Increasing dynamic range of display output

1. A method of controlling an electroluminescent display system that receives a three-component input image signal having triplets of intensity values, the intensity values having at least an image range and a highlight range, the smallest intensity value of the highlight range being greater than the greatest intensity value of the image range, including:

(a) providing a plurality of light-emitting elements for emitting red, green, and blue light and at least one additional light-emitting element for emitting at least one additional color of light, the luminance of the emitted light being responsive to a current provided to each light-emitting element; and

(b) controlling the current to each light-emitting element to cause each light-emitting element to produce a corresponding luminance value, wherein the corresponding luminance value of the at least one additional light-emitting element is greater than the corresponding luminance value of at least one of the red, green, or blue light-emitting elements at the same current;

(c) transforming the received three-component input image signal to a four-or-more-component drive signal and providing the four-or-more-component drive signal to control the current to each light-emitting element; and

(i) transforming at least one of the triplets having an intensity value within the image range to a four-or-more-component drive signal to produce a luminance less than the sum of the corresponding luminance values of the red, green and blue light-emitting elements; and

(ii) transforming at least one of the intensity values within a triplet having an intensity value within the highlight range to a four-or-more-component drive signal to produce a luminance greater than the sum of the corresponding luminance values of the red, green, and blue light-emitting elements,

wherein the four-or-more-component drive signal is a digital signal and the drive signal for the additional light-emitting element has a greater bit-depth than the drive signal for the red, green, or blue light-emitting elements.

2. The method of claim 1 , wherein the at least one additional light-emitting element emits white light.

3. The method of claim 1 , wherein transforming at least one of the triplets further includes limiting the four-or-more component drive signal for driving the red, green, and blue light-emitting elements to values less than the four-or-more component drive signal for driving at least one of the one or more additional light-emitting elements.

4. The method of claim 3 , wherein transforming at least one of the triplets further includes increasing the four-or-more component drive signals for driving at least one of the one or more additional light-emitting elements as a function of a reduction in the four-or-more component drive signals for driving the red, green, and blue light-emitting elements that results from the limiting step.

5. The method of claim 1 , wherein transforming at least one of the triplets further includes enhancing the tone-scale.

6. The method of claim 1 , wherein in response to a triplet of intensity values within the highlight range:

(a) at least one of the four-or-more-component drive for driving the red, green, and blue light-emitting elements is greater than zero and the four-or-more-component drive signal for driving at least one of the remaining red, green, or blue light-emitting elements equals zero; and

(b) the four-or-more component drive signal for driving at least one of the one or more additional light-emitting elements is greater than zero.

7. The method of claim 1 , wherein in response to a triplet of intensity values within the highlight range:

(a) each of the four-or-more-component drive signals for driving the red, green, and blue light-emitting elements is greater than zero; and

(b) the four-or-more component drive signals for driving at least one of the one or more additional light-emitting elements is greater than zero.

8. An electroluminescent display system for receiving a three-component input image signal having triplets of intensity values, the intensity values having at least an image range and a highlight range, the smallest intensity value of the highlight range being greater than the greatest intensity value of the image range, including:

(a) an electro-luminescent display comprising:

(i) a plurality of light-emitting elements for emitting red, green, and blue light and at least one additional light-emitting element for emitting at least one additional color of light, the luminance of the light being responsive to a current provided to each light-emitting element;

(ii) one or more circuits for controlling the current to each light-emitting element, the circuits providing a current to each light-emitting element to cause each light-emitting element to produce a corresponding luminance value, wherein the corresponding luminance value of the at least one additional light-emitting element is greater than the corresponding luminance value of at least one of the red, green, or blue light-emitting elements at the same current;

(b) one or more display drivers responsive to the received three-component input image signal for transforming the three-component input image signal to a four-or-more-component drive signal and providing the four-or-more-component drive signal to the one or more circuits to control the current to each light-emitting element; and

(c) wherein the display driver(s) transforms at least one of the triplets having an intensity value within the image range to a four-or-more-component drive signal that produces a luminance less than the sum of the corresponding luminance values of the red, green and blue light-emitting elements and transforms at least one of the intensity values within a triplet having an intensity value within the highlight range to a four-or-more-component drive signal that produces a luminance greater than the sum of the corresponding luminance values of the red, green, and blue light-emitting elements,

wherein the four-or-more-component drive signal is a digital signal and the drive signal for the additional light-emitting element has a greater bit-depth than the drive signal for the red, green, or blue light-emitting elements.

9. The electroluminescent display system of claim 8 , wherein the corresponding luminance value of the at least one additional light-emitting element is greater than the sum of the corresponding luminance values of the red, green, and blue light-emitting elements.

10. The electroluminescent display system of claim 8 , wherein the additional light-emitting element emits substantially white light.

11. The electroluminescent display system of claim 8 , wherein at least one triplet of image signal values is rendered to have a luminance that is at least 2 times higher than the sum of the corresponding luminance values of the red, green, and blue light-emitting elements.

12. The electroluminescent display system of claim 8 , wherein the one or more display drivers adjust the four-or-more-component drive signal to cause the reduction of the color saturation for triplets of image signal values within at least a portion of the highlight range but do not cause the reduction of the color saturation for triplets of image signal values within at least a portion of the image range.

13. The electroluminescent display system of claim 8 , wherein the one or more display drivers analyze the total current of the display and adjust the four-or-more-component drive signal to cause a reduction of the image signal values to limit the current of the display device.

14. The electroluminescent display system of claim 8 , wherein the one or more display drivers adjust the four-or-more-component drive signal to cause the triplets of image intensity values within the image range to be transformed so that the four-or-more-component drive signal causes three or fewer of the red, green, blue, and at least one additional light-emitting element to produce light and wherein at least a portion of the triplets of the image intensity values within the highlight range are transformed such that the four-or-more-component drive signal causes each of the red, green, blue and at least one additional light-emitting element to produce light.

15. The electroluminescent display system of claim 8 , wherein the three-component input image signal provides information defining a display white point and includes triplets of image intensity values within the highlight range and wherein the one or more display drivers adjust the four-or-more-component drive signal to scale triplets of image intensity values so that a triplet of image intensity values at the display white point is produced on the display with a luminance that is within 20% of the sum of the maximum luminance values of the red, green, an blue light-emitting elements.

16. The electroluminescent display system of claim 8 , wherein the one or more display drivers adjust the four-or-more-component drive signal to limit the maximum intensity values for driving the red, green, and blue light-emitting elements within the four-or-more component drive signal to values less than the maximum intensity values for driving the at least one additional light-emitting elements.

17. The electroluminescent display system of claim 8 , wherein the one or more display drivers adjust the four-or-more-component drive signal to provide a tone-scale enhancement.

18. The electroluminescent display system of claim 8 , wherein the efficiency of the at least one additional light-emitting elements is greater than the efficiency of the red, green, and blue light-emitting elements.