US-12621573-B2 - Brightness measurement apparatus, brightness measurement method, brightness measurement program, and camera system

US12621573B2US 12621573 B2US12621573 B2US 12621573B2US-12621573-B2

Abstract

A processor of a brightness measurement apparatus sets, on an imaging region of a camera, a brightness measurement region that has a center part and peripheral parts that surround the center part. The brightness measurement region includes subregions. The subregions include central subregions located in the center part of the brightness measurement region, and peripheral subregions located in the peripheral parts of the brightness measurement region. A size of at least one of the central subregions is different from a size of at least one of the peripheral subregions. The processor measures, for each subregion, a brightness of the corresponding subregion in accordance with a pixel value of at least one pixel of a frame image captured by the camera through the imaging region. The pixel value of the at least one pixel of the frame image is included in the corresponding subregion.

Inventors

Ikuko Komura

Assignees

DENSO CORPORATION

Dates

Publication Date: 20260505
Application Date: 20240111
Priority Date: 20230113

Claims (19)

1 . A brightness measurement apparatus comprising: a memory storing computer-program instructions; and a processor communicable with the memory and a camera, the processor being configured to execute the computer-program instructions to accordingly: set, on an imaging region of the camera, a brightness measurement region that has a center part and peripheral parts that surround the center part, the brightness measurement region comprising a plurality of subregions, the plurality of subregions including: central subregions located in the center part of the brightness measurement region; and peripheral subregions located in the peripheral parts of the brightness measurement region, a size of at least one of the central subregions being different from a size of at least one of the peripheral subregions; and measure, for each of the plurality of subregions of the brightness measurement region, a brightness of a corresponding one of the plurality of subregions of the brightness measurement region in accordance with a pixel value of at least one pixel of a frame image captured by the camera through the imaging region, the pixel value of the at least one pixel of the frame image being included in the corresponding one of the plurality of subregions.
2 . The brightness measurement apparatus according to claim 1 , wherein: the processor is configured to set the brightness measurement region such that the sizes of the plurality of subregions substantially decrease toward an outer periphery of the imaging region.
3 . The brightness measurement apparatus according to claim 1 , wherein: the camera comprises a lens that has a predetermined aberration; and the processor is configured to alter a shape of the brightness measurement region in conformity with the predetermined aberration of the lens of the camera.
4 . The brightness measurement apparatus according to claim 1 , wherein: each of the plurality of subregions comprises a plurality of cells; and the processor is configured to: exclude, from the plurality of cells of at least one selected subregion in the plurality of subregions, at least one cell; and measure, for the at least one selected subregion, the brightness of the at least one selected subregion in accordance with the pixel value of the at least one pixel of the frame image, the pixel value of the at least one pixel of the frame image being included in remaining cells of the at least one selected subregion.
5 . The brightness measurement apparatus according to claim 1 , wherein: the camera comprises a lens and the lens of the camera is one of a wide-angle lens and a telephoto lens; the wide-angle lens has a predetermined barrel aberration; the telephote lens has a predetermined pincushion aberration; and the processor is configured to: alter a shape of the plurality of subregions in conformity with the predetermined barrel aberration of the wide-angle lens of the camera if the lens of the camera is the wide-angle lens; and alter a shape of the plurality of subregions in conformity with the predetermined pincushion aberration of the telephoto lens of the camera if the lens of the camera is the telephoto lens.
6 . A method to be executed by a processor in accordance with computer-program instructions stored in a memory, the method comprising: setting, on an imaging region of a camera, a brightness measurement region that has a center part and peripheral parts that surround the center part, the brightness measurement region comprising a plurality of subregions, the plurality of subregions including: central subregions located in the center part of the brightness measurement region; and peripheral subregions located in the peripheral parts of the brightness measurement region, a size of at least one of the central subregions being different from a size of at least one of the peripheral subregions; and measuring, for each of the plurality of subregions of the brightness measurement region, a brightness of a corresponding one of the plurality of subregions of the brightness measurement region in accordance with a pixel value of at least one pixel of a frame image captured by the camera through the imaging region, the pixel value of the at least one pixel of the frame image being included in the corresponding one of the plurality of subregions.
7 . The method according to claim 6 , wherein: the setting sets the brightness measurement region such that the sizes of the plurality of subregions substantially decrease toward an outer periphery of the imaging region.
8 . The method according to claim 6 , wherein: the camera comprises a lens that has a predetermined aberration; and the method further comprises: altering a shape of the brightness measurement region in conformity with the predetermined aberration of the lens of the camera.
9 . The method according to claim 6 , wherein: each of the plurality of subregions comprises a plurality of cells; the method further comprises: excluding, from the plurality of cells of at least one selected subregion in the plurality of subregions, at least one cell; and the measuring measures, for the at least one selected subregion, the brightness of the at least one selected subregion in accordance with the pixel value of the at least one pixel of the frame image, the pixel value of the at least one pixel of the frame image being included in remaining cells of the at least one selected subregion.
10 . The method according to claim 6 , wherein: the camera comprises a lens and the lens of the camera is one of a wide-angle lens and a telephoto lens; the wide-angle lens has a predetermined barrel aberration; the telephote lens has a predetermined pincushion aberration; and the method further comprises: altering a shape of the plurality of subregions in conformity with the predetermined barrel aberration of the wide-angle lens of the camera if the lens of the camera is the wide-angle lens; and altering a shape of the plurality of subregions in conformity with the predetermined pincushion aberration of the telephoto lens of the camera if the lens of the camera is the telephoto lens.
11 . A processor-readable program product comprising: a non-transitory computer-readable storage medium; and a set of computer-program instructions stored in the storage medium, the computer-program instructions causing a processor to: set, on an imaging region of a camera, a brightness measurement region that has a center part and peripheral parts that surround the center part, the brightness measurement region comprising a plurality of subregions, the plurality of subregions including: central subregions located in the center part of the brightness measurement region; and peripheral subregions located in the peripheral parts of the brightness measurement region, a size of at least one of the central subregions being different from a size of at least one of the peripheral subregions; and measure, for each of the plurality of subregions of the brightness measurement region, a brightness of a corresponding one of the plurality of subregions of the brightness measurement region in accordance with a pixel value of at least one pixel of a frame image captured by the camera through the imaging region, the pixel value of the at least one pixel of the frame image being included in the corresponding one of the plurality of subregions.
12 . The processor-readable program product according to claim 11 , wherein: the computer-program instructions cause the processor to set the brightness measurement region such that the sizes of the plurality of subregions substantially decrease toward an outer periphery of the imaging region.
13 . The processor-readable program product according to claim 11 , wherein: the camera comprises a lens that has a predetermined aberration; and the computer-program instructions cause the processor to alter a shape of the brightness measurement region in conformity with the predetermined aberration of the lens of the camera.
14 . The processor-readable program product according to claim 11 , wherein: each of the plurality of subregions comprises a plurality of cells; and the computer-program instructions cause the processor to: exclude, from the plurality of cells of at least one selected subregion in the plurality of subregions, at least one cell; and measure, for the at least one selected subregion, the brightness of the at least one selected subregion in accordance with the pixel value of the at least one pixel of the frame image, the pixel value of the at least one pixel of the frame image being included in remaining cells of the at least one selected subregion.
15 . The processor-readable program product according to claim 11 , wherein: the camera comprises a lens and the lens of the camera is one of a wide-angle lens and a telephoto lens; the wide-angle lens has a predetermined barrel aberration; the telephote lens has a predetermined pincushion aberration; and the computer-program instructions cause the processor to: alter a shape of the plurality of subregions in conformity with the predetermined barrel aberration of the wide-angle lens of the camera if the lens of the camera is the wide-angle lens; and alter a shape of the plurality of subregions in conformity with the predetermined pincushion aberration of the telephoto lens of the camera if the lens of the camera is the telephoto lens.
16 . A camera system comprising: a camera comprising a lens; and a brightness measurement apparatus configured to: set, on an imaging region of the camera, a brightness measurement region that has a center part and peripheral parts that surround the center part, the brightness measurement region comprising a plurality of subregions, the plurality of subregions including: central subregions located in the center part of the brightness measurement region; and peripheral subregions located in the peripheral parts of the brightness measurement region, a size of at least one of the central subregions being different from a size of at least one of the peripheral subregions; and measure, for each of the plurality of subregions of the brightness measurement region, a brightness of a corresponding one of the plurality of subregions of the brightness measurement region in accordance with a pixel value of at least one pixel of a frame image captured by the camera through the imaging region, the pixel value of the at least one pixel of the frame image being included in the corresponding one of the plurality of subregions.
17 . The camera system according to claim 16 , wherein: the brightness measurement apparatus is configured to set the brightness measurement region such that the sizes of the plurality of subregions substantially decrease toward an outer periphery of the imaging region.
18 . The camera system according to claim 16 , wherein: the lens has a predetermined aberration; and the brightness measurement apparatus is configured to alter a shape of the brightness measurement region in conformity with the predetermined aberration of the lens of the camera.
19 . The camera system according to claim 16 , wherein: each of the plurality of subregions comprises a plurality of cells; and the brightness measurement apparatus is configured to: exclude, from the plurality of cells of at least one selected subregion in the plurality of subregions, at least one cell; and measure, for the at least one selected subregion, the brightness of the at least one selected subregion in accordance with the pixel value of the at least one pixel of the frame image, the pixel value of the at least one pixel of the frame image being included in remaining cells of the at least one selected subregion.

Description

CROSS REFERENCE TO RELATED APPLICATION This application is based on and claims the benefit of priority from Japanese Patent Application No. 2023-003857 filed on Jan. 13, 2023, the disclosure of which is incorporated in its entirety herein by reference. TECHNICAL FIELD The present disclosure relates to brightness measurement apparatuses, brightness measurement methods, brightness measurement programs, and camera systems. BACKGROUND Technologies using a vehicular camera installed in a vehicle, include (i) display of camera's captured images, (ii) recognition of solid objects, such as other vehicles, and lane markers, and (iii) travel control based on the recognition results. These technologies require an increase in the visibility of the captured images. In order to increase the visibility of captured images, it is important to control exposure of a vehicular camera appropriately depending on the brightness of each captured image. For example, Japanese Patent Application Publication No. 2009-157085 discloses a technical concept that specifies a part of an image captured by a vehicular camera as a recognition region for recognizing a recognition target, and measures the brightness of the recognition region. Then, the inventive concept controls exposure of the vehicular camera in accordance with the brightness of the recognition region. Because the recognition region included in a captured image is used to measure the brightness thereof, the recognition region can be referred to as a brightness measurement region. SUMMARY Some vehicles may use a wide-angle camera equipped with a wide-angle lens, such as a fish-eye lens. The wide-angle camera used by a vehicle can capture, by one shot, a wide-angle view around the vehicle. The term “wide angle” in the present disclosure typically represents a wide angle of camera's view, which is substantially between 60° and 100°. The term “wide angle” in the present disclosure can include a super-wide angle of camera's view, which is substantially between 100° and 180° or is over 180°. The term “wide angle” in the present disclosure can also include a range from 50° to 60°. Image signal processors (ISP) are used to perform a sequence of various operations of image-signal processing on images captured by a vehicular camera, such as a wide-angel camera. Such an ISP typically sections the brightness measurement region into a predetermined number of subregions, and performs the sequence of various operations of the image-signal processing for each divided subregion of the brightness measurement region. An image captured by such a wide-angle camera may have a great degree of distortion, that is, a great degree of barrel distortion. Let us assume that the brightness measurement region of a captured image is divided equally into a predetermined number of subregions. In this assumption, the barrel distortion of the captured image may cause the center of the captured image to be larger than the peripheries of the captured image. The larger center of the captured image may result in real dimensions, such as real length and/or real size, in any subregion included in the center of the captured image being relatively smaller. Similarly, the smaller peripheries of the captured image may result in real dimensions in any subregion included in the peripheries of the captured image being relatively larger. The brightness distribution measured in the brightness measurement region in the captured image may therefore become different from the brightness distribution in a corresponding region in real space. Additionally, the distortion, such as the barrel distortion, in a captured image may result in a low degree of flexibility in specifying a brightness measurement region in the captured image. In view of the circumstances set forth above, an exemplary aspect of the present disclosure seeks to provide technologies, each of which is capable of specifying, in a captured image, a brightness measurement region whose brightness distribution matches a brightness distribution of a corresponding region in real space. Additionally, each of the technologies provided by the exemplary aspect of the present disclosure is capable of achieving a higher degree of flexibility in specifying a brightness measurement region in a captured image. A first exemplary measure of the present disclosure provides a brightness measurement apparatus. The brightness measurement apparatus includes a memory storing computer-program instructions, and a processor communicable with the memory and a camera. The processor is configured to execute the computer-program instructions to accordingly set, on an imaging region of the camera, a brightness measurement region that has a center part and peripheral parts that surround the center part. The brightness measurement region includes a plurality of subregions. The plurality of subregions includes central subregions located in the center part of the brightness measurement region, and peri