Dynamic range compression method

• US 20040036797A1
• Filed: 01/06/2003
• Published: 02/26/2004
• Est. Priority Date: 07/05/2000
• Status: Active Grant

• Current Assignee: Vision-Sciences Incorporated (2941881 Canada, Inc.)
• Original Assignee: Vision-Sciences Incorporated (2941881 Canada, Inc.)
• Inventors: Stark, Moshe
• Granted Patent: US 7,336,309 B2
• Time in Patent Office: Days
• US Class Current: 348/362
• CPC Class Codes: H04N 23/741 by increasing the dynamic range of the image compared to the dynamic range of the electronic image sensors
• CPC Class Codes: H04N 25/533 by using differing integration times for different sensor regions
• CPC Class Codes: H04N 25/57 Control of the dynamic range
• CPC Class Codes: H04N 25/571 involving a non-linear response
• CPC Class Codes: H04N 25/74 Circuitry for scanning or addressing the pixel array

Abstract

A method for compressing the dynamic range of an image sensor (202) including a multiplicity of pixels. The method includes the steps of exposing each of the pixels to light and producing an associated photocurrent per pixel, representative of the light exposure. Then, on a per-pixel basis, controlling exposure time of each of the pixels on the basis of a monotonically rising convex function of the associated photocurrent of each of the pixel.

Claims

1. A method for compressing the dynamic range of an image sensor comprising a multiplicity of pixels, the method comprising the steps of:

exposing each of said pixels to light and producing an associated photocurrent per pixel, representative of said light exposure; and

on a per-pixel basis, controlling exposure time of each said pixels on the basis of a monotonically rising convex function of said associated photocurrent of each said pixel.

2. The method according to claim 1, and further comprising the step of calculating said exposure time of each said pixel on the basis of said monotonically rising convex function.

3. The method according to claim 1, and further comprising the step of calculating said exposure time of each said pixel on the basis of said associated photocurrent.

4. The method according to claim 2, and wherein said step of controlling comprises the steps of:

storing said calculated exposure times per pixel;

accessing said stored exposure times from said memory; and

programming said pixels according to said accessed exposure times.

5. The method according to claim 1, further comprising calculating a first derivative of said monotonically rising convex function based upon a desired sensitivity of said exposure time of each said pixel.

6. The method according to claim 1, further comprising;

accumulating charge generally linearly representative of said photocurrent; and

calculating said photocurrent as a product of said accumulated charge.

7. An exposure controller for use in an image sensor comprising a multiplicity of pixels, the controller comprising:

a memory for storing calculated exposure time values;

a per-pixel parameter table containing local parameters of said pixels; and

a processor for combining based on a set of convergence criteria, said stored exposure time values and said parameters in order to determine, on a per-pixel basis, an exposure time of said pixels.

8. The exposure controller of claim 7, wherein said set of convergence criteria is based on a set of algorithms capable of deriving an appropriate exposure time for every pixel based on said monotonically rising convex function.

9. The exposure controller of claim 8, wherein said set of algorithms is capable of deriving a fine tuned exposure time of said pixels.

10. The exposure controller of claim 7, wherein said exposure controller is a chip-set external to said image sensor.

11. The exposure controller of claim 7, wherein said exposure controller is at least partially integrated on the same substrate as said image sensor.