KR20070035802A - Apparatus and method for distortion compensation of camera lens in the mobile terminal - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a camera lens distortion compensating apparatus and method for compensating image distortion caused by a camera lens, in particular, in a portable terminal.

In the portable terminal according to the present invention, a camera lens distortion compensating apparatus comprises: distance measuring means for measuring a distance between a lens center and each pixel from horizontal and vertical synchronization signals of image data to be photographed; Weight determination means for determining a weight for each pixel according to the measured distance; And weighting means for correcting screen brightness between the lens center and the peripheral part by applying the weight for each pixel to the image data to be photographed.

Handheld, camera, lens, distortion, correction

Description

Apparatus and method for distortion compensation of camera lens in the mobile terminal

1 is a view showing a video image passing through the lens.

FIG. 2 is a diagram illustrating lens brightness distribution along horizontal and vertical directions in FIG. 1; FIG.

 3 is a block diagram illustrating a lens distortion compensating device in a mobile terminal according to the present invention;

4 is a detailed configuration diagram of the distance measuring unit of FIG. 3.

5 is a detailed configuration diagram of the weight determining unit of FIG. 3.

6 is a diagram illustrating an example of a table operation for the weight determiner of FIG. 3.

7 is a detailed configuration diagram of the weight applying unit of FIG. 3.

8 is a flowchart illustrating a method for compensating for lens distortion of a camera in a mobile terminal according to the present invention.

<Explanation of symbols for the main parts of the drawings>

110 Distance measuring unit 111 Horizontal counter

112 ... Vertical Counter 113,114,132 ... Subtractor

115,116 ... square 112 ... vertical counter

120 ... weight determination section 121 ... weight table

122 Interpolator 130 Weighting unit

131 ... Multiplier 133 ... Operation mode selector

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a camera lens distortion compensating apparatus and method for compensating image distortion caused by a camera lens, in particular, in a portable terminal.

Today's portable terminals offer not only a simple telephone function, but also a variety of additional functions. In particular, composite portable terminals (hereinafter referred to as portable terminals) in which a telephone function and other additional functions are combined in a portable terminal have been developed. Among them, a mobile terminal, which is a combination of a camera and a mobile phone, can take a picture, store it, play it when necessary, use it as a wallpaper, and send it to another device using an email or a phone number.

Since the camera module applied to such a portable terminal is miniaturized in nature, the optical performance of the lens is relatively low. In particular, lens distortion, that is, lens shading, in which brightness decreases from the center of the lens toward the periphery thereof is representative. Although the need for the conventional low-level CIF / VGA module has not been raised much, the application in the mega pixel class (1.3M, 2M, 3M, etc.) camera module that is recently released is required.

The lens shading phenomenon is that light coming from the outside is refracted by the lens and formed into an image sensor. The refraction of light causes a phenomenon in which the intensity of light in the image sensor is not constant.

1 and 2 illustrate a change in screen brightness due to lens shading.

FIG. 1 is a diagram illustrating a subject 20 displayed on a screen 10, and FIG. 2A is a graph illustrating a change in image brightness due to lens shading at a horizontal position of a lens, and FIG. ) Is a graph showing the change in image brightness due to lens shading at the vertical position of the lens. In FIG. 2, due to lens shading, the central portion of the lens has a high brightness of light and the brightness of the light decreases nonlinearly as it moves away from the central portion of the lens.

In order to compensate for such a lens shading phenomenon, an apparatus for compensating for brightness of an image according to a distance from a center position of a lens is required.

According to the first aspect of the present invention, after measuring the distance from the center of the lens for each pixel, by applying a nonlinear interpolation coefficient generated according to the distance from the center of the pixel to the data of each pixel, An object and method for compensating for lens distortion in a camera system to compensate for brightness may be provided.

Camera lens distortion compensation device in a mobile terminal according to the present invention for achieving the above object,

Distance measuring means for measuring a distance between the lens center and each pixel from the horizontal and vertical synchronizing signals of the image data to be captured;

Weight determination means for determining a weight for each pixel according to the measured distance;

And weighting means for correcting screen brightness between the lens center and the peripheral part by applying the weight for each pixel to the image data to be photographed.

Preferably, the distance measuring means is a horizontal and vertical counter for generating information corresponding to the horizontal and vertical position of the image data by receiving the horizontal and vertical synchronization signal of the image data, the horizontal generated by the horizontal and vertical counter And a normalization unit configured to subtract the vertical position information and square the subtracted result, and normalize the subtracted and squared position information to measure the distance.

Preferably, the weight determining means includes a weight table having a nonlinear correction coefficient and outputting a slope between adjacent pixels for each distance inputted from the distance measuring unit and a weight of each pixel using the nonlinear correction coefficient, and outputting the weight table from the weight table. And an interpolation unit configured to linearly interpolate the slope and the weight of each pixel and determine and output the linear interpolated weight as a weight.

Preferably, the weight applier is configured to multiply the image data by the weight, an adder that adds the image data to the weight, and an output characteristic of the multiplier or the adder in order to apply the determined weight to the image data. It characterized in that it comprises an operation mode selection unit for selecting and outputting one.

Camera lens distortion compensation method of a mobile terminal according to the present invention,

Counting horizontal and vertical synchronizing signals of the captured image data to measure the distance between each pixel from the center of the lens;

Determining a weight of distance information between each pixel from the measured lens center by using a nonlinear correction coefficient and outputting the determined weight;

And correcting by adding or multiplying the determined weight value according to the degree of offset of the image data, and outputting the corrected image data.

Hereinafter, with reference to the accompanying drawings as follows.

3 is a block diagram illustrating a camera lens distortion compensating device in a mobile terminal according to the present invention.

Referring to FIG. 3, a distance measuring unit 110 measuring distances by horizontal and vertical synchronization signals of image data to be photographed; A weight determination unit 120 outputting a weight determined by a nonlinear interpolation coefficient corresponding to the measured distance; And a weight applying unit 130 that applies the output weight to the image data of each imaged pixel.

Referring to the accompanying drawings, a camera lens distortion compensating apparatus for a mobile terminal according to an exemplary embodiment of the present invention configured as described above is as follows.

Referring to FIG. 3, the distance measuring unit 110 receives horizontal and vertical synchronization signals of image data output from an image sensor (not shown) such as a charge coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS). The distance between each pixel from the center of the lens is measured. The weight determining unit 110 determines a weight by applying a nonlinear interpolation coefficient according to the measured distance, and the weight applying unit 130 applies the determined weight to each pixel of the image data to determine each pixel with the center of the lens. It can compensate the screen brightness according to the distance between them.

In detail, the distance measuring unit 110 receives the horizontal and vertical synchronization signals of the image data in order to measure the distance of each pixel from the center of the lens. Here, in the assembling process of the camera lens and the image sensor, the center of the lens cannot always coincide with the center of the image sensor, so that the center of the lens in the screen can be changed and set. For example, the center of the lens may be set so that the brightness of the light is the strongest.

The distance measuring unit 110 calculates the position information by counting the horizontal and vertical synchronizing signals by a clock signal, and then measures the distance between each pixel with the set lens center.

For this purpose, the distance between the lens center and each pixel can be obtained as follows. Equation 1 generally calculates a distance between two positions. If two positions are (x, y) (x1, y1), Equation 1 may be obtained as follows.

----- 수학식 1

----- Equation 1

The distance measuring unit 110 of the present invention does not use the above Equation 1, but removes the root operation in order to minimize the complexity of the hardware, the distance measurement formula between the two positions is applied as shown in Equation 2 .

-----수학식 2

----- Equation 2

Here, N is a coefficient for normalizing the generated distance information.

As shown in FIG. 4, the distance measuring unit 110 includes horizontal and vertical counters 111 and 112, a subtractor 113 and 114, a squarer 115 and 116, and a normalization unit 117. The horizontal and vertical counters 111 and 112 receive the vertical synchronization signal and the horizontal synchronization signal of the image data, respectively, and generate information (x, y) (x1, y1) about the horizontal and vertical positions of the current image data.

The generated position information is generated as distance information as shown in Equation 2 by using the subtractors 113 and 114 and the squarers 115 and 116.

The normalization unit 117 multiplies the generated distance information by the normalization coefficient N to obtain a distance between each pixel from the center of the lens. Here, the normalization coefficient (N) is a value for compensating a route according to two location information, and a value corresponding to predetermined distance location information is applied. The distance value measured according to the center value of the lens of the number of pixels of the image sensor is different for each camera product or camera module. That is, since the range of the input value of the normalization unit 117 using the distance information cannot be predicted, the range of the input value is controlled using the normalization coefficient. For example, since the difference between the minimum and maximum values is too large according to the resolution of 640 * 480 and 1600 * 1200, the range of the normalization coefficient may be determined from a minimum of 0 to a maximum of 2047.

The weight determiner 120 determines a correction factor according to the distance information measured by the distance measurer 110. As shown in FIG. 5, the weight determining unit 120 includes a weight table 121 and an interpolator 122, and the weight table 121 corresponds to a nonlinear curve inversely proportional to the distance from the center of the lens. It will have data (nonlinear correction coefficient). These nonlinear correction coefficients are data determined by a table operation method for performing nonlinear arithmetic operations because the distances from the lens center to the lens periphery are different for each type or characteristic of the lens. That is, it is the curve value of root.

In addition, in the weight table, when a predetermined number (eg, nine) data of a nonlinear curve according to distance information is determined, a slope between adjacent pixels and a weight according to each distance are determined. That is, in FIG. 6, the weight y2 = s (x1-x2) + y1 is obtained, and the slope s = (y1-y2) / (x1-x2) is obtained. Here, x1 and y1 are lens centers, and the x-axis distance values are known as fixed values.

When the slope and the weight for each distance are determined, the interpolator 122 linearly interpolates the data by determining the linear interpolated weight from the center of the lens to the periphery.

The weight applying unit 130 applies the weight determined by the weight determining unit to the image data. The weight applying unit 130 includes a multiplier 131, an adder 132, and an operation mode selector as shown in FIG. 7. 133, wherein the weight determined by the weight determiner 120 is input to the multiplier 131 and the adder 132 according to an operation mode and output as corrected image data. The operation mode selector 133 selects an offset according to an operation mode selected by the user, and selects and outputs the image data corrected by the multiplier or the image data corrected by the adder.

Here, the operation mode corrects the image data by the multiplication method when the multiplier 131 is selected. However, the operation mode has the advantage of making the compensation of the image data stronger, but has a problem of making the noise contained in the data relatively large. The addition method that selects the adder 132 is resistant to noise as the overall level of image data increases, but weakens the compensation. The operation mode may be set by the user or set at the time of product shipment according to the module characteristics. As another example, an offset scheme may be controlled by controlling the operation of the multiplier or the adder.

8, according to the camera lens distortion compensation method of the mobile terminal according to the present invention, when image data is input (S101), horizontal and vertical synchronization signals are counted to measure the distance between the center of the lens and each pixel (S103). .

When the distance between each pixel is obtained from the lens center, the weight corresponding to the distance at each pixel position is obtained by using the nonlinear interpolation coefficient by the weight determining unit, and the weight is linearly interpolated and determined as the linear interpolated weight ( S105).

The corrected image data is output by correcting by reflecting the determined weight on the image data according to the offset adjusted operation mode (S107).

So far, the present invention has been described with reference to the preferred embodiments, and those skilled in the art to which the present invention pertains to the detailed description of the present invention and other forms of embodiments within the essential technical scope of the present invention. Could be implemented. Here, the essential technical scope of the present invention is shown in the claims, and all differences within the equivalent range will be construed as being included in the present invention.

The lens distortion compensating apparatus in the camera system according to the present invention has an effect of compensating image distortion due to lens shading by assigning different weights according to the distance of each pixel from the center of the lens.

In addition, since the shaping is performed according to the number of pixels and the position of the center of the image sensor, lens shading may be applied to the sensor and the center of the lens of various pixels.

Claims (5)

Distance measuring means for measuring a distance between the lens center and each pixel from the horizontal and vertical synchronizing signals of the image data to be captured; Weight determination means for determining a weight for each pixel according to the measured distance; And weighting means for correcting screen brightness between a lens center and a periphery by applying the weight for each pixel to the image data to be photographed. The method of claim 1, The distance measuring means receives horizontal and vertical synchronization signals of the image data and generates horizontal and vertical counters corresponding to the horizontal and vertical positions of the image data, and horizontal and vertical positions generated by the horizontal and vertical counters. And a normalization unit configured to subtract the information and square each subtracted result, and a normalizer configured to measure the distance by normalizing the subtracted and squared position information. The method of claim 1, The weight determining means includes a weight table having a nonlinear correction coefficient and outputting a slope between adjacent pixels for each distance input from the distance measuring unit and a weight of each pixel using the nonlinear interpolation coefficient, and a slope output from the weight table. And an interpolation unit configured to linearly interpolate the weight of each pixel and determine and output the linear interpolated weight as a weight. The method of claim 1, In order to apply the determined weight to the image data, the weight applying unit selects one of a multiplier for multiplying the image data by the weight, an adder for adding the image data to the weight, and an offset characteristic of the multiplier or the output of the adder. Camera lens distortion correction device for a mobile terminal, characterized in that it comprises an operation mode selection unit for outputting. Counting horizontal and vertical synchronizing signals of the captured image data to measure the distance between each pixel from the center of the lens; Determining a weight of distance information between each pixel from the measured lens center by using a nonlinear correction coefficient and outputting the determined weight; And correcting by adding or multiplying the determined weight value according to the degree of offset of the image data, and outputting the corrected image data.

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