Method and system for stray light compensation

Abstract

To provide a method for compensating for lens flare / stray light existing in an image, a storage medium and a system.SOLUTION: A system 100 for stray light compensation acquires a first image with a first imaging device 110 covering a first field-of-view 111, acquires a second image with a second imaging device 120 covering a second field-of-view 121 larger than the first field-of-view, estimates stray light components in pixels of the first image from pixel data of pixels in the second image, and compensates for stray light in the first image by subtracting the estimated stray light components in pixels of the first image.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to stray light compensation, and more particularly to stray light compensation in images captured by a digital camera. [Background technology]

[0002] Stray light is light within an optical system, such as a camera, that was not intended by the design. Stray light can originate from an intended source but may follow a path other than the intended one, or may originate from a source other than the intended one. Stray light is sometimes referred to as lens flare. Lens flare occurs when light is scattered or flared within a lens system. More precisely, light is scattered by the lens system itself, for example, through internal reflection and forward scattering from material imperfections in the lenses of the lens system. Lens flare can cause an image to appear "washed out" by reducing contrast and color saturation (adding light to dark image areas and adding white to color-saturated areas, reducing their saturation). Lens flare is particularly caused by bright light sources. As such, lens flare is widely distributed across an image and, although typically an invisible side effect, reduces the signal-to-noise ratio, or contrast, of the image. Therefore, lens flare sets an operational limit for the dynamic range of an image. In particular, lens flare limits the level of detail in darker parts of the image.

[0003] There is a need to either reduce lens flare / stray light or have some means to compensate for lens flare / stray light present in the image. Summary of the Invention

[0004] In view of the above, it is an object of the present invention to provide compensation for stray light present in images, especially digital images.

[0005] An object is to mitigate, alleviate or eliminate one or more of the above-identified deficiencies and drawbacks in the art singly or in any combination, or to solve at least the aforementioned problems.

[0006] According to a first aspect, a method for stray light compensation is provided. The method includes acquiring a first image using a first imaging device covering a first field of view, acquiring a second image using a second imaging device covering a second field of view, where the second field of view is wider than the first field of view and the first field of view is included within the second field of view, estimating stray light components in pixels of the first image from pixel data of pixels in the second image, and compensating for stray light in the first image by subtracting the estimated stray light components in pixels of the first image. This reduces stray light in the first image and improves the first image. Note that even if the stray light compensation discussed above is not fully calibrated, the applied stray light compensation can still be useful because the stray light compensation improves the signal-to-noise ratio of the first image. Therefore, an improvement in the dynamic range of the first image is achieved. A possible effect of this stray light compensation is to compensate for stray light arising from a light source outside the field of view of the first imaging device. This is because such stray light components are estimated from a second image captured by a second imaging device that has a wider field of view than the first imaging device.

[0007] Estimating the stray light component in the pixels of the first image may include filtering the second image, filtering the second image with a series of Gaussian filters to form a series of filtered second images, and linearly combining the filtered second images to form a stray light image that includes the stray light component from the pixels in the first image.

[0008] Estimating the stray light component in the pixels of the first image may include one or more of identifying portions of the second image that overlap with the first image, compensating for exposure differences between the second image and the first image, compensating for gain setting differences between the first imaging device and the second imaging device, compensating for pixel density differences between the second image and the first image, compensating for angle of view differences between the second image and the first image, and compensating for aperture setting differences between the first and second imaging devices.

[0009] According to a second aspect, there is provided a non-transitory computer-readable storage medium storing instructions for performing the method according to the first aspect when executed on a device having processing capability.

[0010] According to a third aspect, a system for stray light compensation is provided, comprising: a first imaging device configured to cover a first field of view and acquire a first image; a second imaging device configured to cover a second field of view and acquire a second image, the second field of view being wider than the first field of view and including the first field of view; and a circuit configured to perform a stray light compensation function. The stray light compensation function is configured to compensate for stray light in the first image by estimating stray light components in pixels of the first image from pixel data of pixels in the second image and subtracting the estimated stray light components in pixels of the first image.

[0011] The resolution of the second imaging device may be lower than the resolution of the first imaging device.

[0012] The first imaging device and the second imaging device may be configured to simultaneously capture the first image and the second image.

[0013] The second imaging device may be configured to capture the second image in a less saturated manner than the first image.

[0014] The second imaging device may comprise a fixed focus lens arrangement.

[0015] The second imaging device may be separate from the first imaging device.

[0016] According to a fourth aspect, there is provided a video camera comprising a system according to the third aspect.

[0017] The foregoing features of the method also apply to the second, third or fourth aspects, when applicable. To avoid undue repetition, reference is made to the above.

[0018] Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the scope of the invention will become apparent to those skilled in the art from this detailed description.

[0019] Therefore, it should be understood that the present invention is not limited to the specific components of the described system or operation of the described method, as such systems and methods may vary. It should also be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. It should be noted that, in this specification and the appended claims, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of an element, unless the context clearly dictates otherwise. Thus, for example, reference to "a device" or "the device" may include several devices, and so forth. Furthermore, the terms "comprising," "including," "containing," and similar phrases do not exclude other elements or steps.

[0020] These and other aspects of the present invention will now be described in more detail with reference to the accompanying drawings, which should not be considered limiting but are used for purposes of explanation and understanding.

[0021] As shown in the figures, the sizes of layers and regions may be exaggerated for illustrative purposes and, therefore, are given to illustrate the overall structure. Like reference numerals refer to like elements throughout. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 illustrates a system for stray light compensation. [Figure 2] 1 is a schematic top view of a system for stray light compensation looking at a scene. [Figure 3] FIG. 3 is a diagram of the scene in FIG. 2. [Figure 4a] 4 is a diagram of the scene of FIG. 3 taken by a first imaging device of a system for stray light compensation before stray light compensation is applied. [Figure 4b] 4a, after stray light compensation has been applied. [Figure 5] FIG. 1 is a block diagram of a method for stray light compensation. DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which presently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and to fully convey the scope of the invention to those skilled in the art.

[0024] The point spread function describes how an optical system represents an ideal point source, i.e., the system's impulse response. The modulation transfer function is the Fourier transform of the point spread function, i.e., the system's frequency response. In the case of an ideal lens (ignoring diffraction), the point spread function is an infinitely narrow impulse, and the Fourier transform of the impulse is unity for all frequencies (i.e., all frequencies are unchanged by the system). Thus, in a perfectly focused, ideal lens, all light from a single point in the scene reaches a single point on the sensor. In reality, the point spread function is never infinitely narrow; some light always reaches neighboring pixels, and a small percentage of light reaches pixels further away. In the frequency domain, this can be seen as a gradual roll-off for higher frequencies in the frequency response modulation transfer function. In a real lens, the point spread function varies depending on many factors, such as the color of the light, the offset from the optical axis, and the depth of field. Lens development is a compromise between cost and performance such that the lens can be optimized to handle "normal" scenes well enough, i.e. the point spread function is assumed to be narrow enough to produce a good enough image in typical situations.

[0025] As we push the boundaries of high-dynamic-range imaging, the requirements on lenses also increase. High-dynamic-range scenes typically contain at least some portions that are significantly brighter than the rest of the scene. Because the point spread function is not ideal, some light from bright areas diffuses into adjacent darker pixels, resulting in undesirable offsets in those pixels and reducing the contrast of the actual signal in the dark areas. Even if only a small percentage of light from a bright area diffuses into dark areas, it can still represent a significant contribution to those areas. This effect clearly worsens as the dynamic range, i.e., the ratio between light and dark, increases. This loss of contrast in dark areas adjacent to bright areas can be understood as a first-order limit on the dynamic range of a lens, as it limits the ability to measure contrast in dark areas. In theory, with perfect knowledge of the point spread function, it may be possible to reconstruct an ideal image by using the point spread function to perform deconvolution, i.e., stray light compensation. However, even if one successfully subtracts out the stray light offset perfectly, one will still be subject to photon shot noise introduced by the stray light, i.e., there is a physical limit to the dynamic range that can be measured for a given lens system due to photon shot noise. This can of course be avoided by collecting more photons and instead reducing the time and / or spatial resolution.

[0026] If we had access to an ideal, i.e., stray-light-free, image, estimating stray light becomes simple and becomes a matter of simply convolving the ideal image with the point spread function. Unfortunately, we obviously do not have access to an ideal image, so instead we use the actual image as an approximation. This may seem counterintuitive at first, but consider the following: psf - point spread function im ideal -Ideal image without any stray light im stray - Stray light offset per pixel imactual -Images actually measured on the sensor From the above definition, im actual =im ideal +im stray What I want to calculate is:im stray =im ideal *psf-im ideal Instead, calculate: actual *psf-im ideal +im stray *psf-im stray =im stray +im stray *psf-im stray =im stray *psf≒im stray In other words, im ideal is convoluted with the point spread function, so im ideal im actual By approximating with im ideal This slightly overestimates the stray light because it incorrectly assumes that the irradiance contributes excessively to the stray light. stray im actual By subtracting from im ideal Note that σ can be improved iteratively by improving the approximation of σ at each iteration.

[0027] A perfect full-resolution psf convolution would be extremely expensive and completely impractical. Instead, we assume that the point spread function can be approximated sufficiently well by a sum of Gaussian filters of various widths, i.e., by filtering the actual image with a series of Gaussian filters, we can reconstruct an approximation of the stray light as a linear combination of the filter results.

[0028] Thus, for a given lens arrangement, a point spread function can be estimated that describes how light is scattered by the lens arrangement. The point spread function can then be used to predict the amount of stray light in an image captured using the lens arrangement. A limitation when estimating stray light in this way is that only light that is actually seen by the lens arrangement can be measured, and light originating from sources outside the field of view cannot be considered.

[0029] The present invention is based on the insight made by the inventors that stray light in pixels of an image captured by a first imaging device can be estimated from an image captured by a separate second imaging device. The second imaging device is configured to have a wider field of view than the first imaging device. The field of view of the first imaging device is included within the field of view of the second imaging device. Furthermore, the second imaging device is typically configured to capture images with less exposure than the images captured by the first imaging device. This allows stray light components in the images captured by the first imaging device resulting from light sources outside the field of view of the first imaging device to be estimated and compensated for. Therefore, the present invention is based on having a separate second imaging device with a wider field of view to capture images of a wider portion of the scene covered by the first imaging device. Furthermore, preferably, the separate second imaging device is configured so that the images captured by the second imaging device and used to estimate stray light in the images captured by the first imaging device are free of saturated light sources. This can be prevented, for example, by using a different (usually lower) exposure for the image captured by the second imaging device than for the image captured by the first imaging device. The image captured by the second imaging device can then be used to estimate and subtract stray light from the image captured by the first imaging device. The second imaging device can be a camera with a lower resolution than the first imaging device. This is because the stray light component, which typically originates from a light source outside the field of view of the first imaging device, is spatially low frequency. Furthermore, the second imaging device can also be a camera with fixed focal length optics.

[0030] FIG. 1 shows a system 100 for stray light compensation. The system 100 includes a first imaging device 110 and a second imaging device 120. The first and second imaging devices 110, 120 are typically separate imaging devices. The first and second imaging devices 110, 120 may be arranged in a single housing, i.e., a camera device having two imaging devices is arranged in the housing. Alternatively, the first and second imaging devices 110, 120 may be separate devices, i.e., separate camera devices. Each imaging device 110, 120 includes a lens assembly 112, 122 and an image sensor 114, 124. That is, the first and second imaging devices 110, 120 are typically digital cameras. The lens assembly 122 of the second imaging device 120 may be a fixed-focus lens assembly. The lens assembly 112 of the first imaging device 110 may be a zoom lens assembly. First imaging device 110 covers a first field of view 111. Second imaging device 120 covers a second field of view 121. Second field of view 121 is wider than first field of view 111. First field of view 111 is contained within second field of view 121. First imaging device 110 is configured to capture one or more first images. Thus, first imaging device 110 may be a still image camera or a video camera. Second imaging device 110 is configured to capture one or more second images. Thus, second imaging device 120 may be a still image camera or a video camera. The resolution of second imaging device 120 may be lower than the resolution of first imaging device 110.

[0031] Preferably, the second field of view 121 is sized so that the second imaging device 120 is configured to represent all light sources from which light reaches the first imaging device 110 .

[0032] Preferably, the second imaging device 120 is configured to capture the second image such that the pixels of the second image are exposed less than the pixels of the first image. This facilitates capturing the second image with less saturated pixels than the first image. Therefore, preferably, the second image has less saturated pixels than the first image. By way of a non-limiting example, the second imaging device 120 is configured to capture the second image such that at least 99% of the pixels of the second image are unsaturated. Thus, a small number of pixels in the second image can be prevented from becoming saturated. This results in improved stray light estimation. To achieve this, the second imaging device 120 is typically configured to use a shorter exposure time than the first imaging device 110. However, other settings in the second imaging device 120 can also be used to prevent a small number of pixels in the second image from becoming saturated. Some non-limiting examples are using a less sensitive image sensor in the second imaging device 120, adjusting the aperture of the second imaging device 120, and using an optical filter such as a neutral density filter in the second imaging device 120. The second imaging device 120 may further be configured to capture the second image as a double-exposure image. The second imaging device 120 may also be a black-and-white camera. This is because the quality of the image captured by the second imaging device 120 is not very important, as long as the image captured by the second imaging device 120 provides information about the position and illuminance of light sources outside the field of view of the first imaging device 110.

[0033] According to one exemplary embodiment, the first imaging device 110 is a detail-view imaging device and the second imaging device 120 is a wide-angle imaging device. The detail-view imaging device covers a detailed field of view and is configured to capture one or more detail-view images. The wide-angle imaging device covers a wide field of view and is configured to capture one or more wide-angle images. The wide field of view is wider than the detailed field of view. The detailed field of view is contained within the wide field of view.

[0034] System 100 further comprises circuitry 130. Circuitry 130 is configured to perform overall control of the functions and operations of system 100. Circuitry 130 may include a processor 131, such as a central processing unit (CPU), microcontroller, microprocessor, etc. Processor 131 is configured to execute program code stored in memory 140 to perform the functions and operations of system 100.

[0035] Memory 140 may be one or more of a buffer, flash memory, a hard drive, removable media, volatile memory, non-volatile memory, random access memory (RAM), or another suitable device. In a typical configuration, memory 140 may include non-volatile memory for long-term data storage and volatile memory that serves as system memory for circuit 130. Memory 140 may exchange data with circuit 130 via a data bus. Associated control lines and address buses between memory 140 and circuit 130 may also be present.

[0036] The functions and operations of system 100 may be embodied in the form of executable logic routines (e.g., lines of code, software programs, etc.) stored on a non-transitory computer-readable medium (e.g., memory 140) of system 100 and executed by circuitry 130 (e.g., using processor 131). Furthermore, the functions and operations of system 100 may be standalone software applications or may form part of a software application that performs additional tasks related to system 100. The described functions and operations may be viewed as ways that corresponding parts of the system are configured to perform. Furthermore, the described functions and operations may be implemented in software; such functions may also be performed via dedicated hardware or firmware, or some combination of hardware, firmware, and / or software.

[0037] The circuit 130 is configured to perform a stray light compensation function 142. The stray light compensation function 142 is configured to estimate stray light components within pixels of an image captured by the first imaging device 110, hereinafter referred to as the first image. Such estimation is configured to be performed based on pixel data of pixels within an image captured by the second imaging device 120, hereinafter referred to as the second image. More precisely, the estimation is performed such that pixel data within the second image is manipulated so that pixel data indicative of stray light components within the first image resulting from a light source outside the field of view of the first imaging device 110 can be estimated. For example, the second image can be manipulated by filtering the second image with a series of Gaussian filters to form a series of filtered second images and linearly combining the filtered second images to form a stray light image that includes stray light components from pixels in the first image. The Gaussian filters used can be evaluated empirically, i.e., iteratively, for the system 100. Thus, the choice of Gaussian filter to use may be discovered by calibration of the system 100. Thus, the stray light component for a pixel in the first image may be estimated from the pixel value in the second image.

[0038] The estimation of the stray light component in the pixels of the first image may further depend on other factors, some non-limiting examples being the overlap of the field of view between the first image and the second image, the exposure of the first and second images, the gain settings of the first and second imaging devices 110, 120, the pixel density of the first and second images, the angle of view of the first and second imaging devices 110, 120, the focus settings of the first and second imaging devices 110, 120, and the aperture settings of the first and second imaging devices 110, 120.

[0039] Overall, the stray light component for a pixel in a first image can be found by applying a transfer function to the pixel values of the pixel in the second image. Such a transfer function conveys how the pixel values of the pixel in the second image affect the stray light in the first image. That is, a transfer function conveying how stray light affects the pixel in the first image can be applied to the pixel values of the pixel in the second image. Such a transfer function can depend on one or more of the factors discussed above. The transfer function can be evaluated empirically, i.e., iteratively, for the system 100. Thus, the transfer function to use for the system 100 can be found by calibration of the system 100.

[0040] The stray light compensation function 142 is further configured to compensate for stray light in the first image by subtracting the estimated stray light component in the pixels of the first image, thereby reducing the stray light in the first image and achieving an improved first image.

[0041] Next, application of the system 100 for stray light compensation will be discussed in connection with FIGS. 2, 3, 4a, and 4b. In FIG. 2, the system 100 for stray light compensation from above is shown viewing a scene including a building 200, a person 210, and a light source 220. In this particular example, the light source 220 is sunlight. In FIG. 3, the scene of FIG. 2 is shown represented by a first imaging device 110 having a first field of view 111 and a second imaging device 120 having a second field of view 121. The first field of view 111 is shown covering the person 210 and a portion of the building 200. Note that the light source 220 is outside the field of view 111 of the first imaging device 110. The second field of view 121 is shown covering the person 210, the building 200, and the light source 220. In FIG. 4a, an image captured by the first imaging device 110 is shown before stray light compensation is performed. In FIG. 4b, the image of FIG. 4a is shown after stray light compensation has been performed.

[0042] As discussed in connection with FIGS. 2, 3, and 4a, a light source 220 outside the field of view 111 of the first imaging device 110 affects the image captured by the first imaging device 110. As schematically indicated by arrow 221 in FIG. 2, light originating from the light source 220 outside the field of view 111 of the first imaging device 110 reaches the first imaging device 110. Such light affects the image captured by the first imaging device 110 as stray light / lens flare. An example of an image captured by the first imaging device 110 is shown in FIG. 4a. In FIG. 4a, stray light originating from the light source 220 outside the field of view 111 of the first imaging device 110 affects the image, mostly in the upper left portion of the image. The effect of stray light is illustrated by a dotted pattern in FIG. 4a. The dotted pattern indicates noise introduced in the image due to stray light originating from the light source 220 outside the field of view 111 of the first imaging device 110.

[0043] FIG. 4b shows the image shown in FIG. 4a after applying stray light compensation function 142. As shown in FIG. 4b, after compensating for stray light using stray light compensation function 142, the signal-to-noise ratio in the image is improved. The improved signal-to-noise ratio results in better representation of details in the stray light-compensated image shown in FIG. 4b. This is exemplified by the better representation of details in brick wall 205 of building 220 in FIG. 4b compared to FIG. 4a. Stray light compensation function 142 relays image data from an image captured by second imaging device 120 having a field of view 121 that includes light source 220 outside the field of view 111 of first imaging device 110. Thus, an estimate of stray light in pixels of the image captured by first imaging device 110 can be made from the image captured by second imaging device 120.

[0044] 5, a method 500 for stray light compensation will be discussed. Some of all of the steps of method 500 may be performed by the system 100 described above. However, it is equally realized that some or all of the steps of method 500 may be performed by one or more other devices having similar functionality. Method 500 includes the following steps. The steps may be performed in any suitable order.

[0045] Acquiring a first image with a first imaging device covering a first field of view (S502).

[0046] Acquiring a second image with a second imaging device (S504) covering a second field of view, the second field of view being larger than the first field of view, the first field of view being contained within the second field of view.

[0047] Estimating stray light components in pixels of the first image from pixel data of pixels in the second image (S506). Estimating stray light components in pixels of the first image (S506) may include filtering the second image with a series of Gaussian filters to form a series of filtered second images, and linearly combining the filtered second images to form a stray light image including the stray light components from pixels in the first image.

[0048] The estimating (S506) may further include one or more of identifying a portion of the second image that overlaps with the first image, compensating for exposure differences between the second image and the first image, compensating for gain setting differences between the first imaging device and the second imaging device, compensating for pixel density differences between the second image and the first image, compensating for angle of view differences between the second image and the first image, and compensating for aperture setting differences between the first and second imaging devices.

[0049] Compensating for stray light in the first image by subtracting the estimated stray light component in the pixel of the first image (S508), thereby reducing the stray light in the first image and achieving an improvement in the first image.

[0050] Those skilled in the art will appreciate that the present invention is by no means limited to the preferred embodiments described above, but on the contrary, many modifications and variations are possible within the scope of the appended claims.

[0051] For example, the first and second imaging devices 110, 120 may be configured to capture the first and second images simultaneously. In this context, simultaneously should be understood to mean that the first and second images have a time overlap when they are captured. However, it should be understood that one of the images may be captured using a longer exposure than the other image. Typically, the second image is captured using a shorter exposure time than the first image to avoid overexposure of pixels in the second image. Simultaneous capture of the first and second images ensures that identical lighting conditions exist in both images. This allows for better quality stray light compensation.

[0052] Moreover, variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. [Explanation of symbols]

[0053] 100 systems 110 first imaging device 120 Second imaging device 111 First View 112 Lens device 114 Image Sensor 121 Second Vision 122 Lens device 124 Image Sensor 130 circuits 131 processors 140 memory 142 Stray light compensation function 200 buildings 205 Brick Wall 210 People 220 light source

Claims

1. 1. A method for stray light compensation, comprising: acquiring a first image by a first imaging device covering a first field of view (S502); acquiring a second image by a second imaging device (S504) covering a second field of view, the second field of view being wider than the first field of view, and the first field of view being included within the second field of view; Estimating stray light components in pixels of the first image from pixel data of pixels in the second image (S506); Including, estimating (S506) a stray light component in a pixel of the first image, filtering the second image with a series of Gaussian filters to form a series of filtered second images; linearly combining the filtered second images to form a stray light image that includes stray light components from pixels in the first image; Including, The method further includes compensating for stray light in the first image by subtracting the estimated stray light component in pixels of the first image (S508).

2. The method of claim 1 , wherein estimating (S506) a stray light component in a pixel of the first image includes identifying a portion of the second image that overlaps with the first image.

3. The method of claim 1 , wherein estimating (S506) a stray light component in a pixel of the first image comprises compensating for an exposure difference between the second image and the first image.

4. 2. The method of claim 1, wherein estimating (S506) a stray light component in a pixel of the first image comprises compensating for differences in gain settings between the first imaging device and the second imaging device.

5. 2. The method of claim 1, wherein estimating (S506) a stray light component in pixels of the first image comprises compensating for differences in pixel density between the second image and the first image.

6. The method of claim 1 , wherein estimating (S506) a stray light component in a pixel of the first image includes compensating for a difference in angle of view between the second image and the first image.

7. A non-transitory computer-readable storage medium storing instructions for implementing the method of any one of claims 1 to 6 when executed on a device having processing capabilities.

8. 1. A system for stray light compensation, comprising: a first imaging device (110) covering a first field of view (111) and configured to acquire a first image; a second imaging device (120) configured to cover a second field of view (121) and to acquire a second image, the second field of view (121) being wider than the first field of view (111) and the first field of view (111) being included within the second field of view (121); Including, The system comprises a circuit (130) configured to perform a stray light compensation function (142), the stray light compensation function (142) comprising: estimating stray light components in pixels of the first image from pixel data of pixels in the second image by filtering the second image with a series of Gaussian filters to form a series of filtered second images and linearly combining the filtered second images to form a stray light image including stray light components from pixels in the first image; Compensating for stray light in the first image by subtracting the estimated stray light component in pixels of the first image. The system is configured as follows:

9. The system of claim 8 , wherein the second imaging device (120) has a lower resolution than the first imaging device (110).

10. The system of claim 8 , wherein the first imaging device and the second imaging device (110, 120) are configured to capture the first image and the second image simultaneously.

11. The system of claim 8 , wherein the second imaging device (120) is configured to capture the second image to be less saturated than the first image.

12. The system of claim 8 , wherein the second imaging device (120) comprises a fixed focus lens arrangement.

13. The system of claim 8 , wherein the second imaging device (120) is separate from the first imaging device (110).

14. A video camera comprising a system (100) according to any one of claims 8 to 13.

Images