Optimizing drive schemes for multiple projector systems

1. A light projector for displaying an image defined by image data, the light projector comprising:

a main light source;

a first imaging element configured to modulate visible light from the main light source;

a second imaging element configured to further modulate the modulated visible light generated by the first imaging element;

a boost light source configured to deliver to the second imaging element visible boost light for modulation by the second imaging element, wherein the visible boost light is not modulated by the first imaging element; and

a controller configured:

to process image data;

to determine a lowest luminance level in the image;

to output control signals for the first imaging element, the second imaging element, the main light source, and the boost light source; and

to output, when low black levels are not required, the control signal for the boost light source such that the visible boost light is added at a level greater than or equal to the lowest luminance level in the image;

wherein the controller is configured to determine a contrast of the image; and

when the contrast is lower than a threshold value:

to simulate a veiling luminance;

to determine a lowest perceivable luminance level in the image based on the veiling luminance; and

to add the visible boost light at a level corresponding to the lowest perceivable luminance level.

2. The light projector of claim 1 wherein the controller is further configured to dim, when low black levels are not required, the main light source to compensate for the visible boost light being added to the image by the boost light source.

3. The light projector of claim 1 wherein the first imaging element is configured to modulate the phase and/or the amplitude of light from the main source.

4. The light projector of claim 1 wherein:

the boost light source is separate from the main light source and comprises a plurality of light sources; and

the light sources are adjacent to an outer perimeter of the first imaging element.

5. The light projector of claim 1 wherein:

the boost light source is separate from the main light source and comprises a plurality of light sources; and

the light sources are individually controllable to yield a pattern of visible boost light on the second imaging element.

6. The light projector of claim 1 wherein the controller is further configured:

to identify, when the contrast is not lower than a threshold value, dark features in the image; and

to add, when all of the dark features are smaller than a threshold size, the visible boost light at the level corresponding to the lowest perceivable luminance level.

7. The light projector of claim 6 wherein the control is further configured:

to turn off the boost light source if any of the dark features is larger than the threshold size; and/or

to turn off the boost light source if the image is predominantly dark.

8. The light projector of claim 1 wherein the second imaging element comprises a spatial light modulator that is a LCD panel, LCOS, reflective LCD panel, or DMD.

9. The light projector of claim 1 wherein:

the boost light source is separate from the main light source; and

the main light source is configured to deliver at least some visible light to the second imaging element.

10. A method for displaying an image defined by image data, the method comprising:

modulating visible light provided by a main light source using a first imaging element;

providing visible boost light to a second imaging element using a boost light source wherein the visible boost light is not modulated by the first imaging element;

combining the visible boost light and the modulated visible light by illuminating a surface of the second imaging element with both the visible boost light and the modulated visible light;

further modulating the combined light using the second imaging element;

processing the image data;

determining a lowest luminance level in the image;

determining a contrast of the image; and

when the contrast is lower than threshold value:

simulating a veiling luminance;

determining a lowest perceivable luminance level in the image based on the veiling luminance;

adding the visible boost light at a level corresponding to the lowest perceivable luminance level;

outputting control signals for the first imaging element, the second imaging element, the main light source, and the boost light source; and

outputting, when low black levels are not required, the control signal for the boost light source such that the visible boost light is added at a level greater than or equal to the lowest luminance level in the image.

11. The method of claim 10 , further comprising dimming, when low black levels are not required, the main light source to compensate for the visible boost light being added to the image by the boost light source.

12. The method of claim 10 wherein the visible boost light comprises structured illumination adapted to illuminate the surface of the second imaging element according to a luminance profile.

13. The method of claim 11 wherein:

the structured illumination has higher luminance on some parts of the surface of the second imaging element than it does in other parts of the surface of the second imaging element; and

the luminance of the highest luminance part of the structured illumination is at least twice a luminance of lowest luminance parts of the structured illumination.

14. The method of claim 10 , further comprising:

determining a contrast of the image;

identifying, when the contrast is not lower than a threshold value, dark features in the image that exceed a threshold size; and

turning off, if any of the dark features is larger than the threshold size, the boost light source.