JP2005295513A - Image signal processing method, image signal processing apparatus and image displaying apparatus - Google Patents

Image signal processing method, image signal processing apparatus and image displaying apparatus Download PDF

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JP2005295513A
JP2005295513A JP2005057255A JP2005057255A JP2005295513A JP 2005295513 A JP2005295513 A JP 2005295513A JP 2005057255 A JP2005057255 A JP 2005057255A JP 2005057255 A JP2005057255 A JP 2005057255A JP 2005295513 A JP2005295513 A JP 2005295513A
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image signal
display device
signal processing
brightness
correction
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JP4899321B2 (en
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Kazuhiro Yamada
和弘 山田
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Panasonic Holdings Corp
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Matsushita Electric Industrial Co Ltd
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<P>PROBLEM TO BE SOLVED: To provide an image signal processing method by which the characteristic of the brightness perceived by human being for image signals can be made linear even when the display brightness of a display device uniformly rises due to the ambient light. <P>SOLUTION: An image signal processing method is provided for nonlinear correcting image signals to be inputted to a display device 103, wherein the nonlinear correction characteristic is modified based on a brightness of the place where the display device 103 is located. According to this method, even when the display brightness of the display device 103 uniformly rises due to the ambient light, the characteristic of the brightness perceived by human being for image signals can be made linear. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

本発明は、画像信号に対して非線形補正を施す画像信号処理方法、画像信号処理装置およびそれを用いた画像表示装置に関する。   The present invention relates to an image signal processing method, an image signal processing apparatus, and an image display apparatus using the image signal processing method for performing nonlinear correction on an image signal.

人間の視覚特性は非線形であり、特に人間が感じる明るさの程度は図５に示すように輝度に対して対数関数的な特性を示す。また、ＣＲＴ（Ｃａｔｈｏｄｅ Ｒａｙ Ｔｕｂｅ）の画像信号に対する表示輝度は、図６（ａ）に示したようにいわゆるガンマ特性をもつ。したがってＣＲＴを用いた表示装置においては、ガンマ特性と対数関数的な視覚特性とが打ち消しあって、人間が感じる明るさの程度は画像信号に対してほぼ線形な特性を示すことになる。   Human visual characteristics are non-linear, and the degree of brightness felt by humans exhibits logarithmic characteristics with respect to luminance as shown in FIG. Further, the display luminance for the CRT (Cathode Ray Tube) image signal has a so-called gamma characteristic as shown in FIG. Therefore, in a display device using a CRT, the gamma characteristic and the logarithmic visual characteristic cancel each other, and the degree of brightness perceived by humans exhibits a characteristic that is almost linear with respect to the image signal.

これに対して、近年登場したＤＭＤ（Ｄｉｇｉｔａｌ Ｍｉｒｒｏｒ Ｄｅｖｉｃｅ）やＰＤＰ（Ｐｌａｓｍａ Ｄｉｓｐｌａｙ Ｐａｎｅｌ）等の表示装置はガンマ特性をもたず、図６（ｂ）に示したように画像信号に対する表示輝度は線形の特性をもっている。したがってこれらの表示装置においては、人間が感じる明るさの程度は画像信号に対して対数関数的な特性を示すことになる。そこで、画像信号に対して人間が感じる明るさの程度を線形な特性に戻すためには、画像信号に非線形補正を施す必要がある。その方法として、例えば図７に示したようにルックアップテーブル（以下、「ＬＵＴ」と略記する）を用いて非線形補正を行う方法が提案されている（例えば、特許文献１参照）。   On the other hand, display devices such as DMD (Digital Mirror Device) and PDP (Plasma Display Panel) that have recently appeared do not have gamma characteristics, and the display luminance for image signals is linear as shown in FIG. 6B. It has the characteristics of Accordingly, in these display devices, the degree of brightness perceived by humans exhibits logarithmic function characteristics with respect to the image signal. Therefore, in order to return the brightness level felt by humans to the image signal to the linear characteristic, it is necessary to perform nonlinear correction on the image signal. As such a method, for example, a method of performing nonlinear correction using a look-up table (hereinafter abbreviated as “LUT”) as shown in FIG. 7 has been proposed (see, for example, Patent Document 1).

図８は、このようなＬＵＴの入出力特性の一例を示す図である。ここで、「入力階調」は補正前の画像信号であって、ＬＵＴへの入力画像信号の信号レベルを「０」〜「２５５」までの２５６段階で表したものであり、「表示階調」は補正後の画像信号であって、ＬＵＴからの出力画像信号の信号レベルを、その最大値が「２５５」となるように規格化したものである。なお図８には、入力階調が「０」、「１０」、「２０」、・・・、「２５０」のときの表示階調についてのみ示している。
特開平１０−１５３９８３号公報 FIG. 8 is a diagram showing an example of the input / output characteristics of such an LUT. Here, the “input gradation” is an image signal before correction, and represents the signal level of the input image signal to the LUT in 256 levels from “0” to “255”. "Is a corrected image signal, and the signal level of the output image signal from the LUT is normalized so that the maximum value is" 255 ". FIG. 8 shows only display gradations when the input gradations are “0”, “10”, “20”,..., “250”.
Japanese Patent Laid-Open No. 10-153983

表示装置が暗所に設置されており周囲光等が無い場合においては、ＰＤＰ等のガンマ特性をもたない表示装置に対して入力階調に図８に示した非線形補正を施すと、入力階調と表示輝度との関係は図９（ａ）の特性線Ａで示したようにガンマ特性を示す。したがって、入力階調に対して人間が感じる明るさの程度は、図９（ｂ）の特性線Ｂで示したようにほぼ線形な特性となる。   When the display device is installed in a dark place and there is no ambient light or the like, if the input gradation is subjected to the non-linear correction shown in FIG. The relationship between the tone and the display luminance indicates the gamma characteristic as indicated by the characteristic line A in FIG. Therefore, the degree of brightness perceived by humans with respect to the input gradation has a substantially linear characteristic as indicated by the characteristic line B in FIG.

しかし、明所においては、図９（ａ）の特性線Ｃで示すように周囲光の影響を受けて表示輝度が一様に上昇してしまうため、従来の非線形補正を施しても人間が感じる明るさの程度を線形な特性に戻すことができなくなる。図９（ｂ）の特性線Ｄはこのときの入力階調に対して人間が感じる明るさの程度を示しており、入力階調の低い部分において、階調の変化をはっきりと認識できなくなる。   However, in a bright place, as indicated by the characteristic line C in FIG. 9A, the display luminance is uniformly increased due to the influence of ambient light, so that humans can feel it even if conventional nonlinear correction is performed. It becomes impossible to return the brightness level to a linear characteristic. The characteristic line D in FIG. 9B indicates the degree of brightness that humans feel with respect to the input gradation at this time, and the change in gradation cannot be clearly recognized in a portion where the input gradation is low.

これは人間の視覚特性に依存するものであり、以下のように考えることができる。暗所においては、図８に示した表示階調がそのまま表示輝度を示すものと仮定すると、入力階調が１０階調から２０階調に増加すると表示輝度は「０．２」から「０．９」に増加し、人間は明るさが４．５倍になったと感じる。ところが、明所においては、周囲光の影響で、例えば「３０」に相当する輝度分だけ表示輝度が上昇したと仮定すると、入力階調が１０階調から２０階調に増加しても表示輝度はそれぞれ「３０．２」から「３０．９」に増加するだけであり、人間には明るさの変化はほとんど感じられない。もちろん明るい画像の場合には、例えば暗所における２４０階調と２５０階調に対する表示輝度の比は２４４．１／２２３．２＝１．０９であり、明所における同表示階調の比、２７４．１／２５３．２＝１．０８と大きな差はなく、周囲光の影響を無視することができる。   This depends on human visual characteristics and can be considered as follows. In the dark place, assuming that the display gradation shown in FIG. 8 shows the display luminance as it is, when the input gradation is increased from 10 gradations to 20 gradations, the display luminance is changed from “0.2” to “0. It increases to 9 ”, and humans feel that the brightness has increased 4.5 times. However, in a bright place, assuming that the display brightness is increased by an amount corresponding to, for example, “30” due to the influence of ambient light, the display brightness is increased even if the input gradation is increased from 10 gradations to 20 gradations. Each increase only from “30.2” to “30.9”, and humans hardly perceive a change in brightness. Of course, in the case of a bright image, for example, the ratio of the display luminance to 240 gradation and 250 gradation in the dark place is 244.1 / 223.2 = 1.09, and the ratio of the display gradation in the bright place is 274. .1 / 25.33.2 = 1.08 is not so different and the influence of ambient light can be ignored.

このように、従来の非線形補正の方法によれば、表示装置が設置されている場所の周囲光の影響を受けるため、人間が感じる明るさの程度を線形な特性に戻すことができず、特に入力階調の低い、暗い画像において階調の変化を認識できなくなり、階調がつぶれてしまうという問題点があった。   As described above, according to the conventional nonlinear correction method, since it is affected by the ambient light in the place where the display device is installed, the degree of brightness felt by humans cannot be returned to a linear characteristic. There is a problem that the gradation change cannot be recognized in a dark image with a low input gradation and the gradation is lost.

本発明は、上記課題を解決するためになされたものであり、画像信号に対する表示輝度が線形の特性をもつ表示装置であっても、周囲光の影響を受けて表示装置の表示輝度が一様に上昇しても、画像信号に対して人間が感じる明るさの特性を線形とすることができる画像信号処理方法、画像信号処理装置およびそれを用いた画像表示装置を提供することを目的とする。   The present invention has been made to solve the above-described problem. Even in a display device having a linear display luminance with respect to an image signal, the display luminance of the display device is uniform under the influence of ambient light. An object of the present invention is to provide an image signal processing method, an image signal processing device, and an image display device using the same, in which the brightness characteristic felt by humans with respect to the image signal can be made linear even when the image signal is increased. .

本発明は表示装置に入力する画像信号に非線形補正を施す画像信号処理方法であって、表示装置が設置される場所の明るさに基づいて非線形補正の特性を変化させることを特徴とする。この方法により、周囲光の影響を受けて表示装置の表示輝度が一様に上昇しても、画像信号に対して人間が感じる明るさの特性を線形とすることができる。   The present invention is an image signal processing method for performing nonlinear correction on an image signal input to a display device, wherein the characteristic of nonlinear correction is changed based on the brightness of a place where the display device is installed. According to this method, even if the display luminance of the display device increases uniformly due to the influence of ambient light, the brightness characteristic felt by humans with respect to the image signal can be made linear.

また、本発明の画像信号処理方法の非線形補正は、補正前の画像信号のγ乗（γ＞１）に比例する画像信号を補正後の画像信号とし、表示装置が設置される場所の明るさが明るいほどγの値を小さい値に設定してもよい。この方法によれば、γの値を変えて非線形補正の特性を変化させることができる。   In addition, the non-linear correction of the image signal processing method of the present invention uses the image signal proportional to the γ power (γ> 1) of the image signal before correction as the corrected image signal, and the brightness of the place where the display device is installed The value of γ may be set to a smaller value as the brightness increases. According to this method, the nonlinear correction characteristic can be changed by changing the value of γ.

また、本発明の画像信号処理方法の非線形補正の特性は、人間の感じる明るさが補正前の画像信号に対して線形となるように設定してもよい。この方法によれば、画像信号に対する表示輝度がどのような特性をもつ表示装置であっても、線形に感じることができる補正の特性を求めることができる。   Further, the nonlinear correction characteristic of the image signal processing method of the present invention may be set so that the brightness perceived by a human is linear with respect to the image signal before correction. According to this method, it is possible to obtain correction characteristics that can be felt linearly regardless of the characteristics of the display luminance with respect to the image signal.

また、本発明は表示装置に入力する画像信号に非線形補正を施す画像信号処理方法であって、表示装置が設置される場所の明るさと表示装置が表示する最大輝度とに基づいて非線形補正の特性を変化させることを特徴とする。この方法によれば、ユーザが表示モードを切替えて表示装置の表示する最大輝度を変えても、人間が感じる明るさの程度を入力階調に対してほぼ線形な特性に戻すことができる。   The present invention is also an image signal processing method for performing non-linear correction on an image signal input to a display device, the non-linear correction characteristic based on the brightness of a place where the display device is installed and the maximum luminance displayed by the display device. It is characterized by changing. According to this method, even if the user switches the display mode to change the maximum luminance displayed by the display device, the degree of brightness perceived by the human can be returned to a characteristic that is substantially linear with respect to the input gradation.

また、本発明の画像信号処理方法の非線形補正は、補正前の画像信号のγ乗（γ＞１）に比例する画像信号を補正後の画像信号とし、表示装置が設置される場所の明るさが明るいほどγの値を小さい値に設定し、かつ表示装置の表示可能な最大輝度が高いほどγの値を大きな値に設定してもよい。この方法によれば、γの値を変えて非線形補正の特性を変化させることができる。   Further, the nonlinear correction of the image signal processing method of the present invention uses the image signal proportional to the γ power (γ> 1) of the image signal before correction as the corrected image signal, and the brightness of the place where the display device is installed The value of γ may be set to a smaller value as the brightness increases, and the value of γ may be set to a larger value as the maximum luminance that can be displayed by the display device increases. According to this method, the characteristic of nonlinear correction can be changed by changing the value of γ.

また、本発明は表示装置に入力する画像信号に非線形補正を施す画像信号処理装置であって、表示装置が設置される場所の明るさを検出する周囲光検出部と、周囲光検出部の検出結果を入力するとともに補正前の画像信号に非線形補正を施して補正後の画像信号に変換する変換部とを備え、変換部は非線形補正の特性がそれぞれ異なる複数のルックアップテーブルと、周囲光検出部の検出結果に基づき複数のルックアップテーブルの中から１つのルックアップテーブルを選択するルックアップテーブル選択部とを備えたことを特徴とする。この構成により、周囲光の影響を受けて表示装置の表示輝度が一様に上昇しても、画像信号に対して人間が感じる明るさの特性を線形とすることができる画像信号処理装置を提供することができる。   Further, the present invention is an image signal processing device that performs nonlinear correction on an image signal input to a display device, the ambient light detection unit detecting the brightness of a place where the display device is installed, and the detection of the ambient light detection unit A conversion unit that inputs a result and performs non-linear correction on the image signal before correction to convert the image signal into a corrected image signal. The conversion unit includes a plurality of look-up tables each having different characteristics of non-linear correction, and ambient light detection. And a lookup table selection unit that selects one lookup table from a plurality of lookup tables based on the detection result of the part. With this configuration, there is provided an image signal processing device capable of linearizing the brightness characteristic felt by humans with respect to an image signal even when the display luminance of the display device increases uniformly under the influence of ambient light. can do.

また、本発明は表示装置に入力する画像信号に非線形補正を施す画像信号処理装置であって、表示装置が設置される場所の明るさを検出する周囲光検出部と、周囲光検出部の検出結果および表示装置が表示する最大輝度を示す信号を入力するとともに補正前の画像信号に非線形補正を施して補正後の画像信号に変換する変換部とを備え、変換部は、非線形補正の特性がそれぞれ異なる複数のルックアップテーブルと、周囲光検出部の検出結果と表示装置が表示する最大輝度に基づき複数のルックアップテーブルの中から１つのルックアップテーブルを選択するルックアップテーブル選択部とを備えたことを特徴とする。この構成によれば、ユーザが表示モードを切替えて表示装置の表示する最大輝度を変えても、人間が感じる明るさの程度を入力階調に対してほぼ線形な特性に戻すことができる。   Further, the present invention is an image signal processing device that performs nonlinear correction on an image signal input to a display device, the ambient light detection unit detecting the brightness of a place where the display device is installed, and the detection of the ambient light detection unit A conversion unit that inputs a signal indicating the result and the maximum luminance displayed by the display device and performs non-linear correction on the image signal before correction to convert the image signal into a corrected image signal. A plurality of different look-up tables, and a look-up table selection unit that selects one look-up table from among the plurality of look-up tables based on the detection result of the ambient light detection unit and the maximum luminance displayed by the display device. It is characterized by that. According to this configuration, even if the user switches the display mode and changes the maximum luminance displayed by the display device, the degree of brightness perceived by humans can be returned to a substantially linear characteristic with respect to the input gradation.

また、複数のルックアップテーブルとルックアップテーブル選択部との機能を演算処理装置を用いて実現した構成としてもよい。この構成によれば、少ない回路部品を用いて変換部を構成できる。   Moreover, it is good also as a structure which implement | achieved the function of the several lookup table and the lookup table selection part using the arithmetic processing unit. According to this configuration, the conversion unit can be configured using a small number of circuit components.

また、本発明の画像表示装置は、上記の画像信号処理装置を備えた画像表示装置である。この構成により、周囲光の影響を受けて表示装置の表示輝度が一様に上昇しても、画像信号に対して人間が感じる明るさの特性を線形とすることができる画像表示装置を提供することができる。   An image display device according to the present invention is an image display device including the above-described image signal processing device. With this configuration, there is provided an image display apparatus capable of linearizing the brightness characteristic felt by humans with respect to an image signal even when the display brightness of the display apparatus increases uniformly due to the influence of ambient light. be able to.

本発明によれば、周囲光の影響を受けて表示装置の表示輝度が一様に上昇しても、画像信号に対して人間が感じる明るさの特性を線形とすることができる画像信号処理方法、画像信号処理装置およびそれを用いた画像表示装置を提供することができる。   According to the present invention, even if the display brightness of the display device is uniformly increased due to the influence of ambient light, the image signal processing method that can linearize the brightness characteristic felt by humans with respect to the image signal. An image signal processing apparatus and an image display apparatus using the same can be provided.

以下本発明の一実施の形態について、図面を参照しながら説明する。   Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

（実施の形態１）
図１は本発明の実施の形態１における画像表示装置１００の回路ブロック図である。画像信号処理装置１０１は入力画像信号、すなわち入力階調に非線形補正を施し表示装置１０３に出力する。表示装置１０３は、ＤＭＤやＰＤＰ等を用いた、ガンマ特性をもたない表示装置である。画像信号処理装置１０１は、周囲の明るさを検出する周囲光検出部１０４と、周囲の明るさに基づいて入力階調を非線形補正する変換部１０５とを備えている。 (Embodiment 1)
FIG. 1 is a circuit block diagram of an image display apparatus 100 according to Embodiment 1 of the present invention. The image signal processing apparatus 101 performs nonlinear correction on the input image signal, that is, the input gradation, and outputs the result to the display apparatus 103. The display device 103 is a display device that does not have gamma characteristics using DMD, PDP, or the like. The image signal processing apparatus 101 includes an ambient light detection unit 104 that detects ambient brightness, and a conversion unit 105 that nonlinearly corrects an input tone based on ambient brightness.

周囲光検出部１０４は、周囲の明るさを検出する光センサ１０６と、光センサ１０６からの検出信号をデジタル信号に変換するＡＤ変換部１０７とを有する。変換部１０５は、入力階調に非線形補正を施すための複数のＬＵＴ１０８１〜１０８４と、複数のＬＵＴ１０８１〜１０８４の中から周囲光検出部１０４の検出信号に基づいて１つのＬＵＴを選択するＬＵＴ選択部１１２とを有する。図１には４つのＬＵＴ１０８１〜１０８４を記載しているが、もちろんＬＵＴの数は４つに限られるものではなく、必要に応じて任意の数で構成することができる。一般的にはＬＵＴの数を増やすことにより、広い範囲の外周光に対応することができ、また、ＬＵＴ切替えに伴う表示輝度の変化を小さく設定することができる。 The ambient light detection unit 104 includes an optical sensor 106 that detects ambient brightness, and an AD conversion unit 107 that converts a detection signal from the optical sensor 106 into a digital signal. Converter 105, selects a plurality of LUT 108 1 -108 4 for performing nonlinear correction, one LUT based on the detection signal of the ambient light detecting unit 104 from a plurality of LUT 108 1 -108 4 to the input gradation And an LUT selection unit 112 to perform. Although four LUTs 108 1 to 108 4 are shown in FIG. 1, of course, the number of LUTs is not limited to four, and any number can be configured as necessary. In general, by increasing the number of LUTs, it is possible to deal with a wide range of ambient light, and it is possible to set a small change in display luminance due to LUT switching.

複数のＬＵＴ１０８１〜１０８４のそれぞれは、
（表示階調）＝Ｋ×（入力階調）γ
にしたがって、入力階調に非線形補正を施す。ここで、ガンマ係数γは１より大きい値であり、ＬＵＴ毎にそれぞれ異なった値に設定されている。また係数Ｋは、表示階調の最大値を入力階調の最大値と等しくするための係数であり、
Ｋ＝（入力階調の最大値）（１−γ）
で表される。 Each of the plurality of LUTs 108 1 to 108 4
(Display gradation) = K × (Input gradation) γ
According to the above, nonlinear correction is applied to the input gradation. Here, the gamma coefficient γ is a value larger than 1, and is set to a different value for each LUT. The coefficient K is a coefficient for making the maximum value of the display gradation equal to the maximum value of the input gradation.
K = (maximum value of input gradation) (1-γ)
It is represented by

本実施の形態においては、ＬＵＴ１０８１は周囲光等の無い暗所における非線形補正用のＬＵＴであり、ガンマ係数γを２．２に設定している。暗所においては、ＬＵＴ１０８１を用いて入力階調に非線形補正を施して画像表示を行うと、入力階調と表示輝度との関係は、図２（ａ）の特性線Ａに示したようになる。そして、人間が感じる明るさの程度は、図２（ｂ）の特性線Ｂに示したように、入力階調に対してほぼ線形な特性を示すことになる。また、図２（ａ）の特性線Ｃに示すように、周囲光の影響を受けて表示輝度が一様に上昇した場合、暗所用のＬＵＴ１０８１を用いて非線形補正を行えば、図２（ｂ）の特性線Ｄに示したように人間が感じる明るさの程度は線形性が損なわれ、入力階調の低い部分において階調がつぶれてしまう。したがってこの場合には、図２（ａ）の特性線Ｅに示すように、ガンマ係数γの小さいＬＵＴ１０８４に切替えて非線形補正を施す。すると、人間が感じる明るさの程度を、図２（ｂ）の特性線Ｆに示したように、入力階調に対してほぼ線形な特性に戻すことができる。 In this embodiment, LUT 108 1 is a LUT for nonlinear compensation in a dark place without such ambient light, have set a gamma coefficient γ to 2.2. In the dark, when an image is displayed by performing non-linear correction on the input gradation using LUT 108 1, the relationship between the input gradation and the display luminance, as shown by a characteristic line A in FIG. 2 (a) Become. The level of brightness perceived by humans exhibits a substantially linear characteristic with respect to the input gradation, as indicated by the characteristic line B in FIG. Further, as shown by the characteristic line C in FIG. 2 (a), when the display luminance uniformly increased by the influence of ambient light, by performing non-linear correction using LUT 108 1 for a dark Shoyo, 2 ( As indicated by the characteristic line D in (b), the degree of brightness perceived by humans is lost in the linearity, and the gradation is crushed at the low input gradation. Therefore, in this case, as shown by the characteristic line E in FIG. 2 (a), performing nonlinear correction is switched to a small LUT 108 4 gamma coefficient gamma. As a result, the brightness level perceived by humans can be returned to a substantially linear characteristic with respect to the input gradation, as indicated by the characteristic line F in FIG.

なお、本実施の形態においては、４つのＬＵＴ１０８１〜１０８４のガンマ係数γをそれぞれ２．２、２．１、２．０、１．９と設定し、周囲光検出部１０４の検出結果に基づきそれらＬＵＴを切替えているが、本発明は、入力階調に施す非線形補正の特性を周囲光に応じて変化させるものであれば、他の構成を用いてもよい。例えば、複数のルックアップテーブルとルックアップテーブル選択部との機能をデジタルシグナルプロセッサ等の演算処理装置を用いて実現し、図３に示したように、変換部２０５として演算処理装置２００を用いて、画像信号と周囲光の検出信号とを入力し表示階調を出力する構成としてもよい。この構成によれば、少ない回路部品を用いて変換部を構成できる。 In this embodiment, the gamma coefficients γ of the four LUTs 108 1 to 108 4 are set to 2.2, 2.1, 2.0, and 1.9, respectively, and the detection result of the ambient light detection unit 104 is used. The LUTs are switched based on the above, but the present invention may use other configurations as long as the characteristics of nonlinear correction applied to the input gradation are changed according to the ambient light. For example, the functions of a plurality of lookup tables and lookup table selection units are realized by using an arithmetic processing device such as a digital signal processor, and as shown in FIG. Alternatively, a configuration may be adopted in which an image signal and an ambient light detection signal are input and display gradation is output. According to this configuration, the conversion unit can be configured using a small number of circuit components.

また、本実施の形態においては、ガンマ係数γの値を変えて非線形補正の特性を変化させているが、他の方法により非線形補正の特性を変化させてもよい。例えば、いろいろな周囲光に対して、人間の感じる明るさが補正前の画像信号に対して線形となるような補正特性を実測することによって非線形補正の特性を求めてもよい。こうすることで、画像信号に対する表示輝度がどのような特性をもつ表示装置であっても、人間の感じる明るさが補正前の画像信号に対して線形に感じることができる補正の特性を求めることができる。   In this embodiment, the nonlinear correction characteristic is changed by changing the value of the gamma coefficient γ. However, the nonlinear correction characteristic may be changed by other methods. For example, the non-linear correction characteristic may be obtained by actually measuring a correction characteristic such that the brightness perceived by humans is linear with respect to the image signal before correction with respect to various ambient lights. In this way, it is possible to obtain a correction characteristic that allows the human-perceived brightness to be felt linearly with respect to the image signal before correction, regardless of the display device having the display luminance with respect to the image signal. Can do.

（実施の形態２）
図４は、本発明の実施の形態２における画像表示装置３００の回路ブロック図である。実施の形態１と同じ回路ブロックには同一の符号を付して説明を省略する。実施の形態２が実施の形態１と異なる点は、非線形補正の特性を周囲光に応じて変化させるだけでなく、表示装置１０３の表示モードにも依存して変化させている点である。例えばＰＤＰを用いた表示装置においてはその駆動原理上、表示できる階調の数（以下、「階調表示能力」と略記する）と表示できる最大輝度との間にはトレードオフの関係がある。そこで、表示装置１０３の表示モードとして「ダイナミックモード」、「スタンダードモード」、「シネマモード」等を設け、ユーザが好みの表示モードを選択することができるように設計されている。ここで、「ダイナミックモード」は階調表示能力をやや犠牲にして最大輝度を高めた表示モードであり、「シネマモード」は最大輝度を抑えて階調表示能力を高めた表示モードであり、「スタンダードモード」はそれらの中間的な表示モードである。 (Embodiment 2)
FIG. 4 is a circuit block diagram of image display apparatus 300 according to Embodiment 2 of the present invention. The same circuit blocks as those of the first embodiment are denoted by the same reference numerals, and description thereof is omitted. The second embodiment is different from the first embodiment in that the nonlinear correction characteristic is changed depending not only on the ambient light but also on the display mode of the display device 103. For example, in a display device using a PDP, there is a trade-off relationship between the number of gradations that can be displayed (hereinafter abbreviated as “gradation display capability”) and the maximum luminance that can be displayed due to its driving principle. Therefore, “dynamic mode”, “standard mode”, “cinema mode”, and the like are provided as display modes of the display device 103 so that the user can select a desired display mode. Here, “dynamic mode” is a display mode in which the maximum luminance is increased at the expense of the gradation display capability, and “cinema mode” is a display mode in which the maximum luminance is suppressed and the gradation display capability is increased. “Standard mode” is an intermediate display mode.

人間が感じる明るさの程度は上述したように周囲光の影響を受けるが、もちろん表示装置の表示する輝度に直接に影響される。そして、人間の感じる明るさの程度を入力階調に対して線形にするためには、周囲光だけでなく、表示装置の表示する最大輝度にも依存して非線形補正の特性を変化させる必要がある。   The degree of brightness perceived by humans is affected by ambient light as described above, but of course is directly affected by the brightness displayed by the display device. In order to make the degree of brightness perceived by humans linear with respect to the input gradation, it is necessary to change the nonlinear correction characteristics depending not only on the ambient light but also on the maximum luminance displayed by the display device. is there.

変換部３０５は、入力階調に非線形補正を施すための複数のＬＵＴ１０８１〜１０８１２と、複数のＬＵＴ１０８１〜１０８１２の中から周囲光検出部１０４の検出信号および表示装置１０３から出力される表示モード信号に基づいて１つのＬＵＴを選択するＬＵＴ選択部３１２とを有する。図４にはそれぞれの表示モードに対して４つのＬＵＴ、合計１２のＬＵＴを備えた構成を示したが、もちろんＬＵＴの数は必要に応じて任意の数で構成することができる。 Conversion unit 305, a plurality of LUT 108 1 -108 12 for performing nonlinear compensation on the input gradation are output from the detection signal and the display device 103 of the ambient light detecting unit 104 from a plurality of LUT 108 1 -108 12 An LUT selection unit 312 that selects one LUT based on the display mode signal. Although FIG. 4 shows a configuration including four LUTs for each display mode, that is, a total of 12 LUTs, of course, the number of LUTs can be configured as desired.

そして同一の表示モードに対しては、周囲光が高くなるにつれてガンマ係数γの小さいＬＵＴに切替える。また、周囲光が同一の場合には、「ダイナミックモード」ではガンマ係数γの大きいＬＵＴに切替え、「シネマモード」ではガンマ係数γの小さいＬＵＴに切替える。   For the same display mode, the LUT is switched to a LUT having a smaller gamma coefficient γ as the ambient light increases. When the ambient light is the same, the “dynamic mode” is switched to an LUT having a large gamma coefficient γ, and the “cinema mode” is switched to an LUT having a small gamma coefficient γ.

このように、周囲光だけでなく、表示装置の表示モードにも依存して非線形補正の特性を変化させることにより、ユーザが表示モードを切替えて表示装置の表示する最大輝度を変えても、人間が感じる明るさの程度を入力階調に対してほぼ線形な特性に戻すことができる。   In this way, by changing the nonlinear correction characteristics depending on not only the ambient light but also the display mode of the display device, even if the user changes the maximum luminance displayed by the display device by switching the display mode, The degree of brightness felt by can be returned to a substantially linear characteristic with respect to the input gradation.

なお、実施の形態２においては表示装置が表示する最大輝度を示す信号として表示装置１０３から出力される表示モード信号を用いたが、表示装置の表示する最大輝度を示す信号であれば他の信号でもよく、例えば補正前の画像信号のＡＰＬを用いてもよい。また、表示装置の最大輝度を示す信号として、表示モードを示す信号と画像信号のＡＰＬとの２つの信号を用いてもよい。   In the second embodiment, the display mode signal output from the display device 103 is used as a signal indicating the maximum luminance displayed by the display device. However, other signals may be used as long as the signal indicates the maximum luminance displayed by the display device. For example, the APL of the image signal before correction may be used. In addition, as a signal indicating the maximum luminance of the display device, two signals of a signal indicating a display mode and an APL of an image signal may be used.

さらに、実施の形態２においても、変換部３０５として複数のＬＵＴを切替える構成を示したが、非線形補正の特性を変化させる構成であれば他の構成を用いてもよい。例えば、変換部３０５として、デジタルシグナルプロセッサ等の演算処理装置を用いて、画像信号と周囲光の検出信号と最大輝度を示す信号とを入力し表示階調を出力する構成としてもよい。   Further, in the second embodiment, a configuration in which a plurality of LUTs are switched as the conversion unit 305 has been described. However, other configurations may be used as long as the nonlinear correction characteristics are changed. For example, the conversion unit 305 may be configured to input an image signal, a detection signal of ambient light, and a signal indicating maximum luminance by using an arithmetic processing device such as a digital signal processor and output a display gradation.

また、実施の形態２においても、非線形補正の特性を変化させる方法として、ガンマ係数γの異なる複数のＬＵＴを切替えたが、いろいろな周囲光および表示装置の最大輝度に対して、人間の感じる明るさの程度が入力階調に対して線形となるような補正特性を実測することによって非線形補正の特性を求めてもよい。   Also in the second embodiment, as a method of changing the characteristics of nonlinear correction, a plurality of LUTs having different gamma coefficients γ are switched. However, the brightness felt by humans with respect to various ambient lights and the maximum luminance of the display device. The nonlinear correction characteristic may be obtained by actually measuring a correction characteristic such that the degree of linearity is linear with respect to the input gradation.

本発明の画像信号処理方法、画像信号処理装置および画像表示装置は、周囲光の影響を受けて表示装置の表示輝度が一様に上昇しても、画像信号に対して人間が感じる明るさの特性を線形とすることができるので、画像信号に対して非線形補正を施す画像表示装置等として有用である。   The image signal processing method, the image signal processing apparatus, and the image display apparatus according to the present invention have the brightness that humans feel with respect to the image signal even when the display luminance of the display apparatus increases uniformly under the influence of ambient light. Since the characteristic can be made linear, it is useful as an image display device that performs nonlinear correction on an image signal.

本発明の実施の形態１における画像表示装置の回路ブロック図1 is a circuit block diagram of an image display device according to Embodiment 1 of the present invention. （ａ）は本発明の実施の形態１の画像信号補正方法における入力階調と表示輝度との関係を示す図、（ｂ）は入力階調と人間が感じる明るさの程度との関係を示す図(A) is a figure which shows the relationship between the input gradation and display luminance in the image signal correction method of Embodiment 1 of this invention, (b) shows the relationship between an input gradation and the brightness level which a human senses. Figure 本発明の実施の形態１における他の画像表示装置の回路ブロック図The circuit block diagram of the other image display apparatus in Embodiment 1 of this invention 本発明の実施の形態２における画像表示装置の回路ブロック図Circuit block diagram of an image display device in Embodiment 2 of the present invention 輝度に対して人間が感じる明るさの程度を示す図A figure showing the degree of brightness that humans feel with respect to brightness （ａ）はＣＲＴの画像信号と表示輝度との関係を示す図、（ｂ）はＤＭＤ、ＰＤＰの画像信号と表示輝度との関係を示す図(A) is a figure which shows the relationship between the image signal of CRT, and a display brightness | luminance, (b) is a figure which shows the relationship between the image signal of DMD, PDP, and a display brightness | luminance. 従来例における画像表示装置の回路ブロック図Circuit block diagram of an image display device in a conventional example ルックアップテーブルの入出力特性の一例を示す図Diagram showing an example of input / output characteristics of the lookup table （ａ）は従来例の画像信号補正方法における入力階調と表示輝度との関係を示す図、（ｂ）は入力階調と人間が感じる明るさの程度との関係を示す図(A) is a figure which shows the relationship between the input gradation and display brightness | luminance in the image signal correction method of a prior art example, (b) is a figure which shows the relationship between an input gradation and the degree of the brightness which a human senses.

符号の説明Explanation of symbols

１００，３００ 画像表示装置
１０１ 画像信号処理装置
１０３ 表示装置
１０４ 周囲光検出部
１０５，２０５，３０５ 変換部
１０８１〜１０８１２ ＬＵＴ
１１２，３１２ ＬＵＴ選択部
２００ 演算処理装置 100,300 image display device 101 an image signal processing device 103 display device 104 the ambient light detector 105, 205, 305 conversion unit 108 1 -108 12 LUT
112, 312 LUT selection unit 200 arithmetic processing unit

Claims (9)

表示装置に入力する画像信号に非線形補正を施す画像信号処理方法であって、
前記表示装置が設置される場所の明るさに基づいて前記非線形補正の特性を変化させることを特徴とする画像信号処理方法。 An image signal processing method for performing nonlinear correction on an image signal input to a display device,
An image signal processing method, wherein the nonlinear correction characteristic is changed based on brightness of a place where the display device is installed. 前記非線形補正は、補正前の画像信号のγ乗（γ＞１）に比例する画像信号を補正後の画像信号とし、
前記表示装置が設置される場所の明るさが明るいほど前記γの値を小さい値に設定することを特徴とする請求項１に記載の画像信号処理方法。 In the non-linear correction, an image signal proportional to the γ power (γ> 1) of the image signal before correction is used as an image signal after correction,
The image signal processing method according to claim 1, wherein the value of γ is set to a smaller value as the brightness of a place where the display device is installed is brighter. 前記非線形補正の特性は、人間の感じる明るさが補正前の画像信号に対して線形となるように設定することを特徴とする請求項１に記載の画像信号処理方法。 The image signal processing method according to claim 1, wherein the characteristic of the nonlinear correction is set so that the brightness perceived by a human is linear with respect to the image signal before correction. 表示装置に入力する画像信号に非線形補正を施す画像信号処理方法であって、
前記表示装置が設置される場所の明るさと前記表示装置が表示する最大輝度とに基づいて前記非線形補正の特性を変化させることを特徴とする画像信号処理方法。 An image signal processing method for performing nonlinear correction on an image signal input to a display device,
An image signal processing method, wherein the nonlinear correction characteristic is changed based on a brightness of a place where the display device is installed and a maximum luminance displayed by the display device. 前記非線形補正は、補正前の画像信号のγ乗（γ＞１）に比例する画像信号を補正後の画像信号とし、
前記表示装置が設置される場所の明るさが明るいほど前記γの値を小さい値に設定し、かつ前記表示装置の表示可能な最大輝度が高いほど前記γの値を大きな値に設定することを特徴とする請求項４に記載の画像信号処理方法。 In the non-linear correction, an image signal proportional to the γ power (γ> 1) of the image signal before correction is used as an image signal after correction,
The value of γ is set to a smaller value as the brightness of the place where the display device is installed is brighter, and the value of γ is set to a larger value as the maximum luminance that can be displayed on the display device is higher. The image signal processing method according to claim 4, wherein: 表示装置に入力する画像信号に非線形補正を施す画像信号処理装置であって、
前記表示装置が設置される場所の明るさを検出する周囲光検出部と、
前記周囲光検出部の検出結果を入力するとともに、補正前の画像信号に非線形補正を施して補正後の画像信号に変換する変換部とを備え、
前記変換部は、非線形補正の特性がそれぞれ異なる複数のルックアップテーブルと、前記周囲光検出部の検出結果に基づき前記複数のルックアップテーブルの中から１つのルックアップテーブルを選択するルックアップテーブル選択部とを備えたことを特徴とする画像信号処理装置。 An image signal processing device that performs nonlinear correction on an image signal input to a display device,
An ambient light detector that detects the brightness of a place where the display device is installed;
A conversion unit that inputs the detection result of the ambient light detection unit and performs nonlinear correction on the image signal before correction to convert the image signal into a corrected image signal,
The conversion unit selects a plurality of lookup tables having different nonlinear correction characteristics and a lookup table selection from the plurality of lookup tables based on the detection result of the ambient light detection unit And an image signal processing apparatus. 表示装置に入力する画像信号に非線形補正を施す画像信号処理装置であって、
前記表示装置が設置される場所の明るさを検出する周囲光検出部と、
前記周囲光検出部の検出結果および前記表示装置が表示する最大輝度を示す信号を入力するとともに、補正前の画像信号に非線形補正を施して補正後の画像信号に変換する変換部とを備え、
前記変換部は、非線形補正の特性がそれぞれ異なる複数のルックアップテーブルと、前記周囲光検出部の検出結果と前記表示装置が表示する最大輝度に基づき前記複数のルックアップテーブルの中から１つのルックアップテーブルを選択するルックアップテーブル選択部とを備えたことを特徴とする画像信号処理装置。 An image signal processing device that performs nonlinear correction on an image signal input to a display device,
An ambient light detector that detects the brightness of a place where the display device is installed;
A detection unit that inputs a detection result of the ambient light detection unit and a signal indicating the maximum luminance displayed by the display device, and a conversion unit that performs nonlinear correction on the image signal before correction and converts the signal into a corrected image signal;
The conversion unit includes a plurality of look-up tables having different nonlinear correction characteristics, a detection result of the ambient light detection unit, and a maximum brightness displayed by the display device, and one look-up table from the plurality of look-up tables. An image signal processing apparatus comprising: a lookup table selection unit that selects an up table. 前記複数のルックアップテーブルと前記ルックアップテーブル選択部との機能を演算処理装置を用いて実現したことを特徴とする請求項６または請求項７に記載の画像信号処理装置。 8. The image signal processing device according to claim 6, wherein the functions of the plurality of lookup tables and the lookup table selection unit are realized by using an arithmetic processing device. 請求項６または請求項７に記載の画像信号処理装置を備えた画像表示装置。 An image display device comprising the image signal processing device according to claim 6.
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