WO1996031051A1

WO1996031051A1 - Passive transceiver for electronic still cameras

Info

Publication number: WO1996031051A1
Application number: PCT/US1996/004150
Authority: WO
Inventors: Werner Metz; Richard G. Egan
Original assignee: Polaroid Corp
Current assignee: Polaroid Corp
Priority date: 1995-03-30
Filing date: 1996-03-27
Publication date: 1996-10-03
Anticipated expiration: 1997-09-30

Abstract

Electronic imaging system for bi-directional communication is disclosed wherein a base unit communicates with at least one electronic still camera using a passive transmission scheme. The base unit transmits a carrier signal encoded with base information to an electronic still camera. The electronic still camera then decodes that information and responds appropriately. When an image is captured by the electronic still camera, the image signal is modulated into the carrier signal then retransmitted from the camera to the base unit where the image can be decoded and stored.

Description

Passive Transceiver for Electronic Still Cameras

Background of the Invention

The present invention is directed to video communication systems and, more particularly, to an improved communication system for use with electronic still cameras wherein a passive transceiver is mounted in an electronic still camera for communicating with a base unit which is remotely located with respect to the electronic still camera.

It is well known in video communication to have a video camera connected via a length of cable to a video receiver. Such a video receiver may be a television receiver or other such video receiving apparatus which displays or transmits a video image captured by the video camera. Such an arrangement allows the video camera to have a reduced physical size and weight since components associated with display and transmission of the video image need not be part of the video camera. The cable presents a mechanical limitation though. The video camera is restricted to movement within a radius of the receiver fixed by the length of the cable.

To eliminate this inconvenience, wireless video cameras were developed which allow a video camera to operate remotely from a receiving system without a need for mechanical attachment. In such video cameras, an output signal from the video camera, which can include both an audio and video signal, is transmitted via radio frequency ("RF") transmission to the receiving system. An example of such a video camera is found in United States Patent No. 5,264,935 entitled "System for Wireless Transmission and Reception of a Video Signal and Corresponding Audio Signal" issued to Yasuhisa Nakajima on November 23, 1993. The video camera described therein uses an active transmitter to transmit via RF transmission audio and video signals and, therefore, add additional electronics to the video camera including a local oscillator, a phase lock-loop and a power amplifier as well as transmission circuitry associated with a transmission scheme of the camera. These added electronics require circuit board space in the video camera thus increasing the size of the camera as well as increased power demands.

Batteries as a source of power for video cameras are common today. These batteries must have a significant lifespan in order to make them useful. Adding the power consumption of an RF transmitter to the video cameras increase power needs thereby requiring higher capacity and, therefore, physically larger and heavier batteries.

In the case of an electronic still camera being part of the video camera, it is often useful to review an image again after it has been captured even if it has already been transmitted to be permanently recorded. And, if the receiving system has reached capacity an appropriate status signal should be sent to the video camera. To accomplish this the receiving system itself must transmit and the video camera must now include additional receiving circuitry further adding to space and power consumption considerations while increasing a cost of manufacturing the video camera.

Summary

The aforementioned and other objects are achieved by the invention which provides, an extremely versatile electronic imaging system for bi-directional communication between a base unit and at least one electronic still camera. The electronic still camera comprises an image acquisition means, a camera reception means, an image processing means and camera transmission means. While the base unit comprises a base transmission means, base reception means, and a base processor means.

The electronic imaging systems allows multiple electronic still cameras to communicate with a single base unit, thereby allowing bi-directional communication between each camera and the base unit.

The electronic still camera captures image-bearing light from a scene through the image acquisition means and transform the image-bearing light into an electronic signal. This is often performed by utilizing a charge coupled device ("CCD") through an analog to digital converter to create a digitized electronic image signal representative of the scene.

In order to transmit the electronic image signal to the base without need of substantial electronic devices in the electronic still camera, the electronic still camera utilizes a carrier signal transmitted from the base unit. The camera reception means receives the carrier signal and passes that carrier signal onto the camera processing means. The carrier signal is encoded with base information such as status information transmitted from the base unit or even image data. The camera -processing means then decodes the base information from the carrier signal and responds accordingly. For example, if the base information is image data then the electronic still camera would project image into the view finder of the electronic still camera. The camera processing means then remodulates the carrier signal to include the electronic image signal thereby forming a remodulated signal. Remodulation scheme can be performed in any various ways. But is generally done so as not to alter the fixed frequency of the carrier signal.

The camera transmission means then retransmits the remodulated carrier back to the base unit.

The base reception means receives the remodulated signal from the electronic still cameras and passes it onto the base processor means. The base processor means processes the remodulated signal to decipher the image information therefrom. The base processor means may then store the image locally or then can transfer the image to a remote location via any various means such as cellular telephone or other means of communication.

The base unit also comprises the base transmission means which transmits the carrier signal encoded with base information. The encoding can be performed on the carrier signal which has a fixed frequency by using amplitude modulation

In further aspects, the invention provides methods in accord with the apparatus described above. The aforementioned and other aspects of the invention are evident in the drawings and in the description that follows.

Brief Description of the Drawings

The foregoing and other objects of this invention, the various features thereof, as well as the invention itself, may be more fully understood from the following description, when read together with the accompanying drawings in which:

Figure 1 shows the block diagram of the electronic imaging system in accordance with the invention;

Figure 2 shows a more detailed block diagram of the receiver and the transmitters in both the electronic still camera and the base unit of Figure 1 ;

Figure 3A is a graph of a typical carrier signal transmitted from the base unit of the invention; and

Figure 3B is a graph of a sub part of the carrier signal of Figure 3 A magnified to show frequency shift keying used by the camera of the invention.

Detailed Description

While the present invention retains utility within a wide variety of photographic devices and may be embodied in several different forms, it is advantageously employed in connection with an electronic still camera. Though this is the form of the preferred embodiment and will be described as such, this embodiment should be considered illustrative and not restrictive.

Electronic imaging cameras for recording still images are in common use today. Such an electronic still camera 10, as show in Figure 1, collects image-bearing light 14 reflected off of a subject 12 through an objective lens 16 and shutter 18 in a well known manner. The image-bearing light then impinges upon a two-dimensional photosensitive array 20 such as a high resolution charge coupled device ("CCD"), a charge injected device ("CID"), or other photosensitive semiconductor device. Charge accumulated on the two-dimensional photosensitive array 20 is then transferred to an analog-to-digital converter 22 which converts the accumulated charge to a digital signal representative of an image represented by the image-bearing light 14. The digital signal is then passed to a digital signal processor ("DSP") 24 which performs image correction. For example, the DSP 24 can perform remapping of a tone scale of the image. The DSP 24 then transfers the image to random access memory ("RAM") 28 for temporary storage.

When the operator desires to transfer the image to the base unit 38, the operator initiates such an action through a user interface (not shown) on the electronic still camera 10. A microprocessor (OP") 26 retrieves the image from RAM for encoding it into a carrier signal 40.

The carrier signal 40 originates from the base unit 38. The base unit 38 transmits the carrier signal 40 at a fixed frequency. In the preferred embodiment, the transmission is in the Instrument, Scientific, and Medical ("ISM") band thus having a fixed frequency in the range of 902 - 928 MHz or 2.4 - 2.48 Ghz. Those skilled in the art will realize that transmission is not limited to those frequency ranges though. The base unit 38 generates the carrier signal 40 using a local oscillator, a phase locked loop, a power amplifier and other electronic components well-known in the art.

These components add additional power consumption requirements to the base unit 38 but the base unit 38 has access to a strong power source, for example a car battery or alternating current, making the additional power drain inconsequential.

The camera 10 uses a passive transciever to receive and retransmit the carrier signal in a re-modulated form with significantly altering the carrier signal itself. The carrier signal 40 is picked up by an antenna 32 in the electronic still camera 10 and transmits the carrier signal 40 to a receiver 42. The receiver 42 is tuned to a self- generated carrier frequency thereby substantially increasing a signal-to-noise ratio of the electronic still camera 10 at the receiver by performing coherent detection.

The carrier frequency is self-generated in the receiver 42 since the receiver 42 accepts a broad band of signals relative to a fixed frequency and modulates any signal having sufficient energy with an image as is later herein described. In this way the electronic still camera 10 does not have to be pre-programmed with a fixed frequency of a carrier signal since it accepts any carrier signal encountered which falls in a predetermined range, or bandwidth.

The carrier signal 40 is modulated to transfer information from the base unit 38 to the electronic still camera 10. The modulation, for example, can be amplitude modulation to transfer various base information from the base unit 38 to the electronic still camera 10. The base information may include, for example, status information such as the storage capacity in the base is nearing full capacity or the base information can be an image stored in the base unit 38 and is later transferred to the electronic still camera 10 to allow viewing of the image by the user. The latter is accomplished by displaying the image on a liquid crystal display ("LCD") in the electronic still camera 10, or other such display screen well known in the art.

Having received the carrier signal 40, the microprocessor 26 decodes the modulation of the carrier signal and responds accordingly. For example, if an image was transferred the image is displayed on the LCD. If a status is sent such as full capacity, the status is displayed on the electronic still camera 10 and transmission of additional images to the base unit 38 is inhibited such that no additional images will be transferred to the base unit 38.

Upon initiation by user, the electronic still camera 10 captures image-bearing light

14 to form an image in electronic form, as previously described. The image can then be viewed on the LCD, discarded or transmitted to the base unit 38 for storage. If the latter is chosen, the microprocessor 26 remodulates the carrier signal 40 to include image data and any other accompanying information which needs to be sent to he base unit. Such accompanying information can include, for example, camera status information, audio annotations, etc.

The remodulated signal is then passed to a transmitter 30 which transmits the remodulated signal out via the antenna 32. The remodulated signal 34 is sent back to the base unit 38 where it is received by another antenna 36 on the base unit 38.

Since the aforementioned transmission is a low power transmission, there is a limited distance that must be maintained between the base unit 38 and the electronic still camera 10. The limited distance is depicted as "D" in Figure 1 and has a maximum range of approximately thirty meters indoors. One skilled in the art will realize that this distance is dependent upon energy in the output signal and is not a specific limitation on the invention itself.

A single base unit 38 can be used with multiple cameras. A practical example of such a use is for multiple photographers to go to a scene with a single base unit stationed in an automobile. Each photographer would have a separate electronic still camera 10 and would be able to capture images of the scene simultaneously. Each electronic still camera 10 has a unique code number, or personal identification number ("PIN"), which is encoded into the re-modulated signal to identify a source of the re¬ modulated signal. In operation, the base unit 38 initiates communication with each electronic still camera 10 by establishing, through a handshaking exchange well- known in the art, a unique communication protocol that the base unit 38 will maintain with the electronic still camera 10 thereby opening a channel with each electronic still camera 10. The protocol can be a unique frequency, a psuedo-random frequency hopping sequence, or psuedo-random discrete sequence for each electronic still camera 10. Once channels are established, the base unit 38 repetitively polls each camera for a sequential, cummulative interchange of data as will be described hereinafter.

Figure 2 illustrates in more detail the transmission and receiving functions of the base unit 38 and the electronic still camera 10. The base unit 38, as previously described, encodes on a carrier signal 40 base information which can include status or instructional information from a user interface 66. The carrier signal is then passed to a transmitter 68 which transmits the carrier signal 40 through an antenna 36.

The carrier signal 40 is received through the camera antenna 32 after which it is amplified through a signal amplifier 44 and passed onto a demodulator 46. Optionally, a clipper circuit (not shown) can follow the signal amplifier 44 to separate modulation from the carrier signal 40. Irrespective of whether the modulation is separated from the carrier signal or not, the demodulator 46 then extracts the modulated base information and passes the base information onto the microprocessor 26. Substantially simultaneously therewith, the microprocessor 26 can also be receiving an image signal 48 from the image acquisition portion of the electronic still camera 10 as previously described.

Upon initiation by the user to transmit the image signal 48, the microprocessor 26 transfers the image signal 48 and the carrier signal 40 to a modulator 50 which encodes the image signal 48 into the carrier signal.

The modulator 50 utilizes a key 52 to encode the carrier signal with the image. In the preferred embodiment, frequency shift keying is utilized to encode the image. In this type of keying, a frequency shift is used to distinguish between a logical zero and a logical one as is later herein described in detail. In an alternative embodiment, phase shift keying can be used as the key 52. In phase shift keying, a phase of the carrier signal 40 is shifted by 180° to differentiate between a logical zero and a logical one. The electronic still camera 10 can then encode the carrier with image data. One skilled in the art will realize that various other keying methods such as amplitude shift keying for example can also be used.

Along with image data, the modulator 50 also includes hand shaking protocol, status and other camera information received from an interface 54. The modulator 50 then retransmits the remodulated signal 34 through the antenna 32 where it is picked up by the base unit 38 at its antenna 36.

The remodulated signal 34 passes into the base unit 38 to a receiver 60 which differentiates the remodulated signal 34 from other electromagnetic interference by isolating the remodulated signal at the fixed frequency of the carrier signal 40. The receiver 60 then demodulates the remodulated signal and passes the remodulated signal 34 to a microprocessor 62 which decodes the remodulated information from the remodulated signal 34 . In the case that the information from the electronic still camera 10 is an image, the image is then passed onto a storage device 64 such as solid state memory, a hard disk or other such device.

The base unit 38 can also be made to manually or automatically retransmit the image date to a distant site such as a newsroom for a newspaper photographer. The base unit 38 would retransmit the image via cellular or conventional telephone communications.

Figures 3A and 3B graphically depict the remodulated signal 34 and an magnified section thereof, respectively. The remodulated signal 34 shown in Figure 3A has not had the modulation which was placed in the carrier signal 40 by the base unit 38 subtracted by a clipper circuit as previously herein described. Therefore, the remodulated signal 34 shows how the carrier signal 40 is amplitude modulated to form an envelope 70 which transmits the base information to the electronic still camera 10. The electronic still camera 10 then encodes image information, for example, into the carrier signal 40. A section 74 of the remodulated signal 34 is magnified and is shown in Figure 3B. The ordinate has units of time but also corresponds to the section 74 of the remodulated signal 34 enclosed by dashed lines in Figure 3A.

The frequency shift keying of the preferred embodiment is used in this example.

The carrier signal 40 is time segmented in intervals of duration T where each duration T designates a single bit of information. Therefore, the duration T is inversely proportional to a data rate to the photographic system.

In the binary system of the preferred embodiment there are two frequencies defined where each corresponds to a logical zero or one. For example, a low frequency, ft, can be defined as being a logical zero and a high frequency, f₂₍ in the interval T can be a logical one. The frequency transition occurs after an end of an interval T thus allowing differentiation of consecutive zeroes or ones. The segment 74 of the remodulated signal 34 would then be decoded as the following logical sequence:

0 1 0

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims

1. An electronic imaging system for bi-directional communication between a base unit and at least one electronic still camera, the at least one electronic still camera comprising image acquisition means for electronically capturing image-bearing light from a scene and transforming the image-bearing light into an electronic image signal; camera reception means for receiving a carrier signal encoded with base information; camera processing means in electrical communication with the camera reception means for decoding the base information from the carrier signal, and for re-modulating the carrier signal to include the electronic image signal thereby forming a re¬ modulated signal; and camera transmission means in electrical communication with the camera processing means for re-transmitting the re-modulated carrier signal, the base unit comprising base transmission means for transmitting the carrier signal modulated with the base information; base reception means for receiving the re-modulated signal from the at least one electronic still camera; and base processor means for processing the re-modulated signal so as to decipher an image therefrom.

2. The electronic imaging system of claim 1 wherein the base unit further comprises a local oscillator which establishes a fixed frequency of transmission of the carrier signal and the electronic still camera does not have a local oscillator.

3. The electronic imaging system of claim 1 wherein the carrier processing means modulates the carrier signal using frequency shift modulation.

4. The electronic imaging system of claim 1 wherein the base transmission means transmits the carrier signal at a fixed frequency and the camera reception means receives only signals transmitted at the the fixed frequency.

5. The electronic imaging system of claim 1 wherein the base transmission means transmits the carrier signal using amplitude modulation to encode the base information.

6. The electronic imaging system of claim 1 wherein the camera processing means re-modulates the carrier signal using frequency shift keying to encode the electronic image signal.

7. The electronic imaging system of claim 6 wherein the camera processing means re-modulates the carrier signal using a first frequency to define a logical zero and a second frequency to define a logical one.

8. The electronic imaging system of claim 1 wherein the camera processing means re-modulates the carrier signal using phase shift keying to encode the electronic image signal.

9. The electronic imaging system of claim 8 wherein the camera processing means re-modulates the carrier signal using a first phase to define a logical zero and a second phase shifted one hundred eighty degrees from the first phase to define a logical one.

10. The electronic imaging system of claim 1 wherein the camera reception means is adapted to receive signals across a wide bandwidth and to remodulate assume that selected ones of the signals are the carrier signal based on a quantification of signal energy.

11. The electronic imaging system of claim 1 wherein the electronic still camera further comprises a liquid crystal display for viewing an image conveyed by the base information.

12. The electronic imaging system of claim 1 wherein each of the at least one electronic still camera a unique code number which is encoded into the re¬ modulated signal to identify a source of the re-modulated signal.

13. The electronic imaging system of claim 1 wherein the base unit establishes a channel with each of the at least one electronic still camera and repetitively polls each camera for a sequential, cummulative interchange of electronic image signals.

14. An electronic imaging system for bi-directional communication comprising a base unit and one or more electronic still cameras where the base unit transmits a carrier signal modulated with base information and the one or more electronic still cameras are adapted to receive the carrier signal, the one or more electronic still cameras decode the carrier signal and respond to instructions contained therein; upon actuation of an electronic still camera to capture an image, the image is modulated into the carrier signal to form a re¬ modulated carrier signal which is re-transmitted, the base unit is adapted to receive the re-modulated carrier signal which that base unit then decodes the modulation of the re-modulated carrier signal to decipher the image therefrom.

15. The electronic imaging system of claim 14 wherein the one or more of electronic still cameras are passive transmitters which re-modulate the carrier signal without altering a frequency of the carrier signal.

16. The electronic imaging system of claim 15 wherein the one or more of electronic still cameras remodulate the carrier signal using frequency shift modulation

17. The electronic imaging system of claim 14 wherein the one or more of electronic still cameras remodulate the carrier signal using phase shift modulation

18. A method for bi-directional communication between a base unit and at least one electronic still camera comprising transmitting a carrier signal at a fixed frequency by the base unit; receiving at least one electronic still camera the carrier signal and decoding the carrier signal to respond to instructions contained therein; capturing an image and translating the image into an electronic image signal; modulating the electronic image signal into the carrier signal to form a re¬ modulated carrier signal which has a frequency substantially equivelant to the fixed frequency; re -transmitting the re-modulated signal; and receiving at the base unit the re-modulated carrier signal and decoding from the the re-modulated carrier signal the electronic image signal to decipher the image therefrom.

19. The method of claim 18 further comprising a step of modulating the carrier signal in the base unit with base information prior to transmission of the carrier signal to the at least one electronic still camera. 0. The method of claim 19 wherein said base information is modulated using amplitude modulation.