Abstract:
A sensing pixel structure for generating a sensed image with uniform resolution is applied in a light sensor. The sensing pixel structure includes a plurality of first sensing pixels and a plurality of second sensing pixels. The location of the plurality of first sensing pixels corresponds to a center region of a lens. Each of the plurality of first sensing pixels has a first pixel area. The location of the plurality of second sensing pixels corresponds to the peripheral region of the lens. Each of the plurality of second sensing pixels has a second pixel area. The first pixel area is larger than the second pixel area, so that number of the sensing pixels corresponding to the peripheral region of the lens is larger than that corresponding to the center region of the lens. Therefore, the light sensor generates the sensed image with uniform resolution.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a sensing pixel structure, and particularly to a sensing pixel structure for generating a sense image with uniform resolution. 
     2. Description of the Prior Art 
     Please refer to  FIG. 1 , which is a diagram of an optical sensor  100  according to the prior art. The optical sensor  100  comprises a sensing pixel structure  110  and an optical lens  120 . The sensing pixel structure  110  is placed corresponding to the optical lens  120 . More specifically, a central region of the sensing pixel structure  110  is positioned corresponding to a central region of the optical lens  120 , and a peripheral region of the sensing pixel structure  110  is positioned corresponding to a peripheral region of the optical lens  120 . The sensing pixel structure  110  is used for receiving light through the optical lens  120  to generate a sense image SIM. 
     Please refer to  FIG. 2 , which is a diagram of the sensing pixel structure  110  according to the prior art. The sensing pixel structure  110  comprises B sense pixels CSU 1 -CSU B . As shown in  FIG. 2 , in the sensing pixel structure  110 , each sense pixel CSU 1 -CSU B  has the same pixel area AREA OLD . In other words, sense pixels (e.g. sense pixel CSU X ) located in the central region of the sensing pixel structure  110  and sense pixels (e.g. sense pixels CSU 1 , CSU B ) located in the peripheral region of the sensing pixel structure  110  have the same pixel area AREA OLD . In other words, the same number of sense pixels correspond to the peripheral region of the optical lens  120  as to the central region of the optical lens  120 . Due to resolution of the central region of the optical lens  120  being better than that of the peripheral region of the optical lens  120 , and the number of sense pixels corresponding to the peripheral region of the optical lens  120  is the same as to the central region of the optical lens  120 . Thus, resolution of the sense image SIM generated by the sensing pixel structure  110  receiving light through the optical lens  120  is uneven (resolution of the central region is better than resolution of the peripheral region). For example, using the optical sensor  100  to sense a scene P shown in  FIG. 3 , the optical sensor  100  generates the sense image SIM shown in  FIG. 4 . It can be seen from  FIG. 3  and  FIG. 4  that the peripheral region and the central region have the same square patterns in the scene P, but because the central region of the optical sensor  100  has better resolution than the peripheral region, the square patterns in the peripheral region of the sense image SIM are distorted. Thus, when the user wants to perform further image processing on the sense image SIM, because the resolution of the sense image SIM is non-uniform, processing methods used on the peripheral region of the sense image SIM must be different from those used on the central region. This causes difficulty when the user performs image processing on the sense image SIM. 
     SUMMARY OF THE INVENTION 
     According to an embodiment, a sensing pixel structure used in an optical sensor is for generating a sense image with uniform resolution and is placed corresponding to an optical lens. The sensing pixel structure comprises a plurality of first pixels and a plurality of second sense pixels. The plurality of first sense pixels is located in a central region of the optical sensor corresponding to a central region of the optical lens. Each first sense pixel of the plurality of first sense pixels has a first pixel area. The plurality of second sense pixels is located in a peripheral region of the optical sensor, relative to the central region of the optical sensor, and corresponding to a peripheral region of the optical lens. Each second sense pixel of the plurality of second sense pixels has a second pixel area. The first pixel area is greater than the second pixel area for the peripheral region of the optical lens to correspond to more sense pixels than the central region of the optical lens for the optical sensor to generate a sense image with uniform resolution. 
     According to an embodiment, an optical sensor for generating a sense image with uniform resolution comprises an optical lens, and a sensing pixel structure. A central region of the sensing pixel structure is positioned corresponding to a central region of an optical lens. A peripheral region of the sensing pixel structure is positioned corresponding to a peripheral region of the optical lens. The sensing pixel structure is used for receiving light through the optical lens to generate a sense image with uniform resolution, and the sensing pixel structure comprises M sense pixels. When resolution of the central region of the optical lens is better than resolution of the peripheral region of the optical lens, in the M sense pixels, sense pixels located in the central region of the sensing pixel structure have larger pixel area than sense pixels located in the peripheral region of the sensing pixel structure, and the peripheral region of the optical lens corresponds to more sense pixels than the central region of the optical lens for the sense image to have uniform resolution. M is a positive integer, and M&gt;1. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of an optical sensor according to the prior art. 
         FIG. 2  is a diagram of the sensing pixel structure according to the prior art. 
         FIG. 3  is a diagram of a scene sensed by the optical sensor. 
         FIG. 4  is a diagram of a sense image generated by the optical sensor sensing the scene of  FIG. 3 . 
         FIG. 5  is a diagram of a sensing pixel structure according to an embodiment. 
         FIG. 6  is a diagram of an optical sensor according to an embodiment. 
         FIG. 7  is a diagram illustrating designing the pixel areas to cause the sense image to have uniform resolution. 
         FIG. 8  is a diagram illustrating using the sensing pixel structure of  FIG. 5  to sense the scene of  FIG. 3  to generate a sense image. 
         FIG. 9  is a diagram of a sensing pixel structure according to another embodiment. 
         FIG. 10  is a diagram of a sense image generated by the sensing pixel structure. 
         FIG. 11  is a diagram illustrating relationships between contrast and spatial frequency of each region of a sense image generated by the sensing pixel structure of  FIG. 9 . 
         FIG. 12  is a diagram of a sensing pixel structure according to another embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In light of the above issues, a sensing pixel structure and optical sensor are provided that are for generating a sense image with uniform resolution that aids the user in later image processing. 
     Please refer to  FIG. 5 , which is a diagram of a sensing pixel structure  510  according to an embodiment. The sensing pixel structure  510  is used in an optical sensor  500  shown in  FIG. 6 . The sensing pixel structure  510  is placed corresponding to an optical lens  520 . More specifically, a central region of the sensing pixel structure  510  is positioned corresponding to a central region of the optical lens  520 , and a peripheral region of the sensing pixel structure  510  is positioned corresponding to a peripheral region of the optical lens  520 . The sensing pixel structure  510  is used for receiving light through the optical lens  520  to generate a sense image SIM. The sensing pixel structure  510  comprises a plurality of first sense pixels and a plurality of second sense pixels. The plurality of first sense pixels is located in the central region of the optical sensor  500 , e.g. sense pixels CSU X -CSU X+3  shown in  FIG. 5 , and is positioned corresponding to the central region of the optical lens  520 , each first sense pixel having pixel area AREA C1 . The plurality of second sense pixels is positioned in the peripheral region of the optical sensor  500  (sense pixels other than sense pixels CSU X -CSU X+3  shown in  FIG. 5  are all second sense pixels), and is positioned corresponding to the peripheral region of the optical lens  520 , each second sense pixel having pixel area AREA C2 . As can be seen from  FIG. 5 , the pixel area AREA C1  of the first sense pixels is greater than the pixel area AREA C2  of the second sense pixels. Thus, the peripheral region of the optical lens  520  corresponds to more sense pixels than the central region of the optical lens  520 . In this embodiment, the optical lens  520  and the optical lens  120  have similar structure and principle of operation, where the central region has better resolution than the peripheral region. However, compared to the optical sensor  100 , in the present embodiment, the peripheral region of the optical lens  520  corresponds to more sense pixels than the central region of the optical lens  520 . In other words, in the present embodiment, resolution of the peripheral region and the central region of the sense image SIM can be adjusted by adjusting pixel area of the first sense pixels and pixel area of the second sense pixels to adjust the number of sense pixels that the peripheral region and the central region of the optical lens  520  correspond to. 
     Please refer to  FIG. 7 , which is a diagram illustrating designing the pixel areas AREA C2 , AREA C1  to cause the sense image to have uniform resolution. Generally speaking, image resolution can be described in terms of a relationship between contrast and spatial frequency. For example, when special frequency is fixed, as contrast increases, image resolution also increases. Thus, to say that the sense image SIM has uniform resolution means that the relationship between the contrast and spatial frequency in the central region of the sense image SIM is approximately the same as the relationship between the contrast and spatial frequency in the peripheral region of the sense image SIM. In  FIG. 7 , CV 1  represents the relationship curve between the contrast and spatial frequency of images corresponding to the central region of the optical sensor  500  in the sense image SIM when the pixel area of sense pixels in the central region of the sensing pixel structure  510  is AREA C2 , where according to known techniques, image contrast can be represented by a modulation transfer function (MTF), and the spatial frequency can be represented by number of unit length line-pairs, e.g. lp/mm in  FIG. 7  representing number of millimeter unit line-pairs. CV 2  represents the relationship curve between the contrast and spatial frequency of images corresponding to the peripheral region of the optical sensor  500  in the sense image SIM when the pixel area of sense pixels in the peripheral region of the sensing pixel structure  510  is AREA C2 . Due to the central region having better resolution than the peripheral region in the optical lens  520 , when the pixel area of sense pixels in the central region of the sensing pixel structure  510  and the pixel area of sense pixels in the peripheral region of the sensing pixel structure  510  are both AREA C2 , in the sense image SIM, resolution of images corresponding to the central region of the optical sensor  500  is better than resolution of images corresponding to the peripheral region of the optical sensor  500  (CV 1 &gt;CV 2 ). If the pixel area of sense pixels in the central region of the sensing pixel structure  510  is increased, number of sense pixels corresponding to the central region of the optical lens  520  can be reduced, such that resolution of images in the central region of the optical sensor  500  (CV 1 ) can also be reduced. It can be seen from  FIG. 7  that when the pixel area of sense pixels in the central region of the sensing pixel structure  510  is increased to AREA C1 , resolution of images corresponding to the central region of the optical sensor  500  (relationship curve CV 3 ) and resolution of images corresponding to the peripheral region of the optical sensor  500  (relationship curve CV 1 ) are approximately the same. In other words, by designing the pixel area of sense pixels in the central region of the sensing pixel structure  510  to be AREA C1 , and designing the pixel area of sense pixels in the peripheral region of the sensing pixel structure  510  to be AREA C2 , the optical sensor  500  can generate the sense image SIM with uniform resolution. Using the optical sensor  500  to sense the scene P shown in  FIG. 3 , the optical sensor  500  will generate the sense image SIM shown in  FIG. 8 . Relative to the sense image SIM in  FIG. 4  generated by the optical sensor  100 , in  FIG. 8 , resolution in the central region and the peripheral region of the optical sensor  500  is approximately the same, so the square patterns in the peripheral region and the central region of the sense image SIM have approximately the same amount of distortion. In other words, when the user wants to perform further processing on the sense image SIM generated by the optical sensor  500 , the same processing methods can be used on both the central region and the peripheral region of the sense image SIM. 
     Further, compared to the sensing pixel structure  110 , in the sensing pixel structure  510 , the pixel area of sense pixels in the central region of the sensing pixel structure  510  is increased, while the pixel area of sense pixels in the peripheral region of the sensing pixel structure  510  is kept the same. In other words, compared to the sensing pixel structure  110 , the sensing pixel structure  510  has fewer sense pixels, i.e. M&lt;B. Thus, by using the sensing pixel structure  510 , area of downstream processing circuits of the optical sensor  500 , e.g. sense pixel readout circuits, can be reduced. 
     Please refer to  FIG. 9 , which is a diagram of a sensing pixel structure  910  according to another embodiment. The sensing pixel structure  910  may be used for realizing the sensing pixel structure  510  of the optical sensor  500 . The sensing pixel structure  910  comprises sense pixels CSU 1 -CSU M . As shown in  FIG. 9 , in the sense pixels CSU 1 -CSU M , sense pixels located in the central region of the sensing pixel structure  910 , e.g. sense pixel CSU X , have greater pixel area than sense pixels located in the peripheral region of the sensing pixel structure  910 , e.g. sense pixels CSU 1 , CSU Y , CSU M . Thus, the peripheral region of the optical lens  510  corresponds to relatively more sense pixels than the central region of the optical lens  510 . 
     Please refer to  FIG. 10 , which is a diagram of a sense image SIM generated by the sensing pixel structure  910 . The sense image SIM can be divided into regions R 1 -R N  (in  FIG. 10 , different regions are depicted by different hatching orientations). For example, region R 1  is formed by images generated by sense pixels in the upper-left corner of  FIG. 9 ; region R 4  is formed of images generated by sense pixels in the lower-left corner of  FIG. 9 . In order to make the resolution the same in all regions R 1 -R N  of the sense image SIM, the sensing pixel structure  910  can be designed so that sense pixels nearer to the central region of the sensing pixel structure  910  have larger pixel area, and sense pixels further from the central region of the sensing pixel structure  910  have smaller pixel area. More specifically, when designing sensing pixel structure  910 , pixel area AREA X  of sense pixels of the central region of the sensing pixel structure  910  (e.g. sense pixel CSU X ) and pixel area AREA Y  of sense pixels of the peripheral region of the sensing pixel structure  910  (e.g. sense pixel CSU Y ) can be determined according to the method illustrated in  FIG. 7 . At this time, pixel area AREA Z  of sense pixels between the central region and the peripheral region of the sensing pixel structure  910  (e.g. sense pixel CSU Z ) can be determined according to the pixel areas AREA X , AREA Y , distance D XY  between the sense pixels CSU X , CSU Y , and distance D XZ  between the sense pixels CSU X , CSU Z . More specifically, the pixel area AREA Z  of sense pixels between the central region and the peripheral region of the sensing pixel structure  910  can be determined by the following equation:
 
(AREA X −AREA Z )/( D   XZ   2 )=(AREA X −AREA Y )/( D   XY   2 )  (1)
 
     In this way, pixel area of all sense pixels located between the central region and the peripheral region of the sensing pixel structure  910  can be determined according to equation (1). Sense pixels closer to the central region of the sensing pixel structure  910  have larger pixel area, and sense pixels further from the central region of the sensing pixel structure  910  have smaller pixel area. Thus, in the optical lens  520 , areas with poorer resolution (e.g. areas near the peripheral region, such as those corresponding to regions R 1 -R 4 ) correspond to a greater number of sense pixels, and areas with better resolution (e.g. areas near the central region, such as those corresponding to regions R L -R (L+1) ) correspond to fewer sense pixels. In this way, relationship curves CV R1 -CV RN  between the contrast and spatial frequency of each region R 1 -R N  of the sense image SIM can be approximately the same (as shown in  FIG. 11 ). In other words, the sense image SIM has uniform resolution. 
     Please refer to  FIG. 12 , which is a diagram of a sensing pixel structure  1210  according to another embodiment. The sensing pixel structure  1210  can be used to realize the sensing pixel structure  510  of the optical sensor  500 . Compared to the above embodiments, in the present embodiment, it is assumed that resolution in the peripheral region of the optical lens  520  is better than resolution in the central region of the optical lens  520 . The sensing pixel structure  1210  comprises sense pixels CSU 1 -CSU M . Different from the sensing pixel structure  910 , in the sensing pixel structure  1210 , sense pixels in the central region of the sensing pixel structure  1210  central region (e.g. sense pixel CSU X ) have smaller pixel area than sense pixels in the peripheral region of the sensing pixel structure  1210  (e.g. sense pixels CSU 1 , CSU M ). Thus, the central region of the optical lens  510  corresponds to a greater number of sense pixels relative to the peripheral region of the optical lens  510 . In the present embodiment, resolution of the peripheral region of the optical lens  520  is better than resolution of the central region of the optical lens  520 . However, by using the sensing pixel structure  1210 , the central region of the optical lens  520  corresponds to more sense pixels than the peripheral region of the optical lens  520 . Thus, the optical sensor  500  can still generate the sense image SIM with uniform resolution. 
     In the above embodiments, the sensing pixel structure adjusts pixel area of sense pixels in the central region and peripheral region of the sensing pixel structure to adjust number of sense pixels corresponded to by the central region and the peripheral region of the optical sensor, thereby causing the optical sensor to generate the sense image with uniform resolution. In this way, when the user desires to perform further processing on the sense image, the same processing method can be used for both the central region and the peripheral region of the sense image. Thus, using the sensing pixel structure and optical sensor provided by the above embodiments can reduce difficulty encountered by the user in performing processing on the sense image. Further, the sensing pixel structure of the above embodiments allows processing circuit area of the optical sensor to be reduced, which saves cost. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.