FIELD

Embodiments disclosed herein relate in general to digital cameras and in particular to zoom digital cameras with video capabilities.

BACKGROUND

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.

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 such cameras to have higher-performance characteristics. One such characteristic possessed by many higher-performance cameras (e.g., standalone digital still cameras) is the ability to vary the focal length of the camera to increase and decrease the magnification of the image. This ability, typically accomplished with a zoom lens, is known as optical zooming. “Zoom” is commonly understood as a capability to provide different magnifications of the same scene and/or object by changing the focal length of an optical system, with a higher level of ZOOM associated with greater magnification and a lower level of zoom associated with lower magnification. Optical zooming is typically accomplished by mechanically moving lens elements relative to each other. Such zoom lenses 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.

Attempts to use multi-aperture imaging systems to approximate the effect of a zoom lens are known. A multi-aperture imaging system (implemented for example in a digital camera) includes a plurality of optical sub-systems (also referred to as “cameras”). Each camera includes one or more lenses and/or other optical elements which define an aperture such that received electro-magnetic radiation is imaged by the optical sub-system and a resulting image is directed towards a two-dimensional (2D) pixelated image sensor region. The image sensor (or simply “sensor”) region is configured to receive the image and to generate a set of image data based on the image. The digital camera may be aligned to receive electromagnetic radiation associated with scenery having a given set of one or more objects. The set of image data may be represented as digital image data, as well known in the art. Hereinafter in this description, “image” “image data” and “digital image data” may be used interchangeably. Also, “object” and “scene” may be used interchangeably. As used herein, the term “object” is an entity in the real world imaged to a point or pixel in the image.

Multi-aperture imaging systems and associated methods are described for example in US Patent Publications No. 2008/0030592, 2010/0277619 and 2011/0064327. In US 2008/0030592, two sensors are operated simultaneously to capture an image imaged through an associated lens. A sensor and its associated lens form a lens/sensor combination. The two lenses have different focal lengths. Thus, even though each lens/sensor combination is aligned to look in the same direction, each combination captures an image of the same subject but with two different fields of view (FOV). 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. A 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 (“fused”) 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 and high power consumption (since both cameras are fully operational).

US 2010/0277619 teaches a camera with two lens/sensor combinations, the two lenses having different focal lengths, so that the image from one of the combinations has a FOV 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 a FOV that is next larger than the requested FOV. Thus, if the requested FOV is less than the smaller FOV combination, the zoomed image is created from the image captured by that combination, using cropping and interpolation if necessary. Similarly, if the requested FOV is greater than the smaller FOV combination, the zoomed image is 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.

In both US 2008/0030592 and US 2010/0277619, different focal length systems cause matching Tele and Wide FOVs to be exposed at different times using CMOS sensors. This 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 registration errors.

US 2011/0064327 discloses multi-aperture imaging systems and methods for image data fusion that include providing first and second sets of image data corresponding to an imaged first and second scene respectively. The scenes overlap at least partially in an overlap region, defining a first collection of overlap image data as part of the first set of image data, and a second collection of overlap image data as part of the second set of image data. The second collection of overlap image data is represented as a plurality of image data cameras such that each of the cameras is based on at least one characteristic of the second collection, and each camera spans the overlap region. A fused set of image data is produced by an image processor, by modifying the first collection of overlap image data based on at least a selected one of, but less than all of, the image data cameras. The systems and methods disclosed in this application deal solely with fused still images.

None of the known art references provide a thin (e.g. fitting in a cell-phone) dual-aperture zoom digital camera with fixed focal length lenses, the camera configured to operate in both still mode and video mode to provide still and video images, wherein the camera configuration does not use any fusion to provide a continuous, smooth zoom in video mode.

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 commonly encountered problems and disadvantages, some of which are listed above.

SUMMARY

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 cameras, a Wide camera and a Tele camera, each camera including a fixed focal length lens, an image sensor and an image signal processor (ISP). The Tele camera is the higher zoom camera and the Wide camera is the lower zoom camera. In some embodiments, the thickness/effective focal length (EFL) ratio of the Tele lens is smaller than about 1. The image sensor may include two separate 2D pixelated sensors or a single pixelated sensor divided into at least two areas. The digital camera can be operated in both still and video modes. In video mode, optical zoom is achieved “without fusion”, by, in some embodiments, switching between the W and T images to shorten computational time requirements, thus enabling high video rate. To avoid discontinuities in video mode, the switching includes applying additional processing blocks, which include in some embodiments image scaling and shifting. In some embodiments, when a no-switching criterion is fulfilled, optical zoom is achieved in video mode without switching.

As used herein, the term “video” refers to any camera output that captures motion by a series of pictures (images), as opposed to “still mode” that friezes motion. Examples of “video” in cellphones and smartphones include “video mode” or “preview mode”.

In order to reach optical zoom capabilities, a different magnification image of the same scene is captured (grabbed) by each camera, resulting in FOV overlap between the two cameras. Processing is applied on the two images to fuse and output one fused image in still mode. The fused image is 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 grabbed images to scale it to the image grabbed by the Tele camera 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.

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).

In a dual-aperture camera image plane, as seen by each camera (and respective image sensor), a given object will be shifted and have different perspective (shape). This is referred to as point-of-view (POV). The system output image can have the shape and position of either camera image or the shape or position of a combination thereof. If the output image retains the Wide image shape then it has the Wide perspective POV. If it retains the Wide camera position then it has the Wide position POV. The same applies for Tele images position and perspective. As used in this description, the perspective POV may be of the Wide or Tele cameras, while the position POV may shift continuously between the Wide and Tele cameras. In fused images, it is possible to register Tele image pixels to a matching pixel set within the Wide image pixels, in which case the output image will retain the Wide POV (“Wide fusion”). Alternatively, it is possible to register Wide image pixels to a matching pixel set within the Tele image pixels, in which case the output image will retain the Tele POV (“Tele fusion”). It is also possible to perform the registration after either camera image is shifted, in which case the output image will retain the respective Wide or Tele perspective POV.

In an exemplary embodiment, there is provided a zoom digital camera comprising a Wide imaging section that includes a fixed focal length Wide lens with a Wide FOV and a Wide sensor, the Wide imaging section operative to provide Wide image data of an object or scene, a Tele imaging section that includes a fixed focal length Tele lens with a Tele FOV that is narrower than the Wide FOV and a Tele sensor, the Tele imaging section operative to provide Tele image data of the object or scene, and a camera controller operatively coupled to the Wide and Tele imaging sections, the camera controller configured to evaluate a no-switching criterion determined by inputs from both Wide and Tele image data, and, if the no-switching criterion is fulfilled, to output a zoom video output image that includes only Wide image data in a zoom-in operation between a lower zoom factor (ZF) value and a higher ZF value.

In an exemplary embodiment there is provided a method for obtaining zoom images of an object or scene using a digital camera, comprising the steps of providing in the digital camera a Wide imaging section having a Wide lens with a Wide FOV and a Wide sensor, a Tele imaging section having a Tele lens with a Tele FOV that is narrower than the Wide FOV and a Tele sensor, and a camera controller operatively coupled to the Wide and Tele imaging sections, and configuring the camera controller to evaluate a no-switching criterion determined by inputs from both Wide and Tele image data, and, if the no-switching criterion is fulfilled, to output a zoom video output image that includes only Wide image data in a zoom-in operation between a lower ZF value and a higher ZF value.

In some exemplary embodiments, the no-switching criterion includes a shift between the Wide and Tele images calculated by global registration, the shift being greater than a first threshold.

In some exemplary embodiments, the no-switching criterion includes a disparity range calculated by global registration, the disparity range being greater than a second threshold.

In some exemplary embodiments, the no-switching criterion includes an effective resolution of the Tele image being lower than an effective resolution of the Wide image.

In some exemplary embodiments, the no-switching criterion includes a number of corresponding features in the Wide and Tele images being smaller than a third threshold.

In some exemplary embodiments, the no-switching criterion includes a majority of objects imaged in an overlap area of the Wide and Tele images being calculated to be closer to the camera than a first threshold distance.

In some exemplary embodiments, the no-switching criterion includes some objects imaged in an overlap area of the Wide and Tele images being calculated to be closer than a second threshold distance while other objects imaged in the overlap area of the Wide and Tele images being calculated to be farther than a third distance threshold.

In some exemplary embodiments, the camera controller includes a user control module for receiving user inputs and a sensor control module for configuring each sensor to acquire the Wide and Tele image data based on the user inputs.

In some exemplary embodiments, the user inputs include a zoom factor, a camera mode and a region of interest.

In some exemplary embodiments, the Tele lens includes a ratio of total track length (TTL)/effective focal length (EFL) smaller than 1. For a definition of TTL and EFL see e,g. co-assigned US published patent application No. 20150244942.

In some exemplary embodiments, if the no-switching criterion is not fulfilled, the camera controller is further configured to output video output images with a smooth transition when switching between the lower ZF value and the higher ZF value or vice versa, wherein at the lower ZF value the output image is determined by the Wide sensor, and wherein at the higher ZF value the output image is determined by the Tele sensor.

In some exemplary embodiments, the camera controller is further configured to combine in still mode, at a predefined range of ZF values, at least some of the Wide and Tele image data to provide a fused output image of the object or scene from a particular point of view.

