WO1995006999B1 - Dynamic gamma correction circuit for use in image projectors - Google Patents
Dynamic gamma correction circuit for use in image projectorsInfo
- Publication number
- WO1995006999B1 WO1995006999B1 PCT/US1994/009676 US9409676W WO9506999B1 WO 1995006999 B1 WO1995006999 B1 WO 1995006999B1 US 9409676 W US9409676 W US 9409676W WO 9506999 B1 WO9506999 B1 WO 9506999B1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- gamma correction
- amplifiers
- transfer function
- correction apparatus
- current
- Prior art date
Links
- 239000002131 composite material Substances 0.000 claims abstract 10
- 239000000203 mixture Substances 0.000 claims abstract 7
- 239000004973 liquid crystal related substance Substances 0.000 claims abstract 6
- 230000000875 corresponding Effects 0.000 claims abstract 4
- 230000000051 modifying Effects 0.000 claims abstract 4
- 230000001808 coupling Effects 0.000 claims 10
- 238000010168 coupling process Methods 0.000 claims 10
- 238000005859 coupling reaction Methods 0.000 claims 10
Abstract
Apparatus that implements a nonlinear function (gain) that provides for gamma correction of nonlinear image projectors. The nonlinearity of the transfer function is designed to compensate for the nonlinearity of a nonlinear light modulator such as a liquid crystal light valve (14) and cathode ray tube combination (12), for example, that is used in the image projector. The gamma correction circuit (20) comprises a plurality of amplifiers that include current sources coupled together to sum their output currents, and each amplifier is adapted to implement a predetermined transfer function, and provide differing levels of current. An optional output resistor may be employed to convert the composite output current into a corresponding output voltage. Each of the plurality of amplifiers typically comprises first and second emitter coupled pair transistors plus their associated current sources. The present invention corrects that gray scale linearity of the image projector in which it is employed. The amplifier configuration of the circuit does not use feedback, so its processing bandwidth remains high. The present invention also produces 'soft' breakpoints, creating a relatively smooth transfer function.
Claims
1. A dynamic gamma correction apparatus for use in an image projector comprising an image source and a nonlinear light modulator, said apparatus comprising: a plurality of amplifiers that are coupled together so as to sum their respective output currents to provide a composite output current, wherein each amplifier comprises at least two transistors and wherein each of the plurality of amplifiers is adapted to implement a predetermined individual transfer function, and wherein the plurality of amplifiers comprise a plurality of current sources that provide differing levels of current to form the composite output current and that cooperate to provide each predetermined individual transfer function; dynamic compensation means having a signal connected to some part of at least one of said amplifiers to dynamically alter the shape of the gamma correction curve; an output means adapted to convert the composite output current into a corresponding output voltage of the apparatus; wherein the combination of amplifiers and current sources is configured to compensate for nonlinearity of the image projector due to the combination of the image source and a nonlinear light modulator; and wherein each of at least two of said amplifiers includes a separate reference voltage input node for application of a reference voltage to selectively alter the transfer function of the associated individual amplifier, wherein said plurality of amplifiers are configured to generate a substantially smooth and continuous gamma correction transfer function having regions of both positive and negative change in slope.
2. The gamma correction apparatus of Claim 1 wherein each of the plurality of amplifiers comprises first and second emitter coupled transistors.
3. The gamma correction apparatus of Claim 1 wherein each of the plurahty of current sources includes a resistor.
-23-
ANIENDED SHEET (ARTICLE 19)
4. The gamma correction apparatus of Claim 2 wherein each of the plurality of current sources includes a resistor.
5. The gamma correction apparatus of Claim 2 wherein different predetermined transfer functions are provided by selectively coupling the output current derived from the first and second emitter coupled transistors to produce differing transfer functions depending upon the particular transistors that are selected.
6. The gamma correction apparatus of Claim 3 wherein different predetermined transfer functions are provided by selectively coupling the output current derived from a selected one of the first and second emitter coupled transistors to the output resistor, which selective coupling produces differing transfer functions depending upon the particular transistors that are selected.
7. The gamma correction apparatus of Claim 4 wherein different predetermined transfer functions are provided by selectively coupling the output current derived from a selected one of the first and second emitter coupled transistors to the output resistor, which selective coupling produces differing transfer functions depending upon the particular transistors that are selected.
8. The gamma correction apparatus of Claim 1 wherein the nonlinear light modulator comprises a liquid crystal light valve.
9. A dynamic gamma correction apparatus for use in an image projector comprising a cathode ray tube and a liquid crystal light valve, said apparatus comprising: a plurality of amplifiers that are coupled together so as to sum their respective output currents to provide a composite output current, wherein each amplifier comprises at least two transistors and wherein each of the plurahty of amplifiers is adapted to implement a predetermined individual transfer function, and wherein the plurality of amplifiers comprise a plurality of current sources that provide differing levels of current to form the composite output current and that cooperate to provide each predetermined individual transfer function;
-25- dynamic compensation means having a signal connected to some part of at least one of said amplifiers to dynamically alter the shape of the gamma correction curve; an output means adapted to convert the composite output current into a corresponding output voltage of the apparatus; wherein the combination of amplifiers and current sources is configured to compensate for nonlinearity of the image projector due to the combination of the cathode ray tube and the liquid crystal light valve; and wherein each of at least two of said amplifiers includes a separate reference voltage input node for application of a reference voltage to selectively alter the transfer function of the associated individual amplifier, wherein said plurality of amplifiers are configured to generate a substantially smooth and continuous gamma correction transfer function having regions of both positive and negative change in slope.
10. The gamma correction apparatus of Claim 9 wherein each of the plurality of amplifiers comprises first and second emitter coupled transistors.
11. The gamma correction apparatus of Claim 9 wherein each of the plurality of current sources includes a resistor.
12. The gamma correction apparatus of Claim 10 wherein each of the plurality of current sources includes a resistor.
13. The gamma correction apparatus of Claim 10 wherein different predetermined transfer functions are provided by selectively coupling the output current derived from the first and second emitter coupled transistors to produce differing transfer functions depending upon the particular transistors that are selected.
14. The gamma correction apparatus of Claim 11 wherein different predetermined transfer functions are provided by selectively coupling the output
-26- current derived from a selected one of the first and second emitter coupled transistors to the output resistor, which selective coupling produces differing transfer functions depending upon the particular transistors that are selected.
-27-
-MENDED SHEET (ARTICLE 19)
15. The gamma correction apparatus of Claim 12 wherein different predetermined transfer functions are provided by selectively coupling the output current derived from a selected one of the first and second emitter coupled transistors to the output resistor, which selective coupling produces differing transfer functions depending upon the particular transistors that are selected.
16. A dynamic gamma correction apparatus for use in an image projector comprising a cathode ray tube and a liquid crystal light valve, said apparatus comprising: a plurahty of amplifiers wherein each amplifier comprises first and second emitter coupled transistors that are coupled together so as to sum their respective output currents to provide a composite output current, and wherein each of the plurahty of amplifiers is adapted to implement a predetermined individual transfer function, and wherein the plurahty of amplifiers comprise a plurahty of current sources that provide differing levels of current to form the composite output current and that cooperate to provide each predetermined individual transfer function; dynamic compensation means having a signal connected to some part of at least one of said amplifiers to dynamically alter the shape of the gamma correction curve; an output means adapted to convert the composite output current into a corresponding output voltage of the apparatus; wherein the combination of amplifiers and current sources is configured to compensate for nonlinearity of the image projector due to the combination of the cathode ray tube and the liquid crystal light valve; and wherein each of at least two of said amplifiers includes a separate reference voltage input node for application of a reference voltage to selectively alter the transfer function of the associated individual amplifier, wherein said plurahty of amplifiers are configured to generate a substantially smooth and continuous gamma correction transfer function having regions of both positive and negative change in slope.
17. The gamma correction apparatus of Claim 16 wherein each of the plurality of current sources includes a resistor.
-28-
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US116,413 | 1993-09-03 | ||
| US08/116,413 US5461430A (en) | 1992-12-04 | 1993-09-03 | Dynamic gamma correction circuit for use in image projectors |
| EP96103231A EP0796009A1 (en) | 1992-12-04 | 1996-03-02 | Dynamic gamma correction circuit for use in image projectors |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| WO1995006999A1 WO1995006999A1 (en) | 1995-03-09 |
| WO1995006999B1 true WO1995006999B1 (en) | 1995-04-20 |
Family
ID=26141780
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| PCT/US1994/009676 WO1995006999A1 (en) | 1993-09-03 | 1994-08-25 | Dynamic gamma correction circuit for use in image projectors |
Country Status (1)
| Country | Link |
|---|---|
| WO (1) | WO1995006999A1 (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5461430A (en) * | 1992-12-04 | 1995-10-24 | Hughes Jvc Tech Corp | Dynamic gamma correction circuit for use in image projectors |
| CN107608167A (en) * | 2017-10-11 | 2018-01-19 | 深圳奥比中光科技有限公司 | Laser projection device and its method of controlling security |
| CN107942612A (en) * | 2017-11-24 | 2018-04-20 | 深圳奥比中光科技有限公司 | The optical projection apparatus and its method for packing of the film containing monitoring |
| CN107991836A (en) * | 2017-12-18 | 2018-05-04 | 深圳奥比中光科技有限公司 | A kind of optical projection module containing safety monitoring function |
Family Cites Families (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3708693A (en) * | 1971-05-19 | 1973-01-02 | Ferrex Corp | Gamma corrector |
| JPS57155884A (en) * | 1981-03-23 | 1982-09-27 | Seiko Epson Corp | Television camera |
| JPS5945775A (en) * | 1982-09-09 | 1984-03-14 | Sharp Corp | Gamma correcting circuit |
| JPS5967784A (en) * | 1982-10-12 | 1984-04-17 | Hitachi Ltd | Gamma correcting circuit |
| JPS60257674A (en) * | 1984-06-04 | 1985-12-19 | Olympus Optical Co Ltd | Broad band gamma correction circuit |
| JP2619858B2 (en) * | 1985-11-11 | 1997-06-11 | ソニー株式会社 | Function approximation function generator |
| EP0235862B1 (en) * | 1986-03-07 | 1991-11-06 | Koninklijke Philips Electronics N.V. | Gamma correction circuit |
| US4868668A (en) * | 1986-08-21 | 1989-09-19 | Electrohome Limited | System and method for image adjustment in an optical projection system |
| JPH02260976A (en) * | 1989-03-31 | 1990-10-23 | Mitsubishi Electric Corp | Gamma correcting circuit |
| JP3026222B2 (en) * | 1989-09-04 | 2000-03-27 | 富士写真フイルム株式会社 | Non-linear amplifier |
| JPH0831972B2 (en) * | 1989-12-15 | 1996-03-27 | シャープ株式会社 | Gamma correction circuit |
| JP2889398B2 (en) * | 1991-05-28 | 1999-05-10 | シャープ株式会社 | Gamma correction circuit for liquid crystal display |
-
1994
- 1994-08-25 WO PCT/US1994/009676 patent/WO1995006999A1/en active Application Filing
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