Abstract:
A method for generating a target gain value of a wide dynamic range (WDR) operation is disclosed including: acquiring an average bright portion luminance corresponding to an average pixel luminance of a bright portion of a video image; acquiring an average dark portion luminance corresponding to an average pixel luminance of a dark portion of the video image; generating an initial gain value of the WDR operation according to a difference between the average bright portion luminance and the average dark portion luminance; and adjusting the initial gain value according to at least one of a color temperature and an exposure duration configuration value of the video image to generate the target gain value.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of priority to Patent Application No. 105101144, filed in Taiwan on Jan. 14, 2016; the entirety of which is incorporated herein by reference for all purposes. 
       BACKGROUND 
       [0002]    The disclosure generally relates to an image processing technology and, more particularly, to a method for generating a target gain value of a wide dynamic range (WDR) operation. 
         [0003]    The high dynamic range (HDR) operation is greatly beneficial to improve clarity of the high contrast images, and thus widely used in many image processing systems, such as digital cameras, smart phones, tablet computers, surveillance systems, and the like. 
         [0004]    The conventional HDR operation configures multiple images of successive points of time to have different exposure durations, and then combines these images to form single image having appropriate luminance in both the dark portion and bright portion. 
         [0005]    However, the conventional HDR operation requires the use of more complex image sensors, and thus the overall circuitry complexity of the image processing system would be inevitably increased. 
       SUMMARY 
       [0006]    An example embodiment of a method for generating a target gain value of a wide dynamic range (WDR) operation is disclosed, comprising: acquiring an average bright portion luminance corresponding to an average pixel luminance of a bright portion of a video image; acquiring an average dark portion luminance corresponding to an average pixel luminance of a dark portion of the video image; generating an initial gain value of the WDR operation according to a difference between the average bright portion luminance and the average dark portion luminance; and adjusting the initial gain value according to at least one of a color temperature and an exposure duration configuration value of the video image to generate the target gain value. 
         [0007]    Both the foregoing general description and the following detailed description are examples and explanatory only, and are not restrictive of the invention as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  shows a simplified flowchart of a method for generating a target gain value of the WDR operation according to a first embodiment of the present disclosure. 
           [0009]      FIG. 2  shows a simplified schematic diagram of adjust the weighting of an initial gain value of the WDR operation according to the average dark portion luminance according to one embodiment of the present disclosure. 
           [0010]      FIG. 3  shows a simplified schematic diagram of adjust the weighting of the initial gain value of the WDR operation according to the total pixel quantity of the dark portion according to one embodiment of the present disclosure. 
           [0011]      FIG. 4  shows a simplified flowchart of a method for generating a target gain value of the WDR operation according to a second embodiment of the present disclosure. 
           [0012]      FIGS. 5-6  show simplified schematic diagrams of the video image according to different embodiments of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Reference is made in detail to embodiments of the invention, which are illustrated in the accompanying drawings. The same reference numbers may be used throughout the drawings to refer to the same or like parts, components, or operations. 
         [0014]      FIG. 1  shows a simplified flowchart of a method for generating a target gain value of the WDR operation according to a first embodiment of the present disclosure. In practical applications, an image processing system, such as a digital camera, a smart phone, a tablet computer, or a surveillance system, is enabled to generate a target gain value for use in conducting the WDR operation on an arbitrary video image by executing software implementing the method of  FIG. 1 . Then, the image processing system may utilize the resulting target gain value to conduct the WDR operation on the video image, so as to increase the visibility and clarity of the resulting video image. 
         [0015]    Before conducting the WDR operation on the arbitrary video image, the image processing system may perform the operation  110  to acquire an average bright portion luminance corresponding to the average pixel luminance of the bright portion of the video image, and to acquire an average dark portion luminance corresponding to the average pixel luminance of the dark portion of the video image. 
         [0016]    In practice, the image processing system may directly acquire the aforementioned average bright portion luminance and average dark portion luminance from other existing circuits, or may independently perform a brightness computation for the video image. 
         [0017]    In the operation  120 , the image processing system may generate an initial gain value of the WDR operation according to the difference between the average bright portion luminance and the average dark portion luminance. In general, a larger difference between the average bright portion luminance and the average dark portion luminance translates to a higher possibility that the arbitrary video image is corresponding to a high contrast scene. On the contrary, a smaller difference between the average bright portion luminance and the average dark portion luminance translates to a lower possibility that the arbitrary video image is corresponding to a high contrast scene. Accordingly, the image processing system may configure the initial gain value to be directly proportional to the difference between the average bright portion luminance and the average dark portion luminance. 
         [0018]    Since the difference between the average bright portion luminance and the average dark portion luminance cannot accurately reflect the scene of the arbitrary video image, the image processing system further proceeds to the operations  130  and  140 . 
         [0019]    In the operation  130 , the image processing system may adjust the initial gain value according to the color temperature of the video image. A higher color temperature translates to a higher possibility that the video image is corresponding to an outdoor scene. On the contrary, a lower color temperature translates to a higher possibility that the video image is corresponding to an indoor scene. In general, when the video image is corresponding to the outdoor scene, there is a higher possibility that the video image is generated under a strong back light situation. A video image of the indoor scene may have the possibility to be taken under a back light situation, but the back light situation in the indoor scene is typically gentler than that in the outdoor scene. Accordingly, the image processing system may configure the initial gain value to be directly proportional to the color temperature. 
         [0020]    In the operation  140 , the image processing system may adjust the initial gain value according to an exposure duration configuration value of the video image. The term “exposure duration configuration value” as used throughout the description and claims refers to the exposure duration setting value of the image sensor when the hardware WDR function is disabled. In general, a smaller exposure duration configuration value translates to a higher possibility that the video image is corresponding to an outdoor scene. On the contrary, a larger exposure duration configuration value translates to a higher possibility that the video image is corresponding to an indoor scene. Accordingly, the image processing system may configure the initial gain value to be inversely proportional to the exposure duration configuration value. 
         [0021]    In order to increase the accuracy of the subsequent WDR operation, the image processing system may take the average dark portion luminance and the total pixel quantity of the dark portion into consideration to further adjust the gain value of the WDR operation. 
         [0022]    For example, after the aforementioned operations  130  and  140 , the image processing system may perform the operation  150  to further adjust a weighting of the initial gain value according to the average dark portion luminance. 
         [0023]    Please refer to  FIG. 2 , which shows a simplified schematic diagram of adjust the weighting of the initial gain value of the WDR operation according to the average dark portion luminance according to one embodiment of the present disclosure. 
         [0024]    As shown in  FIG. 2 , if the average dark portion luminance of the video image is lower than a threshold luminance L 1 , then the image processing system may configure the weighting of the initial gain value to be fixed at a first predetermined weighting W 1 . If the average dark portion luminance is greater than the threshold luminance L 1 , then the image processing system may configure the weighting of the initial gain value to be inversely proportional to the average dark portion luminance, such as a linearly inversely proportional relationship shown in  FIG. 2 . 
         [0025]    In addition, after adjusting the weighting of the initial gain value based on the average dark portion luminance, the image processing system may perform the operation  160  to further adjust the weighting of the initial gain value according to the total pixel quantity of the dark portion of the video image. 
         [0026]    Please refer to  FIG. 3 , which shows a simplified schematic diagram of adjust the weighting of the initial gain value of the WDR operation according to the total pixel quantity of the dark portion according to one embodiment of the present disclosure. 
         [0027]    As shown in  FIG. 3 , if the total pixel quantity of the dark portion of the video image is between a first predetermined quantity Q 1  and a second predetermined quantity Q 2 , then the image processing system may configure the weighting of the initial gain value to be directly proportional to the total pixel quantity of the dark portion, such as a linearly directly proportional relationship shown in  FIG. 3 . If the total pixel quantity of the dark portion exceeds the second predetermined quantity Q 2 , then the image processing system may configure the weighting of the initial gain value to be fixed at a second predetermined weighting W 2 . 
         [0028]    In the embodiment of  FIG. 1 , the image processing system may utilize the resulting initial gain value after weighting adjustment to be the target gain value, and conduct the WDR operation on the video image based on the target gain value. 
         [0029]    It can be appreciated from the foregoing descriptions that when the method of  FIG. 1  is adopted by the image processing system, the image processing system is enabled to obtain the target gain value of the WDR operation based on merely the data of only one video image, without conducting computations on the data of other video images. Therefore, the required computations of the image processing system can be significantly reduced. 
         [0030]    In addition, since the image processing system is enabled to compensate the high contrast image by conducting digital computations, the circuit structure of the image sensor can be simplified to reduce the overall circuitry complexity. 
         [0031]    Furthermore, in addition to the difference between the average bright portion luminance and the average dark portion luminance, the method of  FIG. 1  also adjusts the gain value of the WDR operation according to the color temperature or the exposure duration configuration value. As a result, the accuracy of the WDR operation can be increased and thus the visibility and clarity of the resulting video image can be further improved. 
         [0032]      FIG. 4  shows a simplified flowchart of a method for generating a target gain value of the WDR operation according to a second embodiment of the present disclosure. The main operations in  FIG. 4  are similar to those in  FIG. 1 , but additional operations  470  and  480  are introduced in the embodiment of  FIG. 4 . 
         [0033]    As shown in  FIG. 4 , after adjusting the weighting of the initial gain value based on the total pixel quantity of the dark portion, the image processing system may perform the operation  470  to further compute a central luminance corresponding to the average pixel luminance of a central region of the aforementioned video image, and to compute a peripheral luminance corresponding to the average pixel luminance of a peripheral region of the video image. 
         [0034]    For example,  FIG. 5  shows a simplified schematic diagram of a video image  500  according to one embodiment of the present disclosure. The video image  500  comprises a rectangular central region  510  and a peripheral region  520  (i.e., the dot-lined region) surrounding the central region  510 . 
         [0035]    For the embodiment of  FIG. 5 , the image processing system may compute a central luminance corresponding to the average pixel luminance of the central region  510  and also compute a peripheral luminance corresponding to the average pixel luminance of the peripheral region  520  in the operation  470 . 
         [0036]    Then, the image processing system may perform the operation  480  to further adjust the weighting of the initial gain value according to the difference between the central luminance and the peripheral luminance to generate the target gain value. Since the human eyes are more sensitive to the central region of an image, the image processing system may configure the weighting of the initial gain value to be directly proportional to the difference between the central luminance and the peripheral luminance to generate the target gain value. 
         [0037]    The foregoing descriptions regarding the operations  110 - 160  of  FIG. 1  and related advantages are also applicable to the embodiment of  FIG. 4 . For the sake of brevity, those descriptions will not be repeated here. 
         [0038]    Since the method of  FIG. 4  takes the luminance difference between the central region and the peripheral region of the video image into consideration, the accuracy of the WDR operation can be further improved by conducting the WDR operation based on the target gain value generated using the method of  FIG. 4 . In this way, the visibility and clarity of the resulting video image can be further increased. 
         [0039]    Please note that the executing order of the operations in  FIG. 1  and  FIG. 4  is merely an embodiment, rather than a restriction to the practical implementations. For example, the operations  130  and  140  may be performed simultaneously or may be swapped. In some embodiments, one of the operations  130  and  140  may be omitted. In some embodiments, the operation  160  or both of the operations  150  and  160  may be omitted. Additionally, both of the operations  470  and  480  may be adjusted to be performed before the operation  150 . In some embodiments, both of the operations  470  and  480  may be omitted to reduce the required computations of the system. 
         [0040]    In addition, the shape of the aforementioned central region  510  is merely an embodiment, rather than restriction to the practical implementations. In practice, t the central region of the video image may be configured to have another shape, such as an elliptical shape, a rounded rectangular shape, a hexagonal shape, an octagonal shape, a square shape, and the like. For example,  FIG. 6  shows a simplified schematic diagram of the video image  500  according to another embodiment of the present disclosure. In the embodiment of  FIG. 6 , the central region  510  has an elliptical shape, instead of the rectangular shape shown in  FIG. 5 . 
         [0041]    Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention indicated by the following claims.