KR20100033737A - Method and apparatus of local contrast enhancement - Google Patents

Abstract

PURPOSE: A method and an apparatus of a local contrast enhancement by adjusting color components using an RGB scaling process are provided to conserve a clear contrast detail inside a high brightness area with a small amount of hardware cost. CONSTITUTION: A method of a local contrast enhancement comprises the following steps: determining the degree of a local contrast increment to recompense a degradation due to a tone mapping(1201); obtaining a weighted sum average of plural pixels and a profile signal by summing up the weighted sum average of an absolute change of the pixels(1202); applying a local shading to a intensity level of an image signal(1203); and maintaining a color property of the pixel by adjusting color components using an RGB scaling process(1204).

Description

METHOD AND APPARATUS OF LOCAL CONTRAST ENHANCEMENT}

The present invention relates generally to a method and apparatus for local contrast enhancement in an image signal processing system, and more particularly, by means of tone mapping for dynamic backlight control in display system applications. A method and apparatus for processing image signal data in order to minimize loss of fine image contrast which is achieved.

Tone mapping is used in the field of image processing and computer graphics to map color sets to other sets to approximate the appearance of higher dynamic range images in the media to a more limited dynamic range. It is a technique used in. However, tone mapping will not be able to reproduce the full range of light intensities present in natural scenes and will result in a reduction in contrast from scene values to the displayable range. Preserving fine image details and color tones in the original scene is an important issue in many areas.

Recently, Dynamic Backlight Control (DBC) in mobile liquid crystal display (LCD) devices has applied tone mapping to enlarge the data image while dimming the backlight to minimize backlight power consumption. It became one of the display applications. However, during tone mapping, image data loses accuracy, especially in high luminance areas.

Accordingly, image data processing methods that can avoid the loss of sharp image detail or contrast in dynamic backlight control applications would be highly desirable in the art.

The local contrast enhancement method may employ a two-dimensional recursive filter to obtain a moving average of intensity variations in all display areas. This moving average is subtracted from the original signal to produce a signal that contains only local changes, which latter signal is amplified or amplified to increase the display contrast.

Another method for local contrast enhancement is to low pass filter the input signal and add such low pass filtered values to the enhanced contrast values. The final output g is obtained according to the following equation (1).

g = K1 (m) + K2 (f-m)

In this case, K1 and K2 represent characteristic curves, m represents the output of the low pass filter, and f represents the input of the low pass filter.

Another similar method for local contrast enhancement is carried out by weighting the signal according to the magnitude of the local contrast of the signal and by adding the weighted signal to the original signal, thus relating to the value of the local contrast. The original signal can be output without loss. The final output y is obtained according to the following equation (2).

y = x + f (│x-m│) (x-m)

Where f () represents the weighting function of | x-m, m represents the output of the low pass filter, and x represents the input of the low pass filter.

Another local contrast enhancement method that focuses on edge-enhanced features is performed by filter processing to generate edge-enhanced signals, which can reduce the required memory capacity and power consumption. Another method includes applying band-pass filter processing to input image pixels in multiple directions to produce an overall sum-of-border value.

In the above methods, the requirement for compensating and adjusting the loss of sharp image contrast due to tone mapping has not been dealt with. In particular, no consideration is given to the nature of the tone-mapping curve and to the subsequent effects of tone mapping in such a method. In addition, the methods described above perform amplification of contrast signals, boosting and shading of image contrast signals. However, contrast signal boosting has the problem of signal saturation and clipping of signal levels in the high luminance region, and thus image contrast is lost or washed out.

It is an object of the present invention to provide a local contrast enhancement method that requires only one-dimensional data processing. Such a method is effective in hardware implementation because the algorithm does not require a block or two-dimensional approach.

It is another object of the present invention to provide a local contrast enhancement method that can compensate for image loss caused by signal clipping or signal saturation of an image signal at high luminance levels when tone mapping is applied.

It is a further object of the present invention to provide a local contrast enhancement method for enhancing the contrast of a signal by shading. Such shading creates amplified lowering of the signal level in signal valleys, thereby making it possible to avoid signal saturation or signal clipping problems that occur at high luminance levels.

It is yet another object of the present invention to carefully control signal shading in order to minimize the effect on the overall luminance level of an image using a variable scaling control to limit most of the shading for the high luminance region of the image. It is to provide a local contrast enhancement method to be applied, where small shading is not visually perceptible and visually desirable.

It is another object of the present invention to provide a method of local contrast enhancement that provides uniform scaling of RGB color stream data and ensures maintenance of image color tones.

It is yet another object of the present invention to provide a method of local contrast enhancement that takes into account the tone mapping characteristics used in dynamic backlight control to promote significant savings in power consumption in electronic image display systems.

It is another object of the present invention to provide a local contrast enhancement method that can suppress the problem of overshooting of local contrast in sharp edged images, which is particularly common in user interface applications.

Aspects of the present invention have been developed in particular in terms of enhancing image contrast to compensate for sharp image contrast loss due to tone mapping used for dynamic control (DBC) systems in liquid crystal displays. After applying tone mapping, part of the sharp contrast signal in the high luminance region will be reduced, clipped, or saturated according to the tone-mapping curve under dynamic backlight control. The quality of the image will deteriorate, and the sharp contrast details of the image will be eroded or reduced beyond the permissible limits. This method of the present invention can be used to enhance the local contrast signal in a special manner prior to the application of tone mapping to pre-compensate for the effect of contrast reduction from tone mapping.

In a particular embodiment, the algorithm consists of five blocks, which block a multiplexer, summation of two weighted sum filters, contrast shading equations, contrast shading table and RGB scaling. Include. The first part includes a multiplexer for selecting a signal having the highest value among the RGB components of the pixel image as a reference image signal for processing. The second part is the sum of the two weighted sum filters used to form the profile signal in accordance with the image signal. Both filters calculate the weighted sum of the image signal and the weighted sum of the absolute signal change over a number of neighboring pixels. The next part is to calculate the shaded value by subtracting the amount of shading, expressed as the product of two factors, from the image signal. The first factor is an envelope contrast signal value calculated by subtracting the image signal from the profile signal. The second factor is a map value from a lookup table that is used to compensate for the effect of the tone-mapping curve on the image signal. Also, to avoid overshooting problems at sharp edges in the image, the amount of this shading is set to zero if the value is negative. Finally, the last part is RGB scaling, where the RGB signal components of the pixel image data are scaled by the same scale factor determined as the ratio of the shaded value to the reference image signal.

In one exemplary embodiment, the multiplexer selects the highest signal among the RGB input stream data as a representative image signal input for digital signal processing to determine the amount of local shading.

In another exemplary embodiment, the method performs local enhancement of unidirectional contrast in the roll-off region of the tone-mapping curve in applying dynamic backlight control. Using the weighted sum average of the absolute signal change between adjacent pixel data and the weighted sum average of the signal input stream, the in-line digital filter and mathematical logic unit in the module process the selected signal input to generate a profile signal. do.

In another exemplary embodiment, the algorithm applies scaled shading to the signal values to generate new signal values, wherein the ratio of the new signal values to the original signal values is prior to the tone mapping used in the DBC. Constructs an RGB color component scaling factor for use in pre-processing RGB color stream data.

In another exemplary embodiment, the amount of shading is made proportional to the amount of signal level below the profile signal level, whereby a unidirectional or shading contrast enhancement effect is achieved.

In another exemplary embodiment, the module has a contrast shading table that can be controlled by the dimming index used in the DBC and is the same dimming index that determines the tone-mapping curve used in the DBC.

Other aspects of the present invention are also described.

Hereinafter, with reference to the accompanying drawings will be described embodiments of the present invention in more detail.

By using the method and apparatus of the present invention, the sharp contrast details of the image in the high luminance region can be preserved at low hardware cost. By applying the present invention, more aggressive power savings for the dynamic backlight control system can also be achieved.

In the following, an improved local enhancement method and apparatus for an image signal is described. In the following description, numerous specific details are set forth, including filter size, image curves, image histograms, tone-mapping curves, contrast curves, and the like. However, from this disclosure of this specification, those skilled in the art will be able to clearly understand the improved embodiments including substitutions and / or adducts within the scope and spirit of the present invention. In other instances, specific details have been omitted in order to avoid obscuring the present invention. Nevertheless, the following description has been written to enable a person skilled in the art to carry out the idea of the embodiments of the present invention without fail.

The present invention relates, in particular, to a method of local enhancement of image data and corresponding hardware designs used to compensate for sharp image contrast losses due to tone mapping in applications such as dynamic backlight control (DBC) systems in liquid crystal displays. A sharp image contrast loss occurs after applying tone mapping to an image, where details of the image in the bright areas are saturated or clipped, thereby degrading the resulting image quality.

Table 1 below shows a list of variables used herein.

RGB color input (R, G, B) RGB color output (R ', G', B ') Representative Image Signal P Shaded Image Signal P ' Profile signal Pc Contrast Shading Table C (P) The degree of contrast effect that can be adjusted by the user α

1 is a block diagram of a local contrast enhancement system 100 for an image signal according to an embodiment of the invention. In an exemplary embodiment, the algorithm includes five main blocks including a multiplexer 101, a non-linear FIR filter 102, a contrast shading processor 103, a contrast shading table 104, and an RGB scaling unit 105. It consists of. The first part of the local contrast enhancement system 100 selects the largest value among the RGB components of the pixel image data as the representative image signal P in order to determine the local scaling factor P '/ P for contrast enhancement. It includes a multiplexer 101 for.

In another exemplary embodiment, the color signal is obtained based on the YUV format instead of the RGB format. In case of YUV format application, the present invention will use the Y signal as the representative image signal.

The second part of the local contrast enhancement system 100 further comprises a non-linear FIR filter generator 102 for generating a profile signal from the sum of the two weighted sum filters in accordance with the image signal. Module 110. The two filters calculate the weighted sum of the image signal and the weighted sum of the absolute change of the image signal, respectively. The local contrast enhancement P / P 'module 110 further includes a processor 103 for calculating the shaded image signal by subtracting the amount of conditional shading from the original image signal. The amount of conditional shading is expressed as the product of two factors extracted from the image signal. The first factor is the amount of image signal level remaining below the profile signal level. The second factor is a map value obtained from reference table 104 used to compensate for the effect of the tone-mapping curve on the image signal, determined by the dimming index under dynamic backlight control. In one exemplary embodiment, to avoid overshooting problems at sharp edges of the image, the amount of conditional shading is set to zero when the image signal level is higher than the profile signal level.

The local contrast enhancement system 100 further comprises an RGB scaling unit 105, wherein the RGB value of the pixel data is in a local scaling factor that is determined as the ratio (P '/ P) of the shaded image signal to the original representative image signal. Scaled uniformly by

2A shows an exemplary image for explaining local contrast enhancement in accordance with the present invention. An example image includes a full moon 202 above a mountain 201. FIG. 2B shows a pixel intensity histogram 210 corresponding to the example image in FIG. 2A. The pixels for the mountain 211 are relatively dark and distributed in the low input signal portion of the histogram 210, while the pixels of the moon 212 are relatively bright and thus distributed in the high input signal portion of the histogram 210. .

In dynamic backlight control for LCDs where the backlight is dimmed to reduce backlight power, the image signal values are scaled up by tone mapping to keep the image brightness and contrast perceptually the same. )do. FIG. 3A shows a histogram of the example image of FIG. 2A after tone mapping, and FIG. 3B shows an example tone-mapping curve for the tone mapping in FIG. 3A. The characteristic of the tone-mapping curve 300 indicated by the dotted line in FIG. 3B may be best explained when referring to the two regions divided by the dashed vertical line 301. One area is a linear area 302 of substantially constant slope within the tone-mapping curve 300. The other is the roll-off area 303 whose slope in the tone-mapping curve 300 changes with increasing luminance value of the image signal. For additional power savings, the dynamic backlight control can apply more dimming to the backlight, thereby expanding the roll-off area 303. In the roll-off area 303, the image signal level is suppressed as it approaches the saturation level 304. In contrast to FIG. 2B, the right side of the image pixel from the dimming index line 310 of FIG. 3A is remapped to the left.

4A shows a histogram of an example image in FIG. 2A after tone mapping under different dimming indices, and FIG. 4B is an example tone-mapping curve for tone mapping in FIG. 4A. If the dimming index line 410 moves to the left, the roll-off area will expand and more pixels will be distributed to the left in the bar graph. The quality of the image is consequently degraded due to the nature of the tone-mapping curve 400 that re-aligns the luminance levels of the pixels.

FIG. 5A is a bar graph showing image loss due to tone mapping, and FIG. 5B is a diagram illustrating an exemplary image corresponding to FIG. 5A. The detail of the lunar region 501 corresponding to the bright region 502 of the histogram is lost.

FIG. 6A is a graph illustrating the original image signal in the example image of FIG. 5B before tone mapping. FIG. For illustrative purposes, the image signal 600 corresponds only to a portion of the example image of FIG. 5B and is shown as a one-dimensional curve. Horizontal dashed line 601 is shown to represent linear region 602 and roll-off region 603.

6B is a graph illustrating the image signal of FIG. 6A after tone mapping without local contrast enhancement signal pre-processing. The low luminance portion of the signal 613 in the linear region indicates that there is little degradation, while the upper portion of the signal in the roll-off region reduces or even reduces the sharp contrast signal 611 due to the saturation level of the signal. Signal clipping 612 is shown.

FIG. 7A is a graph showing the original image signal after local contrast enhancement signal pre-processing according to the present invention, and FIG. 7B is a graph showing the image signal of FIG. 7A after tone mapping. In order to preserve a clear image contrast signal in the high luminance region, local contrast enhancement is applied locally to the image signal prior to tone mapping so that sharp image contrast can be maintained even after tone mapping. The dotted curve 702 shown in FIG. 7A shows the newly updated output signal of the image signal 701, which represents the shading effect achieved by the local contrast enhancement method of the exemplary embodiment. In FIG. 7B, the upper portion of the signal 703 in the roll-off area maintains image contrast, because image degradation and signal clipping are successfully prevented.

8 shows an exemplary circuit diagram 800 of local contrast enhancement in accordance with the present invention. In an exemplary embodiment, the circuit flow begins by supplying a representative image signal P 801 of the original image signal. According to an embodiment of the present invention, the representative image signal P 801 is selected from the largest signal among the RGB components of the pixel data by a multiplexer (not shown).

The profile signal Pc 803 is then calculated by the non-linear FIR filter 802. According to an embodiment of the present invention, the profile signal Pc 803 corresponds to the weighted sum of the representative image signal P 801 and the weighted sum of the absolute signal change of the representative image signal P 801, respectively. It is obtained by summing the output of the filter. Assume that the representative image signal at position n is P (n), and the absolute change between the values of P (n) 801 of neighboring pixels at position n and position n + 1 is D (n). Assume that The profile signal Pc (n) 803 is calculated by the following equation (3). In other words:

Where 2w + 1 is the magnitude of the weighted sum filters; w1 and w2 are weighting coefficients of the weighted sum filter; D (n) = | P (n + 1) -P (n) | is the absolute signal change of the representative image signal P (n) 801.

The window size of the filter can affect the sharpness of the enhancement effect, that is, the profile signal will change more sharply for narrower windows and vice versa. . If the change in the profile signal becomes too sharp, it will provide undesirable artificial visual effects. On the other hand, if the window size is too wide, the contrast enhancement effect will disappear. On the other hand, if the window size is too large, it may cause image change over a visible extended range.

In an exemplary embodiment, the weighting coefficients for both filters are symmetrical to avoid asymmetrical enhancement visible effects. The sum of the coefficients for each filter is preferably a multiplier of two, that is, 4, 8, 16, 32, 64, 128, etc., for easy hardware implementation. Examples of weighting factors are: 4, 6, 8, 9, 10, 9, 8, 6, 4, with a sum of 64.

The representative image signal P 801 is then subtracted from the profile signal Pc 803 by an adder 804 to obtain the envelope contrast signal X 805. Comparator 806 then checks envelope contrast signal X 805 and assigns X 805 to comparator output Y 807 if X 805 is greater than zero, otherwise comparator output Y 807 It is set to zero. Meanwhile, the representative image signal P 801 is used for reference contrast value information stored in the reference table 808. The lookup table 808 stores a large number of contrast curves corresponding to various dimming indices. By inputting an image signal or representative image signal P 801, a dimming index 809, and a tuning parameter α, the reference table 808 generates a contrast value αC (P) 810. Such a contrast value αC (P) 810 is then multiplied by Y 807 by the multiplier 811. The output of the multiplier 811 is subtracted from the representative image signal P801 by the adder 812 to obtain a shaded image signal P ′ 813. Finally, a ratio P '/ P 815 to color component scaling is computed by the divider 814.

9A is a graph illustrating the application of contrast shading in local contrast enhancement in accordance with an embodiment of the present invention, and FIG. 9B shows a contrast curve 920 and tone mapping curve 910 corresponding to the contrast shading of FIG. 9A. One graph. To compensate for image loss due to tone-mapping curve 910, the values of 'P 901' and 'Pc 902' along roll-off area 940 of tone-mapping curve 910 are added to the contrast dynamics of the image. Can affect In order to compensate for the loss of image detail, a series of contrast values C1, C2, C3 920 are defined to compensate for the corresponding tone-mapping curves R1, R2, R3 910 and stored in a reference table. In general, the characteristics of the tone-mapping curves 910 can be classified into two regions, a linear region 930 and a roll-off region 940. In one exemplary embodiment, the value of the contrast curve 920 is set to zero in the linear region 930 of the corresponding tone-mapping curve 910. The contrast curve 920 then rises as the slope of the tone-mapping curve 910 decreases in the roll-off area 940. Contrast curve 920 is determined to compensate for the loss due to the roll-off effect of tone-mapping curve 910. The compensation curve slope increases as the corresponding roll-off curve slope decreases. The relationship between the compensation curve and the tone-mapping curve also depends on display characteristics, human visual perception, and image content.

In one exemplary embodiment, each contrast curve 920 is represented by a reference table that is considered as a contrast shading table and is pre-defined for real-time hardware implementation.

In accordance with an embodiment of the invention, compensation for degradation due to the tone-mapping curve shades a representative image signal P 904 indicated by a point along the solid curve 901 based on a pixel by pixel. By updating to the completed image signal P'905. In comparison with the solid line curve 901 of the original representative image signal P 904, the local signal change or contrast of the dashed line curve 903 of the shaded image signal P ′ 905 is magnified or enhanced by signal shading. In an exemplary embodiment, the shaded image signal P ′ 905 is calculated from the original representative image signal P 904 according to the contrast shading equation below.

In this case, C (P) is a contrast shading table for compensation of the tone-mapping curve, and α is a parameter for tuning the degree of contrast effect. The parameter α allows user selection control as needed for personal preference for a particular image. In an exemplary embodiment, α is set to 1 (unity) for contrast enhancement activation, while contrast enhancement is turned off by setting α to zero.

As a result, the shaded value P ′ 905 is less than or equal to the value of the original representative image signal P 904. The local contrast in signal P 904 is magnified by the calculated depressing of the signal valley called signal shading.

10A is a graph showing image signals before and after contrast enhancement according to a conventional method. Solid curve 1001 represents an exemplary original image signal. Dotted line curve 1002 represents the enhanced output signal. In typical local contrast enhancement, the low pass signal indicated by dashed curve 1003 is used to enhance the image signal with boosting and shading. However, if the original signal is already at a high level close to the system highest level, saturation or clipping 1004 of the image signal will occur in the boosted signal. When tone-mapping is applied to dynamic backlight applications, additional saturation or clipping of the boosted signal will result.

10B is a graph showing the same image signal as FIG. 10A after contrast enhancement according to the present invention. In accordance with an embodiment of the present invention, the image local contrast signal 1012 is magnified only by shading, thereby avoiding the problem of clipping or saturation. In one exemplary embodiment, when the level of the profile signal 1013 is higher than the level of the original image signal 1011, the output signal valleys are intentionally lowered to enhance local contrast.

11A is a graph illustrating the overshooting problem in an image signal after contrast enhancement according to a conventional method. Such overshooting problems exist at the sharp edges of the image signal and are commonly found in GUI graphics when the level of the profile signal 1101 is lower than the level of the image signal 1102, and consequently in the enhanced contrast signal 1103. This results in an unusually bright edge 1104.

FIG. 11B is a graph showing the same image signal as FIG. 11A showing after contrast enhancement according to the present invention. FIG. In an exemplary embodiment, the amount of shading is set to zero when the level of the profile signal 1112 is lower than the level of the image signal 1111 to remove bright edge defects. The overshooting problem is completely eliminated according to Equation (4) above, where the amount of shading is set to zero under the condition of Pc > P.

12 is a flowchart illustrating a local contrast enhancement method for an image signal according to an embodiment of the present invention. This method enhances image quality in a tone mapping application and begins at decision step 1201, in which the local contrast increment degree for the image signal is determined to compensate for the degradation due to tone mapping. do. In filtering step 1202, a profile signal is obtained by summing the weighted sum average of the plurality of neighboring pixels and the weighted sum average of the absolute change of the plurality of neighboring pixels. In shading step 1203, local shading is applied to the luminance level of the image signal, where local shading is proportional to the degree of local contrast increment and the difference between the image signal and the profile signal.

In an exemplary embodiment, the strongest signal between the color components of the image signal is selected as the primary representative image signal to which local shading is applied. Local shading then generates a shaded image signal, where the local shading is proportional to the degree of local contrast increment and the difference between the primary representative image signal and the profile signal.

In scaling step 1204, the color components are proportionally adjusted by the RGB scaling process to maintain the color characteristics of the pixel. In one exemplary embodiment, the representative value P and the shaded value P 'of the value are the ratio P' / P by the divider and the three multipliers, as shown in Equation 5 below. It is used to change the RGB components by scaling each component value with.

In addition to RGB, the color components of the image signal may be determined according to color models such as CMYK, HSV, HSL, YUV, and YIQ.

By using the method and apparatus of the present invention, the sharp contrast details of the image in the high luminance region can be preserved at low hardware cost. By applying the present invention, more aggressive power savings for the dynamic backlight control system can also be achieved.

The above description of the embodiments of the present invention is not limited, so that those skilled in the art will be able to readily appreciate the updates or improvements to the embodiments of the present invention, and accordingly the claims to determine the scope of the present invention Should be based on.

1 is a block diagram illustrating local contrast enhancement in accordance with the present invention.

2A illustrates an exemplary image for explaining local contrast enhancement in accordance with the present invention.

FIG. 2B is a bar graph illustrating pixel intensities corresponding to the example image of FIG. 2A.

FIG. 3A is a bar graph illustrating the example image of FIG. 2A after tone mapping. FIG.

3B is a graph illustrating an example tone-mapping curve for tone mapping in FIG. 3A.

4A is a bar graph illustrating the example image of FIG. 2A after tone mapping under different dimming indexes.

4B is a graph illustrating an example tone-mapping curve for tone mapping in FIG. 4A.

5A is a bar graph showing image loss due to tone mapping.

FIG. 5B is a diagram illustrating an example image corresponding to FIG. 5A.

6A is a graph illustrating the original image signal before tone mapping.

6B is a graph illustrating the image signal of FIG. 6A after tone mapping without local contrast enhancement signal pre-processing.

7A is a graph illustrating an original image signal that has undergone local contrast enhancement signal pre-processing according to the present invention.

7B is a graph illustrating the image signal of FIG. 7A after tone mapping.

8 is an exemplary circuit diagram of local contrast enhancement in accordance with the present invention.

9A is a graph illustrating the application of contrast shading in local contrast enhancement in accordance with an embodiment of the present invention.

FIG. 9B is a graph illustrating a contrast curve and a tone mapping curve corresponding to the contrast shading of FIG. 9A.

10A is a graph showing image signals before and after contrast enhancement according to a conventional method.

FIG. 10B is a diagram illustrating before and after contrast enhancement according to the present invention, and is a graph illustrating the same image signal as FIG. 10A.

11A is a graph illustrating an overshooting problem in image signals before and after contrast enhancement according to a conventional method.

FIG. 11B is a diagram illustrating before and after contrast enhancement according to the present invention, and is a graph showing the same image signal as FIG. 11A.

12 is a flowchart illustrating a local contrast enhancement method for an image signal according to an embodiment of the present invention.

Claims (15)

As a method of local contrast enhancement on an image signal for image quality enhancement in tone mapping applications in a dynamic backlight control system: Determining a degree of local contrast increment for the image signal to compensate for degradation due to tone mapping; Obtaining a profile signal based on a weighted sum average of the image signals and a weighted sum average of absolute changes of the image signals; And Applying local shading to the luminance level of the image signal when the profile signal is greater than the image signal, The local shading is proportional to the degree of local contrast increment and to the difference between the image signal and the profile signal. How to enhance local contrast. The method of claim 1, The profile signal obtaining step further includes summing a weighted sum average of a plurality of neighboring pixels and a weighted sum average of an absolute change of the plurality of neighboring pixels. How to enhance local contrast. The method of claim 1, Selecting the strongest signal among the color components of the image signal as a primary representative image signal for obtaining the profile signal; If the profile signal is greater than the image signal, applying local shading to the primary representative image signal to produce a shaded image signal, wherein the local shading is at a degree of the local contrast increment and the primary representative image Applying local shading, proportional to the difference between the signal and the profile signal; And Scaling a color component of the primary representative image signal by a ratio of the shaded image signal to the primary representative image signal to achieve local contrast enhancement of the image signal; How to enhance local contrast. The method of claim 3, wherein The color components of the image signal are determined according to a color model selected from the group consisting of RGB, CMYK, HSV, HSL, YUV and YIQ. How to enhance local contrast. The method of claim 1, The local contrast enhancement is applied to dynamic backlight control for LCD applications to minimize signal degradation or signal saturation. How to enhance local contrast. The method of claim 1, Acquiring the profile signal As the profile signal

Calculating a; Where P (n) is the image signal at position n; D (n) is the absolute difference between the values of the neighboring pixel at position n and position n + 1 and is represented by D (n) = | P (n + 1) -P (n) | 2w + 1 is the magnitude of the weighted sum filters; And w ₁ , w ₂ are the weighting coefficients of each weighted sum filter How to enhance local contrast. The method of claim 1, Applying the local shading comprises calculating P-α (Pc-P) C (P) as a shaded image when Pc is greater than P; And determining P as a shaded image when Pc is not greater than P, Where P is an image signal; Pc is the profile signal of the image signal; C (P) is the contrast shading for P to compensate for tone-mapping; And α is the degree of contrast effect How to enhance local contrast. The method of claim 1, Scaling the color components comprises calculating I '= I (P' / P); Wherein I is the color component; I 'is the scaled color component of I; P is an image signal; And P 'is the shaded image signal of P How to enhance local contrast. As a local contrast enhancement device for image signals for enhancing image quality in tone mapping applications in dynamic backlight control systems: A first filter for generating a weighted sum of the image signal over a plurality of neighboring pixels in the image; A second filter for generating a weighted sum of absolute differences of the image signals over a plurality of neighboring pixels; An adder for generating a profile signal by adding outputs from the first filter and the second filter; And A processor for applying local shading to the luminance level of the image signal when the profile signal is greater than the image signal, The local shading is proportional to the degree of local contrast increment and to the difference between the image signal and the profile signal. Local Contrast Enhancer. The method of claim 9, A multiplexer for selecting the strongest of the color components of the image signal as the primary representative image signal; A processor for applying local shading to the primary representative image signal to produce a shaded image signal when the profile signal is greater than the image signal, the local shading being at a predetermined degree of local contrast increments. And a processor for applying local shading, proportional to the difference between the primary representative image signal and the profile signal; And Further comprising a multiplier for scaling color components of said primary representative image signal by a ratio of said shaded image signal to said primary representative image signal to achieve local contrast enhancement of said image signal. Local Contrast Enhancer. The method of claim 10, A reference table for storing a predetermined degree of local contrast increment corresponding to the level of the image signal, The predetermined degree of local contrast increment compensates for the degradation due to tone-mapping. Local Contrast Enhancer. The method of claim 10, It further includes a plurality of reference tables corresponding to different levels of dynamic backlight control for LCD applications. Local Contrast Enhancer. The method of claim 9, The first filter is

Calculate; The second filter is

Calculate; The adder is

Is calculated as the profile signal; Where P (n) is the image signal at position n; D (n) is the absolute difference between the values of the neighboring pixel at position n and position n + 1 and is represented by D (n) = | P (n + 1) -P (n) | 2w + 1 is the size of the first filter and the second filter; w ₁ Is a weighting coefficient of the first filter; And w ₂ Is a weighting factor of the second filter Local Contrast Enhancer. The method of claim 9, The processor calculates P-α (Pc-P) C (P) as a shaded image when Pc is greater than P; And determines P as a shaded image when Pc is not greater than P; Where P is an image signal; Pc is the profile signal of the image signal; C (P) is the contrast shading for P to compensate for tone-mapping; And α is the degree of contrast effect Local Contrast Enhancer. The method of claim 9, The multiplier calculates I '= I (P' / P); Wherein I is the color component; I 'is the scaled color component of I; P is an image signal; And P 'is the shaded image signal of P Local Contrast Enhancer.

Images