WO1994005115A1

WO1994005115A1 - Arrangement for reading and converting optical information to electronic representation

Info

Publication number: WO1994005115A1
Application number: PCT/SE1993/000686
Authority: WO
Inventors: Lennart STÅLFORS; Henrik Lind
Original assignee: Victor Hasselblad Ab
Priority date: 1992-08-20
Filing date: 1993-08-18
Publication date: 1994-03-03
Also published as: SE505477C2; SE9202388L; SE9202388D0

Abstract

The present invention relates to an arrangement and a method respectively for reading and converting optic information to electronic representation. According to the invention this conversion takes place without any analogue intermediate storing and each pixel forming a picture element comprises a light valve device which is controllable by a controlling device and the arrangement furthermore comprises photo detecting devices (2') of a detecting unit (2) wherein to each photo detecting device (2') at least one light valve device of a light valve unit is arranged, wherein the photo detecting device(-s) (2') detects/detect incident photo energy and when a given value of photo energy is reached deliver/delivers a signal for controlling the corresponding controlling device.

Description

Arrangement for reading and converting optical information to electronic representation.

TECHNICAL FIELD:

The present invention relates to an arrangement for direct reading and converting optic information to electronic representation as stated in the first part of claim 1. The invention further relates to a method for converting optic information to electronic representation according to claim 23. At the conversion of optic information to electronic representation the requirements on the arrangement are high to assure that no information is lost or changed or attenuated. This often makes arrangements of this kind expensive and the resolution is kept on a lower level to simplify the fabrication and keep the expenses on an acceptable level. The arrangement may particularly be used in photography. According to a particular embodiment, as given in claim 15, the arrangement is constructed so that it is also possible to show or review stored images.

STATE OF THE ART:

Arrangements as initially referred to are known and there are a number of types of so called matrix sensors in which optic information is transmitted from an image of light to electronic representation.

A known matrix sensor comprises the CCD-sensor (Charge Coupled Device) . In a such incident light energy is converted to electronic charges. The surface of the sensor is divided into a number of picture elements, pixel, separated from each other, in which the photo energy is converted. CCD-sensors are used in cameras wherein the electronic representation of light energy in each pixel is converted to an electronical storable image which can be reproduced on a monitor or be printed as a photographic

image in a printer. The use of such CCD-sensors however involves a number of problems and leads to a number of practical limitations. One problem is difficulties to obtain the same sensitivity in every pixel. A number of difficulties are also involved in the transporting of the charges which have been generated in each pixel respectively out of the sensor without being influenced and changed by other phenomena such as e.g. rest charges, dark current, cross talk, e t c, before they are registered with a corresponding digital value in an A/D-converter.

Due to these and other difficulties it gets too technically complicated as well as expensive to fabricate a CCD-matrix sensor. It particularly involves difficulties to fabricate a CCD-matrix sensor which gives a sufficiently good image representation since the image quality depends on the number of pixels, i.e. the more pixels (picture elements) a sensor comprises, the more picture elements the incident picture will be divided into and the higher the resolution, i.e. the better is the reproducibility of the image.

SUMMARY OF THE INVENTION:

The object of the present invention is to provide a device for reading and converting optic information to electronic representation. It is a further object of the invention to provide an image sensor wherein a higher resolution can be obtained in a simple and cheap way. A further object is to convert the image of the optic information to electronic representation without any degeneration. A further object of the invention is in a simple way to enable that the light sensitive elements of the arrangement or the sensor be given uniformity. Further objects of the invention is a simple fabrication of an arrangement which also is cheap, easy to use, e t c.

More particularly it is an object of the invention to provide an arrangement for reading and converting optic information to electronic representation or recording by which stored image information also can be reviewed or shown. Such an arrangement is given by claims 15 to 22.

A further object of the invention is to provide a method for reading and converting optic information to electronic representation.

An arrangement through which those as well as further objects are achieved is given by the characteristics of the characterizing part of claim 1. A method for reading and converting optic information to electronic representation is given in claim 23. Preferred embodiments are given by the characteristics of the subclaims.

According to the invention the conversion of the optic information to electronic representation is effected directly without analogue intermediate storing. Every pixel comprises a light valve device controllable by a controlling device wherein a light valve unit is formed by a number of light valve devices. Through a number of photo detecting devices forming a photo detecting unit wherein to each photo detecting device at least one light valve device is arranged, the photo detecting device detects incident photo energy in the relevant pixel and when a given value of photo energy has been reached, the photodetecting device delivers a signal for controlling the controlling device of the actual light valve device. The arrangement may of course take a number of different forms. For example, one photo detecting device can be arranged to a number of light valve devices or to just a single one and the controlling device can be separate or common to the different light valve devices. Particularly, if the given photo energy is reached in a particular pixel the controlling device interrupts an opening process in the light valve device. When more than one light valve device corresponds to each detecting device, the detecting device may either read out the light valve devices sequentially or two or more simultaneously according to different embodiments. The photo detecting device may particularly be a photo transistor which delivers an electrical signal when its surface is hit by photo energy or according to a further embodiment it may comprise a photo diode or a photo diode in combination with a light emitting diode. Particularly, the controlling device controls the actual or corresponding light valve device in such a way that this is opened with a velocity which follows a given curve up to a given value of photo energy detected by the photo detecting device whereupon this delivers a signal. This given curve is particularly such that it all the time has a positive differential coefficient during opening. The control can particulary be carried out in such a way that the detected light energy corresponds to the sensitivity characteristic of the eye. Alternatively it is adapted so that the detecting device reads out the light with a curve which does not correspond to the response curve of the eye why a so called r-function is superposed for compensation and adjustment respectively. This r-compensation can particularly be achieved by the use of a saw tooth generator. The detector can also be linearized. When the opening speed is constant, the compensation has to be done later on.

The resolution is varied through variation of the detection density in a way which is known per se. According to a particular embodiment a number of pixels can be so arranged that they form a matrix for forming a so called matrix sensor wherein an array of detecting devices are arranged in connection to the light valve matrix comprising a number of pixels. According to a particularly advantageous embodiment the light valve device comprises ferroelectric liquid crystals, FLC. The ferroelectric liquid crystals are preferably in smectic A^*-phase. Preferably, the liquid crystal is surface-stabilized wherein the voltage across the crystals of the grating can be varied with the use of a generator means, for example a saw tooth generator and wherein the detecting devices are arranged in a plane which is parallel to the light valve matrix device. Through a control unit is indicated which pixel or which pixels are to be activated on the liquid crystal. For storing of the light energy detected in the pixels respectively the device further comprises an address register and a digital storing means wherein further a computer is arranged for digitalizing the value of the light image before storing in the address register whereupon the information together with the address is stored in a digital storage means.

According to an alternate embodiment a number of pixels are arranged in a row so that the device forms a linear array sensor. A such can be convenient when the objects are stationary, e t c. This linear array sensor can be movable wherein the sensor is swept in relation to the optic information which is to be converted to form an image. Alternatively, the optic information can be swept in relation to the linear array sensor or both alternatives may be combined.

According to a particular embodiment the arrangement can be so formed that it can be used as a monitor. The detecting unit then comprises means for absorbing light and stored images can be shown or displayed by activation of a display selection device. This can be so formed that for showing images it is possible to choose between stepping in the one or the other direction. The absorbing means may comprise an absorbing black surface and in the storage medium stored images are shown through the indication of the address in the address register with the use of the display selection device. Via the control unit and driving electronics image data are thus displayed as an image on the light valve matrix. The arrangement, as well as sensor and monitor can be arranged in a camera or similar. To form a monitor the arrangement can be arranged as a back or similar of the camera which is arranged in relation to the camera in such a way that the images easily can be illustrated. The device can particularly be demountable or rotatably arranged in relation to the camera or form part of this so that the pictures easily can be looked at merely through making a simple grip or similar. According to one alternative, in the case wherein the camera e.g. comprises a single lens reflex camera the finder mirror and the focusing screen of the camera can be so formed that they can be rotated to such extent that the image matrix through the reflection can be illustrated and can be looked at through the view finder hood. The finder mirror will particularly comprise a reflective coating on the front as well as the back side. According to an alternate embodiment it is possible to arrange or to integrate an array of photo diodes or similar in the detecting units for illumination of the matrix.

Through the invention it is possible to, with high resolution and in a simple and cheap way, convert optic information to electric representation. According to a particular embodiment it gets possible to illustrate stored electronic representation. BRIEF DESCRIPTION OF THE DRAWINGS:

The invention will in the following be further described by reference to the accompanying drawings in an explanatory and by no means limiting way wherein

Fig. 1 illustrates an arrangement in the form of a sensor for reading and converting optic information to electronic representation, Fig. 2 illustrates an arrangement according to the invention which can be used for showing images, Fig. 3a externally illustrates an arrangement which can be used as a sensor and a monitor arranged on a camera, Fig. 3b illustrates the arrangement of 3a with an exposed image plan, Fig. 4a schematically illustrates a camera of a single lens reflex type with an arrangement according to the invention used as a sensor, Fig. 4b schematically illustrates a camera and the arrangement of Fig. 4a but now in position for monitoring.

PREFERRED EMBODIMENTS:

According to a particular embodiment described in Fig. 1, a surface stabilized photoelectric liquid crystal (FLC) is arranged in the form of a matrix. Behind the liquid crystal matrix 1 a detecting unit 2 in the form of a photo sensitive matrix of photo detecting devices 2' is arranged.

The matrix 1 can be said to comprise a number of pixels arranged in the form of a matrix. As simplified for one pixel, light can be said to be incident onto a light valve device behind which a detecting device 2' is arranged, e.g. in the form of a photo transistor. If the detecting device 2 ' is hit by light, i.e. the light valve device is open, this delivers an electric signal. If the light valve device initially is closed consequently no signal will be delivered from the detecting device 2' when light is incident onto the light valve device. If however an opening operation of the light valve device starts at a time t₀ by the use of a controlling device, with a given velocity, the detecting device 2', or according to a particular embodiment the photo transistor, which is so connected that it at the incidence of a given light energy delivers a trigger signal but when a given light energy is reached, the opening operation of the light valve device is to be interrupted at the time t_τ. Therethrough a value is obtained which is proportional to the incident photo energy. What has been described herein can be said to represent a pixel and the device can thus be said to comprise a number of pixels arranged in a matrix. With such a sensor according to the invention the image information can be directly read spot by spot without any analogue intermediate storing and wherein the reading furthermore can be effected in a desired way so that among others the resolution can be varied. For example if only every third or every fourth pixel on every third or fourth line is read, an image with a low resolution is obtained in a simple manner, e t c. The light valve device described above can particularly comprise a liquid crystal of ferroelectric type in a smectic A^*-phase.

The particular embodiment according to Fig. 1 will in the following be described in a more detailed manner and it can be said to constitute an essentially complete sensor for direct digitalization of image information. The liquid crystal matrix 1 (also called light valve matrix) comprises according to the described embodiment a surface stabilized ferroelectric liquid crystal (FLC) in A^*-phase which is arranged between two plates of glass with electrodes thereon in a manner known per se. Behind this a detecting unit 2 is arranged in the form of a photo sensitive matrix of photodetecting devices 2 ' wherein the detecting devices 2 ' e.g. may comprise phototransistors or photodiodes or photo-, and light emitting diodes in combination. According to a particular embodiment (not shown) the photo detecting unit 2 could be arranged directly on the liquid crystal matrix, or the light valve matrix 1, or on its rear plate of glass. In the illustrated embodiment the detecting unit is arranged at a distance from the light valve matrix 1 and parallel with this. For the use of e.g. a saw tooth generator 3 an electric field is produced over the liquid crystal matrix or the light valve matrix 1. The strength of this field increases in a linear dependence of time until the field has reached a given maximum voltage whereupon the field is built up again. Through the controlling device or the control unit 4 is controlled which element or elements in the light valve matrix 1 which are to be opened at a given time, i.e. a pixel on the FLC and corresponding photodetecting device 2 ' respectively are activated. The control unit 4 opens and closes thereby the light valve devices in e.g. a linear scanning movement. Each liquid crystal element in the light valve matrix 1 or the liquid crystal matrix functions as combined diaphragm and shutter. Since one or more adjacent elements can be activated at the same time an image can be resampled. In an inactivated position the liquid crystal matrix 1 is opaque. In order to in every image spot receive information on the greyscale the opening operation is effected in the liquid crystal matrix (light valve device respectively) in an accelerating way, i.e. a differential coefficient which is positive in each point of the opening velocity function. Thus the light transmission is low in the beginning and high in the end. The light that goes through the liquid crystal matrix or in the light valve devices comprised by the light valve unit or the light valve matrix 1, is detected by the photo detecting devices 2 ' , e.g. comprising photodiodes. If there are a number of light sensitive elements, the outputs s,, s₂,...,s_n of the different detecting devices 2 ' are added and compared in a comparator 10 with a reference signal, V_ref. If a signal exceeds V_ref the ongoing opening operation of a light valve device or a liquid crystal element is interrupted whereupon a new cycle with new light valve devices or liquid crystal elements is initiated since the cycle has been fulfilled by the control unit 4 which thus advances to the next one. By letting the detecting devices 2 ' , e.g. the photo diodes, being sensitive to different wavelengths of light it gets possible to read in a colour picture. The greyscale information is obtained since the timeperiodcounter (computor) 6 is read out at the end of each cycle. This information together with the information on which element/elements are activated or which light valve devices that are opened is stored in an address register 5 as a cycle has been run through. A counter 6 thus calculates a digital value of in each pixel detected photolevel and the address register 5 thus obtains an image in a digital form. The digitalized picture information is thereafter stored in a digital storage medium 7. The registration of a picture is thus carried out in such a way wherein if the liquid crystal matrix 1 is seen as a light valve matrix with one light valve device per pixel, if a picture has been projected on the sensor, the reading takes place pixel by pixel according to a sequence stored in an address register 5 wherefrom the control unit 4 picks up its information on which pixel is to be read. This pixel is then activated according to the above entioned by the electrical field from the saw tooth generator 3 and the drive signals A, B which form control signals for the liquid crystal matrix 1. Simultaneously also the photo detecting devices 2 ' (for reasons of simplicity are all detecting devices denoted 2 ' even if those may be different) are activated. At the beginning of a ramp in a saw tooth generator 3 also a starting signal is given to the counter 6 which then receives a stopping signal from the control unit 4 when a given photo energy has been detected or when a given diaphragm opening is attained. The information in the computer on photo energy in the activated pixel or picture element is thereafter transmitted as described above to the address register 5 for storing together with information on the address in the storage medium 7. Then the counter 6 is set to zero and the following address in the address register 5 as stated by the given sequence is activated. In an analogue way addresses which are stored in the address register 5 are prosecuted until they are stored together with corresponding information in the storage medium 7. The shown in the embodiment liquid crystal forming a matrix is controlled by driving electronics 9 comprising driving circuits. Then the image spot address Q and the transparency respectively of the actual element/elements of the matrix (signal from the saw tooth generator 3) form input signals. The clock reference of the counter 6 is the clock generator 8. The control signals denoted A and B respectively in the figure thus form control signals for the liquid crystal (the matrix) .

According to an alternate embodiment (not shown) a number of pixels as defined by the invention may be arranged in a row instead of in a matrix thus forming a linear array sensor. To enable an electronic representation of the image must then either the linear array sensor be swept over an optical image in an image plan or the optical image must be swept across the sensor whereupon this line by line registers and builds up an electronical representation of the optical image. Such an application is e.g. usable for immovable images. What has been described above in relation to a so called matrix sensor is essentially true also for a linear array sensor. The invention can advantageously be formed in a number of different ways. The produced image can for example come from an image forming camera optics or from the projection of a transparency or a print as in a scanner. Furthermore, the number of detecting devices does not have to be the same as the number of picture elements, pixels, in the liquid crystal. Furthermore, also other alternatives to a ferroelectric liquid crystal are possible. As mentioned above a detecting device can cover or correspond to a number of pixels or picture elements; it is however essential that only one of those pixels or picture elements (which corresponds to one and the same detecting device) are activated each time, i.e. they are read and activated separately.

Fig. 2 gives an example of how the arrangement also can be used for monitoring. The description above of Fig. 1 is to a large extent also applicable on this embodiment why only the displaying-(showing-)function is described. In the described embodiment the detecting unit 2 is provided with an absorbing, black surface (not shown) . After images have been registered and stored in the digital storage medium 7 those images can be shown ("reviewed") by activation of an image-showing selector 11, e.g. comprising two push-buttons or similar through which it is possible to step by step go through the stored images in a desired direction, forwards or backwards, depending on which button is pressed. A number of other embodiments are of course possible and the stepping can be achieved in a number of different ways. If e.g. the button + denoted is pressed the latest registered image is shown since the address of this image is indicated in the address register 5 so that image data from the digital storage medium 7 via the controlling device or the control unit 4 and (FLC)-drive electronics 9 are shown as a picture on the image matrix or the FLC-matrix 1. In another alternative for reviewing or showing of pictures (not shown) an active light source is arranged behind the image matrix as well as the detection unit. Alternatively an array of light diodes or similar can be arranged or integrated in the detecting unit for showing of the stored images for reasons of illumination. Address generation is done for reviewing e.g. according to the same linear scanning function as upon recording but the velocity can be chosen in a different manner.

In Fig. 3a is schematically illustrated an example of how an arrangement according to the invention finds its application in combination e.g. with a system camera 13. The arrangement may then be provided in a demountable, alternatively extendable or similar, back 12, analogue to a film magazine. In order to watch stored images the back 12 is then removed (shown separately in Fig. 3b) , it could also be extended or similar whereby the image matrix (FLC- matrix) 1 is exposed and with use of the image selector 11 the images can be shown on the image matrix through stepping in one or the other direction.

In Figs. 4a and 4b respectively the application of the arrangement with a camera 16 of a so called single lens reflex type 16 is illustrated. In Fig. 4a the view finder mirror 14 and focusing screens 15 respectively are arranged in a position for image registration whereas the view finder mirror 14 and the focusing screens 15 of Fig. 4b are rotated by 90° so that the image matrix or the FLC-matrix 1 is visible through the viewfinder hood, i.e. the arrangement is used for image monitoring. In this case the viewfinder mirror 14 can be provided with a reflective coating on its back-, as well as on its frontside. The invention shall of course not be limited to the described embodiments but may freely be varied within the scope of the claims.

Claims

CLAIMS :

1. Arrangement for direct reading and converting optic information to electronic representation wherein the arrangement comprises a number of pixels, c h a r a c - t e r i z e d in that the conversion takes place directly without any analogue intermediate storing wherein each pixel comprises a light valve device controllable by a controlling device (4) , the light valve devices forming a light valve unit, in that the arrangement further comprises a number of photodetecting devices (2') comprised by at least one detecting unit (2) wherein to each photo detecting device (2') at least one light valve device of a light valve unit is arranged wherein the photo detecting device(-s) (2') detects/detect incident photo energy and which when a given value of the photo energy is reached deliver(s) a signal for controlling the corresponding controlling device.

2. Arrangement according to claim 1, c h a r a c t e r i z e d in that when the given photo energy in one pixel is reached, the controlling device (4) interrupts an opening operation going on in the light valve device.

3. Arrangement according to any one of the claims 1 or 2, c h a r a c t e r i z e d in that to each detecting device (2') corresponds a separate light valve device.

4. Arrangement according to claim 1 or 2, c h a r a c t e r i z e d in that to each detecting device (2') corresponds more than one light valve device wherein the detecting device (2') reads out the light valve devices consecutively.

5. Arrangement according to any one of the claims l or 2, c h a r a c t e r i z e d in that the detecting device (2') reads more than one light valve device simultaneously.

6. Arrangement according to any one of the preceding claims, c h a r a c t e r i z e d in that the photo detecting device (2') comprises a photo transistor which delivers an electric signal when its surface is hit by photo energy.

7. Arrangement according to any one of claims 1-5, c h a r a c t e r i z e d in that the photo detecting device (2') comprises a photo diode or a photo diode and a light emitting diode in combination.

8. Arrangement according to any one of the preceding claims, c h a r a c t e r i z e d in that the controlling device of the control unit (4) controls actual or corresponding light valve device in such way that the diaphragm is opened with a velocity which follows a given curve until a given value of the photo energy which has been detected by the photo detecting device (2') is reached whereupon this delivers a signal.

9. Arrangement according to any one of the preceding claims, c h a r a c t e r i z e d in that a number of pixels comprising a light valve device are so arranged that they form a matrix (1) for formation of a matrix sensor wherein in connection to said light valve matrix (1) an array of detecting devices (2') are arranged.

10. Arrangement according to any one of the preceding claims, c h a r a c t e r i z e d in that the light valve device comprises by a ferroelectric liquid crystal (FLC) .

11. Arrangement according to claim 10, c h a r a c t e r i z e d in that the ferroelectric liquid crystal is in smectic A^*-phase.

12. Arrangement for direct digitalization of image information according to claim 11, c h a r a c - t e r i z e d in that the liquid crystal is surface- stabilized, in that the voltage across the crystals forming a grating can be varied by use of a generator means (3) , preferably a saw tooth generator, wherein an array of detecting devices (2') are arranged in a plane which is parallel to the light valve matrix (1) wherein the arrangement further comprises a control unit or a controlling device (4) for activating pixels on the liquid crystal matrix (1) and to respective pixels corresponding detecting devices (2') wherein the arrangement further comprises an address register (5) and a digital storage means (7) for storing detected photo-energy in the respective pixels wherein further a computer (6) is arranged for digitalization of the value before storing, whereupon the information on photo energy and belonging address is stored in a digital storage means (7) .

13. Arrangement according to any one of claims 1-8, 10-12, c h a r a c t e r i z e d in that a number of pixels are arranged in a row so that the arrangement forms a linear array sensor.

14. Arrangement according to claim 13, c h a r a c t e r i z e d in that the linear array sensor is movable so that for generation of an electronically represented image the sensor is caused to sweep across the optic information which is to be converted or alternatively the optic information is swept passing the linear array sensor or a combination of both.

15. Arrangement according to any one of the preceding claims, c h a r a c t e r i z e d in that the detecting unit (2) comprises means for absorbing light and in that stored images are shown or reviewed by activation of a display selecting device (11) .

16. Arrangement according to claim 15, c h a r a c t e r i z e d in that the display selecting device (11) is so formed that for image showing can be chosen between stepping or similar in an optional direction

(+-).

17. Arrangement according to any one of claims 15 or 16, c h a r a c t e r i z e d in that said means for absorbing comprises an absorbing, black surface and that in the storage medium stored images are shown via the display selecting device (11) in the address register (5) indicated address wherethrough image data via the control unit (4) and driving electronics (9) is represented as an image on the matrix (1) .

18. Arrangement according to any one of claims 15-17, c h a r a c t e r i z e d in that it is arranged in a camera (13) or similar and forms a unit (12) such as a back or similar which is so arranged in the camera (13) that the images become visible.

19. Arrangement according to claim 18, c h a r a c t e r i z e d in that the arrangement is detachable or rotatably arranged in the camera (13) or similar.

20. Arrangement according to any one of the preceding claims arranged in a camera of e.g. single lens reflex type (13'), c h a r a c t e r i z e d in that the viewfinder mirror (14) and the focusing screen (15) of the camera (13') are so formed that they can be rotated so much that the image matrix through reflection can be represented and viewed through the viewfinder hood.

21. Arrangement according to any one of claims 1-14, c h a r a c t e r i z e d in that an active lightsource is arranged behind image matrix and detecting units (2) for showing in the arrangement stored images.

22. Arrangement according to any one of claims 1-14, c h a r a c t e r i z e d in that an array of photodiodes or similar are arranged or integrated in the detecting unit (2) for showing of in the arrangement stored images.

23. Method for converting optic information to electronic representation wherein a sensor comprising a number of comprising pixels a light valve device, obtains optic information e.g. in the form of a projected image or similar, c h a r a c t e r i z e d in that

- detecting devices (2') of a detecting unit (2) detect the photo energy in a to a detecting device (2') belonging pixel, - the detecting device (2') controls the light valve device belonging to said pixel when a given threshold value is reached the light valve device is closed wherein each light valve device belonging to a particular detecting device (2') is activated separately.

24. Method according to claim 23, c h a r a c t e r i z e d in that the light valve devices of a light valve unit are separately controllable through at least one controlling device or control unit and wherein the method comprises the following steps:

- in an address register (5) information is stored on reading sequence of different pixels, a control unit (4) receives information from the address register (5) on which pixel is to be read, a control unit (4) delivers a signal to the given pixel whereupon this pixel and the detecting device belonging thereto are activated,

- the controlling device controls activated light valve device (2') to be opened with a given velocity, simultaneously with the opening of the light valve device being initiated, a counter (6) is started,

- the detecting device (2') delivers a signal when a certain given threshold value of photo energy is reached, said signal leads to interruption of the opening operation,

- the counter (6) is stopped,

- the in the counter (6) registered value of the photo energy is stored and the registered value is stored together with the address of the corresponding pixel in the storage medium (7) ,

- the counter (6) is reset to zero,

- the address register (5) provides a control unit (4) with the new address indication for the following pixel and the corresponding detecting device (2') according to the given frequency, - the steps are repeated until in the address register (5) given addresses are gone through.

25. Method according to claim 23 or 24, c h a r a c t e r i z e d in that the light valve unit comprises a ferroelectric liquid crystal (FLC) .

26. Method according to any one of claims 23-25, c h a r a c t e r i z e d in that the light valve devices are arranged forming a matrix (1) and in that the detecting devices (2') form an array of e.g. photo transistors or photo diodes which preferably are arranged in a plane behind the matrix (1) .

27. Method according to any one of claims 23-25, c h a r a c t e r i z e d in that the light valve devices are arranged in a row to form a linear array sensor wherein the linear array sensor either is movable in relation to the optic information or the other way around.