Method of digital grayscale control using modulation of a slow-acting light source

• US 6,262,829 B1
• Filed: 07/29/1999
• Issued: 07/17/2001
• Est. Priority Date: 07/29/1999
• Status: Expired due to Fees

• Current Assignee: Hewlett-Packard Company (HP Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Kuramoto, Akinobu, Helbing, Rene P.
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): THOMPSON, TIMOTHY J
• Application Number:
  US09/364,618
• Time in Patent Office: 719 Days
• Field of Search: 359/315, 359/275, 359/265, 359/320, 359/566-569, 359/888
• US Class Current: 359/237
• CPC Class Codes: G09G 2310/0237 Switching ON and OFF the backlight within one frame
• CPC Class Codes: G09G 2320/0633 by amplitude modulation of the brightness of the illumination source
• CPC Class Codes: G09G 3/2018 by time modulation using two or more time intervals
• CPC Class Codes: G09G 3/2025 the sub-frames having all the same time duration
• CPC Class Codes: G09G 3/34 by control of light from an independent source
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336
• CPC Class Codes: H04N 2005/745 Control circuits therefor
• CPC Class Codes: H04N 2005/7466 Control circuits therefor
• CPC Class Codes: H04N 5/7416 involving the use of a spatial light modulator, e.g. a light valve, controlled by a video signal

Abstract

A method of digital grayscale control using light source modulation. First, a light valve, grayscale data, and a light source are provided. The light valve includes a spatial light modulator with at least one pixel. The grayscale data indicates desired grayscale level for the pixel during a frame period. The light source is configured to illuminate the pixel, to generate light with increasing intensity for a rise-time after electric power to the light source is substantially increased, and to generate light with decreasing intensity for a decay-time after electric power to the light source is substantially reduced. The light source may be an arc-lamp. The rise-time and the decay-time taken together may constitute a majority of the frame period. During the frame period, the electric power to the light source is substantially increased and is substantially decreased. Substantially decreasing the electric power to the light source may include turning off the electric power. The frame period is divided into at least four time slices with independent durations so that at least one of the at least four time slices occurs completely during the decay time. This may include selecting the at least four independent durations so that a product of each of the at least four independent durations and an average intensity of the light generated by the light source over each of the at least four time slices, respectively, has a binary weighted value, respectively. The pixel is independently set to one of an 0 state and an 1 state during each of the at least four time slices of the frame period based on the grayscale data.

Claims

1. A method of digital grayscale control using light source modulation, the method comprising:

providing a light valve including a spatial light modulator with at least one pixel;

providing grayscale data that indicates desired grayscale level for the pixel during a frame period;

providing a light source configured to illuminate the pixel, the light source generating light with increasing intensity for a rise-time after electric power to the light source is substantially increased and generating light with decreasing intensity for a decay-time after electric power to the light source is substantially reduced;

measuring response of the light source;

increasing substantially the electric power to the light source;

reducing substantially the electric power to the light source;

dividing the frame period into at least four time slices with independent durations, the durations being varied as a function of the measured response so that each time slice has a binary weighted value; and

independently setting a pixel to one of an 0 state and an 1 state during each of the at least four time slices of the frame period based on the grayscale data.

2. The method of digital grayscale control using light source modulation according to claim 1, in which:

increasing substantially the electric power to the light source occurs at the beginning of the frame period; and

reducing substantially the electric power to the light source occurs after a first occurring of the at least four time slices is completed.

3. The method of digital grayscale control using light source modulation according to claim 2, in which:

reducing substantially the electric power to the light source occurs after both the first occurring of the at least four time slices and a second of the at least four time slices are completed.

4. The method of digital grayscale control using light source modulation according to claim 1, in which:

reducing substantially the electric power to the light source occurs at the beginning of the frame period; and

increasing substantially the electric power to the light source occurs after a first occurring of the at least four time slices is completed.

5. The method of digital grayscale control using light source modulation according to claim 4, in which:

increasing substantially the electric power to the light source occurs after both the first occurring of the at least four time slices and a second of the at least four time slices are completed.

6. The method of digital grayscale control using light source modulation according to claim 1, in which:

the frame period has a duration of less than 0.05 second.

7. The method of digital grayscale control using light source modulation according to claim 6, in which:

the intensity of the light generated by the light source is decreasing during a majority of the frame period.

8. The method of digital grayscale control using light source modulation according to claim 6, in which:

the intensity of the light generated by the light source is increasing and decreasing during a majority of the frame period.

9. The method of digital grayscale control using light source modulation according to claim 8, in which:

the intensity of the light source is increasing and decreasing during more than seventy-five percent of the frame period.

10. The method of digital grayscale control using light source modulation according to claim 8, in which:

the intensity of the light generated by the light source is increasing and decreasing during more than ninety-five percent of the frame period.

11. The method of digital grayscale control using light source modulation according to claim 7, in which the intensity of the light generated by the light source is increasing during more than twenty-five percent of the frame period.

12. The method of digital grayscale control using light source modulation according to claim 8, in which:

the light source provided is an arc-lamp.

13. The method of digital grayscale control using light source modulation according to claim 8, in which:

substantially reducing the electric power includes switching off the electric power.

14. A method of using a light source to perform digital grayscale control of a pixel in spatial light modulator, the method comprising:

measuring response of the light source; and

configuring a frame period during which the light source provides illumination, the frame period being configured by dividing the frame period into at least four time slices, durations of the time slices being varied as a function of the measured response so that each time slice has a binary weighted value.

15. The method of claim 14, wherein the light source is slow-acting.

16. Apparatus comprising:

a spatial light modulator; and

a lamp for providing illumination over at least one frame period; and

means for causing lamp power to be substantially increased and decreased during each frame period, each frame period having a plurality of time slices, durations of the time slices being a function of measured response of the lamp.

17. The apparatus of claim 16, wherein the durations result in binary weighted values for the time slices.

18. The apparatus of claim 16, wherein the lamp is slow-acting.

19. The apparatus of claim 16, wherein the lamp is an arc lamp.