Two narrow band and one wide band color filter for increasing color image sensor sensitivity

• US 7,477,304 B2
• Filed: 08/26/2004
• Issued: 01/13/2009
• Est. Priority Date: 08/26/2004
• Status: Active Grant

• Current Assignee: Micron Technology, Inc.
• Original Assignee: Micron Technology, Inc.
• Inventors: Hu, Shane Ching-Feng
• Primary Examiner(s): Ho; Tuan V
• Application Number:
  US10/926,345
• Publication Number:
  US 20060044427A1
• Time in Patent Office: 1,601 Days
• Field of Search: 348/266, 348/272, 348/273, 348/275, 348/276, 348/222.1
• US Class Current: 348/272
• CPC Class Codes: H04N 23/12 with one sensor only
• CPC Class Codes: H04N 23/843 Demosaicing, e.g. interpolating colour pixel values
• CPC Class Codes: H04N 25/133 including elements passing panchromatic light, e.g. filters passing white light
• CPC Class Codes: H04N 25/134 based on three different wavelength filter elements

Abstract

A color filter to increase the low light sensitivity of an image sensor. The color filter has two narrow band color filters and one wide band filter. Also disclosed is a unique way of processing a tri-stimulus signal to dynamically adjust color contrast depending on the illumination conditions.

Claims

1. An imaging device comprising:

a plurality of imager pixel cells for capturing an image, each cell comprising a photosensor and generating a pixel signal based on light from one of a transparent filter, a red filter, or a blue filter;

a color filter array formed over the plurality of cells, said array comprising alternating rows of a first and second type, wherein the first type of rows comprises said transparent and red color filters respectively formed over the cells and the second type of rows comprises said transparent and blue color filters respectively formed over the cells; and

a processor for adjusting a color contrast of the image based on a readout of the cells formed under the transparent filters, said processor configured to

generate an interpolated signal for each cell based on its respective pixel signal and said pixel signals of its neighboring cells,

perform a lens dependent matrix transformation of each interpolated signal, each of said transformed signals having a luminance component determined from at least one of said pixel signals based on light from at least one of said transparent filters; and

individually modify, for each of said transformed signals, a preset color contrast adjustment based on said respective luminance component.

2. The imaging device of claim 1, further comprising at least one of an infrared or a ultraviolet filter formed over the plurality of imager pixel cells.

3. The imaging device of claim 2, further comprising a light shield layer formed above the dielectric layer but below the color filter array, for shielding areas of said pixel cells from light exposure.

4. The imaging device of claim 1, wherein the imager pixel cells comprise CMOS imager pixel cells.

5. The imaging device of claim 1, wherein the first type of row comprises alternating transparent and red color filters.

6. The imaging device of claim 1, wherein the second type of row comprises alternating transparent and blue color filters.

7. A color imaging device comprising:

an array of image pixel sensors for forming an image, comprising;

a plurality of a first type of image sensors that produce a first pixel signal indicative of an amount of incident light having wavelengths within a first narrow band of color;

a plurality of a second type of image sensors that produce a second pixel signal indicative of an amount of incident light having wavelengths within a second narrow band of color;

a plurality of a third type of image sensors that produce a third pixel signal indicative of an amount of incident light having wavelengths within the whole visible spectrum; and

a processor for adjusting a color contrast of the image based on a readout of the third type of image sensors, said processor configured to

generate an interpolated signal for each of said image pixel sensors based on its respective pixel signal and said pixel signals of its neighboring cells,

perform a lens dependent matrix transformation of each interpolated signal, each of said transformed signals having a luminance component determined from at least one said third pixel signals, and

individually modify, for each of said transformed signals, a preset color contrast adjustment based on said respective luminance component.

8. The color imaging device of claim 7, wherein the first narrow band of color and the second narrow band of color correspond to primary colors.

9. The color imaging device of claim 8, wherein one of the first and second narrow bands of color corresponds to red.

10. The color imaging device of claim 8, wherein one of the first and second narrow bands of color corresponds to blue.

11. The color imaging device of claim 8, wherein the image sensors are arranged in an array having alternating rows of first and third image sensor types with rows of second and third image sensor types.

12. A processing system comprising:

an imaging device comprising;

a color filter array having a plurality of red, blue and transparent color filters;

an array of image sensors located below the filter array, each sensor corresponding to one of the red, blue and transparent color filters and for producing a pixel signal representing an amount of light received at the sensor; and

a processor for processing said signals to produce an image captured by the image sensors and for adjusting a color contrast of the image based on readout of the sensors corresponding to the transparent filters, said processor configured to

generate an interpolated signal for each image sensor based on its respective pixel signal and said pixel signals of its neighboring cells,

perform a lens dependent matrix transformation of each interpolated signal, each of said transformed signals having a luminance component based on said light from at least one of said transparent color filters, and

individually modify, for each of said transformed signals, a preset color contrast adjustment based on said respective luminance component.

13. The processing system of claim 12, wherein the color filter array comprises:

a plurality of a first type of rows comprising alternating transparent and red color filters; and

a plurality of a second type of rows comprising alternating transparent and blue color filters, wherein the rows form a pattern of alternating first and second type of rows.

14. The processing system of claim 12, wherein the image sensors are CMOS pixel sensor cells.

15. A method of processing a digital color signal comprising the acts of:

obtaining a pixel signal from each of a plurality of image sensors including first, second, and third image sensors corresponding to applied light with wavelengths in one of the red, blue and whole visible light spectrum, respectively;

producing a tri-stimulus signal for each image sensor based on its respective pixel signal and said pixel signals of its neighboring image sensors;

performing a lens dependent matrix transformation of each tri-stimulus signal, each of said transformed signals having a luminance component determined from at least one pixel signal generated by at least one of said third image sensors; and

individually modifying, for each of said transformed signals, a preset color contrast adjustment based on said respective luminance component.

16. The method of claim 15, wherein the step of producing a tri-stimulus signal comprises interpolation based on the signal obtained from adjacent image sensors.

17. The method of claim 15, further comprising the step of filtering the ultraviolet and infrared light.

18. The method of claim 15, wherein the external interface comprises any one of a computer monitor, a camera screen and a printer output.

19. A method of processing a digital color signal comprising the acts of:

obtaining a signal from each of a plurality of image sensors including first, second, and third image sensors corresponding to applied light with wavelengths in one of the red, blue and whole visible light spectrum, respectively;

producing a tri-stimulus signal for each signal obtained;

processing the tri-stimulus signal in order to reproduce the image including

transforming the tri-stimulus signal for each pixel to XYZ space,

performing a saturation adjustment, and

transforming the signal for compatibility with an external interface; and

adjusting a color contrast of the image based on a readout of the third image sensors.

20. The method of claim 19, wherein said step of transforming the signal for compatibility comprises a D65 matrix transformation.

21. The method of claim 19, wherein the step of dynamically adjusting the color contrast comprises the steps of:

externally setting at least one contrast parameter to a pre-determined value; and

and adjusting said at least one contrast parameter to an adjusted level depending on the illumination surrounding the desired image.

22. The method of claim 21, wherein the at least one adjusted contrast parameter is used in the step of performing a saturation adjustment.