JPH04110920A - Gradation correcting circuit - Google Patents
Gradation correcting circuitInfo
- Publication number
- JPH04110920A JPH04110920A JP2231671A JP23167190A JPH04110920A JP H04110920 A JPH04110920 A JP H04110920A JP 2231671 A JP2231671 A JP 2231671A JP 23167190 A JP23167190 A JP 23167190A JP H04110920 A JPH04110920 A JP H04110920A
- Authority
- JP
- Japan
- Prior art keywords
- circuit
- signal
- apl
- white
- black
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
- 238000012937 correction Methods 0.000 claims description 27
- 238000001514 detection method Methods 0.000 claims description 11
- 238000003786 synthesis reaction Methods 0.000 claims description 9
- 230000015572 biosynthetic process Effects 0.000 claims description 8
- 230000006835 compression Effects 0.000 abstract description 4
- 238000007906 compression Methods 0.000 abstract description 4
- 239000011159 matrix material Substances 0.000 abstract description 2
- 238000010586 diagram Methods 0.000 description 7
- 239000004973 liquid crystal related substance Substances 0.000 description 6
- 238000013459 approach Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000003384 imaging method Methods 0.000 description 2
- 230000003321 amplification Effects 0.000 description 1
- 239000003990 capacitor Substances 0.000 description 1
- 238000003199 nucleic acid amplification method Methods 0.000 description 1
- 238000002834 transmittance Methods 0.000 description 1
Landscapes
- Controls And Circuits For Display Device (AREA)
- Liquid Crystal (AREA)
- Projection Apparatus (AREA)
- Liquid Crystal Display Device Control (AREA)
Abstract
Description
【発明の詳細な説明】
（イ）産業上の利用分野
本発明は、液晶プロジェクションに好適な階調補正回路
に関する。DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a gradation correction circuit suitable for liquid crystal projection.
（ロ）従来の技術
現在一般に行われている階調補正としてはγ補正がある
。これは、撮像側と受像側のトータルのγ値が１となる
ようあらかじめ撮像側で補正をするもので、主としてＣ
ＲＴを念頭においている。(b) Prior Art A gradation correction commonly performed at present is γ correction. This is a correction performed on the imaging side in advance so that the total γ value on the imaging side and the image receiving side is 1.
I have RT in mind.
一方、ＬＣＤパネルを用いたデイスプレィの場合、その
電圧−輝度特性は一般にＣＲＴのそれとは異なる。On the other hand, in the case of a display using an LCD panel, its voltage-luminance characteristics are generally different from those of a CRT.
従って、例えば、特公平２−６０６９号公報に記載のよ
うにパネルの特性に応じて黒伸張や白伸張などの処理が
一般に行われている。Therefore, for example, as described in Japanese Patent Publication No. 2-6069, processing such as black extension or white extension is generally performed depending on the characteristics of the panel.
一方、自然界における光のコントラストは非常に幅が広
く、これを再現する映像機器はそれだけのダイナミック
レンジをもっていない。特にＬＣＤパネルをライトバル
ブとして用いた液晶プロジェクタは、ピーク輝度が光源
によって制限されており、一般にＣＲＴ方式に比べてダ
イナミックレンジは狭い。On the other hand, the contrast of light in the natural world has a very wide range, and the video equipment that reproduces this does not have that much dynamic range. In particular, a liquid crystal projector using an LCD panel as a light valve has peak brightness limited by the light source, and generally has a narrower dynamic range than a CRT type.
（ハ）発明が解決しようとする課趙 本発明は上述の点に鑑み為されたものであり。(c) The problem that the invention aims to solve The present invention has been made in view of the above points.
液晶プロジェクタ等のダイナミックレンジの狭い映像機
器においても大きなコントラスト比が得られる階調補正
回路を提供するものである。The present invention provides a gradation correction circuit that can obtain a large contrast ratio even in video equipment with a narrow dynamic range such as a liquid crystal projector.
（ニ）課組を解決するための手段
本発明は入力映像信号の黒側の信号を伸張し白側の信号
を圧縮する第１階調補正回路と、前記入力映像信号の白
側の信号を伸張し、黒側の信号を圧縮する第２階調補正
回路と、
前記入力映像信号の平均輝度レベル検出する検出回路と
、
この検出回路出力により制御され、前記平均輝度レベル
に応じて前記第１若しくは第２階調補正回路出力を異な
る合成比で合成して出力する合成回路とからなる階調補
正回路である。(d) Means for solving the problem The present invention includes a first gradation correction circuit that expands the black side signal of the input video signal and compresses the white side signal, and a first gradation correction circuit that expands the black side signal of the input video signal and compresses the white side signal of the input video signal. a second gradation correction circuit that expands and compresses the black side signal; a detection circuit that detects the average luminance level of the input video signal; and a detection circuit that detects the average luminance level of the input video signal; Alternatively, it is a gradation correction circuit including a synthesis circuit that synthesizes the outputs of the second gradation correction circuit at different synthesis ratios and outputs the result.
（ホ）作 用
上述の手段により平均輝度レベルが低いときは黒伸張、
白圧縮がなされ、平均輝度レベルが高いときは白伸張、
黒圧縮がなされる。(e) Effect When the average luminance level is low by the above-mentioned means, black extension,
White compression is performed, and when the average brightness level is high, white expansion is performed.
Black compression is performed.
（へ）実施例 以下、図面に従い本発明の一実施例を説明する。(f) Example An embodiment of the present invention will be described below with reference to the drawings.
第１図は液晶パネルをノーマリホワイト駆動させた時の
透過率−電圧特性を示し、この様な特性を有する液晶パ
ネルにおいて良好なリニアリテノをえるためには映像信
号に吋り、第２図の様な階調補正いわゆる逆γ補正を行
なう必要がある。Figure 1 shows the transmittance-voltage characteristics when the liquid crystal panel is driven in normally white mode. It is necessary to perform various gradation corrections, so-called inverse γ corrections.
第４図に本実施例回路の回路図を示す。図中、入力端子
（１功・ら入力されるＹ信号（輝度信号）は第１及び第
２階調補正回路（２）（３）に夫々供給される。FIG. 4 shows a circuit diagram of the circuit of this embodiment. In the figure, a Y signal (luminance signal) input from an input terminal (1) is supplied to first and second gradation correction circuits (2) and (3), respectively.
この第１、第２階調補正回路（２）（３）出力は合成回
路（４）で合成される。この合成回路は入力）゛信号の
ＡＰＬ（平均輝度レベル）を検出するＡＰＬ検出回路（
５）出力によりその合成比が制御される。そして、合成
回路（４）出力はＩ信号及びＱ信号と共にマトリクス回
路（６）に供給され、ＲｌＧ、Ｂ原色信号に復調される
。The outputs of the first and second gradation correction circuits (2) and (3) are combined by a combining circuit (4). This synthesis circuit is an APL detection circuit (input) that detects the APL (average luminance level) of the signal.
5) The synthesis ratio is controlled by the output. The output of the synthesis circuit (4) is then supplied to the matrix circuit (6) together with the I signal and the Q signal, and demodulated into RlG and B primary color signals.
前記第１階調補正回路（２）は第３図（イ）に示す特性
を有し、第２図の特性に対し過補正となる。The first gradation correction circuit (2) has the characteristics shown in FIG. 3(A), and overcorrects compared to the characteristics shown in FIG. 2.
また、前記第２階調補正回路（３）は第３図（ロ）に示
す如くリニアな特性を有する。尚、両特性の出力Ｐ −
Ｐ ｆｆｆｉは同じである。Further, the second gradation correction circuit (3) has linear characteristics as shown in FIG. 3(b). In addition, the output P − of both characteristics
Pfffi is the same.
そして、前記合成回路（４）はＡＰＬ検出回路（５）出
力によりＡＰＬが低い時は特性（イ）に近付け、ＡＰＬ
が高い時は特性（ロ）に近付ける様、制御される。Then, when the APL is low, the synthesis circuit (4) approaches the characteristic (A) according to the output of the APL detection circuit (5), and the APL
When is high, it is controlled so that it approaches characteristic (b).
即ち、ＡＰＬが低い時は黒伸張が行なわれ、ＡＰＬが高
い時は電気的にはリニアな特性であるが、第１図の様な
パネル自身の特性により結果的に白伸張が行なわれる。That is, when the APL is low, black expansion is performed, and when the APL is high, the characteristics are electrically linear, but as a result, white expansion is performed due to the characteristics of the panel itself as shown in FIG.
次に第５図に第１及び第２階調補正回路の具体的実施例
について説明する。Next, a specific example of the first and second gradation correction circuits will be described with reference to FIG.
第５図において、入力端子（１）より入力されたＹ信号
はトランジスタ（Ｑｌ）と抵抗（Ｒ１）により構成され
るバッファを介しトランジスタ（Ｑ 、）（Ｑ ｓ）の
ベースに入力される。トランジスタ（Ｑ 、）（Ｑ 、
）及び（Ｑ 、）（Ｑ 、）のベースは夫々共通であり
、またトランジスタ（Ｑ 、）（Ｑ ｔ）には共通の負
荷抵抗（Ｒ４）が接続されている。In FIG. 5, a Y signal inputted from an input terminal (1) is inputted to the base of a transistor (Q, ) (Qs) via a buffer composed of a transistor (Ql) and a resistor (R1). Transistor (Q,) (Q,
) and (Q , ) (Q , ) have a common base, and a common load resistor (R4) is connected to the transistors (Q , ) (Q t).
ＡＰＬ検出回路（５）からの制御電圧が充分高い時、負
荷抵抗（Ｒ１）を流れる電流のほとんどはトランジスタ
（Ｑ、）からトランジスタ（Ｑ、）に流れ、トランジス
タ（Ｑ、）には流れない。このときトランジスタ（Ｑ、
）のエミッタ電圧が抵抗（Ｒ１）（Ｒ，。）によりベー
スバイアスされているトランジスタ（Ｑ、）のエミッタ
電圧より低くなるとトランジスタ（Ｑ、）がオンとなり
、トランジスタ（Ｑ、）のエミッタ抵抗は抵抗（Ｒ７）
と（Ｒ，）の合成抵抗となる。When the control voltage from the APL detection circuit (5) is sufficiently high, most of the current flowing through the load resistor (R1) flows from transistor (Q, ) to transistor (Q, ) and does not flow to transistor (Q, ). At this time, the transistor (Q,
) becomes lower than the emitter voltage of the transistor (Q,) which is base biased by the resistor (R1) (R,.), the transistor (Q,) turns on, and the emitter resistance of the transistor (Q,) becomes the resistor. (R7)
and (R,) become the combined resistance.
従って、トランジスタ（Ｑ、）のベースバイアスを適当
に設定することにより、トランジスタ（Ｑ、）のエミッ
タ出力（ＹＯＬ：Ｔ）は入力映像信号のレベルに応じて
ゲインが変わる折れ線特性となり、第３図（イ）の特性
が実現される。Therefore, by appropriately setting the base bias of the transistor (Q,), the emitter output (YOL:T) of the transistor (Q,) has a polygonal characteristic whose gain changes depending on the level of the input video signal, as shown in Figure 3. Characteristic (a) is realized.
一方、前記制御電圧が充分低い時、負荷抵抗（Ｒ１）を
流れる電流はトランジスタ（Ｑ、）からトランジスタ（
Ｑ、）に流れ、トランジスタ（Ｑ、）にはほとんど流れ
ない。この時の出力特性は第３図（ロ）の様なリニアな
特性になる。On the other hand, when the control voltage is sufficiently low, the current flowing through the load resistor (R1) flows from the transistor (Q,) to the transistor (
Q, ), and almost no current flows to the transistor (Q, ). The output characteristic at this time becomes a linear characteristic as shown in FIG. 3 (b).
そして、トランジスタ（Ｑりのエミッタ抵抗（Ｒ８）を
適当な値に設定することによりダイナミックレンジ（Ｖ
ｔ〜Ｖｓ）を（イ）と（ロ）で同一とすることができる
。The dynamic range (V
t~Vs) can be made the same in (a) and (b).
更に、制御電圧がトランジスタ（Ｑ 、）（Ｑ ６）の
ベースバイアス近傍にあるとき、出力特性（＝第３図（
イ）と（ロ）の中間的な特性となる。部ち、制御電圧を
可変することにより（イ）と（ロ）の間で出力特性を連
続的に変化する。Furthermore, when the control voltage is near the base bias of the transistor (Q,) (Q6), the output characteristic (= Fig. 3 (
This is an intermediate characteristic between (a) and (b). Partly, by varying the control voltage, the output characteristics are continuously changed between (a) and (b).
次に第６図はＡＰＬ検出回路の具体的実施例を示し、ト
ランジスタ（Ｑ、。）のベースに入力されたＹ信号は抵
抗（Ｒ、、）及びコンデンサ（Ｃ４）により構成される
ローパスフィルタを通過することによりＡＰＬに応じた
直流となる。そして、第５図の階調補正回路との整合を
得るため、オペアンプ（ＯＰ １）（ＯＰ 、）等によ
りレベルシフト、増幅が行なわれる。Next, FIG. 6 shows a specific example of the APL detection circuit, in which the Y signal input to the base of the transistor (Q, .) is passed through a low-pass filter composed of a resistor (R, .) and a capacitor (C4). By passing through it, it becomes a direct current according to the APL. Then, in order to obtain matching with the gradation correction circuit shown in FIG. 5, level shifting and amplification are performed by operational amplifiers (OP1) (OP1), etc.
（ト）発明の効果
上述の如く本発明に依れば、暗い画面では黒伸張、明る
い画面では白伸張を行なうため、液晶プロジェクタ等の
ダイナミンクレンジの狭い機器においてもそのダイナミ
ックレンジを有効に使うことができ、大きいコントラス
ト比を得ることができる。(g) Effects of the Invention As described above, according to the present invention, black is stretched for dark screens and white is stretched for bright screens, so the dynamic range can be used effectively even in equipment with a narrow dynamic range such as a liquid crystal projector. It is possible to obtain a large contrast ratio.
−かも従来の逆γ補正機能も兼ねているため回路購成の
合理化が計れる。-It also serves as a conventional inverse gamma correction function, allowing for rationalization of circuit purchasing.
第１図は液晶パネルの透過率−を田特性図、第２図は逆
ガンマ補正の特性図である。
第３図は本発明回路による特性図、第４図は本発明の一
実施例における回路図、第５図は第１、第２階調補正回
路の具体的回路図、第６図はＡＰＬ検出回路の具体的回
路図である。
（２）（３）・・・第１、第２階調補正回路、（４）・
・合成回路、（５）・・・ＡＰＬ検出回路。FIG. 1 is a characteristic diagram of the transmittance of a liquid crystal panel, and FIG. 2 is a characteristic diagram of reverse gamma correction. Fig. 3 is a characteristic diagram of the circuit of the present invention, Fig. 4 is a circuit diagram of an embodiment of the present invention, Fig. 5 is a specific circuit diagram of the first and second gradation correction circuits, and Fig. 6 is APL detection. It is a specific circuit diagram of a circuit. (2) (3)...first and second gradation correction circuits, (4).
-Synthesis circuit, (5)...APL detection circuit.
Claims (1)
圧縮する第１階調補正回路と、前記入力映像信号の白側
の信号を伸張し、黒側の信号を圧縮する第２階調補正回
路と、 前記入力映像信号の平均輝度レベルを検出する検出回路
と、 この検出回路出力により制御され、前記平均輝度レベル
に応じて前記第１若しくは第２階調補正回路出力を異な
る合成比で合成して出力する合成回路とからなる階調補
正回路。(1) A first gradation correction circuit that expands the black side signal of the input video signal and compresses the white side signal, and a first gradation correction circuit that expands the white side signal of the input video signal and compresses the black side signal. a two-tone correction circuit; a detection circuit that detects an average brightness level of the input video signal; and a detection circuit that is controlled by the output of the detection circuit to vary the output of the first or second tone correction circuit depending on the average brightness level. A gradation correction circuit consisting of a synthesis circuit that synthesizes at a synthesis ratio and outputs the result.
Priority Applications (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2231671A JPH04110920A (en) | 1990-08-31 | 1990-08-31 | Gradation correcting circuit |
| US07/740,169 US5257108A (en) | 1990-08-06 | 1991-08-05 | Video signal processing circuit for improving contrast for an LCD display |
| DE69125433T DE69125433T2 (en) | 1990-08-06 | 1991-08-06 | Video signal processing circuit |
| CA002048446A CA2048446C (en) | 1990-08-06 | 1991-08-06 | Video signal process circuit |
| EP91113215A EP0470579B1 (en) | 1990-08-06 | 1991-08-06 | Video signal process circuit |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2231671A JPH04110920A (en) | 1990-08-31 | 1990-08-31 | Gradation correcting circuit |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPH04110920A true JPH04110920A (en) | 1992-04-13 |
Family
ID=16927161
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2231671A Pending JPH04110920A (en) | 1990-08-06 | 1990-08-31 | Gradation correcting circuit |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH04110920A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6529211B2 (en) * | 1998-06-22 | 2003-03-04 | Texas Instruments Incorporated | Histogram-based intensity expansion |
| WO2009150749A1 (en) * | 2008-06-13 | 2009-12-17 | 富士通株式会社 | Picture correcting device, picture correcting program and picture correcting method |
| US7737963B2 (en) | 2001-09-27 | 2010-06-15 | Samsung Electronics Co., Ltd. | Liquid crystal display having gray voltages with varying magnitudes and driving method thereof |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5542445B2 (en) * | 1973-12-20 | 1980-10-30 | ||
| JPH01241272A (en) * | 1988-03-22 | 1989-09-26 | Mitsubishi Electric Corp | Gradation correction circuit |
-
1990
- 1990-08-31 JP JP2231671A patent/JPH04110920A/en active Pending
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5542445B2 (en) * | 1973-12-20 | 1980-10-30 | ||
| JPH01241272A (en) * | 1988-03-22 | 1989-09-26 | Mitsubishi Electric Corp | Gradation correction circuit |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6529211B2 (en) * | 1998-06-22 | 2003-03-04 | Texas Instruments Incorporated | Histogram-based intensity expansion |
| US7737963B2 (en) | 2001-09-27 | 2010-06-15 | Samsung Electronics Co., Ltd. | Liquid crystal display having gray voltages with varying magnitudes and driving method thereof |
| WO2009150749A1 (en) * | 2008-06-13 | 2009-12-17 | 富士通株式会社 | Picture correcting device, picture correcting program and picture correcting method |
| JP5110161B2 (en) * | 2008-06-13 | 2012-12-26 | 富士通株式会社 | Image correction apparatus, image correction program, and image correction method |
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