Abstract:
A dual-aperture zoom digital camera comprising a Wide imaging section and a Tele imaging section, each section including a lens with a respective FOV, image sensor and image signal processor, and a camera controller coupled to the Wide and Tele imaging sections and operative to process Wide and Tele sensor data to obtain a fused image of the object in a capture or stills mode, and to process without fusion Wide and Tele sensor data to obtain, in a video mode, images with an output resolution and a smooth transition when switching between a lower zoom factor (ZF) value and a higher zoom factor value or vice versa, wherein at the lower ZF the output resolution is determined by the Wide sensor and wherein at the higher ZF value the output resolution is determined by the Tele sensor.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Continuation application of U.S. patent application Ser. No. 14/365,711 filed Jun. 16, 2014 (now allowed), and is related to and claims priority from U.S. Provisional Patent Application No. 61/834,486 having the same title and filed Jun. 13, 2013, which is incorporated herein by reference in its entirety. 
     
    
     FIELD 
       [0002]    Embodiments disclosed herein relate in general to digital cameras and in particular to thin zoom digital cameras with both still image and video capabilities 
       BACKGROUND 
       [0003]    Digital camera modules are currently being incorporated into a variety of host devices. Such host devices include cellular telephones, personal data assistants (PDAs), computers, and so forth. Consumer demand for digital camera modules in host devices continues to grow. 
         [0004]    Host device manufacturers prefer digital camera modules to be small, so that they can be incorporated into the host device without increasing its overall size. Further, there is an increasing demand for cameras in host devices to have higher-performance characteristics. One such characteristic that many higher-performance cameras (e.g., standalone digital still cameras) have is the ability to vary the focal length of the camera to increase and decrease the magnification of the image, typically accomplished with a zoom lens, now known as optical zooming Optical zooming is typically accomplished by mechanically moving lens elements relative to each other. Such zoom lens are typically more expensive, larger, and less reliable than fixed focal length lenses. An alternative approach for approximating the zoom effect is achieved with what is known as digital zooming With digital zooming, instead of varying the focal length of the lens, a processor in the camera crops the image and interpolates between the pixels of the captured image to create a “magnified” but lower-resolution image. 
         [0005]    Attempts to use two different lenses to approximate the effect of a zoom lens are known, see e.g. US Patent Publications No. 2008/0030592 and 2010/0277619. In US 2008/0030592, the two sensors are operated simultaneously to capture an image. The respective lenses have different focal lengths, so even though each lens/sensor combination is aligned to look in the same direction, each will capture an image of the same subject but with two different fields of view (FOVs). One sensor is commonly called “Wide” and the other “Tele”. Each sensor provides a separate image, referred to respectively as “Wide” (or “W”) and “Tele” (or “T”) images. The W-image reflects a wider FOV and has lower resolution than the T-image. The images are then stitched (fused) together to form a composite image. In the composite image, the central portion is formed by the relatively higher-resolution image taken by the lens/sensor combination with the longer focal length, and the peripheral portion is formed by a peripheral portion of the relatively lower-resolution image taken by the lens/sensor combination with the shorter focal length. The user selects a desired amount of zoom and the composite image is used to interpolate values from the chosen amount of zoom to provide a respective zoom image. The solution offered by US 2008/0030592 requires, in video mode, very large processing resources in addition to high frame rate requirements, high power consumption (since both cameras are fully operational). It does not provide reference to disparity range and does not provide reference of how to avoid registration errors. 
         [0006]    US 2010/0277619 teaches a camera with a pair of lens/sensor combinations, the two lenses having different focal lengths, so that the image from one of the combinations has a field of view approximately 2-3 times greater than the image from the other combination. As a user of the camera requests a given amount of zoom, the zoomed image is provided from the lens/sensor combination having the field of view that is next larger than the requested field of view. Thus, if the requested field of view is less than the smaller field of view combination, the zoomed image will be created from the image captured by that combination, using cropping and interpolation if necessary. Similarly, if the requested field of view is greater than the smaller field of view combination, the zoomed image will be created from the image captured by the other combination, using cropping and interpolation if necessary. The solution offered by US 2010/0277619 leads to parallax artifacts when moving to the Tele camera in video mode. It does not provide reference to disparity range and its heavy computational requirements and does not provide reference of how to avoid registration errors. 
         [0007]    In both US 2008/0030592 and US 2010/0277619, different focal length systems cause Tele and Wide matching FOVs to be exposed at different times using CMOS sensors, which degrades the overall image quality. Different optical F numbers (“F #”) cause image intensity differences. Working with such a dual sensor system requires double bandwidth support, i.e. additional wires from the sensors to the following HW component. Neither US 2008/0030592 nor US 2010/0277619 deal with false registration. 
         [0008]    Therefore there is a need for, and it would be advantageous to have thin digital cameras with optical zoom operating in both video and still mode that do not suffer from the commonly encountered problems and disadvantages, some of which are listed above. 
       SUMMARY 
       [0009]    Embodiments disclosed herein teach the use of dual-aperture (also referred to as dual-lens or two-sensor) optical zoom digital cameras. The cameras include two camera “subsets”, a Wide subset and a Tele subset, each subset including a lens, an image sensor and an image signal processor (ISP). The Tele subset is the higher zoom subset and the Wide subset is the lower zoom subset. In some embodiments, the lenses are thin lenses with short optical paths of less than about 9 mm The thickness/effective focal length (EFL) ratio of the Tele lens is smaller than 0.9. Such a camera includes two sensors or a single sensor divided into at least two areas. Hereinafter, the description refers to “two sensors”, with the understanding that they may be sections of a single physical sensor (imager chip). The camera may be operated in both still and video modes. In still mode, zoom is achieved by fusing W and T images, with the resulting “fused” image including always information from both images. In video mode, full and smooth optical zoom is achieved by switching between the W and T images. To avoid discontinuities in video mode, the switching includes applying additional processing blocks. 
         [0010]    In order to reach optical zoom capabilities, a different magnification image of the same scene is captured by each camera subset, resulting in FOV overlap between the two subsets processing is applied on the two images grabbed by the multi-aperture imaging system to fuse and output one image processed according to a user zoom factor request. As part of the fusion procedure, up-sampling may be applied on one or both of the images to scale it to the image grabbed by the Tele subset or to a scale defined by the user. The fusion or up-sampling may be applied to only some of the pixels of a sensor. Down-sampling can be performed as well if the output resolution is smaller than the sensor resolution. 
         [0011]    The cameras and associated methods disclosed herein address and correct many of the problems and disadvantages of known dual aperture optical zoom digital cameras. They provide an overall zoom solution that refers to all aspects: optics, algorithmic processing and system hardware (HW). The proposed solution distinguishes between video and capture mode in the processing flow, and specifies the optical requirements and HW requirements. In addition, it provides an innovative optical design which enables low TTL focal length ratio using a specific lens curvature order. 
         [0012]    In addition to enabling optical zoom, a dual-aperture zoom system described herein can also enable a unique photography feature which is typically not available in compact camera modules currently available in cell-phones. This feature is very shallow depth of focus (DOF), particularly suited for portrait photos. The DOF of a lens decreases as the focal length increases. 
         [0013]    When portrait photos are captured with large cameras (such as DSLRs), usually a 50-80 mm lens is used, coupled with a wide-open aperture setting to create a shallow DOF effect. Due to the large focal length, objects that are in front or behind the plane of focus appear very blurry, and a nice foreground-to-background contrast is achieved. However, it is difficult to create such a blur using a compact camera with a relatively short focal length and small aperture size, such as a cell-phone camera. In some embodiments, a dual-aperture zoom system disclosed herein can be used to capture a shallow-DOF photo by taking advantage of the longer focal length of the Tele lens. The reduced DOF effect provided by this relatively long focal length can be further enhanced in the final image by fusing data from an image captured with the Wide-lens at the same time. Depending on the object distance, while the Tele lens is focused on the subject of the photo, the Wide lens can be focused to a very near distance, so that objects behind the subject appear very blurry. Once the two images are captured, information from the out-of-focus blurred background in the Wide image is fused with the original Tele image background information, to result in a blurrier background and even shallower DOF. 
         [0014]    In an embodiment there is provided a dual-aperture zoom digital camera comprising a Wide imaging section operative to provide a Wide image of an object, the Wide imaging section including a lens with a wide FOV, a Wide sensor and a Wide image signal processor 
         [0015]    (ISP), a Tele imaging section operative to provide a Tele image of the object, the Tele imaging section including a lens with a narrow FOV, a Tele sensor and a Tele ISP, and a camera controller coupled to the Wide and Tele imaging sections and operative to process Wide and Tele sensor data to obtain a fused image of the object in a capture or stills mode, and to process without fusion Wide and Tele sensor data to obtain, in a video mode, images with an output resolution and a smooth transition when switching between a lower zoom factor (ZF) value and a higher ZF value or vice versa, wherein at the lower ZF the output resolution is determined by the Wide sensor and wherein at the higher ZF value the output resolution is determined by the Tele sensor, whereby the processing provides a continuous zoom. 
         [0016]    In an embodiment there is provided a method for providing continuous optical zoom in a digital camera that includes a Wide imaging section including a lens with a wide FOV, a Wide sensor and a Wide ISP and a Tele imaging section including a lens with a narrow FOV, a Tele sensor and a Tele ISP, the method comprising the steps of: imaging an object to obtain 
         [0017]    Wide sensor data and Tele sensor data, processing with fusion the Wide and Tele sensor data to obtain a fused image of the object in a capture or stills mode, and processing without fusion the Wide and Tele sensor data to obtain, in a video mode, images with an output resolution and a smooth transition when switching between a lower zoom factor (ZF) value and a higher ZF value or vice versa, wherein at the lower ZF the output resolution is determined by the Wide sensor and wherein at the higher ZF value the output resolution is determined by the Tele sensor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    Non-limiting examples of embodiments disclosed herein are described below with reference to figures attached hereto that are listed following this paragraph. Identical structures, elements or parts that appear in more than one figure are generally labeled with a same numeral in all the figures in which they appear. The drawings and descriptions are meant to illuminate and clarify embodiments disclosed herein, and should not be considered limiting in any way. 
           [0019]      FIG. 1  shows schematically a block diagram illustrating a dual-aperture zoom imaging system disclosed herein; 
           [0020]      FIG. 2  shows an example of Wide sensor, Tele sensor and their respective FOVs; 
           [0021]      FIG. 3  shows a schematically embodiment of CMOS sensor image grabbing vs. time; 
           [0022]      FIG. 4  shows schematically a sensor time configuration which enables sharing one sensor interface using dual sensor zoom system; 
           [0023]      FIG. 5  shows an embodiment of a method disclosed herein for acquiring a zoom image in capture mode; 
           [0024]      FIG. 6  shows an embodiment of a method disclosed herein for acquiring a zoom image in video/preview mode; 
           [0025]      FIG. 7  shows a graph illustrating an effective resolution zoom factor; 
           [0026]      FIG. 8  shows one embodiment of a lens block in a thin camera disclosed herein; 
           [0027]      FIG. 9  shows another embodiment of a lens block in a thin camera disclosed herein. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]      FIG. 1  shows schematically a block diagram illustrating an embodiment of a dual-aperture zoom imaging system (also referred to simply as “camera”) disclosed herein and numbered  100 . Camera  100  comprises a Wide imaging section (“subset”) that includes a Wide lens block  102 , a Wide image sensor  104  and a Wide image processor  106 . Camera  100  further comprises a Tele imaging section (“subset”) that includes a Tele lens block  108 , a Tele image sensor  110  and a Tele image processor  112 . The image sensors may be physically separate or may be part of a single larger image sensor. The Wide sensor pixel size can be equal to or different from the Tele sensor pixel size. Camera  100  further comprises a camera fusion processing core (also referred to as “controller”)  114  that includes a sensor control module  116 , a user control module  118 , a video processing module  126  and a capture processing module  128 , all operationally coupled to sensor control block  110 . User control module  118  comprises an operational mode function  120 , a region of interest (ROI) function  122  and a zoom factor (ZF) function  124 . 
         [0029]    Sensor control module  116  is connected to the two sub-cameras and to the user control module  118  and used to choose, according to the zoom factor, which of the sensors is operational and control the exposure mechanism and the sensor readout. Since zoom is achieved by sensor oversampling, for most zoom factors, only one sensor is operational in video mode. This is also true for the Auto Focus (AF) mechanism. Mode choice function  120  is used for choosing capture/video modes. The capture mode may include a “burst mode”. ROI function  122  is used to choose region of interest. Zoom factor function  124  is used to choose a zoom factor. Video processing module  126  is connected to the mode choice function  120  and used for high frame rate video processing. Capture processing module  128  is connected to the mode choice function  120  and used for high image quality still mode images. 
         [0030]    The video processing module is applied when the user desires to shoot in video mode. The capture processing module is applied when the user wishes to shoot still pictures. Following is a detailed description and examples of different methods of use of camera  100 . 
         [0000]    Design for continuous Zoom in Video Mode 
         [0031]    In order to reach high quality optical continuous zooming in video mode while reaching real optical zoom, optical system design is taken into account as follows: 
         [0000]      Tan(FOV WIDE )/Tan(FOV TELE )=PL WIDE /PL video    (1)
 
         [0000]    “Tan” refers to “tangent”, while FOV WIDE  and FOV TELE  refer respectively to Wide and Tele lens fields of view (in degrees). The FOV is measured from the center axis to the corner of the sensor. PL WIDE  and PL video  refer respectively to the “in-line” (i.e. in a line) number of sensor pixels and in-line number of output video format pixels. For example, in order to get full optical zoom continuous experience with a 12 Mp sensor (sensor dimensions: 4000×3000) and a required 1080p (dimension: 1920×1080) video format, the FOV ratio should be 4000/1920=2.083. Moreover, if the Wide lens FOV is given as FOV WIDE =37.5°, the required Tele lens FOV is 20.2°. The zoom switching point is set according to the ratio between sensor pixels in-line and the number of pixels in-line in the video format and defined as: 
         [0000]        Z   switch   =PL   WIDE   /PL   video    (2)
 
         [0000]    Maximum optical zoom is reached according to the following formula: 
         [0000]        Z   max =Tan(FOV WIDE )/Tan(FOV TELE )·* PL   TELE   /PL   video    (3)
 
         [0000]    For example: for the configuration defined above and assuming PL Tele =4000 and PL video =1920, Zmax=4.35. 
         [0032]    In an embodiment, the sensor control module has a setting that depends on the Wide and Tele FOVs and on a sensor oversampling ratio, the setting used in the configuration of each sensor. In an embodiment, the Wide and Tele FOVs and the oversampling ratio satisfy the condition 0.8*PL WIDE /PL video &lt;Tan (FOV WIDE )/Tan (FOV TELE )&lt;1.2*PL WIDE /PL video . “Oversampling ratio” is defined as the ratio between the number of pixels in the sensor vs the number of pixels in the output image. For example, when using a 4000×3000 sensor and when outputting a 1920×1080 image, the oversampling ratio is 4000/1920=2.0833 
       Still Camera Mode Operation/Function 
       [0033]    In still camera mode, the obtained image is fused from information obtained by both sub-cameras at all zoom levels, see  FIG. 2 , which shows a first (“Wide”) sensor  202  and a second (“Tele”) sensor  204  and their respective FOVs. Exemplarily, as shown, the Tele sensor FOV is half the Wide sensor FOV. The still camera mode processing includes two stages: (1) setting HW settings and configuration, where a first objective is to control the sensors in such a way that matching FOVs in both images (Tele and Wide) are scanned at the same time. A second objective is to control the relative exposures according to the lens properties. A third objective is to minimize the required bandwidth from both sensors for the ISPs; and (2) image processing that fuses the Wide and the Tele images to achieve optical zoom, improves SNR and provides wide dynamic range. 
         [0034]      FIG. 3  shows image line numbers vs. time for an image section captured by CMOS sensors. A fused image is obtained by line (row) scans of each image. To prevent matching FOVs in both sensors to be scanned at different time, a special configuration is applied on both image sensors while keeping the same frame rate. The difference in FOV between the sensors determines the relationship between the rolling shutter time and the vertical blanking time for each sensor. The scanning is synchronized such that the same points of the object in each view are obtained simultaneously. 
         [0035]    Specifically with reference to  FIG. 3  and according to an embodiment of a method disclosed herein, the fused image acquisition process includes setting the Tele sensor vertical blanking time VB Tele  to equal the Wide sensor vertical blanking time VB Wide  plus half the Wide sensor rolling shutter time RST Wide , setting the Tele and Wide sensor exposure times ET Tele  and ET Wide  to be equal or different, setting the Tele sensor rolling shutter time RST tele  to be half the Wide sensor rolling shutter time RST Wide  and setting the frame rates of the two sensors to be equal. This procedure results in identical image pixels in the Tele and Wide sensor images being exposed at the same time. 
         [0036]    The exposure times applied to the two sensors could be different, for example, in order to reach same image intensity using different F # and different pixel size for the Tele and Wide systems. In this case, the relative exposure time should be configured according to the formula below: 
         [0000]        ET   Tele   =ET   Wide ·( F#   Tele   /F#   wide ) 2 ·(Pixel size Tele /Pixel size Wide ) 2    (4)
 
         [0000]    Other exposure time ratios may be applied to achieve wide dynamic range and improved 
         [0037]    SNR. Fusing two images with different intensities will result in wide dynamic range image. 
         [0038]    In more detail with reference to  FIG. 3 , in the first stage, after the user chooses a required zoom factor ZF, the sensor control module configures each sensor as follows: 
         [0039]    1) Cropping index Wide sensor: 
         [0000]        Y   Wide start =½· PC   Wide (1−1 /ZF ))
 
         [0000]        Y   Wide end =½· PC   Wide (1+1 /ZF )
 
         [0000]    where PC is the number of pixels in a column, and Y is the row number 
         [0040]    2) Cropping index Tele sensor: 
         [0000]    If ZF&gt;Tan (FOV Wide )/Tan (FOV Tele ), then 
         [0000]        Y   Tele start =½· PC   Tele (1−(1 /ZF )·Tan(FOV Tele )/Tan(FOV Wide )))
 
         [0000]        Y   Tele end =½· PC   Tele (1+(1 /ZF )·Tan(FOV Tele )/Tan(FOV Wide ))
 
         [0000]    If ZF&lt;Tan (FOV Wide )/Tan (FOV Tele ), then 
         [0000]      Y Tele start 0 
         [0000]      Y Tele end =PCTele 
         [0000]    This will result in start exposing the Tele sensor with a delay of: 
         [0000]      (1− ZF/ ((Tan(FOV Wide )/Tan(FOV Tele )))·1/(2·PFS)   (5)
 
         [0000]    where FPS is the sensors frame per second configuration. In cases where ZF&gt;Tan (FOV Wide )/Tan (FOV Tele ), no delay will be introduced between Tele and Wide exposure starting point. For example, for a case where Tan (FOV wide )/Tan (FOV Tele )=2 and ZF=1, the Tele image first pixel is exposed ¼·(1/PFS) sec after the Wide image first pixel was exposed. 
         [0041]    After applying the cropping according to the required zoom factor, the sensor rolling shutter time and the vertical blank should be configured in order to satisfy the equation to keep the same frame rate 
         [0000]        VB   Wide +RST Wide   =VB   Tele +RST Tele    (6)
 
         [0042]      FIG. 3  exemplifies Eq. (6), One way to satisfy Eq. (6) is to increase the RST Wide ·Controlling the RST Wide  may be done by changing the horizontal blanking (HB) of the Wide sensor. This will cause a delay between the data coming out from each row of the Wide sensor. 
         [0043]    Generally, working with a dual-sensor system requires multiplying the bandwidth to the following block, for example the ISP. For example, using 12 Mp working at 30 fps, 10 bit per pixel requires working at 3.6 Gbit/sec. In this example, supporting this bandwidth requires 4 lanes from each sensor to the respective following ISP in the processing chain. Therefore, working with two sensors requires double bandwidth (7.2 Gbit/sec) and 8 lanes connected to the respective following blocks. The bandwidth can be reduced by configuring and synchronizing the two sensors. Consequently, the number of lanes can be half that of a conventional configuration (3.6 Gbit/sec). 
         [0044]      FIG. 4  shows schematically a sensor time configuration that enables sharing one sensor interface using a dual-sensor zoom system. For simplicity, assuming the Tele sensor image is magnified by a factor of 2 compared with the Wide sensor image, the Wide sensor horizontal blanking time HB Wide  is set to twice the Wide sensor line readout time. This causes a delay between output Wide lines. This delay time matches exactly the time needed to output two lines from the Tele sensor. After outputting two lines from the Tele sensor, the Tele sensor horizontal blanking time HB Tele  is set to be one Wide line readout time, so, while the Wide sensor outputs a row from the sensor, no data is being output from the Tele sensor. For this example, every 3 rd  line in the Tele sensor is delayed by an additional HB Tele . In this delay time, one line from the Wide sensor is output from the dual-sensor system. After the sensor configuration stage, the data is sent in parallel or by using multiplexing into the processing section. 
         [0045]      FIG. 5  shows an embodiment of a method disclosed herein for acquiring a zoom image in capture mode. In ISP step  502 , the data of each sensor is transferred to the respective ISP component, which performs on the data various processes such as denoising, demosaicing, sharpening, scaling, etc, as known in the art. After the processing in step  502 , all following actions are performed in capture processing core  128 : in rectification step  504 , both Wide and Tele images are aligned to be on the epipolar line; in registration step  506 , mapping between the Wide and the Tele aligned images is performed to produce a registration map; in resampling step  508 , the Tele image is resampled according to the registration map, resulting in a re-sampled Tele image; in decision step  510 , the re-sampled Tele image and the Wide image are processed to detect errors in the registration and to provide a decision output; in fusion step  512 , the decision output, re-sampled Tele image and the Wide image are fused into a single zoom image. 
         [0046]    To reduce processing time and power, steps  506 ,  508 ,  510 ,  512  could be bypassed by not fusing the images in non-focused areas. In this case, all steps specified above should be applied on focused areas only. Since the Tele optical system will introduce shallower depth of field than the Wide optical system, defocused areas will suffer from lower contrast in the Tele system. 
       Video Mode Operation/Function 
       [0047]    In this mode, sensor oversampling is used to enable continuous zoom experience in video mode. Processing is applied to eliminate the changes in the image during crossover from one sub-camera to the other. Zoom from 1 to Z switch  is performed using the Wide sensor only. From Z switch  and on, it is performed mainly by the Tele sensor. To prevent “jumps” (roughness in the image), switching to the Tele image is done using a zoom factor which is a bit higher (Z switch +ΔZoom) than Z switch.  AZoom is determined according to the system&#39;s properties and is different for cases where zoom-in is applied and cases where zoom-out is applied (ΔZoom in ≠ΔZoom out ). This is done to prevent residual jumps artifacts to be visible at a certain zoom factor .The switching between sensors, for an increasing zoom and for decreasing zoom, is done on a different zoom factor. 
         [0048]    The zoom video mode operation includes two stages: (1) sensor control and configuration, and (2) image processing. In the range from 1 to Z switch , only the Wide sensor is operational, hence, power can be supplied only to this sensor. Similar conditions hold for a 
         [0049]    Wide AF mechanism. From Z switch +ΔZoom to Z max  only the Tele sensor is operational, hence, power is supplied only to this sensor. Similarly, only the Tele sensor is operational and power is supplied only to it for a Tele AF mechanism. Another option is that the Tele sensor is operational and the Wide sensor is working in low frame rate. From Z switch  to Z switch +ΔZoom, both sensors are operational. 
         [0050]      FIG. 6  shows an embodiment of a method disclosed herein for acquiring a zoom image in video/preview mode for 3 different zoom factor (ZF) ranges: (a) ZF range=1:Z switch ; (b) ZF range=Z switch :Z switch +ΔZoom in ; and (c) Zoom factor range=Z switch +ΔZoom in :Z max . The description is with reference to a graph of effective resolution vs. zoom value ( FIG. 7 ). In step  602 , sensor control module  116  chooses (directs) the sensor (Wide, Tele or both) to be operational. Specifically, if the ZF range=1:Z switch , module  116  directs the Wide sensor to be operational and the Tele sensor to be non-operational. If the ZF range is Z switch :Z switch +ΔZoom in , module  116  directs both sensors to be operational and the zoom image is generated from the Wide sensor. If the ZF range is Z switch +ΔZoom in :Z max , module  116  directs the Wide sensor to be non-operational and the Tele sensor to be operational. After the sensor choice in step  602 , all following actions are performed in video processing core  126 . Optionally, in step  604 , color balance is calculated if two images are provided by the two sensors. Optionally yet, in step  606 , the calculated color balance is applied in one of the images (depending on the zoom factor). Further optionally, in step  608 , registration is performed between the Wide and Tele images to output a transformation coefficient. The transformation coefficient can be used to set an AF position in step  610 . In step  612 , an output of any of steps  602 - 608  is applied on one of the images (depending on the zoom factor) for image signal processing that may include denoising, demosaicing, sharpening, scaling, etc. In step  614 , the processed image is resampled according to the transformation coefficient, the requested ZF (obtained from zoom function  124 ) and the output video resolution (for example 1080p). To avoid a transition point to be executed at the same ZF, AZoom can change while zooming in and while zooming out. This will result in hysteresis in the sensor switching point. 
         [0051]    In more detail, for ZF range  1  : Z switch , for ZF&lt;Z switch , the Wide image data is transferred to the ISP in step  612  and resampled in step  614 . For ZF range=Z switch :Z switch +ΔZoom in , both sensors are operational and the zoom image is generated from the Wide sensor. The color balance is calculated for both images according to a given ROI. In addition, for a given ROI, registration is performed between the Wide and Tele images to output a transformation coefficient. The transformation coefficient is used to set an AF position. The transformation coefficient includes the translation between matching points in the two images. 
         [0052]    This translation can be measured in a number of pixels. Different translations will result in a different number of pixel movements between matching points in the images. This movement can be translated into depth and the depth can be translated into an AF position. This enables to set the AF position by only analyzing two images (Wide &amp; Tele). The result is fast focusing. 
         [0053]    Both color balance ratios and transformation coefficient are used in the ISP step. In parallel, the Wide image is processed to provide a processed image, followed by resampling. For ZF range=Z switch +ΔZoom in :Z max  and for Zoom factor&gt;Z switch, +ΔZoom in , the color balance calculated previously is now applied on the Tele image. The Tele image data is transferred to the ISP in step  612  and resampled in step  614 . To eliminate crossover artifacts and to enable smooth transition to the Tele image, the processed Tele image is resampled according to the transformation coefficient, the requested ZF (obtained from zoom function  124 ) and the output video resolution (for example 1080p). 
         [0054]      FIG. 7  shows the effective resolution as a function of the zoom factor for a zoom-in case and for a a zoom-out case ΔZoom up  is set when we zoom in, and ΔZoom down  is set when we zoom out. Setting ΔZoom up  to be different from ΔZoom down  will result in transition between the sensors to be performed at different zoom factor (“hysteresis”) when zoom-in is used and when zoom-out is used. This hysteresis phenomenon in the video mode results in smooth continuous zoom experience. 
       Optical Design 
       [0055]    Additional optical design considerations were taken into account to enable reaching optical zoom resolution using small total track length (TTL). These considerations refer to the Tele lens. In an embodiment, the camera is “thin” in the sense that is has an optical path of less than 9 mm and a thickness/focal length (FP) ratio smaller than about 0.85. Exemplarily, as shown in  FIG. 8 , such a thin camera has a lens block that includes (along an optical axis starting from an object) five lenses: a first lens element  802  with positive power and two lenses  804  and  806  and with negative power, a fourth lens  808  with positive power and a fifth lens  810  with negative power. In the embodiment of  FIG. 8 , the effective focal length (EFL) is 7 mm and the optical total track length (TTL) is 5.8 mm Thus the Tele lens TTL/EFL ratio is smaller than 0.9. 
         [0056]    In another embodiment of a lens block in a thin camera, shown in  FIG. 9 , the camera has a lens block that includes (along an optical axis starting from an object) a first lens element  902  with positive power a second lens element  904  with negative power, a third lens element with positive power  906  and a fourth lens element with negative power  908 , and a fifth filed lens element  910  with positive or negative power. Lens data is also shown in  FIGS. 8 and 9 . 
         [0057]    In conclusion, dual aperture optical zoom digital cameras and associate methods disclosed herein reduce the amount of processing resources, lower frame rate requirements, reduce power consumption, remove parallax artifacts and provide continuous focus (or provide loss of focus) when changing from Wide to Tele in video mode. They provide a dramatic reduction of the disparity range and avoid false registration in capture mode. They reduce image intensity differences and enable work with a single sensor bandwidth instead of two, as in known cameras. 
         [0058]    While this disclosure has been described in terms of certain embodiments and generally associated methods, alterations and permutations of the embodiments and methods will be apparent to those skilled in the art. The disclosure is to be understood as not limited by the specific embodiments described herein, but only by the scope of the appended claims.