KR100437810B1 - Apparatus for correcting image brightness - Google Patents

Abstract

The present invention relates to an image brightness compensator for compensating for non-uniformity of brightness existing in a display device. Particularly, characteristics of the display device prior to providing an image to a display device such as an LCD panel using an external memory that has been previously used for other purposes. By inversely correcting the brightness of the image, the displayed image has a uniform distribution of brightness while reducing the amount of hardware required. In addition, in the case of dividing an image into an arbitrary number of regions and separately performing correction for each image, the size and number of regions to be divided are not limited. Also, after the image is divided into an arbitrary size, the correction for each image is performed. This has a possible effect.

Description

Apparatus for correcting image brightness}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for controlling the brightness of a display screen. In particular, in the case where brightness unevenness is large for each display area, such as an LCD (Liquid Crystal Display), an image brightness correction that removes the unevenness of brightness existing in a display device is performed. Relates to a device.

With the introduction of digital TV and the development of display technology, various kinds of display devices have recently been introduced. In addition to the conventional direct-type TV, projection TV using PRT (Picture Ray Tube), projection TV using LCD (Liquid Crystal Display), projection TV using DLP (Digital Light Processor), LCD TV using thin film LCD, PDP ( Various types of products such as Plasma Display Panel are being introduced.

In particular, the display device using the LCD is capable of high resolution display and can be manufactured at low cost, light weight, and small size, and is being used in a wide variety of fields, and is gradually expanding its use area.

In the case of LCD panels, performance has been continuously improved, and many studies have been conducted to obtain low power consumption and high contrast ratio for various applications.

However, the above-described LCD panel often generates an output image in the form of spots due to the characteristics of the display when an image having the same brightness is input to the entire screen. In particular, the brightness of the entire panel is uniform compared to the CRT or PDP due to a manufacturing process problem. Since the castle is inferior, correction is necessary.

In other words, in the case of CRT, the center of the image is brighter and darker toward the boundary.However, the uniformity changes gradually and the user does not feel this difference easily, whereas in the case of LCD, the brightness changes in the non-periodic position. The user can easily identify the difference. In other words, when an image having a similar brightness distribution is input, the LCD panel outputs a blob-shaped image, thereby outputting a very visually disturbing image to the user.

Therefore, researches to improve the brightness uniformity of LCD panels are also widely conducted at present.

As a prior art for improving the brightness uniformity of the LCD panel, Korean Patent Laid-Open No. 2001-0072960 proposes a method of improving the brightness uniformity by adding a light-type microsurface structure on the panel manufacturing process. However, this method has a problem in that it cannot fundamentally solve the brightness nonuniformity caused by the nonuniform distribution of the liquid crystal.

In addition, Korean Utility Model Publication No. 1999-005298 proposes a method of improving brightness uniformity of an LCD projector using an illumination system. This method proposes a lamp structure for improving brightness uniformity, but has a problem in that it cannot be independently applied to brightness unevenness uniquely generated for each LCD panel.

Therefore, in order to completely solve the problem of having different brightness non-uniformity characteristics for each LCD panel, it is necessary to correct for the characteristics of each panel. This problem can be solved by measuring the brightness distribution of the LCD panel and correcting the image inputted to the panel using image processing using this data.

The prior art to which the above method is applied is a method of storing a correction function of a brightness distribution of an LCD panel using a lookup table and correcting brightness non-uniformity using the same. However, in order to correct the brightness distribution, as shown in FIG. 1, the correction data for the maximum, minimum, and median values of the images must be stored at about 1000 positions on the LCD panel, and a large amount of lookup tables must be used for this purpose. There is a disadvantage.

In addition, the above-described method has a disadvantage in that it does not fully correspond to the characteristics of the LCD panel despite the need to use a very large lookup table because the correction position cannot be extended.

The present invention is to solve the above problems, an object of the present invention is to reverse the brightness of the image to match the characteristics of the panel prior to providing the image to the LCD panel using the external memory was used for other purposes, An object of the present invention is to provide an image brightness compensator for reducing the amount of hardware required to have a uniform brightness distribution.

Another object of the present invention is not to limit the size and number of regions for dividing an image, and to provide an image brightness correction apparatus capable of correcting each after separating an image into an arbitrary size.

1 shows an example of a general adjustment point division

2 is a block diagram of an image brightness correction device according to an embodiment of the present invention;

3 illustrates an example of input level interpolation in accordance with the present invention.

4 shows an example of adjustment point segmentation in accordance with the present invention;

5A to 5C show examples of division of interpolation levels at respective adjustment points according to the present invention.

6 illustrates an example of correcting an interpolation level of each adjustment point according to the present invention.

7A to 7C illustrate a process of generating an interpolation level at a current input image position according to the present invention.

8 is a block diagram illustrating a configuration of an image brightness correction device according to another embodiment of the present invention.

Explanation of symbols for main parts of the drawings

100: external memory 200: memory interface

300: synchronization generating unit 400: brightness correction unit

401: level selector 402: adjustment value generator

403: Position interpolator 404: Level interpolator

803 temporary buffer

In order to achieve the above object, an image brightness correction apparatus according to the present invention divides an image into an arbitrary number of regions and stores brightness interpolation information for each divided region and uses the information when the image is displayed. By performing interpolation, the image of the LCD panel to be finally displayed has a uniform brightness distribution.

To this end, the image brightness correction device according to the present invention, by sharing the external memory generally used in the environment using the external memory and corrects the brightness non-uniformity of the LCD panel using the interface thereof, the amount of hardware used It is characterized in that the correction performance is increased while reducing.

According to an embodiment of the present invention, an image brightness correcting apparatus may include an external memory and at least a corresponding number of adjustment points of a divided region after dividing an area of an input image by a required number in a horizontal direction and a vertical direction. A control unit for storing two or more level interpolation data for each adjustment point in the external memory, and reading the level interpolation data of the adjustment points including the current input pixel from the external memory to generate the level interpolation data of the current pixel position through interpolation. Afterwards, it comprises a brightness correction unit for correcting the brightness level of the input pixel by applying interpolation to the level interpolation data of the current pixel position.

The brightness compensator determines a level interpolation method according to the input pixel level and the input pixel level and outputs the interpolation method, and reads and outputs the level interpolation data of each control point of the divided region corresponding to the position of the input pixel from an external memory. A position interpolation unit for generating level interpolation data at a current pixel position by applying linear interpolation to the level interpolation data generated by the adjustment value generator and the position information of the current pixel; And a level interpolator for correcting the brightness level of the input pixel by using the level interpolation data generated by the input signal, the level of the input pixel output from the level selector, and the interpolation method.

The level selector may set at least two fixed brightness level values, and determine an interpolation method according to which part of the brightness level the input pixel level belongs to.

The position interpolator may set the interpolation level data of the adjustment point as interpolation level data of the current position when the position of the input pixel coincides with one of the adjustment points of the division area.

The position interpolation unit applies linear interpolation to the level interpolation data of four adjustment points of the divided region when the position of the input pixel is located inside or inside a quadrangle of one divided region. And generating data.

The brightness compensator is provided for each of R, G, and B colors, and the brightness correction of the input pixel is independently performed for each of R, G, and B. The external memory includes a divided region for each of R, G, and B. At least two or more level interpolation data corresponding to each adjustment point are stored.

A memory interface unit is provided between the external memory and the brightness compensator, and the memory interface unit reads the level interpolation data at each control point of the divided region stored in the external memory and separates the data into R, G, and B processing data. And an adjustment value generator of each of the brightness compensators of R, G, and B.

And a buffer for temporarily storing interpolation level data output from the adjustment value generator, wherein the buffer temporarily stores interpolation level data of two lines among data provided from the adjustment value generator and is stored according to a synchronization signal. The interpolation level data is periodically updated with new interpolation level data line by line.

Other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments taken in conjunction with the accompanying drawings.

Hereinafter, with reference to the accompanying drawings illustrating the configuration and operation of the embodiment of the present invention, the configuration and operation of the present invention shown in the drawings and described by it will be described as at least one embodiment, By the technical spirit of the present invention described above and its core configuration and operation is not limited.

In general, when converting a format using image processing, the external memory is mostly used, and when the noise canceling function is performed, the external memory is often used.

In the present invention, by sharing the external memory previously used as described above, it is to correct the nonuniformity of the LCD panel without using the look-up table.

That is, by dividing the image into any number of areas by sharing the external memory used for other purposes, by storing the brightness interpolation information for each area and performing the interpolation using this information when the image is displayed, The amount of hardware required is drastically reduced while ensuring that the final displayed image has a uniform brightness distribution.

In this case, there is no need to limit the size and the number of regions for dividing the image, and it is possible to correct the respective images after separating the image into an arbitrary size. That is, if necessary, the image area can be corrected by increasing the desired number of images, and the image quality correction can be performed more precisely.

FIG. 2 is a block diagram illustrating an image brightness correction apparatus according to the present invention, in which an external memory 100, a synchronization generator 300, a brightness correction unit 400, and an area of an input image are required in a horizontal direction and a vertical direction. A control unit 500 that separates the number and stores correction levels corresponding to each vertex in the external memory 100, and a memory interface that controls data input / output between the external memory 100 and the brightness correction unit 400; It consists of 200.

The brightness corrector 400 sets a maximum, a middle, and a minimum value of an input image, determines a level of the input pixel, and determines a correction method of the input pixel, and receives a sync signal from the sync generator 300. Receives and outputs the level interpolation value of the position corresponding to the vertex of the rectangle stored in the external memory 100, that is, the four level interpolation values surrounding the current pixel, in accordance with the position of the image through the memory interface 200. A position interpolation unit 403 for generating a level interpolation value at the position of the current pixel by using the adjustment value generator 402 and the level interpolation value generated by the adjustment value generator 402 and the position information of the current pixel. And an output image having a uniform brightness distribution by using the level interpolation value generated by the position interpolator 403, the level of the input pixel output from the level selector 401, and an interpolation method. Which consists of a level interpolator 404.

The brightness compensator 400 is provided for each of R, G, and B colors, and the memory interface 200 reads interpolation values of respective areas stored in the external memory 100 to read each color (R, G, The adjustment value generator 402 of the brightness correction unit 400 of B) is appropriately provided.

In the present invention configured as described above, in order to correct the brightness level at one point to another value, an output value for each input level is required. However, if the brightness level is different for each position of the image, in theory, it should have different correction data for input and output of the image at every position. In this case, a very large amount of correction data must be stored, which is very difficult.

However, in the case of LCD panels, even if the nonuniformity of the brightness distribution is very large, it has a continuous feature in terms of pixels.

Therefore, in correcting the brightness level at a point, without using corresponding values for all values, as shown in FIG. 3, the correction values (eg, MIN, MID, MAX) of input / output images for several levels are stored. In addition, the remaining values can be calculated using linear interpolation to achieve the desired brightness control performance.

In addition, when it is necessary to adjust the brightness level at all points on the two-dimensional plane, as shown in FIG. 4, the image is divided at regular intervals without storing correction data for all points of the image, and the correction data is stored only at important points, and By performing two-dimensional interpolation on the brightness level, the brightness uniformity of the LCD panel can be improved.

At this time, the brightness level used may use only two level values, the maximum value and the minimum value, as shown in FIG. 5A, or three levels of the maximum value (MAX), the intermediate value (MID), and the minimum value (MIN) as shown in FIG. 5B. Alternatively, as shown in FIG. 5C, four levels of a maximum value, a median value 1, a median value 2, and a minimum value may be used. It is also possible to use more level values to increase the interpolation accuracy.

In the present invention, as an example, a case having three levels of interpolation values of the maximum value MAX, the intermediate value MID, and the minimum value MIN will be described.

As mentioned above, in the case of the LCD panel, the brightness characteristics are non-uniform in two dimensions, and thus adjustment is necessary. To do this, two-dimensional planes are separated into appropriate sizes, and the transform information is stored in the main position, and the rest can be used by interpolation. That is, in FIG. 4, interpolation values for three levels are stored for four vertices constituting one rectangle, respectively, and level interpolation values are generated at the current position using level interpolation values of four vertices. The brightness of the image is corrected using the interpolation value corresponding to. And if the image is located inside or inside the quadrilateral, the interpolation values for the three levels at the four vertices are calculated using the interpolation values at the four vertices and the final image brightness is interpolated. .

To this end, the level selector 401 of the brightness compensator 400 of FIG. 2 determines various pieces of information for converting an input image into an output image using linear interpolation. That is, each pixel of the input image generates output by linear interpolation as shown in FIG. 3, and the processing method varies depending on which part of the image level the input image belongs to.

For example, if the brightness of the input image is greater than the determined maximum value, the maximum value is used to interpolate the image. On the contrary, if the brightness of the input image is less than the predetermined minimum value, the minimum value is used to interpolate the image. When the brightness of the input image is smaller than the maximum value and larger than the median value, the brightness of the output image is determined by the A interpolation rule of FIG. 3. In addition, when the brightness of the input image is smaller than the middle value and larger than the minimum value, the B interpolation rule is applied.

That is, after setting a plurality of fixed level values, for example, maximum, middle, and minimum values, the maximum value is equal to or greater than the maximum value if the input pixel is greater than or equal to the maximum value, and the minimum value is less than or equal to the minimum value. Is output. Further, if the input pixel is between the maximum value and the intermediate value, the A interpolation rule is output to the level interpolation unit 404 together with the input pixel level. If the input pixel is between the intermediate value and the minimum value, the input pixel level and B An interpolation rule is output to the level interpolator 404.

As shown in FIG. 3, the interpolation rule may be different in the case where the brightness of the input image is greater than the median value and less than the median value, and the level selection unit 401 needs to consider this. If more than one intermediate value is used for interpolation, more accurate interpolation can be performed, but the amount of hardware is slightly increased.

On the other hand, the control unit 500 is a type of CPU, and separates the area of the input image by the required number in the horizontal direction and the vertical direction as shown in Figure 4, each level interpolation value corresponding to each vertex (eg , MAX, MID, MIN) are stored in the external memory 100. The external memory 100 stores level values required for interpolation at the vertices of each divided region.

If three levels are set and used by the level selector 401, data to be stored at one vertex (that is, an adjustment point) becomes 3x3 bytes in consideration of R, G, and B images. For example, when dividing the image into 10x10 images, 11x11 adjustment points are used for interpolation, and the level interpolation values of 3x3x11x11 bytes must be stored in the external memory 100 because the level interpolation values must be stored at each point. . In this case, when the level value required for correction is stored in the external memory 100, the amount occupied by the external memory 100 is extremely small, and thus, an arbitrary level and an arbitrary number of adjustment points may be stored as necessary.

Existing applications using the external memory 100 support an operation of reading or writing data to an arbitrary address of the external memory 100. Therefore, the operation of writing interpolation data of the adjustment point required in the present invention to the external memory 100 may use a read / write operation of memory data that has been previously used, and a separate data storage unit needs to be additionally designed in most cases. none.

The memory interface 200 reads out the level interpolation value at each control point stored in the external memory 100, separates the data into R, G, and B processing data, and then adjusts the value generator 402 of each brightness compensator. To provide. At this time, in order to interpolate data at any position using the level interpolation value of each adjustment point, the level interpolation value is read from the memory 100 at four points forming a rectangle as shown in FIGS. 6 and 7. 402, which is responsible for this function in the memory interface 200.

The adjustment value generator 402 uses four levels of adjustment points to be used at the current input pixel position by using a level interpolation value read from the memory 100 and a synchronization signal applied from the synchronization generator 300 simultaneously with the image input. Output the level interpolation value. To this end, the adjustment value generator 402 must request the memory interface 200 to use the synchronization signal in advance for a later level interpolation value, and perform the control so that it can be used without any problem at a necessary time. The interpolator 403 should provide the correct level interpolation value.

As illustrated in FIG. 6, the position interpolator 403 uses the level interpolation information for the four adjustment points provided by the adjustment value generator 402 and the new pixel interpolation information at the current pixel position. Generates information through linear interpolation.

As shown in FIG. 7, the planes connecting the MAX, MID, and MIN values at four points become slightly curved planes, not perfect planes.

Theoretically, the plane connecting three independent points may be unique, but there are no planes connecting four independent points. However, as shown in FIG. 7, the approximate position may be calculated using linear interpolation. In this case, the result value may vary according to the calculation order.

For example, using the adjustment points (i, j) and (i, j + 1) of FIG. 7, the interpolation values of point A are calculated and the adjustment points (i + 1, j) and (i + 1, After calculating the interpolation value of point B using j + 1), the result of calculating the interpolation value at the final point using point A and B, and the adjustment points (i, j) and (i + 1, j Calculate the interpolation value of C point using), calculate the interpolation value of D point using adjustment points (i, j + 1) and (i + 1, j + 1), and then use C and D points. Therefore, the result of calculating the interpolation value at the final point may be different. Therefore, to keep the interpolation results consistent, the method of calculating the interpolation values must be kept constant.

The level interpolator 404 finally generates a brightness corrected image. That is, the brightness level of the input pixel is converted and output by using the input pixel level and the linear interpolation method output from the level selector 401 and the level interpolation value at the current pixel position generated by the position interpolator 403. . That is, the brightness level of the input pixel is corrected by applying the level interpolation value at the current pixel position to the input linear interpolation method.

FIG. 8 is a block diagram illustrating an apparatus for correcting brightness of another embodiment, in which a temporary buffer 803 is further added to the brightness corrector 800. In this case, the interpolation level data of each vertex can be eliminated frequently from the external memory 100.

The temporary buffer 803 temporarily stores the level interpolation values of two lines among the level interpolation values provided by the adjustment value generator 802, and repeatedly uses them as necessary during image processing. The level interpolation value is periodically filled with new data in line with the synchronization signal.

That is, the adjustment point data on the first line and the level interpolation data on the second line are temporarily stored in the temporary buffer 803 to be applied to the image data on the m line to correct the image. After that, the interpolation data of the second line and the third line is temporarily stored in the temporary buffer 803, and the image data of the next m line is corrected. As such, image data of 2m line is generally corrected by using the level interpolation data of one line, and the buffer 803 capable of storing the level interpolation data of two lines is stored in the brightness compensator 800, thereby The amount of level interpolation data read from the memory 100 can be minimized.

Otherwise, the level interpolation data required for every image line should be repeatedly read from the external memory 100. In most cases, this operation is not a problem, but when the external memory is frequently used for other image processing, the above advantages can be obtained by simultaneously using a small internal memory (ie, a temporary buffer) as shown in FIG. 8. .

In this case, the temporary buffer 803 stores level interpolation data by double buffering. Also, a lookup table may be used instead of the temporary buffer.

That is, the image brightness correction device having the structure as shown in FIG. 2 can be used by increasing the number of image adjustment points in the horizontal direction or the vertical direction as desired. Can exhibit the performance of.

On the other hand, the image brightness correction device having the structure as shown in FIG. 8 can be used to increase the number of image adjustment points as desired in the vertical direction, but is limited by the amount of the buffer used internally in the horizontal direction. However, even in this case, since only the memory for storing the control point data of the two lines is needed, a sufficient area can be secured in the horizontal direction, and in most cases, it can be used without any problem. In addition, this method has various advantages as in the method of FIG. 2 because the use of external memory can be minimized.

Meanwhile, referring to the case of using the conventional lookup table and the case of using the external memory of the present invention, as shown in FIG. 5C, it is assumed that level interpolation values for four levels are stored at one adjustment point. As described above, when the panel is divided into 32x24 and the image is corrected at a specific position, and the correction is performed through linear interpolation for the remaining regions, correction data for 33x25 positions should be stored. In this case, considering that each of the R, G, and B panels must be performed independently, a lookup table having 3x33x25x4x8 bit = 79200 bits is required.

On the other hand, when the commonly used 64Mbit SDRAM is used as an external memory, 1024x32 bits of data can be stored in one row address. Therefore, 2.4 rows of memory space is required to store the above-mentioned 79200 bits of data. do. Given that the SDRAM has 2048 rows, it takes up 0.1% of the memory space and uses an almost negligible area.

As described above, according to the image brightness correction device according to the present invention, by increasing the brightness uniformity of the LCD panel by sharing an external memory which is generally used, it is possible to improve the brightness uniformity of the image with very simple hardware. In addition, while reducing the use of hardware, the performance can be significantly improved compared to the conventional method, and the user can adjust various parameters according to the characteristics of the LCD, it can cope with various uneven images.

In addition, the use of a small temporary buffer has the advantage of minimizing the external memory bandwidth used without significantly increasing the complexity of the hardware.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit of the present invention.

Therefore, the technical scope of the present invention should not be limited to the contents described in the embodiments, but should be defined by the claims.

Claims (10)

External memory; A controller for dividing an input image area by a required number in a horizontal direction and a vertical direction, and storing at least two or more level interpolation data corresponding to each adjustment point of the divided area in the external memory for each adjustment point; And After reading the level interpolation data of the adjustment points including the current input pixel from the external memory and generating the interpolation data of the current pixel position through interpolation, the interpolation is applied to the level interpolation data of the current pixel position. And a brightness compensator for correcting the brightness level of the image brightness compensator. The method of claim 1, wherein the brightness correction unit A level selector which determines and outputs an interpolation method according to the input pixel level and the input pixel level; An adjustment value generator which reads and outputs the level interpolation data of each adjustment point of the divided region corresponding to the position of the input pixel from the external memory; A position interpolation unit for generating the level interpolation data at the current pixel position by applying linear interpolation to the level interpolation data generated by the adjustment value generator and the position information of the current pixel; And a level interpolation unit configured to correct the brightness level of the input pixel by using the level interpolation data generated by the position interpolator and the level and interpolation method of the input pixel output from the level selector. . The method of claim 2, wherein the level selector At least two fixed brightness level values are set, and the interpolation method is determined according to which part of the brightness level the input pixel level belongs to. The method of claim 2, wherein the level selector When the fixed brightness level is set to the maximum value, the median value, or the minimum value, the maximum value is output for interpolation when the level of the input pixel is greater than the maximum value, and the minimum value is output for interpolation when the value is smaller than the minimum value. An image brightness compensator for outputting a level and a first interpolation method of an input pixel when it is smaller than a maximum value and a larger value than an intermediate value, and a level and a second interpolation method of an input pixel when a value smaller than a mean value and larger than a minimum value. . The method of claim 4, wherein The first and second interpolation methods of the level selector are interpolation methods having different rules. The method of claim 2, wherein the position interpolation unit And if the position of the input pixel coincides with one of the adjustment points of the division area, setting the interpolation level data of the corresponding adjustment point as interpolation level data of the current position. The method of claim 2, wherein the position interpolation unit When the position of the input pixel is located on the side or inside of a rectangle forming one division area, linear interpolation is applied to the level interpolation data of four adjustment points of the division area to generate the level interpolation data at the current position. Image brightness correction device, characterized in that. The method of claim 1, The brightness compensator is provided for each of R, G, and B colors, and the brightness correction of the input pixel is independently performed for each of R, G, and B. The external memory includes a divided region for each of R, G, and B. And at least two level interpolation data corresponding to each adjustment point are stored. The method of claim 1, A memory interface unit is provided between the external memory and the brightness compensator. The memory interface unit reads the level interpolation data at each adjustment point of the divided region stored in the external memory, divides the data into R, G, and B processing data, and then sends them to the adjustment value generator of each of the R, G, and B brightness correction units. Image brightness correction device, characterized in that provided. The method of claim 2, A buffer for temporarily storing interpolation level data output from the adjustment value generator is further included between the adjustment value generator and the position interpolator. The buffer temporarily stores interpolation level data of two lines among data provided by the adjustment value generator, and periodically updates the interpolation level data stored in accordance with the synchronization signal with new interpolation level data line by line. Brightness correction device.