The present invention relates to a video printer and more particularly to a device for recording an electronically-produced picture on a photographic medium.

Existing techniques for producing photographs from electronically-produced pictures employ thermal printing, which requires special thermal paper and is expensive.

The present invention seeks to provide a relatively inexpensive way of photographing electronically- produced pictures and also to provide photographs of improved quality.

According to the present invention there is provided a video printing device comprising means for mounting a photographic film, a liquid crystal television screen, means for providing an electrical signal to the screen to produce a picture thereon, means for passing a light beam through the screen, and an optical system arranged for directing the light beam after it has passed through the screen onto a photographic film located in said mounting means.

The invention also relates to a method of obtaining a photograph employing such a device.

In a modification the device further includes a projection screen and the optical system includes a beam splitter whereby part of the light beam is directed towards the photographic film mounting means and part of the light beam is directed towards the projection screen.

In a preferred embodiment a controllable light source is located behind a colour LCD television screen. The light source comprises a halogen lamp or a strobe lamp, or a combination of the two with a beam splitter. The screen comprises a plurality of pixels which are activated in response to incoming television picture signals.

The signals may originate from a TV set, a TV aerial, a video cassette, a video camera e.g. camcorder, or any other suitable source. The screen is liquid-cooled by means of a glycerine-distilled water mixture located in a chamber on the side of the screen facing the light source. A glycerine-distilled water mixture is used which has the same refractive index as the glass walls of the chamber. The heat absorbed by the liquid is dissipated in a conveniently-situated heat sink. Such cooling is more efficient than conventional air cooling and so the liquid crystals can be driven brighter without thermal overload. Furthermore, the problems of dust and dirt accumulation with air cooling systems are avoided and any dust that does collect is no longer at the point of focus.

Upon emerging from the screen, the light beam incorporating the colour picture information impinges upon a beam splitter. Part of the light (e.g. a half) passes to a camera shutter whereas the remainder of the light passes via a mirror and/or lens optical system to a rear projection screen for displaying the TV picture. This permits a user to constantly monitor the current TV picture to decide when to operate the camera mechanism. The screen is of acrylic material and comprises a plurality of short optical fibres extending in parallel fashion between the front and the back of the screen. This has the advantage that,

despite the screen being a rear projection screen, the image appears at the front surface of the screen, i.e. the output ends of the optical fibres. Furthermore the screen is very efficient at suppressing the effects of ambient light.

The first part of the light passing to the camera shutter also passes through another mirror and/or lens optical system to an instant, e.g. Polaroid, film held in the mounting means. The mounting means may be similar to that found in a normal instant, e.g. Polaroid camera (Polaroid is a Registered Trade Mark). Upon pressing a button, or activating another trigger or switch, the shutter is activated and the emission of the light source is modified as appropriate for the camera mode as described below.

To ensure a satisfactory photograph a number of factors should be taken into account. Firstly, the period during which the shutter is opened should begin with the start of a TV frame and finish at the end of the frame. To effect this in one embodiment, a circuit responsive to the TV synchronisation signal delays opening of the shutter by the button until the next TV frame begins. The circuit also includes means for detecting the end of the frame and closing the shutter accordingly. Alternatively the shutter may close a predetermined time after opening. To avoid the timing problems involved in achieving this synchronisation, it is arranged in another embodiment that the camera photographs a "frozen" TV picture.

The second factor to be considered is that a certain characteristics of the light beam such as its intensity and colour balance need to be matched to the instant film to obtain a satisfactory photograph. A possible

problem with Polaroid films arises when there is excess white in the picture which can cause saturation. This is corrected by white peak clipping (known as gamma correction) in which the white level of the picture is constantly monitored and the intensity of the light source is instantaneously lowered if too high a light level occurs. This correction process, which is known as controlling the depth of the flash, can be switched off after the photograph has been taken. Subject to the overriding limit of the automatic white peak clipping, the white level may be manually-adjusted by a user to obtain desired lighting effects, e.g. for portraits.

Another picture characteristic which needs to be mentioned is colour balance. This may be achieved with a standard device such as a colour bar generator and any incorrect colour variations in the liquid crystal screen are detected and compensated. Similarly the contrast is constantly detected and kept at its correct level.

Before display on the liquid crystal screen, the picture signals may be subjected to a signal enhancement process.

The result of the above measures is a photograph of a quality which can be higher than that taken by a camera in the conventional manner. In addition telephoto and zoom pictures can be photographed which is normally impracticable with instant cameras in view of aperture problems.

The film and the film mounting means used can be of any type, e.g. a cassette or reel with a plurality of exposures, or a single plate. These films are widely

available and relatively inexpensive. On a single plate there may be produced an array of, say, nine different pictures, either successive frames or frames selected by the user; this can serve as a proof-reading option with the selected picture, which has been stored, then being recalled for display and full-size photographing.

The film and the mounting means may be replaced or, by means of a suitable further beam-splitter, supplemented by a slide printer and/or a moving celluloid film camera. The latter can be used for transferring videos to a medium suitable for showing in cinemas.

The optical system for detecting the light beam onto the film, if modified accordingly, may be located between the light source and the liquid crystal screen.

When the device does not have its own display screen, the light source may be a flash lamp, the duration of illumination of which may also be controllable together with the shutter to obtain a high quality photograph. In a modification, the duration of the flash controls the exposure and the shutter control may be omitted.

The initiation of taking a photograph and the various adjustments may be effected by means of a remote control unit.

The device may be used in association with a video telephone. A picture derived from the telephone line may be photographed for a permanent record. The device could also be used to print photographs which are for newspapers and which have been transmitted from the site of a news event via a telephone line.

The device offers an improved security system in banks etc. A photograph can be taken for incorporation in a credit card or other plastic card, possibly with the incorporation of encrypted pixels to permit forgeries to be detected. Identity checks could be made by comparison with computerised data.

Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, of which:

Fig. 1 is a schematic diagram of a video printer in accordance with a first embodiment of the present invention;

Fig. 2 is a schematic diagram of a video printer in accordance with a second embodiment of the invention and incorporating a display screen for a television picture;

Fig. 3 is a block circuit diagram showing control circuitry for the first embodiment; and

Fig. 4 is a block circuit diagram showing the elements of a third embodiment of the invention.

Referring to the drawings Fig. 1 shows a video printer 10 comprising a liquid crystal display screen or plate 11. A flash source 12 is located behind the screen 11. In front of the screen along the optical axis 17 are located a camera shutter 14, a lens 15 and a mirror 16 which is arranged to reflect light passing along the optical axis towards a photographic film 18 mounted in the printer. When the flash source 12 is actuated and the shutter 14 is open, light passes through the television picture on screen 11 and is focussed by lens

15 on to the film 18.

Fig. 2 shows a printer 20 in accordance with a second embodiment in which the printer of Fig. 1 is supplemented by a beam splitter 21 and an optical system, comprising a lens 22, and a mirror 23, which serves to focus the light on the rear of a projection screen 24. The flash source is replaced by a light source 28 which is continuously illuminated to provide a picture on display screen 24.

Referring now to Fig. 3 there is shown a control circuit 30 suitable for operating the printer of Fig. 1. A video input signal arriving at input terminal 31 passes through a video amplifier 32 which produces composite output signals 33.

The signals 33 are supplied to a vertical and horizontal correction circuit 35, where they undergo quality enhancement as mentioned previously; and then to a white peak control circuit 36, which effects the above-mentioned white peak clipping and an automatic contrast control circuit 37. From circuit 37 signals pass to a drive circuit 38 for the liquid crystal screen 11.

The signals 33 are also supplied to a frame synchronisation circuit 40 which produces synchronisation or timing signals 41. These are passed to a variable frame control circuit 42, the output of which is connected to a synchronisation trigger circuit 43. Circuit 43 also receives an input from the camera operating switch or button 50; the circuit 43 ensures that the control signal for the flash circuit 60 is delayed until the beginning of the next frame of the TV picture, and that the flash is terminated at the end of

the frame .

The flash circuit 60 actuates the flash tube 61, the peak light emission of which is detected by circuit 62 which appropriately adjusts the depth of flash by means of a flash energy circuit 68. The circuit also includes a shutter control.

Referring now to Fig. 4 there is shown a block circuit diagram of a third embodiment of the present invention in which a T.V. picture is "frozen" before it is photographed. A video printer 80 comprises six major functional elements: the print engine optics, the control panel assembly, the print engine microprocessor controller, the mother board, the chroma processor/freeze field, and the remote control.

The mother board 90 provides the support circuits and interconnections for the other circuits, in particular linear power supply 91, flash power supply 92, run- motor interface 93, battery relay 94. Audio/video switching circuits are also located on the mother board and include a front/rear switch 95 for this purpose and an r.f. modulator 96 and a rear input/output panel 97.

The board 90 is connected via wiring W3 to a film tray 100 of the instant camera, and via wiring W4 to a flash lamp 101 located at the other side of the LCD television screen 102. Flash lamp 101 has a maximum recharge time of five seconds. Wiring W7 connects a power transformer assembly 103 to the board 90.

Wiring W2 connects a print engine microprocessor controller 110 to the board 90, wiring W8 connects a front input panel board 120, and wiring W6 connects a video/freeze board 130. Wiring Wl interconnects the

controller 110 to a control panel board 140 which in turn can be controlled by means of an infra red link from a remote controller 145. Wiring W5 connects the block 130 to a driver board 150 for the LCD screen 102.

The print engine controller 110 comprises a microprocessor 111 and interfaces 112-114 for the control panel, the flash and the film tray. Controller 110 decodes the IR remote control sensor input, maintains and drives the status display, controls the print cycle, synchronises the print to the vertical interval sync, controls the print exposure, and initialises at power-up.

The video freeze board 130 comprises a lattice logic array 131, and a digital memory 132 e.g. a 262,214 word x 8-bit field memory chip. It further comprises a front/rear selector 133 dependent on the position of the front/rear switch, a gain control 134, an A/D converter 135, a synchronisation stage 136, a D/A converter 137, a live/frozen video selector 138, and a chroma processor 139. The freeze field block sub- functions include: video signal anti-alias filtering, A/D conversion, digital memory and memory storage management, D/A conversion, analog filtering output, and timing and control logic.

The memory 132 digitally stores one field of video information. It should be noted that printer 80 always prints from the memory 132 to eliminate LCD persistence effects. The printer maintains the frozen image while the unit is off but still powered. The freeze function captures and reproduces the image without visible degradation of image quality.

When the printer 80 is in the "freeze" mode, the print engine LCD array and a video monitor connected to the video output display the stored field. The stored field is an odd field. When viewed on a high resolution monitor, the frozen image will reveal the missing alternate interlace lines associated with the even field. When not frozen, the normal sequence of video frames will be output.

As long as the printer receives the input video, it will not lose field/frame synchronisation when switching from freeze mode to normal mode.

The chroma processor 139 converts the input composite video signal to three signals (R,G, and B) with proper balanced video drives for the LCD driver board 150.

The chroma processor controls sharpness, colour balancing, contrast, and gamma correction. Factory adjustments set these levels. The chroma processor provides sync separation and generation. It automatically configures for the active video standard and provides video processing functions. The processor

139 is preferably a Toshiba TA8795BF PAL/NTSE/SECAM video chroma synchronous signal processor for LCD TV. For direct drive of the board 150, additional PCB circuits provide a switched, bi-phase, level shifted signal.

The LCD driver board 150 drives the LCD TV panel 102 with an RGB video signal that is sourced from the video/freeze board 130. The board 150 comprises red, green and blue chromafloppers 151, 152, 153, an LCD timing controller 154 preferably a Matsushita MN83803 component, and a configuration control circuit 155 which can be arranged to set controller 154 for any of the four specified worldwide transmission standards.

Each of the colour signals from board 130 is cyclically inverted by its prospective chromaflopper and is then translated pixel-by-pixel in the LCD timing controller 154.

In use the video printer 80 captures an image from an external video source, stores it in a field buffer, freezes the image on user command, and makes an instant camera print of the stored image on user command. It receives a composite video signal from a VCR, camcorder or other compatible video source via a front or rear panel input connector. It is factory configured for NTSC, PAL A/I, PAL B/G, or SECAM.

The factory standard configuration consists of an appropriate modulator, chroma processor support components, and freeze field oscillator. Other circuits automatically configure for correct operation by using the multi-standard chroma processing chip 139.

The video printer 80 is operated by individual controls on panel 140. Control is by means of a momentary pushbutton on panel 140. While off but still connected to a power source, printer 80 keeps the RF modulator in the bypass position and the audio/video inputs in the pass-through condition. In this state the printer awaits an "on" command from the control panel 140 or remote control unit 145 and activates a stand-by display LED to indicate powered status.

A print instruction is given by means of another momentary pushbutton on panel 140. When pressed, a picture is printed in film tray 100 if the flash 101 is charged. If the flash is not charged, pressing the "print" button will have no effect. Printer 80 will only make a print when an image is stored in the video

frame memory 132.

A freeze instruction is given by means of a further momentary pushbutton on panel 140. When pressed, a field of the active video input is captured and stored in memory 132. The field is continuously provided to the video output, the modulated video output, and the print engine.

When pressed again, the "freeze" button unfreezes the image and connects the active video input to the outputs and print engine.

The "freeze" and"print" commands make three operational states available to the user. The states are: "Live Video", "Video Frozen", and "Make Print". When the printer 80 is turned on, it is in the "Live Video" state and this sends the selected video to the LCD 102 and the outputs. Pressing the "freeze" button moves the printer 80 to the "Video Frozen" state as described above. When in this state pressing the "freeze" button returns the printer to the "Live Video" state. Pressing the "print" button when in the "Video Frozen" state moves the printer 80 to the "Make Print" state. This initiates the printing cycle, which exposes the film, ejects it and returns the printer to the "Video Frozen" state.

Pressing the "print" button when in the "Live Video" state first freezes the image, and then immediately with no further user commands transfers the printer to the "Make Print" state. The printer then remains in the "Video Frozen" state until released as above.

A linear potentiometer on the control panel sets the exposure level for the print. A centre position is

normal, whereas left is dark print, and right is light print. An icon or text indicates the setting effect.

A two-position front/back slide switch is located near the front inputs of the printer. In one position, the switch selects the active video and audio source from the front input connectors. In the other position, the switch selects the rear input connectors. The selected video signal has at least 43 dB isolation from the unselected source. Selected audio signals have at least 50 dB isolation from the unselected source.

For NTSC units, a two position slide switch built into the modulator and accessible from the rear of the unit, selects the channel ("3" or "4") onto which the modulator imposes the active video source. For PAL and SECAM units, a two position slide switch and screwdriver adjust potentiometer built into the modulator and accessible from the rear of the unit, respectively select the test mode and modulator channel. A cutout plate or insert provides holes in the appropriate positions for each standard.

The control panel 140 also incorporates a two digit seven-segment numerical display. A displayed number indicates the number of exposures remaining, when the unit is on and loaded with film, the flash is charged, and there is at least one exposure remaining n the pack. The display "CH" is indicated while the flash is charging, when the unit is on, loaded with film, and there is at least one exposure remaining in the pack. When the film pack is empty and the unit is on the display indicates "FE".

The control panel 140 also incorporates a number of LED indicators. When the freeze field store 132 has a

field captured and the unit is on, an LED adjacent to the "freeze" button will be lit. When the printer 80 is receiving AC line voltage, an LED adjacent to the On/Off button will be lit. While the printer is unable to take a picture because the flash unit is charging, an LED beside the seven-segment display will be lit.

Selected buttons on the control panel 140 are duplicated by controls on the remote control unit 145. An infra-red coded data link connects the hand held, battery powered command transmitter unit 145 to a receiver unit mounted in the main unit. Three separate pushbuttons on the remote control unit activate the functions: Print, Freeze, and On/Off. Both the transmitter LEDs in the remote control and the receiver in the main unit are mounted behind suitably infra-red transparent windows.

The various signal connections made to the printer 80 are summarised below:

Video In (104): Front panel and rear panel. One of these is the course of the video signal used to generate the instant print, as selected by the switch.

Video Out (105): Rear panel. Input as selected by the switch.

Left and Right Audio In: Front panel and rear panel. The selected left and right audio signals will loop through to the audio outputs when the printer is in the "Off" state and is receiving AC input power. When the printer is not receiving power the signal in is not looped through.

Left and Right Audio Out: Rear panel. Input as selected by the switch.

RF In: Rear panel. Antenna or cable rf video in. This signal is boosted (16 dB ± 3 dB) and looped through the RF Modulator when the printer is in the "Off" state and is receiving input power. When the printer is not receiving power, the signal in is not looped through. The RF input signal cannot be the source of the printed picture.

RF Out: Rear panel. Carries the "Video In" signal frozen, if "Freeze" is on. The signal is processed, and selected video, and the audio left plus right mono signal modulated onto selected rf channel, when the printer is in the "On" state.

The printer 80 is supplied to the customer with two cables with appropriate SCART connectors for input from a SCART-equipped VCR etc to the printer.

The above described printers have numerous advantages. Their configuration is flexible so that they can operate according to NTSC, PAL A/I, PAL B/G or SECAM standards. Each printer is a compact, lightweight device which operates from mains a.c. It has a low power consumption; typically its rating is less than 24 watts and its power consumption does not significantly change when the on/off button is pressed.

The printer can be supplied by a range of sources and the remote control alternative is a convenient arrangement for image freezing and capture. Freezing of the picture facilitates selection of the best image

and avoids LCD persistence effects.

Various modifications may be made to the above- described embodiments. In particular, their features may be interchanged as appropriate.