Image processing apparatus, image processing method, and storage medium for gain adjustment

Patent metadata

Field	Value
Publication number	US-10628928-B2
Application number	US-201815883740-A
Country	US
Kind code	B2
Filing date	Jan 30, 2018
Priority date	Feb 7, 2017
Publication date	Apr 21, 2020
Grant date	Apr 21, 2020

Abstract

Image processing generates reference gain information based on a first tone characteristic by using an input image, the reference gain information including a gain value corresponding to a luminance value for each pixel, the first tone characteristic including a luminance range in which a gain signal monotonically increases; generates a correction signal to correct the reference gain information based on a second tone characteristic in which the gain signal monotonically decreases or monotonically increases regardless of the luminance range by using the input image and a low-frequency image generated from the input image; and performs gain processing on the input image based on gain information obtained after the reference gain information is corrected by the correction signal.

First claim

What is claimed is:

1. An image processing apparatus comprising:
at least one processor and/or circuit configured to:
generate reference gain information by replacing the luminance value of each pixel of an input image with the gain value of a first tone characteristic corresponding to said luminance value, the first tone characteristic including a luminance range in which a gain signal monotonically increases;
generate a correction signal to correct the reference gain information based on a second tone characteristic in which the gain signal monotonically decreases or monotonically increases regardless of the luminance range by using the input image and a low-frequency image generated from the input image; and
perform gain processing on the input image based on gain information obtained after the reference gain information is corrected by the correction signal.

2. The image processing apparatus according to claim 1 , wherein the at least one processor and/or circuit further configured to,
generate first gain information by replacing the luminance value of each pixel of the input image with the gain value of the second tone characteristic corresponding to said luminance value,
generate second gain information by replacing the luminance value of each pixel of the low-frequency image with the gain value of the second tone characteristic corresponding to said luminance value, and
generate, as the correction signal, a difference between the first gain information and the second gain information.

3. The image processing apparatus according to claim 2 , further comprising a correction unit configured to generate gain information obtained after the difference is added to the reference gain information to correct the reference gain information by the correction signal.

4. The image processing apparatus according to claim 1 , wherein the at least one processor and/or circuit further configured to, generate first gain information by replacing the luminance value of each pixel of the input image with the gain value of the second tone characteristic corresponding to said luminance value,
perform reduction processing on the input image to generate a plurality of low-frequency images having different frequency levels, and combines a plurality of pieces of gain information, each generated by replacing the luminance value of each pixel of one of the plurality of low-frequency images, respectively, with the gain value of the second tone characteristic corresponding to said luminance value, to generate the second gain information, and
generate as the correction signal, a difference between the first gain information and the second gain information.

5. The image processing apparatus according to claim 1 , wherein the at least one processor and/or circuit further configured to, generate the first tone characteristic based on the input image, and generate the second tone characteristic based on the first tone characteristic.

6. The image processing apparatus according to claim 5 , wherein the at least one processor and/or circuit further configured to, generate the second tone characteristic in which the gain signal monotonically decreases by inverting a gradient of a characteristic portion that monotonically increases in the first tone characteristic and by replacing the characteristic portion of the first tone characteristic with the gradient-inverted version of said characteristic portion.

7. The image processing apparatus according to claim 5 , wherein the at least one processor and/or circuit further configured to, generate the second tone characteristic in which the gain signal monotonically increases by inverting a gradient of a characteristic portion that monotonically decreases in a tone characteristic obtained after a sign of a characteristic in an entire luminance range of the first tone characteristic is inverted and by replacing the characteristic portion of the first tone characteristic with the gradient-inverted version of said characteristic portion.

8. The image processing apparatus according to claim 1 , wherein the input image is an image including a luminance signal.

9. An image processing method for an image processing apparatus, the method comprising:
generating reference gain information by replacing the luminance value of each pixel of an input image with the gain value of a first tone characteristic corresponding to said luminance value, the first tone characteristic including a luminance range in which a gain signal monotonically increases;
generating a correction signal to correct the reference gain information based on a second tone characteristic in which the gain signal monotonically decreases or monotonically increases regardless of the luminance range by using the input image and a low-frequency image generated from the input image; and
performing gain processing on the input image based on gain information obtained after the reference gain information is corrected by the correction signal.

10. A non-transitory, computer-readable storage medium storing a program for causing a computer to execute a method comprising:
generating reference gain information by replacing the luminance value of each pixel of an input image with the gain value of a first tone characteristic corresponding to said luminance value, the first tone characteristic including a luminance range in which a gain signal monotonically increases;
generating a correction signal to correct the reference gain information based on a second tone characteristic in which the gain signal monotonically decreases or monotonically increases regardless of the luminance range by using the input image and a low-frequency image generated from the input image; and
performing gain processing on the input image based on gain information obtained after the reference gain information is corrected by the correction signal.

Assignees

• Canon Kk

Inventors

• Kimura Naoto

Classifications

• H04N5/243

  Electricity · mapped topic

• G06T5/009 Primary

  Physics · mapped topic

• H04N23/76

  by influencing the image signals · CPC title

• G06T5/92 Primary

  based on global image properties · CPC title