KR19990051003A - Apparatus and method for optimizing video signal distribution of digital still camera - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal processing technique of a digital still camera. In order to quickly and accurately correct an imbalance distribution of an image, an analog video signal input by photographing a digital still camera is converted into RGB image data and stored in a memory (35). Camera signal processing unit 34 for storing; A microcomputer (36) for controlling read / write operations of the memory (35) to perform enhancement on the image data stored in the memory (35); The gray level of the image data input from the memory 35 is divided into a light portion and a dark portion to estimate the change of the gray level, and a manipulation function between two points is selected according to the estimation result to distribute the image signal. It is configured to include an enhancement processing unit 37 to be changed to.

Description

Apparatus and method for optimizing video signal distribution of digital still camera

The present invention relates to a video signal processing technology of a digital still camera, and in particular, by processing the image evenly, the corrected image appears excessively dark when the image is inclined to a bright part, The present invention relates to an apparatus and a method for optimizing video signal distribution of a digital still camera, in which a portion is also darkened to prevent an unbalance of an image from occurring.

The video signal is evaluated as a good image when the distribution of 256 gray levels has a median value, that is, when there are many signals of 100 to 150 gray levels. When there are a lot of signals below 100 gray level, not only the screen looks dark but also it is difficult to distinguish the dark image. When there are many signals above 150 gray level, the screen looks bright overall.

In order to solve such an imbalance of the image, a point-to-point operation technique that changes the brightness for each pixel is typically used. FIG. 1 shows an example of this manipulation technique, and an image applied to the understanding thereof is shown in FIGS. 2A and 2B.

Histogram smoothing is the most commonly used unbalanced image solving method. It calculates the image distribution and calculates the distribution function of the image that can make the image the same distribution in all gray levels. Based on this, two points for each pixel Carry out the operation.

In addition, the gamma correction technique is a slightly different concept from the histogram smoothing, but is a widely used two-point operation technique, in which case the operation function is changed by the gamma value.

However, in the conventional image unbalancing technology, since the image is simply distributed evenly, the corrected image appears excessively dark and the intermediate brightness image appears too dark when the image is biased in the bright part, and vice versa. There was a problem appearing. Moreover, when using the flash in a digital still camera, such an image imbalance was more serious.

Accordingly, an object of the present invention is to optimize the distribution of image signal by dividing the gray level of the image into two groups and to differentiate the distribution of the image signal by determining the operation function between two points based on the sum of the derivatives. And providing a method.

1 is a graph showing an example of operation between two points in the enhancement process.

Figure 2 (a) is an illustration of a damaged image.

Figure 2 (b) is an illustration of the image reconstructed by the prior art.

Figure 3 is a block diagram showing an embodiment of an image signal distribution optimization device of a digital still camera according to the present invention.

4 is a detailed block diagram illustrating an embodiment of an enhancement processing unit in FIG. 3;

5 (a) is a graph of the distribution of the ideal image.

Figure 5 (b) is a graph of the distribution of the unbalanced image.

5C is a graph of distribution of a general image.

FIG. 6 is a graph of distribution change of an image determined by the sum of derivatives in FIG. 4. FIG.

Figure 7 (a) is an illustration of a damaged image.

Figure 7 (b) is an illustration of a reconstructed image according to the present invention.

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

31: Lens 32: CD

33: preprocessor 34: camera signal processor

35: memory 36: microcomputer

37: enhancement processing unit 41: histogram processing unit

42A, 42B: Differential 43: Operation function selector between two points

44: operation point between two points

FIG. 3 is a block diagram of an exemplary embodiment of an apparatus for optimizing video signal distribution of a digital still camera for achieving the object of the present invention. As shown in FIG. 3, an optical signal incident through the lens 31 is photographed by photographing a subject. A CD 32 for converting an ordinary signal; A preprocessor (33) for removing noise included in the signal output from the CD (32) and converting the noise to an appropriate level; A camera signal processor 34 for converting an analog image signal output from the preprocessor 33 into a digital signal, and converting the analog image signal into RGB image data and storing it in a memory 35; The microcomputer 36 which controls the operation of the camera signal processor 34 and controls the read / write operation of the memory 35 to perform enhancement on the image data stored in the memory 35. )Wow; The gray level of the image data input from the memory 35 is divided into a light portion and a dark portion to estimate the change of the gray level, and a manipulation function between two points is selected according to the estimation result to distribute the image signal. It consisted of the enhancement process part 37 changed into a.

The enhancement processor 37 includes a histogram processor 41 for determining N (m) by counting gray level values of each pixel in a given image as shown in FIG. 4; A differentiator 42A for differentiating the gray level values of the lower group among the gray level values counted by the histogram processor 41, and a differentiator 42B for differentiating the gray level values of the upper group; A two-point manipulation function selector 43 for determining a function to be applied by the two-point manipulation unit 44 based on the sum values A _k and B _{k of the} derivatives obtained at the differentiators 42A and 42B. )Wow; Between two points for changing the unbalance distribution in a desired direction by selectively applying manipulation functions F _il (n) and F _ih (n) to the input image data under the control of the manipulation function selector 43 between the two points. An operation unit 44; When it is determined that the image has an ideal distribution in the two-point operation function selector 43, the switch is configured to switch the image data supplied to the two-point inter-operation unit 44 side. When described in detail with reference to Figures 5 to 7 attached to the operation of the present invention.

The optical signal incident through the lens 13 by the photographing of the subject is converted into an electrical signal by the CCD (Charge Coupled Device) 32 and then correlated double sampled circuit (CDS) function of the preprocessing unit 33. Noise is removed by the control unit, and adjusted to an appropriate level by the AGC (Auto Gain Control) function.

In addition, the analog video signal output from the preprocessor 33 is converted into a digital signal by the camera signal processor 34 and interpolated as necessary to be converted into image data and stored in the memory 35.

Meanwhile, the microcomputer 36 accesses the memory 35 so as to perform enhancement on the image data stored in the memory 35, and the image data x (n) sequentially outputted therefrom is stored in the microcomputer 36. The image data y (n) supplied to the enhancement processor 37 and enhanced by the enhancement processor 37 is stored in the memory 35 by the microcomputer 36. Thus, no memory is required to perform the enhancement.

The enhancement processor 37 divides the gray level of the input image data x (n) into light and dark portions to estimate a change in the gray level, and then operates between two points according to the estimation result. Determines the function to be applied to and changes the distribution of the video signal.

Hereinafter, the operation of the enhancement processor 37 will be described in more detail with reference to FIG. 4.

The image data x (n) input from the memory 35 to the enhancement processor 37 is data about RGB information of each pixel, which is converted into luminance information of the pixel and supplied to the histogram processor 41. .

The histogram processor 41 determines N (m) by counting gray level values of each pixel in a given image, where m is 0 to 255.

At this time, the differentiator 42A differentiates the gray level values of the lower group (m = 0, .., 127) among the gray level values counted by the histogram processing unit 41, and the differentiator 42B is the upper group m. = 128, .., 255) to differentiate the gray level value, where the following equation is defined.

When k is 1 in the above equation, it is possible to estimate the change of gray level based on A _i or B _i value. Also, based on the sum of the derivatives A _k , the distribution of the signals having a level smaller than the median value can be known, and on the basis of the sum of the derivatives B _k , the distribution of the signals having a level greater than the median value can be known.

Here, the k value represents the precision with respect to the derivative, and may be generally set to "1". Increasing the value of k reduces the amount of calculation, but decreases the precision of the overall change.

The two-point operation function selector 43 determines a function to be applied in the two-point operation unit 44 based on the sum values A _k and B _k of the derivatives obtained at the differentiators 42A and 42B. .

In general, when a distribution of an image is converted into a probability function, a distribution of 0 to 255 is obtained, and an image is ideally distributed when each coefficient has a value of 1/256. However, when the probability distribution of the image becomes the middle value, it is poorly evaluated. (A) of FIG. 5 illustrates an ideal image distribution, (b) an unbalanced image distribution, and (c) a general image distribution form.

Fig. 6 shows an example of two-point operation determined by the sum values A _k and B _k of the derivatives. That is, d _i and d _h are determined in proportion to the sum values A _k and B _k of the derivatives, and operation functions F _il (n) and F _ih (n) that are appropriate to the values are determined. As the sum of the derivatives A _k and B _k increases, d _i and d _h increase and the imbalance distribution of the image is changed to be closer to the ideal distribution.

If the sum of the derivatives A _k is a positive value, it is determined as an image having a general distribution and the control signal CS is output as "low", whereby the switch SW is short-circuited to the fixed terminal a so that the image The data x (n) is bypassed without being supplied to the operation point 44 between the two points. That is, the operation between the two points is not made.

In addition, when the sum value B _k of the derivative is negative, it is judged as an image having a general distribution, and the control signal CS is output as "low" at this time, whereby the switch SW causes the fixed terminal ( Shorted to a), operation between two points is not performed as described above.

However, when the sum value A _k of the derivative does not appear as a positive value or the sum value B _k of the derivative does not appear as a negative value, the control signal CS is output as "high" so that the switch SW is fixed. Shorted to the terminal b, the video data x (n) is supplied to the operation unit 44 between the two points.

Accordingly, the two-point manipulation unit 44 selectively applies manipulation functions F _il (n) and F _ih (n) to the input image data x (n) so that an image having an unbalanced distribution is close to an ideal distribution. Is changed.

7 (a) shows an example of an unbalanced image, and (b) shows that an image having a normal distribution has been restored by the present invention.

As described in detail above, the present invention divides the gray level of the image into two groups, differentiates them, and determines an operation function between two points based on the sum of the derivatives to change the distribution of the image signal, thereby making the image excessively excessive. Not only can it prevent the image imbalance such as appearing dark or the part of the medium brightness is dark, but also has the effect of enabling high-speed processing, and has the effect of showing better performance in the environment using flash.

Claims (4)

A camera signal processing unit 34 for converting an analog video signal input by shooting a digital still camera into RGB video data and storing it in the memory 35; A microcomputer (36) for controlling read / write operations of the memory (35) to perform enhancement on the image data stored in the memory (35); The gray level of the image data input from the memory 35 is divided into a light portion and a dark portion to estimate the change of the gray level, and a manipulation function between two points is selected according to the estimation result to distribute the image signal. The image signal distribution optimization device for a digital still camera, comprising: an enhancement processing unit (37) configured to change the shape. The apparatus according to claim 1, wherein the enhancement processor (37) comprises: a histogram processor (41) for counting gray level values of each pixel in a given image; A differentiator 42A for differentiating the gray level values of the lower group among the gray level values counted by the histogram processor 41, and a differentiator 42B for differentiating the gray level values of the upper group; A two-point manipulation function selector 43 for determining a function to be applied by the two-point manipulation unit 44 based on the sum values A _k and B _{k of the} derivatives obtained at the differentiators 42A and 42B. )Wow; Between two points for changing the unbalance distribution in a desired direction by selectively applying manipulation functions F _il (n) and F _ih (n) to the input image data under the control of the manipulation function selector 43 between the two points. An image signal distribution optimization device for a digital still camera, comprising: an operation unit (44). The switch SW of claim 2, wherein the switch SW is switched to block the image data supplied to the operation point 44 between the two points if it is determined that the image has an ideal distribution. And a video signal distribution optimization device for a digital still camera. A first step of sequentially reading image data x (n) stored in a memory, converting the image data x (n) into luminance information, and counting gray level values of each pixel; A second step of dividing the counted gray level values into upper and lower groups to differentiate them respectively; A third step of determining a function to be applied when manipulating between two points based on the summed values differentiated into upper and lower groups; According to the result determined in the third step, by applying a different operation function to the image data by selectively changing the image having an unbalanced distribution to an ideal distribution and the fourth step of storing in the memory image signal of the digital still camera Distribution optimization method.