Three-dimensional image recording and display apparatus

The invention relates to three-dimensional image recording apparatus and display apparatus.

In confocal microscopy (also referred to as laser scanning confocal microscopy) a focused spot of laser light is used to illuminate a point in a three dimensional (3D) object. Light which is scattered/reflected back along the same path is then collected through a confocal aperture onto a light detector. The detector gives a signal output which is proportional to the reflectance of point. The focal spot is then scanned in a raster manner line-by-line across the object, to gather information in two dimensions across the object. Moving the focal spot to sequential planes allows a 3D image to be obtained. Use of a confocal aperture provides the advantage that objects which lie above and below the focal spot contribute very little to the signal that reaches the detector. However, there are two major difficulties with this approach. Firstly, each point imaged (commonly referred to as a Voxel or a three dimensional pixel) is measured by a single detector as a level of intensity and does not have any information on the pattern of the out-of-focus planes. Secondly, when the 3D image is displayed, it is done so on a two dimensional screen, such as a cathode ray tube (CRT) or a liquid crystal display (LCD), so that only two dimensional images can be displayed, with no depth information in the displayed images. If a viewer were to move their head sideways or up/down, the image remains the same and two objects within an image which were spaced apart in the object space do not move relative to one another, ie they do not exhibit parallax.

According to a first aspect of the present invention there is provided three- dimensional image recording apparatus comprising: an optical source operable to generate an illuminating optical signal; illuminating optical signal focussing means of variable focal plane, operable to control the plane to be recorded within an object space; illuminating optical signal path directing means operable to control the position of the focal point within a selected focal plane; reflected optical signal path directing means; and reflected optical signal capture means comprising reflected optical signal focussing means, an optical aperture spaced from and arranged optically in series with the focussing means, and a two-dimensional array of optical detectors arranged optically in series with the optical aperture.

The use of a two dimensional array detector positioned behind the confocal aperture enables information about the shapes of any objects located in front of the plane of object space being imaged to be captured, thereby making a record of each voxel together with information about its surroundings. A two dimensional record of each voxel within the object space is therefore provided.

The optical source is preferably a collimated optical source, and is most preferably a laser.

The illuminating optical signal focussing means preferably comprises a movably mounted optical lens. The optical lens is preferably mounted for movement along its optical axis. The illuminating optical signal focussing means may alternatively comprise an optical focussing element of variable focal length.

The illuminating optical signal path directing means preferably comprises a movably mounted reflective optical element, and most preferably comprises a pivotably mounted mirror.

The reflected optical path directing means preferably comprises at least one reflective optical element, most preferably a mirror, which may be a partially transmitting reflective optical element.

The reflected optical signal focussing means preferably comprises an optical lens. The optical aperture is preferably a confocal aperture.

The optical detectors are preferably photodetectors. The optical detectors most preferably capture spectral information.

The reflected optical signal capture means preferably further comprises memory means in communication with the optical detectors, operable to receive and store detected signal intensity information from one or more of the optical detectors.

According to a second aspect of the present invention there is provided three- dimensional image display apparatus comprising: an optical source operable to generate an illuminating optical signal;

a two-dimensional variable spatial optical modulation means comprising an array of image pixels, each image pixel being operable to impart intensity information to the respective area of an illuminating optical signal; modulated optical signal focussing means of variable focal plane, operable to control the plane to be illuminated within an image space; and modulated optical signal path directing means operable to control the position of the focal point within a selected focal plane.

The two-dimensional variable spatial optical modulation means causes a two- dimensional record of a voxel to be impressed upon an illuminating optical signal, to thereby recreate the voxel taking into account any effect on the voxel of other object shapes between the voxel and a viewer.

The optical source is preferably a collimated optical source, and is most preferably a laser. The apparatus preferably comprises a plurality of optical sources, each operable to generate an illuminating optical signal of a different colour.

Preferably, each image pixel is further operable to impart colour information to the respective area of an illuminating optical signal.

The two-dimensional variable spatial optical modulation means may comprise a transmissive liquid crystal display or may comprise a digital light processor.

The modulated optical signal focussing means preferably comprises a movably mounted optical lens. The optical lens is preferably mounted for movement along its optical axis. The illuminating optical signal focussing means may alternatively comprise an optical focussing element of variable focal length.

The modulated optical signal path directing means preferably comprises a movably mounted reflective optical element, and most preferably comprises a pivotably mounted mirror.

According to a third aspect of the present invention there is provided three- dimensional image recording and display apparatus comprising:

three-dimensional image recording apparatus according to the first aspect of the invention; and three-dimensional image display apparatus according to the second aspect of the invention.

Preferably, the number of image pixels is equal to the number of photodetectors.

Embodiments of the invention will now be described in detail, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic representation of three-dimensional image recording apparatus according to a first embodiment of the invention;

Figure 2 is a schematic representation of path of the reflected optical signal of the apparatus of Figure 1 , recording an alternative object;

Figure 3 is a schematic representation of three-dimensional image display apparatus according to a second embodiment of the invention; and

Figure 4 is a schematic representation of the apparatus of Figure 3, displaying the image recorded by the apparatus of Figure 2.

Referring to Figures 1 and 2, a first embodiment of the invention provides three- dimensional image recording apparatus 10. The image recording apparatus 10 comprises a laser (not shown) operable to generate a laser beam 12 (which has been expanded using conventional optics), a partially reflecting mirror 14, illuminating optical signal path directing means in the form of an XY scanning mirror 16, illuminating optical signal focussing means in the form of a first lens 18 movably mounted for movement along its optical axis, reflected optical signal focussing means in the form of a second lens 20, a confocal aperture 22, and a two-dimensional array of photodetectors 24.

Use of the image recording apparatus 10 will now be described in relation Figure 1 , in which the object space 26 contains a square object 28 and a circular object 30, positioned parallel to each other but spaced apart. The expanded laser beam 12 is

transmitted by the partially reflecting mirror 14, reflected by the scanning mirror 16 and focused by the first lens 18 onto a voxel 32 on the square object 28. Light reflected back by the voxel 32 on the square object 28 passes back through the lens 18, and is reflected by the XY scanning mirror 16 and partially reflected by the mirror 14 to the second lens 20. The second lens 20 focusses the reflected optical signal in the plane of the confocal aperture 22. Having been filtered by the confocal aperture 22, the reflected optical signal expands and falls on the array of photodetectors 24, located a suitable distance behind the confocal aperture 22. Each of the photodetectors 24 detects the intensity level of its respective part of the reflected optical signal, and the outputs from each of the photodetectors 24 is recorded in a computer memory, to provide a two-dimensional angular reflectance record of the voxel 32.

It will be noticed that the circular object 30 partially covers the view of the illuminated image voxel 32. The effect of this is that the image of the voxel 32 which falls on the photodetector array 24 has an obscured area 34.

To record another voxel on the square object 28 the XY scanning mirror 16 is moved to cause the illuminating optical signal to focus on the new voxel to be recorded, and an image acquired in the same manner. This process is repeated to record lines of voxels across the square object 28. Once the square object 28 has been recorded, the circular object 30 can then be recorded by moving the lens 18 towards the scanning mirror 16, along its optical axis, so that the focal plane of the lens 18 aligns with the plane of the circular object 30. The circular object 30 can then be scanned and recorded by repeating the process. A three-dimensional recording of the whole of the object space 26 can thus be obtained by scanning all the required planes.

When the circular object 30 is illuminated there are no intervening objects, and thus no shadow is cast across the photodetector array, resulting in all of the photodetectors giving the same reading. Because of the values of the photodetector "pixels" being the same, it would be possible to store the image in a smaller storage space.

Figure 2 illustrates the reflected optical beam of the image recording apparatus 10 of Figure 1 when recording two different objects, namely a letter A and a letter T. As

shown, when recording the image of the letter A, a shadow 34 is created by the letter T, located in front of the letter A in the object space 26, across the photodetector array 24.

Referring to Figure 3, a second embodiment of the invention provides three- dimensional image display apparatus 40 comprising a laser (not shown) operable to generate a laser beam 42 (which has been expanded using conventional optics), two-dimensional variable spatial optical modulation means in the form of a transmissive liquid crystal display (LCD) 44, modulated optical signal focussing means in the form of a lens 46 movably mounted for movement along its optical axis, and modulated optical signal path directing means in the form of a static mirror 48 and an XY scanning mirror 50.

The LCD 44 comprises an array of image pixels 44a (being the same number as photodetectors 24 in the photodetector array of the image recording apparatus 10), each of which impresses on an illuminating laser beam 42 intensity information corresponding to the intensity information recorded by the respective photodetector. The reflected optical signal of the image recording apparatus 10 is thereby recreated. The transmitted light is reflected by the static mirror 48 and the XY scanning mirror 50 to the lens 46, which focuses the light into a voxel 52 in the image space 54. A viewer positioned to the other side of the apparatus 40 would see the voxel 52 as a point of an object, specifically of the square object 28 recorded by the apparatus 10 of Figure 1. If the voxel corresponds to a point on the square object 28 which has the circular object 30 in front of it, then the viewer will only see light from the voxel 52 in directions apart from the chord 56 where the circular object 30 is to be displayed as the LCD 44 would obscure the light in chord 56. So although there are no physical barriers in the position of the circlular object 30, the voxel 52 does not shine through the position of the circular object 30.

The display process is repeated in a raster manner, by tilting the XY mirror 50 to alter the direction of the modulated optical signal, to scan the image across the image space 54 to recreate the square object 28. By moving the lens 46, further planes of the image can be created, including the plane containing the circular object 30, to create a three-dimensional image.

Figure 4 illustrates the modulated optical beam of the image display apparatus 40 of Figure 3 when displaying the image recorded in Figure 2.

Various modifications may be made without departing from the scope of the invention. For example, the variable spatial optical modulation means may alternatively comprise a digital light processing (DLP) chip illuminated in a reflective arrangement, the XY scanning mirror can be replaced with a fast acousto-optical tuneable filter.

A plurality of lasers may alternatively be used, each operable to generate an illuminating optical signal of a different colour, enabling each image pixel to additionally impart colour information to the respective area of an illuminating optical signal and thus to different parts of an image being displayed.

A number of display planes may be used, from a simple case of one plane to a full volumetric display. It will also be appreciated that more than two objects of differing shapes and sizes can be imaged and displayed in this manner. The colour of the voxel may also be controlled by the variable spatial optical modulation means in order to recreate the same from the object in conjunction with using multiple colour lasers.

A number of differing display methods can be employed such as head up displays, large area reflective displays to implement the display method described in this invention.

The described embodiments may be used to record and display three-dimensional static or moving images, system where large objects are imaged and displayed. It will also be appreciated that the image display apparatus may be used to display images generated electronically by a computer, or captured by other imaging means, such as confocal microscopy, digital and film cameras, multiple video cameras, computed tomography imaging, magnetic resonance, ultrasound imaging etc and stored and processed in computers to generate three-dimensional maps of objects which can then be displayed by the image display apparatus.

It should also be noted that the surface properties of objects differ, for example metals have a high specular reflection giving them a shine, whereas materials such as wood and skin are more diffusing. Such rendering information about the objects is retained by this invention and can be used in the display method described.

For some applications, such as in teaching anatomy, it may be preferable to display only some of the total number of objects in the object space, or to give them pseudo- colours, for the purposes of clarity. It may also be beneficial to make some of the objects translucent by allowing light to pass through them.

A plurality of image recording apparatus or image display apparatus may be combined in order to speed up the recording or display process, or for displaying a wider or deeper field of view.