GB2482562A

GB2482562A - Light control device

Info

Publication number: GB2482562A
Application number: GB1013323.9A
Authority: GB
Inventors: Morten Hjerde
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-08-06
Filing date: 2010-08-06
Publication date: 2012-02-08
Also published as: GB201013323D0

Abstract

In accordance with embodiments there are provided methods and devices for use in photography. In one embodiment the device comprises a variable filter 305 arranged to vary characteristics of light received from a light source 303, the variable filter 305 being arranged to emit the varied light onto a subject 20 of an image being recorded, and a processor 202 arranged to control the variable filter 305. In another the device comprises an interface 204 for receiving a communication identifying camera characteristics, and a processor 202 arranged to vary at least one characteristic of light emitted by a light source 303 in accordance with the camera characteristics. In another the device comprises an interface 204 for receiving one or more communications identifying a plurality of open periods of a camera shutter, and a controller 202 arranged to instruct a light source 303 to emit light in accordance with the camera shutter open periods. In another the device comprises a light receiving part arranged to receive a coloured light, and a light colour compensator arranged to compensate colour characteristics of light to be emitted by a light source 305 in accordance with the received light.

Description

Light Control Device The present invention relates to a light control device. More specifically, the present invention relates to a device and corresponding method for controlling the emission of light by a light source used in conjunction with a camera or such like.

Photography is a technique using a camera for capturing images, which generally refers to capturing still images such that they can be viewed again after the event took place. Photography can also refer to the capturing of moving images, however, the process of capturing moving images can also be referred to as film.

In photography, both for still and moving images, the lighting of a subject being captured in the photograph is very important. When a still camera or digital video camera records an image it does this by exposing a digital sensor to light through a tens that forms an image on the sensor (or in the case of analogue photography to a film stock such as celluloid film). The amount of light that reaches the sensor is in part determined by the transmittance of the lens assembly and in part by the exposure time.

The apparatus that regulates the exposure time is called the camera shutter.

The camera shutter regulates exposure time by opening and closing the light path for a precise amount of time. The most common type of shutter is the focal plane shutter, which consists of two curtains, When the exposure starts, the first curtain called the front curtain opens, and when the exposure time is over the second curtain called the rear curtain closes. In conventional cameras, the direction of travel of the curtains is vertical (or along the shortest axis). The exposure time is generally a very short instance in time. Commonly used exposure times range from 1/60 second to 1/1000 second, but the capability of many cameras typically extends well beyond these in both directions.

For exposure times longer than 1/200 second (typical), there is a period when the entire sensor is exposed with no part of the front or rear curtain covering the sensor.

For exposure times shorter than 1/200 second (typical), since the curtain travel takes a finite amount of time, the rear curtain must start to close before the front curtain is fully open. In this case the entire sensor is not exposed at any one time, rather the two shutter curtains form a slit that moves across the sensor, thereby exposing light to portions of the sensor as the slit moves across the sensor. The shorter the exposure time, the narrower the slit. The parallel movement of the curtains ensures that all areas of the sensor receive the same amount of light.

While movement of the slit controls the amount of light passing onto the photographic sensor of the camera, the light which can reach the sensor is also affected by the light which is applied to the subject being photographed. Furthermore, the lighting applied to the subject being photographed will affect how the subject looks in the photograph.

Hence, lighting applied to a subject being photographed is of utmost importance in photography.

In general, lighting is used to ensure that a photograph is clear and that the subject being captured can be seen. In other words, lighting is used in order to achieve proper exposure. Furthermore, in order to achieve a desired image, photographers use a variety of means to adjust how light falls on to the subject of interest. While, altering the position of a subject in respect of natural light emitted from the sun is a common way to adjust the lighting applied to a subject being photographed it is also common practice to utilise artificial lighting, and in particular photography specific lighting, such as spot lights, flood lights, and photographic flashes. Other means for adjusting the lighting applied to a subject include use of light shaping tools like reflectors, diffusers, or gobos (items that obstruct the light) to adjust how the subject is lit.

Often spot lighting and photographic flashes are provided in order to provide light to parts of a subject that would otherwise be in shade, or insufficiently well lit.

Photographic lighting can also be used in order to provide a mood' to a photograph, for example, by adding a light of a particular colour, or from a particular direction.

It has in recent years, particularly due to prominence of digital photography, become popular for photographers to enhance images further after the exposure by using post-production techniques. Such post-production techniques can be used in order to change the tonal qualities of the image, brighten or darken particular parts of the image and so forth. Such post-production techniques allow for the apparent lighting of the photograph to be adjusted after the exposure takes place, thus providing photographers with even more control over the photograph. These techniques allow photographers to enhance photographs, in particular, enhance the lighting of a photograph. This may allow for interesting lighting effects to be produced which would not usually be possible by use of natural lighting or photographic lighting.

While post-processing provides photographers with a great amount of control over their images, it is a common myth that anything' is possible in post-processing. This is not the case. In extreme cases an image can be enhanced to such a degree that it is basically re-drawn by hand by a painter or illustrator. However, such techniques are time consuming and can therefore be financially expensive.

While current post-production techniques provide photographers with a great deal of control over the look of a final image, there is always a need amongst photographers for ways of creating new looks, and also for making effects applied to photographs more natural without having to use such expensive and time-consuming post-production techniques.

The present invention aims to at least partly mitigate some of the above mentioned problems.

In accordance with an aspect of the present invention, there is provided a device for use in photography, the device comprising: a variable filter arranged to vary characteristics of light received from a light source, the variable filter being arranged to emit the varied light onto a subject of an image being recorded; and a processor arranged to control the variable filter.

The variable filter may comprise a plurality of variable filter elements arranged in an array, each filter element arranged to vary the characteristics of the light passing therethrough.

The variable filter may be arranged to vary colour characteristics of the light.

The variable filter may be arranged to vary intensity characteristics of the light.

The device may further comprise an optical assembly arranged to focus the light emitted from the variable filter.

The processor may further comprise a tracking means arranged to track a position of a feature of the subject of the image being recorded and control the variable filter to vary the characteristics of the light in accordance with the tracking of the feature, The processor may be arranged to control the variable filter to vary the characteristics of the light in accordance with the tracking of the feature by applying the same light characteristics to the feature when the feature moves position.

In accordance with another aspect of the present invention there is provided a device for use in photography, the device comprising an interface for receiving a communication identifying camera characteristics; and a processor arranged to vary at least one characteristic of light emitted by a light source in accordance with the camera characteristics.

The camera characteristics may include information identifying a camera shutter opening time, and the processor may be arranged to vary the at least one characteristic of the light each time new information identifying a camera shutter opening time is received.

The camera characteristics may include information identifying a camera shutter opening period and the processor may be arranged to vary the at least one characteristic of the light during the camera shutter opening period.

The at least one characteristic of the light varied by the processor may include a colour characteristic of the light.

The at least one characteristic of the light varied by the processor may include an intensity of the light.

At least one characteristic of the light may be varied spatially.

The device may further comprise a light source arranged to emit light; and a filter arranged to vary the at least one characteristic of the light.

The filter may be a matrix of variable filter elements.

In accordance with yet another aspect of the present invention there is provided a device for use in recording video images, the device comprising: an interface for receiving one or more communications identifying a plurality of open periods of a camera shutter; and a controller arranged to instruct a light source to emit light in accordance with the camera shutter open periods.

The controller may be arranged to instruct the light source to emit light throughout the period when the camera shutter is open.

The one or more communications may identify a camera shutter opening time and a camera shutter opening period.

The one or more communications may also identify a frequency of camera shutter opening.

The controller may be arranged to instruct the light source to emit light during a portion of the period that the camera shutter is closed.

In accordance with a further aspect of the present invention there is provided a device for ambient light colour compensation, the device comprising: a light receiving part arranged to receive a coloured light; and a light colour compensator arranged to compensate colour characteristics of light to be emitted by a light source in accordance with the received light.

The light colour compensator may be arranged to compensate for the colour characteristics of the light to be emitted such that the light to be emitted has the same colour characteristics as the received light.

The light receiving part may comprise: a red light sensor arranged to receive red light; a green light sensor arranged to receive green light; a blue light sensor arranged to receive blue light; and a white light sensor arranged to receive all colours of light, wherein the white light sensor is used to determine a received light intensity.

The received light may be ambient light falling on a subject to be photographed.

The light colour compensator may be arranged to apply an offset of green and/or magenta to the light to be emitted in order to further correct for the colour of light when the colour of light is defined in terms of colour temperature.

The device may be arranged to turn off the light source while taking a measurement.

In accordance with yet a further aspect of the present invention there is provided a device including two or more of the above devices.

The device may be an illumination device including a light source.

The device may be a camera.

In accordance with an aspect of the invention there is provided a method for use in photography, the method comprising: varying, at a variable filter, characteristics of light received from a light source such that the varied light is emitted onto a subject of an image being recorded; and controlling, at a processor, the variable filter.

The varying characteristics of the light may comprise varying colour characteristics of the light.

The varying characteristics of the light may comprise varying intensity characteristics of the light.

The method may further comprise focusing, at an optical assembly, light emitted from the variable filter.

The method may further comprise tracking, at a a tracking means, a position of a feature of the subject of the image being recorded; and controlling the variable filter to vary the characteristics of the light in accordance with the tracking of the feature.

The step of controlling may comprise controlling the variable filter to vary the characteristics of the light in accordance with the tracking of the feature by applying the same light characteristics to the feature when the feature moves position.

In accordance with another aspect of the present invention there is provided a method for use in photography, the method comprising: receiving a communication identifying camera characteristics; and varying at least one characteristic of light emitted by a light source in accordance with the camera characteristics.

The camera characteristics may include information identifying a camera shutter opening time, and the method further comprises varying the at least one characteristic of the light each time new information identifying a camera shutter opening time is received.

The camera characteristics may include information identifying a camera shutter opening period and the method may further comprise varying the at least one characteristic of the light during the camera shutter opening period.

The at least one characteristic of the light which is varied may include a colour characteristic of the light.

The at least one characteristic of the light which is varied may include an intensity of the light.

The at least one characteristic of the light may be varied spatially.

In accordance with yet another aspect of the present invention there is provided a method for use in recording video images, the method comprising: receiving one or more communications identifying a plurality of open periods of a camera shutter; and instructing a light source to emit light in accordance with the camera shutter open periods.

The light source may be instructed to emit light throughout the period when the camera shutter is open.

The method may further comprise instructing the light source to emit light during a portion of the period that the camera shutter is closed.

In accordance with a further aspect of the present invention, there is provided a method for ambient light colour compensation, the method comprising: receiving a coloured light; and compensating colour characteristics of light to be emitted by a light source in accordance with the received light.

The step of compensating for the colour characteristics of the light to be emitted may be performed such that the light to be emitted has the same colour characteristics as the received light.

The method may further comprise applying an offset of green and/or magenta to the light to be emitted in order to correct for the colour of light when the colour of light is defined in terms of colour temperature.

The method may further comprise turning off the light source while taking a measurement.

In accordance with another aspect of the present invention there is provided a method including two or more of the above mentioned method steps.

In accordance with yet a further aspect of the present invention there is provided a carrier medium carrying computer readable code for configuring a suitable computer as the apparatus of any of the devices mentioned above.

In accordance with yet another aspect of the present invention there is provided a carrier medium carrying computer readable code for controlling a suitable computer to carry out the method of any of the method steps mentioned above.

Embodiments of the present invention relate to modulating a light source for use in photography. In particular, the light may be modulated spatially and/or over a period of time. Furthermore, the modulation may take place in accordance with the opening and closing of a camera shutter in order to save energy. Furthermore, the modulation may take place in order to compensate for ambient light.

Embodiments of the present invention relate to modulating the emission of light while the two shutter curtains moves across the sensor at speeds slower than or faster than 1/200 seconds (typ) in such a way that the subject is unevenly illuminated by the light source.

In accordance with embodiments of the present invention, for long exposure times, i.e. longer than 1/200 second (typ), modulating the light will allow the photographer to achieve various effects, for example capture several impressions of a moving object in a single frame, and to have the individual impressions individually exposed. The photographer may also be able to capture an impression of movement (blur) while still having the subject of interest appear sharp. This effect can be used for artistic or technical purposes.

In accordance with embodiments of the present invention, for short exposure times, i.e. shorter than 1/200 second (typ), modulating the light will allow the photographer to e.g. put a colour gradation on or behind the subject of interest, or a hairline light that varies in colour or intensity. Ambient light hitting the subject will be evenly exposed, while the emission of light from the light source can be modulated. This effect can be used for artistic or technical purposes.

Embodiments of the present invention relate to a situation where the quality of the light is made to vary at high speeds during the exposure.

Embodiments of the present invention allow for the colour of the emitted light to be modulated during the exposure.

Embodiments of the present invention allow for the colour temperature to be modulated during the exposure.

Embodiments of the present invention allow for the intensity of the light to be modulated during the exposure.

Embodiments of the present invention allow for both colour and intensity to be simultaneously and individually modulated during exposure.

Embodiments of the present invention allow for both colour temperature and intensity to be simultaneously and individually modulated during exposure.

Embodiments of the present invention allow for the modulation of light to be slow or rapid, thereby creating different effects.

Embodiments of the present invention allow for the modulation of light to be linear or non-linear across the exposure.

Embodiments of the present invention allow for the lighting to provide a strobing effect.

Embodiments of the present invention provide a system having a light source which has the ability to vary aspects of its light emission (intensity, colour or colour temperature) at high speeds, and can do this synchronised to the movement of a camera shutter.

Embodiments of the present invention relate to photographic devices, that is illumination devices, cameras, camcorders, or any other photographic equipment arranged to perform any of the above functionality.

Embodiments of the present invention are arranged to illuminate a subject to be photographed. A subject may be a person scene, object or such like. Further embodiments of the present invention are arranged to track features of the subject, for example of the subject is a traffic scene, a specific car may be the feature, or if the subject is a person the face of the person may be the feature.

The present invention shall now be described with reference to the drawings, in which: Figure 1 illustrates a scenario for use of a first embodiment of the present invention; Figure 2 illustrates a system provided in accordance with a first embodiment of the present invention; and Figure 3 illustrates a cross-sectional view of an illumination device.

Throughout this specification like reference numerals refer to like parts.

Figure 1 provides an overview of a first embodiment of the present invention. In this first embodiment of the present invention a camera 100 is mounted on a tripod 10 for taking a photograph of a subject 20, which in this case is a person. It will be appreciated that the subject could be anything; for example, a person, an object, or a scene. An illumination device 200 is mounted on the camera 100. It will be appreciated that any suitable mounting means could be provided, for example, the illumination device 200 could be mounted separately from the camera 100.

The camera 100 and illumination device 200 are communicatively coupled via a communications channel 150, which in this case is a cable connector. It will be appreciated that the communications channel could take many forms, including various different types of wired connectors and wireless connection means. For example, the communication between the camera 100 and illumination device 200 may occur through connectors in the camera hotshoe. Alternatively, the communication may occur optically via a built in or separate flash mounted on the camera. In yet another embodiment the communication may occur via a separate wireless radio transmitter/receiver. In a further embodiment a separate sync wire between the camera 100 and the illumination device 200 may be used.

In operation the camera 100 is arranged to provide control signals to the illumination device 200 such that operation of the illumination device 200 is synchronised with operation of the camera 100. As a consequence, various functions of the present invention can be achieved.

Figure 2 illustrates a system provided in accordance with a first embodiment of the present invention.

In Figure 2, a representation of the functional components of camera 100 and illumination device 200 is shown. The camera 100 includes a power circuit 101, a microcontroller 102, a memory 103, an external device interface 104, a shutter assembly 105, a sensor assembly 106 and a user interface 107. The illumination device 2 is shown to include a power circuit 201, microcontroller 202, memory 203, camera interface 204, light emitting assembly 205 and user interface 206.

The arrangement of the system of this first embodiment of the present invention shall now be explained in more detail.

The power circuit 101 is arranged to provide power to each of the components of the camera 101. In this embodiment of the present invention the power circuit is a battery, however, any form of power supply, internal or external, could be utilised.

The power circuit includes, a power supply switch, a power control circuit and a power supply. The power supply switch is arranged such that when the switch is in an ON position the power control circuit can regulate the voltage from the power supply to the other components of the camera 100.

The microcontroller 102 controls the operation of the camera 100. In particular, the microcontroller 102 acts as the central processor and is capable of processing information received from the user interface, and also adjusting parameters of the shutter assembly 105 accordingly. For example, the microcontroller 102 is arranged to perform shutter speed control. Furthermore, the microcontroller 106 is arranged to receive image data from the sensor assembly and store this information in memory 103. The memory 103 represents the memory used by the camera both for data storage and for processing performed by the camera 100. It will be appreciated that separate memory components could be provided for each part of this functionality.

The external device interface 104 is arranged to provide a port through which the camera 100 can communicate with external devices such as illumination devices. The microcontroller 102 is able to send control signals via the external device interface 104 to the illumination device 200. Furthermore, image data can be streamed from camera to illumination device for certain functionalities, such as the use of multiple illumination devices, as discussed below.

The shutter assembly 105 is a standard shutter assembly as described above in respect of the prior art. In particular, it is standard dual curtain assembly. However, it will be appreciated that other types of shutter assembly could be utilised. The shutter assembly 105 also includes the necessary control circuitry for operating the curtains.

The sensor assembly 106 includes a CMOS or CCD imaging element, a microcontroller for managing the operation of the imaging element, and a memory for storing the recorded image information. The sensor assembly is arranged such that it is capable of determining characteristics of the light being photographed. Hence, the light being sensed may just be the ambient light, it may be a combination of the ambient light and light emitted from a photographic illumination device, or it may be the photographic light alone.

The user controls the camera 100 via its user interface 107. The user interface 107 is provided with a graphical user interface (GUI) thus providing the user with a display screen and controls such that the user is able to adjust parameters of the camera 100, and thus parameters of photographs to be taken by the camera 100. The user interface may also include one or more buttons, dials or such like for controlling parameters of the camera, in addition to operating the camera shutter. While the camera described in respect of this embodiment of the invention has various features including a graphical user interface, it will be appreciated that in alternative embodiments the only requirements for use with the illumination device of embodiments of the present invention is a way to adjust shutter speed and a flash hotshoe.

Now referring to the illumination device 200, the power circuit 201 takes the same form as that provided for the camera. However, it is noted that in alternative embodiments of the invention the illumination device could be powered by the camera, thus only requiring a power receiving interface instead of a full power circuit.

The microcontroller 202 of the illumination device 200 is arranged to control each of the components of the illumination device 200, and also perform any processing as necessary. In particular, the microcontroller 202 can receive control signals from the user interface 206, the camera interface 204, and the optical trigger in order to control the light emitting assembly accordingly. The functionality of the microcontroller is discussed in more detail below. It is noted that the camera interface 204 is a general purpose interface providing a communication port for connecting with various remote devices.

The memory 203 is connected to the microcontroller 202 and is used to store any data necessary for performing the operations of the illumination device.

The camera interface 204 provides a means for allowing for the illumination device to communicate with the camera 100. In particular, the camera interface 204 is arranged to receive control signals from the camera 100 and pass these on to the microcontroller 202 such that the microcontroller can transform these control signals into signals suitable for controlling the light emitting assembly 205. The camera interface 204 may receive such controls signals via a wired or wireless connection as discussed above in respect of Figure 1.

The light emitting assembly 205 includes an array of light emitting elements for emitting light. Such a light-emitting array comprises a plurality of light emitters including a red, green, blue and either amber or white emitter. The light emitters may be four or more high power LEDs (Light Emitting Diode) each of a different colour, red, green, blue and either amber or white. The relative intensity of the four colours is changed by the microcontroller in order to produce a light of any colour. The emitters are mounted in close proximity to each other. The light emitting assembly may form part of an optical assembly consisting of various lenses and diffusers designed to create an even light from the emitter array.

The LEDs are driven to about lOW in continuous mode, However, it is noted that when the LEDs are in flash mode they are in some circumstances driven with higher power.

The reason for a lOW limit is primarily due to limitations in battery capacity and heat dissipation for a small portable device. As such a much higher powered device could be built by using larger and/or more emitters, a bigger case, and mains powered.

The lighting-emitting array may be provided by close mounted individual LED chips and multi-die emitters where four or more diodes sit on a common die. The advantage of multi-die is that better colour mixing can be achieved since the emitters sit closer together. A collating optical lens assembly will generally preserve the relative entrance angle of the light through the system. As the emitters have different colours, the light reaching the subject may not be a perfectly even light, but show colour fringing. The centre spot may be an even white', but the edges may show a colour cast reflecting the position of the individual emitters within the optic assembly. In order to mix the colours better, the light has to be diffused. Diffusion introduces a loss of optical efficiency. The closer the emitters are positioned relative to each other, the less diffusion is necessary and the better the optical efficiency can be.

Each individual LED can be driven by a switch mode current sink in order to achieve improved power efficiency and colour stability. A PWM driver circuit shunts the current sink and turns on and off the individual LED about 25000 times each second. The length of each pulse then determines the light output. Furthermore, the length of the pulses is continuously adjusted to compensate for drift in the emitters.

The current is not simply regulated through the LEDs because the colour of the LEDs shifts slightly when the current changes. Consequently, when the emitted light is dimmed, the light would become a little greener, for example, and such colour shifting is generally seen as unacceptable.

The emitter assembly also includes two sensors that feed back to the microcontroller.

A temperature sensor to guard against thermal runaway, and an optical sensor that is used to compensate for drift.

Overall, the light emitting assembly is arranged to emit light powerful enough to provide improved iflumination of a subject. The light emitting assembly 205 is arranged to emit light responsive to control signals from the microcontroller 202. In particular, the light emitting assembly 205 can vary its luminance levels over a period of time in accordance with the received instructions.

The light emitting assembly may also include a variable electronically controlled filter along with the light emitting device. This is discussed in more detail below, with respect to Figure 3.

The arrangement of the light emitting assembly 205 within the illumination device 200 is illustrated in the cross-sectional diagram of Figure 3.

In Figure 3, the illumination device 300 includes a casing 301, which encloses the other portions of the device except for the emission surface 302 which is transparent. The light emitting assembly 205 is all arranged inside the casing 301, such that light is emitted out from the emission surface 302, The light emitting assembly 205 includes the emitter array 303 which is arranged to emit light as discussed above. An optical assembly 304 is provided in order assist in projection and channelling of the light through the emission surface 302. In this first embodiment of the present invention the optical assembly 304 includes a TIR optic consisting of a multitude of optical surfaces designed to collate the light and shape it into a suitable beam. The TIR optic also includes diffusion surfaces to help with colour mixing. The optical assembly 304 also includes a movable Fresnel lens, arranged in front of the hR optic, designed to zoom' or alter the beam spread. Furthermore, the filter 305 is provided between the emitter array 303 and the emission surface 302, such that it can control or vary characteristics of the emitted light passing therethrough.

Also shown in Figure 3 is the user interface 206, which allows for the user to control the illumination device 200. In Figure 3 the user interface is provided on the back surface of the illumination device. However, it will be appreciated that the user interface could be provided on a separate device, either proprietary or part of another device such as a laptop. In the case where the user interface is a remote device it may be connected via wire or wireless like WiFi or Bluetooth.

The user interface 206 may be a graphical user interface which allows the user to set parameters of the illumination device 200. A display is provided along with a means for the user to input controls and information. This may be a touch screen display or alternatively some form of keypad, provided alongside a separate display screen. In particular, it is necessary that such controls are suitable for a user to select particular light emission settings, as well as perform the necessary steps to synchronise the illumination device with the camera, in the event that such steps are not performed automatically. Furthermore, the display should, for certain embodiments, be capable of providing a graphical representation of the scene being photographed, and be able to provide the user control over the lighting applied to that scene.

The filter 305 is arranged to reduce light intensity emitted towards certain positions of the subject, as well as change the colour, or colour temperature emitted towards certain portions of the subject. Such characteristics can be varied both spatially and over time. The filter 305 may take the form of a matrix of binary shutters that can open/close to obstruct or pass light through, or could take the form of a liquid crystal construction. A liquid crystal based structure would be arranged with a gradual opacity to achieve such control of the light, in terms of position and intensity. Furthermore, in order to achieve colour variation the filter may comprise three layered liquid crystal devices, one for filtering red light, one for filtering green light and the other for filtering blue light. Alternatively, a binary state reflective type filter could be used, which would be made out of a matrix of microscopic mirrors (DLP). In any case it may be necessary to employ separate filters to deal with intensity modulation and colour modulation. A filter with gradual opacity would regulate the light by changing the opacity of each pixel'. In a binary state filter the apparent opacity would change by changing the duration of high-speed light pulses. Which ever system is utilised, the filter, or the combination of the light source and the filter, allows for the intensity of each of the red, green and blue colours to be varied for each pixel.

Since the filter may be capable of altering colour characteristics of the emitted light, in alternative embodiments of the invention a white light source replaces the coloured LED array. As such, all control over the light is carried out at the filter. In such embodiments it is possible for the filter to be separate from the light source. For example, a standard light source could be provided and utilised alongside the filter, along with the required control circuitry. Such embodiments may allow for a brighter and/or more energy efficient light sourse to be utilised.

Since the filter can be a separate item, a large liquid crystal based filter could be utilised in order to provide a single large light source. For example, the filter could form a 3m2 panel. In order to illuminate the panel it would be possible to use a high power light source directly behind the panel, or in order to reduce the space required by the device, a reflector could be used in order to expand or spread the width of the light emitted from the light source.

In yet a further embodiment of the invention, the aforementioned light source may vary characteristics of the light it emits, such as the colour, and as such the filter may not be required.

In a further embodiment of the invention an LED panel is utilised in place of the above mentioned light source and filter. As such a coloured LED array can be used to represent each individual pixel of the light source. The modulation effects can then be applied across the pixels of the LED panel. In order to improve performance it may be necessary to include a specialist optical assembly, such as a lens arrangement, in order to ensure that the LED panel provides a focussed light source, as required for lighting up a subject in photography.

The various uses and functionalities of the first mentioned embodiment of the present invention shall now be described with reference to the figures.

The first parameter of light that can be controlled by the light emitting assembly is the intensity. For photography, the intensity of emitted light can be regulated in exposure value (EV) steps. Full steps, half steps, 1/3 steps, or 1/10 steps where each full step corresponds to a full step increase or decrease of camera aperture or shutter speed.

One full step equals a halving or doubling of light intensity. Alternatively, for video it is quite common to use a continuous 0-100 scale. The photographer can then choose the preferred scale according to his or her preferences.

The overall intensity of light emitted can be varied by changing the intensity of light emitted by the light emitters themselves. However, the filter allows for positional intensity changes to be provided in addition to universal changes, as discussed below.

The filter can act to block or reduce the intensity of light emitted by the light emitting assembly such that certain areas of the light projected onto a subject have reduced light levels. In particular, certain portions of the filter can be arranged to block light while others are arranged to pass light. In further embodiments, some of the light can be partially passed or partially blocked. As such the filter can provide different levels of light intensity to different areas of the scene being photographed.

An example of a useful application of variations in positional intensity shall now be discussed. Control of the variations in light intensity can be achieved by using a light sensor, which may be provided from the camera or on the device itself, which receives light from the exact same area as the area that the light emitted by the light emitting assembly is projected onto. Alternatively, the device can receive an image feed from the camera used for capturing the image. Hence, this camera can take in an image of the scene to be photographed. Some parts of the scene will be lighter, some will be darker. The photographer can then brighten dark areas without affecting the brightness of the light areas. The image from the light sensor can be used to determine which areas are dark and which areas are bright. Based on this information the microcontroller of the device can control the emitted light such that the intensity of light projected onto the parts of the scene that are dark is greater than the intensity of light projected onto those parts that are already light. In order to achieve this, the microcontroller can take the image from the image sensor invert the image intensity and emit light accordingly. Thus, the dark areas are illuminated more than the light areas. As such the dark areas of the scene can be brightened without adding unwanted glare or brightness to other areas of the scene.

The light emitting assembly is also capable of varying colour. As mentioned above, the emitting elements are capable of emitting light of any colour by selecting a ratio of the different coloured LEDs. Furthermore, the intensity of each colour can be controlled by controlling each LED individually. The user can apply an overall colour setting, which is applied universally to the light source. Colour can be changed by entering a set of colour coordinates in one of common colour spaces like RGB, Lab, HLS, etc. Colour can also be selected from a list of named colours like "Summer Green", "Dark orange", etc. Obviously, in alternative embodiments, these colours could be varied by the filter. Furthermore, as mentioned above, the intensity of each colour for each pixel can be controlled independently.

Another colour parameter that the user can set is the colour temperature, CT (or more technically accurate, the Correlated Colour Temperature). CT is also called white balance, The colour temperature can be regulated by entering the desired colour temperature along a continuous scale. The scale boundary depends somewhat on the colour coordinates for the particular emitters used, but would typically be from 2000 to 10000 Kelvin. The CT can also be regulated by selecting from a list of predefined named values, for example Daylight, Cloudy, Fluorescent and so forth, where the Daylight setting would be a CT of 5600 Kelvin. The CT can also be changed by adding an electronic compensating gel', Many photographers are accustomed to adding gelatine filters to their lights, and to accommodate those who are accustomed to working this way, the device lets the photographer select from a list of common filters like CTO, CTB, or Plusgreen. The device will then adjust the CT of the emitted light to a value equal to the effect of adding a physical gelatine filter. The colour can be changed either by adjusting the colour emitted by the emitter array 303 or by applying a universal colour adjustment to the filter 305.

In respect of both the overall colour and colour temperature, the selected colour can be achieved by varying either the light emitters or the filter 305.

The filter allows for further control over the emitted light, in particular, in respect of colour positioning. Such colour positioning is also achievable if a light source panel array, as discussed above, is utilised in place of the light source and filter combination.

For example, a colour gradient can be applied which varies the colour across the image. It may be that the colour is set up to gradually change from top to bottom or left to right, in order provide the effect of a light source from a particular direction. It is noted that light intensity gradation can be applied in a similar way. Further examples of more complex uses of the colour variation capabilities provided by the filter are set out below.

The filter array can provide specific positional coloured light. For example, if it is desired to provide a blue line of light across the subject this can be achieved in accordance with an embodiment of the present invention.

The user display can be used in order to control the painting' of light onto the position of the scene as desired. In particular, the image sensor records an image of the scene, and the position of the light source(s) with respect to the scene has thus been determined. The microcontroller is then able to allow input from a user onto the user display, or any other user interface, to identify regions where the line of blue light should be provided. In such a case the microcontroller is able to control both the light emitters and the filter such that the blue light is provided. This can be achieved by the emitters emitting a white light, and the filter providing a blue filter to specific portions of the light such that the blue line specified by the user is project onto the scene.

While the above example of painting light' is applied to blue light, it will be appreciated that any light parameter, such as colour and intensity with respect to position, could be altered using this technique.

Another parameter adjustable by the user is the light mode. A video mode can be selected where the device emits a continuous light suited to recording of moving images. The meaning of continuous light also includes the case where the light is turned off during the time when the camera shutter is closed, for the purpose of saving energy. The other light mode is flash, where the device emits a flash. In flash mode the device may emit a constant low power modelling light used to aid the photographer in positioning the light.

The emitter feedback assembly 207 may include a light sensing device, which is used for calibrating the light emitting assembly, in addition to providing feedback useful for certain processes performed by the illumination device 200. This light sensing device could be the same light sensing device as that used above in respect of recording the image for user control over the projected light. However, separate sensors for the specific applications could also be provided. Such a light sensing device may be a broad-spectrum high-speed photodiode that produces a current relative to the amount of light that hits the sensor surface. This current is converted to a voltage, amplified and fed to an analogue-digital converter on the microcontroller. In order to perform a reading the microcontroller turns on one single emitter, for example the red one, reads the voltage from the sensor, then turns on the green, reads the voltage from the sensor and so on. Since this is a high-speed sensor, the entire measurement cycle can be performed in less than lOOps. This measurement cycle can form part of the general PWM control, in a way that the output can be continuously monitored without affecting the quality of the light. Such feedback is useful because the luminance and the colour (the centre wavelength) of each emitter change with age and temperature in a highly non-linear fashion. The feedback sensor helps to stabilise such a high-quality light source.

The emitter feedback assembly may also include the circuitry necessary to process the emitter feedback functionality, however, in this first embodiment of the invention such functionality is integrated within the microcontroller.

The operation of the system illustrated in the Figures shall now be described.

The microcontroller 202 is the main processor and controller of the illumination device 200. The microcontroller 202 is arranged to initialise each of the circuits of the illumination device such that they are in a ready state, that is in a state ready to perform any functionality provided by the illumination device 200. Once the illumination device 200 is initialised it awaits input from the user via the user interface 206 or from the camera via the camera interface 204. The camera 100 can be initialised in a similar way.

Periodically, the illumination device may be calibrated. In particular, because luminance of light emitting sources can vary, and generally degrade overtime, it is advantageous to regularly perform a calibration such that a user of the illumination device obtains expected luminance levels. In this embodiment of the present invention the luminance calibration is performed every time that the illumination device 200 is initialised, However, in alternative embodiments this calibration could be limited to an automatic weekly or monthly occurrence, or alternatively only take place upon specific instructions from the user. Furthermore, calibration could be performed whenever there is a change in a monitored parameter, such as temperature, which could affect the device performance. It will be appreciated that in some circumstances a calibration may not be necessary.

When the calibration takes place the microcontroller 202 instructs the light emitting assembly to cycle through each emitter. That is, each light emitting element of the the light emitting array emits light on its own, with each light emitting element of the emitter array doing this sequentially. The emitter feedback assembly 207 is arranged to capture a part of the emitted light and this captured light is used to calibrate the light emitting elements. In particular, the emitter feedback assembly 207 feeds back the luminance level to the microcontroller 202, which in turn compares the received light level with the expected light level. Furthermore, the microcontroller is able to relate each light level received from the emitter feedback assembly 207 with a particular emitter of the emitter array of the light emitting assembly 205. Hence, if any of the luminance levels are deemed incorrect then the microcontroller 202 can reset the luminance by adjusting the ON time of the specific light emitting element.

Consequently, a fully calibrated emitter array is achieved which emits a stable and constant light.

When the calibration is complete and no instructions to emit light from the light source are received, the light emitting assembly 205 keeps the light emitting elements, or emitters, in an OFF state. At this point the camera interface 204 and the user interface 206 are set to listen for commands from the camera. The state of the device can be displayed for the user via the user interface 206.

At this point the user is able to set the parameters of both the camera 100 and the illumination device 200 via the respective user interfaces. Such settings will control the appearance of the photo taken. The type of settings available were discussed in detail with respect to Figure 1, however, further detail is provided below. It will be appreciated that these settings may include a plurality of preset functions, or may provide specific control for the user to set individual parameters.

At a time when a camera shutter button of the user interface 107 of the camera 100 is engaged, the camera 100 sends a light emission control signal to the illumination device via the external device interface 104 and the camera interface 204. This light emission control signal is a request for the illumination device 200 to control emission of light from the emitters of the light emitting assembly 205. This first control signal is simply a pre-flash message, and instructs the illumination device to emit a short flash.

During this pre-flash, the camera measures how much light is reflected from the scene and determines the appropriate exposure. The pre-flash, relay of information ready for re-calculation for the main flash, and the main flash itself all occur very quickly and as such only a single flash would be observed in most cases. It is noted that the sensor assembly 106 of the camera 100 can detect the emitted light. In alternative embodiments of the invention the pre-flash is not carried out.

Once the settings for the photograph are determined by the camera 100, the camera 100 will send a communication message to the illumination device 200. The communication message may contain a channel number, a shutter speed, a flash duration, a guide number (GN) and/or a variety of other commands from the camera to exchange information about the intended exposure.

When the illumination device 200 receives a communication message from the camera indicating that the camera shutter is opening, the microcontroller of the illumination device instructs the light emitting assembly to start emitting light according to the settings made by the photographer and/or the camera.

The sensor assembly 106 of the camera is then able to receive light including light originating from the illumination device and reflected from the subject 20. The overall photograph taken by the camera can then be stored in memory 103.

In accordance with this first embodiment of the present invention the functionality of the light emitting assembly 205, and the different types of emission possible via the light emitting assembly 205 shall be discussed.

As mentioned above, prior to the exposure the photographer will have entered instructions into the illumination device 200, which include specific control signals and parameters to be applied to the light emitting assembly.

The light emitting assembly 205 is arranged such that it is able to modulate the colour of the light emitted by the emitter array over the exposure time. Furthermore, the light emitting assembly 205 is arranged such that it is able to modulate the colour temperature or the light intensity of the light emitted by the emitter array spatially across the image during the exposure time, or any combination thereof. Such modulation was discussed in more detail with respect to Figure 1.

The illumination device is set up so that the user may individually control the parameters of the above-mentioned functions. For example, the user may control the modulation rate, the range of colour modulation or colour temperature modulation. The illumination device also provides a set of predefined effects having each of these characteristics pre-set. The user may then select one or more of these effects accordingly. Also, the user may apply or paint' light onto specific areas of the scene to be photographed, as discussed in more detail above.

In use, prior to exposure, the illumination device 200 receives a communication from the camera 100 as to what amount of light is required to achieve the desired exposure value. This exposure value will have been determined as mentioned above. The microprocessor unit uses this information to calculate an equivalent relative light level.

Consequently, when such a time comes that the camera sends a trigger signal to the device indicating that the exposure is starting, the device may not emit a single shot flash, but may emit a changing light during the time period when the shutter is open.

When the exposure is over, the illumination device 200 returns to its standby ready mode.

The affect that these effects of the present invention have on the resulting image varies depending on the sethngs entered by the photographer, the shutter speed of the camera, the relative positioning of the camera 100 and illumination device 200 in relation to the subject 20. The actual perceived effects include but are not limited to: colour gradation effects, strobe effects, a combination of blur and sharpness, and a variation in exposure across the image.

The above-mentioned first embodiment of the present invention talks specifically about use of the present invention when taking still photographs. While such techniques could be applied constantly across a plurality of frames of a moving image, in accordance with a second embodiment of the invention uses specific to video recording shall be described. All those parts of the invention not described herein can be assumed to be the same as the first embodiment.

Video images are the result of a series of still images, taken at a rate such that when played back at the rate they were taken a smooth constant image stream is observed.

The frequency of images taken for video images is typically between 24 and 30 frames per second.

When used in video embodiments of the present invention are able to modulate the light over a series of video frames. Different modulation or variation of light characteristics can be provided between each frame, and this modulation may be linear or non-linear, repeating or non-repeating. Some of these effects are discussed below.

A short ramp-up of light intensity with a slow decay during the exposure of each individual frame gives a restlessness and disharmony to, for example, a city scene.

Such techniques are great for scenes that portray urgency. Furthermore, a casual viewer may experience the scene as having higher intensity or uneasiness, but will probably not be able point to the exact cause.

A slow-strobing effect can be achieved by, for example, strobing on every other or third frame. Hence, strobing involves varying the light intensity between consecutive frames, or for example on 1 of every x frames. When such a technique is used in lighting something moving through a scene the subject will look unnatural, out of place, on the verge of flickering.

Combining intra-frame modulation techniques with modulation over many frames enables the photographer to, for example, smoothly fade in or out an effect on any part of the scene that is lit by the device.

The above described techniques are a selection of many such techniques which could be applied in accordance with embodiments of the present invention.

This second embodiment of the present invention is, therefore, able to provide a photographer with further available effects. In particular, effects such as simulation of flickering light from a campfire, a TV-set, or a neon tube can be achieved.

Furthermore, a number of other lighting effects that may be desirable when recording moving images can be achieved.

While this second embodiment discusses the use of changing modulation characteristics between frames of a video, the same techniques could be used for a series or sequence of still images.

In accordance with a third embodiment of the present invention several illumination devices are used in conjunction. In particular, the illumination devices can be spaced apart and operated together in synchronisation in order to simulate a moving or larger light source. Hence, the photographer may use more than one device to achieve improved or alternative effects.

For example, take the simple example of a campfire. The photographer wants to record a video scene with a couple of actors around a campfire. The natural light from the campfire itself is not suitable for illuminating the actors; it is not strong enough for a proper exposure in camera. So for the actual close-ups, the photographer arranges for a stronger light source. The colour of the light coming from a campfire will vary slightly over time. This effect is possible to simulate well with a single device set to vary the colour gradually within a range with some amount of stochastic motion similar to an actual campfire. A campfire also has a certain physical size; it is not a point sized light source as the device is. If the actors were placed around a campfire in such a way that they cast a shadow onto something, their shadow would flicker somewhat depending on how large the campfire is and how windy it is. A single point sized light source would not be able to simulate the moving shadows, but two or more lights would. Two or more lights could be set to simulate a campfire independently, or they might be synchronised through the external interface.

In practice, this embodiment of the invention can be implemented by a photographer having a laptop where he or she can see the image from the camera. This is a constant feed, like a video feed. The laptop is also connected to a plurality of illumination devices. One of the microcontrollers or microprocessors in this system acts as a master. For example, the microprocessor of the laptop may act as a master, with the equivalent component of the camera I illumination device acting as a slave.

Each of the light sources provided can have an associated light sensor or device camera. By combining the images received from the device cameras, the system is able to determine which parts of the subject are lit by which illumination device. The user is then able to view a representation of the illuminated scene, and the affect of each of the light sources on a single user display screen. Each illumination device can then control the intensity, colour and position of light emitted onto the scene. As such embodiments of the present invention allow for a very finely grained control over the emitted light.

The master can determine how each illumination device affects the scene or subject of interest by any combination of three methods: 1. A diagram of the relative positioning of the illumination devices with respect to the subject, as entered into the system by the operator. In alternative embodiments of the invention the positioning of the illumination devices may be automatically determined by triangulating via wireless radio or such like.

2. By evaluating the images from the cameras built into the illumination devices. Each device sees the scene from a different angle and these images are combined to build a three dimensional representation of the scene.

3. The master commands each device in turn to illuminate the scene or subject by scanning a spot of light from e.g. left to right and/or top to bottom or vice versa. The scanning is done by changing the opacity of the filters correspondingly. The master then sees how each spot of light affects the scene or subject.

The master then has an internal representation of the scene where it is known how each pixel of light' from each emitter affects the lighting. The operator can then alter any aspect of the lighting by interacting with the display. Light in areas that form hotspots can be toned down. Unwanted reflections from the forehead of a subject is an example of such an unwanted hotspot. Other typical uses are to increase or decrease the illumination of the background and change its colour. Also, the device may be used to paint light' onto a subject in order to change the dynamics and mood of the lighting.

While the above example provides a laptop as the master, it will be appreciated that a laptop is not required. One of the plurality of illumination devices used could act as the master and the user could control all of the illumination devices from the master illumination device.

When an illumination device, or a plurality of illumination devices, is used to illuminate an object that may move, for example a person, feature tracking may be used to constantly correct the internal representation of the scene. If a particular lighting is applied to a particular part of the subject, say a shoulder, feature tracking can help the system maintain the same lighting of the shoulder even when the person moves.

The embodiments of the invention described above, therefore, provide the photographer with control over an image at the point of taking the photo. While post-production techniques can be used to provide some of these effects, such techniques are expensive to provide because they require specialised technical personnel to carry them out. Hence, an image that requires substantial work in post-production is typically of less value to the customer. The above described embodiments of the invention thus provide means for providing lighting effects without the need for extensive and costly post-production techniques.

In accordance with yet another embodiment of the present invention the emission of light by the illumination device can be synchronised with the opening and closing of the camera shutter in order to save energy.

When a camera records video, it records a number of frames in quick succession. As mentioned previously, the frequency is typically between 24 and 30 frames per second for normal video, but may go significantly slower or faster depending on technical or artistic factors. If the frame rate is, say, 24 frames per second, there is approximately 42 ms between each individual exposure. The exposure time for each individual frame must be shorter than the time between each frame, but is otherwise independent of the frame rate.

The exposure time is set by the camera or by the photographer to a suitable value in order to get the desired exposure based on the available light, in addition to other factors. Typical exposure times may be 1/60 s, 1/125 s or 1/250 s. So in a typical scenario the shutter may be open for 4 to 16 ms during each 42 ms period.

This embodiment of the present invention thus provides an illumination device arranged to only emit light when the shutter is open. Given that when recording video a constant light source is provided, this embodiment saves significant amounts of energy compared to known techniques because light is only emitted during those periods that the shutter is open. As a consequence, the illumination device can be emitting light for much less of the time than systems that employ a constant light source. Energy saving is equal to the ratio of frame rate to exposure time. For a frame rate of 24 fps and a shutter time of 1/60 second, the energy saving is roughly 59%.

Hence, for a shutter time of 1/250 second, the energy saving is roughly 88%.

One problem with this energy saving technique is that the frequency at which the illumination device is turned ONIOFF may be visible to the human eye. Humans have individual and varying sensitivity to light flicker. In order to prevent the illumination device causing a flicker, which may be seen as a nuisance by some people, a further embodiment of the present invention involves the device emitting one or more additional light emissions, or blind fires, during the time when the camera shutter is closed. That is, light is emitted for a period shorter than the amount of time the camera shutter is shut, but a significant amount of time such that the frequency of emitted light is increased. This so called flicker reduction mode of the illumination device therefore increases rate at which the flashes take place, thus increasing to the frequency to a rate, for example 48Hz, 72Hz or 96Hz for a 24Hz frame rate, which will not be observable by the human eye. This flicker reduction mode eradicates flicker problems without unduly increasing the time the illumination device is ON.

It will be appreciated that the concept of turning ON/OFF of the light source in synchronisation with the camera shutter can be applied with or without use of the modulation effects and features of previously discussed embodiments. In particular, this energy saving technique could be applied to any technique in order to help reduce energy consumption.

In yet another embodiment of the present invention an ambient light colour compensation mechanism is provided which includes an ambient light sensor and a colour adjusting means. In particular, this embodiment of the present invention relates to adjusting colour temperature in order to correct for photographic discrepancies that can occur when artificial lighting is used, as discussed in more detail below.

Colour temperature is a characteristic of visible light that has important applications in photography and related fields. The colour temperature of a light source is the temperature of an ideal black-body radiator that radiates light of comparable hue to that light source. The temperature is conventionally stated in units of absolute temperature, Kelvin (K). Higher colour temperatures (5,000 K or more) are called cool colours (blueish white); lower colour temperatures (2,700-3,000 K) are called warm colours (yellowish white through red). Domestic light sources, like an incandescent lamp that emits light as a result of thermal radiation, behaves for practical purposes like a black-body radiator in the context of colour temperature.

The absolute or specific colour temperature of the light source that illuminates a scene is not usually critical. Cameras may automatically find the correct white balance, or if not, the photographer can easily do it in post production. However, a problem arises when a scene is lit by two or more light sources with differing colour temperatures. If a warm (low CT) light falls on a person from one side and a cold (high CT) light from the other side, then there is no white balance to be found where all the colours in the image will be correct or natural looking. If the white balance is adjusted such that anything illuminated by the warm light have natural colours, then anything illuminated by the cold light will look pale and ghostly. If the correct colour balance is set for the cold light, then anything lit by the warm light will turn orange and red.

The abovementioned problem limits the conditions under which photographers can take successful pictures when out on location. It is also a severe problem for video recording such as reporting or news gathering.

This embodiment of the present invention provides an illumination device having additional features to compensate for such ambient light problems. In particular, the ambient light colour compensation mechanism of the illumination device has the ability to a) vary the colour temperature of light emitted by the luminance device, b) measure the colour temperature of the existing ambient light, and c) perform the necessary compensation automatically or manually, wherein automatic compensation involves varying of the colour temperature of the emitted tight in response to the measured colour temperature.

The ambient tight colour compensation mechanism can be provided as a separate processing device or alternatively its functionality can be provided by the microcontroller 202 of the illumination device 200.

The features of the illumination device in accordance with this embodiment of the present invention shall now be described in detail, The ambient light colour compensation mechanism of the illumination device has a built in colorimeter. This is an assembly of four tight sensors, having a red, a blue, a green and a clear filter respectively. The colour sensor assembly will typically point in the same direction as the light emitter such that it receives light from where the light emitter will be emitting light. The colour sensor measures the red, green and blue components of the existing or ambient light, and the microcontroller uses this information to calculate a corresponding colour temperature. The clear channel is used to measure the overall light level.

The microcontroller receives information regarding the amount of red, green and blue light from the colour sensor assembly. The microcontroller then combines this into an RGB value. The microcontroller uses a 3x3 correlation matrix to transform these values to CIE XYZ tristimulus values. CIE XYZ colour space is a mathematical representation of the human visual system as it relates to colour. The CIE tristimulus values correspond to the sensitivity of a normalized human eye. The human eye has three types of cone cells for colour vision. These cone cells are sensitive to red, green and blue. The XYZ tristimulus values are the relative amounts of red green and blue that makes up a particular colour, adjusted for the sensitivity of the human eye. The correlation matrix is a formula that is used to transform the light values from the ambient light sensor, which does not precisely match the sensitivity of a human eye, into values that correspond to the sensitivity of a human eye.

From the XYZ tristimulus values a further 3:2 transformation is performed to map the values on to a standard 2-dimensional CIE 1931 colour coordinate system. Lastly a calculation is performed in order to find the correlated colour temperature point on the CIE plancian locus, and the offset in the green or magenta direction.

The green/magenta offset is a value used to correct for the effect that is often present when the existing light is not a result of thermal radiation. For example, the sun or an incandescent light bulb emits light as a result of being heated. Light emitted as a result of thermal radiation falls along the plancian locus and ranges from red-ish white through yellowish to blue-ish white. The plancian locus is the range of colours that a black body emits as its temperature rises. These colours lies along a curve in the CIE colour coordinate system.

White light that is not generated as a result of heating, like e.g fluorescent light which is generated by exiting a gas typically does not fall exactly on the plancian locus but somewhere nearby. This light will have an additional green or magenta colour component to it. A fluorescent light may for example have a green tint. Similar to above, this tint may not be noticed by a human eye, but may strongly influence a photographic image. This offset from the plancian locus is taken into account by the illumination device in order to mimic the colour of the existing light as closely as possible.

It will be appreciated that while Colour Temperature is the most common way to describe light specifically intended for illumination, the device can measure light of any colour and emit light of any colour (within the constraints of the particular emitters and sensors used).

In alternative embodiments of the present invention a colour sensor of a different construction is utilised. In particular, a diffraction spectrometer is utilised in order to perform the measurements needed to arrive at the correlated colour temperature.

Once the colour sensor measurement values and the calculated values are obtained, these can be used to adjust the light emitter to emit light with the same correlated colour temperature as measured by the colour sensor. The green/magenta offset calculated by the microprocessor is then added.

As the device is capable of emitting light of any colour (within the constraints of the particular emitters used), the device could also mimic a light source with an emission spectrum that falls outside the definition of white light. For example, a pure red light.

In order to be able to measure the existing or ambient light while simultaneously emitting light, the ambient light colour compensation mechanism of the illumination device instructs all the emitters to be turned off for a short period of time. This can be repeated at regular intervals in order to compensate for variations in ambient colour when recording video or a sequence of photographs. The turn off duration is usually about 4Ops (typ). This duration is so short that the human eye or camera will not notice that the emitters were turned off, but is sufficiently long for a measurement to be taken.

The resulting small loss in average light output due to such turning off of the emitters can be compensated by increasing the light output by an equal amount in the periods between the measurements. The turn off duration is too short for the analog-digital (AD) converter to perform a complete measurement, so a sample-and hold circuitry is employed in order for the AD converter to complete the integration over several measurement cycles.

The ambient light colour compensation mechanism can also be used to perform further functionality. For example, a photographer using the device may point the illumination device at another light source such that the device mirrors the colour temperature of the other light source. This may, for example, allow for good natural light colour to be achieved because the ambient light colour compensation mechanism can provide light which is an exact copy of natural day light.

Another functionality of the ambient light colour compensation mechanism is that it allows for a photographer to set the illumination device to automatically adjust its correlated colour temperature to the dominant colour temperature in the scene.

Alternatively, the photographer could set the device to accentuate a prominent colour temperature in a scene, such the colour emitted by an open fire.

In the following, photography should be taken to mean both still photography and moving images (video). Photographer should be taken to mean both still photographer and videographer.

The camera 100 may be any type of camera which is capable of linking up with an external illumination device or flash. In particular, the camera must have an interface circuit such that the operation of the camera and device can be synchronised. A HDSLR may be preferable, but any camera could be used.

Each of the components of the camera and illumination device may be provided on a respective circuit board or integrated within the individual device. Furthermore, while certain components have been described as separate entities, and other components as performing multiple functions, it will be appreciated that many functionalities could be combined within a single component, or separated into distinct components as appropriate. Furthermore, the overall functionality of the camera and illumination device could be combined into a single unit.

While the invention has primarily been described with respect to use with a digital camera it will be appreciated that the invention would work equally well with an analogue based photographic recording means.

While the above described embodiments of the invention disclose that the functionality of the present invention is incorporated within an illumination device, it will be appreciated that the functionality could also be incorporated within a camera, video camera, or stand alone device. The functionality of the above described invention could be integrated within a camera with or without an illumination device such as a flash. If the camera does not include an illumination device the camera incorporating the functionality of the present invention is arranged to instruct the illumination device when to illuminate. The functionality could also be provided in a stand alone device separate from a camera and an illumination device. Such a stand alone device is arranged to receive control signals from a camera and convert these control signals into new control signals to control the illumination device in accordance with the various embodiments of the present invention set-out above. Hence, the stand alone device acts as an interface between the camera and illumination device.

The term illumination device refers to a camera flash or any other suitable lighting device for use with a camera, video camera, camcorder, mobile phone camera, or any other image recording device.

The present invention can be implemented in dedicated hardware, using a programmable digital controller suitably programmed, or using a combination of hardware and software.

Alternatively, the present invention can be implemented by software or programmable computing apparatus. This includes any computer, or such like. The code for each process in the methods according to the invention may be modular, or may be arranged in an alternative way to perform the same function.

Each of the functionalities of the invention can in whole, or in part, be implemented by the combination of a processor and associated memory, or by a standard computer system. Furthermore, functions described herein as being implemented as part of a single unit may be provided separately, communicatively coupled across a network.

The present invention can encompass a carrier medium carrying machine readable instructions or computer code for controlling a programmable controller, computer or number of computers as the apparatus of the invention. The carrier medium can comprise any storage medium such as a floppy disk, CD ROM, DVD ROM, hard disk, magnetic tape, or programmable memory device, or a transient medium such as an electrical, optical, microwave, RF, electromagnetic, magnetic or acoustical signal. An example of such a signal is an encoded signal carrying a computer code over a communications network, e.g. a TCP/IP signal carrying computer code over an lP network such as the Internet, or an intranet, or a local area network.

It is appreciated that various features of the invention which are, for clarity, described in the contexts of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment may aiso be provided separately or in any suitable subcombination.

It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the invention is defined only by the claims.

Claims

CLAIMS: 1. A device for use in photography, the device comprising: a variable filter arranged to vary characteristics of light received from a light source, the variable filter being arranged to emit the varied light onto a subject of an image being recorded; and a processor arranged to control the variable filter.
2. The device according to claim 1, wherein the variable filter comprises a plurality of variable filter elements arranged in an array, each filter element arranged to vary the characteristics of the light passing therethrough.
3. The device according to claim I or 2, wherein the variable filter is arranged to vary colour characteristics of the light.
4. The device according to any preceding claim, wherein the variable filter is arranged to vary intensity characteristics of the light.
5. The device according to any preceding claim, further comprising: an optical assembly arranged to focus the light emitted from the variable filter.
6. The device according to any preceding claim, wherein the processor further comprises: a tracking means arranged to track a position of a feature of the subject of the image being recorded and control the variable filter to vary the characteristics of the light in accordance with the tracking of the feature.
7. The device according to claim 6, wherein the processor is arranged to control the variable filter to vary the characteristics of the light in accordance with the tracking of the feature by applying the same light characteristics to the feature when the feature moves position.
8. A device for use in photography, the device comprising: an interface for receiving a communication identifying camera characteristics; and a processor arranged to vary at least one characteristic of light emitted by a light source in accordance with the camera characteristics.
9. The device according to claim 8, wherein the camera characteristics include information identifying a camera shutter opening time, and the processor is arranged to vary the at least one characteristic of the light each time new information identifying a camera shutter opening time is received.
10. The device according to claim 8 or 9, wherein the camera characteristics include information identifying a camera shutter opening period and the processor is arranged to vary the at least one characteristic of the light during the camera shutter opening period.
11. The device according to any one of claims 8 to 10, wherein the at least one characteristic of the light varied by the processor includes a colour characteristic of the light.
12. The device according to any one of claims 8 to 11, wherein the at least one characteristic of the light varied by the processor includes an intensity of the light.
13. The device according to any one of claims 8 to 12, wherein at least one characteristic of the light is varied spatially.
14. The device according to any one of claims 8 to 13, further comprising: a light source arranged to emit light; and a filter arranged to vary the at least one characteristic of the light.
15. The device according to claim 14, wherein the filter is a matrix of variable filter elements.
16. A device for use in recording video images, the device comprising: an interface for receiving one or more communications identifying a plurality of open periods of a camera shutter; and a controller arranged to instruct a light source to emit light in accordance with the camera shutter open periods.
17. The device according to claim 16, wherein the controller is arranged to instruct the light source to emit light throughout the period when the camera shutter is open.
18. The device according to claim 16 or 17, wherein the one or more communications identifies a camera shutter opening time and a camera shutter opening period.
19. The device according to claim 18, wherein the one or more communications also identifies a frequency of camera shutter opening.
20. The device according to any one of claims 16 to 19, wherein the controller is arranged to instruct the light source to emit light during a portion of the period that the camera shutter is closed.
21. A device for ambient light colour compensation, the device comprising: a light receiving part arranged to receive a coloured light; and a light colour compensator arranged to compensate colour characteristics of light to be emitted by a light source in accordance with the received light.
22. The device according to claim 21, wherein the light colour compensator is arranged to compensate for the colour characteristics of the light to be emitted such that the light to be emitted has the same colour characteristics as the received light.
23. The device according to claim 21 or 22, wherein the light receiving part comprises: a red light sensor arranged to receive red light; a green light sensor arranged to receive green light; a blue light sensor arranged to receive blue light; and a white light sensor arranged to receive all colours of light, wherein the white light sensor is used to determine a received light intensity.
24. The device according to any one of claims 21 to 23, wherein the received light is ambient light falling on a subject to be photographed.
25. The device according to any one of claims 21 to 24, wherein the light colour compensator is arranged to apply an offset of green and/or magenta to the light to be emitted in order to further correct for the colour of light when the colour of light is defined in terms of colour temperature.
26. The device according to any one of claims 21 to 25, wherein the device is arranged to turn off the light source while taking a measurement.
27. A device including two or more of: the device of any one of claims I to 7; the device of any one of claims 8 to 16; the device of any one of claims 16 to 20; and the device of any one of claim 21 to 26.
28. The device according to any preceding claim, wherein the device is an illumination device including a light source.
29. The device according to any preceding claim, wherein the device is a camera.
30. A method for use in photography, the method comprising: varying, at a variable filter, characteristics of light received from a light source such that the varied light is emitted onto a subject of an image being recorded; and controlling, at a processor, the variable filter.
31. The method according to claim 30, wherein the variable filter comprises a plurality of variable filter elements arranged in an array, each filter element arranged to vary the characteristics of the light passing therethrough.
32. The method according to claim 30 or 31, wherein the varying characteristics of the light comprises varying colour characteristics of the light.
33. The method according to any one of claim 30 to 32, wherein the varying characteristics of the light comprises varying intensity characteristics of the light.
34. The method according to any one of claims 30 to 33, further comprising: focusing, at an optical assembly, light emitted from the variable filter.
35. The method according to any one of claims 30 to 34, further comprising: tracking, at a a tracking means, a position of a feature of the subject of the image being recorded; and controlling the variable filter to vary the characteristics of the light in accordance with the tracking of the feature.
36. The method according to claim 35, wherein the step of controlling comprises controlling the variable filter to vary the characteristics of the light in accordance with the tracking of the feature by applying the same light characteristics to the feature when the feature moves position.
37. A method for use in photography, the method comprising: receiving a communication identifying camera characteristics; and varying at least one characteristic of light emitted by a light source in accordance with the camera characteristics.
38. The method according to claim 37, wherein the camera characteristics include information identifying a camera shutter opening time, and the method further comprises varying the at least one characteristic of the light each time new information identifying a camera shutter opening time is received.
39. The method according to claim 37 or 38, wherein the camera characteristics include information identifying a camera shutter opening period and the method further comprises varying the at least one characteristic of the light during the camera shutter opening period.
40. The method according to any one of claim 37 to 39, wherein the at least one characteristic of the light which is varied includes a colour characteristic of the light.
41. The method according to any one of claims 37 to 40, wherein the at least one characteristic of the light which is varied includes an intensity of the light.
42. The method according to any one of claims 37 to 41, wherein the at least one characteristic of the light is varied spatially.
43. A method for use in recording video images, the method comprising: receiving one or more communications identifying a plurality of open periods of a camera shutter; and instructing a light source to emit light in accordance with the camera shutter open periods.
44. The method according to claim 43, wherein the light source is instructed to emit light throughout the period when the camera shutter is open.
45. The method according to claim 43 or 44, wherein the one or more communications identifies a camera shutter opening time and a camera shutter opening period.
46. The method according to claim 45, wherein the one or more communications also identifies a frequency of camera shutter opening.
47. The method according to any one of claims 43 to 46, further comprising instructing the light source to emit light during a portion of the period that the camera shutter is closed.
48. A method for ambient light colour compensation, the method comprising: receiving a coloured light; and compensating colour characteristics of light to be emitted by a light source in accordance with the received light.
49. The method according to claim 48, wherein the step of compensating for the colour characteristics of the light to be emitted is performed such that the light to be emitted has the same colour characteristics as the received light.
50. The method according to claim 48 or 49, wherein the received light is ambient light falling on a subject to be photographed.
51. The method according to any one of claims 48 to 50, further comprising applying an offset of green and/or magenta to the light to be emitted in order to correct for the colour of light when the colour of light is defined in terms of colour temperature.
52. The method according to any one of claims 48 to 51, further comprising turning off the light source while taking a measurement.
53. A method including two or more of: the method steps of any one of claims 30 to 36; the method steps of any one of claims 37 to 42; the method steps of any one of claims 43 to 47; and the method steps of any one of claim 48 to 52.
54. A carrier medium carrying computer readable code for configuring a suitable computer as the apparatus of any of claims I to 29.
55. A carrier medium carrying computer readable code for controlling a suitable computer to carry out the method of any one of claims 30 to 53.