Abstract:
The present invention relates to the field of devices with a possibility of recording light data, the device having a flash and more particular to such devices having a flash ( 300 ) which light cone ( 306 ) is adaptable. The present invention provides a method for adapting a light cone ( 306 ) from a flash ( 300 ) of a device using a liquid lens ( 302 ) and a device implementing such a method.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to the field of devices with a possibility of recording light data, the device having a flash and more particular to such devices having a flash which light cone is adaptable. The present invention provides a method for adapting a light cone from a flash of such a device and a device implementing such a method. 
       BACKGROUND OF THE INVENTION 
       [0002]    Using a flash of a device with the possibility to record light data, e.g. a flash of a digital camera, video recording device or a IR camera, can be troublesome as quite often the target, i.e. an object or part of a scene in front of the device which the user of the device intends to e.g. take a photo of, is out of reach of the flash or the flash illuminates the target and its surroundings in a disadvantageous way. 
         [0003]    In some devices, a typical flash solution is a LED flash with some sort of lens in front of the LED. The lens solution can be everything from a plastic window to a total inner reflection (TIR) Fresnel lens. Such a flash solution  200  is shown in  FIG. 2 . The flash  200  comprises a light source  206  emitting light  208 , for example a LED light source. The flash  200  further comprises a TIR element  204  for guiding the emitted light  208  (with minimum light loss due to the TIR property of the TIR element  204 ) into a Fresnel lens  202 . 
         [0004]    For any type of lens to be used in a flash, a few important parameters needs to be taken into consideration, e.g. what uniformity of illumination is required, what lens gain is desired and what is the factory tolerances. The lens gain is a value that describes how much the lens will collect the light compared to a using a bare LED without a lens. A lens with a high lens gain thus provides a light cone from the flash which reaches far but only illuminates a small portion of the scene in front of the device. 
         [0005]    A solution to the problem of not illuminating the target with the flash when e.g. taking a picture with the device may be to use a Xenon flash, but this requires high voltage and space, which often not is provided by compact devices such as a camera in a mobile phone. Another solution may be to use a high power LED with super capacitors to be able to feed the LED with higher current, which also is an unsuitable solution for compact devices such as a camera in a mobile phone. 
         [0006]    Moreover, depending on the scene which a user of the device intends to capture, using different light cones may be advantageous. This may not be possible using a lens arrangement as described above and shown in  FIG. 2 . 
         [0007]    It is within this context that embodiments of the invention arise. 
       SUMMARY OF THE INVENTION 
       [0008]    In view of the above, an objective of the invention is to solve or at least reduce one or several of the drawbacks discussed above. Generally, the above objective is achieved by the attached independent patent claims. 
         [0009]    According to a first aspect, the present invention is realized by a method for adapting a light cone from a flash of a device comprising an image sensor, the flash comprising a liquid lens, the method comprising the steps of: retrieving, by using a processor, one or more features indicative of an image to be captured by the image sensor, and adapting the light cone from the flash by changing properties of the liquid lens based on the one or more features. 
         [0010]    The present invention is based on the realization that a liquid lens has properties that may be changed in order to adapt the light cone. The liquid lens external shape is fixed, there are no moving parts: only internal liquids in the liquid lens change shape. This means that the focal point of a liquid lens can be precisely controlled and dynamically changed by modifying the surface tension of the internal liquids by using different voltages. Since no other changes to the lens are required, e.g. rotation of the lens or replacement of the lens, in order to adapt the light cone, a reduced complexity of a lens arrangement in the flash may be achieved. By adapting the light cone from the flash by changing properties of the liquid lens, i.e. by changing the surface tension of its internal liquids, based on one or more features indicative of an image to be captured by the image sensor, the light cone can advantageously be adapted based on e.g. light conditions in a scene and/or type or distance to the target and/or based on properties of the device such as the current focus setting and shutter setting. All these features influences the image to be captured by the image sensor, and by adapting the light cone in view of one or more of these features, the flash may illuminate the target/scene in an advantageous way. 
         [0011]    As used herein, the term “scene” should be understood to represent the environment/location which the device is directed at and that will be captured in an image (picture, video sequence etc.) if the device is used. In other words, the scene is the target of e.g. the image or video sequence, and its surroundings. 
         [0012]    According to a second aspect, the present invention is realized by a device comprising an image sensor and a flash comprising a liquid lens, the device comprising a processor configured for retrieving one or more features indicative of an image to be captured by the image sensor, and an electrowetting device for changing properties of the liquid lens based on the one or more features, thereby adapting the light cone from the flash. 
         [0013]    The second aspect may generally have the same features and advantages as the first aspect. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and non-limiting detailed description of embodiments of the present invention, with reference to the appended drawings, where the same reference numerals will be used for similar elements, wherein: 
           [0015]      FIG. 1  shows a method for adapting a light cone from a flash of a device according to embodiments of the invention, 
           [0016]      FIG. 2  shows a flash of a device according to prior art, 
           [0017]      FIG. 3  schematically shows the use of a liquid lens for adapting a light cone from a light source, 
           [0018]      FIG. 4  shows a flash of a device according to a first embodiment of the invention, 
           [0019]      FIG. 5  shows a flash of a device according to a second embodiment of the invention, 
           [0020]      FIG. 6  shows how a light cone of a flash is adapted based on one or more features indicative of an image to be captured by an image sensor of the device, 
           [0021]      FIG. 7  shows by way of example a device with a flash according to embodiments of the invention. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0022]    In the following description, the device with a possibility of recording light data will be exemplified as a digital camera, but this is only by way of example. The device may be any device with a possibility of recording light data, e.g. a digital camera, a digital video camera, a IR camera etc. 
         [0023]      FIG. 1  show by way of example a method for adapting a light cone from a flash of a digital camera. The camera comprises an image sensor and a processor. The camera further comprises regular camera settings. An example of such a setting is shutter speed (which determines the exposure time) of the camera which is the length of time a camera&#39;s shutter is open when taking a photograph (capturing an image). A further example is the focal length of the camera lens, which determines the focus distance of the camera, i.e. the distances the camera will attempt to focus at when capturing an image. Other properties may be used, e.g. a light sensitivity of the image sensor. Moreover, the image sensor may be configured to regularly capture light to produce image data, e.g. for show in a viewfinder display at the camera. Such image data may be analyzed by the processor of the camera in order extract e.g. scene luminance in a specified region, possible targets to focus on, distance to targets, movement of targets etc. It should be noted that the above mentioned image data do not need to be shown on a viewfinder display, the image sensor may anyway be configured to regularly capture light to produce image data. According to some embodiments, a user of the camera may provide manual input for adapting the light cone, for example by pointing and pressing on the viewfinder display. 
         [0024]    The first step of the method of  FIG. 1  is retrieving S 102 , by using the processor, one or more features indicative of an image to be captured by the image sensor. As described above, such feature or features may be retrieved from different sources. 
         [0025]    According to one embodiment, the step of retrieving S 102  one or more features comprises retrieving S 106  an exposure time of the digital camera, and extracting at least one of the one or more features from the exposure time. Since an increased exposure time means that light from the scene is captured to a higher extent, the light cone may advantageously be adapted such that the light of the target is improved, i.e. by increasing a lens gain of the liquid lens and this achieving a narrow light cone. 
         [0026]    According to one embodiment, the step of retrieving S 102  one or more features comprises retrieving S 104  a focus distance property of the digital camera, and extracting at least one of the one or more features from the focus distance property. For example, at small distances a wide light cone (low lens gain) may be advantageous in order to provide a more even illumination. At long distances, a narrow light cone (increased lens gain) may be advantageous in order for the light of the flash to reach a target of the image. 
         [0027]    According to one embodiment, the step of retrieving S 102  one or more features comprises capturing light by the image sensor of the digital camera to produce image data, analyzing the image data using the processor, and extracting at least one of the one or more features from the image data. As described above, the image data may be shown on the viewfinder display of the camera. In this case, the method comprises analyzing S 108  the viewfinder image using the processor in order to extract at least one of the one or more features. According to some embodiments, the step of analyzing the image data comprises using an object recognition algorithm, e.g. for finding a possible target. This will be further described in conjunction with  FIG. 6  below. According to some embodiments, the step of analyzing the image data comprises measuring an amount of light in at least one part of the image data. For example, the light may be measured near or on the target in the scene. Other embodiments of measuring of light may be used in order to retrieve the one or more features indicative of an image to be captured by the image sensor will be described in conjunction with  FIG. 6  below. 
         [0028]    The next step of the method for adapting a light cone is the step of adapting S 110  the light cone from the flash by changing properties of the liquid lens based on the one or more features. In this way, the adaptation of the light cone may be well substantiated, e.g. made in view of light conditions of the scene, the position of the targets in the scene, distance to target in the scene etc. By considering some or all of the above described parameters, the properties of the liquid lens can be changed and thus direct the light to the correct part of the scene with a lens gain that is appropriate to the content and surroundings. 
         [0029]    According to some embodiments, the step of adapting the light cone comprises altering S 112  the focal point of the liquid lens based on the one or more features. The focal point is adapted by changing the surface tension of internal liquids in the liquid lens. Such adaptation thus does not require a plurality of lens elements as in a mechanical zoom lens, but can instead be achieved by just modifying the surface tension of the internal liquids using different voltages. According to some embodiments, the focal point is altered by altering S 116  a position of a center of curvature of the liquid lens. In this way, the direction of the light cone from the flash may be changed. According to some embodiments, the focal point is altered by altering S 114  a radius of curvature of the liquid lens. In this way, the light cone of the flash may be made narrower or wider. In other words, the lens gain of the liquid lens is changed. 
         [0030]    After the light cone has been automatically adapted as described above, a user of the digital camera may capture S 118  an image and thus illuminate the scene in an advantageous way using the adapted light cone. 
         [0031]      FIG. 3  schematically shows operations of a liquid lens  302  for adapting a light cone  306  of a flash  300 . The flash comprises a light source  206  emitting light  208 . The light source  206  may be a LED light source or any other suitable light source. The liquid lens  302  is coupled to an electrowetting device  304  which is adapted for modifying a surface tension of internal liquids (not shown) of the liquid lens using different voltages. In this way, properties of the liquid lens  302  may be changed, and thereby adapting the light cone  306  from the flash  300 . For example, by increasing the voltage applied to the liquid lens  302 , the radius of curvature of the liquid lens  302  is increased which means that the focal point in the light cone  306  will be closer to the liquid lens, i.e. the focal length of the liquid lens will decrease. As described above, the light cone  306  can both be made narrower or wider (increase or decrease the lens gain of the liquid lens  302 ), and the direction of the light cone  306  may be altered to some extent by altering a position of a center of curvature of the liquid lens  306 . 
         [0032]    Usually the liquid lens is convex and the curvature of the convex lens can be changed. Also the center of the lens can be shifted as described above. Flash LEDs usually have a really wide light cone so a concave lens is thus not required. If a Laser LED is used as the light source  206 , a concave lens may be advantageous. According to some embodiments, the flash  300  comprises two liquid lenses, wherein one lens is concave and the other is convex. The properties of these lenses are controllable as in the same way as described above. 
         [0033]      FIG. 4  shows a flash  400  according to embodiments of the invention. The flash  400  comprises a total inner reflection, TIR, element  204 . By using such TIR element  204 , the light source  206  may be placed farther away from the liquid lens  302  than would be possible (without a high loss of light) if no TIR element  204  was used. This in turn makes it possible to have the liquid lens close to an outer surface of the digital camera, which is advantageous for the flexibility of direction and spreading of the light cone, while the light source  206  is placed in an inner part of the digital camera, e.g. at the printed circuit board of the digital camera. Moreover, the TIR element  204  also can be employed for guiding light from the light source  206  such that the liquid lens  302  may be made smaller, or in order to control the light cone emitted from the liquid lens  302 . Any suitable material may be used for the TIR element, e.g. a glass material or PMMA. 
         [0034]      FIG. 5  shows a flash  500  according to embodiments of the invention. The flash  500  comprises a TIR element  204 , and a Fresnel lens  202 . In the particular embodiment shown in  FIG. 5 , the liquid lens  302  is arranged to alter a light cone coupled out from the Fresnel lens  202 . According to some embodiments, the liquid lens  302  is arranged to direct light  208  emitted from the light source  206  into the TIR element  204 . According to other embodiments, the liquid lens  302  is arranged to direct light  208  emitted from the light source  206  directly into the Fresnel lens  202  and thus remove the need of the TIR element  208 . 
         [0035]      FIG. 6  shows how a light cone of a flash is adapted based on one or more features indicative of an image to be captured by the image sensor.  FIG. 6  comprises two images  600   a ,  600   b . These may be images shown on the viewfinder display of a camera. The images  600   a ,  600   b  are representations of image data produced from captured light by an image sensor of the camera. Both images comprise a target  606 , which also constitute a foreground part  610  of the images  600   a ,  600   b . The remaining parts of the images  600   a ,  600   b  constitute a background part  608 . A dotted circle  602  in the images  600   a ,  600   b  represent an outer boundary the light cone from the flash of the camera, and the dotted circle  604  represent a center part of the light cone, i.e. where the light from the flash is the brightest. As described in  FIG. 6 , the light cone may be adapted such that the brightest part is not in the center of the outer boundary of the light cone, by altering the position of the center of curvature of the liquid lens. 
         [0036]    According to some embodiments, a processor of the camera analyzes such image data in order to extract at least one of the one or more features from the image data. According to embodiments, the step of analyzing the image data comprises using an object recognition algorithm, such as a face recognition algorithm or a smile detection algorithm. Such algorithms are often already implemented in software installed in the camera. Consequently, using these kinds of object recognition algorithm(s) in order to extract at least one of the one or more features from the image data may not require further developments of the image analysis software of the camera. By employing such algorithms, the properties of the liquid lens, e.g. a radius of curvature of the liquid lens and/or a center of curvature of the liquid lens, may be continuously altered in order to adapting the light cone of the flash to follow the target  606  and advantageously illuminate the target. For example, if the digital camera is used for recording a movie of a scene in front of the digital camera, such an implementation may be advantageous to achieve good illumination of a moving target  606 . Such implementation may also be useful in other scenarios, e.g. if a sequence of images are captured in a row (for example if a bracketing mode or burst mode of the camera is employed). In  FIG. 6 , the center  604  of the light cone is following the target  606  when it is moving between the two images  600   a ,  600   b.    
         [0037]    According to some embodiments, the step of analyzing the image data comprises measuring an amount of light in at least one part of the image data. For example, the step of analyzing the image data may comprise separating the image data into a background part  608  and a foreground part  610 , wherein the amount of light is measured in the background part and/or the foreground part. For example, if the focus distance is sat to medium distance, and the background part  608  of the image  600   a ,  600   b  is dark, the analysis made by the processor may result in a high lens gain (narrow light cone) since in general there is no information of interest in the corners of such an image. On the other hand, if the background  608  comprises strong lighting, e.g. on a sunny day, the flash may advantageously be employed for fill flash purposes (i.e. for brighten deep shadow areas on the target  610 ). In this case, extreme lens gain may be desired. 
         [0038]    At a close distance to the target  608 , in order to not get an over exposed center  604  which may be the case if a narrow light cone is used, a low lens gain and thus a wider light cone is advantageous. 
         [0039]      FIG. 7  shows by way of example a mobile phone  700  implementing a flash  702  as described herein. Consequently, images captured through a camera lens  704  may be advantageously illuminated based on one or more features indicative of an image to be captured by the image sensor as described above.