Method for adjusting liquid crystal display device backlight lightness and contrast

A technology for liquid crystal display and backlight brightness, which is applied in static indicators, instruments, optics, etc. It can solve problems such as LCD TV backlight and contrast cannot be adjusted, and achieve the effects of increasing layering, prolonging service life, and reducing power consumption

Active Publication Date: 2008-12-17
SHENZHEN TCL NEW-TECH CO LTD
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AI-Extracted Technical Summary

Problems solved by technology

[0004] The purpose of the present invention is to provide a method for adjusting the brightness and contrast of the backlight of a liquid crystal disp...
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Abstract

The invention provides a method for adjusting the brightness of the backlight and the contrast of an LCD. The method comprises the steps as follows: 1. calculating the brightness distribution ratio of the pixels of an image; 2. calculating the parameters of the contrast coefficient and the brightness distribution uniformity according to the brightness distribution ratio, and calculating the backlight coefficient according to the contrast coefficient and the brightness distribution uniformity; and 3. controlling the backlight of the LCD display according to the backlight control ratio and calculating the contrast of images according to the contrast ratio. By adopting the technical proposal provided by the invention, a backlight strip lamp does not keep the constant brightness; instead, the brightness of the strip lamp varies dynamically with the brightness of the image displayed. The power consumption of the strip lamp is reduced more efficiently, and the service life of the strip lamp is improved. In addition, the image contrast is not a constant which is adjusted artificially; instead, the image contrast can be adjusted dynamically with the brightness of the images so as to show the details of the images better, and improve the hierarchy of the images.

Application Domain

Static indicating devicesNon-linear optics

Technology Topic

Image contrastLiquid-crystal display +7

Image

  • Method for adjusting liquid crystal display device backlight lightness and contrast
  • Method for adjusting liquid crystal display device backlight lightness and contrast
  • Method for adjusting liquid crystal display device backlight lightness and contrast

Examples

  • Experimental program(1)

Example Embodiment

[0026] The technical solution provided by the present invention is: first calculate the brightness distribution ratio of a frame image, then transmit the obtained brightness distribution ratio data to the microprocessor MCU of the display device, perform predetermined calculations, and then provide the backlight coefficient and Contrast factor for backlight and control of contrast and gamma curves:
[0027] 1. Backlight control: Calculate the backlight coefficient according to the uniformity of the image brightness distribution. When the image brightness distribution is not When uniform, the calculated backlight coefficient is larger, and the brightness of the backlight is adjusted accordingly according to the calculated backlight coefficient;
[0028] 2. Contrast control: The calculation of the contrast coefficient is based on the proportion of high-brightness and low-brightness image content. In principle, it is necessary to ensure that all the brightness signals occupy the gray level that the LCD screen can display A certain space to ensure no overflow) but not overflow, that is, the overall contrast of the image is placed at the highest under the premise of ensuring that the image is not distorted;
[0029] When controlling the contrast of the image, it can be controlled through the gamma curve: according to the distribution of brightness, the contrast of more details is increased and the contrast of less details is reduced to highlight the details.
[0030] In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.
[0031] The technical solution process provided by the embodiment of the present invention is as follows: figure 1 Shown, specifically include the following steps:
[0032] 1. Calculate the brightness distribution ratio and brightness distribution uniformity parameters of each pixel in a frame of image;
[0033] First of all, the brightness of a frame of image can be represented by 0 to 255 gray levels. In the embodiment of the present invention, these 256 levels are divided into 16 equal parts, hereinafter referred to as each equal group, represented by B1 to B16 respectively , each equal part contains 16 gray levels, as follows: B1 includes 0~15 gray levels, B2 includes 16~31 gray levels, B332~47 gray levels, B4 includes 48~63 gray levels, B5 includes 64~79 gray levels, B6 includes 80~95 gray levels, B7 includes 96~111 gray levels, B8 includes 112~127 gray levels, B9 includes 128~143 gray levels, B10 includes 144~159 gray levels B11 includes 160~175 gray levels, B12 includes 176~191 gray levels, B13 includes 192~207 gray levels, B14 includes 208~223 gray levels, B15 includes 224~239 gray levels, B16 includes 240 gray levels ~255 gray levels.
[0034] see figure 2 , where B n A total of 16 groups (brightness intervals) corresponding to the above-mentioned B1~B16, C n is the gray value corresponding to each brightness interval, D n is the proportion of each gray level in the whole image, E n is C n with D n the product of F n for D n squared. And define the parameters as follows:
[0035] Scale root mean square: j = D 1 2 + D 2 2 + · · · + D 16 2 = F 1 + F 2 + · · · + F 16 , It is used to reflect the uniformity parameter of image brightness distribution;
[0036] 2. Calculate the backlight coefficient and the contrast coefficient according to the brightness distribution ratio calculated in step 1 and the uniformity parameter of the brightness distribution;
[0037] Preset constants: J=75, K=0.25, L=5, (experimentally measured, the constants can be set reasonably according to the actual adjustment effect)
[0038] Maximum brightness level mh: Σ n = mh 16 E n ≤ L (mh≥10), mh (reflects the level of the highest brightness)
[0039] Minimum brightness level ml: Σ n = 0 ml E n ≤ L (ml≤6), ml (response to the level of the lowest brightness)
[0040] Thus, calculate
[0041] (1) Backlight factor: b = K j × c , (where c is the contrast coefficient, and b takes ≤1) to adjust the backlight by using the uniformity of image brightness distribution. When the image brightness distribution is uneven, the value of j is larger, then the backlight coefficient is correspondingly smaller, and the brightness of the backlight can be adjusted down; When the brightness distribution of the image is more uniform, the j value is smaller, so the backlight coefficient is larger, and the backlight brightness is adjusted accordingly.
[0042] (2) Contrast ratio: c = 16 mh - ml , The contrast coefficient is affected by the highest brightness level and the lowest brightness level, that is, by the brightness distribution. When the entire screen is dominated by dark and bright screens, the mh-ml value is larger and the contrast coefficient is smaller to ensure high brightness. The signal does not overflow; when the picture is dominated by intermediate brightness, the mh-ml value is small and the contrast coefficient is large, which greatly improves the image contrast. Before the brightness signal is multiplied by the contrast coefficient, it is necessary to subtract Cml from the brightness of the current image.
[0043] 3. Adjust the backlight brightness according to the backlight coefficient; adjust the contrast according to the contrast coefficient; adjust the gamma curve according to the brightness distribution ratio.
[0044] see image 3 , the following is mainly low-brightness and uneven brightness distribution for analysis:
[0045] From the brightness distribution diagram, we can see that most of the picture is dark, and the bright part only accounts for a very small proportion.
[0046] Backlight processing: In this case, the brightness of the image is uneven, the variables j and c are relatively large, and the backlight coefficient b = K j × c Smaller, puts the backlight at a lower brightness.
[0047] Contrast processing: Calculate the sum of the brightness En of the high brightness level and the low brightness level to be equal to the brightness level Bmh and Bml of L, take the values ​​of mh and ml, and take the contrast coefficient c = 16 mh - ml . like image 3 As shown, the highest brightness is less than 5, then mh<16, that is, mh-ml<16, c>1, the contrast is improved, and the brightness distribution of the image after contrast processing is as follows image 3 shown.
[0048] Gamma curve: According to Gn=J×Dn, the contrast of the part with a small proportion of brightness (highlight part) is reduced, and the contrast of a part with a large proportion is increased, that is, the slope of the low-brightness part is increased, so that the brightness of the dark part of the picture is increased. Enhanced, increased contrast and details become clear. Although the contrast of the highlighted part at this time is reduced and some details are sacrificed, but because this part accounts for a small proportion of the entire screen, it can almost be ignored, so this is suitable for the viewing effect of the overall screen.
[0049] For a picture dominated by mid-brightness and high-brightness, the adjustment method is similar to the above situation, such as Figure 4 , Figure 5 shown.
[0050] From the above example, we can see that the algorithm is to dynamically detect the brightness distribution of each picture. When the picture is detected as a dark picture, the dark picture will be brightened and the brightness of the backlight will be reduced; When in master mode, expand the brightness downwards, increase the contrast of the highlighted part, reduce the brightness of the backlight, and make it easier to reproduce the brightness details of the highlighted picture; when the mid-bright part of the picture is in the majority, increase the contrast of the mid-bright part , to enhance the sense of depth of the entire screen and reduce the brightness of the backlight. When the brightness distribution is uniform, that is, when the brightness ratio of each level is close to 6.25%, the backlight coefficient b is the largest, and its value is 1, and the brightness of the backlight lamp is the highest.
[0051] The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

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