GB2307126A - Video camera system - Google Patents

Abstract

A camera system for generating a composite image of a subject superimposed on a background, has a video camera 90 generating foreground images of the subject in front of a chromakey screen; a background image store 30 storing a plurality of background images, one of which is selected by the subject to form the background of the composite image; a matte generator for generating a matte from at least one of the foreground images; a chromakey image combiner for combining a current foreground image and the stored background image in accordance with the matte; a logic unit 20 controlling the operation of the system; and a flash unit 100 controllable by the logic unit to illuminate the subject prior to the capture of the current foreground image. The composite image is generated from the combination of the back ground image with the current foreground image in accordance with a matte that has been generated prior to illumination of the subject by the flash unit 100.

Description

CAMERA SYSTEM This invention relates to a camera system and in particular to a photo booth incorporating that system.

There are currently a large number of different photo booths available for use by the public. Of these, most tend to operate in a similar manner. Typical Photo Booths comprise a cabinet within which is provided a light source for illuminating the subject, an adjustable stool for seating the subject and a variety of curtain-like cloth backdrops. The user enters the booth, adjusts the stool and then places the requisite monies in a slot within the booth. As an option, one of the backdrops may be selected by the user and dragged into place. These photo booths are typically provided for the taking of passport photographs and the like.

Upon deposit of the requisite monies in the slot, a sequence is initiated that starts a timer running. After a predetermined quantity of time, a light flashes that indicates to the user that a photograph will shortly be taken. Shortly thereafter, a flash is illuminated and a photograph is taken. The process repeats itself until all required photos have been taken. The user then exits the booth and awaits the developing of the photographs. After a short period of time, typically around 5 minutes, the developed photographs are delivered from a slot in the front of the machine.

These systems suffer from a number of disadvantages in that the user is limited to a set number of plain backdrops, usually provided by curtains, and is required to wait around for the developing of the film. Similarly, as the device operates with photographic materials, the interior components of the machine are complex and expensive.

Steps have been taken to overcome these problems by providing a degree of choice to the user with regard to the type of backdrop that is selectable. United States Patent No 5,343,386, for example, describes a such a system.

This system incorporates so-called "chromakey" technology to superimpose an image of a subject over a computer generated backdrop. The particular chromakeying technology utilised by this machine is known from studio video production and will not be described in detail herein.

In use, the subject selects a backdrop from a variety of different possibilities and then seats himself in front of a blue chromakey screen. A camera provided within the body of the machine then captures an image of the subject and superimposes that image over the backdrop in accordance with conventional chromakeying techniques.

The image of the subject and selected backdrop is then passed to a high quality printer that prints the composite image onto a postcard.

This system is intended to provide users with novelty postcards which may be sent to friends or relatives. However, it exhibits a number of serious deficiencies that limit the quality of the produced image.

In particular, this system provides a light source that is utilised to light the subject and to front-light the backdrop (a blue screen). This lighting arrangement causes a reduction in contrast between the subject image and the backdrop image and hence a reduction in the quality of the matte produced from that image. This reduction in contrast is due to the fact that the foreground and the background are both lit by similar quantities of light. Similarly, prior to the capture of an image of the subject, a flash is fired in order to properly illuminate the subject. However, a large amount of this flash light is reflected by the highly reflective backdrop and causes poor resolution between the image of the subject and the image of the background.

In summary, a machine of this kind needs to provide a good lighting environment for both the backdrop and the subject. The abovementioned system provides a compromise between the two requirements that causes an overall reduction in quality of the final image.

In accordance with the present invention, there is provided a camera system for generating a composite image of a subject superimposed on a background, the system comprising: (a) a video camera for generating foreground images of the subject in front of a chromakey screen; (b) a background image store for storing a plurality of background images, one of said background images being selected by said subject to form the background of said composite image; (c) a matte generator for generating a matte from at least one of said foreground images; (d) a chromakey image combiner for combining a current foreground image and said stored background image in accordance with said matte; (e) a logic unit for controlling the operation of the system; and (f) a flash unit controllable by said logic unit for illuminating said subject prior to the capture of said current foreground images; wherein said composite image is generated from the combination of said back ground image with said current foreground image in accordance with a matte that has been generated prior to illumination of said subject by said flash unit.

Preferably, the logic unit reduces the gain of said camera immediately prior to firing said flash. In this way, it is assured that the camera is not overloaded by the light from the flash.

Alternatively or additionally, the logic unit may at least partially activate a shutter immediately prior to firing said flash to reduce the quantity of light entering said camera.

It is generally preferable to provide a chromakey screen that is backlit. This further improves the contrast between the foreground and background images and thus aids foreground/background discrimination and the generation of a suitable matte.

In one embodiment, the image store may be a hard disk, or in another embodiment, the image store may be a CD-ROM.

Preferably, the logic unit includes a control unit, said control unit comprising: (a) a timer; and (b) a synchronisation module for synchronising said timer with video signals generated by said camera; wherein upon instruction by said subject, the control unit first instructs said matte generator to store the last generated matte in a matte store, then instructs said camera to reduce its gain, and then instructs the flash unit to illuminate the subject.

Alternatively, the matte generator may include a delay circuit which delays said matte by at least one image so that each composite image is derived using said current foreground image and a previous matte.

Preferably, the camera system includes a high quality printer for printing said composite image. Obviously though, a soft copy, on disk for example, could also be provided.

Another aspect of the present invention may provide a method of operating a camera system, the method comprising the steps of: (a) generating a first foreground image of a subject in front of a chromakey screen; (b) generating a matte from said first foreground image; (c) reducing the gain of a camera used to generate said foreground image; (d) firing a flash unit to generate a second foreground image; (e) combining said second foreground image with a background image from a background image store in accordance with said matte to generate a final composite image.

It will be apparant to the skilled man that the abovementioned method may be performed with any of the embodiments of the camera apparatus according to the present invention.

In these aspects of the invention, the gain of said camera may be reduced by way of a shutter, operation of which reduces the quantity of light entering said camera.

As mentioned above, the method may further comprise the step of printing said final composite image with a printer.

The device according to the present invention thus provides an arrangement whereby both the background and the foreground are correctly lit so as to enable the generation of a sharply discriminated matte and a corresponding high quality final image. Advantageously, the first image provides an improved image of the chromakey screen and the flash enables the proper illumination of the subject in the second image.

Thus, both background and foreground are captured in an improved manner with respect to the prior art.

The present invention will now be described by way of example only and with reference to the appended drawings, in which: Figure 1 is a schematic illustration of a known chromakey apparatus; Figure 2 is a schematic illustration of the operating principles of the apparatus depicted in Figure 1; Figure 3 is a schematic illustration of the apparatus according to an embodiment of the present invention; Figure 4 is a schematic illustration of the chromakey apparatus used with the apparatus depicted in Figure 3; Figure 5 is a schematic representation of a number of video frames; and Figures 6A and 6B are a flow chart depicting the various stages in the operation of the apparatus depicted in Figure 3.

At this juncture, it is appropriate to devote a few paragraphs to a discussion of the basic principles of chromakey photography. Figure 1 shows such a prior art chromakey arrangement. A foreground camera 120 captures a real time image of a subject standing in front of a blue screen. A background camera 110 captures a real time image of a background scene in which it is desired to place the subject. Signals from the cameras 110, 120 are passed to a background processor 130 and a foreground processor 140. These processors 130, 140 translate analogue signals from the cameras 110, 120 to digital signals for subsequent processing and mixing. Connected to the foreground processor 140 is a Matte Generator 150 that generates a matte. The matte is basically a map of the foreground image showing which parts of that image belong to the subject and which belong to the blue screen.

Digital signals from the processors 130, 140 are then passed to a switching unit 160 which combines the background and foreground signals in accordance with instructions provided by the matte that has been produced by the matte generator 150.

A combined foreground/background composite chromakey image is outputted from the switch 160. These techniques have been employed for many years in the television field and have been commonly used to superimpose a weather reader, for example, on an image of a weather map.

Skilled readers will of course realise that chromakey techniques were originally developed for use with analogue technology. The colour blue was found to be a particularly useful chromakey colour for use with analogue colours. Digital systems, on the other hand, may use any colour as the chromakey colour. In this connection, it should be noted that the term "blue screen" (whilst being generally known throughout the field as a chromakey screen) does not necessarily refer to a blue screen.

Figure 2 illustrates schematically the known chromakey process. A foreground image FI is captured by the foreground camera 120. The foreground image comprises a subject image SI and a chromakey screen image CS. Similarly, a background image BI is captured by the background camera 110. A matte M is generated from the foreground image FI, and comprises a black area CS that corresponds to the chromakey screen and a white area SI that corresponds to the subject image. The foreground image FI is then combined with the background image BI by the switch 160 in accordance with the matte M. A final composite image showing the subject image superimposed on the background may then be outputted from the switch 160.

With reference to Figure 3, an embodiment of the present photo booth 10 includes a computer 20, an image store 30, a high quality printer 40, a monitor 50, external entertainment devices generally referenced as 60, a money slot 70, an interface unit 80, a camera 90 and a flash unit 100. The booth also includes a blue screen (not shown) in front of which may be seated a subject who wishes to have their image reproduced.

The image store 30 may comprise a standard hard disk, for example, or may comprise a solid state memory. The image store is preloaded with a variety of different images, each of which may be used as a backdrop in the resulting image of the subject. It will be noted that alternative image storage devices are also conceivable, such as a CD-ROM or other optical or magnetic storage media. Indeed, any type of storage media is usable. In addition, it will be noted that the image store 30 is illustrated as being external to the computer 20. Obviously, the image store 30 may equally well be housed within the computer 20 as is usually the case.

It will also be apparent that the above list of booth components is not an exhaustive list and that other components may also be provided.

The booth 10 adopts the standard shape to which consumers have become familiar. Namely, it comprises a large cabinet within which is provided an aperture.

The aperture has a stool placed therein for seating the subject. Prior Art booths typically provided a screw mounted stool that could be wound up and down to manually adjust the height of the subject prior to the taking of a photograph. As an advantageous alternative, however, the camera 90 may be mounted on a motor driven mount that is adjustable by the user so that their image is placed in the centre of the final image.

The external entertainment devices 50 may comprise a high resolution monitor and a pair of stereo loudspeakers so that a high quality movie or advertisement film may be displayed to passers-by. As an option, the external devices 50 may be configured to show an image of the person inside the booth 10 when it is in use.

The money slot 60 comprises a standard cash receiving device adapted for use with the particular currency of the country in which the booth 10 is to be used. The slot 60 senses the insertion of coins and can also detect the attempted insertion of counterfeit coins and the like. A variety of such devices are currently offered for sale by a variety of different companies.

The interface unit 80 comprises a switching box that allows the user to position the camera 90, if that option is provided, and select the background against which they are to be depicted. The interface unit 80 may also provide a number of other functions. As with the other unit 60 discussed above, such interface units 80 are commonly available from a variety of different manufacturers.

The monitor 50 is mounted within the booth 10 and serves to relay a real-time image of the subject placed within the selected background. The monitor is also used for display of messages to the subject which may prompt the subject to select a particular function or operation. These messages are preferably generated by the computer in response to instructions contained within a suitable computer program.

The camera 90 preferably comprises a CCD R-G-B (red, green, blue) camera which provides a high quality image of the subject seated in front thereof.

Advantageously, the blue screen mentioned above may be back lit by a suitable light source to provide a high contrast environment for capturing the image of the subject.

Once again, a variety of different cameras are currently available from a variety of different manufacturers.

The flash unit 100 may be under direct control of the computer 20 so that the flash 100 may accurately be fired at an appropriate point in the image-rendering process.

As mentioned above, it has been noted that the use of a flash with a blue screen causes a reduction in contrast between the subject and the screen in front of which they are seated. This contrast reduction, caused by a large amount of reflected light, can lead to a reduction in quality of any matte produced from that image. Thus, whilst the flash has correctly illuminated the subject so that a good foreground image may be obtained, it has also generated a large amount of reflected light which can lead to an over exposure of the image. This~over exposure causes a decrease in background/foreground discrimination in the matte and thus causes a reduction in quality of the final composite image.

In contrast, the flash 100 is fired by the computer 20, moments after a matte has been stored, so that the flash does not affect the quality of the background/foreground discrimination.

Figure 4 illustrates an exemplary schematic of one embodiment of the present invention. With reference to Figure 4, the apparatus comprises a foreground processor 170, a control unit 180, a matte generator 190, a matte store 200 and a chromakey switch 210. Advantageously, all of these components may be provided on a single printed circuit board for use in the computer 20.

The user, when prompted for a response by the computer 20, presses a suitable button on the interface unit 80 to signify that they wish a print to be taken of their combined image. This signal is transmitted to the control unit 180 which incorporates a synchronisation module therein. The control module 180 synchronises an internal timer with the video signals received from the camera 90.

At a suitable time interval after the user has signified their wish to print a composite image, the control unit instructs the matte generator 190 to cease generating mattes and dump its last generated matte to a matte store 200. Simultaneously, the control unit 180 decreases the gain of the camera's built-in amplifier. The control unit 180 then fires the flash 100 and a flashed foreground image is recorded by the camera 90. This foreground image is processed by the foreground processor 170 and passed to the switch 200 in the normal way. The switch then combines the flashed image with an image from the image store under control of the matte that has been previously stored in the matte store 200.

As will immediately be appreciated, it is apparent that the flashed foreground image is combined with a background image under control of a matte that is not generated from a flashed image and thus, the matte has an improved contrast with respect to a matte produced by a prior art arrangement. In this way, a final composite image is produced that alleviates the problems associated with the prior art.

It will also be appreciated that a variety of different methods may be adopted to vary the gain of the camera 90. If the camera 90 is not provided with an in-built amplifier, then a shutter may be employed in front of the camera to reduce the quantity of light recorded by the camera. The shutter would, of course, be under the control of the control unit 180 for proper synchronisation and could even be provided with a camera 90 that does have a built-in amplifier.

Figure 5 illustrates a schematic time representation of a video signal used with the present invention. A series of video frames F1, F2, F3 etc. are shown separated over time. These frames have been generated by the camera 90. The user notifies the booth, at some point before the first frame F1, that he requires a hard copy of any displayed combined image (generally indicated at "ACQUIRE IMAGE" in Figure 5).

At a suitable juncture between frames, the control unit 180 instructs the matte generator 190 to store the most recent matte in the matte store 200 (indicated at point I in Figure 5). The control unit 180 then lowers the gain of the camera 90 by way of a shutter or otherwise (indicated at point II in Figure 5). At the start of the next frame F2, the flash is fired (indicated at point III in Figure 5). The flashed image is then transferred to the switch 210 in the normal way (indicated at point IV in Figure 5).

The system may then be reset, ready for a second and subsequent capture of the subject image (indicated at point V in Figure 5).

Figures 6A and 6B are a flow chart depicting the various stages of the present technique.

With reference to Figures 6A and 6B, upon powering up the booth 10 the money slot, external devices and interface unit are initialised and prepared for operation (as shown by a step 300). Then, as an option mentioned above, an external video may be played on the external devices 50 to attract potential customers (as shown by a step 310). The computer 20 interrogates the money slot 60 to ascertain whether a user has entered the booth and attempted to use it (as shown by a step 320).

If the requisite monies are detected, the computer 20 instructs the booth to allow the user to select a background by way of the interface unit 80 and its buttons (as shown by a step 330 and a step 340). Once a background is selected, that background image is loaded from the image store 30 (as shown by a step 350) and an image of the subject from the camera 90 is displayed superimposed upon the chosen background image (as shown by a step 360). The user is then prompted as to whether they are happy with the image and wish to be provided with a hard copy (as shown by a step 370). If the user is not happy with the image, then they are provided with an option to return and select an alternative background image from the image store (as shown by a step 380).

Once the user has selected a background that meets their requirements, they signify their desire to produce a hard copy by activating the interface unit 80 when prompted by the computer 20 (as shown by a step 370). The computer 20 then starts a timer and generates some graphic that is displayed on the monitor 50 and notifies the user that an image is soon to be captured (as shown by a step 380). Typically, a preferred graphic is in the form of a bar that decreases in length as it moves across the monitor 50. The computer then synchronises its timer with the frames of the video signal from the camera 90 (as shown in a step 390). As shown in figure 4, a matte is generated and stored (as shown in a step 400), shortly after which the gain of the camera 90 is reduced and the flash 100 is fired (as shown in a step 410).The flashed image of the subject is stored (as shown in a step 420) and may then be combined with the chosen background in accordance with the stored matte (as shown in a step 430). The composite image is displayed to the user, stored and the gain is reset (as shown in steps 440, 450).

The user is then prompted as to whether they require the capture of another image (as shown in a step 460). If one image is sufficient, the user answers in the negative and the stored composite image is printed via the printer 40 (as shown in a step 470). Printing may occur relatively swiftly, thereby alleviating one of the disadvantages of prior art photography based systems. The booth 10 then resets itself and returns to point B on Figure 6A.

If the user requires a second image, then the money slot 60 is activated again to sense whether the requisite monies have been inserted (as shown in a step 480).

The user is then provided with a choice as to whether they wish to be superimposed on the same background image or a different background image (as shown by a step 490). If they wish to retain the same background, then the booth 10 is rest to point D on Figure 6A. If not, then the booth 10 is reset to point C on Figure 6A.

As an option, a further step may be provided that allows the user to adjust the attitude of the camera 90 to ensure that their image is correctly placed within the final image.

It will be understood of course, that one embodiment of the present invention has been described above by way of example only and that modifications may be made within the scope of the appended claims.

For example, it will be apparent to the skilled man that this system may be yet further simplified by incorporating a time delay into the combination of the matte with the background and foreground images. In this way, a flashed foreground image would be combined with a matte that had not been subject to a flash, the matte having been generated some time prior to the flashed image. Whilst such an arrangement would be simpler than the technique described above, there would be a disadvantage in that the real time display, prior to any requested image capture, of the subject's image superimposed over the selected background would be subject to a dragging effect caused by the delayed matte.

Claims (19)

1. A camera system for generating a composite image of a subject superimposed on a background, the system comprising: (a) a video camera for generating foreground images of the subject in front of a chromakey screen; (b) a background image store for storing a plurality of background images, one of said background images being selected by said subject to form the background of said composite image; (c) a matte generator for generating a matte from at least one of said foreground images; (d) a chromakey image combiner for combining a current foreground image and said stored background image in accordance with said matte; (e) a logic unit for controlling the operation of the system; and (f) a flash unit controllable by said logic unit for illuminating said subject prior to the capture of said current foreground images; wherein said composite image is generated from the combination of said back ground image with said current foreground image in accordance with a matte that has been generated prior to illumination of said subject by said flash unit.

2. A camera system according to Claim 1 wherein said foreground image is superimposed upon said background image without firing said flash unit thereby to provide the subject with a trial view prior to any image capture.

3. A camera system according to Claim 1 or Claim 2 wherein said logic unit reduces the gain of said camera immediately prior to firing said flash.

4. A camera system according to any one of Claims 1 to 3 wherein said logic unit at least partially activates a shutter immediately prior to firing said flash to reduce the quantity of light entering said camera.

5. A camera system according to any one of Claims 1 to 4 wherein said chromakey screen is backlit.

6. A camera system according to any one of Claims 1 to 5 wherein said image store is a hard disk.

7. A camera system according to any one of Claims 1 to 5 wherein said image store is a CD-ROM.

8. A camera system according to any one of Claims 1 to 7 wherein said computer includes a control unit, said control unit comprising: (a) a timer; and (b) a synchronisation module for synchronising said timer with video signals generated by said camera; wherein upon instruction by said subject, the control unit first instructs said matte generator to store the last generated matte in a matte store, then instructs said camera to reduce its gain, and then instructs the flash unit to illuminate the subject.

9. A camera system according to Claim 8 wherein said control unit additionally instructs said matte generator to cease generating mattes prior to instructing the matte generator to store the last generated matte.

10. A camera system according to any one of Claims 1 to 7 wherein said matte generator includes a delay circuit which delays said matte by at least one image so that each composite image is derived using said current foreground image and a previous matte.

11. A camera system according to any one of Claims 1 to 9 comprising a printer for printing said composite image.

12. A photo booth comprising a camera system according to any of the preceding claims.

13. A method of operating the camera system according to any preceding claim, the method comprising the steps of: (a) generating a first foreground image of said subject in front of said chromakey screen; (b) generating a matte from said first foreground image; (c) reducing the gain of said camera; (d) firing said flash unit to generate a second foreground image; (e) combining said second foreground image with a background image in accordance with said matte to generate a final composite image.

14. A method of operating a camera system, the method comprising the steps of: (a) generating a first foreground image of a subject in front of a chromakey screen; (b) generating a matte from said first foreground image; (c) reducing the gain of a camera used to generate said foreground image; (d) firing a flash unit to generate a second foreground image; (e) combining said second foreground image with a background image from a background image store in accordance with said matte to generate a final composite image.

15. A method according to Claim 13 or Claim 14 wherein the gain of said camera is reduced by way of a shutter, operation of which reduces the quantity of light entering said camera.

16. A method according to any one of Claims 13 to 15 further comprising: (f) printing said final composite image with a high quality printer.

17. A camera system substantially as hereinbefore described and as shown in Figures 2 to 6 of the appended drawings.

18. A photo booth substantially as hereinbefore described and as shown in Figures 2 to 6 of the appended drawings.

19. A method of operating a camera system as hereinbefore described and as shown in Figures 6A and 6B of the appended drawings.