Image processing method and apparatus for correcting photographic images

• US 20040184672A1
• Filed: 01/30/2004
• Published: 09/23/2004
• Est. Priority Date: 02/03/2003
• Status: Abandoned Application

• Current Assignee: Noritsu Koki Co., Ltd.
• Original Assignee: Noritsu Koki Co., Ltd.
• Inventors: Murakami, Kenji
• Application Number:
  US10/768,879
• Publication Number:
  US 20040184672A1
• Time in Patent Office: Days
• US Class Current: 382/274
• CPC Class Codes: G06T 2207/10008 from scanner, fax or copier
• CPC Class Codes: G06T 2207/20192 Edge enhancement; Edge preservation
• CPC Class Codes: G06T 2207/20204 Removing film grain; Adding simulated film grain
• CPC Class Codes: G06T 5/20 using local operators
• CPC Class Codes: G06T 5/70 Denoising; Smoothing

Abstract

An area setting unit 12 is provided for distinguishing underexposed areas and overexposed areas in an original photo image. A noise and graininess suppressing power calculating unit 14 and a noise and graininess suppressing filter generating unit 15 set a filter for use in image processing of each pixel in the underexposed areas and overexposed areas according to the value of a parameter indicating an edge strength. A noise and graininess suppression processing unit 16, by using this filter, corrects a pixel value of each pixel in the underexposed areas and overexposed areas.

Claims

1. An image processing method for correcting a pixel value of each pixel forming image data of an original photo image, comprising the computer-implemented steps of:

distinguishing underexposed areas and overexposed areas in said original photo image;

setting a filter for use in correcting each pixel in said underexposed areas and said overexposed areas according to a value of a parameter indicating an edge strength; and

correcting the pixel value of each pixel in said underexposed areas and said overexposed areas by using said filter.

2. An image processing method for correcting a pixel value of each pixel forming image data of an original photo image, comprising the computer-implemented steps of:

distinguishing underexposed areas and overexposed areas in said original photo image;

extracting, as low frequency image data, image data of areas showing low frequency components in a spatial frequency from image data obtained by shading said original photo image data in said underexposed areas and said overexposed areas;

extracting, as high frequency image data, image data of areas showing high frequency components in a spatial frequency from image data obtained by shading said original photo image data in said underexposed areas and said overexposed areas;

removing noise components from said high frequency image data;

creating superposed image data by superposing said low frequency image data and said high frequency image data with the noise components removed therefrom; and

correcting the image data of said underexposed areas and said overexposed areas of the original photo image to said superposed image data.

3. A computer-readable medium having stored thereon computer-executable instructions which when executed perform an image processing method, the method comprising the steps of:

distinguishing underexposed areas and overexposed areas in an original photo image;

setting a filter for use in correcting each pixel in said underexposed areas and said overexposed areas according to a value of a parameter indicating an edge strength; and

correcting the pixel value of each pixel in said underexposed areas and said overexposed areas by using said filter.

4. A computer-readable medium having stored thereon computer-executable instructions which when executed perform an image processing method, the method comprising the steps of:

distinguishing underexposed areas and overexposed areas in an original photo image;

extracting, as low frequency image data, image data of areas showing low frequency components in a spatial frequency from image data obtained by shading said original photo image data in said underexposed areas and said overexposed areas;

extracting, as high frequency image data, image data of areas showing high frequency components in a spatial frequency from image data obtained by shading said original photo image data in said underexposed areas and said overexposed areas;

removing noise components from said high frequency image data;

creating superposed image data by superposing said low frequency image data and said high frequency image data with the noise components removed therefrom; and

correcting the image data of said underexposed areas and said overexposed areas of the original photo image to said superposed image data

5. An image processing apparatus for correcting a pixel value of each pixel forming image data of an original photo image, comprising:

area distinguishing means for distinguishing underexposed areas and overexposed areas in said original photo image;

filter setting means for setting a filter for use in correcting each pixel in said underexposed areas and said overexposed areas according to a value of a parameter indicating an edge strength; and

correcting means for correcting the pixel value of each pixel in said underexposed areas and said overexposed areas by using said filter.

6. An image processing apparatus as defined in claim 5, wherein said filter setting means is arranged to set a sharpening filter when the value of the parameter indicating the edge strength is large, and set a smoothing filter when the value of the parameter is small.

7. An image processing apparatus as defined in claim 5, wherein said filter setting means includes power calculating means for calculating an image processing power according to the pixel value of each pixel, and filter generating means for changing a median which is a value of a filter factor located at a center of a filter factor matrix forming said filter, according to the value of the parameter indicating the edge strength, and fixing factors other than said median to a uniform value.

8. An image processing apparatus as defined in claim 7, further comprising shading mask image creating means for creating a shading mask image for the image data of the original photo image.

9. An image processing apparatus as defined in claim 5, wherein said area distinguishing means is arranged to determine pixels with a pixel value of each color smaller than a threshold α

to be underexposed pixels, determine pixels with a pixel value of each color larger than a threshold β

to be overexposed pixels, determine an area of the original photo image with a density of the underexposed pixels exceeding a threshold ψ

to be an underexposed area, and determine an area of the original photo image with a density of the overexposed pixels exceeding the threshold ψ

to be an overexposed area.

10. An image processing apparatus for correcting a pixel value of each pixel forming image data of an original photo image, comprising:

area distinguishing means for distinguishing underexposed areas and overexposed areas in said original photo image;

low frequency image data extracting means for extracting, as low frequency image data, image data of areas showing low frequency components in a spatial frequency from image data obtained by shading said original photo image data in said underexposed areas and said overexposed areas;

high frequency image data extracting means for extracting, as high frequency image data, image data of areas showing high frequency components in a spatial frequency from image data obtained by shading said original photo image data in said underexposed areas and said overexposed areas;

noise removing means for removing noise components from said high frequency image data;

image superposing means for creating superposed image data by superposing said low frequency image data and said high frequency image data with the noise components removed therefrom; and

correcting means for correcting the image data of said underexposed areas and said overexposed areas of the original photo image to said superposed image data.

11. An image processing apparatus as defined in claim 10, wherein said high frequency image data extracting means is arranged to extract the high frequency image data by subtracting said low frequency image data from the image data of the original photo image.

12. An image processing apparatus as defined in claim 10, wherein said area distinguishing means is arranged to determine pixels with a pixel value of each color smaller than a threshold α

to be underexposed pixels, determine pixels with a pixel value of each color larger than a threshold β

to be overexposed pixels, determine an area of the original photo image with a density of the underexposed pixels exceeding a threshold ψ

to be an underexposed area, and determine an area of the original photo image with a density of the overexposed pixels exceeding the threshold ψ

to be an overexposed area.