JP2018074421A - Imaging apparatus, control method therefor and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging apparatus capable of detecting a flash band even in a case where the quantity of light in a peripheral part of a screen is reduced, a control method therefor and a program.SOLUTION: A luminance level for each line of a CMOS sensor 102 that is controlled in accordance with a rolling shutter system, is detected. When a difference of the detected luminance level between a target frame and a frame adjacent thereto is calculated as a luminance difference, in a case where a line of which the luminance difference exceeds a threshold for flash band detection is continued, it is discriminated that a flash band is present in the target frame, and the flash band is corrected. The threshold for flash band detection is corrected based on a level of peripheral light quantity reduction for each line of an optical lens 101 that forms a subject image on an imaging device of the CMOS sensor 102, before the correction of the flash band.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an imaging apparatus, a control method thereof, and a program, and more particularly to an imaging apparatus that detects a flash band, a control method thereof, and a program.

  In an imaging apparatus using a CMOS sensor in which imaging elements are arranged in a two-dimensional manner and converts light incident through a lens into a video signal, the CMOS sensor is controlled using a rolling shutter system. Specifically, charge accumulation is started at a different timing for each line of the CMOS sensor, and control is performed to read an image signal for each line after a predetermined charge accumulation time has elapsed.

  This rolling shutter system has a feature that the time for reading out the image signal for each line is different, so if there is an illumination component such as a flash or strobe that has a very short emission time, for example, only the upper half of the screen is bright. A dark phenomenon occurs in the lower half. This is called a flash band.

  Regarding the detection of the flash band, according to the invention described in Patent Document 1, the brightness in the line direction of the screen is calculated, and when a region where the brightness difference between frames is higher than a predetermined threshold exists in a band shape, it is determined as a flash band. A method for performing correction is disclosed.

JP 2010-135922 A

  However, when the flash band is detected based on the luminance in the line direction of the screen as in the invention described in Patent Document 1, the amount of light at the peripheral portion of the screen decreases if the lens has a large peripheral light amount drop level. For this reason, there is a possibility that the flash band cannot be detected because the luminance level in the line direction decreases even at the top of the screen.

  Accordingly, the present invention is to provide an imaging apparatus capable of detecting a flash band even when the amount of light at the periphery of the screen is reduced, a control method therefor, and a program.

  An image pickup apparatus according to the present invention is an image pickup apparatus that includes a sensor in which image pickup elements are arranged in a two-dimensional manner, an optical lens that couples a subject image to the image pickup element, and a control unit that controls the sensor using a rolling shutter system. A luminance detection means for detecting a luminance level for each line of the sensor; a luminance difference calculating means for calculating a difference between the detected luminance levels between the target frame and a frame adjacent thereto as a luminance difference; and A flash band determining unit that determines that a flash band exists in the target frame when a line whose luminance difference exceeds a threshold value continues; and the flash band determining unit determines that the flash band exists when the flash band determining unit determines that the flash band exists. Flash band correcting means for correcting the band, and the optical lens for each line. The basis of the level of light falloff at edges, characterized in that it comprises a threshold value correction means for correcting the threshold value prior to determination by the flash band determination unit.

  According to the present invention, it is possible to detect a flash band even when the amount of light at the periphery of the screen drops.

It is a figure which shows the hardware constitutions of the imaging device of this invention. It is a figure for demonstrating the flash band determination method by CPU in FIG. It is a flowchart which shows the procedure of the detection control process of the flash band in the 1st Embodiment of this invention. It is a figure for demonstrating the correction method of the threshold value for flash band detection performed by step S103 of FIG. It is a flowchart which shows the procedure of the detection control process of the flash band in the 2nd Embodiment of this invention.

  Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.

<First Embodiment>
FIG. 1 is a diagram illustrating a hardware configuration of an imaging apparatus according to the present invention.

  In FIG. 1, an optical lens 101 has a focus mechanism for focusing, a diaphragm mechanism for adjusting the amount of light and depth of field, and a zoom mechanism for changing the focal length.

  The CMOS sensor 102 is a sensor composed of a plurality of image sensors arranged in a two-dimensional manner, and combines the subject image with each image sensor by the optical lens 101 and converts it into a video signal. The video signal output from the CMOS sensor 102 is temporarily recorded in a memory (not shown) and then input to the line direction luminance detection unit 103.

  The line direction luminance detecting unit 103 detects a luminance level horizontally integrated in the line direction (luminance detecting means).

  The CPU 107 controls the entire imaging apparatus.

  Further, the CPU 107 determines whether or not a flash band is generated (flash band determination) based on the luminance level detected by the line direction luminance detection unit 103. The CPU 107 corrects the threshold value for detecting the flash band by the amount of attenuation of the light amount due to the decrease in the peripheral light amount based on the information of the optical lens 101 by the method described later with reference to FIG. Thereafter, the corrected flash band detection threshold value is read from the memory, and the CPU 107 performs flash band determination.

  The video signal processing unit 104 performs flash band correction when it is determined by the CPU 107 that the flash band has been generated. The video signal processing unit 104 further performs video signal correction processing, development processing, and the like. The data output from the video signal processing unit 104 is output to the display unit recording medium 105.

  The sensor control unit 106 controls the shutter speed, gain, and frame rate of the CMOS sensor 102 based on a signal from the CPU 107. In the present embodiment, the sensor control unit 106 starts charge accumulation at different timings for each line, and uses a rolling shutter method in which the video signal is read for each line after a predetermined charge accumulation time has elapsed. To control.

  Next, the flash band detection will be described in detail.

  FIG. 2 is a diagram for explaining a method of determining a flash band by the CPU 107.

  FIG. 2A shows the external flash generation timing and the image signal output at that time when the horizontal axis represents time and the vertical axis represents the number of lines in the vertical direction. FIG. 2B shows the detection result of inter-frame luminance difference, and shows a graph with the horizontal axis representing the number of vertical lines and the vertical axis representing the luminance difference for each frame.

  As shown in FIG. 2A, an external flash is generated during the charge accumulation period of the frames 3 and 4. The output image at this time has a flash band at the bottom of the screen in frame 3 and a flash band at the top of the screen in frame 4.

  In FIG. 2B, for each vertical line, the average luminance value in the horizontal direction of the target frame and the preceding and subsequent frames adjacent thereto is calculated, and the calculated average luminance value of the preceding and following frames and the luminance value of the target frame are calculated. The difference is calculated as a luminance difference (luminance difference calculating means). When the line where the calculated luminance difference exceeds the threshold Th continues, the CPU 107 determines that a flash band has occurred.

  However, in the flash band determination method of FIG. 2, when the luminance level of the flash band in the peripheral portion of the screen is lowered due to a decrease in the amount of peripheral light, even if a flash band is generated, the luminance difference becomes smaller than the threshold Th. There is a problem. In the present embodiment, such a problem is solved by performing the processing of FIG. 3 below.

  FIG. 3 is a flowchart showing a procedure of flash band detection control processing according to the first embodiment of the present invention. This process is executed by the CPU 107 developing a program held in a ROM (not shown).

  First, when the user selects the flash band correction mode (YES in step S100), the luminance level horizontally integrated in the line direction is detected (step S101).

  Next, it is determined whether the peripheral light amount drop correction is performed on the image data acquired in step S102. As a result of the determination, if the peripheral light amount drop correction is performed (YES in step S102), the corrected threshold value for detecting the flash band is acquired from the memory, and the process proceeds to step S104. On the other hand, if the peripheral light amount drop correction is not performed (NO in step S102), the process proceeds to step S103.

  In step S103, the threshold for flash band detection is corrected by the amount of attenuation of the light amount due to the decrease in the peripheral light amount based on the information from the optical lens 101 by the method described later in FIG. 4 (threshold correction means).

  In step S104, the luminance levels between frames are compared based on the luminance level detected in step S101 and the corrected threshold value for detecting the flash band. As a result of this comparison, if a flash band has occurred (YES in step S105), the process proceeds to step S106, and after performing flash band correction, the present process is terminated. On the other hand, if a flash band has not occurred (NO in step S105), the flash band correction is not performed and the present process is terminated.

  An example of a method for calculating the threshold value for detecting the flash band when the peripheral light amount drop occurs will be described with reference to FIG.

  FIG. 4 is a diagram for explaining the threshold correction method for flash band detection executed in step S103 of FIG.

  First, FIG. 4A is a diagram illustrating image data obtained using the optical lens 101 in which a peripheral light amount drop occurs. Here, a method for calculating the threshold value for detecting the flash band in the H (n) line of the image data will be described. a represents the image height from the center of the screen to the center of the H (n) line. b represents the image height from the center of the screen to the left end of the H (n) line.

  FIG. 4B is a diagram showing the level of decrease in peripheral light amount with respect to the image height in the H (n) line of the image data in FIG. In the case of the H (n) line, the amount of attenuation of the light amount due to the decrease in the peripheral light amount can be expressed by an integrated value C (n) of the light amount drop level from the image height a to the image height b. When the threshold for flash band detection when there is no decrease in the amount of peripheral light is Th, the threshold Th (n) for the H (n) line is calculated by the following equation (1).

Th (n) = Th / C (n) (1)
As described above, in the flash band determination, it is possible to improve the accuracy of flash band detection by correcting the flash band detection threshold using the peripheral light amount drop level.

<Second Embodiment>
In the first embodiment, the flash band detection area is set for all areas of the image data. However, if the amount of light loss around the lens is very large, the flash band may be erroneously detected even if the flash band detection threshold is corrected.

  Therefore, the second embodiment is characterized in that the flash band detection is not performed in the peripheral portion of the image data area when the peripheral light amount drop level is larger than a predetermined value.

  Control according to the second embodiment of the present invention will be described with reference to the flowchart of FIG.

  FIG. 5 is a flowchart showing the procedure of flash band detection control processing in the second embodiment of the present invention. Similar to FIG. 3, this processing is also executed by the CPU 107 developing a program held in a ROM (not shown).

  The basic process is the same as that of the first embodiment, but the processes in steps S204 and S205 are different. In step S204, it is determined whether the level of the peripheral light amount drop is larger than a predetermined value. If it is larger than the predetermined value, there is a possibility of erroneous detection of the flash band. Therefore, the area for detecting the flash band is set to an area where the peripheral light amount drop level is smaller than the predetermined value. Thereafter, processing is performed in the area set in step S205 until the determination of the flash band in step S207.

  As described above, the flash band erroneous detection can be further reduced by changing the flash band detection area according to the level of the peripheral light amount drop.

  In the first and second embodiments, the threshold value for flash band detection is corrected. However, the gain may be corrected based on the level of decrease in peripheral light amount without performing this correction (gain correction means). ). In addition, when the flash band correction mode is selected by the user, the user may be inquired about whether to correct the threshold for flash band detection or to correct the gain (inquiry means). For example, this inquiry may be displayed on a display unit (not shown) in the imaging apparatus of the present invention.

  Although the present invention has been described in detail based on preferred embodiments thereof, the present invention is not limited to these specific embodiments, and various forms within the scope of the present invention are also included in the present invention. included. A part of the above-described embodiments may be appropriately combined. Also, when a software program that realizes the functions of the above-described embodiments is supplied from a recording medium directly to a system or apparatus having a computer that can execute the program using wired / wireless communication, and the program is executed Are also included in the present invention. Accordingly, the program code itself supplied and installed in the computer in order to implement the functional processing of the present invention by the computer also realizes the present invention. That is, the computer program itself for realizing the functional processing of the present invention is also included in the present invention. In this case, the program may be in any form, such as an object code, a program executed by an interpreter, or script data supplied to the O step S as long as it has a program function. As a recording medium for supplying the program, for example, a magnetic recording medium such as a hard disk or a magnetic tape, an optical / magneto-optical storage medium, or a nonvolatile semiconductor memory may be used. As a program supply method, a computer program that forms the present invention is stored in a server on a computer network, and a connected client computer downloads and programs the computer program.

DESCRIPTION OF SYMBOLS 101 Optical lens 102 CMOS sensor 103 Line direction brightness | luminance detection part 104 Image | video signal processing part 105 Display part recording medium 106 Sensor control part 107 CPU

Claims (7)

In an imaging apparatus comprising: a sensor in which an imaging element is arranged in a two-dimensional manner; an optical lens that couples a subject image to the imaging element; and a control unit that controls the sensor by a rolling shutter system.
A luminance detecting means for detecting a luminance level for each line of the sensor;
A luminance difference calculating means for calculating a difference between the detected luminance levels between the target frame and a frame adjacent thereto as a luminance difference;
A flash band determination unit that determines that a flash band exists in the target frame when a line in which the calculated luminance difference exceeds a threshold continues;
A flash band correcting unit that corrects the flash band when the flash band determining unit determines that the flash band exists;
An image pickup apparatus comprising: a threshold correction unit that corrects the threshold before the determination by the flash band determination unit based on a level of decrease in peripheral light amount of the optical lens for each line.   The imaging apparatus according to claim 1, further comprising a second holding unit that holds the threshold value corrected by the threshold value correcting unit.   3. The imaging device according to claim 1, wherein the flash band is detected in an area where the peripheral light amount drop level is smaller than a predetermined value when the peripheral light amount drop level is larger than a predetermined value. Further comprising gain correction means for correcting the gain based on the level of the peripheral light amount drop,
The imaging apparatus according to claim 1, wherein when the gain correction unit is executed, the threshold correction unit does not correct the threshold value.   5. The imaging apparatus according to claim 4, further comprising inquiry means for inquiring a user whether to execute the threshold correction means or the gain correction means. In a control method of an image pickup apparatus, comprising: a sensor in which an image pickup element is arranged in a two-dimensional manner; an optical lens that couples a subject image to the image pickup element; and a control unit that controls the sensor in a rolling shutter system.
A luminance detection step for detecting a luminance level for each line of the sensor;
A luminance difference calculating step for calculating a difference in the detected luminance level between the target frame and a frame adjacent thereto as a luminance difference;
A flash band determination step for determining that a flash band exists in the target frame when a line in which the calculated luminance difference exceeds a threshold continues; and
A flash band correcting step for correcting the flash band when it is determined that the flash band is present in the flash band determining step;
And a threshold value correcting step for correcting the threshold value before the determination in the flash band determining step based on the level of decrease in peripheral light amount of the optical lens for each line.   A program for executing the control method according to claim 6.