WO2006106371A1

WO2006106371A1 - Display method and apparatus

Info

Publication number: WO2006106371A1
Application number: PCT/HU2006/000023
Authority: WO
Inventors: Zoltán NÉMETH
Original assignee: Innoráció Fejlesztö És Kutatás-Hasznosító Kft.
Priority date: 2005-04-04
Filing date: 2006-03-27
Publication date: 2006-10-12
Also published as: HU0500357D0

Abstract

The invention is a display method and apparatus, in which a direction of vision is detected, and a foveal part of an image is displayed in a first resolution, said foveal part being dedicated to be imaged in a high resolution area of the retina, and a remaining part of the image is displayed in a second resolution, said second resolution being lower than the first resolution. According to the invention, on a first display surface (22) the foveal part (52) is displayed in the first resolution and the first display surface (22) is imaged through a diaphragm aperture (42) with a first angular resolution into the eye, wherein an objective unit (OU3) mapping the diaphragm aperture (42) essentially in the centre of rotation (48) of the eye is used for this imaging, and on a second display surface (32) at least the remaining part of the image is displayed in the second resolution and the second display surface (32) is imaged into the eye in such a perceived image size, that would correspond to an perceived image size of imaging the full image displayed in the first resolution with the first angular resolution into the eye.

Description

DISPLAY METHOD AND APPARATUS

TECHNICAL FIELD

The invention relates to a display method and apparatus, in fact to such a method and apparatus, by which imaging of stationary or moving pictures becomes possible in a higher resolution to the high resolution area of the retina, and in a lower resolution to the peripheral part of the retina. In this way the eye finds the picture of low resolution displays to be equivalent with that of a higher resolution display, i.e. the effective resolution of the display will be larger.

BACKGROUND ART

There is an increasing demand for high resolution display units. The increasingly applied high definition television (HDTV) standards also require high resolution devices. On the other hand, with the proliferation of mobile communication, mobile computers and entertainment equipment, demands are growing for light and portable displays. In many applications, it would be optimal to wear a screen on the head, e.g. on the spectacles, hat or helmet, but the widespread use of these units is limited by the fact that they cannot satisfy the joint requirement of high quality and low price. The resolution of most of the current wearable displays is a fraction of that of an average desktop monitor, but their prices are even higher than that of high resolution flat screens.

Furthermore, the problem is also known that in the case of small size, preferably head-mountable optical display units, it is extremely difficult to ensure high resolution. The reason for this is that in the case of small size displays, the pixels must be displayed in a size even smaller than that of normal displays, and as a result, increasing the optical resolution runs into physical limitations.

In the prior art, it has been recognised that this problem can be remedied by display units which - instead of homogenous resolution - project the image into the eye by a dynamic resolution that tracks the direction of vision. This is because in case the direction of vision of the eye is tracked, and the part of the picture corresponding to the direction of vision, i.e. the so-called foveal part of the picture is displayed in a high resolution, the human brain perceives that the whole image has a high resolution. The remaining part of the image, which is projected to the low resolution part of the retina, can be displayed in a lower resolution.

There is a number of such prior art approaches. In JP 09 305 156 A2 a method and apparatus are described which track the direction of vision and generate a high resolution image in the centre of the direction of vision. The apparatus displays the image with inhomogeneous resolution by means of a special display unit.

According to US 5,726,670, the higher resolution of the foveal part is generated by displaying a distorted image, followed by restoring with a special optic. This solution also necessitates the application of a special display unit.

By means of the system described in US 5,422,653, again a video image of inhomogeneous resolution is displayed. In this approach, an image of varying resolution is displayed to a passive observer in accordance with the changes taking place in the visual information, and the observer's vision is directed to the required point by altering the resolution. This approach does not involve the tracking of the eye and therefore is not suitable for accomplishing the objects of our invention.

In US 2002/0126065 A1 a solution is described, in which special optical units are used to project into one eye a small part of an image in high resolution and into the other eye the remaining part of the image in a lower resolution.

In US 2004/0227703 A1 a display of inhomogeneous resolution is described, which achieves the inhomogeneous image by means of special hardware-based measures. The images are displayed by means of a display unit of physically changing resolution and a lens of changing magnification is applied on the signal source side.

In US 2001/0043163 A1 a solution is described which tracks the direction of vision by reflected infrared radiation, and the foveal part is displayed in a high resolution by means of a special dynamic lens. In US 6,417,867 B1 a system is described, in which - corresponding to the direction of vision or the cursor position - a particular specific area of the display appears in magnification and high resolution, while the rest is displayed in a smaller resolution.

In US 5,635,947, an image with large optical angle and lower resolution and an image with a smaller optical angle and high resolution are generated by means of two displays. The images are projected with cut-out covering into the eye in accordance with the direction of vision. According to this approach, the projecting optical units are moved according to the direction of vision.

The system described in US 5,751 ,259 projects into the eye in the direction of vision a high resolution image and in the remaining part another image combined with the former and having a lower resolution. The system comprises display surfaces generating a high resolution image and a lower resolution image, an optical system which combines and projects into the eye the light beams generated by the display surfaces as well as a mechanism moving the optical means.

It is a common disadvantage of the prior art systems that they have extremely complicated design and can only be produced in a costly way. The displays and/or optical systems providing for inhomogeneous resolution are not built of standard components, which raises the costs extremely. In case the inhomogeneous resolution is implemented by a display which is suitable for displaying the whole high resolution image, the equipment will not be suitable for the purpose of our invention, because the size reduction and cost limits mentioned in the introduction prevail. In some other prior art equipment, display corresponding to the direction of vision is achieved by physically moving the optical elements. These actuating mechanisms further increase the cost of the equipment and may easily break down or become misadjusted.

DESCRIPTION OF THE INVENTION

It is an object of our invention to provide a display method and apparatus which are exempt from the problems of prior art approaches.. It is also an object of our invention to create a method and apparatus which implement inhomogeneous resolution subject to the direction of vision by stationary optical elements. It is a further object to provide a method and apparatus which do not necessitate special optical elements and/or display units. A further object of our invention is to provide a display method and apparatus, in which a high resolution part of the picture is always automatically imaged into the high resolution part of the retina in accordance with the eye movement as a result of a special design of the optical system. It is a further object to provide a method and apparatus by which the image of low resolution low cost displays can be modified in a way that therefrom practically the same information would reach the vision centre of the brain than in the case of a high resolution display.

Accordingly, as a first aspect, the invention is a display method in which a direction of vision is detected, and a foveal part of an image is displayed in a first resolution, said foveal part being dedicated to be imaged in a high resolution area of the retina, and a remaining part of the image is displayed in a second resolution, said second resolution being lower than the first resolution. According to the invention,

- on a first display surface the foveal part is displayed in the first resolution and the first display surface is imaged through a diaphragm aperture with a first angular resolution into the eye, wherein an objective unit mapping the diaphragm aperture essentially in the centre of rotation of the eye is used for this imaging, and

- on a second display surface at least the remaining part of the image is displayed in the second resolution and the second display surface is imaged into the eye in such a perceived image size, that would correspond to an perceived image size of imaging the full image displayed in the first resolution with the first angular resolution into the eye.

The basic idea of the invention is that the light beams projected to the fovea centralis always pass through the centre of rotation of the eye (the pupil, the centre of rotation and the fovea centralis are located along a straight line), consequently, if a diaphragm is arranged in a way that the diaphragm aperture is imaged by an optical system into the centre of rotation of the eye, the light beams passing through the diaphragm fall onto the fovea. Only a small portion of these beams reach simultaneously the eye depending on the direction of vision, but all light beams passing through the diaphragm aperture fall onto the fovea if they get into the eye. According to the invention, under angular resolution the optical angle of neighbouring pixels is understood. For the user, the perceived size of the image must be made as if he/she saw the whole image in high resolution, i.e. in the first resolution. Therefore, the second display surface must be imaged into the eye with such a perceived image size - i.e. for example by an optical angle perceived by the user - which would correspond to the imaging with the first angular resolution of the total image displayed in the first resolution.

By means of the method according to the invention, it is ensured that the high resolution picture imaged through the centre of rotation of the eye is always projected to the high resolution part of the retina, while the imaging of the lower resolution picture according to the invention ensures that the lower resolution surroundings of the high resolution part of the image is projected into the eye. The imaging of the high resolution picture through the diaphragm aperture and the centre of rotation of the eye makes sure automatically that the foveal part of the image is projected onto the fovea, and therefore by detecting the direction of vision in a way known per se and by displaying the appropriate part of the image on the first display surface, a dynamic display can be created. According to the invention, under imaging or mapping the diaphragm aperture into the centre of rotation of the eye, imaging with a specified tolerance to the centre of rotation and to its surrounding is also understood.

It can be seen that the invention is based on the following idea: in a given moment only a fraction of the information carried by an image of a high resolution monitor reaches the vision centre of the brain, and hence a method can be created which provides this information by applying a lower resolution, lower cost display. When the intention is to process the full information content of an image, the smaller areas of the image are monitored sequentially one after the other. Therefore, it is sufficient to display only that part of the image in a high resolution which is imaged to the largest resolution area of the retina, the so-called central fovea (fovea centralis). The definition of the retina rapidly decreases with the distance from the central fovea, and therefore it is sufficient to display the picture details imaged to more remote areas by a lower resolution. The optical image of the area displayed by a high resolution automatically tracks the eye according to the invention.

Preferably, the first display surface is projected by a first optical unit through the diaphragm aperture to generate a first optical image and the second display surface is projected by a second optical unit to generate a second optical image, said first optical image and the second optical image being imaged into the eye by means of the objective unit. According to the invention, under optical image an image generated by optical elements or a combination thereof from a display surface is understood.

A preferred embodiment of the invention is characterised in that light beams of the first optical image and the second optical image are combined with a common optical axis between the diaphragm aperture and the eye, wherein the centre of rotation of the eye, the centre of the diaphragm aperture and the centre of the first display surface are arranged essentially on the optical axis. According to this embodiment, the combined light beams can be projected to the eye extremely preferably through a common objective.

According to another preferred embodiment the combination of beams is implemented by a first mirror including an angle with the optical axis and having the diaphragm aperture. The special mirror according to the invention provides both the imaging through the diaphragm aperture and the combination of light beams.

According to a further preferred embodiment, two parts of a display surface of a single display unit are used as the first display surface and as the second display surface. This embodiment enables that the apparatus according to the invention can be produced at an extremely low cost.

According to an especially preferred embodiment the first optical image and the second optical image are generated coincidentally in the same size, and the first optical image comprises the optical image of the foveal part in a position corresponding to the direction of vision. In this preferred embodiment, the first image comprises in a position corresponding to the direction of vision the high resolution optical image. The first optical image is preferably generated by multiplying the foveal part. As an example, the multiplication may be carried out by prism type optical means. In this embodiment, as an example, an objective consisting of a single objective lens can be used for projecting the optical images into the eye, in the focal plane of which the first and the second optical images are generated.

Another especially preferred embodiment is characterised in that the first optical image only comprises the optical image of the foveal part and the first optical image and the second optical image are generated in the same image plane, wherein the size ratio between the first optical image and the second optical image corresponds to the size ratio between the foveal part and the full image. Consequently, in this embodiment, it is not necessary to multiply or to use another fill-up for generating the first optical image, but a further lens moving together with the eye, preferably a contact lens is needed for setting the sharpness.

According to another aspect, the invention is display apparatus, comprising

- means for tracking the direction of vision,

- a first display surface displaying in a first resolution a foveal part of an image to be displayed, said foveal part being dedicated to be imaged in a high resolution area of the retina,

- a second display surface displaying in a second resolution lower than the first resolution at least the part of the image outside the foveal part, and

- an optical system imaging the first display surface and the second display surface into the eye. According to the invention, the optical system comprises

- an optical means having a diaphragm aperture,

- a first optical unit generating a first optical image through the diaphragm aperture from the first display surface,

- a second optical unit generating a second optical image from the second display surface, and - an objective unit imaging the first optical image into the eye with a first angular resolution and imaging into the eye the second optical image as well, said objective unit mapping the diaphragm aperture essentially into the centre of rotation of the eye, wherein the perceived image size of imaging the second optical image corresponds to a perceived image size of such an image that would appear by imaging into the eye with the first angular resolution the full image displayed in the first resolution.

BRIEF DESCRIPTION OF THE DRAWINGS

Hereinafter, the invention will be described by means of preferred embodiments as shown in the drawings, where

Fig. 1 is a diagram showing the characteristic curve of a human eye's sensitivity,

Fig. 2 is a block diagram of an example of a display apparatus according to the invention,

Fig. 3 is a schematic optical drawing of a display apparatus according to an especially preferred embodiment of the invention,

Fig. 4 is a diagram of an image multiplicating display method used in the embodiment according to Fig. 3,

Fig. 5 is a diagram of an example of an optical arrangement enabling image multiplication, and

Fig. 6 is an optical diagram of a display apparatus according to another especially preferred embodiment of the invention.

MODES FOR CARRYING OUT THE INVENTION

The diagram shown in Fig. 1 depicts the characteristic curve of a human eye's sensitivity, showing the relative resolution of the eye as against the maximum, subject to the angular deviation measured in degrees to the direction of vision. The diagram shows well that the sensitivity of the eye is the highest at the fovea, i.e. in the centre of the diagram, and subject to the distance it drops steeply, reaching a relatively low level. This biological fact is utilised in the inventive display method and apparatus, according to which the foveal part of the image to be displayed and imaged in the high resolution part of the retina is displayed in a first resolution and the remaining peripheral part in a second resolution which is lower than the first resolution. To track the direction of vision, there are numerous prior art approaches; in this respect reference is made to the description of prior art in the introduction. The foveal part to be displayed in a high resolution of the original high resolution image is determined according to the direction of vision, preferably by a software or by using an appropriate special-purpose hardware. The size and shape of the foveal part can be different, and according to our invention any size or shape can be involved which is suitable for imaging into the fovea, into a significant area of the fovea or including the area of the fovea.

Fig. 2 shows a block diagram of a display apparatus according to the invention, an input 10 of which receives a high resolution, for example 1024 x 768 (XGA) image signal. The image signal is that of a high resolution signal source, e.g. TV₁ video or computer, which is converted according to the invention in a way that the image part in the direction of vision, imaged to the fovea, is displayed in the full original resolution, while other parts of the image, farther from the direction of vision are displayed in a lower resolution, on a display unit of lower resolution than that of the original image. This image signal is thus converted by means of an image converter unit 12 in a way to be discussed later, and the converted image is displayed on a display unit 14. By way of example, the display unit 14 may be of 640 x 480 (VGA) or 320 x 240 pixel resolution. For controlling the image converter 12 and the display unit 14, a microcontroller 16 is preferably applied. As described above, the eye is tracked by a tracking means 18, and the result of tracking is forwarded to the microcontroller 16. The sensed direction of vision determines the image conversion operation carried out by the image converter 12. The picture displayed by the display unit 14 is imaged into the eye by means of the optical system 20 according to the invention.

It can be seen that the tracking carried out by the tracking means 18 only serves as an input to the image conversion operations, i.e. it is not necessary to control the optical system, as it comprises fixed elements. This advantage can be achieved by the special optical system described below. In the depicted preferred embodiment, the first display surface and the second display surface form two parts of a display surface of the same display unit 14. This is because by means of the image converter unit 12, it is extremely efficient to display electronically side by side on the divided display surface the low and high resolution images. In the given case of course the first and second display surfaces can be implemented by separate displays as well.

A further important characteristic of the display unit 14 is that it has a lower resolution than that of the image signal received on the input 10. It is advisable to use a maximum resolution on the first display surface, i.e. the original resolution of the image signal received on the input 10, and the second display surface should have a resolution decreased by omitting and/or averaging the pixels.

Fig. 3 shows a diagram of an optical system of a display apparatus according to an especially advantageous embodiment of the invention. The foveal part of the picture to be displayed, which is to be imaged onto the high definition surface of the retina, is displayed on a first display surface 22. From the first display surface 22, by means of a first optical unit OU 1, through a diaphragm aperture 42, a first optical image OH comprising the foveal part is generated.

The apparatus furthermore comprises a second display surface 32, in which at least the part of the displayable image outside the foveal part - i.e. in the given case for example even the foveal part or a part thereof - is displayed in a second resolution which is lower than the first one. From the second display surface 32, by means of a second optical unit OU2, a second optical image OI2 having an optical axis 44 identical with the first optical image OH is generated. The second resolution may also be inhomogeneous, and in the given case by increasing the distance from the foveal part, the resolution of the peripheral part may also decrease. This can be implemented e.g. by increasing the extent of averaging as a function of the distance from the direction of vision. In this case, the image distortion resulting from the inhomogeneous resolution must be compensated by appropriate optical means. According to the invention, of course, an optical axis does not only mean a straight line optical axis but for example also an imaging direction broken by mirrors or defined by an elastic light conductor, i.e. the expression Optical axis' is interpreted in the broadest possible sense.

According to the depicted preferred embodiment, the optical means having a diaphragm aperture 42 is a first mirror 40 including an angle with the optical axis 44 and comprising the diaphragm aperture 42 in the centre. The mirror 40 preferably includes an angle of 45° with the optical axis 44, and the diaphragm aperture 42 is formed as a gap in the quicksilvering. By means of the mirror 40, the combination of the light beams of the first optical image 011 and the second optical image OI2 can be implemented extremely advantageously in the common optical axis 44, and in this way the joint imaging into the eye of the first and second optical images OH , OI2 can be ensured. In the preferred depicted embodiment used as an example, the first optical image OH and the second optical image OI2 are generated in an aligned coincident way and in the same size, wherein the optical images are consequently right in scale, and the first optical image OH comprises in a position corresponding to the direction of vision the optical image of the foveal part.

The first optical image OM is preferably generated by multiplying the optical image of the foveal part, which multiplied image also includes in a position corresponding to the direction of vision an appropriate optical image part. The light beams associated with the multiplied image parts other than those in foveal position are not entering the eye. All beams arriving through the diaphragm aperture proceed across the centre of the eye, and among these, those beams which are really entering the eye through the pupil may only reach the fovea.

According to the discussion above, the first optical unit OU1 hence comprises a first lens 24 and an optical multiplier means 26. The second optical unit OU2 comprises a second lens 34 and a second mirror 36. According to the description, the display surfaces 22 and 32 may be designed by dividing the display surface of the same display unit 14. In this case the optical system may comprise further mirrors and in the given case lenses as well. The optical images 011 and OI2 generated as described above are preferably created in the focus plane of the objective 46 forming a part of the objective unit OU3. In this preferred embodiment, the objective 46 serves as a beam deflecting and ocular lens. The objective 46 may consist of a single objective lens, but for this purpose any other optical element or group of elements functioning as an objective may also be used. The figure shows that the centre of the first display surface 22, the centre of the diaphragm aperture 42 and the centre of rotation 48 of the eye are in the optical axis 44. Alignment with the common optical axis 44 may of course be implemented according to the invention with a smaller or larger tolerance.

Consequently, according to the invention by means of the objective unit OU3, which actually images into the centre of rotation 48 of the eye the diaphragm aperture 42, the first optical image OM is imaged to the eye by a first angular resolution, and the second optical image OI2 by a second angular resolution. The second angular resolution is smaller than the first, i.e. the optical angle of neighbouring pixels is larger in the case of the second optical image OI2 than in the case of the first optical image OH . For the user, the image must appear in such a perceived size as if the full image in a large resolution were seen, i.e. in the first resolution. Therefore, the second display surface and the second optical image OI2 imaged therefrom must be imaged into the eye with such a perceived image size - i.e. by for example with an optical angle perceived by the user - which would correspond to the full picture displayed in the first resolution, which imaged by the first angular resolution. Therefore, to the environment of the fovea, i.e. to the lower resolution parts of the retina, this low resolution image will be imaged.

By imaging the high resolution part of the image through the centre of rotation 48 of the eye according to the invention, it is ensured that regardless of the direction of vision, the eye will see the picture displayed on the first display surface 22 in a high resolution. And, making use of the signal of the tracking means 18 designed to track the direction of vision, on the first display surface 22 we are able to display the actual foveal part of the image in a higher resolution. By means of the thick dash-and-dot line shown in Fig. 3, with the eye looking upwards, the light beam entering the eye from the bottom edge of the first display surface 22 is depicted. In this position, the eye - looking upwards - sees the optical image of the first display surface 22 through the diaphragm aperture 42. When the eye looks down, the light beam marked with a thin dash-and-dot line indicates the light beam falling onto the fovea from the other edge of the first display surface 22. Consequently, in this position the eye sees the optical image of the first display surface 22, i.e. the optical image seems to be moving when the eye is moved. It can be observed that during the movement of the eyeball, light from different points of the image arrives into the central fovea, but always through the diaphragm aperture, while the other parts of the retina receive light from the surface of the first mirror 40.

The second optical image OI2 generated from the second display surface 32 is projected into the eye in an image size corresponding to extreme positions indicated by dashed lines. A thick dashed line indicates in the upper position the light beam entering the eye, and a thin dashed line marks the light beam introduced into the eye in the bottom position. The projection of the second optical image OI2 into the eye results in the fact that it will not move subject to the direction of vision, but it forms a fixed background of the virtually moving optical image 011.

The approach offered by the invention may also be understood in a way that the parts displayed in a lower resolution are magnified by the optical system and/or the full resolution part is made smaller. The full visible image size of the unit preferably corresponds to the visible image size of a monitor, the full resolution of which is nearly equal to the original resolution of the signal source and the angular resolution of which is roughly equal to that of the converted image part being in the direction of vision.

Fig. 4 shows stages of the picture generating method realised by the optical system according to Fig. 3. In the image 50 to be displayed at the top of the figure, the fovea! part 52 corresponding to the detected direction of vision is marked. As it has already been discussed, the foveal part may have any appropriate shape and size, which is preferably subject to the optical system applied. In the depicted preferred embodiment used as an example, the foveal part 52 is one quarter of the area of the image 50 and has a similar shape. In this version, from the image 50 received on the input 10, a low resolution image 60 can be preferably generated by averaging the pixels of the image 50 (increased calculation needs) or by omitting every second pixel vertically and horizontally (lower calculation needs). However, of course, any other method for reducing the resolution can be applied. In the low resolution image 60, the part corresponding to the foveal part 52 may also be left empty, but in the given case by displaying the full image 50 in a low resolution, this foveal part may be filled also with the low resolution optical image of the foveal part.

Considering the functioning of the optical system according to the invention, it can be seen that if a light beam does not proceed across the centre of rotation of the eye, it can not fall onto the fovea centralis. From the area of the low resolution image 60 corresponding to the foveal part 52, no light reaches the eye, because the diaphragm aperture cuts out those of the beams reflected from the first mirror 40 which might reach the fovea. This means that in principle there is no difference whether on the second display surface the image is displayed by leaving the foveal part empty, because no light may reach the eye from there anyway. Such an omitting may be advantageous from the aspect that less information must be processed. From the low resolution image 60, an image 62 is generated by means of the second optical unit OU2.

The foveal part 52 must be displayed in the correct position in a high resolution. This can be advantageously implemented by multiplying the foveal part 52. The multiplication is preferably carried out in a way that the image 50 is divided by a virtual dividing grid corresponding to the multiplication, which means that in the depicted preferred embodiment the image is divided in four parts by a vertical and a horizontal line. The foveal part 52 is cut up by these dividing lines, by means of which the image quarters corresponding to the image 54 are defined. The image 54 is converted in a way that these image quarters are exchanged with each other in horizontal and vertical directions, and this converted image 56 must be displayed on the first display surface 22 for image multiplication. This is how an image 58 is generated as shown in the bottom of Fig. 4. It can be seen in the image 58 that by the multiplication of the image with exchanged quarters, in a position corresponding to the direction of vision, an optical image corresponding to the foveal part 52 appears.

By generating the image 58 shown in the bottom of Fig. 4 as the first optical image 011 , and image 62 as the second optical image OI2, and projecting those into the eye according to the invention, the object of the invention can be achieved.

Fig. 5 shows another example of image multiplication, which is similar to that depicted in Fig. 4. In Fig. 5, an image 66 is generated from the image 64, which includes the image 64 sixteen times. The image multiplication is preferably implemented by two prisms 70, 72. These prisms 70 and 72 are special pentaprisms, which have an incidental side perpendicular to the optical axis and four exit sides including an angle with the optical axis. The refraction angles of the prisms determine how far the four part-images of the multiplied part are shifted as against the original position. These refraction angles can be simply calculated subject to the optical arrangement. Consequently, the first prism 70 generates from the image 64 in the horizontal direction a multiplied image consisting of four periodically repeated images, which multiplied image is multiplied four times also vertically by the prism 72.

The image multiplication can of course be implemented not only by prisms but also by other appropriate optical elements, for example by an arrangement consisting of partially transparent mirrors or a lens arrangement.

Fig. 6 shows another preferred embodiment of the optical system according to the invention. This embodiment partly differs from the embodiment shown in Fig. 3 in that it does not comprise the optical multiplication unit 26 and the first optical image OH only contains the optical image of the foveal part 52.

In this embodiment, the first and second optical images OH, OI2 are generated in the same image plane, but in this case the size ratio between the first optical image OH and the second optical image OI2 corresponds to the size ratio between the foveal part 52 and the full image 50. The joint image plane of the first and second optical images 011 , OI2 is different from the focal plane of the objective 46. By mapping the first display surface 22 in the centre of rotation of the eye through the diaphragm aperture 42, it is ensured also in this embodiment that it will always be the high resolution image which is projected to the high resolution part of the retina.

It can be seen that in this embodiment, the second optical image OI2 corresponding to the background is relatively magnified, i.e. its resolution will be lower. The objective 46 deflects the light beams also in this embodiment in a way that the optical image of the first display surface 22 seems to be moving with the motion of the eye and tracks the eye as well. Consequently, the high resolution part of the image is shown in the proper position in the case of all directions of vision, and the proportion of resolution is also of the desired extent, but in this embodiment, in order to achieve appropriate sharpness, it is necessary to have a further lens forming a part of the objective unit OU3, preferably a contact lens 49. Therefore, in this embodiment the functions of an ocular (contact lens 49) and the light beam deflecting role (objective 46) are separated.

The contact lens moving together with the eye as an ocular lens is a simple spherical lens in this embodiment, which spherical lens can be implemented in a much more simple way as against the varying magnification lenses of prior art approaches and can be handled easier. If, for example, one has to 'look out of the display module, it is not necessary to remove the contact lens, but its effect can be compensated by a simple spectacles lens.

According to the invention, the foveal part of the image is not necessarily determined according to the direction of vision in the strict sense, but as an example it can only be selected on the basis of the position of a pointer of a cursor, mouse or other positioning unit. This is because these specific positions may correspond to the direction of attention i.e. to the direction of vision. In these cases, the tracking means 18 is preferably a software module which detects the position. In the specification and also in the claims, the expression 'direction of vision' is used in such a broader meaning. Consequently, by means of the imaging method and apparatus according to the invention it can be ensured that regardless of the direction of vision, the light arrives at the high resolution part of the retina from a first source, and at the remaining peripheral parts from another source. All this is implemented without the application of moving parts, exclusively in an optical way.

The method and apparatus according to the invention are of course suitable for displaying still and moving pictures.

The invention can be applied in all areas which require the use of a high resolution display, but where their much higher cost, complexity and/or weight is not acceptable. Because the invention requires the presence of an optical system in the vicinity of the eye, the application is advantageous primarily but not exclusively in the case of head mountable displays (spectacles, helmet, etc.). Such an application can be a portable video display, TV, HDTV, portable computers (notebook, PDA), game and virtual reality systems and the display of a mobile phone or video phone. It can be used advantageously instead of a desktop monitor and also in medical or military applications.

It is an advantage of the approach according to the invention that by making use of low priced low resolution displays it provides the impression of high resolution displays to the user. Because low resolution displays develop at least just as fast as their high resolution counterparts and the new technologies also appear first in this segment, the solution according to the invention will continue to provide for a long time at a beneficial price the same or even a better quality than the high resolution techniques.

For a person skilled in the art it is obvious that the invention is not limited to the preferred embodiments detailed by way of example, but further modifications and changes are also possible within the scope of the following claims.

Claims

1. A display method in which a direction of vision is detected, and a foveal part of an image is displayed in a first resolution, said foveal part being dedicated to be imaged in a high resolution area of the retina, and a remaining part of the image is displayed in a second resolution, said second resolution being lower than the first resolution, c h a r a c t e r i s e d in that

- on a first display surface (22) the foveal part (52) is displayed in the first resolution and the first display surface (22) is imaged through a diaphragm aperture (42) with a first angular resolution into the eye, wherein an objective unit (OU3) mapping the diaphragm aperture (42) essentially in the centre of rotation (48) of the eye is used for this imaging, and

- on a second display surface (32) at least the remaining part of the image is displayed in the second resolution and the second display surface (32) is imaged into the eye in such a perceived image size, that would correspond to an perceived image size of imaging the full image displayed in the first resolution with the first angular resolution into the eye.

2. The method according to claim 1 , characterised in that the first display surface (22) is projected by a first optical unit (OU1) through the diaphragm aperture (42) to generate a first optical image (011) and the second display surface (32) is projected by a second optical unit (OU2) to generate a second optical image (OI2), said first optical image (OH) and the second optical image (OI2) being imaged into the eye by means of the objective unit (OU3).

3. The method according to claim 2, characterised in that light beams of the first optical image (OH) and the second optical image (OI2) are combined with a common optical axis (44) between the diaphragm aperture (42) and the eye, wherein the centre of rotation (48) of the eye, the centre of the diaphragm aperture (42) and the centre of the first display surface (22) are arranged essentially on the optical axis (44).

4. The method according to claim 3, characterised in that the combination of beams is implemented by a first mirror (40) including an angle with the optical axis (44) and having the diaphragm aperture (42).

5. The method according to claim 1, characterised in that two parts of a display surface of a single display unit (14) are used as the first display surface (22) and as the second display surface (32).

6. The method according to any of claims 2 to 5, characterised in that the first optical image (011) and the second optical image (OI2) are generated coincidentally in the same size, and the first optical image (OH) comprises the optical image of the foveal part (52) in a position corresponding to the direction of vision.

7. The method according to claim 6, characterised in that the first optical image (OH) is generated by multiplying the optical image of the foveai part (52).

8. The method according to claim 7, characterised in that the multiplication is carried out by a prism type optical multiplying unit (26).

9. The method according to claim 6, characterised in that the first optical image (OH) and the second optical image (OI2) are generated in the focus plane of an objective (46) forming a part of the objective unit (OU3), said objective (46) also serving for mapping the diaphragm aperture (42) into the centre of rotation (48) of the eye.

10. The method according to any of claims 2 to 5, characterised in that the first optical image (OH) only comprises the optical image of the foveal part (52) and the first optical image (OH) and the second optical image (OI2) are generated in the same image plane, wherein the size ratio between the first optical image (OH) and the second optical image (OI2) corresponds to the size ratio between the foveal part (52) and the full image (50).

11. The method according to claim 10, characterised in that the objective unit (OU3) comprises an objective (46) imaging the first optical image (OH) and the second optical image (012) into the eye, and a further lens ensuring sharpness, preferably a contact lens (49), moving together with the eye.

12. A display apparatus, comprising

- means for tracking the direction of vision,

- an optical system imaging the first display surface and the second display surface into the eye, c h a r a c t e r i s e d in that the optical system comprises

- an optical means having a diaphragm aperture (42),

- a first optical unit (OU1) generating a first optical image (OH) through the diaphragm aperture (42) from the first display surface (22),

- a second optical unit (OU2) generating a second optical image (OI2) from the second display surface (32), and

- an objective unit (OU3) imaging the first optical image (OH) into the eye with a first angular resolution and imaging into the eye the second optical image (OI2) as well, said objective unit (OU3) mapping the diaphragm aperture (42) essentially into the centre of rotation (48) of the eye, wherein the perceived image size of imaging the second optical image (OI2) corresponds to a perceived image size of such an image that would appear by imaging into the eye with the first angular resolution the full image displayed in the first resolution.

13. The apparatus according to claim 12, characterised in that the centre of rotation (48) of the eye, the centre of the diaphragm aperture (42) and the centre of the first display surface (22) are arranged essentially on a same optical axis (44) and the optical means having the diaphragm aperture (42) is a first mirror (40) including an angle with the optical axis (44).

14. The apparatus according to claim 13, characterised in that the first optical unit

(OU 1) comprises a first lens (24) and the second optical unit (OU2) comprises a second lens (34) and a second mirror (36).

15. The apparatus according to claim 12, characterised in that the first display surface (22) and the second display surface (32) are two parts of a display surface of a single display unit (14).

16. The apparatus according to any of claims 12 to 15, characterised in that the first optical unit (OU 1) and the second optical unit (OU2) generate the first optical image (OH) and the second optical image (OI2) coincidentally and in same size, wherein the first optical image (OH) comprises the optical image of the foveal part (52) in a position corresponding to the direction of vision.

17. The apparatus according to claim 16, characterised in that the first optical unit (OU1) comprises optical means (26) for multiplying the optical image of the foveal part (52).

18. The apparatus according to claim 16, characterised in that the objective unit (OU3) comprises an objective (46) mapping the centre of the diaphragm aperture (42) into the centre of rotation (48) of the eye, wherein the first and second optical units (OU1 , OU2) are designed to generate the first and second optical images (OH , OI2) in the focus plane of the objective (46).

19. The apparatus according to any of claims 12 to 15, characterised in that the first optical image (OH) only consists of the optical image of the foveal part (52) and the first and second optical units (OU 1 , OU2) generate the first optical image (OH) and the second optical image (OI2) in the same image plane, wherein the size ratio between the first optical image (OH) and the second optical image (OI2) corresponds to the size ratio between the foveal part (52) and the full image (50).

20. The apparatus according to claim 19, characterised in that the objective unit (OU3) comprises an objective (46) imaging the first optical image (OH) and the second optical image (012) into the eye, and a further lens ensuring sharpness, preferably a contact lens (49), moving together with the eye.