Method and device for correcting lightness of image

• US 6,788,822 B1
• Filed: 08/30/2000
• Issued: 09/07/2004
• Est. Priority Date: 08/31/1999
• Status: Expired due to Term

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.), Soliton Systems K.K.
• Original Assignee: Synthesis Corp. (Fujioka Family), Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Niwa, Akimasa, Zhang, Xiaomang, Kubo, Noboru, Okuhata, Hiroyuki
• Primary Examiner(s): Ahmed, Samir
• Assistant Examiner(s): Bali, Vikkram
• Application Number:
  US09/651,117
• Time in Patent Office: 1,469 Days
• Field of Search: 382/254, 382/260, 382/274, 382/162, 382/279, 358/447, 358/448, 358/530, 358/532
• US Class Current: 382/254
• CPC Class Codes: G06T 2207/10024 Color image
• CPC Class Codes: G06T 2207/20016 Hierarchical, coarse-to-fine, multiscale or multiresolution image processing; Pyramid transform
• CPC Class Codes: G06T 5/94 based on local image properties, e.g. for local contrast enhancement

Abstract

A method for correcting lightness of an image includes the steps of: calculating a first scale and a second scale based on an image scale of an original image from image information of the original image; multiscale retinex processing the original image with respect to the first scale and the second scale; and synthesizing a result of the multiscale retinex processing with the image information of the original image.

Claims

1. A method for correcting lightness of an image, comprising the steps of:

calculating a first scale and a second scale, which correspond to an inputted image size, based on an image scale of an original image including a plurality of pixels from image information of the original image;

multiscale retinex processing the original image with respect to the first scale and the second scale to produce a multiscale retinex processing result;

calculating an offset correction value based on a histogram of a lightness value against the number of pixels of the original image;

correcting said multiscale retinex processing result based on a gain correction value and said offset correction value to produce a corrected multiscale retinex processing result; and

synthesizing said corrected multiscale retinex processing result with the image information of the original image to produce an output image.

2. A method for correcting lightness of an image according to claim 1, wherein the first scale is a small scale, and the second scale is a large scale.

3. A method for correcting lightness of an image according to claim 2, wherein a radius of the large scale is about ½

of a longer side of the original image.

4. A method for correcting lightness of an image according to claim 2, wherein a radius of the small scale is about ⅕

of a longer side of the original image.

5. An image processing device, comprising:

a scale size calculating section for calculating a first scale and a second scale, which correspond to an inputted image size, based on an image scale of an original image including a plurality of pixels from image information of the original image;

a scale retinex processing section for multiscale retinex processing the original image with respect to the first scale and the second scale to produce a multiscale retinex processing result, and

a correction value calculating section for calculating an offset correction value based on a histogram of a lightness value against the number of pixels of the original image,

wherein said scale retinex processing section corrects said multiscale retinex processing result based on a gain correction value and said offset correction value to produce a corrected multiscale retinex processing result, and

wherein said scale retinex processing section synthesizes said corrected multiscale retinex processing result with the image information, thereby generating an output image.

6. An image processing device according to claim 5 wherein the first scale is a small scale, and the second scale is a large scale.

7. An image processing device according to claim 6, wherein a radius of the large scale is about ½

of a longer side of the original image.

8. An image processing device according to claim 6, wherein a radius of the small scale is about ⅕

of a longer side of the original image.