Projection optical systems and methods having variable diaphragm based on average luminance and grayscale

1. An illumination device, comprising:

an illumination optical system that includes a first variable diaphragm and a second variable diaphragm in order of incidence of light from a light source, and that generates illumination light used for generation of an image by a pulse width modulation method on a basis of light from the light source;

a scheduler, wherein the scheduler comprises:

a luminance calculator that calculates average luminance at least for each frame in an image signal;

a gray-scale evaluation computer that evaluates a gray-scale value in a screen for each display period of at least a unit gray-scale bit;

a first aperture diameter determiner that determines an aperture diameter of the first variable diaphragm on a basis of the calculated average luminance calculated by the luminance calculator; and

a second aperture diameter determiner that determines an aperture diameter of the second variable diaphragm on a basis of the evaluation by the gray-scale evaluation computer, wherein the second variable diaphragm is configured to perform an opening-closing operation at a higher speed than the first variable diaphragm.

2. The illumination device according to claim 1 , wherein the luminance calculator calculates average luminance for each scene including at least one frame.

3. The illumination device according to claim 1 , wherein a variable range of the aperture diameter of the second variable diaphragm is smaller than a variable range of the aperture diameter of the first variable diaphragm.

4. The illumination device according to claim 1 , wherein the first variable diaphragm performs an opening-closing operation at least for each frame.

5. The illumination device according to claim 1 , wherein

the second aperture diameter determiner determines the aperture diameter of the second variable diaphragm at least for each unit gray-scale bit, and

the second variable diaphragm performs an opening-closing operation at least for each display period of each unit gray-scale bit.

6. The illumination device according to claim 1 , wherein the second variable diaphragm performs an opening-closing operation at least in a period after the aperture diameter of the first variable diaphragm becomes an aperture diameter determined by the first aperture diameter determiner.

7. The illumination device according to claim 1 , wherein the first and second variable diaphragms each include an iris diaphragm.

8. A display apparatus comprising:

a light modulation element that modulates illumination light by a pulse width modulation method to generate an image;

an illumination optical system that includes a first variable diaphragm and a second variable diaphragm in order of incidence of light from a light source, and generates illumination light used for generation of the image by the pulse width modulation method on a basis of light from the light source;

a scheduler, wherein the scheduler comprises:

a luminance calculator that calculates average luminance at least for each frame in an image signal:

a gray-scale evaluation computer that evaluates a gray-scale value in a screen for each display period of at least a unit gray-scale bit;

a first aperture diameter determiner that determines an aperture diameter of the first variable diaphragm on a basis of the average luminance calculated by the luminance calculator; and

a second aperture diameter determiner that determines an aperture diameter of the second variable diaphragm on a basis of the evaluation by the gray-scale evaluation computer, wherein a variable range of the aperture diameter of the second variable diaphragm is smaller than a variable range of the aperture diameter of the first variable diaphragm.

9. The display apparatus according to claim 8 , further comprising a projection optical system that projects the image generated by the light modulation element.

10. The display apparatus according to claim 8 , wherein the second variable diaphragm is configured to perform an opening-closing operation at higher speed than the first variable diaphragm.

11. A method of generating illumination light, comprising:

providing an illumination optical system that includes a first variable diaphragm and a second variable diaphragm in order of incidence of light from a light source, wherein the illumination optical system is operable to generate an image by a pulse width modulation method on a basis of light from the light source;

calculating average luminance at least for each frame in an image signal;

evaluating a gray-scale value in a screen for each display period of at least a unit gray-scale bit;

determining an aperture diameter of the first variable diaphragm on a basis of the calculated average luminance; and

determining an aperture diameter of the second variable diaphragm on a basis of the evaluating, wherein the second variable diaphragm is configured to perform an opening-closing operating at a higher speed than the first variable diaphragm.

12. The method according to claim 11 , wherein a variable range of the aperture diameter of the second variable diaphragm is smaller than a variable range of the aperture diameter of the first variable diaphragm.

13. The method according to claim 11 , wherein the first variable diaphragm performs an opening-closing operation at least for each frame of the image signal.

14. The method according to claim 11 , wherein the aperture diameter of the second variable diaphragm at least for each unit gray-scale bit is determined, and

the second variable diaphragm performs an opening-closing operation at least for each display period of each unit gray-scale bit.

15. The method according to claim 11 , wherein the second variable diaphragm performs an opening-closing operation at least in a period after the aperture diameter of the first variable diaphragm becomes a determined aperture.