This invention relates to eyewear to enable stereoscopic viewing of images.

Many known three-dimensional ("3D") or stereoscopic systems require that a viewer wears a pair of eyeglasses in order to experience stereoscopic viewing of images such as those projected or displayed in cinema films or television programmes. Such well-known eyeglasses-based stereoscopic viewing methods include using colour anaglyphs, wavelength (colour) multiplexing, linearly or circularly polarised light, and synchronised shuttering. Another system uses a combination of a stereogram (two offset images of a scene) along with a prism or mirror based optical system that presents each offset image such that a human viewer perceives a stereoscopic image.

In all these cases the eyeglasses work with systems that present simultaneously (or nearly simultaneously) sufficient information from which the human visual system is able to generate the illusion of a three dimensional image. Such information primarily consists of the left and right "views" which together comprise a

stereoscopic image. The function of the eyeglasses in all these well-known cases is to discriminate between these left and right views and ensure that only the left view is presented to the left eye and that the right view is presented to the right eye.

Unfortunately these eyeglasses prevent, or make difficult, the wearing of normal corrective eyeglasses that are required by many individuals to correct defects in their vision and are worn as a normal matter of course. This is a problem as a significant proportion of individuals use or require correction to their vision (up to two-thirds of the population in developed countries). Unless a viewer is wearing contact lenses or has had corrective refractive surgery then he or she will not be able to view stereoscopic material with the sharpness of vision that they would otherwise expect due to their impairment in visual focus.

The recent availability of stereoscopic systems for the home market combined with so-called high definition ("HD") wide-screen television systems, means that people with uncorrected defective vision are not easily able to appreciate the enhanced detail offered by such systems. With the prospect of three-dimensional media being delivered by a variety of visual displays mounted in devices such as mobile phones, personal media players, computer displays and the like, it is possible that correction may be needed for people for a range of devices.

An added complication is presbyopia, which is an aging related reduction in a person's ability to focus on nearby objects. This will affect an individual's quality of experience of three-dimensional media presented on devices viewed at near distances, such as mobile phone screens.

The issues set out above will affect the number of people who have access to stereoscopic or three-dimensional content at the best quality available and hence artificially reduce the market size for three-dimensional viewing. From a first aspect the invention provides an optical apparatus for wearing by a human user to enable viewing of stereoscopic images, comprising at one or more lenses and means for viewing stereoscopic images, wherein the lens and the means for viewing stereoscopic images are provided within a unitary structure. Thus it will be appreciated by those skilled in the art that the present invention allows a user comfortably to view stereoscopic images using a single unitary piece of equipment with a corrective lens thus presenting the image in focus, which previously the user was unable to do unless they settled for the uncomfortable compromise of placing a pair of stereoscopic filter glasses over their prescription eyeglasses.

In a set of preferred embodiments the optical apparatus resembles a pair of spectacles - that is comprising a frame adapted to be supported on the user's nose and ears. However other possibilities are envisaged such as apparatus in the form of goggles or a helmet - e.g. in the manner of a head-mounted display. In these cases the unitary structure comprising the stereoscopic means and lens could be separate or separable from the frame or housing, but preferably the unitary structure includes the frame or housing. Alternatively the optical apparatus could take the form of contact lenses; in this case the unitary structure would comprise the contact lens itself. The unitary structure could take many different forms. The means for viewing stereoscopic images and the lens may be discrete respective components of the structure - e.g. with the viewing means provided by a cover of the apparatus, while in other embodiments the viewing means could be intimately combined with the lens, or cover (where provided), e.g. as a coating or substrate, or a coloured lens.

Although in the broadest scope of the invention a single lens could be provided for both eyes, in preferred embodiments separate lenses are provided for each eye.

The means for viewing stereoscopic images preferably comprises differential filters associated with each eye. The means may comprise one of a colour filter (e.g. a primary colour filter or a bandpass filter), a polarisation sensitive filter or a time- gated shuttering system (e.g. a liquid crystal panel). The means for viewing stereoscopic images are matched to the type of stereoscopic image being viewed, i.e. it is necessary to view an anaglyph with a colour filter, it is necessary to view a polarised image with a polarisation sensitive filter, and it is necessary to view a system which presents alternating left eye and right eye images with a

synchronised shuttering system.

Although generally one type of filter would be provided, embodiments are envisaged where two or more different types of means for viewing stereoscopic images are provided, e.g. a shuttering system equipped with a polariser on the front to allow the user to be able to view two different types of stereoscopic images. Whichever type of means for viewing the stereoscopic image is used, they all act to provide slightly different views of the same image, i.e. from two offset positions, to the right and left eyes which thus gives the illusion to the user of viewing a 3D image. Preferably the or each lens is a variable power lens. Preferably the apparatus comprises means for allowing user adjustment of the power of the lens. The ability to adjust the optical power of the lens gives the advantage that a "one size fits all" device can be provided that a user can adjust as necessary to suit their optical prescription. This allows a relatively low cost device to be provided as the lenses do not have to be custom made but can simply be adjusted by a user before use. The variable power lens also enables multiple users with different optical prescriptions to use the same apparatus which would be of benefit in an

environment such as a cinema where viewing equipment may be borrowed by many different viewers.

In the set of embodiments in which variable power lenses are provided, the or each lens may comprise: a fluid filled lens, an Alvarez-based lens, an electroactive lens, a diffractive lens or a diffractive Alvarez lens. In one set of embodiments the adjustment means provides all the necessary adjustment of the lens, i.e. the adjustment range is large enough to be suitable for a large proportion of the population. Such an apparatus would therefore be suitable for cinema viewing or as a mass-market product for use at home. However embodiments are also envisaged in which the lens comprises one or more fixed power prescription elements. Providing a fixed power prescription element allows a range of different power elements to be used according to the needs of the user. This means that either no variable power lens is necessary or that the variable power lens could just be used for fine tuning of the optical power, i.e. the adjustment range is small. Having a small adjustment range can result in number of benefits, e.g. if a fluid filled lens is provided only a small volume of fluid is needed, or if an Alvarez lens is provided only a small distance of translation between the two lens elements is needed.

If a fixed power prescription element is provided, the prescription can comprise one or more components from a spherical correction, a cylinder correction, an axis correction or any other higher order aberration correction. The different corrections may either be provided in a single element or separately in different elements. The higher order corrections could be provided to a surface of the optical apparatus. This could be in addition to or instead of providing a separate prescription element.

The means for adjusting the variable power lens may be chosen dependent on the type of lens used. If the lens is fluid filled the adjustment means comprises one of a pump, syringe, plunger, cam-operated actuator, bladder or bellows. If the lens is an Alvarez lens or a diffractive Alvarez lens, the adjustment means preferably comprises an actuator to move the two sections of the lens relative to each other, e.g. a manual screw, an electro-mechanically driven actuator. In an Alvarez lens either both or only one of the lens elements can be moved to adjust the lens. It is preferable to move both lens elements as moving just one introduces a small amount of prism, although this is tolerable. If the lens is an electroactive lens, the adjustment means preferably comprises means to apply an electric field across the lens, controlled by e.g. a switch, such as a binary on-off or dial.

Where, as is preferred, separate lenses are provided for each eye, a single adjustment means for the two lenses may be provided. In these embodiments the two lenses are therefore linked or coupled such that a single adjustment can be made to alter simultaneously the power of both lenses. Alternatively separate adjustment means for each lens can be provided. This enables users who require different power of lens correction for each eye to be able to adjust the two lenses individually to suit their prescription.

In one set of embodiments the lens adjustment means is controlled by the user. This could be by simple trial and error, or by means of a stored setting. In another set of embodiments the adjustment means is controlled by an external signal - e.g. from the system displaying the stereoscopic image which might be a television. This allows different profiles for lens power values to be stored in the display system, which, when selected, automatically activate the adjustment means to adjust the lenses to the required powers. Situations in which such profiles could advantageously be used include different users who have different optical prescriptions but want to use the same optical apparatus, or for an individual user in different situations, e.g. for viewing images from different distances or on different devices.

In a preferred set of embodiments the apparatus comprises means for protecting the lens and/or the means for viewing stereoscopic images. This can be a simple covering plate or a sealed container, and is chosen to be suitable for whichever type of 3D filter or variable power lens is being employed. In one set of

embodiments the means for protecting the lens comprises the means for viewing stereoscopic images, e.g. the 3D filter acts as the cover for the variable power lens. In the set of embodiments which are used to view a colour based stereoscopic image, the means for viewing stereoscopic images, i.e. a colour filter, and the lens can be provided in either order between the stereoscopic image and the user's eye. Also they could be combined with or separate from the lens. There are a number of advantageous embodiments which are envisaged for the set of embodiments in which a variable power lens is provided. For example, the colour filter could be provided as a coloured fluid in the set of embodiments in which a fluid filled lens is provided. In the set of embodiments in which an Alvarez lens is provided either or both of the lens elements could be made from a coloured material. Another option for an Alvarez lens is to provide a multilayer filter or colour coating on any surface of the lens elements through which the stereoscopic image passes. In the set of embodiments in which an electroactive or diffractive lens is provided a coloured substrate could be provided as the stereoscopic viewing means. The means for protecting the lens and/or the filter could be a cover or a sealed container. If the filter is provided as a coloured fluid or gel, or if the lens is a fluid filled lens, advantageously a sealed container is provided.

In the set of embodiments which are used to view a polarisation based (linear or circularly polarised) stereoscopic image, the means for viewing stereoscopic images, i.e. a polariser, is preferably foremost in the apparatus, i.e. closest to the source of the stereoscopic image. This is because light travelling through any other structure may undergo a change in polarisation which would adversely affect the presentation of distinct stereoscopic images to each eye and so degrade the visual experience and three-dimensional illusion. The means for protecting the lens and/or the filter could be a cover or a sealed container. If the lens is a fluid filled lens, advantageously a sealed container is provided.

In the set of embodiments which are used to view a shuttering based stereoscopic image, the means for viewing stereoscopic images, typically a liquid crystal panel, and the lens can be provided in either order between the stereoscopic image and the user's eye. In this set of embodiments the apparatus also requires means to synchronise it with the shuttered stereoscopic image to allow it to function properly. These means can comprise a control circuit in the apparatus, and means for communicating with or receiving signals or instructions from the display system. This could be light sensitive sensors, radio timing, wireless communication, Bluetooth communication, etc. The apparatus also requires a supply of power to drive the shuttering and any control circuit. The power could be supplied by batteries or through a cable. If the power is supplied through a cable this could be directly from a dedicated power supply or advantageously from the display system with the cable also carrying the synchronising control signals. Optionally a user interface could be provided on the apparatus, e.g. to allow the user to select different preset profiles. The means for protecting the lens and/or the filter could be a cover or a sealed container. If the lens is a fluid filled lens, advantageously a sealed container is provided.

The apparatus may comprise means to determine the distance between the optical apparatus and the stereoscopic image. This would enable the apparatus to automatically adjust the variable power lenses dependent on the determined distance which is particularly useful if the user changes from viewing an image close up, e.g. a computer screen, to an image far away, e.g. a television screen. In addition the apparatus may comprise a variable prism which can be adjusted to bring the stereoscopic images into alignment with respect to the viewer as this will change depending on the distance the user is from the image. Certain preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figs. 1 and 2 show perspective views of embodiments in accordance with the present invention.

Fig. 1 shows a schematic view of the main components of a pair of spectacles 1 embodying the present invention through which a user can view stereoscopic images. The spectacles 1 comprise a frame 2, a variable power lens 4 for each eye, a front cover 6 and a rear cover 8. The means for adjusting the power of the lenses is not shown in this schematic view but they could, for example, be fluid- filled lenses with syringe adjustment as described in more detail in W096/38744 although any other known adjustment arrangement could be used. Either the front cover 6 or rear cover 8 includes the 3D filter, e.g. a colour filter or polariser, and also can include a fixed prescription element, and both can offer protection to the variable power lens 4. Fig. 2 shows a perspective view of another pair of spectacles 101 embodying the present invention that shows the variable power lens 104 and its adjustment means. As with the embodiment shown in Fig. 1 the spectacles 101 comprise a frame 102, a variable power lens 104 for each eye, a front cover 106 and a rear cover 108. The variable power lens 104 is a fluid filled lens which comprises a fluid filled cavity 1 12 held sealed between the front cover 106 and the rear cover 108. In this example the fluid filled cavity 1 12 is shown in a negative power configuration. Also, as with the embodiment shown in Fig. 1 the front cover 106 or the rear cover 108 include the 3D filter and also if necessary a fixed prescription element, and both can act as a protective cover.

The adjustment means 1 10 comprises a rotatable knob 1 14 which is connected to a rack and pinion 1 16. On the end of the rack and pinion 1 16 is mounted a plunger 1 18 which is arranged to move back and forth in a fluid cavity 120 in the arms of the spectacles. The fluid cavity 120 is connected via a fluid channel 122 to the fluid filled cavity 1 12 in the lens.

Operation of the embodiments shown in Figs. 1 and 2 will now be described. A user places the pair of spectacles 1 , 101 in front of their eyes like any normal pair of spectacles. The 3D filter included in either the front cover 6, 106 or the rear cover 8, 108 allows the user to view a stereoscopic image through the spectacles 1 , 101. The variable power lenses 4, 104 allow the user to adjust the power of the variable power lenses 4, 104 to suit their optical prescription. In the example shown in Fig. 2 this is achieved by turning the rotatable knob 1 14 which acts on the plunger 1 18 via the rack and pinion 1 16. The plunger either increases or decreases the volume of fluid in the fluid cavity 120 depending on which direction the rotatable knob 1 14 was turned. The change in volume of fluid in the fluid cavity 120 changes the volume of fluid in the fluid filled cavity 1 12 in the variable power lens 104 as they are connected by the fluid channel 122. The change in volume of fluid in the fluid filled cavity 1 12 in the variable power lens 104 adjusts the power of the variable power lens 104. If more fluid is pumped into the fluid filled cavity 1 12 the power of the variable power lens 104 increases; if fluid is withdrawn from the fluid filled cavity 1 12 the power of the variable power lens 104 decreases. It can therefore be seen that the user can easily adjust the variable power lenses 104 to suit their prescription simply by turning the rotatable knobs 1 14 associated with each of the variable power lenses 104 until they can see objects through the spectacles in clear focus. Since each lens is adjustable individually this allows for differential adjustments which take account not only of differing prescriptions for each eye but also for the slight change in focal length resulting from different coloured lenses (where a colour-based stereoscopic system is used).

The user is then ready to view stereoscopic images clearly. If another user with a different optical prescription (or none) subsequently wishes to use the spectacles 101 to view stereoscopic images, they can adjust the variable power lenses 104 as described to suit their prescription.

It will be appreciated by those skilled in the art that only a small number of possible embodiments have been described and that many variations and modifications are possible within the scope of the invention. For example any type of filter suitable for viewing stereoscopic images can be used; the invention is not limited to those mentioned. Likewise any type of variable power lens suitable for using in the apparatus can be used, with any means suitable for adjusting the lens. The invention is also not limited to providing the lenses in a pair of spectacles, contact lenses or any other suitable device could be employed.