Abstract:
An electronic camera includes optics for focusing an image of a subject at an image plane, an area image sensor disposed at the image plane for receiving the image subject and producing a digital image having a plurality of pixels that represent the subject, and a storage structure coupled to the area image sensor for storing the digitized image of the subject. A non-emissive display for displaying an image corresponding to the stored image, includes field-driven solid phase particles disposed in a matrix that can change reflective density in the display in response to an applied electric field, and an electronic addressing arrangement including electrodes for applying voltages across the field-driven particles at particular locations corresponding to pixels in response to the stored image to produce a displayed image of the subject.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present invention is related to commonly assigned U.S. patent application Ser. No. 08/934,371 filed Sep. 19, 1997, entitled “A Portable Electronic Recording and Displaying Device” to Wen et al U.S. patent application Ser. No. 08/951,017 filed Oct. 15, 1997, entitled “Camera With Microfluidic Printer” to McIntyre “ADDRESSING NON-EMISSIVE COLOR DISPLAY DEVICE” by Wen/MacLean. The disclosure of this related application is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a camera which include a display for displaying an image of a subject stored in the camera. 
     BACKGROUND OF THE INVENTION 
     It is known in the prior art to provide an electronic camera which uses an area image sensor. Digital images produced from the image sensor are stored in memory and these images can be shown on a liquid crystal display (LCD) so that the user can determine which image should be stored for use in producing hard copy images. Typically, these images can be stored in a magnetic disk or in a solid state Memory Card. 
     In U.S. Pat. No. 4,262,301 an electronic camera is disclosed which includes a display device. The camera also includes a digital-to-analog converter which sends signals to the display. Also, the digital-to-analog converter selectively sends these images to a magnetic tape for storage. Images on the magnetic tape can then be produced as a hard copy by a printer which is provided on the camera. A problem with the approach in U.S. Pat. No. 4,262,301 is the difficulty in achieving small product size. 
     A shortcoming with prior electronic cameras is that the display is of the emissive type. This requires the use of power to generate light. In turn this additional power demand requires a larger battery to power the light generating means. The light generating means often requires additional space. This is the case in the use of the liquid crystal display. The display provides switching elements which control the light. A separate light generating means is required to generate the light. 
     For simplicity, the invention as described does not include a printing device. It is understood that a printing device may be included without altering the present invention. Such a printing device is disclosed the commonly assigned U.S. patent application Ser. No. 08/951,017 filed Oct. 15, 1997, entitled “Camera With Microfluidic Printer” to McIntyre. 
     Liquid crystal displays (LCD) are, of course, well known in the art and are employed on numerous cameras. Liquid crystal displays use molecules in liquid crystalline phases to change the polarization of light. A user views an image on the display through a pair of cross polarizers which are part of the display. Polarizers can cause a significant amount of light loss degrading a viewed image. In order to overcome this problem, the LCDs use a significant amount of power. Also, it is difficult to get high levels of density variations which can effect the quality of the image on the display. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an electronic camera having a display which can be made small, requires low power levels, and can produce a high quality image. 
     This object is achieved by an electronic camera, comprising: 
     a) means for focusing an image of a subject at an image plane; 
     b) area image sensor means disposed at the image plane for receiving the image subject and producing a digital image having a plurality of pixels that represent the subject; 
     c) storage means coupled to the area image sensor for storing the digitized image of the subject; and 
     d) a display for displaying an image corresponding to the stored image, including: 
     i) field-driven solid phase particles disposed in a matrix that can change reflective density in the display in response to an applied electric field; and 
     ii) electronic addressing means including electrodes for applying voltages across the field-driven particles at particular locations corresponding to pixels in response to the stored image to produce a displayed image of the subject. 
     ADVANTAGES 
     This invention is particularly useful in that solid phase field-driven particle, when used in a display, operate in a reflective mode and use available light to illuminate the image. The use of available light imaging improves viewing the displayed image in areas of high ambient light. Also, it is a feature of the invention that it requires low power and does not require complicated optics found in prior displays. 
     In bright lighting, emissive displays fail to produce sufficient light output, and the ambient light severely washes out the generated light. The present invention produces superior images in high lighting areas. 
     This invention has the additional advantage in that non-emissive field-driven particle displays consume less power than traditional emissive displays. This reduction in power requirements reduces battery energy requirements. In turn this permits the use of batteries of lower power and smaller size. 
     This invention has the additional advantage that non-emissive displays have wider viewing angles than LCDs. 
     This invention has the additional benefit that non-emissive displays do not require a light generating device. This results in a significant reduction of display volume and thickness. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of an electronic camera having a non-emissive display in accordance with the present invention with the necessary electronics for operating the camera and the display; 
     FIG. 2 is a side view showing a user viewing the display on the electronic camera in accordance with the present invention; 
     FIG. 3 a  is a bottom view of a portion of the display in the electronic camera in the present invention; 
     FIG. 3 b  is a cross-sectional view of the interconnect portion of the display; 
     FIG. 4 a  is a cross-sectional view of the display in the electronic camera in the present invention showing the field driven particles in the white state; 
     FIG. 4 b  is a cross-sectional view of the display in the electronic camera in the present invention showing the field driven particles in the black state; and 
     FIG. 5 is a schematic of the driver electronic circuit in the display. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A block diagram the electronic camera  1  is shown in FIG. 1. A subject S is positioned in front of the imaging lens  3 . The camera  1  includes an area image sensor  20  arranged to coincide with the axis of the imaging lens  3 . A non-emissive display  38  is embodied in a panel type structure. An image of the subject is focused on the area image sensor  20 . Area image sensor  20  can be a full frame charge coupled device (CCD) or, alternatively, can be an interline device with, for example, photodiode pixels which are adapted to deliver charge to interline CCDs. The area image sensor  20  can also be fabricated by Complimentary Metal-Oxide-Semiconductor (CMOS) technology. Conventional electronic circuitry (not shown) is associated with the image sensor  20 . After the image sensor  20  receives light representative of the image of the subject S, the circuitry sets up, acquires, and transfers electronic signals from the area image sensor  20 . Such electronics are well known in the art and their description is omitted for clarity of discussion. 
     Logic and control unit  32  causes the area image sensor  20  to transfer electrical signals to signal processor  34 . The signal processor  34  will be understood to include that circuitry necessary for converting the area image sensor signals to electrical signals and includes gain control and analog-to-digital circuitry as well known in the art. The logic and control unit  32  can, of course, include a microprocessor as is well known to those skilled in the art. The signal processor  34  delivers, under the control of logic and control unit  32 , signals into a storage location in a temporary image memory  35  which can be either a floppy disk or semiconductor memory under the control of logic and control unit  32 . These signals, when stored, represent a digital image of the subject. The logic and control unit  32  causes the digital signals in memory to be applied to a display driver  37  which, in turn, applies signals to a non-emissive display  38 . The display driver  37  will be understood to include a digital-to-analog converter and formatting control which is appropriate for the type of display device as well known in the art. The non-emissive display  38  may be embodied as a liquid crystal display. As well understood to those skilled in the art, the logical and control unit  32  provides refresh signals to the non-emissive display  38 . It will be understood that the logic and control unit  32  can also deliver the digital image to an external device such as a personal computer. 
     The logic and control unit  32  is shown to include a central processing unit  32   a  which may be provided by a microprocessor chip. Execution memory  32   b  is also shown and is typically provided by random access memory (RAM). This memory is used for computation during image adjustment of the various parameters. As is well known to those in this art, the program memory  32   c  (typically ROM) can include conventional image processing algorithms for changing image resolution and the color content by so-called color management programs. A mode control unit  32   d , including a keyboard, a manual switch or a combination of both, permits a user to select the appropriate program by directly inputting interrupt signals into the central processing unit  32   a.    
     Many of such image processing algorithms have been implemented as commercially available packages such as: Photoshop (trademark of Adobe Systems Incorporated), Color Studio (trademark of Letraset), and PhotoMac (trademark of Avalon Development Group). For examples of color management systems including color transforms for changing color content such as contrast, brightness, and gamut, see U.S. Pat. Nos. 5,313,611 and 5,432,906, the disclosures of which are incorporated herein by reference. 
     A cross-sectional view of the electronic camera  1  is shown in FIG. 2. A subject S is positioned in front of the imaging lens  3 . The camera  1  includes an area image sensor  20  arranged to coincide with the axis of the imaging lens  3 . A non-emissive display  38  can be viewed, in this particular example, from the opposite side of lens  3  on the camera  1 . It is understood that the non-emissive display  38  can also locate at other positions on the camera  1 . 
     Electrical connection is shown in FIG. 3 a  shows a bottom view of a portion of the display. Row electrodes  240  and column electrodes  250  terminate in conductive pads  114 . Pin  110  having piercing point  112  is disposed in a rigid non-conductive matrix (not shown). The pin  110  is pressed into display  38  so that piercing points  112  are driven through conductive pads  114  at the termination of row electrode  240  and column electrode  250  into pin matrix  116 . The piercing action provides an electrical interconnection to the row electrode  240  and the column electrode  250 . 
     FIG. 4 a  and  4   b  shows a more detailed cross-sectional view of the non-emissive display  38 . The non-emissive display  38  is shown to comprise a plurality of field-driven particles  200 . In FIG. 1, the field-driven particles  200  are exemplified by bi-chromatic particles, that is, half of the particle is white and the other half is of a different color density such as black, yellow, magenta, cyan, red, green, blue, etc. The bi-chromatic particles are electrically bi-polar. Each of the color surfaces (e.g. white and black) is aligned with one pole of the dipole direction. The field-driven particles  200  are suspended in a fluid  210  such as oil which are together encapsulated in a microcapsule  220 . The microcapsules  220  are immersed in matrix  230 . Addressing electrodes are arranged in pairs with row electrode  240  above and column electrode  250  below the matrix in a pixelized fashion. One example of the materials for the electrodes is Indium Tin Oxide. Upon the application of a electric potential difference between each pair of addressing electrodes, a displacement electric field induced in the microcapsule  220  align the field-driven particles  200  to a low energy direction in which the ends of the dipole are respectively aligned to the electrodes of the opposite charges. The term “field-driven particle” will be understood to include a particle that is solid phase typically immersed in fluid in a microcapsule. FIG. 4 a  shows the particle  200  in the white state with a negative potential applied to the row electrode  240  and a positive potential applied to the column electrode  250 . FIG. 4 b  shows the particle  200  in the black state with a positive potential applied to the row electrode  240  and a negative potential applied to the column electrode  250 . 
     The state of the particle  200  is dependent on the applied field and not on the prior state of the particle  200 . The non-emissive display  38  may perform multiple write and erase cycles without effecting performance. The terms write and erase will be understood to be applying a voltage to set the particles to a foreground and background color respectively. A user may chose foreground and background colors. Details of the fabrication of the bi-chromatic dipolar particles and their addressing configuration are disclosed in U.S. Pat. Nos. 4,143,103, 5,344,594, and 5,604,027, and in “A Newly Developed Electrical Twisting Ball Display” by Saitoh et al p249-253, Proceedings of the SID, Vol. 23/4, 1982, the disclosure of these references are incorporated herein by reference. Another type of field-driven particle is disclosed in PCT Patent Application WO 97/04398. It is understood, however, that the present invention is compatible with many other types of field-driven particles that can display different color densities under the influence of an electrically activated field. 
     A detailed electronic diagram of the display driver  37  of FIG. 1 is shown in FIG.  5 . The display driver  37  includes row electrodes  240  and column electrodes  250  which are embodied by conductive stripes which are shown for convenience as lines. Furthermore, some of the electrodes will be transparent to permit the user to see through from the viewing side of the non-emissive display  38 . The row electrode  240  is driven by row driver  420  through interconnect  440 . The column electrode  250  is driven by column driver  410  through interconnect  440 . The intersection of each row and column electrode forms an addressable pixel  400 . For a more complete description of the display driver  37 , see the above referred commenly assigned patent application entitled “Addressing Circuitry for Display Device”. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
     PARTS LIST 
     S subject 
       1  camera 
       3  imaging lens 
       20  area image sensor 
       32  logic and control unit 
       32   a  central processing unit 
       32   b  execution memory 
       32   c  program memory 
       32   d  mode control unit 
       34  electrical signal processor 
       35  temporary image memory 
       37  display driver 
       38  non-emissive display 
       110  pin 
       112  piercing point 
       114  conductive pads 
       116  pin matrix 
       200  field driven particles 
       210  fluid 
       220  microcapsules 
       230  matrix 
       240  row electrode 
       250  column electrode 
       400  addressable pixel 
       410  column driver 
       420  row driver