Image processing apparatus and method, and recording medium therefor

• US 6,781,595 B2
• Filed: 10/22/2001
• Issued: 08/24/2004
• Est. Priority Date: 10/23/2000
• Status: Expired due to Fees

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Ono, Hiroaki, Kobayashi, Seiji, Sato, Nobuyuki, Mitsunaga, Tomoo, Nakajima, Ken, Sano, Chikako
• Primary Examiner(s): Bella, Matthew C.
• Assistant Examiner(s): TRAN, TAM D
• Application Number:
  US10/035,711
• Publication Number:
  US 20020171663A1
• Time in Patent Office: 1,037 Days
• Field of Search: 345/589, 345/597, 345/600, 345/601, 345/274
• US Class Current: 345/589
• CPC Class Codes: G06T 2207/10024 Color image
• CPC Class Codes: G06T 2207/20208 High dynamic range [HDR] image processing
• CPC Class Codes: G06T 5/40 using histogram techniques
• CPC Class Codes: G06T 5/50 using two or more images, e.g. averaging or subtraction
• CPC Class Codes: G06T 5/92 based on global image properties
• CPC Class Codes: H04N 1/6005 with luminance or chrominance signals, e.g. LC1C2, HSL or YUV
• CPC Class Codes: H04N 1/6027 Correction or control of colour gradation or colour contrast H04N1/6058 takes precedence
• CPC Class Codes: H04N 23/843 Demosaicing, e.g. interpolating colour pixel values
• CPC Class Codes: H04N 25/134 based on three different wavelength filter elements
• CPC Class Codes: H04N 25/136 using complementary colours
• CPC Class Codes: H04N 9/77 Circuits for processing the brightness signal and the chrominance signal relative to each other, e.g. adjusting the phase of the brightness signal relative to the colour signal, correcting differential gain or differential phase circuits for matrixing H04N9/67

Abstract

An image processing apparatus and method and a recording medium therefor control the occurrence of a change in a hue. The histogram of a luminance signal Y is generated in a first step S1. In a second step S2, the histograms of the luminance signals Y are accumulated to generate a cumulative histogram, and the cumulative histogram is subjected to logarithmic approximation thereby to generate a lookup table (LUT) for correcting luminance signals. In a third step S3, a color-difference signal correction parameter LUT is generated by referring to the LUT for correcting luminance signals. In a fourth step S4, an input luminance signal Y is applied to the LUT for correcting luminance signals thereby to acquire a corrected luminance signal Y₀. In a fifth step S5, the input luminance signal Y is applied to a color-difference signal correction parameter LUT so as to acquire a correction parameter k. In a sixth step S6, input color-difference signals Cr and Cb are multiplied by the correction parameter k to acquire corrected color-difference signals Cr₀ and Cb₀.

Claims

1. An image processing apparatus for correcting the gray level of an image signal, comprising:

first generating means for generating a first conversion rule by using a first element of the image signal that has been input;

second generating means for generating a second conversion rule on the basis of the first conversion rule;

first correcting means for correcting the first element of the input image signal by using the first conversion rule;

acquiring means for acquiring a correction parameter associated with the first element of the input image signal by using the second conversion rule; and

second correcting means for correcting a second element of the input image signal by using the correction parameter.

2. An image processing apparatus according to claim 1, wherein

the first and second conversion rules are lookup tables.

3. An image processing apparatus according to claim 1, wherein

the first element of the image signal is a luminance signal, and

the second element of the image signal is a color-difference signal.

4. An image processing apparatus according to claim 1, wherein

the first generating means comprises:

preparing means for preparing a histogram of the first element of the input image signal;

accumulating means for accumulating the histogram to prepare a cumulative histogram; and

approximating means for approximating the cumulative histogram to a predetermined logarithmic curve thereby to generate the first conversion rule.

5. An image processing apparatus according to claim 1, wherein

the second correcting means corrects the second element of the input image signal by multiplying the second element by the correction parameter.

6. An image processing apparatus according to claim 1, further comprising:

converting means for converting an optical signal of a subject into a color signal; and

calculating means for calculating the first and second elements of the image signal on the basis of the color signal.

7. An image processing apparatus according to claim 6, wherein

the converting means converts the optical signal of the subject into a red signal, a green signal, or a blue signal.

8. An image processing apparatus according to claim 6, wherein

the converting means coverts the optical signal of the subject into a yellow signal, a cyan signal, or a green signal.

9. An image processing apparatus according to claim 6, wherein

the converting means coverts the optical signal of the subject into a yellow signal, a cyan signal, a magenta signal, or a green signal.

10. An image processing method for an image processing apparatus for correcting the gray level of an image signal, the image processing method comprising:

a first generating step for generating a first conversion rule by using a first element of the image signal that has been input;

a second generating step for generating a second conversion rule on the basis of the first conversion rule;

a first correcting step for correcting the first element of the input image signal by using the first conversion rule;

an acquiring step for acquiring a correction parameter associated with the first element of the input image signal by using the second conversion rule; and

a second correcting step for correcting a second element of the input image signal by using the correction parameter.

11. An image processing method according to claim 10, wherein

the first and second conversion rules are lookup tables.

12. An image processing method according to claim 10, wherein

the first element of the image signal is a luminance signal, and the second element of the image signal is a color-difference signal.

13. An image processing method according to claim 10, wherein

the first generating step comprises:

a preparing step for preparing a histogram of the first element of the image signal that has been input;

an accumulating step for accumulating the histogram to prepare a cumulative histogram; and

an approximating step for approximating the cumulative histogram to a predetermined logarithmic curve thereby to generate the first conversion rule.

14. An image processing method according to claim 10, wherein

the second correcting step corrects the second element of the input image signal by multiplying the second element by the correction parameter.

15. An image processing method according to claim 10, further comprising:

a converting step for converting an optical signal of a subject into a color signal, and a calculating step for calculating the first and second elements of the image signal.

16. An image processing method according to claim 15, wherein

the converting step converts the optical signal of the subject into a red signal, a green signal, or a blue signal.

17. An image processing method according to claim 15, wherein

the converting step coverts the optical signal of the subject into a yellow signal, a cyan signal, or a green signal.

18. An image processing method according to claim 15, wherein

the converting step coverts the optical signal of the subject into a yellow signal, a cyan signal, a magenta signal, or a green signal.

19. A recording medium in which a computer-readable image processing program for correcting the gray level of an image signal has been recorded, the program comprising:

a first generating step for generating a first conversion rule by using a first element of the image signal that has been input;

a second generating step for generating a second conversion rule on the basis of the first conversion rule;

a first correcting step for correcting the first element of the input image signal by using the first conversion rule;

an acquiring step for acquiring a correction parameter associated with the first element of the input image signal by using the second conversion rule; and

a second correcting step for correcting a second element of the input image signal by using the correction parameter.

20. A recording medium, in which a computer-readable image processing program for correcting the gray level of an image signal has been recorded, according to claim 19, wherein

the first and second conversion rules are lookup tables.

21. A recording medium, in which a computer-readable image processing program for correcting the gray level of an image signal has been recorded, according to claim 19, wherein

the first element of the image signal is a luminance signal, and

the second element of the image signal is a color-difference signal.

22. A recording medium, in which a computer-readable image processing program for correcting the gray level of an image signal has been recorded, according to claim 19, wherein

the first generating step comprises:

a preparing step for preparing a histogram of the first element of the image signal that has been input;

an accumulating step for accumulating the histogram to prepare a cumulative histogram; and

an approximating step for approximating the cumulative histogram to a predetermined logarithmic curve thereby to generate the first conversion rule.

23. A recording medium, in which a computer-readable image processing program for correcting the gray level of an image signal has been recorded, according to claim 19, wherein

the second correcting step corrects the second element of the input image signal by multiplying the second element by the correction parameter.

24. A recording medium, in which a computer-readable image processing program for correcting the gray level of an image signal has been recorded, according to claim 19, further comprising:

a converting step for converting an optical signal of a subject into a color signal; and

a calculating step for calculating the first and second elements of the image signal.

25. A recording medium, in which a computer-readable image processing program for correcting the gray level of an image signal has been recorded, according to claim 24, wherein

the converting step converts the optical signal of the subject into a red signal, a green signal, or a blue signal.

26. A recording medium, in which a computer-readable image processing program for correcting the gray level of an image signal has been recorded, according to claim 24, wherein

the converting step coverts the optical signal of the subject into a yellow signal, a cyan signal, or a green signal.

27. A recording medium, in which a computer-readable image processing program for correcting the gray level of an image signal has been recorded, according to claim 24, wherein

the converting step coverts the optical signal of the subject into a yellow signal, a cyan signal, a magenta signal, or a green signal.