JP2007300320A - Imaging device and imaging method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform suitable white balance correction, even if the sensitivity is high. <P>SOLUTION: According to photographic conditions when a subject is photographed, the size to which a photographed image obtained by the photographing has been divided into a plurality blocks is changed, and it is determined whether each of the plurality of divided blocks is white; and pixel values of blocks determined as being white blocks are integrated, and a WB coefficient is calculated from the value of the integration result so as to perform white balance correction. Consequently, noise components generated, when the sensitivity is high, are smoothed and image quality is prevented from deteriorating during high-sensitivity photography. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an imaging apparatus, an imaging method, a program, and a recording medium, and more particularly to a technique suitable for use in white balance control at high sensitivity.

  In general, a signal output from an image sensor is digitized by AD conversion, and the digitized captured image is divided into a plurality of blocks as shown in FIG. The block signal is composed of color signals including R, G, and B, and the following formulas (1-1) and (1-2) are examples of color evaluation value calculation for the block.

  Next, when the color evaluation value (Cx [i], Cy [i]) is included in the preset white detection range, it is determined that the block is white. Then, the integral values SumR, SumG, and SumB of the color pixels that have entered the white detection range are calculated, and the white balance coefficients (WBCo_R, WBCo_G, WBCo_B) are calculated as in the following equations (2-1) to (2-3). ) Is calculated.

  By the way, digital cameras currently on the market have a mechanism that can be switched to a plurality of sensitivity settings such as ISO 100, 200, 400, 800, 1600 (see, for example, Patent Document 1). The larger these values are, the higher the sensitivity is, and the smaller the amount of light can be taken, and even the faster shutter speed can be taken with appropriate brightness. If the sensitivity is constant, the shutter speed will be automatically reduced when shooting in an environment where the brightness is insufficient, such as in a room or at night, but increasing the sensitivity will reduce the shutter speed. You will be able to speed up.

JP-A-8-220589

  However, as the sensitivity is increased, the image has a lot of noise components and has a harmful effect as an image, and high-sensitivity shooting has a trade-off relationship with image quality. Therefore, when the white balance correction at the time of high sensitivity is relatively high as in ISO 800 and 1600, there is a problem that a lot of noise is mixed in each pixel and appropriate white determination cannot be performed. For this reason, for example, when a white uniform surface is photographed, as shown in FIG. 3A, a stable integration result for each block is obtained at low sensitivity, as shown in FIG. 3B. There was a phenomenon in which the integration results varied as the sensitivity increased.

  An object of the present invention is to make it possible to perform appropriate white balance correction even at high sensitivity in view of the above-described problems.

  An imaging apparatus according to the present invention is an imaging apparatus that captures a subject and processes the obtained captured image, and divides the captured image acquired according to the capturing conditions when capturing the subject into a plurality of blocks. A block dividing unit; a first white balance correcting unit that determines whether the block divided by the block dividing unit is white, calculates a first white balance correction value, and performs white balance correction; The block dividing unit determines whether the block divided into a size different from the block used by the first white balance correcting unit is white, calculates a second white balance correction value, and calculates white And a second white balance correction means for performing balance correction.

  The imaging method of the present invention is an imaging method for capturing a subject and processing the obtained captured image, and divides the captured image acquired in accordance with the capturing conditions when capturing the subject into a plurality of blocks. A block dividing step; a first white balance correcting step of determining whether the block divided in the block dividing step is white and calculating a first white balance correction value to perform white balance correction; In the block dividing step, it is determined whether or not the block divided into a size different from the block used in the first white balance correcting step is white, and a second white balance correction value is calculated to obtain a white And a second white balance correction step for performing balance correction.

  The program of the present invention is a program for causing a computer to execute an imaging method for capturing a subject and processing the obtained captured image, and a plurality of captured images acquired according to the capturing conditions when capturing the subject. A block dividing step for dividing the block into blocks, and a first white for performing white balance correction by determining whether the block divided in the block dividing step is white and calculating a first white balance correction value In the balance correction step and the block division step, a second white balance correction value is determined by determining whether the block divided into a size different from the block used in the first white balance correction step is white. And a second white balance correction step for calculating white balance and performing white balance correction Characterized in that to execute.

  The recording medium of the present invention is characterized in that the program is recorded.

  According to the present invention, the captured image is divided into blocks of different sizes according to the sensitivity information at the time of shooting, and white balance correction is performed, so that the noise component can be smoothed. Thereby, appropriate white balance correction can be performed even at high sensitivity.

(First embodiment)
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram illustrating a configuration of an imaging apparatus according to the present embodiment. Hereinafter, the present embodiment will be described with reference to FIG.
In FIG. 1, reference numeral 101 denotes a solid-state imaging device made of a CCD, a CMOS, or the like, and its surface is covered with, for example, an RGB color filter such as a Bayer array so that color photography can be performed.

  The CPU 114 calculates the shutter speed and aperture value so that the entire image has a predetermined brightness, and calculates the driving amount of the focus lens so that the subject in the focusing area is focused. The exposure value (shutter speed, aperture value) calculated by the CPU 114 and the driving amount of the focus lens are sent to the control circuit 113 and controlled based on each value.

  A white balance (WB) control unit 103 calculates a WB correction value based on information from the image signal stored in the memory 102, and uses the calculated WB correction value to store the image signal stored in the memory 102. WB correction is performed on. The detailed configuration of the white balance (WB) control unit 103 and the method for calculating the WB correction value will be described later.

  Reference numeral 104 denotes a color matrix circuit that converts the color difference signals RY and BY by applying a color gain so that the image signal WB corrected by the WB control unit 103 is reproduced with an optimum color. Reference numeral 105 denotes a low-pass filter (LPF) circuit that limits the bands of the color difference signals RY and BY, and reference numeral 106 denotes CSUP that suppresses a false color signal in a saturated portion of the image signal band-limited by the LPF circuit 105. (Chroma Suppress) circuit.

  On the other hand, the WB corrected image signal by the WB control unit 103 is also output to the luminance signal (Y) generation circuit 111 to generate the luminance signal Y, and the edge enhancement circuit 112 performs edge processing on the generated luminance signal Y. Emphasis processing is performed.

  The color difference signals RY and BY output from the CSUP circuit 106 and the luminance signal Y output from the edge emphasis circuit 112 are converted into RGB signals by the RGB conversion circuit 107, and the gamma correction circuit 108 converts the gradation signals Y to B and Y. Tone correction is applied. Thereafter, it is converted into a YUV signal by the color luminance conversion circuit 109, further compressed by the JPEG compression circuit 110, and recorded as an image signal on an external recording medium or an internal recording medium.

Next, a method for calculating the WB correction value at the time of low sensitivity will be described with reference to the flowchart of FIG.
First, the image signal stored in the memory 102 is read, and the screen based on the image signal is divided into arbitrary m blocks as shown in FIG. 2 (step S101). Then, for each block (1 to m), the pixel values are added and averaged to the respective colors to calculate the color average values (R [i], G [i], B [i],). Color evaluation values (Cx [i], Cy [i]) are calculated using the equations (1-1) and (1-2) (step S102).

  Next, it is determined whether or not the color evaluation value (Cx [i], Cy [i]) of the i-th block calculated in step S102 is included in the preset white detection range 301 shown in FIG. (Step S103).

  The white detection range 301 is obtained by photographing white under different light sources in advance and plotting the calculated color evaluation values. In FIG. 3A, the negative direction of the x coordinate (Cx) is a color evaluation value when white of a high color temperature subject is photographed, and the positive direction is a color evaluation value when white of a low color temperature subject is photographed. Further, the y coordinate (Cy) means the degree of the green component of the light source, and indicates a light source in which the G component increases as it goes in the negative direction, that is, a fluorescent lamp.

  As a result of the determination in step S103, when the calculated color evaluation values (Cx [i], Cy [i]) are included in the white detection range 301 (the determination result in step S103 is YES), the block is white. Judge that there is. In this case, the process proceeds to step S104, and the color average values (R [i], G [i], B [i]) of the block are integrated. If the result of determination in step S103 is not included in the white detection range 301 (the result of determination in step S103 is NO), the process proceeds to step S105 without integration. The processing of step S103 and step S104 can be expressed by the following equations (3-1) to (3-3).

  Here, in the expressions (3-1) to (3-3), when the color evaluation value (Cx [i], Cy [i]) is included in the white detection range 301, Sw [i] is included in 1. If not, Sw [i] is set to 0. Thereby, the process of whether or not to add the color evaluation values (R [i], G [i], B [i]) is substantially performed based on the determination in step S103.

  In step S105, it is determined whether or not the processing has been performed for all blocks. As a result of the determination, if there is an unprocessed block, the process returns to step S102 and the processes of steps S102 to S105 described above are repeated. If the processes of all the blocks have been completed, the process proceeds to step S106.

  In step S106, from the integrated values (SumR, SumG, SumB) of the obtained color evaluation values, using the following equations (4-1) to (4-3), the first WB correction value (WBCol_R, WBCol_G, WBCol_B) is calculated.

Next, a method for calculating the WB correction value at the time of high sensitivity will be described.
FIG. 6 is a flowchart illustrating an example of a procedure for calculating a WB correction value at the time of high sensitivity in the present embodiment. The processes in steps S202 to S206 shown in FIG. 6 are the same as the processes in steps S102 to S106 shown in FIG.

  In this embodiment, the difference from the WB correction value calculation method shown in FIG. 5 described above is that when dividing into arbitrary blocks in step S201, the block unit area is compared with the division processing performed in step S101. To make it different. That is, as shown in FIG. 4, the block unit area is narrowed when the sensitivity is low, and wide when the sensitivity is relatively high. That is, when the sensitivity is high, the noise component is smoothed by increasing the block unit area. In this way, when the sensitivity is high, the block unit area is increased and white determination is performed, so that when the sensitivity is high, a large amount of noise is mixed in each pixel, preventing the inconvenience that proper white determination cannot be performed. I am doing so. This makes it possible to obtain a stable integration result of pixel values for each block at low sensitivity, while suppressing the phenomenon that the integration result of pixel values varies when the sensitivity is increased, and the WB due to mixing of noise components is suppressed. A big malfunction can be suppressed.

(Second Embodiment)
In the first embodiment described above, when the sensitivity is relatively low, the WB correction value calculation process (first WB correction value calculation process) at the time of low sensitivity shown in FIG. 5 is performed, and the sensitivity is relatively high. At that time, a desired WB correction can be obtained by performing a WB correction value calculation process (second WB correction value calculation process) at the time of high sensitivity shown in FIG. In the present embodiment, how these two processes are used together and how they are switched will be described.

FIG. 7 is a flowchart illustrating an example of a procedure for calculating a WB correction value in the present embodiment.
First, the first WB correction value calculated by the procedure shown in the flowchart of FIG. 5 and the second WB correction value calculated by the procedure shown in the flowchart of FIG. 6 are input (step S301).

  Next, Mix processing by weighted addition is performed based on sensitivity information at the time of shooting (step S302). In this Mix process, when the sensitivity is lower than the first sensitivity (Sv_1) as shown in FIG. 8, only the first WB correction value is used, and the sensitivity is higher than the first sensitivity (Sv_1). In this case, the first WB correction value and the second WB correction value are mixed according to the sensitivity. When the sensitivity is higher than the second sensitivity (Sv_2), the block usage rate at the time of high sensitivity is maximized. That is, when the sensitivity is higher than the second sensitivity (Sv_2), the ratio of mixing the second WB correction value is maximized.

  Next, when the Mix processing by weighted addition is performed, the weighted and added WB correction value (third WB correction value) is calculated, and the processing ends.

  Here, the Mix Ratio Max shown in FIG. 8 may be changed from 0% to 100% depending on the characteristics of the image sensor. That is, when the Mix Ratio Max is 100%, if the sensitivity is higher than the sensitivity (Sv_2), only the second WB correction value is used, and when the Mix Ratio Max is less than 100%, the sensitivity is high. In addition, the first WB correction value is mixed not a little.

  Further, the Mix processing here may be applied to only one of the Cx direction (color temperature direction) and the Cy direction (green direction). By realizing the processing as described above, appropriate white determination can be performed even at high sensitivity, and a desired WB correction value can be obtained.

(Third embodiment)
In the second embodiment, when the third WB correction value is calculated, weighted addition is performed based on the sensitivity information at the time of shooting, but in this embodiment, the sensitivity information at the time of shooting and the white ratio that occupies the screen are used. A method of performing weighted addition will be described. A difference from the second embodiment is a method of calculating a third WB correction value, and the first WB correction value calculation process and the second WB correction value calculation process are the same, and thus the description thereof is omitted.

FIG. 9 is a diagram illustrating a change in the weighted addition method based on the sensitivity information and the white ratio (white detection rate) at the time of shooting in the present embodiment.
WS1 to WS3 are thresholds for the white detection rate. When the white detection rate is equal to or greater than the third threshold WS3, only the first WB correction value is used. If it is less than the third threshold WS3, the first WB correction value and the second WB correction value are weighted and added. That is, when the sensitivity is low, the white detection rate threshold is set to the first threshold WS1 (set low), and when high sensitivity is set, the white detection rate threshold is set to the third threshold WS3 (set high). Thereby, a large block is actively used at the time of high sensitivity, and a desired WB correction coefficient can be obtained.

The processing procedure of this embodiment will be described with reference to the flowchart shown in FIG.
First, the sensitivity information is acquired from the shooting conditions, and the white detection rate threshold WS at that time is acquired (step S401). Next, the first WB correction value is calculated, and the white detection rate at that time is acquired (step S402).

  Next, the white detection rate threshold value WS obtained in step S401 is compared with the white detection rate obtained in step S402 (step S403). As a result of this comparison, if the white detection rate is less than the white detection rate threshold WS, a second WB correction value is calculated (step S404). Then, a weighted addition of the first WB correction value calculated in step S402 and the second WB correction value calculated in step S404 is performed to calculate a third WB correction value (step S405), which is the final WB. A correction coefficient is set (step S406).

  For example, in FIG. 9, when the white detection rate threshold value (third threshold value WS3) at the time of high sensitivity is 80% and the white detection rate is 20% as a result of the first WB correction value calculation process, The WB correction value of 1 and the second WB correction value are weighted and added 1: 3.

  On the other hand, if the white detection rate is equal to or greater than the white detection rate threshold WS as a result of the comparison in step S403, the first WB correction value obtained in step S407 is used as the final WB correction coefficient as the final result (step S406). ).

  As described above, in this embodiment, the white detection rate threshold is set low when the sensitivity is low, and the white detection rate threshold is set high when the sensitivity is high. As a result, a large block is actively used at high sensitivity, and a desired WB correction value can be obtained.

(Other embodiments according to the present invention)
Each means constituting the image pickup apparatus and each step of the image pickup method in the embodiment of the present invention described above can be realized by operating a program stored in a RAM or ROM of a computer. This program and a computer-readable recording medium recording the program are included in the present invention.

  Further, the present invention can be implemented as, for example, a system, apparatus, method, program, or recording medium. Specifically, the present invention may be applied to a system including a plurality of devices. The present invention may be applied to an apparatus composed of a single device.

  In the present invention, a software program (in the embodiment, a program corresponding to the flowcharts shown in FIGS. 5 to 7 and 10) for realizing the functions of the above-described embodiments is directly or remotely supplied to the system or apparatus. This includes the case where the system or the computer of the apparatus is also achieved by reading and executing the supplied program code.

  Accordingly, since the functions of the present invention are implemented by computer, the program code installed in the computer also implements the present invention. In other words, the present invention includes a computer program itself for realizing the functional processing of the present invention.

  In that case, as long as it has the function of a program, it may be in the form of object code, a program executed by an interpreter, script data supplied to the OS, and the like.

  Examples of the recording medium for supplying the program include a floppy (registered trademark) disk, a hard disk, an optical disk, and a magneto-optical disk. Further, there are MO, CD-ROM, CD-R, CD-RW, magnetic tape, nonvolatile memory card, ROM, DVD (DVD-ROM, DVD-R) and the like.

  As another program supply method, there is a method of connecting to a homepage on the Internet using a browser of a client computer. The computer program itself of the present invention or a compressed file including an automatic installation function can be downloaded from the homepage by downloading it to a recording medium such as a hard disk.

  It can also be realized by dividing the program code constituting the program of the present invention into a plurality of files and downloading each file from a different homepage. That is, a WWW server that allows a plurality of users to download a program file for realizing the functional processing of the present invention on a computer is also included in the present invention.

  As another method, the program of the present invention is encrypted, stored in a recording medium such as a CD-ROM, distributed to users, and encrypted from a homepage via the Internet to users who have cleared predetermined conditions. Download the key information to be solved. It is also possible to execute the encrypted program by using the key information and install the program on a computer.

  Further, the functions of the above-described embodiments are realized by the computer executing the read program. Furthermore, based on the instructions of the program, an OS or the like running on the computer performs part or all of the actual processing, and the functions of the above-described embodiments can be realized by the processing.

  As another method, the program read from the recording medium is first written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer. Then, based on the instructions of the program, the CPU or the like provided in the function expansion board or function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are also realized by the processing.

It is a block diagram which shows the function structural example of the imaging device in the 1st Embodiment of this invention. It is a figure which shows an example of the state by which the picked-up image was divided | segmented into the some block. It is a figure which shows the example of the white determination result at the time of low sensitivity and the time of high sensitivity. It is a figure which shows the example which made the block unit variable at the time of low sensitivity and high sensitivity in the 1st Embodiment of this invention. 5 is a flowchart illustrating an example of processing for calculating a WB correction value at low sensitivity in the first embodiment of the present invention. 5 is a flowchart illustrating an example of processing for calculating a WB correction value at high sensitivity in the first embodiment of the present invention. 14 is a flowchart illustrating an example of processing for calculating a third WB correction value in the second embodiment of the present invention. It is a figure which shows an example of the weighted addition process at the time of high sensitivity in the 2nd Embodiment of this invention. It is a figure which shows an example of the weighted addition process in the 3rd Embodiment of this invention. It is a flowchart which shows an example of the process which calculates the 3rd WB correction value in the 3rd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Image pick-up element 102 Memory 103 WB control part 104 Color conversion MTX circuit 105 LPF circuit 106 CSUP circuit 107 RGB conversion circuit 108 Gamma correction circuit 109 Color luminance conversion circuit 110 JPEG compression circuit 111 Y generation circuit 112 Edge emphasis circuit 113 Control circuit 114 CPU

Claims (10)

An imaging device for photographing a subject and processing an obtained image signal,
Block dividing means for dividing a captured image acquired in accordance with imaging conditions when imaging the subject into a plurality of blocks;
First white balance correction means for determining whether or not the block divided by the block dividing means is white, calculating a first white balance correction value, and performing white balance correction;
The block dividing unit determines whether the block divided into a size different from the block used by the first white balance correcting unit is white, calculates a second white balance correction value, and calculates white An image pickup apparatus comprising: a second white balance correction unit that performs balance correction.   Third white balance correction means for performing white balance correction by weighting and adding the white balance correction values calculated by the first white balance correction means and the second white balance correction means in accordance with the shooting conditions; The imaging apparatus according to claim 1, further comprising:   The shooting condition is sensitivity information, and the third white balance correction unit weights and adds the first white balance correction value and the second white balance correction value based on the sensitivity information. The imaging apparatus according to claim 2, characterized in that:   The third white balance correction means calculates a white balance correction coefficient by weighted addition of the first white balance correction value and the second white balance correction value, and a white ratio in the entire photographed image. The image pickup apparatus according to claim 2, wherein white balance correction is performed by weighted addition based on the image. An imaging method for photographing a subject and processing an obtained image signal,
A block dividing step of dividing a captured image acquired according to shooting conditions when shooting the subject into a plurality of blocks;
A first white balance correction step of determining whether the block divided in the block division step is white, calculating a first white balance correction value, and performing white balance correction;
In the block dividing step, it is determined whether or not the block divided into a size different from the block used in the first white balance correcting step is white, and a second white balance correction value is calculated to obtain a white And a second white balance correction step for performing balance correction.   A third white balance correction step of performing white balance correction by weighting and adding the white balance correction values calculated in the first white balance correction step and the second white balance correction step according to the photographing condition; 6. The imaging method according to claim 5, further comprising:   The shooting condition is sensitivity information, and the third white balance correction step weights and adds the first white balance correction value and the second white balance correction value based on the sensitivity information. The imaging method according to claim 6.   In the third white balance correction step, a white balance correction coefficient is calculated by weighted addition of the first white balance correction value and the second white balance correction value, and a white ratio in the entire photographed image is calculated. The imaging method according to claim 6, wherein white balance correction is performed by weighted addition based on the image. A program for causing a computer to execute an imaging method for capturing a subject and processing the obtained captured image,
A block dividing step of dividing a captured image acquired according to shooting conditions when shooting the subject into a plurality of blocks;
A first white balance correction step of determining whether the block divided in the block division step is white, calculating a first white balance correction value, and performing white balance correction;
In the block dividing step, it is determined whether or not the block divided into a size different from the block used in the first white balance correcting step is white, and a second white balance correction value is calculated to obtain a white A program for causing a computer to execute an imaging method including a second white balance correction step for performing balance correction.   A computer-readable recording medium on which the program according to claim 9 is recorded.

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