Patent Application
20120062707
This application claims priority under 35 U.S.C. §119(a) to an application filed in the Korean Industrial Property Office on Sep. 14, 2010 and assigned Serial No. 10-2010-0090144, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates generally to a stereo camera for acquisition of a three-dimensional (3D) image, and more particularly, to a method and an apparatus for determining a convergence angle of a subject photographed by the stereo camera.
2. Description of the Related Art
A stereoscopic 3D image refers to an image capable of expressing a 3D effect of an object, in addition to depth and space formation information, which cannot be achieved through a 2D image. Basically, a 3D effect is obtained by a difference between right and left images as seen by both eyes, and a stereoscopic 3D image is recognized through a synthesizing process by the brain. In order to photograph a stereoscopic 3D image, a stereo camera including two cameras that are operated in conjunction with each other is used.
Generally, a stereo camera refers to an apparatus for generating a stereoscopic image, and the stereoscopic image is generated using a difference between view angles of both eyes, i.e., the right and left eyes. More specifically, the two eyes of a human being are spaced apart from each other by a distance, and a binocular disparity is generated because an image based on a view angle of the right eye differs from an image based on a view angle of the left eye. Thus, two cameras, i.e., right and left cameras, which are spaced apart from each other by a distance similar to that of human eyes, are used to generate an image showing a 3D effect similar to one generated by eyes. Accordingly, a stereo camera includes at least a right camera and a left camera, and a stereoscopic image is generated by using the right and left cameras photographing a subject at different positions, which is similar to a stereoscopic image generated due to a binocular disparity of human eyes.
Referring to
Further, a distance measuring unit 16 measures a distance from a subject, a convergence angle adjusting mechanism 45 adjusts a convergence angle, a first lens driving circuit 41 drives an Auto Focus (AF) lens of a right photographing optical system RL, a second lens driving circuit 42 drives an AF lens of a left photographing optical system LL, a first Charge Coupled Device (CCD) driving circuit 43 drives a right CCD 23, and a second CCD driving circuit 44 drives a left CCD 24. Also, a first Liquid Crystal Display (LCD) driving circuit 46 drives a right LCD 17R and a second LCD driving circuit 47 drives a left LCD 17L. Additionally, a first Correlated Double Sampling/Automatic Gain Control (CDS/AGC) circuit 48 is connected to the right CCD 23, and a second CDS/AGC circuit 49 is connected to the left CCD 24.
The stereo camera also includes a first Analog-to-Digital (A/D) converter 50, a second A/D converter 52, a signal processor 53, and a memory controller 54. Further, an image storage 55 stores image data in a memory medium, e.g., a flash memory.
In the stereo camera, an image signal acquired by the right CCD 23 is A/D-converted by the first A/D converter 50 via the first CDS/AGC circuit 48 and is stored in the memory 52. Likewise, an image signal acquired by the left CCD 24 is A/D-converted by the second A/D converter 51 via the second CDS/AGC circuit 49 and is also stored in the memory 52. The image signals stored in the memory 52 are processed by the signal processor 53, and are output through the right LCD 17R and the left LCD 17L, respectively.
The conventional stereo camera measures a distance from a subject using a distance measuring unit 16 and adjusts convergence angles of both cameras through the convergence angle adjusting mechanism 45, based on the measured distance. However, because the distance measuring unit 16 is an additional physical component, the size and volume of the conventional stereo camera are large and its manufacturing expense is high.
Accordingly, the present invention has been made to solve at least the above-described problems occurring in the prior art, and an aspect of the present invention is to provide a method and apparatus for measuring a distance from a stereo camera to a subject and a convergence angle.
In accordance with an aspect of the present invention, a method is provided for determining an optimum convergence angle of a stereo camera including a first camera and a second camera. The method includes setting interest regions in images to be photographed by the first camera and the second camera, respectively, the interest regions having a same size and being symmetric to each other with respect to a central vertical axis of the images to be photographed; photographing images by the first camera and the second camera while varying a convergence angle of the stereo camera by a predetermined degree for each photographed image of the first camera and the second camera, respectively; analyzing image histograms of the interest regions for each of the images photographed by the first camera and the second camera; and setting a convergence angle, at which differences between image histograms of the interest regions of an image photographed by a the first camera and image histograms of the interest regions of the image photographed by the second camera are smallest, as an optimum convergence angle.
In accordance with another aspect of the present invention, an apparatus for determining a convergence angle of a stereo camera is provided. The apparatus includes a first camera; a second camera; a first drive for driving the first camera; a second drive for driving the second camera; a memory; and a controller. The controller sets interest regions in images to be photographed by the first camera and the second camera, respectively, the interest regions having a same size and being symmetric to each other with respect to a central vertical axis of the images to be photographed; controls the first camera and the second camera to photograph images while varying a convergence angle of the stereo camera by a predetermined degree for each photographed image of the first camera and the second camera, respectively; analyzes image histograms of the interest regions for each of the images photographed by the first camera and the second camera; and sets a convergence angle, at which differences between image histograms of the interest regions of an image photographed by a the first camera and image histograms of the interest regions of the image photographed by the second camera are smallest, as an optimum convergence angle.
The above and other aspects, features, and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:
Hereinafter, various embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, same elements will be designated by same reference numerals although they are shown in different drawings. Further, various specific definitions found in the following description are provided only to help general understanding of the present invention, and it is apparent to those skilled in the art that the present invention can be implemented without such definitions. Further, in the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted to avoid obscuring the subject matter of the present invention.
In accordance with an embodiment of the present invention, a method is provided for determining a convergence angle of a stereo camera. For this purpose, the method may include setting interest regions in each image photographed by the stereo camera. The interest regions have a same size and are symmetric to each other with respect to a central vertical axis of the photographed image. A photographing operation is performed through the stereo camera while varying a convergence angle of the stereo camera and a convergence scanning operation is then performed by analyzing image histograms of the interest regions of each image photographed at a corresponding angle. A photographing angle, at which differences between image histograms of the interest regions of the image photographed by a left camera of the stereo camera and image histograms of the interest regions of the image photographed by a right camera of the stereo camera are minimal, is then determined as the optimum convergence angle.
Referring to
When determining a convergence angle, the controller 205 sets two pairs of interest regions. The interest regions have a same size and are symmetric to each other with respect to central vertical axes of images photographed by the first camera 201 and the second camera 202 on opposite sides. The controller 205 then controls the cameras 201 and 202 to perform photographing operations with a convergence angle of the stereo camera being varied and performs a convergence scanning operation by analyzing image histograms of the interest regions of the images photographed at a corresponding angle. The controller 205 also determines a convergence angle that minimizes a difference between image histograms of the interest regions of the image photographed by the left camera 201 and image histograms of the interest regions of the image photographed by the right camera 202, as an optimum convergence angle.
For example, the interest regions may be set to have one or more rectangular regions, which are symmetric to each other with respect to central vertical axes of the photographed images on opposite sides.
During the convergence scanning operation, while varying a convergence angle of the stereo camera, the controller 205 calculates a difference between image histograms of the interest regions of the image photographed by the left camera 201 and image histograms of the interest regions of the image photographed by the right camera 202 for the varied convergence angles, respectively, and stores a minimum value of the differences of the image histograms in the memory 206.
If a difference between image histograms of the interest regions of the image photographed by the left camera 201 and image histograms of the interest regions of the image photographed by the right camera 202 for a convergence angle is greater than a predetermined multiple (n) of a minimum value of the differences of the stored image histograms, the convergence scanning operation is completed.
The controller 205 performs calculates a distance between the stereo camera and a subject, and determines a binocular disparity of a central subject based on the calculated distance between the stereo camera and the subject. Specifically, the controller 205 calculates a crossed disparity, an uncrossed disparity, a maximum crossed disparity, and a maximum uncrossed disparity using both a view distance of a display input by a user and size information of the display.
Referring to
Referring to
Referring to
Referring to
When a convergence angle of the stereo camera is too small or large as illustrated in
Image histograms are tools used to show information regarding contrast values of images, and configurations of images, i.e., contrasts and distribution of contrast values can be recognized using histograms. Generally, an image histogram expresses contrast values in a bar graph. Contrast values of pixels are expressed on the x-axis and frequencies of the contrast values are expressed on the y-axis.
A convergence angle of the stereo camera is set to be suitable for a distance of a central subject, such that the images displayed in the interest regions of first camera 201 and second camera 202 are similar to each other, making the image histograms of the interest regions similar. Accordingly, in accordance with an embodiment of the present invention, an angle at which differences between image histograms of the interest regions of the image photographed by the first camera and image histograms of the interest regions of the image photographed by the second camera is minimal, is determined as an optimum convergence angle for photographing the subject. Therefore, a convergence angle of a stereo camera may be expressed as shown in Equation (1).
In Equation (1), W represents an image histogram in an interest region. For example, W1,L represents an image histogram of the interest region 305 on the left side of an image photographed by the first camera 201, W1,R represents an image histogram of the interest region 307 on the left side of the image photographed by the second camera 202, W2,L represents an image histogram of the interest region 306 on the right side of an image photographed by the first camera 201, and W2,R represents an image histogram of the interest region 308 on the right side of the image photographed by the second camera 202
Referring to
Referring to
In step 515, three Sum of Absolute Difference (SAD) variables, i.e., SADcur, SADmin, and SADslope, are updated. SAD indicates a sum of absolute values of a value obtained by subtracting a pixel of a previous reference frame from a pixel of a current frame with respect to a specific area of an image.
SADcur is a value of |W1,L−W1,R|+|W2,L−W2,R| which is calculated at a current camera angle, SADmin is a smallest value of SADcur values calculated at different angles, i.e., Min(SADcur, SADmin), and SADslope represents a difference between a current SADcur value and a SADcur value calculated at a previous angle, i.e., SADcur-SADcur-1. In accordance with an embodiment of the present invention, when image histograms are obtained, Green (G) channels of RGB channels of images are used to obtain the image channels.
Generally, when a convergence scanning operation is performed, e.g., starting from a convergence angle of zero, SADcur per angle has a form of a parabola having a minimum value similar to a quadratic function. Thus, when SADcur has a positive value, this indicates that a convergence angle of the current camera exceeds an optimal convergence angle. Accordingly, when it is determined that the SADslope value is larger than zero in step 520, and that SADcur is larger than n times SADmin in step 525, the convergence scanning operation is completed in step 530. That is, if SADcur increases from SADmin by more than a predetermined ratio, the convergence scanning operation is completed in step 530, and an angle corresponding to SADmin is determined as an optimum convergence angle in step 535. The n is a threshold value for determining whether a convergence scanning operation is to be stopped if SADcur is larger than SADmin by a predetermined times.
However, when it is determined that either the SADslope value is not larger than zero in step 520, or that SADcur is not larger than n times SADmin in step 525, the operation returns to step 510.
After the optimum convergence angle is set, in step 540, a distance between the stereo camera and the subject is calculated. For example, the distance between the stereo camera and the subject may be calculated as shown in Equation (2).
Do=ICD/(2*tan ∇) (2)
In Equation (2), Do is a distance between the stereo camera and the subject, Inter Camera Distance (ICD) is a distance between the cameras, and ∇ represents the convergence angle set in step 535.
In step 545, a binocular disparity of a subject which is to be applied to an actual display is determined based on the distance information of the subject, in which method an approximate view distance of the display and a size of the display are input through a User Interface (UI) during a stereo photographing operation, and a max crossed disparity and a max uncrossed disparity where a user begins to feel fatigue while watching a stereo image in a corresponding display view environment are calculated.
Referring to
The disparity calculated in units of distances are converted into units of pixels of the display, and the result is transferred in a stereo matching step. Through such an operation, a convergence angle determining process of the stereo camera is completed, and the cameras perform an automatic focusing operation.
As described in the embodiments of the present invention above, a distance between a stereo camera and a central subject can be measured without using a separate mechanical distance measuring apparatus to determine a convergence angle of the stereo camera. Accordingly, costs for manufacturing a stereo camera system are reduced. Further, fatigue of a user can be alleviated while the user is watching a stereo image by suggesting a disparity adjusting value for stereo matching using a distance between the stereo camera and a subject.
While the present invention has been shown and described with reference to certain embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2010-0090144 | Sep 2010 | KR | national |
