Abstract:
A camera having a depth of field which can be modified to produce desired photographic effects. The camera determines the depth of field for a subject when the subject is focused upon. A modification to the depth of field is determined based upon the distance to the subject, and the depth of field is modified to produce the desired photographic effect. In one embodiment, the depth of field is reduced, while, in another embodiment, the depth of field is shifted to place the subject slightly out of focus and to alter the focus of the background.

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to electronic devices having camera functionality. More particularly, the present invention relates to digital cameras having an adjustable depth of field. 
   BACKGROUND OF THE INVENTION 
   Cameras are widely used by average consumers, hobbyists, and professionals. While film-based photography has been popular for decades, digital cameras are quickly becoming the principal photography device for most households. Indeed, many electronic devices are being integrated with digital camera functionality, and traditional film cameras are being fitted with electronic features as well. For example, mobile telephones which include a digital camera are becoming increasingly common. 
   A well known photographic method involves utilizing a different depth of field (“DOF”) to produce an image with the subject slightly out of focus, which is sometimes called “soft-focus” or portrait-style. Depth of field is the distance between the farthest and nearest points which are in focus. This can also be identified as the zone of acceptable sharpness in front of and behind the subject, to which the lens is focused on. While “acceptably sharp” is a somewhat subjective standard, it has been defined mathematically by those skilled in the art. In general, the suggested photographic procedure is to place ⅓ of the DOF in front of the subject and ⅔ behind the subject. 
   The DOF is determined from several variables and is a function of the size of the image capturing device (i.e. film or photoelectric sensor), aperture, focal length, and distance to the subject. In portrait photography, it is common to utilize a shallow DOF in order to place the subject in sharper contrast to the surroundings. 
   Film-based cameras have utilized various methods such as special lenses, filters, or even gels to achieve a shallower DOF. However, since DOF is inversely proportional to the size of the image capturing device, film-based cameras have traditionally had much greater control over DOF than digital cameras, due at least in part to the relative large size of film in comparison to photoelectric sensors used in digital cameras. Thus, the relatively small size of the image capturing device used in digital cameras has traditionally resulted in a large DOF. Therefore, there is a need for a method and apparatus to allow for a shallower DOF, such that a user can employ various photographic techniques such as portrait photography. 
   SUMMARY OF THE INVENTION 
   The present invention relates to a camera having a depth of field which is modifiable to produce a desired image of a subject. In one embodiment, a user selects to either take photographs as normal or in a “modify depth of field” mode. In the modify depth of field mode, the user focuses the camera on a subject. The camera determines the distance to the subject. The necessary modification to the camera to produce the desired modification to the depth of field is determined, in one embodiment, through the use of look-up-tables. 
   In one embodiment, the change is a shifting of the depth of field in relation to the subject by refocusing the camera at a point in front of the subject. In another embodiment, the change is a shrinking of the depth of field to place the foreground and background less in focus than under the normal depth of field. 
   These and other objects, advantages, and features of the invention, together with the organization and manner of operation thereof, will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, wherein like elements have like numerals throughout the several drawings described below. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional side view of a generic digital camera constructed according to the principles of the present invention; 
       FIG. 2  is a perspective view of a mobile telephone that can be used in the implementation of the present invention; 
       FIG. 3  is a schematic representation of the telephone circuitry of the mobile telephone of  FIG. 2 ; 
       FIG. 4  is a flow diagram showing a generic process for the implementation of the present invention; 
       FIG. 5  is a flow diagram showing a process utilized by one embodiment for modifying the depth of field; 
       FIG. 6A  is an illustration the standard depth of field; 
       FIG. 6B  is an illustration of a reduced or shallow depth of field in accordance with the principles of the present invention; and 
       FIG. 6C  is an illustration of a shifted depth of field in accordance with the principles of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention relates to methods and apparatus for reducing the DOF of a camera. A generic digital camera constructed according to one embodiment of the present invention is shown at  10  in  FIG. 1 . The digital camera  10  can be a stand-alone device or can be incorporated into another electronic device, such as a portable telephone. The digital camera  10  includes a housing  11  which contains a shutter  13  covering at least one lens  12 , the shutter  13  serving to control the length of the exposure. An aperture  15  is located between the shutter  13  and lens  12  for controlling the amount of light. Also included is a primary memory unit  14 , a camera processor  16 , and at least one image sensor  18 . The primary memory unit  14  can be used to store digital images and computer software for performing various functions in the digital camera  10 , as well as to implement the present invention. In one embodiment, a removable, secondary memory unit  20 , in the form of a memory card, can also be included in the digital camera  10  to provide extra memory space. In one embodiment, the image sensor  18  can be a charge coupled device (CCD), a complementary metal oxide semiconductor (CMOS), or another system as known in the art. The digital camera  10  also includes a user interface  26 , such as, in one embodiment, one or more input buttons, a graphical user interface, or a combination thereof, for entering information and/or taking a picture. In one embodiment, a DOF adjustment mode selector (not shown) is provided either separately or as part of the user interface  26 . 
   When a digital file capturing an image or subject  605  is created, the at least one lens  12  focuses the image  605  onto the at least one image sensor  18  which electronically records light reflected from the image  605 . The camera processor  16  then breaks this electronic information down into digital data (via an analog-to-digital conversion) for a digital image which can be stored on a memory unit, such as the primary memory unit  14  and/or the secondary memory unit  20 , as a file. The digital camera  10  also includes a data communication port  22  to enable the transmission of digital images from the digital camera  10  to a remote terminal, such as a personal computer. The data communication can be in either wired or wireless form and can be configured for USB, Bluetooth, infrared, or other connections. 
   The digital camera of the present may be one component of another device such as a video camera, a mobile telephone, a personal digital assistant, a watch, or an audio player. When the digital camera is a component of another device, various parts may be common to the devices. For example, in one embodiment of the present invention, a mobile telephone includes a digital camera component and a telephone component, both of which may share a housing, memory, processor, etc. 
     FIGS. 2 and 3  show one representative mobile telephone  112  within which the present invention may be implemented. It should be understood, however, that the present invention is not intended to be limited to one particular type of mobile telephone  112  or other electronic device.  FIG. 2  depicts a mobile telephone having digital camera functionality in accordance with the principles of the present invention. The mobile telephone  112  of  FIG. 2  includes a housing  130 , a display  132  in the form of a liquid crystal display (LCD), a keypad  134 , a microphone  136 , an ear-piece  138 , a battery  140 , an infrared port  142 , an antenna  144 , a smart card  146 , in the form of a universal integrated circuit card (UICC) according to one embodiment of the invention, a card reader  148 , radio interface circuitry  152 , codec circuitry  154 , a controller  156  and a memory  158 . It should be noted that the controller  156  can be the same unit or a different unit than the camera processor  16 . Individual circuits and elements are all of a type well known in the art, for example in the Nokia range of mobile telephones. Other types of electronic devices within which the present invention may be incorporated can include, but are not limited to, personal digital assistants (PDAs), integrated messaging devices (IMDs), desktop computers, and notebook computers.  FIG. 3  illustrates a schematic of the components of the mobile phone  112  of  FIG. 2 . 
     FIG. 4  is a flow chart showing the operation of one embodiment of the implementation of the present invention. Initially, a determination of whether the camera is in “modify DOF mode” is made at step  501 . If the camera is not in modify DOF mode, the camera proceeds to function as a typical prior art camera would by focusing the lens at step  503  and capturing the image at step  505 . No determination or modification of DOF occurs. In the event the camera is in modify DOF mode, then the camera focuses and locks the focus at step  507 . The camera modifies the DOF at step  509 , for example in one embodiment by creating a shallower DOF or in another embodiment by altering the focus point of the camera to move the subject within the DOF. This step is explained in detail below regarding  FIG. 5 . Once the DOF has been modified in step  509 , the camera captures the image at step  505 . However, in one embodiment, a user is able to see a display of the image with the recomposed DOF at step  510  prior to capturing the image. The captured image may then be processed and stored in the secondary memory unit  20  at step  511  as is known in the prior art. 
   One embodiment of modifying the DOF, is further illustrated in  FIG. 5 . Once the camera has focused on the subject (step  507  in  FIG. 4 , the distance to the subject is determined in step  513 . This can be accomplished by any of the various mechanism known to one skilled in the art, such as audio mechanisms (including radio and sound) and light reflective mechanisms (including lasers). Once the distance has been determined in step  513 , the distance is used, in combination with the current state of the camera in regard to DOF, i.e. aperture, sensor size, focal length, etc., to determine the appropriate adjustments to make to the camera state to have the desired affect on the DOF. For example, in one embodiment, this can be accomplished at step  515  by accessing a look-up-table (“LUT”) which contains information regarding changes necessary to achieve a specific DOF. The distance to the subject can also be determined using the position sensors in the lens system. In one embodiment, the distance value is stored in EXIF data to allow a user to be able to check what the distance was to the subject. The changes can either selected by a user or a default DOF for use in the DOF modification mode. In one exemplary embodiment, the LUT contains information regarding the position of the lens for use during the modify DOF mode. For example, where the modify DOF mode is set to result in portrait type photographs, the LUT can be accessed for information regarding focusing the lens in front of the subject. As it is generally accepted in the photographic arts that a viewer is more distracted from a subject when the background is in focus than when the foreground is in focus, focusing the camera in front of the subject effectively moves the subject back in the DOF, resulting in more the background being out of focus than if the camera had focused on the subject. In one embodiment, the LUT is stored in the primary memory unit  14 . The necessary change to implement the new DOF is determined in step  517 . At step  519 , the changes determined to be necessary to implement the new DOF are implemented. For example, the camera can refocus using the new lens positions determined when the LUT was accessed at this step. 
     FIGS. 6B-6C  illustrates two different embodiments for modifying the depth of field.  FIG. 6A  represents a standard prior art camera  601  with a default depth of field  603  with the camera  601  focused on a subject  605  with a foreground object  611  and a background object  613 , both within the field of depth  603 .  FIG. 6B  illustrates the changed depth of field  607  of the camera  10  of one embodiment of the present invention where the depth of field is reduced or made shallow. The foreground object  611  and the background object  613  are now both outside of the depth of field  607 , meaning they will be more out of focus than the subject  605 .  FIG. 6C  illustrates the changed the depth of field of the camera  10  in another embodiment of the present invention where -the depth of field  615  is shifted in relation to the subject  605 . The foreground object  611  is still in the focus and is closer to the center of the depth of field  615 . The subject  605  is shifted back within the depth of field  615 , resulting in the subject not being in focus as in  FIG. 6A . This is often a desirable feature-for portraits. In addition, while the foreground object  611  is still within the depth of field  615 , the background object  613  is now outside of the depth of field  615 , meaning it will be relatively out of focus, also a commonly desirable feature for portraits. In another embodiment, the change may consist of a combination of shifting and shrinking the depth of field. 
   In one embodiment, the user may reposition the camera to place the subject in the desired position within the modified depth of field. As mentioned previously, the general convention is for the subject to be ⅓ of the way from the front of the depth of field, but since the focus is locked, the user may position the subject anywhere without the camera refocusing. 
   While the present invention has primarily been described in the context of digital cameras, the invention can include the use of a film-based camera having the describe apparatus or using the described methods for altering depth of field. 
   The present invention is described in the general context of method steps, which may be implemented in one embodiment by a program product including computer-executable instructions, such as program code, executed by computers in networked environments. 
   Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Computer-executable instructions, associated data structures, and program modules represent examples of program code for executing steps of the methods disclosed herein. The particular sequence of such executable instructions or associated data structures represent examples of corresponding acts for implementing the functions described in such steps. 
   Software and web implementations of the present invention could be accomplished with standard programming techniques, with rule based logic, and other logic to accomplish the various database searching steps, correlation steps, comparison steps and decision steps. It should also be noted that the words “component” and “module” as used herein, and in the claims, is intended to encompass implementations using one or more lines of software code, and/or hardware implementations, and/or equipment for receiving manual inputs. 
   The foregoing description of embodiments of the present invention have been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the present invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the present invention. The embodiments were chosen and described in order to explain the principles of the present invention and its practical application to enable one skilled in the art to utilize the present invention in various embodiments, and with various modifications, as are suited to the particular use contemplated.