Optical system and method for image sampling in a video projection system

• US 4,827,334 A
• Filed: 11/13/1987
• Issued: 05/02/1989
• Est. Priority Date: 08/22/1986
• Status: Expired due to Term

• Current Assignee: Christie Digital Systems Incorporated (Ushio Incorporated)
• Original Assignee: Electrohome Limited
• Inventors: Kykta, Martin A., Jarrett, Steven M., Johnson, Richard H.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Faris, E. Anne
• Application Number:
  US07/120,557
• Time in Patent Office: 536 Days
• Field of Search: 358/60, 358/61, 358/62, 358/64, 358/230, 358/231-233, 358/237, 358/250, 350/401, 350/402, 350/403, 350/408, 350/171, 350/173
• US Class Current: 348/752
• CPC Class Codes: H04N 9/31 Projection devices for colour picture display , e.g. using electronic spatial light modulators [ESLM]

Abstract

An optical system and method for image sampling in a video projection system is provided. A beam of illumination light is passed through a first beam-splitting polarizer to provide a first beam of a first polarization state and a second beam of a second polarization state. The first beam is passed through a second beam-splitting polarizer which is oriented at 90° with respect to the first prism. The light from the second prism is then provided to a modulation device which produces a polarization modulated image in reflected outgoing light. The reflected outgoing light is passed through the second prism such that a first portion is directed to an image display screen and a second portion, which contains an image sample, is directed toward the first prism. The image sample is reflected by the first prism and provided to an image detector which detects characteristics of the sample. The detected characeristics are utilized to control the outgoing light.

Claims

1. A method of sampling an optical image such as that generated by a video projection system of the type wherein illumination light is passed through a polarizing means and then directed to a light modulation device which receives a light image and provides an intensity-modulated optical image as outgoing light, the outgoing light being passed through a projection lens to display the optical image, the method comprising:

sampling a portion of the outgoing light prior to the projection lens;

directing the sampled portion to a detector which detects optical image registration of the outgoing light; and

utilizing the detected image registration characteristic to control the outgoing light passed through the projection lens.

2. A method as in claim 1 wherein said detector also detects image brightness, and wherein the utilizing step also utilizes the image brightness to control the outgoing light passed through the projection lens.

3. A method of sampling an optical image such as that generated by a video projection system of the type wherein illumination light is passed through a polarizing means and then directed to a light modulation device which receives a light image and provides an intensity-modulated optical image as outgoing light, the outgoing light being passed through a projection lens to display the optical lens, the method comprising:

sampling a portion of the outgoing light prior to the projection lens wherein the sample portion is taken from the outgoing light utilizing a MacNeille prism;

directing the sampled portion to a detector which detects a characteristic of the outgoing light; and

utilizing the detected characteristic to control the outgoing light passed through the projection lens.

4. An optical system for sampling an optical image such as that generated by a light valve projection system of the type wherein illumination light is passed through polarizing means and then directed to a liquid crystal light valve system which receives a light image and provides an intensity-modulated optical image as outgoing light, the outgoing light being passed through a projection lens to display the optical image, the optical system comprising:

means including a polarizing beam-splitting device for sampling a portion of the outgoing light prior to the projection lens;

a detector which receives the sampled portion and detects a characteristic of the outgoing light; and

a controller which utilizes the detected characteristic to control the outgoing light passed through the projection lens.

5. An optical system as in claim 4 wherein the detected characteristic is image registration.

6. An optical system as in claim 4 wherein the polarizing beam-splitting device comprises a MacNeille prism.

7. A method for image sampling in a light valve projection system, the method comprising:

passing a beam of illumination light through a prepolarizing prism such that the light is split into a first beam of a first polarization state and a second beam of a second polarization state;

passing the first beam through a second beam-splitting polarizing prism oriented at 90°

with respect to the prepolarizing prism;

directing the output beam from the second prism to a modulation device which produces an intensity-modulated image which is reflected as outgoing light,

passing the outgoing light through the beam-splitting polarizing prism such that a first portion is directed to a projection screen to display the modulated image and a second portion is directed to the prepolarizing prism;

directing the second portion from the prepolarizing prism to an image detector which detects a characteristic of the second portion; and

utilizing the detected characteristic to control the first portion.

8. A method as in claim 7 wherein the prepolarizing prism is a Mac Neille prism.

9. A method as in claim 8 wherein the second prism is a Mac Neille prism.

10. A method for image sampling in a full-color light valve projection system, the method comprising:

passing a beam of illumination light through a first polarizing beam-splitting device such that the light is split into a first beam of a first polarization state and a second beam of a second polarization state;

passing the first beam through a second polarizing beam-splitting device oriented at 90°

with respect to the first beam-splitting device;

directing light from the second beam-splitting device to means for splitting the light into red, green and blue beams;

directing each of the red, green and blue beams to an individual light modulation device which receives an image of corresponding color and produces an intensity-modulated image which is reflected from the modulation device;

recombining the red, green and blue intensity-modulated images to form outgoing light which contains a full-color image;

directing the outgoing light to a projection lens;

sampling a portion of the outgoing light prior to the projection lens;

directing the sampled portion to a detector which detects from the sampled portion the registration of the red, green and blue images in the outgoing light; and

utilizing the detected image registration to control said registration in the outgoing light.

11. A method as is claim 10 wherein the sampled portion comprises light of the first polarization state and light of the second polarization state.

12. A method as in claim 11 including the further step of passing the sampled portion through a polarization device located prior to the detector such that the sample portion arriving at the detector is of a single polarization state.

13. A method as in claim 10 wherein the first beam-splitting device is a MacNeille prism.

14. A method as in claim 13 wherein the second beam-splitting device is a MacNeille prism.

15. An optical system for sampling an optical image such as that generated by a light valve projection system of the type wherein illumination light is passes through polarizing means and then directed to a liquid crystal light valve system which receives a light image and provides an intensity-modulated optical image as outgoing light, the outgoing light being passed through a projection lens to display the optical image, the optical system comprising:

means for sampling a portion of the outgoing light prior to the projection lens;

a detector which receives the sampled portion and detects a registration of images within the outgoing light; and

a controller which utilizes the detected image registration to control the outgoing light passed through the projection lens.

16. In a projector of a type having a plurality of image forming devices and a plurality of light valves, one light valve associated with a single one of the image forming devices and receiving its formed image, a source of illumination, and optical means for directing the illumination in a beam toward the light valves, combining individual images on the light valves obtained from their associated image forming devices, and projecting a single combined image beam to a location outside of the projector, the improvement wherein said optical means comprising:

at least one passive optical element positioned in the path of the combined image beam that is characterized by inherently continuously directing a small proportion of the intensity of the combined image beam along a path in a direction that is different than that of the combined image beam,

a two-dimensional light detector positioned in the path of said small intensity beam, whereby the nature of the combined image beam may be monitored from within the projector, and

means receiving at least one signal from said detector for adjusting registration of the individual images in said combined image beam.

17. The projector according to claim 16 which additionally comprises means receiving at least one signal from said detector for adjusting the relative brightness of the individual images in said combined image beam.

18. The projector according to claim 16 wherein said optical element is further characterized by polarizing at least some of the light incident thereon and said small intensity beam is reflected therefrom.

19. The projector according to claim 16 wherein said optical element comprises a MacNeille prism.

20. A projector, comprising:

a plurality of image forming devices,

a plurality of light valves, each of the type that modulates light incident upon one surface by polarizing such light in accordance with an image incident upon an opposite surface thereof, each of said light valves being positioned to receive on its said opposite surface an image formed on one of said plurality of image forming devices,

a source of an illuminating light beam,

a first polarizing beam splitting device positioned in the path of said illuminating light beam, thereby to pass a portion of the illuminating beam intensity as a first polarized beam and reflect another portion of that intensity as a second polarized beam,

a second polarizing beam splitting device positioned in the path of said first polarized beam in a manner to reflect said beam onto said one surface of each of said plurality of light valves and receive light reflected therefrom in a composite image beam that is passed through said second device,

said second device being characterized by reflecting a small portion of the intensity of the composite image beam in a direction substantially along the path of said first polarized beam to said first device by which it is reflected as a low intensity beam that is separated from the source and composite image beams,

a light detector positioned in the path of said low intensity beam, and

a projection lens positioned in the path of said composite beams, whereby light valve images contained in said combined beam may be projected onto a surface displaced from the projector while a reduced intensity version thereof is received by said detector for monitoring its characteristics.

21. The projector according to claim 20 wherein each of the image devices carries a different color component of a single image scene, and which additionally comprises means receiving a signal from said detector for maintaining said components spatially registered with each other.