Digital image system and method for noise compensation

• US 7,136,095 B2
• Filed: 06/03/2002
• Issued: 11/14/2006
• Est. Priority Date: 06/03/2002
• Status: Expired due to Fees

• Current Assignee: Sharp Microelectronics of the Americas (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Laboratories of America Incorporated (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Patej, Edward Jerzy
• Primary Examiner(s): Vu, Ngoc Yen
• Assistant Examiner(s): MADDEN, GREGORY VINCENT
• Application Number:
  US10/161,358
• Publication Number:
  US 20030222996A1
• Time in Patent Office: 1,625 Days
• Field of Search: 348/216.1, 348/229.1, 348/241, 348/255, 348/216, 382/282, 382/233, 382/232, 375/245, 250/208.1
• US Class Current: 348/216.1
• CPC Class Codes: H04N 1/409 Edge or detail enhancement; Noise or error suppression
• CPC Class Codes: H04N 23/76 by influencing the image signals
• CPC Class Codes: H04N 5/20 Circuitry for controlling amplitude response
• CPC Class Codes: H04N 5/52 Automatic gain control

Abstract

For a digital imaging device having automatic gain control, a system and method have been provided for noise compensation in low-light conditions. The method comprises: receiving digital image information; compressing the image information; supplying the compressed image information; monitoring an automatic gain control signal; comparing the monitored gain control signal to a predetermined threshold gain value; in response to monitoring a high gain control signal, selecting a low-light processing algorithm; and, in response to the low-light algorithm, controlling the volume of the supplied compressed image information. Selecting a low-light processing algorithm includes selecting an algorithm that limits decreases in the compression ratio by changing parameters in a compression algorithm. Alternately, the low-light processing algorithm, prior to compressing, filters noise from the received digital image information. Subsequent to filtering noise from the received digital information, an approximately constant compression ratio is maintained.

Claims

1. In a digital imaging device having automatic gain control, a method for noise compensation in low-light conditions, the method comprising:

receiving digital image information;

compressing the image information;

supplying the compressed image information;

monitoring an automatic gain control signal;

in response to monitoring an automatic gain control signal below a high gain threshold, selecting a processing algorithm that increases compressed image information as the automatic gain control signal increases;

in response to monitoring an automatic gain control signal above the high gain threshold, selecting a low-light processing algorithm; and

,

in response to selecting the low-light algorithm, limiting the volume of the supplied compressed image information.

2. The method of claim 1 wherein selecting a low-light processing algorithm includes selecting an algorithm from the group including:

limiting the compression ratio by changing parameters in a compression algorithm; and

,

prior to compressing, filtering noise from the received digital image information.

3. The method of claim 2 wherein selecting a low-light processing algorithm further includes:

subsequent to filtering noise from the received digital information, maintaining an approximately constant compression ratio.

4. The method of claim 2 wherein monitoring the automatic gain control signal includes monitoring the gain control signal rate of change;

and,

wherein limiting the compression ratio includes variably limiting the compression ratio in response to variations in the rate of change.

5. The method of claim 2 wherein monitoring the automatic gain control signal includes monitoring the gain control signal rate of change;

and,

wherein filtering noise from the received digital information includes varying the filter parameters in response to variations in the rate of change.

6. The method of claim 1 wherein monitoring the automatic gain control signal includes monitoring an analog gain control signal.

7. The method of claim 1 wherein monitoring the automatic gain control signal includes monitoring a digital gain control signal.

8. The method of claim 1 wherein receiving digital image information includes receiving video image information;

wherein compressing the image information includes compressing image information into I frames and P frames; and

,

wherein limiting the volume of the supplied compressed image information includes limiting the byte size of the I frames.

9. In a digital imaging device having noise compensation in low-light conditions, the device comprising:

a light sensing device having an input to receive an image and an output to supply digital image information;

a gain control unit having an input to receive light exposure information, the gain control unit automatically supplying a gain control signal in response to the light exposure information;

a compensation unit having an input to monitor the gain control signal, an input to accept a threshold gain value, and an output to supply a compensation signal in response to the gain control signals;

a compression unit to accept digital image information from the light sensing device and supplying compressed image information at an output with a volume that is responsive to the compensation signal; and

,

where the compensation unit supplies a compensation signal to increase the volume of compressed image information as the gain control signal increases, when the gain control signal is below the threshold gain value, and a compensation signal to limit the volume of compressed image information, when the gain control signal exceeds the threshold gain value.

10. The device of claim 9 wherein the compression unit limits the volume of the compressed image information, by changing parameters in a compression algorithm, in response to the compensation signal.

11. The device of claim 10 wherein the compensation unit monitors the gain control signal rate of change and changes the compensation signal in response to the gain control signal rate of change;

and,

wherein the compression unit variably limits the volume of the compressed image information in response to variations in the gain control signal rate of change.

12. The device of claim 9 further comprising:

a noise reduction filter having an input to accept the digital image information from the light sensing device, an output to supply filtered digital image information to the compression unit, and an input to accept the compensation signal for enabling the filtering.

13. The device of claim 12 wherein the compensation unit monitors the gain control signal rate of change and supplies a compensation signal responsive to the monitored rate of change;

and,

wherein the noise reduction filter variably changes the filter parameters in response to variations in the gain control signal rate of change.

14. The device of claim 9 wherein the gain control unit supplies an analog gain control signal.

15. The device of claim 9 wherein the gain control unit supplies a digital gain control signal.

16. The device of claim 9 wherein the light sensing device supplies video image information;

and,

wherein the compression unit compresses image information into I frames and P frames, and supplies controlled byte size I frames in response to the compensation signal.