Apparatus and method for automatically controlling exposure time using a mean value of green pixels

• US 6,784,939 B1
• Filed: 10/28/1999
• Issued: 08/31/2004
• Est. Priority Date: 10/28/1998
• Status: Expired due to Fees

• Current Assignee: Intellectual Ventures II LLC (Intellectual Ventures LLC)
• Original Assignee: Hyundai Electronics Industries Co. Ltd. (SK Hynix Inc.)
• Inventors: Lee, Suk-Joong, Hwang, Gyu-Tae
• Primary Examiner(s): Christensen, Andrew
• Assistant Examiner(s): Harris, Tia M.
• Application Number:
  US09/428,534
• Time in Patent Office: 1,769 Days
• Field of Search: 348/362
• US Class Current: 348/364
• CPC Class Codes: H04N 23/71 Circuitry for evaluating the brightness variation
• CPC Class Codes: H04N 23/73 by influencing the exposure time
• CPC Class Codes: H04N 23/84 for processing colour signals
• CPC Class Codes: H04N 25/134 based on three different wavelength filter elements

Abstract

A method for automatically controlling an exposure time in image sensor having a pixel array includes the steps of producing total pixel value of the green pixels from the pixel array, producing a mean value of the green pixels dividing the total pixel value of the green pixels by the number of the green pixels, producing a deviation value, wherein the deviation value is an absolute value of a difference between the mean value and a predetermined reference value, comparing the deviation value with a predetermined boundary value, in case where the deviation value is smaller than the predetermined boundary value, capturing a next image according to a current exposure time, and in case where the deviation value is larger than the predetermined boundary value, calculating an exposure control rate and determining whether an automatic exposure control mode is enabled, and in case where the automatic exposure control mode is disabled, capturing the next image according to the current exposure time, and in case where the automatic exposure control mode is enabled, capturing the next image according a next exposure time, wherein the next exposure time is calculated multiplying the current exposure time by the exposure control rate.

Claims

1. A method for automatically controlling an exposure time in a CMOS image sensor, wherein the image sensor includes a pixel array, the method comprising the steps of:

a) producing a total pixel value only for a number of the green pixels from the pixel array;

b) producing a mean value of the green pixels by dividing the total pixel value of the green pixels by the number of the green pixels;

c) producing a deviation value, wherein the deviation value is an absolute value of a difference between the mean value of the green pixels and a predetermined reference value;

d) comparing the deviation value with a predetermined boundary value;

e) in case where the deviation value is smaller than the predetermined boundary value, capturing a next image according to a current exposure time, and in case where the deviation value is larger than the predetermined boundary value, calculating an exposure control rate and determining whether an automatic exposure control mode is enabled, said exposure control rate being calculated instead of performing the steps of a) and b) in a first line and a last line of the pixel array; and

f) in case where the automatic exposure control mode is disabled, capturing the next image according to the current exposure time, and in case where the automatic exposure control mode is enabled, capturing the next image according to a next exposure time, wherein the next exposure time is calculated by multiplying the current exposure time by the exposure control rate.

2. The method as recited in claim 1, wherein the step a) is performed line by line.

3. The method as recited in claim 1, wherein the predetermined reference value is programmed by a user.

4. The method as recited in claim 1, wherein the boundary value is programmed by a user.

5. The method as recited in claim 1, wherein the exposure control rate is calculated by dividing the reference value by the mean value of green pixels.

9. The method as recited in claim 1, wherein the number of the green pixels, which are used for calculating the exposure control rate, is (N−

2)×

(M/2) if the pixel array has N×

M pixels, with N being a number of lines and M being a number of pixels in each line.

10. The method as recited in claim 9, wherein N and M are positive integers having a value of at least 2.

6. A CMOS image sensor for automatically controlling an exposure time, comprising:

a) an operation means for receiving a size of window in window mode, green pixel values from a plurality of green pixels, a current exposure time and a predetermined reference value to perform an addition and shift operation in response to a control signal;

b) a storage means for storing operation results from the operation means in response to a clock signal;

c) an operation control means for receiving the operation results from the storage means, an area of the window for calculating a number of the green pixels in window mode and a line number to output the control signal, wherein the operation results include an updated exposure time, an exposure control rate, a mean value of the green pixels only and the number of the green pixels, said exposure control rate being calculated instead of performing the steps of a) and b) in a first line and a last line of the pixel array;

d) an update determination means for determining whether to update an exposure time and outputting an updating signal in response to the predetermined reference value, a predetermined boundary value and the mean value of the green pixels only from the storage means; and

e) an exposure time generating means for receiving the updated exposure time and outputting the updated exposure time as a next exposure time of a next image in response to the updating signal from the update determination means and an automatic exposure control mode.

7. The image sensor as recited in claim 6, wherein the predetermined reference value is programmed by a user.

8. The image sensor as recited in claim 6, wherein the boundary value is programmed by a user.

11. The image sensor as recited in claim 6, wherein the number of the green pixels, which are used for calculating the exposure control rate, is (N−

2)×

(M/2) if the pixel array has N×

M pixels, with N being a number of lines and M being a number of pixels in each line.

12. The image sensor as recited in claim 11, wherein N and M are positive integers having a value of at least 2.