Abstract:
A digital camera including a photosensor with a plurality of picture elements that define an image resolution that is adjustable.

Description:
BACKGROUND  
         [0001]    The process of capturing images includes forming a visible image of a subject on a photosensitive surface by introducing light or other forms of radiation thereto. Image capturing devices are widely used for videography, photography, infrared photography, ultraviolet photography, stereoscopic photography, microphotography, and thermography. Such devices generally include video cameras, film cameras, and digital cameras.  
           [0002]    Cameras basically include a light-tight body having an image capturing medium at a back end thereof, a shutter mechanism in front of the image capturing medium, an aperture in front of the shutter, and a lens disposed oppositely of the image capturing medium at a front end of the camera. The lens focuses light from a photographic subject through the aperture and shutter and onto the image-capturing medium to form an image of the subject thereon. The shutter and aperture together control exposure of the image-capturing medium. The shutter controls the length of time the image-capturing medium is exposed to light from the subject and the aperture is adjustable in size to control the amount of light from the subject that impinges on the image-capturing medium. Other camera features typically include a viewfinder to show the photographic subject, flash units to illuminate the photographic subject, and exposure meters to measure light.  
           [0003]    Digital cameras are increasingly popular and technology advances are rapidly resulting in increased performance capability. A digital camera captures a subject, scene, or view in elemental portions and generates an electronic signal that is representative of the subject, scene, or view. Unlike conventional film cameras that use a photoresponsive film as the image capturing medium, digital cameras typically use electronic photosensors such as one or more charge coupled device (CCD) chips. The CCD chips are configured to receive light reflecting from the photographic subject and to convert the reflected light into an electronic signal. A CCD chip includes an array of very fine picture elements or “pixels” arranged in horizontal rows and vertical columns.  
           [0004]    Upon exposure to imaging light from a subject, the CCD chips collect an array of discrete light energies or photon charges that correspond to or map the photographic subject column-by-column, row-by-row, and pixel-by-pixel such that a photon charge representation of the subject is seized. The CCD uses off-chip electronic circuits to process the photon charges and convert them into useful digital signals that can be stored in electronic memory either on or off-camera. Thus, digital cameras provide highly convenient features such as instant picture display and electronic storage format among many others, but provide image quality that is not as capable of handling low-light conditions as that of conventional film cameras.  
           [0005]    Image resolution in digital cameras continues to improve as CCD chips with finer pixel sizes are developed that enable finer elemental representations of a photographic subject. Unfortunately, finer pixel size tends to adversely affect the already compromised low-light performance of a digital camera. More particularly, the light sensitivity or light gathering ability of a CCD decreases with reductions in pixel size over a given surface area of the CCD. In other words, for a CCD of a given surface area, the light gathering ability of the CCD decreases with increases in pixel count. This is because the CCD tends to lose optical sensing surface area to accommodate the width of borderlines between adjacent pixels. The result is increased image resolution via finer parsing of the view, but at a cost of reduced light gathering ability and hence reduced low-light level performance.  
           [0006]    Low-light performance in digital cameras has typically been adjusted by varying the typical mechanical exposure settings of shutter speed, and aperture size, and also by adjusting the electronic setting of CCD output gain. One problem in varying shutter speed is a blurred image caused by relative movement between the camera and photographic subject while the shutter is open for a relatively long period of time to let more light into the camera. Also, a problem in varying gain is that increases in gain result in increases in noise and corresponding decreases in image quality. Digital cameras combine gain and exposure control into an automatic image enhancement feature. Unfortunately, such features are still susceptible to blur and noise problems and do not provide a user with readily accessible independent and dynamic range control of the resolution and light gathering ability of the image capturing medium.  
         SUMMARY  
         [0007]    One embodiment of the present invention may comprise a digital camera including a means for directing radiant energy into the digital camera and a means for capturing an image from the radiant energy. The means for capturing includes a plurality of elements that define an image resolution, and the embodiment further includes a means for selectively and dynamically adjusting the image resolution.  
           [0008]    Another embodiment of the present invention may comprise a digital camera including a lens for directing radiant energy into the digital camera and an image-capturing medium upon which the radiant energy impinges. The image-capturing medium includes a plurality of pixels that define an image resolution of the digital camera. A resolution control selector is in communication with the image-capturing medium to vary the image resolution.  
           [0009]    Yet another embodiment of the present invention may comprise a digital camera including a lens for directing light into said digital camera and a body connected to the lens, wherein the body includes a CMOS sensor having an array of pixels that define an image resolution of the digital camera. A resolution selector is provided for varying the image resolution to adjust low light performance of the digital camera. The resolution selector is attached to at least one of the lens and the body and is in communication with the CMOS sensor.  
           [0010]    Still another embodiment of the present invention may comprise a method of imaging including: directing radiant energy into a digital camera; capturing an image from the radiant energy on a plurality of elements that define an image resolution; and selectively and dynamically adjusting the image resolution.  
           [0011]    A further embodiment of the present invention may comprises a sensor assembly including a CMOS photosensor having a plurality of pixels arranged in a grid, and further including a light sensor that senses ambient light levels and generates a control signal in response thereto. A control system selectively groups pixels of the plurality of pixels and sums signal outputs of selectively grouped pixels of the plurality of pixels in response to the control signal.  
           [0012]    Yet a further embodiment of the present invention may comprise a digital camera having a CMOS photosensor having a plurality of pixels arranged in a grid, and further including a light sensor that senses ambient light levels and generates a control signal in response thereto. A control system selectively groups pixels of the plurality of pixels and sums signal outputs of selectively grouped pixels of the plurality of pixels in response to the control signal. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a block diagrammatic view of a digital camera according to an embodiment of the present invention.  
         [0014]    [0014]FIG. 1A is a flow chart illustrating an alternative automatic function of the digital camera according to an embodiment of the present invention.  
         [0015]    [0015]FIG. 2A is a partial view of an image capturing medium having an unsummed array of pixels in the digital camera of FIG. 1.  
         [0016]    [0016]FIG. 2B is a partial view of the image capturing medium of FIG. 2A wherein the array of pixels are summed into 2×2 groups.  
         [0017]    [0017]FIG. 2C is a partial view of the image capturing medium of FIG. 2B wherein the array of pixels have been further summed from 2×2 groups into 4×4 groups.  
     
    
     DETAILED DESCRIPTION  
       [0018]    Referring now in detail to the Figures, there is shown in FIG. 1 a block diagram of a digital camera  10  according to one embodiment of the present invention. The digital camera  10  generally includes a lens or lens assembly  12  attached to a body  14 , and within the body  14  there is a viewfinder  16 , an aperture  18 , a shutter  20 , and a stepper motor  22  for adjusting the lens assembly  12 , aperture  18 , and shutter  20 . Also within the body  12  there is an image capturing medium  24 , a gain control device  26 , an analog-to-digital (A-D) converter  28 , a digital-to-analog (D-A) converter  30 , a microprocessor  32 , a memory controller  34 , an internal memory unit  36 , and a memory card  38 . A display  40  and control panel  42  are provided on the body  12  for input/output with the user. Power is provided by a power unit such as a battery (not shown).  
         [0019]    The digital camera  10  is capable of operation in a variety of lighting conditions ranging from the very bright sunlit outdoors to very dimly lit or dark situations. Low-light performance of the digital camera  10  is implemented in a variety of ways, as will be discussed in greater detail below. In one embodiment, the digital camera  10  adjusts to low-light conditions by modifying one or more of the following settings: size of the aperture  18 , speed of the shutter  20 , gain from the image capturing medium  24 , and resolution capability of the image capturing medium  24 .  
         [0020]    Starting at the front of the camera  10 , the lens assembly  12  may be an integral part of the body  14  or may be separately and removably connected to the front thereof. In any case, the lens assembly  12  is used to direct radiant energy into the digital camera  10  by focusing, isolating, or framing a selected subject, scene, or view of the world from which emanates or reflects rays of energy. In other words, the lens assembly  12  provides a conduit into which rays of light, shown specifically at  11 , are received and through which the rays of light travel to the inside of the digital camera  10 . The stepper motor  22  couples to and adjustably drives the lens assembly  12  to magnify, zoom, or otherwise enlarge the appearance of a framed view. A light splitting device  13 , such as a dichromic mirror, splits and directs the incoming light  11  into a first light path  11   a  that passes through the viewfinder  16  and a second light path  11   b  that leads to medium  24 . The viewfinder  16  is typically integrated within the body  14  and is provided to optically communicate a framed view of the world to a user looking into the viewfinder  16 . This view generally corresponds to an optical image projected onto the medium  24  by lens assembly  12 .  
         [0021]    The aperture  18  is located within the body  14  of the digital camera  10  along imaging light path  11   b  behind the lens assembly  12  and variably regulates, over a range of opening sizes, the amount of imaging light that passes through the lens assembly  12  into the body  14  of the digital camera  10 . The shutter  20  is mounted in the imaging light path  11   b  behind the lens assembly  12  and aperture  18  and is a normally closed device that snaps open to let light pass therethrough and impinge on the image capturing medium  24 . The stepper motor  22  is coupled to and adjustably drives the aperture  18  and shutter  20  independently or in combination with one another to vary the exposure of the image-capturing medium  24  to imaging light, which passes through the lens assembly  12 , aperture  18 , and shutter  20 . Accordingly, the low-light level performance of the digital camera  10  can be regulated by increasing or decreasing the exposure of the image capturing medium  24 . But, increasing the exposure of the image capturing medium  24  requires increased camera stability while the digital camera  10  captures an image of a view. Alternatively, the shutter  20  need not be a mechanical device, but rather can be an electronic function of the image-capturing device. Regardless, the function of the shutter  20  is to momentarily, over a variable range of time, permit light to expose the photoresponsive elements of the image-capturing medium  24 .  
         [0022]    The image capturing medium  24  may be a complimentary metal oxide semiconductor (CMOS) sensor that is positioned behind the lens, aperture, and shutter within the body of the camera. The image capturing medium encompasses any device or material that is capable of capturing radiant energy and at least partially capable of converting same into an electronic signal that becomes a virtual representation of the optical image projected onto the sensor  24  by the lens assembly  12 .  
         [0023]    The image-capturing medium may be a CMOS sensor  24 , which is a photoresponsive device that includes very fine sub-elements, sub-sensors, or pixels that are typically arranged in rows and columns to define an array or grid. Upon exposure to light energy, or photons, reflecting from a view and passing through the lens, aperture, and shutter, each pixel of the array gets “filled” with a photoelectronic charge that represents an elemental portion of a virtual representation of the subject, scene, or view. The more pixels in an array, the better the representation, or resolution, of the view. Digital camera technology has progressed such that significant reductions in pixel size, and thus, increases in resolution capability, have been achieved. Today, CMOS sensors have a resolution of millions of pixels and, for example, a four mega-pixel (4 Mp) sensor provides an array of 2,000 rows by 2,000 columns of individual pixels. CMOS sensors are known in the art and examples of such are disclosed in the following patents which are hereby incorporated by reference herein: U.S. Pat. No. 6,215,113 to Chen et al., and U.S. Pat. No. 6,344,669 to Pan.  
         [0024]    The gain control device  26  is connected the CMOS sensor  24  to amplify the electronic signals therefrom. The gain control device  26  may be a variable analog amplifier that is connected between the A-D converter  28  and the CMOS sensor  24  to regulate the intensity of the electronic signal passing from the CMOS sensor  24  to the microprocessor  32  via the A-D converter  28 . The intensity of the signal is also regulated by the microprocessor  32  via the DA  30  converter that is interposed the microprocessor  32  and gain control device  26 . The A-D converter converts the amplified analog signals from the gain control device  26  into digital signals of acceptable levels that are appropriate for the microprocessor  32 .  
         [0025]    The low-light level performance of the digital camera  10  can also be regulated by the gain control device  26 . The microprocessor  32  can signal the gain control device  26  to amplify the signal from the CMOS sensor  24  to make up for a weak signal due to low-light conditions, with some attendant amplification of inherent noise from the CMOS sensor  24 . The gain control device  26 , aperture  18 , and shutter may be adjustable together in any combination or adjustable independently to constitute an image enhancement apparatus that is automatically controlled by the microprocessor  32 .  
         [0026]    The microprocessor  32  operates under control programs or software that are stored in the internal memory unit  36  to which the microprocessor  32  is connected. The memory controller  34  is connected to the microprocessor  32  and internal memory unit  36  for controlling the handling of images captured by the digital camera  10  and stored on the removable memory card  38  which is removably plugged into the memory controller  34 . Such captured images are made available to the user for viewing on the display panel  40  which is driven by the microprocessor  32 .  
         [0027]    The user sees a representative image of the view on the display panel  40  and controls the digital camera  10  via the control panel  42  which are both communicated with the microprocessor  32  of the digital camera  10 . The display panel  40  can be an LCD screen, gas plasma screen, or other display device.  
         [0028]    The control panel  42  is attached to the body  14  of the digital camera  10  and includes a set of control selectors including buttons, switches, knobs, or the like, including a power on/off button  44 , a mode selection switch  46 , zoom in-zoom out buttons  48  and  50 , a resolution control knob  52 , and a shutter button  54 . The resolution control knob  52  can also be a dial, button, switch, and the like.  
         [0029]    The resolution control knob  52  is a user input selector device that provides the user the opportunity to selectively and dynamically adjust image resolution among multiple different resolution settings and at any time such as while framing a view, zooming a view, and/or while the digital camera  10  is focusing or adjusting. Especially in the case of low light conditions, the resolution control knob  52  is provided to independently and dynamically control the camera&#39;s image resolution and, thus, the camera&#39;s low light performance, by virtually changing the size of the pixels of the CMOS sensor  24  via the microprocessor  32  and D-A converter  30 , as shown in FIG. 1 and as further described below with respect to FIGS.  2 A- 2 C.  
         [0030]    Alternatively, and still referring to FIG. 1, it is contemplated that the resolution control could also be carried out in an automatic mode using information from a light-level sensor  55  as input to the microprocessor  32 . The light-level sensor  55  senses the ambient light conditions under which the digital camera  10  is operating, and outputs a signal for use by the microprocessor  32  in deciding how and how much to adjust low-light performance of the digital camera  10 . In turn, the microprocessor  32  outputs signals directly to the stepper motor  22 , and indirectly to the CMOS sensor  24  and gain control device  26  via the D-A converter  30 . Again, the microprocessor  32  operates under pre-programmed instructions that are loaded to the internal memory unit  36  and communicated to the microprocessor  32 . Such instructions, or software, can enable the microprocessor  32  to decide whether to adjust aperture size, shutter speed, CMOS gain, or CMOS resolution, or any combination thereof, based at least in part on input from the light-level sensor  55 .  
         [0031]    [0031]FIG. 1A charts the automatic mode of the present invention. At step  110 , the light-level sensor  55  measures the ambient light-level of the environment in which the camera is operated. At step  120 , the light-level measurement is output to the microprocessor  32  of FIG. 1, which at step  130  references a look-up table that is stored in the internal memory  36  of FIG. 1. The look up table includes information pertaining to changes in the level of light intensity that can trigger an adjustment in CMOS pixel resolution. In this respect, the resolution of the CMOS sensor may be varied substantially incrementally in response to detected changes in the ambient light level. For example, for a given light level measurement of X candelas, the corresponding pixel resolution could be 1×1. For 0.5X candelas the corresponding pixel resolution could be 2×2, and so forth as shown in step  130 . Once the microprocessor references the correct pixel resolution for the measured light-level, a control signal is output to the CMOS sensor to adjust pixel resolution as reflected at step  140 . It is contemplated that a fitting formula or the like could be used to instruct the microprocessor and CMOS sensor instead of the look up table.  
         [0032]    Referring now to FIG. 2A, there is shown a portion of an array of pixels  56  of the CMOS sensor  24 , wherein each individual pixel  58  can be dimensionally characterized as 1×1 in horizontal and vertical directions. Electronically, pixel size is virtually adjustable wherein the pixels  58  are combinable together into groups of 2, 3, 4, 8, or any other size group, as depicted in FIGS. 2B and 2C. If a view is insufficiently lit, a user can turn the resolution control knob (shown in FIG. 1) to adjust the resolution and light gathering ability of the CMOS sensor  24 . In other words, the user can turn the resolution control knob to sum the pixels  58  from 1×1 to 2×2 and vice-versa. The user can then reevaluate whether further increases or decreases in resolution are necessary to yield a desired image quality. Accordingly, FIG. 2B illustrates a portion of the CMOS sensor  24  having pixels  58  summed into groups of 2×2 pixels  60 , wherein a 2000×2000 pixel sensor would effectively reduce to a 1000×1000 pixel sensor for improved light gathering capability. Similarly, FIG. 2C illustrates a portion of the CMOS sensor  24  wherein the pixels  58  have been summed into groups of 4×4 pixels  62 , wherein a 2000×2000 pixel sensor would effectively reduce to a 500×500 pixel sensor for even further improved light gathering capability.  
         [0033]    The summing process takes place on the CMOS sensor  24  itself and entails combining two or more photoelectronic charges of a given group of pixels. This has the effect of virtually increasing the pixel size of a given sensor. For a 4 Mp sensor then, pixel size can be varied from 4,000,000 1×1 actual pixels, to 2,000,000 2×2 virtual pixels, to 1,000,000 4×4 virtual pixels, etc., on up to one 2000×2000 virtual pixel. The result is groups of net photoelectronic charges that equal the sum of the individual photoelectronic charges of each group of summed pixels. For light gathering purposes, summing provides increased signal-to-noise ratio because the light gathering signal increases but the inherent noise from the CMOS sensor  24  remains constant since the summing function occurs before any gain is applied to the signal. Hence, summing increases the light gathering ability of the CMOS sensor  24  at the acceptable expense of a proportional reduction in resolution with no attendant increase in noise.  
         [0034]    This tradeoff between light sensitivity and resolution is a net benefit, especially in low light level situations and with or without relying on the camera&#39;s automatic exposure and gain adjustment. Now, a user is able to change the light gathering ability of the camera under low-light level conditions before, during, and after the camera automatically corrects for low light level via exposure and gain control. Moreover, a user can flexibly or dynamically improve the low light performance as desired and independently of any automatic exposure and/or gain adjustments. In other words, a user can decide whether to sacrifice image resolution in favor of improved light gathering ability to arrive at a desired overall image quality, independently of or simultaneously with other image enhancement features such as gain and exposure compensation.  
         [0035]    While the present invention has been described in terms of a limited number of embodiments, it is apparent that other forms could be adopted by one skilled in the art. In other words, claim elements are not limited to the imperfections of the exact language used, but encompass as well other structure that fulfills the same functional purpose. In other words, the teachings of the present invention encompass any reasonable substitutions or equivalents of claim limitations except insofar as limited by the prior art. Those skilled in the art will appreciate that other applications, including those outside of the digital camera industry, are possible with this invention. For instance, the present invention is applicable to apparatus associated with videography, photography, infrared photography, ultraviolet photography, stereoscopic photography, microphotography, thermography, and the like. Accordingly, the present invention is not limited to only digital cameras. Accordingly, the scope of the present invention is to be limited only by the following claims.