Flicker correction apparatus, flicker correction method, and image sensing apparatus

• US 8,089,524 B2
• Filed: 11/13/2008
• Issued: 01/03/2012
• Est. Priority Date: 11/27/2007
• Status: Expired due to Fees

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Urisaka, Shinya
• Primary Examiner(s): Dang, Hung
• Application Number:
  US12/270,163
• Publication Number:
  US 20090135276A1
• Time in Patent Office: 1,146 Days
• Field of Search: 348/222.1, 348/226.1, 348/227.1, 348/228.1, 348/234.1
• US Class Current: 348/222.1
• CPC Class Codes: H04N 23/70 Circuitry for compensating brightness variation in the scene
• CPC Class Codes: H04N 23/745 Detection of flicker frequency or suppression of flicker wherein the flicker is caused by illumination, e.g. due to fluorescent tube illumination or pulsed LED illumination

Abstract

A flicker detection region in which an image signal has values relating to luminance and colors within predetermined ranges is extracted from a plurality of flicker detection regions allocated in the vertical and horizontal directions of an image. A flicker component is detected using the luminance information of the image signal in the extracted flicker detection region. A correction value to correct the flicker component is generated from the detected flicker component. This makes it possible to accurately correct, using a simple arrangement, a flicker component contained in an image sensed under a light source whose brightness periodically changes even when the object or the image sensing apparatus moves.

Claims

1. A flicker correction apparatus for correcting a flicker component in an image signal obtained by an image sensor, comprising:

an allocation unit which allocates a plurality of flicker detection regions by dividing the image signal of one frame in a vertical direction and a horizontal direction;

an extraction unit which extracts a flicker detection region from the plurality of flicker detection regions, in which the included image signal has values relating to luminance and colors within predetermined ranges;

a detection unit which detects a flicker component using luminance information of the image signal in the flicker detection region extracted by said extraction unit;

a generation unit which generates, from the flicker component detected by said detection unit, a correction value to correct the flicker component; and

a correction unit which corrects the flicker component by applying the correction value generated by said generation unit to the image signal of said one frame.

2. The apparatus according to claim 1, wherein the predetermined ranges include values relating to luminance and colors in correct exposure, which are obtained based on an image signal obtained by the image sensor before the image signal of said one frame.

3. The apparatus according to claim 1 further comprising a selection unit which selects a flicker detection region to be used to detect the flicker component from the flicker detection regions extracted by said extraction unit,

wherein said detection unit detects the flicker component using luminance information of an image signal in the flicker detection region selected by said selection unit.

4. The apparatus according to claim 3, further comprising a computation unit which computes a degree of reliability concerning flicker detection for each of the flicker detection regions extracted by said extraction unit,

wherein said selection unit selects a flicker detection region whose degree of reliability computed by said computation unit satisfies a predetermined degree of reliability.

5. The apparatus according to claim 4, wherein said selection unit selects a flicker detection region having a highest degree of reliability from the flicker detection regions extracted by said extraction unit which each position of the flicker detection regions in the vertical direction.

6. The apparatus according to claim 3, wherein if a plurality of flicker detection regions selected by said selection unit exist at the same position of the flicker detection regions in the vertical direction, said detection unit detects the flicker component using luminance information obtained from luminance information of the plurality of flicker detection regions.

7. The apparatus according to claim 3, wherein said detection unit detects the flicker component using, as luminance information to detect a flicker component at, out of positions of the flicker detection regions in the vertical direction, a position where no flicker detection region selected by said selection unit exists, luminance information obtained from luminance information of flicker detection regions selected by said selection unit at positions on upper and lower sides of the position where no flicker detection region selected by said selection unit exists.

8. The apparatus according to claim 3, wherein said detection unit detects the flicker component using, of the image signal included in the flicker detection region selected by said selection unit, luminance information of an image signal having values relating to luminance and colors within the predetermined ranges.

9. An image sensing apparatus comprising:

an image sensor;

a lens which forms an object image on said image sensor;

a signal processing unit which reads out an image signal from said image sensor and performing signal processing for the readout image signal;

a flicker correction apparatus of claim 1, which corrects a flicker component in the image signal output from said signal processing unit.

10. A flicker correction method of correcting a flicker component in an image signal obtained by an image sensor, comprising the steps of:

allocating a plurality of flicker detection regions by dividing the image signal of one frame in a vertical direction and a horizontal direction;

extracting a flicker detection region from the plurality of flicker detection regions, in which the included image signal has values relating to luminance and colors within predetermined ranges;

detecting a flicker component using luminance information of the image signal in the flicker detection region extracted in the extracting step;

generating, from the flicker component detected in the detecting step, a correction value to correct the flicker component; and

correcting the flicker component by applying the correction value generated in the generating step to the image signal of said one frame.