JP2004302217A - Image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image display device capable of correcting color variations of light emission elements at every display units, making the color variations among the display units inconspicuous and performing high quality image display. <P>SOLUTION: The image display 10 is made by two-dimensionally combining a plurality of display units 11. The display units 11 are provided with a plurality of pixels 14 comprising three LEDs 13R, 13G, 13B of R, G, B, color matrix circuits 19 which are disposed at every pixels 14 so as to convert an input image signal to a lighting signal of a pulse width in accordance with gradation by performing color correction by means of a correction coefficient set at each of display units 11, driving circuits 17R, 17G, 17B which separately light LEDs 13R, 13G, 13B according to the lighting signals, random number generating circuits 20 disposed at each of LEDs 13R, 13G, 13B and a gradation error correction circuit 21 which omits an error part of the pulse width or raises the same to a unit with the probability in accordance with the random number value. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００１９】
上記の式中のカラーマトリクス係数（補正係数）は、各表示ユニット１１に搭載されるＬＥＤ１３Ｒ、１３Ｇ、１３Ｂの特性を考慮して、表示ユニット１１ごとに設定される。
【００２０】
カラーマトリクス回路１９から出力される点灯信号（Ｒｓ、Ｇｓ、Ｂｓ）のパルス幅は、階調表現可能な値からのずれ、すなわち誤差分（ΔＲｓ、ΔＧｓ、ΔＢｓ）を含んでいる。たとえば、各色ごとに２５６（８ビット）階調表現を行う場合、０〜２５５の間に存在する２の乗数値（０，１，２，・・・・，２５４，２５５）に対応するパルス幅によって階調が表現されるが、カラーマトリクス回路１８から出力される点灯信号（Ｒｓ、Ｇｓ、Ｂｓ）のパルス幅は０．５、１．２５、０．１２５といった演算結果の少数部分（０．５、０．２５、０．１２５，・・・）に相当する誤差を含んでいる。
【００２１】
乱数発生回路２０は、点灯信号（Ｒｓ、Ｇｓ、Ｂｓ）のパルス幅の階調表現可能な値すなわち２の乗数値に対応するパルス幅からの誤差分（ΔＲｓ、ΔＧｓ、ΔＢｓ）に比例した傾向で乱数を発生させる。たとえば、０〜１の間の乱数を発生させる場合、０．５相当の誤差分であれば１／２の確率で１、１／２の確率で０の乱数を発生させ、０．２５相当の誤差分であれば１／４の確率で１、１／４の確率で０の乱数を発生させる。
【００２２】
階調誤差補正回路２１は、乱数発生回路２０からの乱数値に応じた確率で誤差分（ΔＲｓ、ΔＧｓ、ΔＢｓ）を切り捨てたり切り上げたりする。たとえば、乱数値が１であれば１／２の確率で、それぞれ誤差分（ΔＲｓ、ΔＧｓ、ΔＢｓ）を切り上げ、それ以外の値の場合は切り捨てる。これにより、点灯信号（Ｒｓ、Ｇｓ、Ｂｓ）のパルス幅がたとえば１．５相当のパルス幅であった場合、１／２の確率で１または２相当のパルス幅に変換される。また、点灯信号（Ｒｓ、Ｇｓ、Ｂｓ）のパルス幅がたとえば１．２５相当のパルス幅であった場合、１／４の確率で１または２相当のパルス幅に変換される。
【００２３】
スイッチング回路１８は、図３に示すように、１発光周期Ｔを複数の時間領域Ｔ１、Ｔ２に分割して、それぞれの時間領域Ｔ１、Ｔ２を別々の画素１４に割り当て、スイッチングにより各画素１４の駆動タイミングを切り替える。すなわち、この映像表示装置１０は、駆動方式としてダイナミック駆動方式を採用している。
【００２４】
つぎに、この実施の形態の作用について説明する。
映像表示装置１０には、図示しない信号源からフレーム周期ごとに１画面分の映像信号が供給される。その映像信号は、映像信号変換装置１５によって表示装置ユニット１１ごとの映像信号に変換され、各ユニットに同時に分配される。
【００２５】
各表示装置ユニット１１内では、演算回路１６により入力映像信号に応じた画素４ごとの各色のＬＥＤ１３Ｒ、１３Ｇ、１３Ｂの点灯信号が生成される。
【００２６】
その際、演算回路１６内では、各カラーマトリクス回路１９により、表示ユニット１１ごとに設定されたマトリクス係数を用いて、入力映像信号（Ｒ、Ｇ、Ｂ）が画素１４ごとに色補正されるとともに階調に応じたパルス幅の点灯信号（Ｒｓ、Ｇｓ、Ｂｓ）に変換され、各ＬＥＤ１３Ｒ、１３Ｇ、１３Ｂのごとに設けられた乱数発生回路２０に入力される。そして、各乱数発生回路２０により点灯信号（Ｒｓ、Ｇｓ、Ｂｓ）のパルス幅の誤差分（ΔＲｓ、ΔＧｓ、ΔＢｓ）に比例した傾向で乱数が生成され、その乱数値に応じた確率で、階調誤差補正回路２１により誤差分（ΔＲｓ、ΔＧｓ、ΔＢｓ）を切り捨てたり切り上げたりする階調誤差補正処理が行われる。
【００２７】
上記のようにして演算回路１６により生成された点灯信号は、各ＬＥＤ駆動回路１７Ｒ、１７Ｂ、１７Ｇに供給される。その結果、ＬＥＤ駆動回路１７Ｒ、１７Ｂ、１７Ｇにより各画素１４の各ＬＥＤ１３Ｒ、１３Ｇ、１３Ｂが点灯信号に従って個別に駆動される。
【００２８】
上記のように、入力映像信号を画素１４ごとに色補正し階調に応じたパルス幅の点灯信号に変換する際、表示ユニット１１ごとに設定されたマトリクス係数を使用することにより、ダイナミック駆動方式を採用した場合でも、表示ユニット１４ごとのＬＥＤ１３Ｒ、１３Ｇ、１３Ｂの色ばらつきを補正することができる。
【００２９】
また、ＬＥＤ１３Ｒ、１３Ｇ、１３Ｂごとに発生させた乱数値に応じた確率で、点灯信号（Ｒｓ、Ｇｓ、Ｂｓ）のパルス幅の誤差分（ΔＲｓ、ΔＧｓ、ΔＢｓ）を切り捨てたり切り上げたりする階調補正処理を行うようにしたので、補正による階調の変化が表示ユニット１１の全画素１４に画一的に生じるのを防止できる。すなわち、補正による階調の変化を各表示ユニット１１の表示面１１ａ全体に空間的かつ時間的に分散させることができる。したがって、表示ユニット１１間における色ばらつきを目立たなくすることができる。
【００３０】
また、上記階調補正処理の基準となる乱数を、誤差分に比例した傾向で発生させるようにしたので、誤差分に比例した確率でその誤差分を切り捨てたり切り上げたりして、誤差分に応じた中間階調表現を行うことができる。
【００３１】
なお、上記実施の形態では、階調誤差補正回路２１を演算回路１６内に設けたが、各ＬＥＤ駆動回路１７Ｒ、１７Ｂ、１７Ｇ内に設けてもよい。
【００３２】
また、上記実施の形態では、表示ユニットごとの構成を説明したが、同様の構成を１画素以上で構成される表示ブロックごとに持っていてもよい。たとえば演算回路１６を表示ユニット内の表示ブロックごとに備えてもよい。
【００３３】
【発明の効果】
以上説明したように、本発明の映像表示装置によれば、表示ユニットごとの発光素子の色ばらつきを補正するとともに表示ユニット間における色ばらつきを目立たなくして高品質の映像表示を行うことができる。
【図面の簡単な説明】
【図１】（ａ）は本発明にかかる映像表示装置の構成例を示す正面図である。
（ｂ）は表示装置ユニットの正面図である。
【図２】図１に示す映像表示装置のブロック図である。
【図３】アクティブ駆動方式におけるＰＷＭ信号（点灯信号）の出力波形の一例を示すタイミング図である。
【図４】補ＰＷＭ信号を使用して色補正を行う従来技術における出力波形の一例を示すタイミング図である。
【符号の説明】
１０：映像表示装置
１１：表示装置ユニット
１１ａ：表示面
１３Ｒ、１３Ｇ、１３Ｂ：ＬＥＤ（発光素子）
１４：画素
１５：映像信号変換装置
１６：演算回路
１７Ｒ、１７Ｂ、１７Ｇ：ＬＥＤ駆動回路（発光素子駆動手段）
１８：スイッチング回路
１９：カラーマトリクス回路（色補正手段）
２０：乱数発生回路（乱数発生手段）
２１：階調誤差補正回路（階調誤差補正手段）[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a video display device in which light emitting elements such as LEDs (Light Emitting Diodes) are arranged in a plane and each of the light emitting elements is individually driven to perform a fine display. And a video display device having a single display surface formed in combination.
[0002]
[Prior art]
Generally, an image display device installed on a wall, a rooftop of a building, a stadium, or the like is formed by combining a plurality of display units in a matrix in accordance with a size requirement. In each display unit, each pixel constituting the display surface is constituted by three colors of LEDs of red LED, green LED and blue LED, and the light emitting state (lighting luminance and lighting time) of these three colors of LEDs is determined for each pixel. A color image is displayed by controlling for each color.
[0003]
In this type of image display device, there is a problem of variations in basic colors (red, blue, and green) caused by manufacturing variations of LEDs and the like. Even if the variation of the LED is corrected by each display unit, it cannot be corrected between the display units constituting the video display device, and therefore, the color variation exists between the display units. If there is color variation among the display units, the display surface of the video display device looks like a tile.
[0004]
As a solution to this problem, for example, when the chromaticity of the emission color of the green LED is deviated with respect to the chromaticity that is the reference of green, another color, that is, a red or blue LED is made to emit light, and the deviated green is There is known a technique of correcting the variation between elements by moving the pixel toward a red side or a blue side to approach a reference chromaticity. In this technique, as shown in FIG. 4, an area of a main PWM signal, which is an original light emission signal, and an area of a complementary PWM signal for color correction are provided within one light emission cycle T. (See Patent Document 1, FIG. 7)
[0005]
[Patent Document 1] Japanese Patent Application Laid-Open No. 2001-188513
[Problems to be solved by the invention]
However, in a video display device that realizes high-definition color expression, as shown in FIG. 3, in order to suppress an increase in the number of LED driving circuits due to an increase in the number of LEDs, a plurality of one light emission periods T in the PWM signal (shown in FIG. In the example, two pixels are divided into two time regions T1 and T2, and the respective time regions T1 and T2 are assigned to different pixels, and the driving timing of each pixel is switched by switching. The time regions T1 and T2 that can be used for controlling the LED of the first embodiment are very short. Therefore, it is difficult to secure a region of the complementary PWM signal having the same gradation as the main PWM signal in the short time regions T1 and T2 as in the related art.
[0007]
The present invention has been conceived to solve the problems of the conventional technology as described above, and its purpose is to provide a light-emitting element of each pixel that can be used in a very short time range. It is an object of the present invention to provide a video display device capable of correcting a color variation of a light emitting element for each display unit and displaying a high quality video by making color variation between display units inconspicuous.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, an image display device of the present invention is an image display device configured by combining a plurality of display units in a two-dimensional manner, wherein the display unit has a plurality of types of light emission having different emission colors. A plurality of pixels comprising a set of elements, and an input video signal are provided for each pixel to convert the input video signal into a lighting signal having a pulse width corresponding to a gradation by performing color correction using a correction coefficient set for each display unit. Color correction means, light emitting element driving means for individually lighting the light emitting elements in accordance with the lighting signal, random number generating means provided for each light emitting element, and an error from a value capable of expressing the pulse width in gradation. And a tone error correction means for correcting the error with a probability according to the random number value from the random number generation means.
[0009]
In the video display device of the present invention configured as described above, the input video signal is subjected to color correction for each pixel, and is converted into a lighting signal having a pulse width corresponding to the gradation. At that time, a correction coefficient set for each display unit is used. Therefore, even under the condition that the time region that can be used for controlling the light emitting element of each pixel is very short, the color variation of the light emitting element for each display unit can be corrected. In addition, the error of the pulse width from the value that can be expressed in gradation is corrected with the probability according to the random number value generated for each light emitting element, so that the change in gradation due to the correction is applied to all pixels of the display unit. It can be prevented from occurring all at once. That is, the change in gradation due to the correction can be spatially and temporally dispersed over the entire display surface of each display unit. Therefore, color variation between display units can be made inconspicuous.
[0010]
In the video display device according to the aspect of the invention, it is preferable that the random number generation unit generates a random number with a tendency proportional to the error.
[0011]
According to the above configuration, since the error is rounded down or rounded up at a probability proportional to the error, it is possible to perform halftone expression according to the error.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described.
[0013]
FIG. 1A is a front view illustrating a configuration example of a video display device according to the present invention. The image display device 10 forms a large-area display surface by attaching a plurality of display device units 11 to the holding frame 12. As shown in FIG. 1B, the display surface 11a of each display device unit 11 has pixels 14 composed of three types of LEDs 13R, 13G, and 13B of R, G, and B arranged in a matrix.
[0014]
FIG. 2 is a block diagram of the video display device 10 shown in FIG.
The video display device 10 includes a video signal conversion device 15 that converts a video signal for one screen transmitted from a signal source (not shown) every frame period into a video signal for each display device unit 11 and distributes the video signal.
[0015]
An arithmetic circuit 16 for generating a lighting signal (PWM signal) for controlling each of the LEDs 13R, 13G, and 13B of each pixel 14 based on an input video signal from the video signal converter 15 is provided in each display device unit 11. An LED driving circuit 17R, 17B, 17G for individually driving each of the LEDs 13R, 13G, 13B according to a lighting signal, and a switching circuit 18 are provided.
[0016]
The arithmetic circuit 16 includes a color matrix circuit 19, a random number generation circuit 20, and a gradation error correction circuit 21. The color matrix circuit 19 is provided for each pixel 14. The random number generation circuit 20 and the gradation error correction circuit 21 are provided for each of the LEDs 13R, 13G, and 13B.
[0017]
The color matrix circuit 19 corrects the color of the input video signal (R, G, B) for each pixel 14 by a matrix operation expression represented by the following expression, and also turns on the lighting signal (Rs, Gs) having a pulse width corresponding to the gradation. , Bs).
[0018]
(Equation 1)

[0019]
The color matrix coefficients (correction coefficients) in the above equation are set for each display unit 11 in consideration of the characteristics of the LEDs 13R, 13G, and 13B mounted on each display unit 11.
[0020]
The pulse width of the lighting signal (Rs, Gs, Bs) output from the color matrix circuit 19 includes a deviation from a value capable of expressing gradation, that is, an error (ΔRs, ΔGs, ΔBs). For example, when 256 (8 bits) gradation expression is performed for each color, a pulse width corresponding to a multiplier value of 2 (0, 1, 2,..., 254, 255) existing between 0 and 255 The gradation is expressed by the following expression, but the pulse width of the lighting signal (Rs, Gs, Bs) output from the color matrix circuit 18 is 0.5, 1.25, 0.125, and a small part (0. 5, 0.25, 0.125,...).
[0021]
The random number generation circuit 20 tends to be proportional to an error (ΔRs, ΔGs, ΔBs) from a pulse width corresponding to a value capable of expressing a gradation of the pulse width of the lighting signal (Rs, Gs, Bs), that is, a power of two. Generates a random number. For example, when a random number between 0 and 1 is generated, if an error corresponding to 0.5 is generated, a random number of 1 is generated with a probability of 1/2, a random number of 0 is generated with a probability of 1/2, and a random number of 0.25 is calculated. If it is an error, a random number of 1 is generated with a probability of 1/4, and a random number of 0 is generated with a probability of 1/4.
[0022]
The gradation error correction circuit 21 rounds down or rounds up the error (ΔRs, ΔGs, ΔBs) with a probability according to the random number value from the random number generation circuit 20. For example, if the random value is 1, the errors (ΔRs, ΔGs, ΔBs) are rounded up with a probability of 、, and the other values are rounded down. Thus, if the pulse width of the lighting signal (Rs, Gs, Bs) is, for example, 1.5, the pulse width is converted to 1 or 2 with a 1/2 probability. If the pulse width of the lighting signal (Rs, Gs, Bs) is, for example, a pulse width of 1.25, it is converted to a pulse width of 1 or 2 with a probability of 1/4.
[0023]
As shown in FIG. 3, the switching circuit 18 divides one light emission cycle T into a plurality of time regions T1 and T2, assigns each time region T1 and T2 to a separate pixel 14, and performs switching of each pixel 14 by switching. Switch the drive timing. That is, the video display device 10 employs a dynamic driving method as a driving method.
[0024]
Next, the operation of this embodiment will be described.
The video display device 10 is supplied with a video signal for one screen every frame period from a signal source (not shown). The video signal is converted into a video signal for each display unit 11 by the video signal conversion device 15 and is simultaneously distributed to each unit.
[0025]
In each display unit 11, the arithmetic circuit 16 generates a lighting signal of the LEDs 13R, 13G, and 13B of each color for each pixel 4 according to the input video signal.
[0026]
At this time, in the arithmetic circuit 16, the input video signals (R, G, B) are color-corrected for each pixel 14 by the color matrix circuit 19 using the matrix coefficient set for each display unit 11. It is converted into a lighting signal (Rs, Gs, Bs) having a pulse width according to the gradation, and is input to the random number generation circuit 20 provided for each of the LEDs 13R, 13G, 13B. Then, each random number generating circuit 20 generates a random number in a tendency proportional to the error (ΔRs, ΔGs, ΔBs) of the pulse width of the lighting signal (Rs, Gs, Bs). The tone error correction circuit 21 performs a tone error correction process in which errors (ΔRs, ΔGs, ΔBs) are rounded down or rounded up.
[0027]
The lighting signal generated by the arithmetic circuit 16 as described above is supplied to each of the LED drive circuits 17R, 17B, and 17G. As a result, the LEDs 13R, 13G, and 13B of each pixel 14 are individually driven by the LED drive circuits 17R, 17B, and 17G according to the lighting signal.
[0028]
As described above, when the input video signal is color-corrected for each pixel 14 and converted into a lighting signal having a pulse width corresponding to the gradation, a dynamic driving method is used by using a matrix coefficient set for each display unit 11. Is adopted, color variations of the LEDs 13R, 13G, and 13B for each display unit 14 can be corrected.
[0029]
Further, a gray scale for rounding off or rounding up the error (ΔRs, ΔGs, ΔBs) of the pulse width of the lighting signal (Rs, Gs, Bs) with a probability according to the random number generated for each of the LEDs 13R, 13G, 13B. Since the correction process is performed, it is possible to prevent a change in gradation due to the correction from occurring uniformly in all the pixels 14 of the display unit 11. That is, the change in gradation due to the correction can be spatially and temporally dispersed over the entire display surface 11a of each display unit 11. Therefore, color variation between the display units 11 can be made inconspicuous.
[0030]
In addition, since the reference random number for the tone correction process is generated with a tendency proportional to the error, the error is truncated or rounded up at a probability proportional to the error, and the error is calculated according to the error. Intermediate gradation expression.
[0031]
In the above embodiment, the gradation error correction circuit 21 is provided in the arithmetic circuit 16, but may be provided in each of the LED drive circuits 17R, 17B, and 17G.
[0032]
In the above embodiment, the configuration for each display unit has been described. However, a similar configuration may be provided for each display block including one or more pixels. For example, the arithmetic circuit 16 may be provided for each display block in the display unit.
[0033]
【The invention's effect】
As described above, according to the video display device of the present invention, it is possible to perform high-quality video display by correcting the color variation of the light emitting element for each display unit and making the color variation among the display units inconspicuous.
[Brief description of the drawings]
FIG. 1A is a front view illustrating a configuration example of a video display device according to the present invention.
(B) is a front view of a display unit.
FIG. 2 is a block diagram of the video display device shown in FIG.
FIG. 3 is a timing chart showing an example of an output waveform of a PWM signal (lighting signal) in the active driving method.
FIG. 4 is a timing chart showing an example of an output waveform in a conventional technique for performing color correction using a complementary PWM signal.
[Explanation of symbols]
10: Video display device 11: Display device unit 11a: Display surface 13R, 13G, 13B: LED (light emitting element)
14: Pixel 15: Video signal converter 16: Arithmetic circuits 17R, 17B, 17G: LED drive circuit (light emitting element drive means)
18: Switching circuit 19: Color matrix circuit (color correction means)
20: random number generation circuit (random number generation means)
21: gradation error correction circuit (gradation error correction means)

Claims (2)

A video display device configured by combining a plurality of display units in a plane,
The display unit comprises:
A plurality of pixels composed of a set of a plurality of types of light emitting elements having different emission colors,
Color correction means provided for each pixel to convert an input video signal into a lighting signal having a pulse width corresponding to a gradation by performing color correction using a correction coefficient set for each display unit,
Light emitting element driving means for individually lighting the light emitting elements according to the lighting signal,
Random number generation means provided for each light emitting element,
A video display apparatus comprising: a tone error correcting unit that corrects an error from a value capable of expressing the pulse width in tone with a probability according to a random number value from the random number generating unit. The random number generating means,
The video display device according to claim 1, wherein a random number is generated with a tendency proportional to the error.

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