JP2010187233A - Image capturing apparatus, method of controlling the same, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce worsening of noise by an increase in gain on a low luminance side in expansion of a dynamic range. <P>SOLUTION: While a live image is continuously displayed before photography, the overexposure amount of the live image is calculated by each frame or frequency of once in a plurality of frames, calculation and update of the overexposure amount are repeated until turning on (half-depression of a release button) of a SW1 is detected. When the turning on of the SW1 is detected, an amount of dynamic range expansion is calculated on the basis of the latest overexposure amount, and after holding the amount of dynamic range expansion as a temporary value, whether ISO sensitivity is higher than a predetermined value is determined, and when it is determined that the sensitivity is high ISO sensitivity, the amount of the dynamic range expansion is restricted. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an imaging apparatus using a solid-state imaging device, a control method thereof, and a program.

  In conventional image processing, as a method for suppressing low luminance noise, there is a method for changing a gamma curve when performing gamma conversion. Japanese Patent Application Laid-Open No. H10-228561 is a method for making a black sink with a gamma curve in order to suppress low luminance noise. Japanese Patent Laid-Open No. 2004-228561 is a method in which blackening is performed with a gamma curve in order to suppress low luminance noise at high ISO.

JP-A-1-292971 JP 2008-67071 A

  However, in the above prior art, the dynamic range is reduced in order to suppress low luminance noise by generating black sun.

  Conversely, with regard to the dynamic range expansion processing, the dynamic range is expanded at the expense of noise deterioration.

  Here, the dynamic range expansion method will be described. In the imaging apparatus, image processing is performed on the output of the solid-state imaging device that converts an optical image into an electrical signal, and digital conversion is performed to generate an output image. Then, the overexposure determination is performed from the digital signal processed output image to determine the dynamic range expansion amount.

  Specifically, as shown in FIG. 5, in the state where the live image is continuously displayed before shooting, the amount of overexposure of the live image is calculated at a frequency of once every frame or a plurality of frames (step S501). The latest whiteout amount is stored, and the calculation and update of the whiteout amount are repeated until SW1 is turned on (half-press of the release button) is detected (step S502). When the SW1 is turned on, the dynamic range expansion amount is determined based on the latest whiteout amount (step S503), and the exposure correction amount and gamma curve are determined (step S504). Furthermore, when SW2 is turned on (full release button is pressed) is detected (step S505), and when SW2 is not turned on, the process returns to the SW1 detection state (step S503). When the on state of SW2 is detected, shooting is performed according to the set exposure correction amount (step S506).

  Further, the operation of the dynamic range expansion process will be described with reference to FIG. In the gamma curves shown in FIGS. 6A and 6B, the curve indicated by the dotted line is the gamma curve S601 at the time of normal photographing, and the curve indicated by the solid line is the gamma curve S602 at the time of dynamic range expansion.

  FIG. 6A is a diagram for explaining the effect of dynamic range expansion. In FIG. 6A, first, the input luminance for gamma conversion, that is, the maximum value of the exposure level is halved from S603 to S604. By using this and the gamma curve S602 at the time of dynamic range expansion, the dynamic range of the output luminance can be expanded by the difference between the normal output luminance S605 and the output luminance S606 at the time of dynamic range expansion (S605-S606).

  FIG. 6B is a diagram for explaining the gain increase in the low luminance part, which is a harmful effect due to the expansion of the dynamic range. In FIG. 6B, the normal exposure brightness appropriate exposure level S607 is changed to the input brightness proper exposure level S608 during dynamic range expansion in order to make the appropriate exposure level before and after the gamma curve change the same. As a result, the output luminance S609 when the dynamic range is expanded is obtained from the appropriate exposure S608 when the dynamic range is expanded and the gamma curve S602 when the dynamic range is expanded. A gain increase amount (S609 / S610) at the same input level can be obtained by comparing with the output level S610 when the normal gamma is used.

  As described above, in the dynamic range expansion method, noise deterioration occurs due to an increase in gain on the low luminance side.

  The present invention has been made in view of the above situation, and an object thereof is to reduce noise deterioration when the dynamic range is expanded.

An imaging apparatus according to the present invention includes a solid-state imaging device that converts an optical image formed by an optical system into an electrical signal, and a control unit that expands a dynamic range, and the control unit has an ISO sensitivity higher than a predetermined value. In this case, the dynamic range expansion amount is limited when performing predetermined image correction processing.
An imaging apparatus control method according to the present invention is a control method for expanding a dynamic range of an imaging apparatus including a solid-state imaging element that converts an optical image formed by an optical system into an electrical signal, and the ISO sensitivity is a predetermined value. When it is higher or when a predetermined image correction process is performed, the dynamic range expansion amount is limited.
The program of the present invention is a program for expanding the dynamic range of an imaging apparatus including a solid-state imaging device that converts an optical image formed by an optical system into an electrical signal, and the ISO sensitivity is higher than a predetermined value. Alternatively, when a predetermined image correction process is performed, the computer is caused to execute a process of limiting the dynamic range expansion amount.

  According to the present invention, it is possible to reduce noise deterioration due to gain increase on the low luminance side when the dynamic range is expanded.

It is a figure which shows the structure of the imaging device which concerns on embodiment. It is a figure which shows the structure which concerns on the image processing of a digital signal processing part. It is a flowchart which shows the dynamic range expansion operation in embodiment. It is a characteristic view which shows the relationship between a luminance level and NR level. It is a flowchart which shows the conventional dynamic range expansion operation. It is a characteristic view which shows the gamma curve at the time of normal time, and the gamma curve at the time of dynamic range expansion.

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.
(First embodiment)
FIG. 1 shows a configuration of an imaging apparatus according to the present embodiment. Reference numeral 301 denotes an optical system that forms an image of incident light on a solid-state imaging device. An optical system control unit 302 controls exposure, zoom, focus, and the like of the optical system. A solid-state imaging element 303 converts an optical image formed by the optical system 301 into an electrical signal. Reference numeral 304 denotes an imaging system control unit for driving the solid-state imaging device 303.

  Reference numeral 305 denotes an analog signal processing unit that performs processing such as clamping and gaining on the output of the solid-state imaging device 303. Reference numeral 306 denotes an analog / digital (A / D) conversion unit that performs digital conversion on an analog signal. A digital signal processing unit 307 generates an output image from the A / D converted digital signal.

  Reference numeral 308 denotes an internal storage unit that temporarily stores image data when the digital signal processing unit 307 generates an output image. Reference numeral 309 denotes an interface (I / F) unit with an external storage device for finally storing the generated image data. Reference numeral 310 denotes an image display unit as an electronic viewfinder that displays a generated image. Reference numeral 311 denotes a D range determination unit that performs overextraction determination from an output image that has been subjected to digital signal processing, and determines a dynamic range expansion amount.

  FIG. 2 shows a configuration relating to image processing of the digital signal processing unit 307. An RGB signal that is a digital signal after A / D conversion is converted / separated into a luminance signal Y and a color difference signal CrCb. The luminance signal Y is output through a luminance NR (noise reduction) unit 401, an edge enhancement unit 402, and a luminance gradation (gamma) conversion unit 403. The color difference signal CrCb is output via the color NR unit 404, the color processing unit 405, and the color gradation conversion unit 406.

  Next, an operation flow of the imaging apparatus according to the present embodiment will be described with reference to FIG. The flowchart of FIG. 3 is executed by the D range determination unit 311 that determines the dynamic range expansion amount. In a state where the live image is continuously displayed before shooting, the overexposure amount of the live image is calculated at a frequency of once every frame or a plurality of frames (step S101). The latest overexposure amount is stored, and the calculation and update of the overexposure amount are repeated until SW1 is turned on (half-press of the release button) is detected (step S102).

  When the on state of SW1 is detected, the dynamic range expansion amount is obtained based on the latest whiteout amount and held as a temporary value (step S103). Here, an ISO sensitivity set separately as a user setting or photographing condition related to an increase in noise level is input (step S104), and whether or not the ISO sensitivity is high, that is, whether or not the ISO sensitivity is higher than a predetermined value. Is determined (step S105).

  If it is determined in step S105 that the ISO sensitivity is high, the dynamic range expansion amount is limited (suppressing the dynamic range expansion amount) (step S106), and the final value of the dynamic range expansion amount is determined (step S107). Specifically, the dynamic range expansion amount held as a temporary value is clipped so that a part of the dynamic range expansion amount is not used. In this case, a table is prepared in advance that associates shooting conditions such as exposure amount and brightness with information (for example, a threshold value) that determines a portion where the dynamic range expansion amount is not used, and uses the dynamic range expansion amount from the table. What is necessary is just to obtain the information which determines the part which is not.

  On the other hand, if it is determined in step S105 that the ISO sensitivity is not high, the dynamic range expansion amount held as the temporary value in step S103 is determined as it is as the final value (step S107).

  An exposure correction amount and a gamma curve are determined based on the dynamic range expansion amount determined in step S107 (step S108). Furthermore, when SW2 is turned on (full release button is pressed) is detected (step S109), and when SW2 is not turned on, the process returns to the SW1 detection state (step S102). When the on state of SW2 is detected, shooting is performed according to the set exposure correction amount (step S110).

  As described above, when the ISO sensitivity is high, by limiting the amount of dynamic range expansion, it is possible to reduce noise deterioration due to gain increase on the low luminance side during dynamic range expansion.

(Second Embodiment)
In the first embodiment, the dynamic range expansion amount is limited according to the determination result of whether or not the ISO sensitivity is high. However, the determination result of whether or not to perform predetermined image correction processing is used. The dynamic range expansion amount may be limited according to the above. For example, in step S104 in FIG. 1, the presence or absence of subtraction (black subtraction) of a light-shielded image that is effective for removing fixed pattern noise is determined. When black subtraction processing is performed, the dynamic range expansion amount is limited. Blackening (dark correction) is a process to reduce the influence of fixed pattern noise that occurs when exposure is performed for a long period of time. This is a process of subtracting from an image showing a subject.

(Third embodiment)
In the first embodiment, in step S106, the dynamic range expansion amount held as a temporary value is clipped so that a part thereof is not used. In the third embodiment, an example will be described in which a dynamic range expansion amount held as a temporary value is multiplied by a coefficient (<1) for limiting the dynamic range expansion amount. In this case as well, a table in which shooting conditions such as exposure amount and luminance are associated with a coefficient for limiting the dynamic range expansion amount is prepared in advance, and the coefficient may be obtained from the table.

(Fourth embodiment)
Next, as a fourth embodiment, an example of reducing noise deterioration due to gain increase on the low luminance side when the dynamic range is expanded by strongly setting the noise reduction level when expanding the dynamic range on the low luminance side will be described. To do.

  As described with reference to FIG. 6, when the normal photographing and the dynamic range expansion are compared, the gain increase is (S609 / S610) times at the brightness level of the appropriate exposure, and the noise increases particularly at low brightness. Here, noise is reduced by controlling the noise reduction (NR) level.

  As shown in FIG. 4, when the NR level S201 at the time of normal shooting is an NR level provided with an NR change point S203 in which the low luminance side is a stronger NR level than the high luminance side, the NR at the time of dynamic range expansion is shown. Level S202 is set as shown. In this case, the NR change point S204 is changed from the normal NR change point S203 to the higher brightness range when the luminance level (range) in which noise on the low luminance side increases due to the dynamic range expansion. Change to the NR change point.

  Further, as the noise level on the low luminance side increases due to the dynamic range expansion, the low luminance NR level S206 is changed from the normal low luminance NR level S205 to the low luminance NR level at the time of dynamic range expansion that further increases the NR. change. Here, the low luminance NR level may be changed by using the gain increase (S609 / S610) at the luminance level of the appropriate exposure described above.

  In addition, although described as NR level here, it may be applied to change of the base clip (coring) amount set at the time of edge enhancement.

  The object of the present invention can also be achieved by supplying a storage medium storing a program code of software for realizing the functions of the above-described embodiments to a system or apparatus. In this case, the computer (or CPU or MPU) of the system or apparatus reads and executes the program code stored in the storage medium.

  In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the program code itself and the storage medium storing the program code constitute the present invention.

  As a storage medium for supplying the program code, for example, a flexible disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.

  Further, the functions of the above-described embodiments are not limited to being realized by executing the program code read by the computer. For example, an OS (basic system or operating system) running on the computer performs part or all of the actual processing based on an instruction of the program code, and the functions of the above-described embodiments are realized by the processing. May be.

  Further, the program code read from the storage medium may be written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer. In this case, after being written in the memory, the CPU of the function expansion board or function expansion unit performs part or all of the actual processing based on the instruction of the program code, and the function of the above-described embodiment is performed by the processing. Is realized.

DESCRIPTION OF SYMBOLS 301 Optical system 302 Optical system control part 303 Solid-state image sensor 304 Imaging system control part 305 Analog signal processing part 306 Analog / digital (A / D) conversion part 307 Digital signal processing part 308 Internal memory | storage part 309 Interface (I / F) part 310 image display unit 311 D range determination unit 401 luminance NR (noise reduction) unit 402 edge enhancement unit 403 luminance gradation (gamma) conversion unit 404 color NR unit 405 color processing unit 406 color gradation conversion unit

Claims (7)

A solid-state imaging device that converts an optical image formed by the optical system into an electrical signal;
Control means for expanding the dynamic range,
The control device limits an amount of dynamic range expansion when the ISO sensitivity is higher than a predetermined value or when a predetermined image correction process is performed.   The control means obtains a dynamic range expansion amount, and does not use a part of the dynamic range expansion amount when the ISO sensitivity is higher than a predetermined value or when a predetermined image correction process is performed. The imaging apparatus according to 1.   The imaging apparatus according to claim 2, further comprising a table for obtaining information for determining an unused portion of the dynamic range expansion amount based on an imaging condition.   The control means obtains a dynamic range expansion amount, and multiplies the dynamic range expansion amount by a coefficient for limiting the dynamic range expansion amount when the ISO sensitivity is higher than a predetermined value or when a predetermined image correction process is performed. The imaging apparatus according to claim 1, wherein:   The imaging apparatus according to claim 4, further comprising a table for obtaining a coefficient for limiting the dynamic range expansion amount based on an imaging condition. A control method for expanding a dynamic range of an imaging apparatus including a solid-state imaging device that converts an optical image formed by an optical system into an electrical signal,
A method for controlling an imaging apparatus, wherein the amount of dynamic range expansion is limited when the ISO sensitivity is higher than a predetermined value or when a predetermined image correction process is performed. A program for expanding a dynamic range of an imaging apparatus including a solid-state imaging device that converts an optical image formed by an optical system into an electrical signal,
A program for causing a computer to execute a process of limiting a dynamic range expansion amount when the ISO sensitivity is higher than a predetermined value or when a predetermined image correction process is performed.

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