CN101568955B - Method of determining luminance values for a backlight of an LCD panel displaying an image - Google Patents

Abstract

A controller for a backlight for a LCD panel has at least two methods for determining an illumination value for the backlight. The controller selects between the two methods based on properties of the image being displayed. The properties of the image include its color and its intensity. Based on the colors and the brightness properties of a plurality of image pixels, a method is selected from a first method and a second method to determine the backlight colors and the brightness of the LCD panel of the image being displayed. The first method to determine an illumination value is based on luma values of pixels in the image block and the second method to determine an illumination value is based on red, green and blue color component values of pixels in the image block.

Description

Confirm backlight color and the method for brightness of the LCD panel of a display image

Technical field

The present invention relates to a kind of backlight color and the method for brightness of LCD panel of definite display image.The present invention also relates to a back light apparatus, be used to provide the LCD panel of giving a display video image backlight, confirm backlight color and brightness value according to video image according to this method.

Background technology

LCD (LCD) panel is not a light emitting device.Be applied to the transmittance that voltage on the LCD panel can change liquid crystal cell in the panel (pixel).The LCD panel can be reflective, thereby the image that on panel, produces can be watched through reflection of ambient light.But, also inapplicable to the LCD panel of large scale or high-contrast.

In the time of in being used for such as TV, graphoscope and hand-hold electronic equipments application, the LCD panel is from behind backlight and illuminated.In great majority were used, backlight was an even and constant light output, and the variation on the luminance of display images is to control through the transmittance that changes liquid crystal cell in the display pannel.In order in higher ambient light, to produce good visuality, backlight must have a higher brightness or intensity rank.Many shortcomings are arranged in this respect, comprise that high energy consumption is overheated with generation.Another shortcoming of constant backlight is its limited dynamic contrast that causes LCD display, light leak (light leakage) occurs because when pixel is in dark or closed condition, pass the meeting backlight of LCD panel.Light leak causes than dark areas a grey performance being arranged, rather than the performance of a complete black.

A kind of technology that is intended to improve the dynamic range of LCD display is the luminance dynamic ground adjustment entire backlight brightness according to video image.If image is relative higher brightness, backlight control is moved light source on higher brightness so.If dark images dims output backlight so to reduce light leak, make the image deepening.An advantage of this backlight technology is to reduce energy consumption backlight.Although this technology can be improved the LCD contrast range, and save energy consumption backlight a little, it possibly cause image fault, and causes the brightness of image fluctuation.

Summary of the invention

So, the purpose of this invention is to provide a back light apparatus and be used to provide backlightly to panel of LCD and a kind of method of controlling panel of LCD backlight color and brightness, it can overcome or alleviate the problems referred to above.

Disclosed a kind of backlight color and the method for brightness of LCD panel of definite display image at this, the surround that comprises that a plurality of independences are controlled backlight, nominally and image be divided into a plurality of image blocks; The corresponding back lighting district of each image block; Image block comprises that a plurality of image slices have pixel color and brightness, and if the backlight color and the brightness of each surround of the LCD panel of confirming display image based on the pixel color and the brightness of said a plurality of image pixels are the pixel of light color and high brightness in the image block; Be that color value is lower than the pixel that first threshold and brightness value are higher than second threshold value; Its number exceeds the 3rd threshold value, then uses the Y-peak method to confirm backlight color and brightness, does not then use the RGB Mean Method to confirm backlight color and brightness if exceed the 3rd threshold value; Wherein color value is lower than first threshold; Pixel is classified into light color, and brightness value is higher than second threshold value, and pixel is had high brightness by classification.

In a preferred embodiment of the present invention, confirm that the first method of illumination value is based on the luma value of image block interior pixel, and confirm that the second method of illumination value is based on redness, green and the blue color value of image block interior pixel.

A back light apparatus is used to provide the LCD panel to a display video image backlight, and it confirms backlight color and brightness according to aforesaid method.

A kind of method backlight of controlling the LCD panel of display video image; Video image comprises a plurality of picture frames; Controller has at least, and Y-peak method and RGB Mean Method are used for confirming the back lighting value; Wherein this method comprises: the characteristic based on picture frame is selected between Y-peak method and RGB Mean Method

The surround that comprises that a plurality of independences are controlled wherein backlight, nominally and picture frame be divided into a plurality of image blocks, the corresponding back lighting district of each image block; Image block comprises that a plurality of image slices have pixel color and brightness, and if the backlight color and the brightness of each surround of the LCD panel of confirming display image based on the pixel color and the brightness of said a plurality of image pixels are the pixel of light color and high brightness in the image block; Be that color value is lower than the pixel that first threshold and brightness value are higher than second threshold value; Its number exceeds the 3rd threshold value, then uses the Y-peak method to confirm backlight color and brightness, does not then use the RGB Mean Method to confirm backlight color and brightness if exceed the 3rd threshold value; Wherein color value is lower than first threshold; Pixel is classified into light color, and brightness value is higher than second threshold value, and pixel is had high brightness by classification.

From the description below in conjunction with example, others of the present invention will be obvious all the more.

Description of drawings

Combine example at present and, will describe exemplary embodiments of the present invention with reference to accompanying drawing, wherein:

Fig. 1 is total synoptic diagram of the LCD TV of an embodiment of the present invention method and apparatus;

Fig. 2 describes the image that will on LCD TV, watch;

Fig. 3 and 4 is two sub-graphs or the image block A in Fig. 2 image, B;

Fig. 5-the 10th, the exemplary image of the backlight color of the definite LCD TV of description and the first method of brightness;

Figure 11-the 16th, the exemplary image of the backlight color of the definite LCD TV of description and the second method of brightness; With

Figure 17 is a process flow diagram of confirming the adaptive approach of backlight color and brightness according to the present invention.

Embodiment

Existing its example will be described in accompanying drawing in detail with reference to an exemplary embodiments of the present invention, and wherein identical reference number is represented components identical.

Said exemplary embodiments is described the present invention and is embodied in the backlight LCD display, and like LCDTV, it is used to show and comprises a plurality of video images of successive frames that each successive frame is made up of a plurality of pixels.This is not to be intended to limit usable range of the present invention or function.The enhancing still image that the present invention is equally applicable on lcd screen, show.For example, many companies, advertiser or artist use lcd screen to show static but periodically variable information, advertisement and/or art picture and image.The present invention can be used to strengthen the performance on screen of this information, advertisement and/or image equally.

Equally, to be embodied in the backlight LCD display be not to be intended to limit usable range of the present invention or function in the present invention.The present invention can be embodied in any display equipment equally, and it uses a light source that image projection to a projection surface or one are used on the FPD face of the direct viewing that comes display image backlight.This display comprises digital micromirror device display (DMDs), liquid crystal on silicon (LCoS) display and LCD display.

11/707,517 li of U.S. Patent application in early days, its content is incorporated into this paper by reference, and the applicant has described one and has had LCD display equipment backlight, a plurality of independent controllable lightings district that is divided into backlight.The brightness of each surround is to control according to the vision signal characteristic of LCD display corresponding region.If shown in image-region become clear, or a higher brightness is arranged, there is higher brightness in then corresponding back lighting district, if image-region is dark, then corresponding back lighting district is not or have lower brightness.Dynamically control the brightness in each back lighting district, the contrast and the dynamic range of image shown in can improving through the characteristic of a counterpart of image shown in accordinging to.In addition, each independent controlled back lighting district can comprise variable-colour light source, like a group controlled redness, green and blueness (RGB) LED separately, thereby the color that can control the surround from the black of chromatogram to white.The characteristic of a counterpart of image shown in backlight illumination and color can according to is dynamically controlled, thereby improves contrast and color dynamic range.

In U.S. Patent application 11/707,517, LED backlight is control separately, so backlight illumination is not unified, can change along with image.Another advantage of this system is that entire backlight brightness is darker than existing constant backlight system usually.This is that it possibly have identical brightness with existing constant backlight system usually because the light color of display image or the backlight of zone of higher brightness will be in its maximal value, but most of image has lower brightness, and therefore meeting backlight is darker.As a result, compare with existing constant backlight, or with entire backlight based on shown in the brightness of image characteristic compared by unified dimming dynamically, what have a plurality of independent controllable lightings district backlightly has on average a more low energy consumption.

With reference to Fig. 1, show total synoptic diagram of a backlight LCD display, like the LCD TV type of in U.S. Patent application 11/707,517, discussing.Display comprises a LCD panel 1 that is positioned at 2 front ends backlight.Backlight 2 are divided into the controlled field of illumination of a plurality of independences.In said embodiment,, have only 5 * 7 zones for ease of describing.In the preferred embodiments of the present invention, each zone comprises one group red 3, green 4 and blue 5LED, thereby the output of the light in zone can be that black from chromatogram is to white.But optional for the purpose of the present invention, in other embodiment, district backlight can include only White LED or other light source.Nominally LCD panel rather than physically be divided into a plurality of viewing areas 6.TV converter 7 receives picture signal through the analog or digital interface from various video source such as PC, DVD player, wired TV etc.After handling input signal, the TV converter produces the vision signal 8 of rgb format, and transmits 8 to brightness controllers 9 of vision signal.Brightness controller 9 is analyzed incoming video signal 8, and the led driver of drive signal 10 to 2 each surround backlight is provided.LED drive signal 10 comprises that color and monochrome information give each surround of backlight 2.In order to optimize backlight dimming, and then save energy consumption, keep simultaneously or maximization picture contrast and quality, use a kind of methods analyst LCD picture signal 8, confirm the drive signal 10 of LED.The method that selection is used for analyzing LCD picture signal 8 is to confirm adaptively according to the pixel characteristic in each image block that takies the viewing area.

Fig. 2 shows an images displayed on LCD panel 1.For the ease of the purpose of duplicating, all images is all by gray level display, but is actually the color image of rgb format.Can see that the image major part is uniform color, have only the central left half of image to have the characteristic of regions of different colours, have a higher contrast ratio with the main color when compared of image.Above the image of Fig. 2, show grid, each image block in grid is represented a nominal piece of corresponding LCD panel 1, and a surround that independence is controlled of corresponding backlight 2.Based on the characteristics of image of image block, be independent controlled aspect color and the light intensity (brightness) in the district backlight of each image block back.Fig. 3 and 4 is respectively the enlarged drawing of image block A and B.Can find that color of image is uniformly substantially in piece B in whole, yet color of image is uniformly substantially in piece A, except two whites or light point in the upper left corner, top.Piece A and B can cause different problems when selecting a suitable backlight color and brightness.In the present invention, can use various criterion to analyze this different masses, so that obtain best final picture quality.Confirm that the reason and the method for appropriate criteria describe hereinafter.

As what those skilled in the art knew; The RGB picture signal has three passages; Promptly red, green and blue, it can be counted as three overlapping gray level images, separately the brightness value of corresponding red, the green and blue color part of each pixel in the memory image.Brightness value is represented by a n-bit integer.To a common 8-bit image, integer range be from 0 in 255.The corresponding color of pixel of this value of 0 value representation partly is " pass ".The corresponding color of pixel of this value of 255 value representations partly is high-high brightness ground " opening ".The first method of confirming led color backlight and brightness is to find out the average brightness value of each Color Channel interior pixel.Image block is divided into redness, green and blue Color Channel, and the brightness value of all pixels carries out totalling in each passage, then divided by the number of pixels in this channel image piece to find out average brightness value.Red, the green and blue mean flow rate of each color part in this display image piece.Each surround backlight is the cohort illumination by redness, green and blue led, thereby district backlight can provide the correspondence image piece of image shown in coloured backlight the arriving.Three average brightness values are used to confirm the drive signal value of each redness, green and blue led in the corresponding surround of back light apparatus.The backlight color and the brightness of expectation are three mean values.Because the drive signal scope of each LED maybe not corresponding drive signal scope, average can be in addition by standardization.

Fig. 5 and 8 is gray scale displaying blocks, backlight color and the brightness of expression when confirming according to above method.Each Color Channel average brightness value of Fig. 3 piece A and Fig. 4 piece B is R=155, G=217, B=158 and R=151, G=216, B=123.Account for the number percent of high-high brightness 255 through the mean value of finding out three channel value, can estimate the shared number percent of backlight power.To Fig. 5, be ((155+217+158)/3)/255 or approximate 70%.To Fig. 8, approximate is 64%.The higher-wattage of Fig. 5 module is to be caused by two on image apex left corner light color points.Fig. 6, the 7 and 9, the 10th, gray scale is represented, describes the effect of confirming backlight color and brightness through the RGB Mean Method.Fig. 6 and 9 shows the scene that the initial pictures piece will be seen when color that is shown by Fig. 5 and 8 respectively and brightness back lighting on LCD display.Fig. 7 and 10 is initial pictures, is used for comparison.Can find easily that in Fig. 6 the brightness and contrast of two light color points on the left corner of top reduces because of effect backlight.Because reduce backlight illumination to 70%,, but need pay the cost of picture quality and contrast so can realize energy-conservationly.Compare with Fig. 9, can find that image is not changed,, thereby can realize energy-conservationly, and can not reduce picture quality even possibly make moderate progress because backlightly dim even strengthen to some extent.So, confirm that the RGB Mean Method of backlight color and brightness is suitable for the parts of images of similar B, but be not suitable for having the parts of images of the piece category-A type of high-contrast.

The second method of confirming LED brightness backlight is a Y-peak method.In the YUV color model, the colouring information of an image and luma unpack.Luma is meant brightness of image, i.e. the black of image or whiteness.The data of each pixel have three integer representations.First or the Y integer be luma or brightness part, and second and the 3rd or U and V integer be colourity or color part.In the Y-peak method, the RGB image block is converted into the YUV color space, and the LED drive signal is based on the peak value Y of all pixels in the image block.Same drive signal is used to all redness, green and blue led, thereby corresponding back lighting district does not have color, only its brightness of control in white light.Figure 11 and 14 is gray scale displaying blocks, shows the backlight illumination of image block A and B when accordinging to the Y-peak method and confirm respectively.To Figure 11, the light color point has maximum brightness, thus the high-high brightness that approximate 100% power is arranged backlight.To Figure 14, the chances are 84% for power.Figure 12, the 13 and 15, the 16th, gray scale is represented, describes the effect of confirming backlight illumination through the Y-peak method.Figure 12 and 15 describes the scene that how the initial pictures piece is seen when the backlight illumination back lighting that is shown by Figure 11 and 14 respectively on LCD display.Figure 13 and 16 is initial pictures pieces, with making comparisons.Can see easily that at Figure 12,13 and 15,16 image does not change, because backlight illumination that the method is calculated even enhancing to some extent.But backlight illumination and power ratio are higher through the RGB Mean Method, so, though keep picture contrast and quality, energy consumption increased.

Therefore, in the present invention, adopt a self-adaptation to dim scheme,, select RGB Mean Method or Y peak method to confirm the backlight color and the brightness of each surround backlight according to the characteristic of the nominal image block of surround illumination.In adaptation scheme, if the light color in the image block and the number of high luminance pixel exceed a predetermined threshold T3, then use the Y-peak method to confirm backlight illumination, otherwise use the RGB Mean Method that image block.

A light pixel is pixel white or that have less color and approaching white.If color saturation or colorfulness are lower than threshold value T1, pixel is classified into light color.Each pixel is to be represented the brightness of its redness, green and blue portion by three n-bit integer.In the present invention, through with the difference between the minimum and maximum brightness value divided by three brightness values with, confirm a color of pixel saturation degree, specifically shown in following equality:

$s=\frac{\max \left(\mathrm{RGB}\right)-\min \left(\mathrm{RGB}\right)}{R+G+B}$

Minimum color saturation is that wherein all three redness, green and blue brightness value equate to a white pixel, thereby the molecule in the above equality is 0.Therefore, be 0 to a white pixel s.The maximum color saturation degree is that it only comprises a main color, is 255:0:0 like rgb value to such pixel, thereby s is 1.In the preferred embodiments of the present invention, threshold value T1 is 0.1, if therefore s is lower than 0.1, then pixel is counted as light.Confirm whether pixel is that light color saturation method is not to be intended to limit usable range of the present invention or function.The technician can understand, this be a definite pixel color and pixel whether be the method for light color, other same effective method also is suitable for.For example, can pixel transitions be become the YUV color space, and partly confirm color from U and V.

If definite brightness value of a pixel is higher than the second threshold value T2, this pixel is had high brightness by classification.In the preferred embodiments of the present invention, the brightness value of a pixel is the average of two highest brightness value of pixel.So, have RGB brightness value such as R=150 at one, G=250, in the pixel of B=180, brightness value is 215 (i.e. (250+180)/2).In context of the present invention, height is a relative terms, and whether pixel has the brightness that high brightness depends on other pixel in image or the image block.In order to consider this situation, in the preferred embodiments of the present invention, the second threshold value T2 is a dynamic value, equals to be assessed the image of pixel or the mean flow rate of all pixels in the image block.If the average of interior two the RGB brightness values the highest of pixel is higher than the average brightness of all pixels in the image block, then this pixel is counted as and has a high brightness.The method whether this definite pixel has high brightness is not to be intended to limit usable range of the present invention or function.The technician can understand, and this is whether a definite pixel has the method for high brightness, and other method also is feasible.For example, a simple method is the mean flow rate of three RGB brightness values of comparison and the predetermined value of a 0-255 brightness range, such as 200.

Figure 17 is the process flow diagram that self-adaptation dims scheme, is used for confirming that which scheme should be used to confirm a characteristic suitable backlight that the surround is backlight from the image block characteristic of correspondence.At first, when 20 li of preparation module were called decision-making module, two variable i and n were set to 0.Variable i is represented the current image pixel of being assessed, and variable n is a counter, is used to the number of interior light color of document image piece and high luminance pixel.Advance to processing module 21, pixel counter i is pursued 1 and is increased progressively, and present analysis is to carry out on the number of pixels 1 in current image block.Advance to processing module 22, this of this method step is to calculate the color saturation of current pixel i, is represented by s.At decision-making module 23, color saturation s and first threshold T1 compare.If color saturation is lower than threshold value T1, be categorized as light pixel, this method advances to next step processing module 24, otherwise this method turns back to processing module 21, pursues 1 and increases progressively pixel counter, and to the next pixel repetitive process 22 in the image block.

In processing module 24, calculate the RGB average of current pixel i, represent by a.Through picture element signal is divided into single redness, green and blue channel, confirms the color value of each passage, each value of suing for peace and with summation divided by 3 (Color Channel numbers), can confirm the RGB average.At decision-making module 25, the RGB average a and the second threshold value T2 compare.If value a is higher than threshold value T2, be categorized as high luminance pixel, this method advances to processing module 26 then, otherwise it turns back to processing module 21, by 1 increase progressively pixel counter i value, and repeating step.

In processing module 26, this method count-up counter n, the number of light color and high luminance pixel promptly has one and is lower than the color saturation s of T1 and the pixel of a RGB average that is higher than T2 in its recording picture module.This method advances to decision-making module 27, the maximum number i-max of its compared pixels counter i and image block interior pixel.If pixel counter i does not also reach maximal value, mean that not every pixel is all analyzed in the module, this method turns back to processing module 21, and it increases progressively pixel counter i, and continues always.

If pixel counter i has reached max pixel value, then do not have pixel to be used for analyzing, thereby process proceed to decision-making module 28, it is counter n and the 3rd threshold value T3 relatively.If n is greater than threshold value T3, the number of pixels of light color and high brightness has exceeded threshold value in the display image piece, and the present invention advances to processing module 29, and it calls the Y-peak method and confirms backlight color and brightness.If counter n is lower than threshold value T3, this method advances to processing module 30, and it calls the RGB Mean Method and confirms backlight color and brightness.

Therefore, according to the present invention, use a self-adaptation solution method to confirm the method for backlight color and brightness, thereby can select optimal colors and brightness for each district backlight backlight from the single pixel characteristic in the image block.Can produce picture quality and the best solution of saving energy consumption like this.

Claims (6)

1. the backlight color of the LCD panel of a definite display image and the method for brightness, the surround that comprises that a plurality of independences are controlled backlight, nominally and image be divided into a plurality of image blocks; The corresponding back lighting district of each image block; Image block comprises that a plurality of image slices have pixel color and brightness, and if the backlight color and the brightness of each surround of the LCD panel of confirming display image based on the pixel color and the brightness of said a plurality of image pixels are the pixel of light color and high brightness in the image block; Be that color value is lower than the pixel that first threshold and brightness value are higher than second threshold value; Its number exceeds the 3rd threshold value, then uses the Y-peak method to confirm backlight color and brightness, does not then use the RGB Mean Method to confirm backlight color and brightness if exceed the 3rd threshold value; Wherein color value is lower than first threshold; Pixel is classified into light color, and brightness value is higher than second threshold value, and pixel is had high brightness by classification.

2. method according to claim 1, wherein each pixel has redness, green and blue brightness value, selects second threshold value to confirm whether the mean value of any two values in said redness, green and the blue brightness value surpasses second threshold value.

3. method according to claim 1, wherein second threshold value is a mean flow rate of all pixels in the image block.

4. method according to claim 1, wherein first threshold be set at a maximum color value 5% to 30% between.

5. method according to claim 4, wherein first threshold is 10% of a maximum color value.

6. a back light apparatus is used to provide the LCD panel to a display video image backlight, and it confirms backlight color and brightness according to the described method of claim 1.

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