Abstract:
A method of enhancing a low-light image includes receiving a first image from an RWB image sensor, receiving a second image from an RGB image sensor, receiving an illumination value from an illumination sensor, and selecting at least one of the first and second images and generating a third image using the at least one selected image.

Description:
PRIORITY STATEMENT 
       [0001]    This application claims priority under 35 U.S.C. §119(a) from Korean Patent Application No. 10-2015-0146914 filed on Oct. 21, 2015, the disclosure of which is hereby incorporated by reference in its entirety. 
       BACKGROUND 
       [0002]    The inventive concept relates to the field of imaging and image processing. More particularly, the inventive concept relates to a device having a dual camera feature and to a method of producing images using a dual camera. 
         [0003]    Recent multimedia devices include a camera module and implement diverse functions in combination with application programs. For instance, multimedia devices generate high-dynamic range images and stereo images or detect or recognize a particular object, using converted images which have been taken by a camera module. 
         [0004]    However, such functions may be influenced by conditions in which multimedia devices having a camera module operate. In particular, when the amount of light incident on a camera module is not sufficient, i.e., in low-light conditions, most pixels are dark, which results in a low-quality image in which an object is unidentifiable and color information is greatly distorted. Therefore, an approach to enhancing the quality of an image generated by a camera module in real time is desired. 
       SUMMARY 
       [0005]    According to some examples of the inventive concept, there is provided a method of operation of a dual camera by which low-light image quality may be enhanced, and which camera includes an RWB image sensor and an RGB image, the method including producing first image information using the RWB image sensor, producing second image information using the RGB image sensor, and selecting at least one of the first and second image information and producing third image information using the at least one selected image information. 
         [0006]    According to other examples of the inventive concept, there is provided a method of operation of a dual camera by which low-light image quality may be enhanced and which camera includes an RWB image sensor and an RGB image sensor, the method including producing first image information and second image information respectively using the RWB image sensor and the RGB image sensor, and selecting at least one of the first image information and the second image information and producing third image information using the at least one selected image information, in dependence on an operation mode of the dual camera and based at least in part on an illumination value of luminance in an environment of the dual camera. 
         [0007]    According to other examples of the inventive concept, there is provided a method by which low-light image quality of an image processing device may be enhanced, and which method includes receiving a first image from an RWB image sensor, receiving a second image from an RGB image sensor, and selecting one of the first image and the second image and outputting the selected image as a final image. 
         [0008]    According to other examples of the inventive concept, there is provided an imaging method of a camera system, the method comprising producing first image information of red, white and blue light in a field of view of the camera system, producing second image information, discrete from the first information, of red, green and blue light in a field of view of the camera system, obtaining a measure of luminance in an environment in which the camera system is located, selectively processing the first and second image information in a manner based, at least in part, on said measure of the luminance, and storing final image information in a memory and/or displaying the final image information on a display, as a result of the selective processing of the image information. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The above and other features and advantages of the inventive concept will become more apparent from the detailed description of examples thereof that follows as made with reference to the attached drawings in which: 
           [0010]      FIG. 1  is a block diagram of an imaging system according to some examples of the inventive concept; 
           [0011]      FIG. 2  is a block diagram of a first pre-processor illustrated in  FIG. 1  according to some examples of the inventive concept; 
           [0012]      FIG. 3  is a block diagram of a rectification engine illustrated in  FIG. 2  according to some examples of the inventive concept; 
           [0013]      FIG. 4  is a block diagram of a first converter illustrated in  FIG. 1  according to some examples of the inventive concept; 
           [0014]      FIG. 5  is a block diagram of an image synthesis circuit illustrated in  FIG. 1  according to some examples of the inventive concept; 
           [0015]      FIG. 6A  is a graph for explaining an output image of an image quality improvement device when the operation mode of image sensors is still mode, according to some examples of the inventive concept; 
           [0016]      FIG. 6B  is a graph, corresponding to a look up table, for explaining an output image of an image quality improvement device when the operation mode of image sensors is video mode, according to some examples of the inventive concept; 
           [0017]      FIG. 6C  is a graph, corresponding to a look up table, for explaining an output image of an image quality improvement device when the operation mode of image sensors is video mode, according to other examples of the inventive concept; 
           [0018]      FIG. 7  is a flowchart of a method of improving a low-light image quality of an image in an image processing device, according to some examples of the inventive concept; 
           [0019]      FIG. 8  is a detailed flowchart of the operation of generating a third image in the method illustrated in  FIG. 7 ; 
           [0020]      FIG. 9  is a block diagram of an imaging system according to other examples of the inventive concept; 
           [0021]      FIG. 10  is a block diagram of an imaging system according to still other examples of the inventive concept; 
           [0022]      FIG. 11  is a block diagram of an imaging system according to further examples of the inventive concept; and 
           [0023]      FIG. 12  is a block diagram of an imaging system according to yet other examples of the inventive concept. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    The inventive concept now will be described more fully hereinafter with reference to the accompanying drawings, in which examples of the invention are shown. This invention may, however, be realized in many different forms and should not be construed as limited to the examples set forth herein. Rather, these examples are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. In the drawings, the size and relative sizes of layers and regions may be exaggerated for clarity. Like numbers designate like elements throughout. 
         [0025]    It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items and may be abbreviated as “/”. 
         [0026]    It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first signal could be termed a second signal, and, similarly, a second signal could be termed a first signal without departing from the teachings of the disclosure. 
         [0027]    The terminology used herein is for the purpose of describing particular examples only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” or “includes” and/or “including” when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof. 
         [0028]    Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and/or the present application, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. For example, the term “image” may not refer to an optical image but in context may alternatively refer to an electronic image. Thus, the term “image information” or “information” of a particular image may refer to electronic information such as individual data or a data stream that is representative of, i.e., defines or is in the format of, a still image or video. Also, it will be readily understood that the term “camera” is not limited to a stand alone camera but may refer to a component that serves as a camera in any electronic product. 
         [0029]    As is traditional in the field of the inventive concepts, examples may be described and illustrated in terms of blocks which carry out a described function or functions. These blocks, which may be referred to herein as units or modules or the like, are physically implemented by analog and/or digital circuits such as logic gates, integrated circuits, microprocessors, microcontrollers, memory circuits, passive electronic components, active electronic components, optical components, hardwired circuits and the like, and may optionally be driven by firmware and/or software. The circuits may, for example, be embodied in one or more semiconductor chips, or on substrate supports such as printed circuit boards and the like. The circuits constituting a block may be implemented by dedicated hardware, or by a processor (e.g., one or more programmed microprocessors and associated circuitry), or by a combination of dedicated hardware to perform some functions of the block and a processor to perform other functions of the block. Each block of the examples may be physically separated into two or more interacting and discrete blocks without departing from the scope of the inventive concepts. Likewise, the blocks of the examples may be physically combined into more complex blocks without departing from the scope of the inventive concepts. 
         [0030]      FIG. 1  is a block diagram of an imaging system  1   a  according to some examples of the inventive concept. The imaging system  1   a  may include an image quality improvement device  10 - 1 , a first camera module  20   a,  a second camera module  20   b,  and a central processing unit (CPU)  30 . 
         [0031]    The first camera module  20   a  may include an RWB image sensor  22   a.  The second camera module  20   b  may include an RGB image sensor  22   b.  In these examples, the RWB image sensor  22   a  includes RWB color pixels which generate red, white and blue color information and the RGB image sensor  22   b  includes RGB color pixels which generate red, green and blue color information. 
         [0032]    Each of the RWB image sensor  22   a  and the RGB image sensor  22   b  may convert the intensity of incident light, which is reflected from an object and comes through lenses of the first camera module  20   a  or the second camera module  20   b,  into an electrical signal using a photoelectric element and may convert the electrical signal into a digital signal. The digital signal may be a stream of sequential digital values corresponding to pixels in a pixel array of each of the RWB image sensor  22   a  and the RGB image sensor  22   b.    
         [0033]    The digital signals (or more broadly “image information”) respectively output from the RWB image sensor  22   a  and the RGB image sensor  22   b  may represent or “form” a first image I 1  and a second image I 2 , respectively. The image information of the first image I 1  and the image information of the second image I 2  (referred to hereinafter simply as the first image I 1  and the second image I 2 ) may be input to a switch circuit of the image quality improvement device  10 - 1 . 
         [0034]    The RWB image sensor  22   a  has better sensitivity in low-light conditions than the RGB image sensor  22   b.  However, the RWB image sensor  22   a  is disadvantageous in that the output of each pixel may be saturated in high-light conditions. In other words, the RWB image sensor  22   a  is more suitable for use in low-light conditions and the RGB image sensor  22   b  is more suitable for use in high-light conditions. Here, the term “suitable” means that the image sensor can produce an image of an object that is closer to an image of the same object as perceived by the human eye. The imaging system  1   a  uses both the RGB image sensor  22   b  and the RWB image sensor  22   a  to minimize the distortion of color information and produce enhanced images in low-light conditions as well as in high-light conditions. 
         [0035]    The first camera module  20   a  and the second camera module  20   b  may be integrated into a single multimedia device, thereby forming a dual camera system. The first image I 1  generated from the first camera module  20   a  and the second image I 2  generated from the second camera module  20   b  may include information about a scene viewed from the same position. However, the information of the first image I 1  and the second image I 2  is not restricted to this example. In other examples, the first image I 1  and the second image I 2  may include information about a scene viewed from different positions in a three-dimensional (3D) reference system. 
         [0036]    The first camera module  20   a  and the second camera module  20   b  may be operated in at least one of various modes. The operation modes may include a still mode and a video mode. When the first and second camera modules  20   a  and  20   b  operate in the still mode, the first image I 1  and the second image I 2  each may be a single image. When the first and second camera modules  20   a  and  20   b  operate in the video mode, each of the first and second images I 1  and I 2  may be a group of a plurality of images I 1 - 1  through I 1 - m  or I 2 - 1  through I 2 - m,  where “m” is an integer of at least 2. 
         [0037]    The first and second camera modules  20   a  and  20   b  may be each selectively turned on and off under the control of the CPU  30 . That is, power may be supplied to or cut off from first and second camera modules  20   a  and  20   b.  For instance, the first and second camera modules  20   a  and  20   b  may be turned on or off depending on the operation mode. 
         [0038]    More specifically, the CPU  30  may send a control signal CONa for turning on or off the power to the first camera module  20   a  or send a control signal CONb for turning on or off the power to the second camera module  20   b.  The CPU  30  may provide a control signal CONi for controlling the image quality improvement device  10 - 1  based on the operation mode of the first and second camera modules  20   a  and  20   b  and an illumination value, where “i” is an integer of at least 1 and at most “n”. Here, the illumination value may be received from an illumination (or light) sensor and thus be a value of the luminance in the field of view of the sensor. However, the inventive concept is not limited to the current examples. The illumination value may be a value based on the brightness of each of the first and second images I 1  and I 2  in other examples. In any case, and generally speaking, the illumination value is a measure of luminance in an environment in which the dual camera is disposed and operating. 
         [0039]    The CPU  30  may determine whether the first and second camera modules  20   a  and  20   b  are in the still mode. When it is determined that the first and second camera modules  20   a  and  20   b  are operating in the still mode, the CPU  30  may determine whether the illumination value is less than a first threshold. When it is determined that the illumination value is less than the first threshold, the CPU  30  may send a control signal CON 1  for connecting the first camera module  20   a  to a first pre-processor  200   a  via a switch circuit  100 . When it is determined that the illumination value is equal to or greater than the first threshold, the CPU  30  may send the control signal CON 1  for connecting the second camera module  20   b  to a second pre-processor  200   b  via the switch circuit  100 . 
         [0040]    When it is determined that the first and second camera modules  20   a  and  20   b  are in the video mode, the CPU  30  may send the control signal CON 1  for connecting the first and second camera modules  20   a  and  20   b  to the first and second pre-processors  200   a  and  200   b,  respectively, via the switch circuit  100 . 
         [0041]    Alternatively, when it is determined that the first and second camera modules  20   a  and  20   b  are in the video mode, the CPU  30  may determine whether the illumination value is less than a second threshold. When it is determined that the illumination value is equal to or greater than the second threshold, the CPU  30  may determine whether the illumination value is less than a third threshold. 
         [0042]    When the illumination value is less than the second threshold, the CPU  30  may send the switch circuit  100  the control signal CON 1  for connecting the first camera module  20   a  to the first pre-processor  200   a  and disconnecting the second camera module  20   b  from the second pre-processor  200   b.  When the illumination value is equal to or greater than the second threshold and less than the third threshold, the CPU  30  may send the switch circuit  100  the control signal CON 1  for connecting the first and second camera modules  20   a  and  20   b  to the first and second pre-processors  200   a  and  200   b,  respectively. When the illumination value is equal to or greater than the third threshold, the CPU  30  may send the switch circuit  100  the control signal CON 1  for disconnecting the first camera module  20   a  from the first pre-processor  200   a  and connecting the second camera module  20   b  to the second pre-processor  200   b.    
         [0043]    The CPU  30  may store information MD_IF about the operation mode of the first and second camera modules  20   a  and  20   b  in a register of the image quality improvement device  10 - 1 . The CPU  30  may send the first and second pre-processors  200   a  and  200   b  of the image quality improvement device  10 - 1  a control signal CON 2  for controlling the first and second pre-processors  200   a  and  200   b.  The control signal CON 2  may be based on sensor characteristic information regarding the RWB image sensor  22   a  and the RGB image sensor  22   b  of the first camera module  20   a  and the second camera module  20   b,  respectively. 
         [0044]    The sensor characteristic information may include at least one among lens shading information, bad pixel information, chromatic aberration information, and rectification information. The sensor characteristic information may be set and stored in an external memory in advance of the operation of the imaging system  1   a.    
         [0045]    The CPU  30  may send a first converter  300   a  and a second converter  300   b  of the image quality improvement device  10 - 1  a control signal CON 3  for controlling the first and second converters  300   a  and  300   b,  respectively. The control signal CON 3  may be information about the size or format of the first and second images I 1  and I 2 . The information about the size or format may be set and stored in an external memory in advance of the operation of the imaging system  1   a.    
         [0046]    The CPU  30  may send an image synthesis circuit  400  of the image quality improvement device  10 - 1  a control signal CON 4  for controlling the image synthesis circuit  400 . The control signal CON 4  may include information about the operation mode of the first and second camera modules  20   a  and  20   b  and the illumination value. 
         [0047]    The image quality improvement device  10 - 1  may receive the first image I 1  and the second image I 2  from the first camera module  20   a  and the second camera module  20   b,  respectively, and may output image information representing an image SO (referred to hereinafter simply as “image SO”) with improved low-light image quality. The image quality improvement device  10 - 1  may include the switch circuit  100 , the first pre-processor  200   a,  the second pre-processor  200   b,  the first converter  300   a,  the second converter  300   b,  and the image synthesis circuit  400 . However, at least one of the elements, e.g., the first and second pre-processors  200   a  and  200   b  and the first and second converters  300   a  and  300   b,  of the image quality improvement device  10 - 1  may be omitted in other examples. 
         [0048]    The switch circuit  100  may selectively transmit at least one of the first and second images I 1  and I 2  respectively output from the first and second camera modules  20   a  and  20   b  to the first and second pre-processors  200   a  and  200   b.  For instance, the switch circuit  100  may connect the first camera module  20   a  to the first pre-processor  200   a  under the control of the CPU  30 , in which case the first image I 1  output from the first camera module  20   a  is input to the first pre-processor  200   a.  The switch circuit  100  may connect the second camera module  20   b  to the second pre-processor  200   b  under the control of the CPU  30 , in which case the second image I 2  output from the second camera module  20   b  is input to the second pre-processor  200   b.    
         [0049]    The switch circuit  100  may selectively connect the first and second camera modules  20   a  and  20   b  to the first and second pre-processors  200   a  and  200   b,  respectively, according to the operation mode of each of the first and second camera modules  20   a  and  20   b  under the control of the CPU  30 . The switch circuit  100  may selectively connect the first and second camera modules  20   a  and  20   b  to the first and second pre-processors  200   a  and  200   b,  respectively, based on the illumination value received from the illumination sensor, under the control of the CPU  30 . 
         [0050]    For instance, when the first and second camera modules  20   a  and  20   b  operate in the still mode and the illumination value is less than the first threshold, the switch circuit  100  may connect the first camera module  20   a  to the first pre-processor  200   a  under the control of the CPU  30 . However, when the illumination value is equal to or greater than the first threshold, the switch circuit  100  may connect the second camera module  20   b  to the second pre-processor  200   b  under the control of the CPU  30 . 
         [0051]    When the first and second camera modules  20   a  and  20   b  operate in the video mode, the switch circuit  100  may connect the first and second camera modules  20   a  and  20   b  to the first and second pre-processors  200   a  and  200   b,  respectively, under the control of the CPU  30 . 
         [0052]    Alternatively, when the first and second camera modules  20   a  and  20   b  operate in the video mode and the illumination value is less than the second threshold, the switch circuit  100  may connect the first camera module  20   a  to the first pre-processor  200   a  and disconnect the second camera module  20   b  from the second pre-processor  200   b  under the control of the CPU  30 . When the illumination value is equal to or greater than the second threshold and less than the third threshold, the switch circuit  100  may connect the first and second camera modules  20   a  and  20   b  to the first and second pre-processors  200   a  and  200   b,  respectively. When the illumination value is equal to or greater than the third threshold, the switch circuit  100  may disconnect the first camera module  20   a  from the first pre-processor  200   a  and connect the second camera module  20   b  to the second pre-processor  200   b.    
         [0053]    Consequently, the switch circuit  100  of the image quality improvement device  10 - 1  may selectively connect the first and second camera modules  20   a  and  20   b  to the first and second pre-processors  200   a  and  200   b  according to the operation mode of the first and second camera modules  20   a  and  20   b  and the illumination value. 
         [0054]    When one of the first and second camera modules  20   a  and  20   b  is not connected to one of the first and second pre-processors  200   a  and  200   b  under conditions as described above, the image I 1  or I 2  generated from the one of the first and second camera modules  20   a  and  20   b  is not processed. Accordingly, i.e., by avoiding the processing of images from one of the first and second camera modules  20   a  and  20   b,  problems associated with computational complexity may be obviated. 
         [0055]    The first and second pre-processors  200   a  and  200   b  will be described in detail with reference to  FIGS. 2 and 3 . The first and second pre-processors  200   a  and  200   b  may have the same structure and functions as each other, and therefore, redundant description of the structure and functions will be omitted. The structure and function of the first pre-processor  200   a  will be mainly described. 
         [0056]      FIG. 2  is a block diagram of the first pre-processor  200   a  illustrated in  FIG. 1  according to some examples of the inventive concept.  FIG. 3  is a block diagram of a rectification engine  240  illustrated in  FIG. 2  according to some examples of the inventive concept. Referring to  FIGS. 1 and 2 , the first pre-processor  200   a  may include a lens shading corrector  210 , a bad pixel corrector  220 , a chromatic aberration corrector  230 , and the rectification engine  240 . 
         [0057]    Under the control of the CPU  30 , the lens shading corrector  210  may correct a difference in shade across the field of view, e.g., correct for a case in which an image becomes darker from the center of each of the RWB image sensor  22   a  and the RGB image sensor  22   b  toward the periphery thereof due to some undesired shading effect, based on shading information LS_IF received. The difference in shade, i.e., the undesired shading effect, may be a lens shading effect caused by the curved surface of a lens of each of the first and second camera modules  20   a  and  20   b.    
         [0058]    Under the control of the CPU  30 , the bad pixel corrector  220  may correct for the outputs of a static bad pixel produced during sensor manufacturing and a dynamic bad pixel produced due to heat generation, based on bad pixel information BP_IF received. The bad pixel corrector  220  may detect a bad pixel, correct a pixel value of the bad pixel, and generate a corrected pixel value. 
         [0059]    Under the control of the CPU  30 , the chromatic aberration corrector  230  may correct a chromatic aberration of each of the first and second camera modules  20   a  and  20   b,  based on chromatic aberration information CA_IF received. Chromatic aberration may occur because the refractive index a lens of each of the first and second camera modules  20   a  and  20   b  varies with the wavelength of light incident on the lens, and light with longer wavelengths is focused at positions farther from the lens. 
         [0060]    Under the control of the CPU  30 , the rectification engine  240  may perform a correction to make the first and second images I 1  and I 2  have the same geometric shape and size, based on rectification information REF_IF received. Referring to  FIGS. 1 and 3 , the rectification engine  240  may include one or more N×N matrix multipliers  240 - 1  through  240 - p,  where “p” is an integer of at least 1. 
         [0061]    The rectification engine  240  may perform geometric transformation on at least one of the first and second images I 1  and I 2  based on the rectification information REF_IF. The geometric transformation may include geometric linear transformation such as rotation transformation, scaling transformation, or affine transformation. 
         [0062]    The first converter  300   a  may convert the size or format of an image PO 1  received from the first pre-processor  200   a  and may output image information of a converted image C 1  (referred to simply as the “converted image C 1 ” hereinafter) to the image synthesis circuit  400 . The second converter  300   b  may convert the size or format of an image represented by image information PO 2  received from the second pre-processor  200   b  and may output image information of a converted image C 2  (referred to simply as the “converted image C 2 ” hereinafter) to the image synthesis circuit  400 . The first and second converters  300   a  and  300   b  will be described in detail with reference to  FIG. 4 . 
         [0063]    The first and second converters  300   a  and  300   b  may have the same structure and functions as each other, and therefore, redundant description of the structure and functions will be omitted. The structure and function of the first converter  300   a  will be mainly described. 
         [0064]      FIG. 4  is a block diagram of the first converter  300   a  illustrated in  FIG. 1  according to some examples of the inventive concept. Referring to  FIGS. 1 and 4 , the first converter  300   a  may include a size converter  302  and a format converter  304 . 
         [0065]    The size converter  302  may convert the spatial resolution of the input image PO 1  based on size information SIZE_IF. The format converter  304  may convert the format of an output image of the size converter  302  based on format information FM_IF to output the converted image C 1 . 
         [0066]    Under the control of the CPU  30 , the image synthesis circuit  400  may output either the output image C 1  of the first converter  300   a  or the output image C 2  of the second converter  300   b  as the output image SO or may mix the output image C 1  of the first converter  300   a  and the output image C 2  of the second converter  300   b  and output (image information of) the synthesized image SO according to the operation mode of the first and second camera modules  20   a  and  20   b.  The image synthesis circuit  400  will be described in detail with reference to  FIGS. 5 through 6C . 
         [0067]      FIG. 5  is a block diagram of the image synthesis circuit  400  illustrated in  FIG. 1  according to some examples of the inventive concept.  FIG. 6A  is a diagram for explaining an output image of an image quality improvement device when the operation mode of image sensors is still mode, according to some examples of the inventive concept.  FIG. 6B  is a diagram for explaining an output image of an image quality improvement device when the operation mode of image sensors is video mode, according to some examples of the inventive concept.  FIG. 6C  is a diagram for explaining an output image of an image quality improvement device when the operation mode of image sensors is video mode, according to other examples of the inventive concept. 
         [0068]    Referring to  FIGS. 1 and 5 , the image synthesis circuit  400  may include a coefficient generator  402  and a composite circuit  404 . The coefficient generator  402  may receive information MD_IF about the operation mode of the first and second camera modules  20   a  and  20   b  and an illumination value IL_IF from the CPU  30 . 
         [0069]    Referring to  FIGS. 1, 5, and 6A , the image synthesis circuit  400  may output the output image C 1  of the first converter  300   a  under the control of the CPU  30  when the first and second camera modules  20   a  and  20   b  operate in the still mode and the illumination value IL_IF is less than the first threshold. When the illumination value IL_IF is equal to or greater than the first threshold, the image synthesis circuit  400  may output the output image C 2  of the second converter  300   b.  The output image C 1  of the first converter  300   a  or the output image C 2  of the second converter  300   b  may be a final image. Meanwhile, the output images C 1  and C 2  of the first and second converters  300   a  and  300   b  may bypass the coefficient generator  402  and the composite circuit  404  of the image synthesis circuit  400 . 
         [0070]    Referring to  FIGS. 1, 5, and 6B , the image synthesis circuit  400  may output the synthesized image SO based on the output image C 1  of the first converter  300   a  and the output image C 2  of the second converter  300   b  under the control of the CPU  30  when the first and second camera modules  20   a  and  20   b  operate in the video mode. At this time, the coefficient generator  402  may access a lookup table of interpolation coefficients correlated with illumination values from an external memory under the control of the CPU  30  and select the coefficient correlated with the current illumination value. The lookup table may be set and stored in the external memory in advance of the operation of the imaging system  1   a.  The synthesized image SO may be represented by Equation 1: 
         [0000]        SO =(1−α)× C 1+α× C 2,   (1)
 
         [0000]    where α is the interpolation coefficient, C 1  is the output image of the first converter  300   a,  and the C 2  is the output image of the second converter  300   b.    
         [0071]    Referring to  FIGS. 1, 5, and 6C , the image synthesis circuit  400  may output the synthesized image SO based on the output image C 1  of the first converter  300   a  and the output image C 2  of the second converter  300   b  under the control of the CPU  30  when the first and second camera modules  20   a  and  20   b  operate in the video mode. At this time, the coefficient generator  402  may access a lookup table of interpolation coefficients correlated with illumination value from an external memory under the control of the CPU  30  and select the coefficient correlated with the current illumination value. The synthesized image SO may be determined by Equation 2: 
         [0000]    
       
         
           
             
               
                 
                   SO 
                   = 
                   
                     { 
                     
                       
                         
                           
                             
                               C 
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                                 2 
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                                   — 
                                 
                                  
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                                 a 
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                                 1 
                               
                               + 
                               
                                 
                                   ( 
                                   
                                     1 
                                     - 
                                     α 
                                   
                                   ) 
                                 
                                 × 
                                 C 
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                                 2 
                               
                             
                             , 
                             
                               
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                                   nd 
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                                 3 
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                                   rd 
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         [0000]    where α is the interpolation coefficient, C 1  is the output image of the first converter  300   a,  the C 2  is the output image of the second converter  300   b,  2nd_th is the second threshold, and 3rd_th is the third threshold. 
         [0072]      FIG. 7  is a flowchart of a method of improving a low-light image quality of an image according to some examples of the inventive concept. Referring to  FIGS. 1 through 7 , the image quality improvement device  10 - 1  may receive the first and second images I 1  and I 2  respectively from the first and second camera modules  20   a  and  20   b  (operation S 100 ) and may receive an illumination value from an illumination sensor (operation S 200 ). 
         [0073]    The image quality improvement device  10 - 1  may determine whether the first and second camera modules  20   a  and  20   b  are operating in the still mode (operation S 300 ). When the first and second camera modules  20   a  and  20   b  are operating in the still mode (i.e., in case of YES in operation S 300 ), the image quality improvement device  10 - 1  may determine whether the illumination value is less than the first threshold (operation S 302 ). 
         [0074]    When the illumination value is less than the first threshold (i.e., in case of YES in operation S 302 ), the image quality improvement device  10 - 1  may output the first image I 1  in operation S 304 - 1  and turn off the second camera module  20   b  (S 304 - 2 ). When the illumination value is equal to or greater than the first threshold (i.e., in case of NO in operation S 302 ), the image quality improvement device  10 - 1  may output the second image I 2  (operation S 306 - 1 ) and turn off the first camera module  20   a  (operation S 306 - 2 ). 
         [0075]    When the first and second camera modules  20   a  and  20   b  are operating in the video mode (i.e., in case of NO in operation S 300 ), the image quality improvement device  10 - 1  may receive a lookup table in operation S 402  and may generate a third image using at least one of the first and second images I 1  and I 2  (operation S 404 ). The lookup table may include an interpolation coefficient corresponding to a change in the illumination value. The lookup table may be set and stored in an external memory in advance of the operation of the imaging system  1   a.  The detailed description of operations S 402  and S 404  has been made with reference to  FIGS. 1, 5, and 6B  above and is thus omitted here. 
         [0076]      FIG. 8  is a detailed flowchart of operation S 404  in the method illustrated in  FIG. 7 . Referring to  FIGS. 1 through 8 , when the first and second camera modules  20   a  and  20   b  operate in the video mode (i.e., in case of NO in operation S 300 ), the image quality improvement device  10 - 1  may receive the lookup table in operation S 402  and may generate the third image using at least one of the first and second images I 1  and I 2  (operations S 404 - 1  through S 404 - 7 ). The detailed description of operations S 404 - 1  through S 404 - 7  has been made with reference to  FIGS. 1, 5, and 6C  and is thus omitted here. 
         [0077]      FIG. 9  is a block diagram of an imaging system  1   b  according to other examples of the inventive concept. Referring to  FIG. 9 , the imaging system  1   b  may include a processor  500 A, the first camera module  20   a,  the second camera module  20   b,  an external memory  530 , and a display  540 . The imaging system  1   b  may be implemented as a personal computer (PC) or a mobile device. The mobile device may be a laptop computer, a cellular phone, a smart phone, a tablet PC, a personal digital assistant (PDA), an enterprise digital assistant (EDA), a digital still camera, a digital video camera, a portable multimedia player (PMP), a personal navigation device or portable navigation device (PND), a handheld game console, a mobile internet device (MID), a wearable computer, an internet of things (IoT) device, an internet of everything (IoE) device, or an e-book. 
         [0078]    The processor  500 A may be implemented as an integrated circuit (IC), a motherboard, a system on chip (SoC), an application processor (AP), or a mobile AP, but the inventive concept is not restricted to these examples. The processor  500 A may include bus architecture (or a bus)  501 , a CPU  510 , a first interface  520 - 1 , a second interface  520 - 2 , an image signal processor (ISP)  530 A, a memory controller  550 , and a display controller  570 . 
         [0079]    The CPU  510 , the ISP  530 A, the memory controller  550 , and the display controller  570  may communicate with one another (transmit a command and/or data from one to the other) through the bus architecture  501 . The bus architecture  501  may be implemented as a bus using an advanced microcontroller bus architecture (AMBA) protocol, a bus using an advanced high-performance bus (AHB) protocol, a bus using an advanced peripheral bus (APB) protocol, a bus using an advanced extensible interface (AXI) protocol, or a combination thereof, but the inventive concept is not restricted to these examples. 
         [0080]    The CPU  510  may correspond to the CPU  30  illustrated in  FIG. 1 . The CPU  510  may control the overall operation of the processor  500 A. For example, the CPU  510  may control the first interface  520 - 1 , the second interface  520 - 2 , the ISP  530 A, the memory controller  550 , and the display controller  570 . The CPU  510  may include one core or more. 
         [0081]    The first interface  520 - 1  may receive image information (“a first image” hereinafter) and first control signals from the first camera module  20   a  and transmit the first image and the first control signals to the ISP  530 A. The second interface  520 - 2  may receive image information (“a second image” hereinafter) and second control signals from the second camera module  20   b  and transmit the second image and the second control signals to the ISP  530 A. The first image may be a first picture (optical image), first image data, a first data stream, or first frame data. The second image may be a second picture (optical image), second image data, a second data stream, or second frame data. 
         [0082]    The first camera module  20   a  may comprise a complementary metal-oxide semiconductor (CMOS) image sensor chip. The first camera module  20   a  may transmit the first image and the first control signals to the first interface  520 - 1  using mobile industry processor interface (MIPI)® camera serial interface (CSI). The second camera module  20   b  may comprise a CMOS image sensor chip. The second camera module  20   b  may transmit the second image and the second control signals to the second interface  520 - 2  using MIPI® CSI. The resolution of the first image may be different from that of the second image. 
         [0083]    The ISP  530 A may perform functions of the image quality improvement device  10 - 1  of the imaging system  1   a  illustrated in  FIG. 1 . In this case, the image quality improvement device  10 - 1  may constitute the ISP  530 A. 
         [0084]    The ISP  530 A may perform time-division multiplexing (TDM) on the first image and/or the second image in units of line data instead of frame data without using the external memory  530 . The ISP  530 A may include a plurality of ISP cores in order to process images output from the first and second camera modules  20   a  and  20   b  in units of line data simultaneously, in parallel, or on the fly in TDM mode. Each of the ISP cores may perform at least one of auto dark level compensation, bad pixel replacement, noise reduction, lens shading compensation, color correction, RGB gamma correction, edge enhancement, hue control, and color suppression. The memory controller  550  may store line data that has been processed by the ISP  530 A in the TDM mode in the external memory  530  under the control of the CPU  510 . 
         [0085]    The display controller  570  may transmit data (e.g., frame data) output from the external memory  530  to the display  540  under the control of the CPU  510 . The display controller  570  may transmit the data (e.g., frame data) output from the external memory  530  to the display  540  using MIPI® display serial interface (DSI) or embedded DisplayPort (eDP). 
         [0086]      FIG. 10  is a block diagram of an imaging system  1   c  according to still other examples of the inventive concept. Referring to  FIGS. 9 and 10 , unlike the imaging system  1   b,  the imaging system  1   c  has an image quality improvement device  10 - 2  provided outside an ISP  530 B. In other words, the image quality improvement device  10 - 2  is implemented as an independent intellectual property (IP) or semiconductor chip. 
         [0087]    The ISP  530 B may convert raw image data in a first format into input image data INPUT in a second format. The first format may be a Bayer pattern but is not restricted thereto. The second format may be YUV, Y′UV, YCbCr, YPbPr, or RGB but is not restricted thereto. 
         [0088]      FIG. 11  is a block diagram of an imaging system  1   d  according to further examples of the inventive concept. Referring to  FIG. 11 , an image quality improvement application  10 - 3  may be software or a computer readable program which can be executed in the CPU  510 . The image quality improvement application  10 - 3  may be stored in the external memory  530  and may be loaded to and executed in the CPU  510  when the imaging system  1   d  is being booted. 
         [0089]    The image quality improvement application  10 - 3  may include a function block which can perform the same function as or a similar function to each of the elements described with reference to  FIGS. 1 through 8 . Each function block may be embodied as computer readable software or program code. 
         [0090]      FIG. 12  is a block diagram of an imaging system  1   e  according to yet other examples of the inventive concept. The imaging system  1   e  may be that of a data processing apparatus, such as a mobile phone, a personal digital assistant (PDA), a portable media player (PMP), an IP TV, or a smart phone that can use or support the MIPI interface. The imaging system  1   e  includes an application processor  1010 , the image sensor  1040 , and a display  1050 . 
         [0091]    A camera serial interface (CSI) host  1012  of the application processor  1010  performs serial communication with a CSI device  1041  of the image sensor  1040  through CSI. For example, an optical de-serializer (DES) may be provided in the CSI host  1012 , and an optical serializer (SER) may be provided in the CSI device  1041 . 
         [0092]    A display serial interface (DSI) host  1011  of the application processor  1010  performs serial communication with a DSI device  1051  of the display  1050  through DSI. For example, an optical serializer may be provided in the DSI host  1011 , and an optical de-serializer may be provided in the DSI device  1051 . 
         [0093]    The imaging system  1   e  may also include a radio frequency (RF) chip  1060  which communicates with the application processor  1010 . A physical layer (PHY)  1013  of the imaging system  1   e  and a PHY of the RF chip  1060  communicate with (i.e., transmit data to) each other according to a MIPI® DigRF standard. 
         [0094]    The imaging system  1   e  may further include at least one of a GPS  1020 , a storage device  1070 , a microphone  1080 , a DRAM  1085  and a speaker  1290 . The imaging system  1   e  may communicate using Wimax (World Interoperability for Microwave Access)  1030 , WLAN (Wireless LAN)  1100  or UWB (Ultra Wideband)  1110 , or the like. 
         [0095]    The present general inventive concept can also be embodied as computer-readable code on a computer-readable medium. The computer-readable recording medium is any data storage device that can store data as a program which can be thereafter read by a computer system. Examples of computer-readable recording medium include read-only memory (ROM), random-access memory (RAM), CD-ROMs, magnetic tapes, floppy disks, and optical data storage devices. Also, program code for estimating object information may be transmitted in carrier wave (e.g., transmission via the Internet) format. 
         [0096]    The computer-readable recording medium can also be distributed over network coupled computer systems so that the computer-readable code is stored and executed in a distributed fashion. Also, functional programs, codes, and code segments to accomplish the present general inventive concept can be easily developed by programmers. 
         [0097]    As described above, according to some examples of the inventive concept, an imaging system uses both an RGB image sensor and an RWB image sensor and thus uses images for which distortion of color information is improved even in low-light conditions as well as in high-light conditions, thereby improving the quality of low-light images (images captured in low light conditions). In addition, the imaging system omits a series of processes involving an image generated from one of camera modules, according to the operation mode of the camera modules and an illumination value. Thus, computational complexity is minimized 
         [0098]    Although the inventive concept has been particularly shown and described with reference to examples thereof, it will be understood by those of ordinary skill in the art that various changes in forms and details may be made to the disclosed examples without departing from the spirit and scope of the inventive concept as defined by the following claims.