METHOD OF AND APPARATUS FOR VIEWING AN IMAGE

• US 20010043163A1
• Filed: 04/09/1998
• Published: 11/22/2001
• Est. Priority Date: 03/15/1996
• Status: Active Grant

• Current Assignee: Intel Corporation
• Original Assignee: Retinal Displays, Inc.
• Inventors: STOREY, JOHN JAMES, WALDERN, JONATHAN DAVID, POPVICH, MILAN MOMCILO
• Granted Patent: US 6,407,724 B2
• Time in Patent Office: Days
• US Class Current: 345/7
• CPC Class Codes: G02B 2027/0138 comprising image capture systems, e.g. camera
• CPC Class Codes: G02B 2027/0187 slaved to motion of at least a part of the body of the user, e.g. head, eye
• CPC Class Codes: G02B 2027/0198 System for aligning or maintaining alignment of an image in a predetermined direction
• CPC Class Codes: G02B 27/0093 with means for monitoring data relating to the user, e.g. head-tracking, eye-tracking
• CPC Class Codes: G02B 27/0103 comprising holographic elements
• CPC Class Codes: G02B 27/017 Head mounted
• CPC Class Codes: G02B 5/1885 Arranged as a periodic array
• CPC Class Codes: G02B 5/32 Holograms used as optical elements
• CPC Class Codes: G03H 2001/2615 in physical contact, i.e. layered holograms
• CPC Class Codes: G06F 3/013 Eye tracking input arrangements G06F3/015 takes precedence

Abstract

Light from an image displayed on a display screen 10 is transmitted to an observer'"'"'s eye 11 by way of a dynamic optical element 12 (such as a spatial light modulator or an electrically switchable holographic composite) which acts as a lens. The characteristics of the dynamic optical element 12 can be altered so that it acts sequentially to direct light of different colors to the observer'"'"'s eye.

In one optional embodiment emitters 17 on the display screen 10 emit infra-red radiation which is projected by the dynamic lens 12 as a broad wash onto the eye 11. Infra-red radiation reflected back from the eye 11 is focussed by the dynamic lens 12 onto detectors 18 also provided on the display screen 10. The detectors 18 are thus able to sense the direction of eye gaze, and the dynamic lens 12 is controlled in dependence on this to create an area of high resolution in an area of interest centered on the direction of gaze, which is moved to follow the eye gaze as its direction alters. Other than in the area of interest, the dynamic lens 12 has a relatively low resolution.

Claims

1. A method of viewing an image, the method comprising transmitting an image into an eye of an observer by means of a dynamic optical device, the dynamic optical device being operative to create a modulation in respect of at least one of phase and amplitude in light transmitted or reflected thereby, said modulation being variable from one point or spatial region in the optical device to another, and wherein the modulation at any point or spatial region can be varied by the application of a stimulus, and altering the characterstics of the dynamic optical device so that the dynamic optical device acts sequentially to direct light of different colours to the observer'"'"'s eye.

2. A method of viewing an image, the method comprising transmitting an image into an eye of an observer by means of a dynamic optical device, the dynamic optical device being operative to create a modulation in respect of at least one of phase and amplitude in light transmitted or reflected thereby, said modulation being variable from one point or spatial region in the optical device to another, and wherein the modulation at any point or spatial region can be varied by the application of a stimulus, and further comprising the steps of controlling the characteristics of the dynamic optical device to create an area of relatively high resolution in the direction of gaze of the observer'"'"'s eye, the dynamic optical device providing a lesser degree of resolution of the image elsewhere, and sensing the direction of gaze of the observer'"'"'s eye and altering the characteristics of the dynamic optical device in accordance therewith, so that the area of relatively high resolution is repositioned to include said direction of gaze as the latter is altered.

3. Apparatus for viewing an image, comprising image generation means, a dynamic optical device, the dynamic optical device being operative to create a modulation in respect of at least one of phase and amplitude in light transmitted or reflected thereby, said modulation being variable from one point or spatial region in the optical device to another, and control means operative to apply a stimulus to the dynamic optical device, whereby the modulation at any point or spatial region can be varied, the control means being operative to alter periodically the characteristics of the dynamic optical device so that the device acts sequentially to direct light of different colours to the observer'"'"'s eye.

4. Apparatus as claimed in

claim 3

wherein the dynamic optical device is generally reflective.

5. Apparatus as claimed in

claim 3

wherein the dynamic optical device is generally transmissive.

6. Apparatus as claimed in

claim 3

wherein the image generation means is configured off-axis from the general direction of view of the observer'"'"'s eye in use.

7. Apparatus as claimed in

claim 6

wherein the apparatus is embodied in a headset with a side portion arranged to be placed in the temple region of an observer'"'"'s head, the image generation means being housed within the side portion.

8. Apparatus as claimed in

claim 3

wherein the apparatus includes left and right image generation means, left and right dynamic optical devices and left and right side portions within which said left and right image generation means are housed, said left and right image generation means being operative to project towards said left and right dynamic optical devices respectively, thereby displaying a binocular image.

9. Apparatus as claimed in

claim 3

, wherein the dynamic optical device comprises a spatial light modulator containing an array of switchable elements in which the optical state of each element can be altered to create a change in phase and/or amplitude in the light incident thereon.

10. Apparatus as claimed in

claim 3

, wherein the dynamic optical device comprises an array of switchable pre-recorded holographic elements.

11. Apparatus as claimed in

claim 10

, wherein the dynamic optical device also comprises non-switchable holographic elements.

12. Apparatus as claimed in

claim 10

, wherein the dynamic optical device comprises an electrically switchable holographic composite.

13. Apparatus as claimed in

claim 3

, wherein the dynamic optical device is used in a range in which the phase and/or amplitude modulation varies substantially linearly with applied stimulus.

14. Apparatus as claimed in

claim 3

, wherein the dynamic optical device is used in a range in which it does not substantially affect the amplitude and/or the wavelength characteristics of the light transmitted or reflected thereby.

15. Apparatus as claimed in

claim 3

, wherein the dynamic optical device is in the form of a screen adapted for mounting close to the observer'"'"'s eye.

16. Apparatus as claimed in

claim 15

, wherein the screen is of generally curved section in at least one plane.

17. Apparatus claimed in

claim 16

, further comprising means for engaging the screen with the observer'"'"'s head in a position such that the curve thereof is generally centred on the eye point.

18. Apparatus as claimed in

claim 3

, wherein the dynamic optical device acts upon light transmitted therethrough, and the image generator is located on a side of the dynamic optical device remote from the intended position of the observer'"'"'s eye.

19. Apparatus as claimed in

claim 3

, wherein the dynamic optical device acts upon light reflected thereby, and the image generator is at least partially light-transmitting and is located between the dynamic optical device and the intended position of the observer'"'"'s eye.

20. Apparatus as claimed in

claim 3

, wherein the control means acts on the dynamic optical device comprises an array of discrete optical elements in close juxtaposition to each other, each of which acts as an individual lens or mirror.

21. Apparatus as claimed in

claim 20

wherein the discrete optical elements are capable of being controlled independently.

22. Apparatus as claimed in

claim 20

, wherein some of the discrete optical elements act to direct to the observer'"'"'s eye light of one colour, while others of the discrete optical elements act to direct to the observer'"'"'s eye light of other colours.

23. Apparatus as claimed in

claim 3

, wherein the dynamic optical device functions to correct aberrations and/or distortions in the image produced by the image generator.

24. Apparatus as claimed in

claim 3

, wherein the dynamic optical device factions to create a desired position, size and/or shape for the exit pupil.

25. Apparatus as claimed in

claim 3

, and further including sensing means operative to sense the direction of gaze of the observer'"'"'s eye, the control means being operative on the dynamic optical device to create an area of relatively high resolution in said direction of gaze, the dynamic optical device providing a lesser degree of resolution of the image elsewhere, the control means being responsive to the sensing means and being operative to alter the characteristics of the dynamic optical device to reposition said area of relatively high resolution to include said direction of gaze as the latter is altered.

26. Apparatus as claimed in

claim 25

, wherein the sensing means utilises radiation which is scattered from the observer'"'"'s eye and which is detected by detector means, and the dynamic optical device also functions to project said radiation onto the eye and/or to project to the detector means the radiation reflected by the eye.

27. Apparatus as claimed in

claim 26

, further comprising sensing means operative to track the head positions of a plurality of observers, a plurality of sensing means each of which is operative to detect the direction of eye gaze of a respective one of the observers, and the dynamic optical device is operative to create a plurality of exit pupils for viewing of the image by the observers, respectively.

28. Apparatus as claimed in

claim 25

, wherein the sensing means includes a plurality of sensors adapted to sense the attitude of the observer'"'"'s eye, the sensors being positioned in or on the dynamic optical device and/or the image generator.

29. Apparatus as claimed in

claim 25

, wherein the sensing means comprises emitter means operative to emit radiation for projection onto the observer'"'"'s eye and detector means operative to detect radiation reflected back from the eye.

30. Apparatus as claimed in

claim 29

. wherein the emitter means and/or the detector means are provided on a light-transmitting screen disposed between the image generator and the dynamic optical device.

31. Apparatus as claimed in

claim 30

, wherein the image generator is in the form of a display screen, and the emitter means and/or the detector means are provided in or on the display screen.

32. Apparatus as claimed in

claim 31

, wherein the emitter means are provided in or on the display screen, a beamsplitter device is disposed between the display screen and the dynamic optical device and is operative to deflect radiation reflected by the observer'"'"'s eye laterally of the main optical path through the apparatus, and the detector means are displaced laterally from the main optical path.

33. Apparatus as claimed in

claim 29

, wherein the image generator produces a pixilated image, and the emitter means and/or detector means are provided at pixel level within the field of view.

34. Apparatus as claimed in

claim 25

, wherein the sensing means utilises infra-red radiation.

35. Apparatus as claimed in

claim 34

, further comprising at least one optical element provided in tandem with the dynamic optical device, which acts upon infra-red light but not upon visible light.

36. Apparatus as claimed in

claim 34

, wherein the detector means are provided on a light-transmitting screen disposed between the image generator and the dynamic optical device.

37. Apparatus as claimed in

claim 36

, wherein a reflector is disposed between the image generator and the light-transmitting screen, and is operative to reflect the infra-red radiation whilst allowing transmission of visible light, such that the infra-red radiation after reflection by the observer'"'"'s eye passes through the dynamic optical device and the light-transmitting screen, and is reflected by said reflector back towards the screen.

38. Apparatus as claimed in

claim 25

, wherein the sensing means utilises visible light.

39. Apparatus as claimed in

claim 38

, wherein the visible light is utilised in short bursts.

40. Apparatus as claimed in

claim 38

, wherein the sensing means include emitter means operative to emit light for projection onto the observer'"'"'s eye, the image generator produces a pixilated image, the emitter means is provided at pixel level within the field of view, and the wavelength of light emitted by the emitter is matched to that of the surrounding pixels in the generated image.

41. Apparatus as claimed in

claim 38

, wherein the visible light is utilised in a specific narrow band of wavelengths.

42. Apparatus as claimed in

claim 3

, wherein the image generator and the dynamic optical device are incorporated into a thin monolithic structure.

43. Apparatus as claimed in

claim 39

, wherein the monolithic structure also includes a micro-optical device operative to perform initial beam shaping.

44. Apparatus as claimed in

claim 3

wherein the dynamic optical device includes an optical shutter operable to selectively expose a portion of the dynamic optical device to light from the image generation means.

45. Apparatus as claimed in

claim 44

wherein the optical shutter is capable of defining a generally light transmitting area of the dynamic optical device in response to a stimulus applied by the control means, the control means further being operable to control the optical shutter to expose all areas of the dynamic optical device sequentially.

46. Apparatus as claimed in

claim 3

, further comprising means to permit the viewing of ambient light from the surroundings, either separately from or in conjunction with the image produced by the image generator.

47. Apparatus as claimed in

claim 46

. wherein the image generator includes discrete light-emitting elements (such as lasers or LEDs) which are located on a generally light-transmitting screen through which the ambient light can be viewed.

48. Apparatus as claimed in

claim 46

, wherein the light-emitting elements are located at the periphery of said screen, and the screen acts as a light guide member and includes reflective elements to deflect the light from the light-emitting elements towards the dynamic optical element.

49. Apparatus as claimed in

claim 46

, wherein the image generator is in the form of a display panel, and the panel is mounted so as to be movable between a first position in which it confronts the dynamic optical device and a second position in which it is disposed away from the dynamic optical device.

50. Apparatus as claimed in

claim 46

, wherein the image generator is in the form of a display screen and displays an input image, and further comprising detection means operative to sense the ambient light, a processor responsive to signals received from the detector means to display on the display screen an image of the surroundings, and means enabling the display screen to display selectively and/or in combination the input image and the image of the surroundings.

51. Apparatus as claimed in

claim 3

, wherein the image generator comprises an array of light-emitting elements each of which is supplied with signals representing a respective portion of the image to be viewed, the signals supplied to each light-emitting element being time-modulated with information relating to the details in the respective portion of the image.

52. Apparatus as claimed in

claim 3

, wherein the image produced by the image generator is pre-distorted.

53. Apparatus as claimed in

claim 3

, wherein the functions of the image generator and the dynamic optical device are combined into a single device.

54. Apparatus as claimed in

claim 53

, wherein said single device comprises a dynamic hologram.

55. Apparatus as claimed in

claim 53

, wherein said single device includes a spatial light modulator operative to produce a dynamic diffraction pattern which is illuminated by at least one reference beam.

56. Apparatus as claimed in

claim 3

, wherein said image for viewing by the observer is displayed on a display screen.

57. Apparatus as claimed in

claim 56

, wherein the display screen is of generally curved section in at least one plane.

58. Apparatus as claimed in

claim 57

, further comprising means for engaging the display screen with the observer'"'"'s head in a position such that the curve thereof is generally centred on the eye point.

59. Apparatus as claimed in

claim 58

, which forms part of a head-mounted device.

101. Apparatus as claimed in

claim 3

. wherein the dynamic optical device includes an optical shutter operable to selectively expose a portion of the dynamic optical device to light from the image generation means.

102. Apparatus as claimed in

claim 101

wherein the optical shutter is capable of defining a generally light transmitting area of the dynamic optical device in response to a stimulus applied by the control means, the control means further being operable to control the optical shutter to expose all areas of the dynamic optical device sequentially.

60. Apparatus for viewing an image, comprising a dynamic optical device, the dynamic optical device being operative to create a modulation in respect of at least one of phase and amplitude in light transmitted or rejected thereby by means of which the observer'"'"'s eye views an image in use, sensing means operative to sense the direction of gaze of the observer'"'"'s eye, and control means which acts on the dynamic optical device to create an area of relatively high resolution in said direction of gaze, the dynamic optical device providing a lesser degree of resolution of the image elsewhere, the control means being responsive to the sensing means and being operative to alter the characteristics of the dynamic optical device to move said area of relatively high resolution to follow said direction of gaze as the latter is altered.

61. Apparatus as claimed in

claim 60

wherein the control means is operative to alter periodically the characteristics of the dynamic optical device so that, at least in said area of relatively high resolution, the dynamic optical device acts sequentially to direct light of different colours to the observer'"'"'s eye.

62. Apparatus as claimed in

claim 60

, wherein the sensing means utilises radiation which is scattered from the observer'"'"'s eye and which is detected by detector means, and the dynamic optical device also functions to project said radiation onto the eye and/or to project to the detector means the radiation reflected by the eye.

63. Apparatus as claimed in

claim 62

, further comprising sensing means operative to track the head positions of a plurality of observers, a plurality of sensing means each of which is operative to detect the direction of eye gaze of a respective one of the observers, and the dynamic optical device is operative to create a plurality of exit pupils for viewing of the image by the observers, respectively.

64. Apparatus as claimed in

claim 60

, wherein the sensing means includes a plurality of sensors adapted to sense the attitude of the observer'"'"'s eye, the sensors being positioned in or on the dynamic optical device and/or the image generator.

65. Apparatus as claimed in

claim 60

, wherein the sensing means comprises emitter means operative to emit radiation for projection onto the observer'"'"'s eye and detector means operative to detect radiation reflected back from the eye.

66. Apparatus as claimed in

claim 65

, wherein the emitter means and/or the detector means are provided on a light-transmitting screen disposed between the image generator and the dynamic optical device.

67. Apparatus as claimed in

claim 66

, wherein the image generator is in the form of a display screen, and the emitter means and/or the detector means are provided in or on the display screen.

68. Apparatus as claimed in

claim 67

, wherein the emitter means are provided in or on the display screen, a beamsplitter device is disposed between the display screen and the dynamic optical device and is operative to deflect radiation reflected by the observer'"'"'s eye laterally of the main optical path through the apparatus, and the detector means are displaced laterally from the main optical path.

69. Apparatus as claimed in

claim 65

, wherein the image generator produces a pixilated image, and the emitter means and/or detector means are provided at pixel level within the field of view.

70. Apparatus as claimed in

claim 60

, wherein the sensing means utilises infra-red radiation.

71. Apparatus as claimed in

claim 70

, further comprising at least one optical element provided in tandem with the dynamic optical device, which acts upon infra-red light but not upon visible light.

72. Apparatus as claimed in

claim 70

, wherein the detector means are provided on a light-transmitting screen disposed between the image generator and the dynamic optical device.

73. Apparatus as claimed in

claim 72

, wherein a reflector is disposed between the image generator and the light-transmitting screen, and is operative to reflect the infra-red radiation whilst allowing transmission of visible light, such that the infra-red radiation after reflection by the observer'"'"'s eye passes through the dynamic optical device and the light-transmitting screen, and is reflected by said reflector back towards the screen.

74. Apparatus as claimed in

claim 60

, wherein the sensing means utilises visible light.

75. Apparatus as claimed in

claim 74

, wherein the visible light is utilised in short bursts.

76. Apparatus as claimed in

claim 74

, wherein the sensing means include emitter means operative to emit light for projection onto the observer'"'"'s eye, the image generator produces a pixellated image, the emitter means is provided at pixel level within the field of view, and the wavelength of light emitted by the emitter is matched to that of the surrounding pixels in the generated image.

77. Apparatus as claimed in

claim 74

, wherein the visible light is utilised in a specific narrow band of wavelengths.

78. Apparatus as claimed in

claim 60

wherein the dynamic optical device is generally reflective.

79. Apparatus as claimed in

claim 60

wherein the dynamic optical device is generally transmissive.

80. Apparatus as claimed in

claim 60

wherein the image generation means is configured off-axis from the general direction of view of the observer'"'"'s eye in use.

81. Apparatus as claimed in

claim 80

wherein the apparatus is embodied in a headset with a side portion arranged to be placed in the temple region of an observer'"'"'s head, the image generation means being housed within the side portion.

82. Apparatus as claimed in

claim 60

wherein the apparatus includes left and right image generation means, left and right dynamic optical devices and left and right side portions within which said left and right image generation means are housed, said left and right image generation means being operative to project towards said left and right dynamic optical devices respectively, thereby displaying a binocular image.

83. Apparatus as claimed in

claim 60

, wherein the dynamic optical device comprises a spatial light modulator containing an array of switchable elements in which the optical state of each element can be altered to create a change in phase and/or amplitude in the light incident thereon.

84. Apparatus as claimed in

claim 60

, wherein the dynamic optical device comprises an array of switchable pre-recorded holographic elements.

85. Apparatus as claimed in

claim 84

, wherein the dynamic optical device also comprises non-switchable holographic elements.

86. Apparatus as claimed in

claim 84

, wherein the dynamic optical device comprises an electrically switchable holographic composite.

87. Apparatus as claimed in

claim 60

, wherein the dynamic optical device is used in a range in which the phase and/or amplitude modulation varies substantially linearly with applied stimulus.

88. Apparatus as claimed in

claim 60

, wherein the dynamic optical device is used in a range in which it does not substantially affect the amplitude and/or the wavelength characteristics of the light transmitted or reflected thereby.

89. Apparatus as claimed in

claim 60

, wherein the dynamic optical device is in the form of a screen adapted for mounting close to the observer'"'"'s eye.

90. Apparatus as claimed in

claim 89

, wherein the screen is of generally curved section in at least one plane.

91. Apparatus claimed in

claim 90

, further comprising means for engaging the screen with the observer'"'"'s head in a position such that the curve thereof is generally centred on the eye point.

92. Apparatus as claimed in

claim 60

, wherein the dynamic optical device acts upon light transmitted therethrough, and the image generator is located on a side of the dynamic optical device remote from the intended position of the observer'"'"'s eye.

93. Apparatus as claimed in

claim 60

, wherein the dynamic optical device acts upon light reflected thereby, and the image generator is at least partially light-transmitting and is located between the dynamic optical device and the intended position of the observer'"'"'s eye.

94. Apparatus as claimed in

claim 60

, wherein the control means acts on the dynamic optical device comprises an array of discrete optical elements in close juxtaposition to each other, each of which acts as an individual lens or mirror.

95. Apparatus as claimed in

claim 94

wherein the discrete optical elements are capable of being controlled independently.

96. Apparatus as claimed in

claim 94

, wherein some of the discrete optical elements act to direct to the observer'"'"'s eye light of one colour, while others of the discrete optical elements act to direct to the observer'"'"'s eye light of other colours.

97. Apparatus as claimed in

claim 60

, wherein the dynamic optical device functions to correct aberrations and/or distortions in the image produced by the image generator.

98. Apparatus as claimed in

claim 60

, wherein the dynamic optical device functions to create a desired position, size and/or shape for the exit pupil.

99. Apparatus as claimed in

claim 60

, wherein the image generator and the dynamic optical device are incorporated into a thin monolithic structure.

100. Apparatus as claimed in

claim 60

, wherein the monolithic structure also includes a micro-optical device operative to perform initial beam shaping.

103. Apparatus as claimed in

claim 60

, further comprising means to permit the viewing of ambient light from the surroundings, either separately from or in conjunction with the image produced by the image generator.

104. Apparatus as claimed in

claim 103

, wherein the image generator includes discrete light-emitting elements (such as lasers or LEDs) which are located on a generally light-transmitting screen through which the ambient light can be viewed.

105. Apparatus as claimed in

claim 103

, wherein the light-emitting elements are located at the periphery of said screen, and the screen acts as a light guide member and includes reflective elements to deflect the light from the light-emitting elements towards the dynamic optical element.

106. Apparatus as claimed in

claim 103

, wherein the image generator is in the form of a display panel, and the panel is mounted so as to be movable between a first position in which it confronts the dynamic optical device and a second position in which it is disposed away from the dynamic optical device.

107. Apparatus as claimed in

claim 103

, wherein the image generator is in the form of a display screen and displays an input image, and further comprising detection means operative to sense the ambient light, a processor responsive to signals received from the detector means to display on the display screen an image of the surroundings, and means enabling the display screen to display selectively and/or in combination the input image and the image of the surroundings.

108. Apparatus as claimed in

claim 60

wherein the image generator comprises an array of light-emitting elements each of which is supplied with signals representing a respective portion of the image to be viewed, the signals supplied to each light-emitting element being time-modulated with information relating to the details in the respective portion of the image.

109. Apparatus as claimed in

claim 108

wherein the area of relatively high resolution is produced by means of the dynamic optical device switching the direction of the light from the light-emitting elements in the region of the direction of gaze of the observer'"'"'s eye.

110. Apparatus as claimed in

claim 60

, wherein the image produced by the image generator is pre-distorted.

111. Apparatus as claimed in

claim 60

, wherein the functions of the image generator and the dynamic optical device are combined into a single device.

112. Apparatus as claimed in

claim 111

, wherein said single device comprises a dynamic hologram.

113. Apparatus as claimed in

claim 111

, wherein said single device includes a spatial light modulator operative to produce a dynamic diffraction pattern which is illuminated by at least one reference beam.

114. Apparatus as claimed in

claim 60

, wherein said image for viewing by the observer is displayed on a display screen.

115. Apparatus as claimed in

claim 114

. wherein the display screen is of generally curved section in at least one plane.

116. Apparatus as claimed in

claim 115

further comprising means for engaging the display screen with the observer'"'"'s head in a position such that the curve thereof is generally centred on the eye point.

117. Apparatus as claimed in

claim 116

, which forms part of a head-mounted device.

118. Apparatus for viewing an image, comprising an image generator operative to generate an image for viewing by an observer'"'"'s eye, an optical system for transmitting said image to the observer'"'"'s eye position, sensing means operative to sense the direction of gaze of the observer'"'"'s eye, and control means responsive to the sensing means and operative to act on the image generator and/or the optical system to modify said image transmitted to the eye in accordance with the direction of gaze of the eye, the sensing means including emitter means operative to emit radiation for projection onto the observer'"'"'s eye, and detector means operative to detect said radiation after reflection by said eye, the optical system also functioning to transmit said radiation from the emitter means onto said eye and/or to transmit said radiation reflected from said eye to the detector means.

119. Apparatus as claimed in

claim 118

, wherein said radiation comprises infra-red radiation.

120. Apparatus as claimed in

claim 118

, wherein the optical system includes at least one optical element which acts upon both visible light and infra-red radiation, and at least one second optical element which acts upon infra-red radiation but not upon visible light.

121. Apparatus as claimed in

claim 118

, wherein the detector means (and preferably also the emitter means) are provided on a light-transmitting screen disposed between the image generator and the optical system.

122. Apparatus as claimed in

claim 121

, wherein a reflector is disposed between the image generator and the light-transmitting screen, and is operative to reflect the infra-red radiation whilst allowing transmission of visible light, such that the infra-red radiation after reflection by the observer'"'"'s eye passes through the optical system and the light-transmitting screen, and is reflected by said reflector back towards the screen.

123. Apparatus as claimed in

claim 122

wherein the reflector is one of a holographic/diffractive reflector and a conventional dichroic reflector.

124. Apparatus as claimed in

claim 118

, wherein the image generator is in the form of a display screen, and the emitter means and/or the detector means are provided in or on the display screen.

125. Apparatus as claimed in

claim 124

, wherein the emitter means are provided in or on the display screen, a beamsplitter device is disposed between the display screen and the optical system and is operative to deflect infra-red radiation reflected by the observer'"'"'s eye and passing through the optical system laterally of the main optical path through the apparatus, and the detector means are displaced laterally from said main optical path.

126. Apparatus as claimed in

claim 118

, wherein the image generator generates a pixilated image, and the emitter means and/or the detector means are provided at pixel level.

127. Apparatus for viewing an image, comprising an image generator operative to generate an image for viewing by an observer'"'"'s eye, an optical system for transmitting said image to the observer'"'"'s eye position, sensing means operative to sense the direction of gaze of the observer'"'"'s eye, and control means responsive to the sensing means and operative to act on the image generator and/or the optical system to modify said image transmitted to the eye in accordance with the direction of gaze of the eye, the tracking means including emitter means operative to emit radiation for projection onto the observer'"'"'s eye, and detector means operative to detect said radiation after reflection by said eye, the emitter means and/or the detector means being provided at pixel level within the field of view of the image.

128. Apparatus as claimed in

claim 127

, wherein the image generator is in the form of a display screen, and the emitter means and/or the detector means are provided at pixel level in or on the display screen.

129. Apparatus as claimed in

claim 127

, wherein the emitter means and/or the detector means are provided at pixel level on a light-transmitting screen disposed between the image generator and the optical system.

130. Apparatus as claimed in

claim 127

. wherein said radiation comprises infra-red radiation.

131. Apparatus as claimed in

claim 127

, wherein the optical system includes at least one optical element which acts upon both visible light and infra-red radiation, and at least one second optical element which acts upon infra-red radiation but not upon visible light.