Auto white balancing apparatus and method

• US 6,791,606 B1
• Filed: 05/09/2000
• Issued: 09/14/2004
• Est. Priority Date: 05/09/2000
• Status: Expired due to Term

• Current Assignee: Apple Inc.
• Original Assignee: Eastman Kodak Company
• Inventors: Miyano, Toshiki
• Primary Examiner(s): Garber, Wendy R.
• Assistant Examiner(s): Ye, Lin
• Application Number:
  US09/567,641
• Time in Patent Office: 1,589 Days
• Field of Search: 348/223.1, 348/225.1, 348/228.1, 348/655, 348/227.1, 348/266
• US Class Current: 348/223.1
• CPC Class Codes: H04N 23/88 for colour balance, e.g. white-balance circuits or colour temperature control

Abstract

An auto white balancing apparatus includes a block split circuit for splitting an image into a plurality of blocks; a representative color calculating circuit which for each split block, derives a representative color of each block on the basis of pixel values within each block; and a block reliability estimating circuit which for each block and for each light source determines the distance between color difference components of the color of a white object under each light source and color difference components of the representative color of each block, to thereby estimate a reliability signal with which each light source lights a scene of each block on the basis of the distances. The auto white balancing apparatus also includes a light source contribution component estimating circuit which for each light source, weights and averages the representative color of each block in accordance with the reliability signal of each light source upon each block, to thereby estimate components of contribution of each light source to the entire image; and a total reliability estimating circuit which for each light source, totals up the reliability signal of each light source upon each block over all blocks contained within the image, to thereby estimate the reliability signal of each light source in the entire image. The auto white balancing apparatus further includes a lighting color estimating circuit for weighting and averaging components of contribution of each light source to the entire image estimated by the light source contribution component estimating circuit, in accordance with the reliability signal of each light source upon the entire image estimated by the total reliability estimating circuit, to thereby estimate the color of lighting which lights the scene of the entire image; and a white balancing circuit for executing white balance processing of each pixel of the image so as to cancel the lighting color estimated.

Claims

1. An auto white balancing apparatus comprising:

(a) a block split circuit for splitting an image into a plurality of blocks;

(b) a representative color calculating circuit which for each split block, derives a representative color of each block on the basis of pixel values within each block;

(c) a block reliability estimating circuit which for each block determines the distance between color difference components of the color of a white object under at least one light source and color difference components of the representative color of each block, to thereby estimate a reliability signal with which the at least one light source lights a scene of each block on the basis of the distances;

(d) a circuit for determining the variance of pixel values of pixels sampled from the block;

(e) a circuit for modifying the reliability signal estimated by the block reliability estimating circuit, in accordance with a predetermined function whose value becomes smaller as the variance of the pixel values increases;

(f) a lighting color estimating circuit for estimating the color of lighting which lights the scene of the entire image in response to the modified reliability signals; and

(g) a white balancing circuit for executing white balance processing of each pixel of the image so as to cancel the estimated lighting color.

2. An auto white balancing apparatus comprising:

(a) a block split circuit for splitting an image into a plurality of blocks;

(b) a representative color calculating circuit which for each split block, derives a representative color of each block on the basis of pixel values within each block;

(c) a block reliability estimating circuit which for each block determines the distance between color difference components of the color of a white object under at least one light source and color difference components of the representative color of each block, to thereby estimate a reliability signal with which the at least one light source lights a scene of each block on the basis of the distances;

(d) a circuit for counting up the number of saturation pixels contained in the block; and

(e) a circuit for modifying the reliability signal estimated by the block reliability estimating circuit, in accordance with a predetermined function whose value becomes smaller as the number of the saturation pixels increases;

(f) a lighting color estimating circuit for estimating the color of lighting which lights the scene of the entire image in response to the modified reliability signals; and

(g) a white balancing circuit for executing white balance processing of each pixel of the image so as to cancel the estimated lighting color.

3. A method of performing auto white balancing adjustment for an image, comprising:

(a) splitting an image to be subjected to white balance processing into a plurality of blocks;

(b) for each split block, deriving a representative color of each block on the basis of pixel values within each block;

(c) for each block and for at least one light source, determining the distance between color difference components of the color of a white object under the at least one light source and color difference components of the representative color of each block, to thereby estimate a reliability signal with which the at least one light source lights a scene of each block on the basis of the distances;

(d) determining the variance of pixel values of pixels sampled from the block;

(e) modifying the reliability signal in accordance with a predetermined function whose value becomes smaller as the variance of the pixel values increases;

(f) estimating the color of lighting which lights the scene of the entire image in response to the modified reliability signal; and

(g) executing white balance processing for each pixel of the image so as to cancel the estimated lighting color.

4. A method of performing auto white balancing adjustment for an image, comprising:

(a) splitting an image to be subjected to white balance processing into a plurality of blocks;

(b) for each split block, deriving a representative color of each block on the basis of pixel values within each block;

(c) for each block and for at least one light source, determining the distance between color difference components of the color of a white object under the at least one light source and color difference components of the representative color of each block, to thereby estimate a reliability signal with which the at least one light source lights a scene of each block on the basis of the distances;

(d) counting up the number of saturation pixels contained in the block;

(e) modifying the reliability signal in accordance with a predetermined function whose value becomes smaller as the number of the saturation pixels increases;

(f) estimating the color of lighting which lights the scene of the entire image in response to the modified reliability signal; and

(g) executing white balance processing for each pixel of the image so as to cancel the estimated lighting color.