Image processing apparatus combining plural sets of image data and method for controlling the same

• US 8,554,010 B2
• Filed: 06/30/2010
• Issued: 10/08/2013
• Est. Priority Date: 07/15/2009
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Hasegawa, Naoyuki
• Primary Examiner(s): Bella, Matthew
• Assistant Examiner(s): HEIDEMANN, JASON E
• Application Number:
  US12/827,289
• Publication Number:
  US 20110013848A1
• Time in Patent Office: 1,196 Days
• Field of Search: None
• US Class Current: 382/274
• CPC Class Codes: G06T 2207/10024 Color image
• CPC Class Codes: G06T 2207/10144 Varying exposure
• CPC Class Codes: G06T 2207/20012 Locally adaptive
• CPC Class Codes: G06T 2207/20208 High dynamic range [HDR] image processing
• CPC Class Codes: G06T 2207/20221 Image fusion; Image merging
• CPC Class Codes: G06T 5/008 Local, e.g. shadow enhancement
• CPC Class Codes: G06T 5/50 using two or more images, e.g. averaging or subtraction
• CPC Class Codes: G06T 5/94 based on local image properties, e.g. for local contrast enhancement
• CPC Class Codes: H04N 23/70 Circuitry for compensating brightness variation in the scene
• CPC Class Codes: H04N 23/741 by increasing the dynamic range of the image compared to the dynamic range of the electronic image sensors

Abstract

An image processing apparatus that generates image data having a high dynamic range by combining a plurality of image data having different exposure amounts includes: an input unit configured to input a plurality of M-bit image data; a determining unit configured to determine reference image data serving as an exposure reference from among the plurality of input M-bit image data; a composition unit configured to combine the plurality of M-bit image data, and generate one N-bit composite image data (N>M); a characteristic parameter setting unit configured to set a characteristic parameter of tone compression on the N-bit composite image data such that a predetermined reference luminance in the reference image data does not change; and a generating unit configured to generate M-bit composite image data by compressing a luminance tone of an image component based on the set characteristic parameter.

Claims

1. An image processing apparatus, comprising:

an input unit configured to input a plurality of sets of M-bit image data that are to be combined;

a determining unit configured to determine reference image data serving as an exposure reference from among the plurality of sets of input M-bit image data;

a composition unit configured to combine the plurality of sets of M-bit image data, and generate one set of N-bit composite image data (N>

M);

a characteristic parameter setting unit configured to set a characteristic parameter of tone compression on the N-bit composite image data such that a predetermined reference luminance in the reference image data does not change; and

a generating unit configured to generate M-bit composite image data by compressing a luminance tone of an image component contained in the N-bit composite image data and having a frequency lower than a predetermined frequency based on the set characteristic parameter,

wherein the image processing apparatus further comprises at least one of;

a shadow pixel ratio determining unit configured to determine a shadow pixel ratio, which is the ratio of the number of pixels having a luminance value smaller than a first predetermined luminance value with respect to the total number of pixels, in the reference image data; and

a highlight pixel ratio determining unit configured to determine a highlight pixel ratio, which is the ratio of the number of pixels having a luminance value larger than a second predetermined luminance value with respect to the total number of pixels in the reference image data,

wherein the characteristic parameter setting unit sets a characteristic parameter that reduces a shadow detail loss of a pixel of the N-bit composite image data having a pixel value smaller than the predetermined reference luminance according to the shadow pixel ratio, and sets a characteristic parameter that reduces a highlight detail loss of a pixel of the N-bit composite image data having a pixel value larger than the predetermined reference luminance according to the highlight pixel ratio.

2. The image processing apparatus according to claim 1, wherein the predetermined reference luminance is a luminance of a predetermined subject in the reference image data.

3. The image processing apparatus according to claim 1, wherein the predetermined frequency is a cut-off frequency of a low-pass filter used to extract a luminance illumination component in the Retinex model.

4. The image processing apparatus according to claim 1, wherein the generating unit adjusts a color component of the M-bit composite image data according to an amount of luminance tone changed by the compression.

5. The image processing apparatus according to claim 1, further comprising:

a gamma characteristic correcting unit configured to correct a gamma characteristic of the M-bit composite image data based on a dynamic range characteristic of an output device that outputs the M-bit composite image data.

7. A non-transitory computer-readable storage medium storing a program for causing a computer to operate as the image processing apparatus according to claim 1.

6. A method for controlling an image processing apparatus, comprising:

an input step, in which an input unit inputs a plurality of sets of M-bit image data that are to be combined;

a determining step, in which a determining unit determines reference image data serving as an exposure reference from among the plurality of sets of input M-bit image data;

a composition step, in which a composition unit combines the plurality of sets of M-bit image data, and generates one set of N-bit composite image data (N>

M);

a characteristic parameter setting step, in which a characteristic parameter setting unit sets a characteristic parameter of tone compression on the N-bit composite image data such that a predetermined reference luminance in the reference image data does not change; and

a generating step, in which a generating unit generates M-bit composite image data by compressing a luminance tone of an image component contained in the N-bit composite image data and having a frequency lower than a predetermined frequency based on the set characteristic parameter,

wherein the method further comprises at least one of;

a shadow pixel ratio determining step, in which a shadow pixel ratio determining unit determines a shadow pixel ratio, which is the ratio of the number of pixels having a luminance value smaller than a first predetermined luminance value with respect to the total number of pixels, in the reference image data; and

a highlight pixel ratio determining step, in which a highlight pixel ratio determining unit determines a highlight pixel ratio, which is the ratio of the number of pixels having a luminance value larger than a second predetermined luminance value with respect to the total number of pixels, in the reference image data;

wherein, in the characteristic parameter setting step, the characteristic parameter setting unit sets a characteristic parameter that reduces a shadow detail loss of a pixel of the N-bit composite image data having a pixel value smaller than the predetermined reference luminance according to the shadow pixel ratio, and sets a characteristic parameter that reduces a highlight detail loss of a pixel the N-bit composite image data having a pixel value larger than the predetermined reference luminance according to the highlight pixel ratio.