Patent Application
20160286199
1. Field of the Invention
The invention relates to processing multi-aperture image data, and, in particular, though not exclusively, to a method and a system for processing multi-aperture image data, an image processing apparatus for use in such system and a computer program product using such method.
2. Description of Related Art
The increasing use of digital photo and video imaging technology in various fields of technology such as mobile telecommunications, automotive, and biometrics demands the development of small integrated cameras providing image quality which match or at least approximate the image quality as provided by single-lens reflex cameras. The integration and miniaturization of digital camera technology however put serious constraints onto the design of the optical system and the image sensor, thereby negatively influencing the image quality produced by the imaging system. Spacious mechanical focus and aperture setting mechanisms are not suitable for use in such integrated camera applications. Hence, various digital camera capturing and processing techniques are developed in order to enhance the imaging quality of imaging systems based on fixed focus lenses.
The increasing use of digital photo and video imaging technology in various fields of technology such as mobile telecommunications, automotive, and biometrics demands the development of small integrated cameras providing image quality which match or at least approximate the image quality as provided by single-lens reflex cameras. The integration and miniaturization of digital camera technology however put serious constraints onto the design of the optical system and the image sensor, thereby negatively influencing the image quality produced by the imaging system. Spacious mechanical focus and aperture setting mechanisms are not suitable for use in such integrated camera applications. Hence, various digital camera capturing and processing techniques are developed in order to enhance the imaging quality of imaging systems based on fixed focus lenses.
Although the use of a multi-aperture imaging system provides substantial advantages over known digital imaging systems, such system may not yet provide same functionality as provided in single-lens reflex cameras. In particular, it would be desirable to have a fixed-lens multi-aperture imaging system which allows adjustment of camera parameters such as adjustable depth of field and/or adjustment of the focus distance. Moreover, it would be desirable to provide such multi-aperture imaging systems with 3D imaging functionality similar to known 3D digital cameras. Hence, there is need in the art for methods and systems allowing which may provide multi-aperture imaging systems enhanced functionality.
The present disclosure overcomes the limitations of the prior art by providing a compound multi-aperture imaging system that includes multiple multi-aperture imaging systems, preferably with overlapping fields of view. In one aspect, each multi-aperture imaging system includes an optical imaging system with two apertures, for example an aperture for the visible wavelength region and a smaller aperture for the infrared wavelength region. An image sensor captures both visible and infrared images. These can be processed to obtain depth information. The visible images can also be stitched together to produce a larger composite image.
In various aspects, the depth information can be used advantageously, for example to facilitate the stitching process. In one approach, the depth information is used to determine corresponding features in images captured by different multi-aperture imaging systems. The corresponding features are used to stitch together the separate images. In another aspect, the depth information is used to help compensate for distortions in the images. In yet another aspect, the depth information from different multi-aperture imaging systems may also be combined to produce a composite depth map corresponding to the stitched-together composite image.
Other aspects include components, devices, systems, improvements, methods processes, applications, computer readable mediums, and other technologies related to any of the above.
The multi-aperture system 108, which will be discussed hereunder in more detail, is configured to control the exposure of the image sensor to light in the visible part and, optionally, the invisible part, e.g. the infrared part, of the EM spectrum. In particular, the multi-aperture system may define at a least first aperture of a first size for exposing the image sensor with a first part of the EM spectrum and at least a second aperture of a second size for exposing the image sensor with a second part of the EM spectrum. For example, in one embodiment the first part of the EM spectrum may relate to a wavelength region corresponding to the color spectrum and the second part to a wavelength region corresponding to the infrared spectrum. In another embodiment, the multi-aperture system may comprise a predetermined number of apertures each designed to expose the image sensor to radiation within a predetermined wavelength region of the EM spectrum.
The exposure of the image sensor to EM radiation is controlled by the shutter 106 and the apertures of the multi-aperture system 108. When the shutter is opened, the aperture system controls the amount of light and the degree of collimation of the light exposing the image sensor 102. The shutter may be a mechanical shutter or, alternatively, the shutter may be an electronic shutter integrated in the image sensor. The image sensor comprises rows and columns of photosensitive sites (pixels) forming a two dimensional pixel array. The image sensor may be a CMOS (Complementary Metal Oxide Semiconductor) active pixel sensor or a CCD (Charge Coupled Device) image sensor. Alternatively, the image sensor may relate to other Si (e.g. a-Si), III-V (e.g. GaAs) or conductive polymer based image sensor structures.
When the light is projected by the lens system onto the image sensor, each pixel produces an electrical signal, which is proportional to the electromagnetic radiation (energy) incident on that pixel. In order to obtain color information and to separate the color components of an image which is projected onto the imaging plane of the image sensor, typically a color filter array 120 (CFA) is interposed between the lens and the image sensor. The color filter array may be integrated with the image sensor such that each pixel of the image sensor has a corresponding pixel filter. Each color filter is adapted to pass light of a predetermined color band into the pixel. Usually a combination of red, green and blue (RGB) filters is used, however other filter schemes are also possible, e.g. CYGM (cyan, yellow, green, magenta), RGBE (red, green, blue, emerald), etc.
Each pixel of the exposed image sensor produces an electrical signal proportional to the electromagnetic radiation passed through the color filter associated with the pixel. The array of pixels thus generates image data (a frame) representing the spatial distribution of the electromagnetic energy (radiation) passed through the color filter array. The signals received from the pixels may be amplified using one or more on-chip amplifiers. In one embodiment, each color channel of the image sensor may be amplified using a separate amplifier, thereby allowing to separately control the ISO speed for different colors.
Further, pixel signals may be sampled, quantized and transformed into words of a digital format using one or more Analog to Digital (A/D) converters 110, which may be integrated on the chip of the image sensor. The digitized image data are processed by a digital signal processor 112 (DSP) coupled to the image sensor, which is configured to perform well known signal processing functions such as interpolation, filtering, white balance, brightness correction, data compression techniques (e.g. MPEG or JPEG type techniques). The DSP is coupled to a central processor 114, storage memory 116 for storing captured images and a program memory 118 such as EEPROM or another type of nonvolatile memory comprising one or more software programs used by the DSP for processing the image data or used by a central processor for managing the operation of the imaging system.
Further, the DSP may comprise one or more signal processing functions 124 configured for obtaining depth information associated with an image captured by the multi-aperture imaging system. These signal processing functions may provide a fixed-lens multi-aperture imaging system with extended imaging functionality including variable DOF and focus control and stereoscopic 3D image viewing capabilities. The details and the advantages associated with these signal processing functions will be discussed hereunder in more detail.
As described above, the sensitivity of the imaging system is extended by using infrared imaging functionality. To that end, the lens system may be configured to allow both visible light and infrared radiation or at least part of the infrared radiation to enter the imaging system. Filters in front of lens system are configured to allow at least part of the infrared radiation entering the imaging system. In particular, these filters do not comprise infrared blocking filters, usually referred to as hot-mirror filters, which are used in conventional color imaging cameras for blocking infrared radiation from entering the camera.
Hence, the EM radiation 122 entering the multi-aperture imaging system may thus comprise both radiation associated with the visible and the infrared parts of the EM spectrum thereby allowing extension of the photo-response of the image sensor to the infrared spectrum.
The effect of (the absence of) an infrared blocking filter on a conventional CFA color image sensor is illustrated in
In order to take advantage of the spectral sensitivity provided by the image sensor as illustrated by
An infrared pixel may be realized by covering a photo-site with a filter material, which substantially blocks visible light and substantially transmits infrared radiation, preferably infrared radiation within the range of approximately 700 through 1100 nm. The infrared transmissive pixel filter may be provided in an infrared/color filter array (ICFA) may be realized using well known filter materials having a high transmittance for wavelengths in the infrared band of the spectrum, for example a black polyimide material sold by Brewer Science under the trademark “DARC 400”.
Methods to realize such filters are described in US2009/0159799. An ICFA may contain blocks of pixels, e.g. 2×2 pixels, wherein each block comprises a red, green, blue and infrared pixel. When being exposed, such image ICFA color image sensor may produce a raw mosaic image comprising both RGB color information and infrared information. After processing the raw mosaic image using a well-known demosaicking algorithm, a RGB color image and an infrared image may obtained. The sensitivity of such ICFA image color sensor to infrared radiation may be increased by increasing the number of infrared pixels in a block. In one configuration (not shown), the image sensor filter array may for example comprise blocks of sixteen pixels, comprising four color pixels RGGB and twelve infrared pixels.
Instead of an ICFA image color sensor, in another embodiment, the image sensor may relate to an array of photo-sites wherein each photo-site comprises a number of stacked photodiodes well known in the art. Preferably, such stacked photo-site comprises at least four stacked photodiodes responsive to at least the primary colors RGB and infrared respectively. These stacked photodiodes may be integrated into the Silicon substrate of the image sensor.
The multi-aperture system, e.g. a multi-aperture diaphragm, may be used to improve the depth of field (DOF) of the camera. The principle of such multi-aperture system 400 is illustrated in
Visible and infrared spectral energy may enter the imaging system via the multi-aperture system. In one embodiment, such multi-aperture system may comprise a filter-coated transparent substrate with a circular hole 402 of a predetermined diameter D1. The filter coating 404 may transmit visible radiation and reflect and/or absorb infrared radiation. An opaque covering 406 may comprise a circular opening with a diameter D2, which is larger than the diameter D1 of the hole 402. The cover may comprise a thin-film coating which reflects both infrared and visible radiation or, alternatively, the cover may be part of an opaque holder for holding and positioning the substrate in the optical system. This way the multi-aperture system comprises multiple wavelength-selective apertures allowing controlled exposure of the image sensor to spectral energy of different parts of the EM spectrum. Visible and infrared spectral energy passing the aperture system is subsequently projected by the lens 412 onto the imaging plane 414 of an image sensor comprising pixels for obtaining image data associated with the visible spectral energy (i.e., the visible image) and pixels for obtaining image data associated with the non-visible (infrared) spectral energy (i.e., the infrared image).
The pixels of the image sensor may thus receive a first (relatively) wide-aperture image signal 416 associated with visible spectral energy having a limited DOF overlaying a second small-aperture image signal 418 associated with the infrared spectral energy having a large DOF. Objects 420 close to the plane of focus N of the lens are projected onto the image plane with relatively small defocus blur by the visible radiation, while objects 422 further located from the plane of focus are projected onto the image plane with relatively small defocus blur by the infrared radiation. Hence, contrary to conventional imaging systems comprising a single aperture, a dual or a multiple aperture imaging system uses an aperture system comprising two or more apertures of different sizes for controlling the amount and the collimation of radiation in different bands of the spectrum exposing the image sensor.
The DSP may be configured to process the captured color and infrared signals.
In a first step 502 Bayer filtered raw image data are captured. Thereafter, the DSP may extract the red color image data, which also comprises the infrared information (step 504). Thereafter, the DSP may extract the sharpness information associated with the infrared image from the red image data and use this sharpness information to enhance the color image.
One way of extracting the sharpness information in the spatial domain may be achieved by applying a high pass filter to the red image data. A high-pass filter may retain the high frequency information (high frequency components) within the red image while reducing the low frequency information (low frequency components). The kernel of the high pass filter may be designed to increase the brightness of the center pixel relative to neighboring pixels. The kernel array usually contains a single positive value at its center, which is completely surrounded by negative values. A simple non-limiting example of a 3×3 kernel for a high-pass filter may look like:
|−1/9 −1/9 −1/9|
|−1/9 8/9 −1/9|
|−1/9 −1/9 −1/9|
Hence, the red image data are passed through a high-pass filter (step 506) in order to extract the high-frequency components (i.e. the sharpness information) associated with the infrared image signal.
As the relatively small size of the infrared aperture produces a relatively small infrared image signal, the filtered high-frequency components are amplified in proportion to the ratio of the visible light aperture relative to the infrared aperture (step 508).
The effect of the relatively small size of the infrared aperture is partly compensated by the fact that the band of infrared radiation captured by the red pixel is approximately four times wider than the band of red radiation (typically a digital infra-red camera is four times more sensitive than a visible light camera). After amplification, the amplified high-frequency components derived from the infrared image signal are added to (blended with) each color component of the Bayer filtered raw image data (step 510). This way the sharpness information of the infrared image data is added to the color image. Thereafter, the combined image data may be transformed into a full RGB color image using a demosaicking algorithm well known in the art (step 512).
In a variant (not shown) the Bayer filtered raw image data are first demosaicked into a RGB color image and subsequently combined with the amplified high frequency components by addition (blending).
The method depicted in
The multi-aperture imaging system thus allows a simple mobile phone camera with a typical f-number of 7 (e.g. focal length N of 7 mm and a diameter of 1 mm) to improve its DOF via a second aperture with a f-number varying e.g. between 14 for a diameter of 0.5 mm up to 70 or more for diameters equal to or less than 0.2 mm, wherein the f-number is defined by the ratio of the focal length f and the effective diameter of the aperture. Preferable implementations include optical systems comprising an f-number for the visible radiation of approximately 2 to 4 for increasing the sharpness of near objects in combination with an f-number for the infrared aperture of approximately 16 to 22 for increasing the sharpness of distance objects.
The improvements in the DOF and the ISO speed provided by a multi-aperture imaging system are described in more detail in related applications PCT/EP2009/050502 and PCT/EP2009/060936. In addition, the multi-aperture imaging system as described with reference to
An image may contain different objects located at different distances from the camera lens so that objects closer to the focal plane of the camera will be sharper than objects further away from the focal plane. A depth function may relate sharpness information associated with objects imaged in different areas of the image to information relating to the distance from which these objects are removed from the camera. In one embodiment, a depth function R may involve determining the ratio of the sharpness of the color image components and the infrared image components for objects at different distances away from the camera lens. In another embodiment, a depth function D may involve autocorrelation analyses of the high-pass filtered infrared image. These embodiments are described hereunder in more detail with reference to
In a first embodiment, a depth function R may be defined by the ratio of the sharpness information in the color image and the sharpness information in the infrared image. Here, the sharpness parameter may relate to the so-called circle of confusion, which corresponds to the blur spot diameter measured by the image sensor of an unsharply imaged point in object space. The blur disk diameter representing the defocus blur is very small (zero) for points in the focus plane and progressively grows when moving away to the foreground or background from this plane in object space. As long as the blur disk is smaller than the maximal acceptable circle of confusion c, it is considered sufficiently sharp and part of the DOF range. From the known DOF formulas it follows that there is a direct relation between the depth of an object, i.e. its distance s from the camera, and the amount of blur (i.e. the sharpness) of that object in the camera.
Hence, in a multi-aperture imaging system, the increase or decrease in sharpness of the RGB components of a color image relative to the sharpness of the IR components in the infrared image depends on the distance of the imaged object from the lens. For example, if the lens is focused at 3 meters, the sharpness of both the RGB components and the IR components may be the same. In contrast, due to the small aperture used for the infrared image for objects at a distance of 1 meter, the sharpness of the RGB components may be significantly less than those of the infra-red components. This dependence may be used to estimate the distances of objects from the camera lens.
In particular, if the lens is set to a large (“infinite”) focus point (this point may be referred to as the hyperfocal distance H of the multi-aperture system), the camera may determine the points in an image where the color and the infrared components are equally sharp. These points in the image correspond to objects, which are located at a relatively large distance (typically the background) from the camera. For objects located away from the hyperfocal distance H, the relative difference in sharpness between the infrared components and the color components will increase as a function of the distance s between the object and the lens. The ratio between the sharpness information in the color image and the sharpness information in the infrared information measured at one spot (e.g. one or a group of pixels) will hereafter be referred to as the depth function R(s).
The depth function R(s) may be obtained by measuring the sharpness ratio for one or more test objects at different distances s from the camera lens, wherein the sharpness is determined by the high frequency components in the respective images.
In one embodiment, R may be defined as the ratio between the absolute value of the high-frequency infrared components Dir and the absolute value of the high-frequency color components Dcol measured at a particular spot in the image. In another embodiment, the difference between the infrared and color components in a particular area may be calculated. The sum of the differences in this area may then be taken as a measure of the distance.
Graph B depicts the resulting depth function R defined as the ratio between Dir/Dcol, indicating that for distances substantially larger than the focal distance N the sharpness information is comprised in the high-frequency infrared image data. The depth function R(s) may be obtained by the manufacturer in advance and may be stored in the memory of the camera, where it may be used by the DSP in one or more post-processing functions for processing an image captured by the multi-aperture imaging system. In one embodiment one of the post-processing functions may relate to the generation of a depth map associated with a single image captured by the multi-aperture imaging system.
Thereafter, the DSP may associate a distance to each pixel p(i,j) or a group of pixels. To that end, the DSP may determine for each pixel p(I,j) the sharpness ratio R(i,j) between the high frequency infrared components and the high frequency color components: R(ij)=Dir(ij)/Dcol(ij) (step 708). On the basis of depth function R(s), in particular the inverse depth function R′(R), the DSP may then associate the measured sharpness ratio R(i,j) at each pixel with a distance s(i,j) to the camera lens (step 710). This process will generate a distance map wherein each distance value in the map is associated with a pixel in the image. The thus generated map may be stored in a memory of the camera (step 712).
Assigning a distance to each pixel may require large amount of data processing. In order to reduce the amount of computation, in one variant, in a first step edges in the image may be detected using a well-known edge-detection algorithm. Thereafter, the areas around these edges may be used as sample areas for determining distances from the camera lens using the sharpness ratio R in these areas. This variant provides the advantage that it requires less computation. Hence, on the basis of an image, i.e. a pixel frame {p(i,j)}, captured by a multi-aperture camera system, the digital imaging processer comprising the depth function may determine an associated depth map {s(i,j)}. For each pixel in the pixel frame the depth map comprises an associated distance value. The depth map may be determined by calculating for each pixel p(i,j) an associated depth value s(i,j). Alternatively, the depth map may be determined by associating a depth value with groups of pixels in an image. The depth map may be stored in the memory of the camera together with the captured image in any suitable data format.
The process is not limited to the steps described with reference to
Further, other ways of determining the distance on the basis of the sharpness information are also possible without departing from the invention. For example instead of analyzing sharpness information (i.e. edge information) in the spatial domain using e.g. a high-pass filter, the sharpness information may also be analyzed in the frequency domain. For example in one embodiment, a running Discrete Fourier Transform (DFT) may be used in order obtain sharpness information. The DFT may be used to calculate the Fourier coefficients of both the color image and the infrared image. Analysis of these coefficients, in particular the high-frequency coefficient, may provide an indication of distance.
For example, in one embodiment the absolute difference between the high-frequency DFT coefficients associated with a particular area in the color image and the infrared image may be used as an indication for the distance. In a further embodiment, the Fourier components may be used for analyzing the cutoff frequency associated with infrared and the color signals. For example if in a particular area of the image the cutoff frequency of the infrared image signals is larger than the cutoff frequency of the color image signal, then this difference may provide an indication of the distance.
On the basis of the depth map various image-processing functions be realized.
P
1
=P
0−(t*N)/(2s) and P2=p0+(t*N)/(2s); (1)
Hence, on the basis of these expressions and the distance information s(i,j) in the depth map, the image processing function may calculate for each pixel po(i,j) in the original image, pixels p1(i,j) and p0(i,j) associated with the first and second virtual image (steps 802-806). This way each pixel p0(i,j) in the original image may be shifted in accordance with the above expressions generating two shifted images {p1(i,j)} and {p2(i,j)} suitable for stereoscopic viewing.
In a first step 902 image data and an associated depth map may be generated. Thereafter, the function may allow selection of a particular distance s′ (step 904) which may be used as a cut-off distance after which the sharpness enhancement on the basis of the high frequency infrared components should be discarded. Using the depth map, the DSP may identified first areas in an image, which are associated with at an object-to-camera distance larger than the selected distance s′ (step 906) and second areas, which are associated with an object-to-camera distance smaller than the selected distance s′. Thereafter, the DSP may retrieve the high-frequency infrared image and set the high-frequency infrared components in the identified first areas to a value according to a masking function (step 910). The thus modified high frequency infrared image may then be blended (step 912) with the RGB image in a similar way as depicted in
It is submitted that various variants are possible without departing from the invention. For example, instead of a single distance, a distance range [s1, s2] may be selected by the user of the multi-aperture system. Objects in an image may be related to distances away from the camera. Thereafter, the DSP may determine which object areas are located within this range. These areas are subsequently enhanced by the sharpness information in the high-frequency components.
Yet a further image processing function may relate to controlling the focus point of the camera. This function is schematically depicted in
Further variants of controlling the focus distance may include selection of multiple focus distances N′,N″, etc. For each of these elected distances the associated high-frequency components in the infrared image may be determined. Subsequent modification of the high-frequency infrared image and blending with the color image in a similar way as described with reference to
In yet another embodiment, the distance function R(s) and/or depth map may be used for processing said captured image using a known image processing function (e.g. filtering, blending, balancing, etc.), wherein one or more image process function parameters associated with such function are depending on the depth information. For example, in one embodiment, the depth information may be used for controlling the cut-off frequency and/or the roll-off of the high-pass filter that is used for generating a high-frequency infrared image. When the sharpness information in the color image and the infrared image for a certain area of the image are substantially similar, less sharpness information (i.e. high-frequency infrared components) of the infrared image is required. Hence, in that case a high-pass filter having very high cut-off frequency may be used. In contrast, when the sharpness information in the color image and the infrared image are different, a high-pass filter having lower cut-off frequency may be used so that the blur in the color image may be compensated by the sharpness information in the infrared image. This way, throughout the image or in specific part of the image, the roll-off and/or the cut-off frequency of the high-pass filter may be adjusted according to the difference in the sharpness information in the color image and the infrared image.
The generation of a depth map and the implementation of image processing functions on the basis of such depth map are not limited to the embodiments above.
The depth function A(s) may be determined by imaging a test object at multiple distances from the camera lens and measuring A at those different distances. A(s) may be stored in the memory of the camera, where it may be used by the DSP in one or more post-processing functions as discussed hereunder in more detail.
In one embodiment one post-processing functions may relate to the generation of a depth information associated with a single image captured by the multi-aperture imaging system comprising a discrete multiple-aperture as described with reference to
Further, the DSP may derive depth information from the high-frequency infrared image data using an autocorrelation function. This process is schematically depicted in
Hence, the auto-correlation function of (part of) the high-frequency infrared image, will comprise double spikes at locations in the high-frequency infrared image where objects are out-of-focus and wherein the distance between the double spike provides a distance measure (i.e. a distance away from the focal distance). Further, the auto-correlation function will comprise a single spike at locations in the image where objects are in focus. The DSP may process the autocorrelation function by associating the distance between the double spikes to a distance using the predetermined depth function a(s) and transform the information therein into a depth map associated with “real distances”.
Using the depth map similar functions, e.g. stereoscopic viewing, control of DOF and focus point may be performed as described above with reference to
Certain image processing functions may be achieved by analyzing the autocorrelation function of the high-frequency infrared image.
The first filter may be configured to transmit both visible and infrared radiation and the second filter may be configured to reflect infrared radiation and to transmit visible radiation. The outer diameter of the outer concentric ring may be defined by an opening in an opaque aperture holder 1408 or, alternatively, by the opening defined in an opaque thin film layer 1408 deposited on the substrate which both blocks infrared and visible radiation. It is clear for the skilled person that the principle behind the formation of a thin-film multi-aperture may be easily extended to a multi-aperture comprising three or more apertures, wherein each aperture transmits radiation associated with a particular band in the EM spectrum.
In one embodiment the second thin-film filter may relate to a dichroic filter which reflects radiation in the infra-red spectrum and transmits radiation in the visible spectrum. Dichroic filters also referred to as interference filters are well known in the art and typically comprise a number of thin-film dielectric layers of specific thicknesses which are configured to reflect infra-red radiation (e.g. radiation having a wavelength between approximately 750 to 1250 nanometers) and to transmit radiation in the visible part of the spectrum.
A second multi-aperture 1410 may be used in a multi-aperture system as described with reference to
The multiple small infrared apertures with respect to each other such that high-frequency information (i.e. edge-information) in image data obtained via these apertures is displaced as a function of the distance between an object and said imaging system. In one embodiment multi apertures may be located as multiple small infrared apertures along the periphery of the first aperture.
Because of the smaller aperture size for the infrared aperture, the blur disk produced by the infrared radiation changes differently than the blur disk produced by the visible radiation, as a function of distance to the object.
Visible spectral energy enters the dual-aperture system through the front aperture 1606, and infrared spectral energy enters the dual-aperture system through side aperture 1604. The hot mirror filter 1602 placed in front of the color aperture 1606 transmits visible radiation and reflects and/or absorbs infrared radiation. The optical path of the separate infrared channel is combined into the color channel through a concave mirror 1610 and a convex mirror 1612. The convex mirror 1612 is part of a wavelength-selective beam combiner to direct visible and infrared spectral energy through the lens system 1620 onto the imaging sensor 1630, which captures the image data for both the color image and the infrared image. A color filter array 1628 is interposed between the lens system 1620 and image sensor 1630. The color filter array may be integrated with the image sensor such that each pixel of the image sensor has a corresponding pixel filter.
A front view of the Cassegrain system is shown on the right. The large circle shows the boundary of a corrector plate large enough to accommodate both the visible aperture 1806 and the IR aperture 1804. Visible and infrared spectral energy passes through the color aperture 1806 or infrared aperture 1804, respectively. Each aperture 1804, 1806 may have a separate filter or coating to reflect and/or absorb unwanted spectral energy. The extent of the secondary mirror 1812 on the back side of the corrector plate is also shown in dashed lines. Note that only portions of the large circle are used so the corrector plate is not required to have the same physical extent as the large circle.
A similar approach can also be applied to optical imaging systems using lenses.
In
In a dual-aperture camera, it is possible to use a smaller, less expensive lens for optical performance while using a wider aperture for depth measurement. For example, it is possible to design a lens with an aperture of f/1 or faster. However, the actual physical lens that is manufactured may only have an aperture of f/2.8 for the color aperture. This color aperture has 6 times less area than an f/1 aperture lens and therefore the cost of this lens is significantly reduced, typically by a factor of 6 or more. The infrared aperture can still be placed at the extreme edge allowable by the f/1 aperture lens, implying the effective aperture for depth measurement is f/1 although the cost of manufacturing is largely determined by the f/2.8 aperture.
For more sophisticated cameras, it may be desirable to switch the camera from a dual or a multiple aperture mode to a normal mode. In the normal mode, the infrared channel is blocked from reaching the image sensor. In one design, the normal mode uses a mechanical closure of the infrared aperture, which is difficult to implement when the infrared aperture is located at the center of the lens. Embodiments that place the infrared aperture to the side of the color aperture can overcome this limitation, and the normal mode can be implemented with the leaf shutter technique. When the aperture system is opened wide, the infrared aperture is exposed to light and infrared radiation passes through the aperture. When the aperture is closed from its maximum aperture, the infrared aperture becomes blocked by the conventional aperture and no further infrared radiation reaches the sensor.
Embodiments of the invention that place the infrared aperture to the side of the lens can also be used with the leaf shutter technique to control the amount of infrared radiation reaching the sensor. For example, in some lighting conditions such as A or Tungsten lighting where the ambient infrared is relatively high, it is desirable to reduce the amount of infrared reaching the sensor. In other lighting conditions, particularly with energy saving light, it is desirable to increase the amount of infrared reaching the sensor.
The control of the amount of infrared radiation reaching the sensor can be achieved using one of several techniques, in accordance with embodiments. One technique is to have multiple infrared apertures near the edge of the color aperture, as shown in
In an alternate design, the blades of the leaf shutter can be closed such that one infrared aperture at a time may be selectively blocked. This technique allows the camera to control the infrared exposure independently of the color exposure. For example, the camera could measure the ambient light balance. Based on the distribution of the color or infrared component, the camera can determine the number of infrared apertures to open and use the blades of the leaf shutter to selectively choose infrared apertures.
This approach of multiple infrared apertures could also be used for coded aperture selection. Different modes of a coded aperture can be achieved by selecting which of several infrared apertures are opened at any one time. Coded aperture selection may have advantages in adapting the depth measurement algorithm for different lighting conditions. In addition, it could be useful for analyzing depth of video sequences. A different mode of a coded aperture could be selected for different frames in the same scene in a video sequence. The same scene can then be analyzed with different modes for more depth measurements, and the average of these depth measurements could be taken as the depth measurement.
Another method to control of the amount of infrared radiation reaching the sensor (in accordance with embodiments) is to have a single larger infrared aperture near the edge of the color aperture. Instead of the entire infrared aperture being either exposed or blocked, the blades of the color aperture have several settings that progressively block the infrared aperture.
The three images obtained from each lens system are combined using an image synthesizer. Two neighboring images overlap with each other. In the overlapped regions 2110, common features exist in two images. For example, object 2120 appears in the images taken by cameras 2102 and 2106. An image translation unit calculates the location of the object 2120 using the depth map information.
The image synthesizer can use the depth information in different ways to help stitch together images from different cameras into a single image. For example, depth information can be used to help determine which objects/features in different images correspond to each other. In
Different views can produce distorted images of the same object, particularly if the object is close to the cameras. This distortion is accounted for in order to stitch together two distorted images of the same object. Knowing the distance to the object is information that can be used to compensate for this distortion. Similarly, the depth measured to edges in an image can be used to distort the image to enable the merging of the edges of images captured from different cameras. This can be useful for virtual reality compound camera systems, which can include sixteen cameras mounted in a circle pointing outwards.
It is to be understood that the above descriptions are only illustrative only, and numerous other embodiments can be devised without departing the spirit and scope of the embodiments.
Embodiments of the invention may be implemented as a program product for use with a computer system. The program(s) of the program product define functions of the embodiments (including the methods described herein) and can be contained on a variety of computer-readable storage media. Illustrative computer-readable storage media include, but are not limited to: (i) non-writable storage media (e.g., read-only memory devices within a computer such as CD-ROM disks readable by a CD-ROM drive, flash memory, ROM chips or any type of solid-state non-volatile semiconductor memory) on which information is permanently stored; and (ii) writable storage media (e.g., floppy disks within a diskette drive or hard-disk drive or any type of solid-state random-access semiconductor memory) on which alterable information is stored.
It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Moreover, the invention is not limited to the embodiments described above, which may be varied within the scope of the accompanying claims.
This application is a continuation of U.S. patent application Ser. No. 14/922,817, “Processing Multi-Aperture Image Data,” filed Oct. 26, 2015; which claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application Ser. No. 62/121,194, “Optical System and Method for Dual-Aperture Camera,” filed Feb. 26, 2015. The subject matter of all of the foregoing is incorporated herein by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62121194 | Feb 2015 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14922817 | Oct 2015 | US |
| Child | 15163438 | US |
