This invention relates to autostereoscopic image receiving, recordal, and display. Autostereoscopic three dimensional display systems are known wherein multiple images of an object are recorded by multiple cameras arranged at varying positions around the object. The recorded multiple images are displayed by recreating each image on a display that makes each image appear to emanate from a different position, so that a viewer perceives a three dimensional image to be present.

Such image recording technology does, however, have the drawback that the provision of multiple cameras is costly, and that the relative positions of the cameras must be accurately maintained in order to provide an acceptable set of images. Employing multiple cameras also makes recordal of images outside of a studio difficult to achieve as systems are generally bulky and non-portable. A further problem with such devices is that they require complex circuitry for device synchronisation and image storage, even for real-time applications.

Accordingly, there is a need to provide a camera which is capable of recording multiple images of different views of an object, yet which is capable of being portable and has a reduced cost.

According to the present invention there is provided a camera comprising: an imaging lens; a shutter disposed adjacent to the imaging lens, the shutter comprising a plurality of individually activated apertures; image receiving means for receiving an image provided by light passing through the imaging lens and shutter; and shutter synchronising means for synchronously activating the image receiving means with each of the apertures in turn for a period long enough to enable the image receiving means to receive an image, to produce

thereby a series of images of an object from different viewpoints.

The shutter apertures must be light transmissive, and preferably they are rectangular, dispersed laterally, and adjacent to one another. Preferably there are more than two apertures.

The image receiving means may receive images in the visible or non-visible spectra, or even in both.

The image receiving means may be a high speed CCD device. Preferably, the CCD device should have a frame rate of at least N x 50Hz, where N equals the number of shutter apertures. The shutter may be a high speed spatial light modulator such as a ferroelectric liquid crystal device. In real-time applications, the imags receiving means output will be transmitted directly to a display. This may require the provision of additional control circuitry to synchronise the camera with an autostereoscopic system. Alternatively, the image receiving means output may be recorded in an electronic storage device or on high speed recording media.

Additional optical devices may be positioned between the object and the shutter and imaging lens arrangement in order to produce an image of adequate size and clarity for the type of receiving means being employed. To provide a colour camera, the image receiving means may be a high frame rate colour CCD. Alternatively, 3 CCDs, each covered by a primary colour filter, may be provided.

The camera may alternatively be adapted to produce polychromatic images by the provision of a colour filter disposed adjacent to the shutter and comprising a plurality of regions each switchable between different colours to enable colour modulation of the received image. The filter may include a rotatable disc having a plurality of differently coloured regions, or may comprise a plurality of regions that are individually switchable between a plurality of colours.

As a single camera is employed, the requirement for accurate alignment of separate receiving means is removed. Also, there is no longer a need for complex receiving means synchronisation circuitry. One example of the present invention will now be described with reference to the accompanying drawings in which:-

Fig. 1 is a diagram showing a prior art three dimensional camera system; Fig. 2 is a diagram showing the optical arrangement employed in a camera according to the present invention;

Fig. 3 is a diagram showing the optical arrangement employed in a polychromatic camera according to the present invention; Fig. 4 and 5 shows further examples of polychromatic cameras according to the present invention; and

Fig. 6 is a diagram showing the synchronisation circuitry employed in the examples of the present invention. Referring to Fig. 1, a traditional 3D camera and display system employs a series of cameras 3 to provide images of an object 2 from a series of different views. In a real-time system the images are relayed directly to a display screen 1, which displays each of the images in turn, with each image being displayed so as to appear to originate from different positions related to the camera position from which they emanated. Because a viewer 4 perceives each of the images to originate from differing positions, if the images are displayed in rapid enough succession, the viewer 4 sees a single, apparently three dimensional, image.

Fig. 2 shows a simplified version of the optical arrangement employed in a camera according to the present invention. The camera is provided with an image receiving means 5. In this example the image receiving means 5 is a monochromatic high frame rate charge-coupled device (CCD) , such as an EEV CCD13 , or similar opto-electronic device.

It will be appreciated that other image receiving apparatus, such as a polychromatic high frame rate CCD may be employed. The image receiving means 5 is coupled to a display (not shown) for real-time applications, or to a recording medium (not shown) for later display ;.n recording applications.

Disposed in front of the image receiving means 5 is an imaging lens 6 and a shutter 8. The shutter 8 comprises an array of individually activated apertures 7. The shutter 8 may be a mechanical device, but is, due to the high speed of switching required, preferably a spatial light modulator, ferroelectric liquid crystal device. Although the shutter is shown in front of the imaging lens 6 in this example, it may also be positioned behind it. The width of the imaging lens 6 is chosen to provide the desired width of viewing position.

Positioned in front of the shutter 8 is an objective lens 9 which is not essential to the invention, but may be provided to allow greater optical design freedom. In this example both the imaging lens 6 and the objective lens 9 are shown as circular, but it will be appreciated that lenses of other shapes may be employed.

In use, a shutter synchronising means 12 (see figure 6) which is an electronic or electromechanical device, triggers each of the apertures to open in turn. At the same time as an aperture 7 opens, the shutter synchronising means also triggers the image receiving means 5, which receives an image corresponding to the open aperture 7. The shutter opening acts as an aperture stop in the lens and so a complete image is formed on the image receiving means 5. The viewpoint of the image is centred on the open aperture centre. The shutter synchronising means then closes the open aperture 7, transfers the received image from the image receiving means 5, resets the image receiving means 5, and opens the next aperture in sequence, and the image receiving process is repeated. The new shutter aperture position produces an image on the

receiving means from the viewpoint of the position of the new aperture.

In recording applications, once an image haε been recorded for each of the apertures 7, a "group" of images has been collected and an indication of the ending of a group is recorded with the image data by the shutter synchronising means. As there are possible variations in aperture opening sequence, an indication of the sequence used by the camera may also be recorded. There may also be provision for interlacing in the image recording format. The whole group image recording process then repeats itself.

As mentioned above, each image is of the object from the viewpoint of the position of the shutter aperture, and thus when the image sequence is reproduced on a display 1 of the type described above, a three dimensional image of the object is generated.

Figure 3 shows a polychromatic camera according to the present invention. The arrangement of the polychromatic camera is similar to that for the camera described above, except for the provision of a switching colour filter 10 adjacent to the shutter 8. This example, and the following examples, may be used in applications where a colour image receiving device of high enough frame rate is not available, or considered too expensive. In this example, the colour filter 10 comprises a plurality of individually activated rectangular regions 11, aligned with the shutter apertures 7, each of which is switchable between a plurality of colours. In this example the regions 11 are each switchable between the three primary colours, red, green and blue. The polychromatic camera operates in a similar fashion to that of the monochromatic camera of Figure 2 , although it produces three " groups" of images in sequence, each group containing an image for each shutter aperture 7, with a group for each of the three shutter colours. This is known as a colour sequential operation. Synchronizing means (figure 6) controls the operation of

the filter 10, changing the colour of each of the regions just after the shutter aperture 7 which corresponds to the respective region 11 has been closed, to maximise the time available for the region to change to the next colour. This enables a filter of slower switching ε;peed to be employed. An example of a colour filter that may be used with the present invention is the NU700S colour shutter from Tektronix Incorporated.

The colour filter 10 may be replaced by a rotatable disk which comprises a plurality of differently coloured regions (see figure 4) . In such a case, the filter synchronising means of figure 6 is adapted to control the speed of rotation of the filter in relation to shutter speed. The disk is rotated at a speed which enables colour modulation of each of the images for all of ^he shutter apertures 7 for each of the colours on the dis<.

Figure 5 shows an example of a further polychromatic camera according to the present invention. In this example, three image receiving devices 5 are provided, with images from the shutter 8 being directed to all three image receiving devices 5 by a beamsplitter 13. In t is example the image receiving devices 5 are high frame rate charge- coupled devices of the type employed in the example of Figure 2, although it will be appreciated that other devices may be employed. The devices may be formed separately or as a single unit combined with the beamsplitter 13. The operation of the device of this example is identical to that of earlier examples, apart from the fact that three image outputs occur. Each image receiving means output is marked as representing a different colour, in this example the three primary colours. Colour filters 14 are provided in front of each of the image receiving devices 5, or the filters can be removed if each image receiving device is sensitive to a different colour. The interlacing or high speed sequential display of the three received images ensures that a display connected to the camera of this example displays a

camera of this example displays a polychromatic image representative of the object being viewed by the camera.

Figure 6 shows a synchronisation circuitry 12 required to operate the shutter 8 and image receiving means 5, together with the colour filter 10 of the example of Figure 3. In this example, the shutter 8 and filter 10 are formed as a single unit. It will be appreciated that simple electronic timing circuitry can be employed to provide the synchronisation circuitry 12, and that such circuitry can be readily adapted to control the examples of Figures 2, 4 and 5.