Method for capturing and storing image information for multiple sampling operations in a digital pixel sensor

• US 6,963,369 B1
• Filed: 04/01/2002
• Issued: 11/08/2005
• Est. Priority Date: 04/01/2002
• Status: Active Grant

• Current Assignee: Pixim, Inc. (Sony Group Corp.)
• Original Assignee: Pixim, Inc. (Sony Group Corp.)
• Inventors: Olding, Benjamin P.
• Primary Examiner(s): Vu, Ngoc-Yen, Vu, Ngoc-Yen
• Assistant Examiner(s): Quiett, Carramah J.
• Application Number:
  US10/114,702
• Time in Patent Office: 1,317 Days
• Field of Search: 348/231.3, 348/231.6, 348/241, 348/294, 348/302, 348307-310
• US Class Current: 348/241
• CPC Class Codes: H04N 25/616 involving a correlated sampling function, e.g. correlated double sampling [CDS] or triple sampling
• CPC Class Codes: H04N 25/771 comprising storage means other than floating diffusion

Abstract

A method for storing image information in a digital pixel sensor is disclosed for reducing the size of the memory needed to facilitate multiple sampling and correlated double sampling. In one embodiment, an image sensor includes a sensor array of pixel elements generating digital pixel data and a data memory for storing pixel data of each pixel element. The data memory allocates for each pixel element an m-bit pixel data field for storing pixel data and an n-bit CDS data field for storing reset value associated with each pixel element. The data memory stores m+n bits of pixel data in the pixel data field and the CDS data field for pixel data exceeding the predetermined threshold level. The data memory stores m bits of pixel data in the pixel data field for pixel data not exceeding the predetermined threshold level.

Claims

1. An image sensor, comprising:

a sensor array comprising a two-dimensional array of pixel elements, said sensor array outputting digital signals as pixel data representing an image of a scene, and said sensor array generating multiple representations of said image at a plurality of exposure times; and

a data memory, in communication with said sensor array, for storing image information for each of said pixel elements, said data memory allocating for each pixel element an m-bit pixel data field for storing pixel data generated by said sensor array and an n-bit CDS data field for storing reset value associated with each pixel element;

wherein said data memory uses a first bit of said pixel data field as a threshold indicator indicating whether pixel data associated with each pixel element has exceeded a predetermined threshold level, said data memory storing m+n bits of pixel data in said pixel data field and said CDS data field for pixel data exceeding said predetermined threshold level and storing m bits of pixel data in said pixel data field for pixel data not exceeding said predetermined threshold level.

2. The image sensor of claim 1, wherein said first bit is the most significant bit of said pixel data field.

3. The image sensor of claim 1, wherein said data memory uses two or more bits as said threshold indicator, said data memory logically ORing said two or more bits of said threshold indicator to determine whether pixel data associated with said pixel element has exceeded said predetermined threshold.

4. The image sensor of claim 3, wherein said two or more bits are the least significant bits of said pixel data field.

5. The image sensor of claim 1, wherein said reset values are generated by resetting said sensor array and reading pixel intensity values from each pixel element of said sensor array after the reset.

6. The image sensor of claim 1, wherein said sensor array outputs said pixel data in codewords, said codewords encoding pixel intensity values and time index values such that each codeword uniquely identifies a pixel intensity value taken at one of said plurality of exposure times.

7. The image sensor of claim 1, wherein said sensor array is fabricated in an integrated circuit.

8. The image sensor of claim 1, wherein said plurality of exposure times comprise any of a relatively short exposure time for capturing image information that is related to high illumination areas in said image, a relatively long exposure time for capturing image information that is related to low illumination areas in said image, and intermediate exposure times for capturing image information that is related to gradually increasing illumination areas in said image;

and wherein a combination of said multiple representations of said image at a plurality of exposure time establishes a wide dynamic range for said sensor array.

9. The image sensor of claim 1, wherein, after pixel data for a first representation of said image is read out and stored in said data memory, pixel data for a second representation of said image is selectively read out into said data memory to improve, update or enhance pixel data stored therein for each of said pixel elements.

10. The image sensor of claim 9, wherein said selective read out of said second representation of said image is controlled by said threshold indicator of each of said pixel elements.

11. A method for generating electrical signals representing an image in a digital image sensor, comprising:

resetting said digital image sensor;

generating digital signals as reset values associated with each pixel element, said reset values being indicative of a pixel intensity value at each of said pixel elements after said resetting;

storing said reset values in a data memory, said reset values being stored in an n-bit CDS data field associated with each pixel element;

generating digital signals as pixel data at a plurality of exposure times, said pixel data being associated with each pixel element in a sensor array of pixel elements and corresponding to a level of an analog signal indicative of a light intensity impinging on said pixel element;

determining if said pixel data of a first pixel element exceeds a predetermined threshold value;

if said pixel data exceeds said predetermined threshold value, storing m+n bits of pixel data in an m-bit pixel data field and said n-bit CDS data field in said data memory; and

if said pixel data does not exceed said predetermined threshold value, storing m bits of pixel data in said pixel data field of said data memory.

12. The method of claim 11, wherein said determining comprises:

examining a first bit of said pixel data field, said first bit functioning as a threshold indicator, said threshold indicator having a first value indicating said pixel data has exceeded said predetermined threshold value and a second value indicating said pixel data has not exceeded said predetermined threshold value.

13. The method of claim 12, wherein said first bit is the most significant bit of said pixel data field.

14. The method of claim 11, wherein said determining comprises:

examining two or more bits of said pixel data field, wherein a logical OR of said two or more bits functions as a threshold indicator, said threshold indicator having a first value indicating said pixel data has exceeded said predetermined threshold value and a second value indicating said pixel data has not exceeded said predetermined threshold value.

15. The method of claim 14, wherein said two or more bits are the least significant bits of said pixel data field.

16. An image sensor, comprising:

a sensor array comprising a two-dimensional array of pixel elements, said sensor array outputting digital signals as pixel data representing an image of a scene, and said sensor array generating multiple representations of said image at k numbers of exposure times; and

a data memory, in communication with said sensor array, for storing image information for each of said pixel elements, said data memory allocating for each pixel element r bits of memory locations for storing pixel data generated by said sensor array and for storing reset value associated with each pixel element;

wherein said data memory uses a first bit of said pixel data field as a threshold indicator indicating whether pixel data associated with each pixel element has exceeded a predetermined threshold level, said data memory storing zero to n-1 bits of reset values for pixel data exceeding said predetermined threshold level at the first to the (k-1)th exposure times, and said data memory storing n bits of rest values for pixel data captured at the (k)th exposure times.

17. The image sensor of claim 16, wherein said data memory stores r to r-n+1 bits of pixel data for pixel data exceeding said predetermined threshold level at the first to the (k-1)th exposure times, and said data memory stores r-n bits of pixel data for pixel data captured at the (k)th exposure times.

18. The image sensor of claim 16, wherein said first bit is the most significant bit of said pixel data field.

19. The image sensor of claim 16, wherein said data memory uses two or more bits as said threshold indicator, said data memory logically ORing said two or more bits of said threshold indicator to determine whether pixel data associated with said pixel element has exceeded said predetermined threshold.

20. The image sensor of claim 19, wherein said two or more bits are the least significant bits of said pixel data field.