KR20120055895A - Image quality enhancement method and display device using the same - Google Patents

Abstract

PURPOSE: An image quality improvement method and a display device using the same are provided to modulate input image data by successively performing a white expansion process, a transfer curve expansion process of all gradation regions, and a black extension process, thereby improving brightness and contrast ratio. CONSTITUTION: A white expansion part(10) comprises a white area histogram analysis part(14) and a statistical analysis part(12). The white expansion part comprises a white area curve generating part(16) and a curve mapping part(18). The white area histogram analysis part calculates a histogram with respect to input image brightness information. The white area histogram analysis part counts the number of pixel data with respect to upper gradation regions of the histogram. The statistical analysis part calculates statistical information such as an average image level, a dispersion value, and maximum and minimum values of the brightness information. The white area curve generating part generates a white expansion transmission curve.

Description

IMAGE QUALITY ENHANCEMENT METHOD AND DISPLAY DEVICE USING THE SAME}

The present invention relates to a method of improving image quality by correcting input image data with a preset algorithm and a display device using the same.

Various flat panel displays (hereinafter referred to as "FPDs") that can reduce weight and volume, which are disadvantages of cathode ray tubes, have been developed. The flat panel display device is an electroluminescent device implemented as a liquid crystal display (LCD), a plasma display panel (PDP), an inorganic electroluminescent device or an organic light emitting diode device (OLED). Electroluminescence Device (EL), Field Emission Display (FED) and Electrophoresis Display (EPD). Such flat panel display devices have improved image quality over cathode ray tubes due to process technology and driving technology.

In order to increase the image quality of the display device, various image quality improvement algorithms have been proposed. As an example, US 7,102 697 discloses an algorithm for contrast enhancement of digital images. This image quality improvement algorithm is an algorithm related to the global contrast enhancement method, which generates a luminance trasfer curve through histogram analysis of the previous frame, and corrects the contrast by correcting the current frame image data with the curve. do. However, since this method generates one luminance transfer curve for each frame and applies it to the current frame image, the contrast ratio of the image can be increased, but the proposed luminance transfer curve includes information that can express the detail of the image. There is a problem that the detail of the image is damaged because it is not.

The present invention provides a method of improving image quality and a display device using the same, which can enhance brightness and contrast ratios, and can express details of an image better.

The image quality improving method of the present invention obtains a white extension transfer curve including an upper gradation region of an input image, and maps the input image luminance information to the white extension transfer curve according to an average image level of the input image to perform primary modulation. Generating luminance information of; Compute histograms of all gray areas based on luminance information of the first modulated image, obtain transfer curves of all gray areas through histogram equalization and transfer curve refinement, and transmit the first modulation to the transfer curves of all gray areas. Mapping the adjusted luminance information to generate second-modulated luminance information; And obtaining a black extension transfer curve including a lower gray level region of the second modulated image, and mapping the second modulated luminance information to the black extension transfer curve according to the average image level of the input image. Generating luminance information of < RTI ID = 0.0 >

The display device of the present invention comprises a display panel; A display panel driver circuit for displaying video data on the display panel; And a scaler configured to adjust the brightness and the contrast ratio of the input image to the display panel driver circuit based on the image quality improving method.

The present invention modulates the data of the input image in the order of white extension, transmission curve expansion of all gradation regions, and black extension in order to increase luminance and contrast ratio and to better express the detail of the image.

1 is a block diagram illustrating an image quality improvement circuit according to an exemplary embodiment of the present invention.
FIG. 2 is a diagram illustrating an operation of the white region histogram analyzer illustrated in FIG. 1.
FIG. 3 is a diagram illustrating an operation of the white region curve generator shown in FIG. 1.
FIG. 4 is a diagram illustrating in detail all gray area curve generating units shown in FIG. 1.
5 is a diagram illustrating a transfer curve refinement.
6 is a diagram showing an example of adjusting the slope of the transfer curve refinement.
FIG. 7 is a diagram illustrating a histogram analysis result and a black extended transfer curve of the black region illustrated in FIG. 1.
8 is a block diagram illustrating a display device according to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Like numbers refer to like elements throughout. In the following description, when it is determined that a detailed description of known functions or configurations related to the present invention may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

Referring to FIG. 1, the image quality improvement circuit 100 of the present invention includes a white expander 10, a histogram-based extender 20, and a black extender 30.

RGB (red-cyan) data of the input image may be separated into luminance information (Y) and color difference (CbCr) information as shown in Equation (1). The luminance information Y of the input image is input to the white extension 10.

The white extension unit 10 includes a white region histogram analyzer 14, a statistical analyzer 12, a white region curve generator 16, and a curve mapping unit 18.

The white area histogram analyzer 14 calculates a histogram of the input image luminance information Y of one frame and counts the number of pixel data for predetermined higher gray areas (or white gray areas) in the histogram. do. For example, the white area histogram analyzer 14 may count the number of pixel data included between W_X1 and W_X2 in the histogram of FIG. 2. W_X1 and W_X2 may be preset in the white region histogram analyzer 14 and adjusted according to the user's preferred image quality.

The statistical analysis unit 12 calculates an average picture level (APL), a maximum value (max value) of the luminance information (Y), and luminance information (Y) from one frame of input image luminance information (Y). Statistical information, such as a min value and a variance, is calculated. The average image level APL may be calculated by dividing the total sum of the luminance information Y by the number of pixels.

The white region curve generator 16 receives luminance information Y of the upper gray scale regions input from the white region histogram analyzer 14 and statistical information input from the statistical analyzer 12 and receives the luminance information. Based on the (Y) and the statistical information, a white extension transfer curve is generated to improve the brightness and contrast of the white tone. For example, the white region curve generator 16 may generate a white extension transfer curve as shown in FIG. 3.

The white-expanded transfer curve of FIG. 3 is a line between the intersection where W_X0 and W_Y0 meet and the line between W_X1 and W_Y1 meet with a straight line having a first slope S1 and the intersection where W_X2 and W_Y2 meet from the intersection where W_X1 and W_Y1 meet. It includes a straight line with two slopes (S2). In FIG. 3, the x-axis is luminance information Y of the input image, and the y-axis is first-modulated luminance information Y 'having improved contrast and luminance of an upper gray level region (or white gray region) in the input image. In FIG. 3, W_X0 is a lower gray level value preset in the white region curve generation unit 16. W_Y0 is set in advance as the primary modulated luminance information value Y 'which meets W_XO. W_X0 may be set to the minimum value of the input image luminance information Y in the histogram and may be adjusted according to the user's preferred image. The slope from the origin to the intersection of W_X0 and W_Y0 may be set to one.

The white region curve generator 16 may set the straight line of the first slope S1 to a slope greater than 1 as shown in FIG. 3. The white region curve generation unit 16 may adjust W_Y1 that meets W_X2 according to an average image level APL, and set W_Y2 that meets W_X2 as the maximum value of the input image luminance information Y. For example, the white area curve generation unit 16 increases the brightness of the white gray area by lowering the second slope S2 by increasing W_Y1 as the average image level APL is lower. The white area curve generation unit 16 increases the contrast ratio of the white gray area by increasing the second slope S2 by lowering W_Y1 as the average image level APL is higher. Therefore, the linear upper limit value W_Y1 of the first slope S1 and the average image level APL of the input image are in inverse proportion.

The curve mapping unit 18 maps the input image luminance information Y to the white extension transfer curve input from the white region curve generation unit 16 and outputs the first modulated luminance information Y '. The first modulated luminance information Y 'has a higher luminance and contrast ratio in the white gradation region than the input image luminance information Y.

In the image quality improving method of the present invention, the white extension 10 is disposed in front of the histogram-based extension 20 and the black extension 30 to increase the brightness while increasing the contrast ratio of the image reproduced in the display device. If the white extension algorithm is applied after adjusting the transmission curves of all the gradation regions, there is a limitation in increasing the luminance of the white gradations due to the slope constraint of the transmission curve previously determined.

The histogram-based expansion unit 20 receives luminance information Y 'having improved luminance and contrast ratio in the white gray area through the white expansion unit 10. The histogram-based extension unit 20 calculates histograms for all gray areas of the luminance information Y 'input from the white extension unit 10, and histogram equalization and transfer curves according to the distribution of the histograms of all the gray area areas. Perform a transfer curve refinement. The histogram-based extension unit 20 obtains the transfer curves of all the gradation regions, generates the second-modulated luminance information Y ″ by mapping the first-modulated luminance information Y ′ to the transfer curve.

The histogram-based extension unit 20 includes all gray area histogram analyzer 24, statistical analyzer 22, all gray area curve generator 26, and curve mapping unit 28.

All gradation area histogram analyzer 24 calculates histograms in all gradation areas with respect to one frame of first-modulated luminance information Y '. The statistical analysis unit 22 calculates the average image level APL, the maximum value of the luminance information Y ', the minimum value of the luminance information Y', the variance value, etc. from the histogram of the first modulated luminance information Y '. Calculate statistical information.

All gradation region curve generators 26 perform histogram equalization and transfer curve refinement according to the histogram distribution of the first modulated luminance information Y 'to obtain transfer curves in all gradation regions. All gradation region curve generation sections 26 include a histogram equalization processing section 42 and a transfer curve refinement processing section 44 as shown in FIG.

The histogram equalization processing section 42 performs histogram equalization input from all the gradation region histogram analysis sections 24. The histogram equalization is as in Equation 2.

Here, n and i are positive integers, and N is the number of histogram bins. Slope (n) means the slope of the n th value of the histogram. A histogram bin can be expressed as a "gradation storage". If there are 16 histogram bins, there are 16 bins for each section. For example, if there are 16 histogram bins in 0 ~ 1023 10bit space, the values of 0 ~ 63 can be stored in histogram bin 1, and the values of 64 ~ 127 can be stored in histogram bin 2. The histogram equalization method obtained by dividing the histogram into three sections of the lower gray level region, the middle gray level region, and the upper gray level region may be expressed as tri-histogram equalization below.

However, N = N ₁ + N ₂ + N ₃ , and n is a value between 1 and N.

The transfer curve output through the histogram equalization processor 42 may improve the image quality to an appropriate level when the histogram is widely distributed in the form of a Gaussian distribution. In the transfer curve output through the histogram equalization processor 42, the contrast ratio is excessively increased when the pixel data are excessively concentrated in some gray levels of the histogram. The transfer curve refinement processing unit 44 refines the slope of the transfer curve when excessively increasing the contrast ratio of the specific gradation portion in the transfer curve input from the histogram equalization processing unit 42. To this end, the transfer curve refinement processor 44 restricts the slope of the transfer curve within a preset minimum slope and maximum slope and adjusts the slopes of the lower gray level region, the middle gray region, and the upper gray scale region according to the pixel data distribution amount. . For example, when the slope of the transfer curve suddenly changes as shown in the left side of FIG. 6, the transfer curve refinement processor 44 may incline the slopes of the grayscale regions within a preset minimum slope and the maximum slope as shown in the center of FIG. 6. Reduce In addition, the transfer curve refinement processor 44 adjusts the slope of the slope S61 of the lower gray scale region, the slope S62 of the middle gray scale region, and the slope S63 of the upper gray scale region in the same manner as in Equation 3 below.

Here, Slope _S61 ′ is an adjustment value of the slope _S61 of the lower gradation region, Slope _S62 ′ is an adjustment value of the slope _S62 of the middle gradation region, and Slope _S63 ′ is an adjustment value of the slope _S63 of the upper gradation region. Means each. Slope _S61 is the slope _S61 of the lower gradation region in the transfer curve inputted to the transfer curve refinement processor 44 through the histogram equalization process, and Slope _S62 is input to the transfer curve refinement processor 44 through the histogram equalization process. The slope S62 and the slope _S63 of the intermediate gradation region in the transfer curve mean the slope S63 of the upper gradation region in the transfer curve input to the transfer curve refinement processor 44 through a histogram equalization process. α is determined as a value of -1 <α <1 according to the distribution of the lower gradations of the histogram, and β is determined as a value of -1 <β <1 according to the distribution of the upper gradations of the histogram.

The curve mapping unit 28 maps the first-modulated luminance information Y 'to the transfer curves input from all the gradation region curve generating units 26 and outputs the second-modulated luminance information Y ″.

Through this process, the histogram-based extension unit 20 excessively increases the contrast ratio when the transfer curve of the first modulated luminance information Y ′ input from the white extension unit 10 is based on the histogram statistical information. Second modulated luminance information Y &quot;

The white gradation and histogram-based expansion process improves the detail of dark areas while the image is bright. However, since the contrast ratio that the user feels with the naked eye in this process is not very high, the present invention further adjusts the slope of the transmission curve of the lower gray scale (black gray scale) with respect to the image which has undergone the white gray scale expansion and the histogram-based scaling process.

The black extension unit 30 includes a black region histogram analyzer 34, a statistical analyzer 32, a black region curve generator 36, and a curve mapping unit 38.

The black region histogram analyzer 34 calculates a histogram for one frame of the second modulated luminance information Y ″, and pixel data of predetermined lower gray level regions (or black gray region regions) in the histogram. For example, the black region histogram analyzer 34 may count the number of pixel data included between B_X1 and B_X2 in the histogram of Fig. 7. B_X1 and B_X2 are the black region histogram analyzer 34. ) May be preset and adjusted according to a user's preferred image quality B_X1 may be selected as the minimum value of the second modulated luminance information Y ″.

The statistical analysis unit 32 calculates the average image level APL, the maximum value of the luminance information Y ″, the minimum value of the luminance information Y ″, and the variance from the second frame-modulated luminance information Y ″. Calculate statistical information such as values.

The black region curve generator 36 receives the luminance information Y ″ of the lower gray scale regions input from the black region histogram analyzer 34 and the statistical information input from the statistical analyzer 32, and the luminance information thereof. A black extension transfer curve is generated to improve the brightness and contrast of the black gradation based on the Y 'and statistical information. For example, the black region curve generator 36 may generate a black extension transfer curve as shown in FIG. 7.

The black extended transfer curve of FIG. 7 is a straight line that rises from B_X1 to an intersection where BX2 and B_Y2 meet at a third slope S3 and a fourth slope S4 from an intersection where B_X2 and B_Y2 meets to an intersection where B_X3 and B_Y3 meet. It includes a straight line that rises. In Fig. 7, the x-axis is the secondary-modulated luminance information Y " and the y-axis is the luminance information Y " 'after black expansion. In FIG. 4, B_X1 is a lower gray level value preset in the black region curve generation unit 36. B_X1 may be determined as the minimum value in the histogram of the secondary modulated luminance information Y ″. B_X2 is a lower gray level value preset in the black region curve generation unit 36 and may be determined as a value larger than B_X1 and smaller than B_X3. Therefore, the linear upper limit value B_X3 of the fourth slope S4 is proportional to the average image level APL of the second modulated luminance information and meets the third upper limit value B_X2 of the third slope S3. The luminance information value B_Y2 of the modulated image is proportional to the average image level APL of the secondary modulated luminance information.

The black region curve generation unit 36 may adjust the third and fourth slopes S3 and S4 according to the average image level APL of the secondary modulated luminance information Y ″. The curve generator 36 adjusts the value of B_X3 higher as the average image level APL of the secondary modulated luminance information Y "is higher, and averages the average image level of the secondary modulated luminance information Y" ( The lower the APL), the lower the value of B_X3. Further, the black area curve generation unit 36 decreases the value of B_Y2 as the average image level APL of the secondary modulated luminance information Y ″ is higher. The lower the average image level APL of the secondary modulated luminance information Y ″, the higher the value of B_Y2 can be adjusted.

The curve mapping unit 38 maps the second-modulated luminance information Y ″ to the black extension transfer curve input from the black region curve generation unit 36 to output the third-modulated luminance information Y ″ ′. .

Finally, the image quality improvement circuit 100 may inversely convert the third-order modulated luminance information Y ″ ′ into RGB data R′G′B ′ as shown in Equation 4. FIG.

8 shows a display device according to an embodiment of the present invention.

Referring to FIG. 8, the display device of the present invention includes a display panel 110, a display panel driving circuit, and a host system 200.

The display panel 110 is implemented by any one of a liquid crystal display (LCD), a plasma display panel (PDP), an electroluminescent device (EL), a field emission display (FED), and an electrophoretic display (EPD). Can be. The display panel 100 crosses the data lines D1 to Dm to which the data voltage is applied and the scan lines G1 to which the scan pulse (or gate pulse) is sequentially applied to the data lines D1 to Dm. Gn), and pixels arranged in a matrix form.

The display panel driver circuit includes a data driver circuit 102, a scan driver circuit 104, and a timing controller 106. The data driving circuit 102 latches the digital video data R'G'B 'input from the timing controller 106. The data driving circuit 102 converts the digital video data R'G'B 'into a gamma compensation voltage to generate a data voltage to be charged in the pixels. The data voltage output from the data driving circuit 102 is supplied to the data lines D1 to Dm. The scan driving circuit 104 sequentially supplies scan pulses synchronized with the data voltages to the scan lines G1 to Gn. The timing controller 106 supplies the digital video data R'G'B 'of the input image input from the host system 200 to the data driving circuit 102. The timing controller 106 receives timing signals such as a vertical synchronization signal Vsync, a horizontal synchronization signal Hsync, a data enable signal Data Enable, DE, and a dot clock CLK input from the host system 200. By using the timing control signals (SDC, GDC) for controlling the operation timing of the data driving circuit 102 and the scan driving circuit 104 is generated.

The host system 200 includes a system on chip (hereinafter referred to as "SoC") including a scaler. The scaler uses the image quality improvement circuit 100 to brighten the brightness of the input image, improve the contrast ratio, and convert the resolution of the input image to match the resolution of the display panel 110. The host system 200 includes the vertical sync signal Vsync, the horizontal sync signal Hsync, the data enable signal Data Enable, and the dot clock CLK together with the data R'G'B 'output from the scaler. And a timing signal such as e.g.).

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be defined by the claims.

10: white extension 20: histogram-based extension
30: black extension

Claims (8)

(a) obtaining a white extension transfer curve including an upper gradation region of an input image, mapping the input image luminance information to the white extension transfer curve according to an average image level of the input image, and obtaining luminance information of a first modulated image; Generating;
(b) calculate a histogram of all gray areas based on luminance information of the first modulated image, obtain transfer curves of all gray areas through histogram equalization and transfer curve refinement, and transfer the curves to the transfer curves of all gray areas. Mapping the first modulated luminance information to generate second modulated luminance information; And
(c) obtaining a black extension transfer curve including a lower gradation region of the second modulated image, mapping the second modulated luminance information to the black extension transfer curve according to an average image level of the input image, and performing third modulation; And generating luminance information of the captured image. The method of claim 1,
Before the step (a), extracting the luminance information and the color difference information from the RGB data of the input image; And
And inversely converting luminance information of the third-order modulated image into RGB data after the step (c). The method of claim 1,
In step (a),
Calculating a histogram including upper gray levels of the input image;
Calculating the average image level from luminance information of the input image;
Adjusting a slope of the white extension transfer curve according to the average image level of the input image; And
And mapping luminance information of the input image to the white extension transfer curve to generate luminance information of the first modulated image. The method of claim 3, wherein
Adjusting the slope of the white extended transfer curve according to the average image level of the input image,
Setting a first slope of a straight line rising in the upper grayscale region to a value greater than 1;
Adjusting a second slope of a straight line that rises from the upper limit of the straight line of the first slope to the maximum value of the input image in the upper grayscale region according to the average image level of the input image,
And a linear upper limit value of the first slope and an average image level of the input image are inversely related to each other. The method of claim 3, wherein
The step (b)
Calculating a histogram in all gray level regions with respect to the first modulated luminance information;
Calculating an average image level from the histogram of the first modulated luminance information;
Performing a histogram equalization and a transfer curve refinement according to the histogram distribution of the first modulated luminance information to adjust a preset minimum slope and a slope of the transfer curves of all the gray scale regions within the preset maximum slope; And
And generating luminance information of the second modulated image by mapping luminance information of the input image to transfer curves of all the gray scale regions. The method of claim 5, wherein
In step (c),
Calculating a histogram including lower gray level regions of the second modulated luminance information;
Calculating an average image level from the histogram of the secondary modulated luminance information;
Adjusting a slope of the black extension transmission curve according to an average image level of the second modulated luminance information; And
And mapping luminance information of the secondary modulated image to the black extension transfer curve to generate luminance information of the secondary modulated image. The method according to claim 6,
Adjusting the slope of the black expansion transmission curve according to the average image level of the second modulated luminance information,
Adjusting a third slope of a straight line rising in the lower gradation region and a fourth slope of a straight line rising from an upper limit of the straight line of the third slope according to an average image level of the second modulated luminance information; ,
The linear upper limit value of the fourth slope is proportional to the average image level of the secondary modulated luminance information, and the luminance information value of the third modulated image that meets the linear upper limit value of the third slope is the second modulated luminance. And a proportional relationship with the average image level of the information. Display panel;
A display panel driver circuit for displaying video data on the display panel; And
A scaler for adjusting a brightness and contrast ratio of an input image to supply the display panel driver circuit;
The scaler is,
Obtaining a white extended transfer curve including an upper gray level region of an input image, mapping the input image luminance information to the white extended transfer curve according to an average image level of the input image, and generating luminance information of a first modulated image;
Compute histograms of all gray areas based on luminance information of the first modulated image, obtain transfer curves of all gray areas through histogram equalization and transfer curve refinement, and transmit the first modulation to the transfer curves of all gray areas. Mapping the generated luminance information to generate the second modulated luminance information,
Obtaining the black extended transfer curve including the lower gradation region of the second modulated image, mapping the second modulated luminance information to the black extended transfer curve according to the average image level of the input image, A display device characterized by generating luminance information.

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