functional hardware unit designed for use with other components or modules. For example, a module may be implemented using discrete electronic components, or it can form a portion of an entire electronic circuit such as an Application Specific Integrated Circuit (ASIC). Numerous other possibilities exist. Those skilled in the art will appreciate that the system can also be implemented as a combination of hardware and software modules. 
     Area scanners using the associated scanning methods described above can be attached to an external device such as a mobile PC (e.g. laptops, notebooks, netbooks) using a cling-on structure as described below. The scanner can be releasably attached to the external device. 
       FIG. 14  is a schematic drawing of a cling-on structure  1402  that comprises a scanner  1410  attached to a mobile PC  1401  with its lid closed, according to an embodiment of the invention. The left figure on  FIG. 14  is a back view of the PC  1401  while the right figure is a side view of the PC  1401 . The cling-on structure  1402  comprises a hook  1406  which is coupled to a band  1408 . The hook  1406  is preferably a rubberized flexible forming hook which clings on to an edge (e.g. a lid) of the PC  1401 . It can advantageously conform to any shape or thickness with minimal obstruction. It can be made of any soft material that does not cause scratches (e.g. 1 mm thick aluminium with rubberized coating). The band  1408  may be made elastic in order to prevent the cling-on structure  1402  from loosening when the lid is opened. The scanner  1410  comprises a scan head  1414  and a microprocessor  1415 . One end of the scanner  1410  is coupled to the band  1408  while the other opposite end is coupled to a non-elastic band  1416 . The non-elastic band  1416  is secured to the bottom of the PC  1401  by means of Velcro  1418  or the like. Velcro allows the user to remove the scanner unit at anytime and can be attached to the base of the laptop. 
       FIG. 15  is a schematic drawing of a cling-on structure  1502  that comprises a scanner  1510  attached to a mobile PC  1501  with its lid open and the scanner  1510  not in use, according to an embodiment of the invention. The left figure on  FIG. 15  is a back view of the PC  1501  while the right figure is a side view of the PC  1501 . Similarly to Figure A above, the cling-on structure  1502  comprises a rubberized flexible hook  1506  which is coupled to a band  1508 . The scanner  1510  comprises a scan head  1514 , a microprocessor  1515 , a first hinge  1512  and a second hinge (not shown). One end of the scanner  1510  is coupled to the band  1508  while the other opposite end is coupled to a non-elastic band  1515 . The non-elastic band  1515  is secured to the bottom of the PC  1501  by means of Velcro  1518  or the like. 
       FIG. 16  is a schematic drawing of a cling-on structure  1602  that comprises a scanner  1610  attached to a mobile PC  1601  with its lid open and the scanner  1610  in use, according to an embodiment of the invention. The left figure on  FIG. 16  is a back view of the PC  1601  while the right figure is a side view of the PC  1601 . The scanner  1610  comprises a scan head  1614 , a microprocessor  1615 , a light source  1616  and a first hinge  1612  that allows the lid  1618  of the scanner to pivot about the width of the scanner  1610  so that the lid can swing up as shown in the direction of arrow A. Documents to be scanned are placed below the scan head  1614  and the scanning direction is in the direction of arrow B. 
       FIG. 17  is a schematic drawing of a cling-on structure  1702  that comprises a scanner  1710  attached to a mobile PC  1701  with its lid open and the scanner  1710  in use, according to an embodiment of the invention. The left figure on  FIG. 17  is a back view of the PC  1701  while the right figure is a side view of the PC  1701 . The scanner  1710  comprises a scan head  1714 , a microprocessor  1715  and a second hinge  1713  that allows the lid of the scanner  1717  to pivot along the length of the scanner body so that the lid  1717  can swing open as shown in the direction of arrow C. Documents to be scanned are placed below the scan head  1714  and the scanning direction is in the direction of arrow D. 
     It will be appreciated that the dual-hinge system advantageously allows the extension of the scan head for scanning at 2 different selectable locations—the back or the side of the mobile PC lid, depending on available desk space to place the document during scanning. When the cling-on structure is integrated with smaller mobile PCs such as netbooks, the scanner may not have sufficient height to scan a bigger area. Accordingly, the cling-on structure may also comprise a slideable mechanism that allows the lid of the scanner to slide upwards in the direction X in  FIG. 16  when the lid is opened. It will also be appreciated that besides scanners, other devices may be affixed to the cling-on structure for integration with a mobile PC. 
     When scanning uneven or unrolled documents (e.g. certificate/receipts), both hands may be needed to straighten or flatten the document. Accordingly, the cling-on structure allow hands-free scanning as the scanner is able to stand alone with the help of the cling-on structure. The cling-on structure is semi-permanent in that it allows users to attach the scanner to laptop but can be detached if the need arises. The structure is easy to use as a minimum number of steps are required to set it up in order to start scanning. The structure is also relatively mobile as users need not carry a separate device such as a conventional mobile scanner which is relatively bulkier and heavier. The cling-on structure has a non-obtrusive shape which allows the putting in and taking out of the mobile PC from its carrier with ease, without the attached scanner coming off. 
     It will be appreciated by a person skilled in the art that the various embodiments described above can be used alone or in conjunction with the other embodiments. 
     The method and system of the example embodiments described above can be implemented on a general microprocessor  1415 ,  1515 ,  1615 ,  1715  located within a scanner. Alternatively, the scanner can be electronically coupled to a computer system  1800 , schematically shown in  FIG. 18 . Suitable software and/or drivers can be used to facilitate communication between the scanner and the computer system  1800 . In addition, a user interface can be provided to facilitate operation and control of the scanner. 
     The method and system of the example embodiments described above may also be implemented as software, such as a computer program being executed within the computer system  1800 , and instructing the computer system  1800  to conduct the method of the example embodiment. 
     The computer system  1800  comprises a computer module  1802 , input modules such as a keyboard  1804  and mouse  806  and a plurality of output devices such as a display  1808 , printer  1810  and scanner  1811 . 
     The computer module  1802  is connected to a computer network  1812  via a suitable transceiver device  1814 , to enable access to e.g. the Internet or other network systems such as Local Area Network (LAN) or Wide Area Network (WAN). 
     The computer module  1802  in the example includes a processor  1818 , a Random Access Memory (RAM)  1820  and a Read Only Memory (ROM)  1822 . The computer module  1802  also includes a number of Input/Output (I/O) interfaces, for example I/O interface  1824  to the display  1808 , I/O interface  1826  to the keyboard  1804  and I/O interface  1825  to the scanner  1811 . 
     The components of the computer module  1802  typically communicate via an interconnected bus  1828  and in a manner known to the person skilled in the relevant art. 
     The application program is typically supplied to the user of the computer system  1800  encoded on a data storage medium such as a CD-ROM or flash memory carrier and read utilising a corresponding data storage medium drive of a data storage device  1830 . The application program is read and controlled in its execution by the processor  1818 . Intermediate storage of program data maybe accomplished using RAM  1820 . 
       FIG. 19  is a flow chart; designated generally as reference numeral  1900 , illustrating a method of scanning, according to an embodiment of the invention. At step  1902 , an ambient video level is measured using an area sensor under the control of a processor means. At step  1904 , a gain and/or a exposure time and/or light source power for an actual flash video level is calculated using a stored reference flash video level and the measured ambient video level such that a summation of the actual flash video level and the ambient video level yields a desired video level in a scan image of the document using the calculated gain and/or exposure time and/or light source power. 
     It will be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the embodiments without departing from a spirit or scope of the invention as broadly described. The embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive. 
     For example, while the example embodiments have mainly been described in the context of a dedicated scanner device, it will be appreciated that the present invention may alternatively be implemented as an additional feature of mode of other devices such as cameras, mobile phones, laptop or desktop computers etc.