Abstract:
An image processing method, applicable to a digital image device, includes the following steps. At least one original image of different brightness ranges is captured, and more images of different brightness ranges are generated from the original image by using an image post-processing technique. Based on characteristics of the image of each brightness range, the weights of the image of each brightness range are defined. Then, hierarchical fusion is performed on the images of the different brightness ranges according to weight relations, so as to form a high-dynamic-range image capable of presenting features of each brightness range.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image processing method, and more particularly to a method of performing brightness feature mixing and hierarchical combination on an original image, so as to obtain a high-dynamic-range image. 
     2. Related Art 
     With the rapid development of technologies and improvement of living standard of modern people, digital image devices, for example, digital still cameras, increasingly become indispensable in people&#39;s lives. Due to advanced researching and developing techniques, the digital still camera is also developed rapidly and becomes the mainstream of the market. 
     Taking the digital still camera for example, when a captured image has a high-contrast scene (for example, both the sunny sky and the buildings in the shadow are present in the scene), due to output limits of software and hardware of the digital still camera, most of the scene in the dynamic range is sacrificed, and the dynamic range of the entire scene cannot be reserved completely as its original appearance. That is to say, as shown in  FIG. 1A , the high-bright region (for example, the cloud in the sky) and the low-bright region (for example, the buildings in the lower part) of the image are quite dim in the imaged picture, and it is rather difficult to present the two regions in one picture without distortion. 
     Recently, in the prior art, a conventional method is to change the output tone mapping according to the brightness distribution of the shot scene. However, the effect of this method is quite limited. Besides, the problems of unnatural colors and excessive artifact are also caused. In addition, when the digital still camera continuously shoots several pictures, as the pictures are continuously shot and the time intervals of shooting are quite short, it is impossible to combine several pictures in a tone mapping manner when the pictures are continuously shot for the same scene in the prior art. Therefore, through the conventional method, the picture without artifact cannot be effectively obtained, and the operation of the user becomes more inconvenient. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is an image processing method, capable of processing an original image captured by an image sensor, thereby effectively reserving brightness features of the original image, and preventing artifact, color dynamic distortion, and other negative effects, so as to solve the above problems. 
     The present invention provides an image processing method, applicable to a digital image device. The image processing method comprises the following steps. 
     An original image is captured. A high-bright image, a medium-bright image, and a low-bright image are obtained from the original image. A high-bright weight array, a medium-bright weight array, and a low-bright weight array are determined according to the high-bright image, the medium-bright image, and the low-bright image. A high-dynamic-range image is obtained according to the high-bright image, the medium-bright image, the low-bright image, the high-bright weight array, the medium-bright weight array, and the low-bright weight array. 
     Therefore, in the image processing method of the present invention, the high-bright image, the medium-bright image, and the low-bright image corresponding to different brightness features are obtained from the original image, the individual relative weights are determined through an edge detection procedure or a brightness determination procedure, and finally the high-dynamic-range image in which the different brightness features are fused is obtained through a weight aggregation method. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description given herein below for illustration only, and thus are not limitative of the present invention, and wherein: 
         FIG. 1A  shows an image picture presented by a conventional image sensor when receiving a high-contrast scene; 
         FIG. 1B  is a schematic structural view of a digital image device according to an embodiment of the present invention; 
         FIG. 2  is a schematic view of a Bayer pattern according to an embodiment of the present invention; 
         FIG. 3A  is a flow chart of an embodiment of the present invention; 
         FIG. 3B  is a flow chart of a second embodiment of Step S 308  according to the present invention; 
         FIG. 3C  is a flow chart of  FIG. 3B ; 
         FIG. 4A  is a schematic view of an original image in a single Bayer pattern according to an embodiment of the present invention; 
         FIG. 4B  is a schematic view of a high-bright image in a single Bayer pattern according to an embodiment of the present invention; 
         FIG. 4C  is a schematic view of a medium-bright image in a single Bayer pattern according to an embodiment of the present invention; 
         FIG. 4D  is a schematic view of a low-bright image in a single Bayer pattern according to an embodiment of the present invention; 
         FIG. 5A  is a schematic view of a high-bright weight array according to an embodiment of the present invention; 
         FIG. 5B  is a schematic view of a medium-bright weight array according to an embodiment of the present invention; 
         FIG. 5C  is a schematic view of a low-bright weight array according to an embodiment of the present invention; 
         FIG. 6A  is a schematic view of a high-bright image in a single Bayer pattern according to an embodiment of the present invention; 
         FIG. 6B  is a schematic view of a high main soft image in a single Bayer pattern according to an embodiment of the present invention; 
         FIG. 6C  is a schematic view of a medium main soft image in a single Bayer pattern according to an embodiment of the present invention; and 
         FIG. 6D  is a schematic view of a low main soft image in a single Bayer pattern according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1B  is a schematic structural view of a digital image device according to an embodiment of the present invention. The digital image device  100  may be a digital still camera, a digital video camera, a webcamcorder, or other electronic products having a digital image capturing function integrated therein, for example, a cell phone or a personal digital assistant (PDA). The digital image device  100  comprises an image sensor  102 , a sensing controller  104 , a micro-processor  106 , an image signal processing unit  108 , a codec unit  110 , a temporary storage  112 , an input/output unit  114 , a display engine unit  116 , and a result storage  118 . Through partition processing of each element (as described above) of the digital image device  100 , an image is displayed on a display device  200 . The image sensor  102  according to the embodiment of the present invention is, for example, an image sensor of a digital still camera, but the present invention is not limited thereto. The common image sensor  102  may be, but is not limited to, a charge-coupled device (CCD). 
     The image sensor  102  has a plurality of sensing pixels, for receiving lights transmitted from a scene, and converting the scene to corresponding image data through photoelectric conversion. In order to obtain a color sensing effect, a plurality of neighboring sensing pixels is grouped to form a filtering pattern. The filtering pattern may be, but is not limited to, a Bayer pattern. In the embodiment of the present invention, the Bayer pattern is used as the filtering pattern, but other types of patterns may also be used to implement the present invention. 
     For example, in  FIG. 2 , every four neighboring sensing pixels  22   R ,  22   Gr ,  22   Gb , and  22   B  form a Bayer pattern  20 . The digital image device  100  receives the lights transmitted from the scene through the sensing pixels  22   R ,  22   Gr ,  22   Gb , and  22   B  in each Bayer pattern  20 , and captures a corresponding original image through photoelectric conversion. For ease of subsequent description, the single Bayer pattern  20  in the original image is used for subsequent explanation and description. 
     According to an embodiment of the present invention, the sensing pixels  22   R ,  22   Gr ,  22   Gb , and  22   B  respectively have 14 bits, but the present invention is not limited thereto, and the sensing pixel may have 12 bits, 10 bits, and 16 bits depending on different image sensors  102 . In the following, the sensing pixel has 14 bits for description. 
       FIG. 3A  is a flow chart of an image processing method according to an embodiment of the present invention. The image processing method is applicable to the digital image device  100 , in which the image sensor  102  has a plurality of sensing pixels  22   R ,  22   Gr ,  22   Gb , and  22   B  in a Bayer pattern  20 , converts the lights transmitted from a scene through the sensing pixels  22   R ,  22   Gr ,  22   Gb , and  22   B , and captures an original image. The image processing method comprises the following steps. 
     In Step S 302 , an original image is captured. 
     In Step S 304 , a high-bright image, a medium-bright image, and a low-bright image are obtained from the original image. 
     In Step S 306 , a high-bright weight array, a medium-bright weight array, and a low-bright weight array are determined according to the high-bright image, the medium-bright image, and the low-bright image. 
     In Step S 308 , a high-dynamic-range image is obtained according to the high-bright image, the medium-bright image, the low-bright image, the high-bright weight array, the medium-bright weight array, and the low-bright weight array. Steps S 302  to S 308  are executed by the micro-processor  106  in  FIG. 1B . 
     For Step S 304 , reference can be made to  FIGS. 4A to 4D , which are schematic views of a high-bright image, a medium-bright image, and a low-bright image obtained from the original image. Referring to  FIG. 4A , the sensing pixels  22   R ,  22   Gr ,  22   Gb , and  22   B  respectively have 14 bits, and in Step S 304 , a bit filtering procedure is executed, so as to obtain the high-bright image S -1  of  FIG. 4B , the medium-bright image S 0  of  FIG. 4C , and the low-bright image S 1  of  FIG. 4D  from the original image K 0 . For example, the sensing pixels  22   R ,  22   Gr ,  22   Gb , and  22   B  respectively have 14 bits, and the bit filtering procedure comprises obtaining the medium-bright image S 0  from a medium bit interval in each sensing pixel of the original image K 0 , obtaining the high-bright image S -1  from a high bit interval in each sensing pixel of the original image K 0 , and obtaining the low-bright image S 1  from a low bit interval in each sensing pixel of the original image K 0 . 
     The medium bit interval may be set as the 2 nd  to 9 th  bits in the 14 bits of each sensing pixel, the high bit interval may be set as the 3 rd  to 10 th  bits in the 14 bits of each sensing pixel, and the low bit interval may be set as the 1 st  to 8 th  bits in the 14 bits of each sensing pixel. The intervals of the sampled bits are different, such that the high-bright image S -1 , the medium-bright image S 0 , and the low-bright image S 1  may respectively reserve features of a brighter region, features of a medium-bright region, and features of a darker region of the original image K 0 . However, the above bit sampling ranges of the medium bit interval, the high bit interval, and the low bit interval are only examples, and are not intended to limit the scope of the present invention. Further, the number of the images that respectively reserve different brightness ranges of the original image K 0  may be determined according to actual demands, and is not limited to three. 
     Specifically, in the high-bright image S -1 , most of the features of the high-bright region are reserved, but the features of the low-bright region are sacrificed. Similarly, in the low-bright image S 1 , most of the features of the low-bright region are reserved, but the features of the high-bright region are sacrificed. In the medium-bright image S 0 , the features of the relatively medium-bright region in the original image are reserved, but the brightness values out of the region are sacrificed. It should be noted herein that the medium bit interval, the high bit interval, and the low bit interval are not limited, and the bit interval of the sampled sensing pixel is determined according to the image to be presented by the digital image device  100 . Besides, in the bit filtering procedure, an imaging sequence of the high-bright image S -1 , the medium-bright image S 0 , and the low-bright image S 1  is not limited to a precedence order. 
     Referring to  FIGS. 4B to 4D , the high-bright image S -1 , the medium-bright image S 0 , and the low-bright image S 1  are the image data obtained from the original image K 0  after the bit filtering procedure is executed, such that the high-bright image S -1 , the medium-bright image S 0 , and the low-bright image S 1  respectively have sensing pixels  22   R-1 ,  22   Gr-1 ,  22   Gb-1 , and  22   B-1 , sensing pixels  22   R0 ,  22   Gr0 ,  22   Gb0 , and  22   B0 , and sensing pixels  22   R1 ,  22   Gr1 ,  22   Gb1 , and  22   B1  in the same Bayer pattern  20 . 
     For Step S 306 , for example, when comparing the same optical filter (taking the red light as an example) of the high-bright image S -1  the medium-bright image S 0 , and the low-bright image S 1  in the same Bayer pattern  20 , the sensing pixels  22   R-1 ,  22   R0 , and  22   R1  respectively have edge values E R-1 , E R0 , and E R1  corresponding to the high-bright image S -1 , the medium-bright image S 0 , and the low-bright image S 1 . Therefore, when the sensing pixels  22   R-1 ,  22   R0 , and  22   R1  are combined, each relative weight W R-1 , W R0 , and W R1  may be Error! Objects cannot be created from editing field codes, Error! Objects cannot be created from editing field codes, and Error! Objects cannot be created from editing field codes. Similarly, the sensing pixels  22   Gr-1 ,  22   Gr0 , and  22   Gr1 , the sensing pixels  22   Gb-1 ,  22   Gb0 , and  22   Gb1 , and the sensing pixels  22   B-1 ,  22   B0 , and  22   B1  have edge values E Gr-1 , E Gr0 , and E Gr1 , edge values E Gb-1 , E Gb0 , and E Gb1 , and edge values E B-1 , E B0 , and E B1  corresponding to the high-bright image S -1 , the medium-bright image S 0 , and the low-bright image S -1 , respectively. Therefore, when comparing the same Bayer pattern  20  of the high-bright image S -1 , the medium-bright image S 0 , and the low-bright image S 1 , a high-bright weight array A -1  corresponding to the high-bright image S -1 , a medium-bright weight array A 0  corresponding to the medium-bright image S 0 , and a low-bright weight array A 1  corresponding to the low-bright image S -1  are determined through the edge detection procedure. The high-bright weight array A -1 , the medium-bright weight array A 0 , and the low-bright weight array A 1  are respectively as shown in  FIGS. 5A to 5C . 
     The high-bright image S -1 , the medium-bright image S 0 , and the low-bright image S 1  respectively reserve the features of the brighter region, the medium-bright region, and the darker region of the original image K 0 , and the respective corresponding weight arrays may also be determined through the edge detection procedure. Therefore, in Step  308 , a high-dynamic-range image after fusion is calculated through a weight aggregation method, that is, a product of the high-bright image S -1  multiplied by the high-bright weight array A -1 , plus a product of the medium-bright image S 0  multiplied by the medium-bright weight array A 0 , and plus a product of the low-bright image S 1  multiplied by the low-bright weight array A 1 , representing the high-dynamic-range image displayed on the display device  200  of  FIG. 1B . 
     Besides, according to another embodiment of the present invention, the manner of determining the high-bright weight array A -1 , the medium-bright weight array A 0 , and the low-bright weight array A 1  in Step S 306  is not limited to the edge detection procedure, and may also be a brightness determination procedure or a chromaticity determination procedure. 
     To sum up, through the image processing method according to the embodiment of the present invention, the image data corresponding to different brightness features is obtained from the original image, then the relative weights of each image data are determined through the edge detection procedure, the brightness determination procedure, or the chromaticity determination procedure, and finally the high-dynamic-range image in which the different brightness features are fused is obtained through the weight aggregation method. 
     In addition, in order to make the colors of the eventually output high-dynamic-range image more natural and remove excessive artifacts, in the image processing method according to the embodiment of the present invention. Step S 308  may be implemented through the embodiment below. 
     Second Embodiment of Step S 308   
       FIG. 3B  is a flow chart of a second embodiment of Step S 308  according to the present invention. The high-bright image S -1 , the medium-bright image S 0 , and the low-bright image S 1  are image data in which the sensing pixel has corresponding 8 bits, such that the micro-processor  106  in  FIG. 1B  may perform a hierarchical procedure on the high-bright image S -1 , the medium-bright image S 0 , and the low-bright image S 1 , as shown in Step S 310 , so as to obtain a high main soft image M -1  corresponding to the high-bright image S -1 , a medium main soft image M 0  corresponding to the medium-bright image S 0 , and a low main soft image M 1  corresponding to the low-bright image S 1 . 
     Referring to  FIGS. 6A and 6B , for example, for the high main soft image M -1 , in the hierarchical procedure of Step S 310 , preferably, a processing procedure (for example, interpolation) is performed on the same optical filter (taking the red light as an example) in each Bayer pattern  20  in the high-bright image S -1 , so as to form a single color optical sensing pixel  24   R-1 . Then, it is deduced through the same method to acquire the remaining sensing pixels  24   Gr-1 ,  24   Gb-1 , and  24   B-1  after the hierarchical procedure is executed, so as to obtain the high main soft image M -1  close to the original high-bright image S -1 . Further, through the same method, the medium main soft image M 0  is obtained from the medium-bright image S 0 , and the low main soft image M 1  is obtained from the low-bright image S 1 . Therefore, for example, when a resolution of the image data of the high-bright image S -1 , the medium-bright image S 0 , and the low-bright image S 1  is 8 M pixels, the high main soft image M -1 , the medium main soft image M 0 , and the low main soft image M 1  are 2 M pixels. 
     For Step S 312 , as shown in  FIGS. 6B to 6D , a high main soft weight array, a medium main soft weight array, and a low main soft weight array are determined through the edge detection procedure, the brightness determination procedure, or the chromaticity determination procedure according to the high main soft image M -1 , the medium main soft image M 0 , and the low main soft image M 1 . Next, as shown in Step S 314 , a softened image that is magnified to have the image data of 8 M pixels is obtained through the weight aggregation method after the micro-processor  106  corrects the sensing pixels of each point. 
     As shown in the flow chart of  FIG. 3C , the softened image is then compared with an artificial image through the edge detection procedure, the brightness determination procedure, or the chromaticity determination procedure, the respective corresponding weight proportion is obtained, and the output high-dynamic-range image is eventually obtained through the weight aggregation method. The artificial image is the image data generated after the weight aggregation method is performed on the high-bright image S -1 , the medium-bright image S 0 , the low-bright image S 1 , the high-bright weight array A -1 , the medium-bright weight array A 0 , and the low-bright weight array A 1  before the hierarchical procedure is executed. 
     Therefore, in the image processing method of the present invention, according to the foregoing embodiment, the hierarchical combining procedure is implemented, but the present invention is not limited to the manner of the embodiment. During the image processing procedure, the designer may determine the quantity of the hierarchies to be combined and the image data, so as to obtain the image data having a higher dynamic-range range, closer to the real chromaticity, and capable of being effectively removed of artifact after the hierarchical fusion.