JP2007053480A - Signal processing method of imaging apparatus, and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a signal processing method of an imaging apparatus, and the imaging apparatus capable of carrying out signal processing according to the transfer efficiency of a CCD imaging element and obtaining an image with a desired image quality. <P>SOLUTION: The signal processing method of the imaging apparatus includes: steps S20, S22 of capturing CCD RAW data from the CCD imaging element by photographing an object; and a step S24 of applying various signal processing such as color correction, white balance adjustment, gamma correction, and simultaneous processing to the CCD RAW data by a digital signal processing section, capturing the transfer efficiency of the CCD imaging element calculated in advance and carrying out the signal processing according to the transfer efficiency by a linear matrix circuit of the digital signal processing section so as to obtain the image with the desired image quality (color reproducibility and resolution). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a signal processing method for an image pickup apparatus and an image pickup apparatus, and more particularly to a technique for improving a problem caused by poor transfer efficiency of a CCD (Charge Coupled Device) image pickup element.

  Conventionally, imaging devices such as an electronic camera, a digital camera, and a camera-equipped mobile phone using a CCD imaging device have been developed. When imaging is performed using such an imaging device, signal charges are accumulated in each pixel of the CCD imaging device according to the exposure time. The signal charge accumulated in each pixel is transferred from the vertical transfer path to the horizontal transfer path and output to the image processing circuit.

  The signal charges accumulated in each pixel are sequentially transferred through potential wells formed in each transfer element of each transfer path. At this time, the signal charge is not completely transferred to the next transfer element but remains slightly. The ratio of the charge transferred to the next well to the charge in the original well is called transfer efficiency. When this transfer efficiency decreases, crosstalk between adjacent pixels increases and image degradation (color reproduction) Various problems such as deterioration of resolution and resolution).

On the other hand, for example, Patent Document 1 discloses a signal correction device for a distance measuring CCD that corrects distortion of an image signal due to a transfer error and eliminates a distance measurement failure. In Patent Document 2, the total of the vertical transfer remaining amount of each image sensor arranged in the TDI stage direction is obtained in advance from the vertical transfer efficiency of the TDI (Time Delay Integration) image sensor, and the sample is imaged by the TDI image sensor. An image processing method is disclosed in which the sum of the previously obtained amount of vertical transfer remaining is subtracted from the output of a TDI image sensor, and image processing is performed using the subtracted output.
JP 7-146139 A JP 2004-295709 A

  However, the invention described in Patent Document 1 uses a distance measuring CCD, and deterioration in transfer efficiency of the distance measuring CCD affects distance measurement. Therefore, the distance measurement result is obtained based on the transfer efficiency. It corrects the image and does not improve image degradation.

  The invention described in Patent Document 1 is limited to the TDI image sensor, and solves the problem of transfer efficiency deterioration particularly in the vertical transfer path. In order to solve this problem, the vertical transfer remaining amount is reduced. Calculated and subtracted from sensor output. That is, the invention described in Patent Document 1 obtains a high-contrast image with no remaining vertical transfer, and does not obtain an image with high color reproducibility that is not affected by fluctuations in transfer efficiency. An enormous amount of computation is required to calculate the remaining amount.

  The present invention has been made in view of such circumstances, and is capable of performing signal processing according to the transfer efficiency of an image sensor and obtaining an image with a desired image quality. The purpose is to provide.

  In order to achieve the above object, a signal processing method of an imaging apparatus according to claim 1 includes a step of acquiring an image signal from an imaging device, a transfer efficiency calculating step of calculating a transfer efficiency of the imaging device, and the calculated And processing the acquired image signal based on transfer efficiency.

  That is, when the transfer efficiency of the image sensor is poor, there are problems such as deterioration in color reproducibility and resolution as compared with the case where the transfer efficiency is good. However, the invention according to claim 1 calculates the transfer efficiency of the image sensor. Then, an image with a desired image quality is obtained by processing the image signal based on the calculated transfer efficiency.

  According to a second aspect of the present invention, in the signal processing method for the image pickup apparatus according to the first aspect, the method includes a step of storing and holding the transfer efficiency calculated in advance, and the transfer efficiency stored and held is a value of the acquired image signal. It is characterized by being read and used during processing.

  According to a third aspect of the present invention, in the signal processing method of the imaging device according to the first aspect, the transfer efficiency calculation step is based on a pixel signal in the effective pixel region and a pixel signal in the optical black region of the image sensor. It is characterized by calculating.

  According to a fourth aspect of the present invention, in the signal processing method of the imaging device, the transfer efficiency calculation step is performed before and after the vertical boundary between the effective pixel region and the optical black region of the imaging element is sandwiched ( The calculation is based on the signal of each pixel in the horizontal direction) or the signals of a plurality of pixels in the vertical direction of each preceding and following pixel. When signals of a plurality of pixels on the effective pixel area side and signals of a plurality of pixels on the optical black area side are used, the signals of the respective pixels are averaged to calculate highly accurate transfer efficiency. it can.

  5. The signal processing method for an imaging apparatus according to claim 1, further comprising a step of selecting a transfer efficiency calculation mode, wherein the transfer efficiency calculation step includes: The transfer efficiency is calculated based on an image signal acquired from the image sensor at the time of selected shooting. Thereby, the shooting for calculating the transfer efficiency is distinguished from the normal shooting, and the transfer efficiency can be calculated at an arbitrary time. At the time of shooting for calculating the transfer efficiency, it is preferable to shoot a monochrome chart under predetermined shooting conditions.

  The signal processing method of the imaging apparatus according to any one of claims 1 to 4, further comprising a step of detecting a change in shooting setting conditions related to transfer efficiency, wherein the transfer efficiency calculating step includes: When a change in the shooting setting condition is detected, an image signal is captured from the image sensor before actual shooting, and transfer efficiency is calculated based on the image signal. That is, the transfer efficiency changes depending on various conditions such as camera sensitivity, CCD drive frequency, and temperature of the image pickup device. When a change in the conditions is detected, the transfer efficiency is newly calculated.

  The signal processing method of the imaging apparatus according to any one of claims 1 to 4, further comprising a step of measuring a time passage, wherein the transfer efficiency calculating step includes a step in which the measured time passage is predetermined. When the threshold value is exceeded, an image signal is taken from the image sensor before the actual photographing, and the transfer efficiency is calculated based on the image signal. That is, the transfer efficiency changes depending on various conditions as described above, and in particular, the temperature of the image sensor rises with the passage of time. Therefore, when the passage of time exceeds a predetermined threshold, the transfer efficiency is newly calculated. .

  The signal processing method for an image pickup apparatus according to any one of claims 1 to 4, further comprising a step of performing automatic focus adjustment based on an image signal from the image pickup device before actual photographing, The transfer efficiency calculating step is characterized in that the transfer efficiency is calculated based on an image signal acquired from the image sensor before completion of focus adjustment at the time of automatic focus adjustment. Thereby, the transfer efficiency suitable for the photographing can be calculated for each main photographing. Note that by using an image signal (an image signal that is out of focus) acquired before the completion of focus adjustment at the time of automatic focus adjustment, it is possible to equalize the image signal in a predetermined region used for calculating transfer efficiency. it can.

  An image pickup apparatus according to claim 9 includes a shooting optical system, an image pickup element on which a subject image is formed by the shooting optical system, an image acquisition unit that acquires an image signal from the image pickup element, and transfer efficiency of the image pickup element. Transfer efficiency acquisition means for acquiring the image signal, and signal processing means for processing the acquired image signal based on the transfer efficiency acquired by the transfer efficiency acquisition means.

  According to a tenth aspect of the present invention, in the imaging apparatus according to the ninth aspect, the image pickup apparatus further includes a storage unit that stores and holds the transfer efficiency calculated in advance, and the transfer efficiency acquisition unit reads the transfer efficiency from the storage unit. It is a feature.

  11. The imaging apparatus according to claim 9 or 10, further comprising transfer efficiency calculation means for calculating transfer efficiency of the image sensor, wherein the transfer efficiency acquisition means transfers data from the transfer efficiency calculation means. It is characterized by obtaining efficiency.

  As described in claim 12, in the imaging device according to claim 11, the transfer efficiency calculation means calculates based on a pixel signal of an effective pixel region and a pixel signal of an optical black region of the image sensor. It is characterized by.

  According to a thirteenth aspect of the present invention, in the imaging device according to the eleventh aspect, the transfer efficiency calculation unit is arranged before and after (horizontal direction) across a vertical boundary between the effective pixel region and the optical black region of the imaging element. The measurement is based on a signal of each pixel or a signal of a plurality of pixels in the vertical direction of each pixel before and after.

  14. The imaging apparatus according to claim 11, further comprising mode selection means for selecting a transfer efficiency calculation mode, wherein the transfer efficiency calculation means is selected by the mode selection means. The transfer efficiency is calculated based on the image signal acquired from the image sensor at the time of shooting in the transfer efficiency calculation mode.

  The imaging apparatus according to any one of claims 11 to 13, further comprising detection means for detecting a change in shooting setting condition related to transfer efficiency, wherein the transfer efficiency calculation means includes the detection When a change in the shooting setting condition is detected by the means, an image signal is captured from the image sensor before actual shooting, and transfer efficiency is calculated based on the image signal.

  The imaging apparatus according to any one of claims 11 to 13, further comprising means for measuring a time passage, wherein the transfer efficiency calculating means has the measured time passage equal to or greater than a predetermined threshold value. In this case, an image signal is taken from the image sensor before the actual photographing, and the transfer efficiency is calculated based on the image signal.

  The image pickup apparatus according to any one of claims 11 to 13, further comprising an automatic focus adjustment unit that performs automatic focus adjustment based on an image signal from the image pickup device before the main photographing. The transfer efficiency calculating means calculates transfer efficiency based on an image signal acquired from the image sensor before completion of focus adjustment during the automatic focus adjustment.

  18. The imaging apparatus according to claim 9, wherein the signal processing unit includes a matrix circuit that performs color correction, and is based on the transfer efficiency acquired by the transfer efficiency acquisition unit. The matrix coefficient of the matrix circuit is controlled.

  According to a nineteenth aspect of the present invention, in the imaging device according to the eighteenth aspect, the matrix circuit is at least one of a linear matrix circuit and a color difference matrix circuit.

  According to the present invention, the transfer efficiency of an image sensor can be calculated, and signal processing corresponding to the transfer efficiency can be performed on an image signal acquired from the image sensor. This makes it possible to obtain an image with a desired image quality regardless of the transfer efficiency.

  Hereinafter, preferred embodiments of a signal processing method for an imaging apparatus and an imaging apparatus according to the present invention will be described with reference to the accompanying drawings.

  In the following description, an imaging device (digital camera) will be described as an example. However, the present invention can also be applied to a mobile phone, a personal digital assistant (PDA), a PC camera, and the like equipped with the imaging device.

[First Embodiment]
FIG. 1 is a block diagram showing a first embodiment of an imaging apparatus according to the present invention.

  An imaging apparatus 1-1 (denoted as camera 1-1 in the following description) shown in FIG. 1 is a digital camera having a function of recording and reproducing still images and moving images, and the operation of the entire camera is a central processing unit. (CPU) 10 performs overall control. The CPU 10 functions as a control means for controlling the camera system according to a predetermined program, and performs various calculations such as automatic exposure (AE) calculation, automatic focus adjustment (AF) calculation, and white balance (WB) adjustment calculation. Functions as a means.

  A RAM (Random Access Memory) 16 and a ROM (Read Only Memory) 18 are connected to the CPU 10 via a bus 12 and a memory interface 14. The RAM 16 is used as a program development area and a calculation work area for the CPU 10, and is also used as a temporary storage area for image data. The ROM 18 stores programs executed by the CPU 10, various data necessary for control, various constants / information related to camera operations, and the like.

  The imaging unit 20 includes an optical unit 22 including a photographing lens and a diaphragm, a CCD imaging device 24 (hereinafter simply referred to as “CCD”), and the like. In the optical unit 22, a focus lens, a diaphragm, and the like are driven via the motor driving unit 32 in accordance with an AF command or AE command from the CPU 10.

  As shown in FIG. 2, the CCD 24 is a CCD type two-dimensional imaging device (image sensor) in which a large number of light receiving elements (photodiodes) 24A are arranged in a horizontal array (row direction) and a vertical direction (column direction) with a constant array period. ). The illustrated configuration is a pixel array called a honeycomb array, in which the center points of the geometric shape of the light receiving element 24A are arranged so as to be shifted by half the pixel pitch (1/2 pitch) every other row direction and column direction. It has become.

  Each light receiving element 24A has an octagonal light receiving surface, and RGB primary color filters are arranged corresponding to each light receiving element 24A. As shown in FIG. 2, the GGGG... Row is arranged in the next stage of the RBRB... Row in the horizontal direction, and the BRBR. In the column direction, the RBRB... Row, the GGGG... Row, and the BRBR.

  A vertical transfer path (VCCD) 24V is formed on the right side (or left side) of each light receiving element 24A. The vertical transfer path 24V extends in the vertical direction by meandering in a zigzag manner in the vicinity of each column of the light receiving elements 24A and avoiding the light receiving elements 24A. Although not shown, transfer electrodes necessary for four-phase driving (φ1, φ2, φ3, φ4) are arranged on the vertical transfer path 24V. The transfer electrode is provided so as to meander in the vicinity of each row of the light receiving elements 16A and extend in the horizontal direction in FIG. 2 while avoiding the opening of the light receiving elements 24A.

  The signal charges generated by photoelectric conversion in each light receiving element 24A are read out to the vertical transfer path 16V adjacent to the right side (or left side) of the light receiving element 24A and transferred downward (V direction) in FIG. 2 according to the transfer pulse. Is done.

  In FIG. 2, a horizontal transfer path (HCCD) 24H for transferring the signal charge transferred from the vertical transfer path 24V in the horizontal direction is provided at the lower end of the vertical transfer path 24V (the most downstream side of the vertical transfer path 24V). .

  The horizontal transfer path 24H is composed of a transfer CCD of two-phase or four-phase drive, and the final stage (the leftmost stage in FIG. 2) of the horizontal transfer path 24H is connected to the output unit 25. The output unit 25 includes an output amplifier, performs charge detection of the input signal charge, and outputs it as a signal voltage to the output terminal 25A. In this way, the signal generated by each light receiving element 24A is output as a dot-sequential signal sequence. The signal output from the output terminal 25A is a signal string RGBGRGBG.

  Returning to FIG. 1, the CCD 24 has an electronic shutter function for controlling the charge accumulation time (shutter speed) of each light receiving element. The CPU 10 controls the charge accumulation time in the CCD 24 via the timing generator 34.

  The CCD signals sequentially read from the CCD 24 are added to the analog signal processing unit 26. The analog signal processing unit 26 includes a CDS circuit, an analog amplifier, and the like. The CDS circuit performs correlated double sampling processing on the input CCD signal, and the analog amplifier outputs from the CDS circuit by a photographing sensitivity setting gain applied from the CPU 10. The CCD signal to be amplified is amplified.

  The CCD signal analog-processed by the analog signal processing unit 26 is added to an A / D converter 28, where it is converted into digital color image data (dot sequential R, G, B signals) for each pixel. .

  The R, G, and B signals are temporarily stored in the RAM 16 via the digital signal processing unit 30. The R, G, and B signals are input to the digital signal processing unit 30, where required signal processing is performed. The details of the image processing in the digital signal processing unit 30 will be described later.

  The operation unit 36 of the camera 1-1 includes a shutter button, a mode switching lever for switching between a shooting mode and a playback mode, a mode dial for selecting a shooting mode (auto shooting mode, manual shooting mode, continuous shooting mode, etc.), and a display. Desired buttons such as a menu button for displaying a menu screen on the display unit (LCD) 40, a multi-function cross key for selecting a desired item from the menu screen, an OK button for confirming selection and execution of processing, and a selection item A BACK button or the like for inputting a command for deleting the target, canceling the instruction content, or returning to the previous operation state is included. An output signal from the operation unit 36 is input to the CPU 10 via the bus 32, and the CPU 10 performs appropriate processing such as shooting and reproduction based on the input signal from the operation unit 36.

  The camera 1-1 includes a flash device 42 for irradiating a subject with flash light. The flash device 42 receives power from the charging unit 4 in response to a light emission command from the CPU 10 and irradiates the flash light.

  The image data (luminance signal Y, color difference signals Cr, Cb) processed by the digital signal processing unit 30 is given to the compression / decompression processing circuit 46, where it is compressed according to a predetermined compression format (for example, JPEG method). . The compressed image data is recorded on the memory card 50 via the external memory interface 48.

  The LCD 40 displays a video (through movie image) during image preparation by an image signal applied via the LCD interface 38, and also displays an image recorded on the memory card 50 in the playback mode.

  FIG. 3 is a block diagram showing a detailed circuit configuration of the digital signal processing unit 30 shown in FIG.

  As described above, the R, G, and B signals temporarily stored in the RAM 16 are added to the offset processing circuit 30A of the digital signal processing unit 30 in the order of R, G, and B dots. The R, G, and B signals are subjected to offset processing in the offset processing circuit 30A. The R, G, B signals (CCD RAW data) output from the offset processing circuit 30A are output to the linear matrix circuit 30B, where color tone correction processing for correcting the spectral characteristics of the CCD 24 and color correction processing according to the present invention are performed. Done.

  That is, the linear matrix circuit 30B performs matrix calculation from the input R, G, B signals and the color correction matrix coefficients (A11, A12,..., A33) of 3 rows × 3 columns, and the color corrected R , G, B signals are calculated.

  The details of the 3 × 3 color correction matrix coefficients (A11, A12,..., A33) used for the matrix calculation will be described later.

  The R, G, B signals output from the linear matrix circuit 30B are output to the white balance (WB) adjustment circuit 30C. The WB adjustment circuit 30C performs white balance adjustment by applying a WB gain for white balance adjustment for each of the R, G, and B signals. The R, G, and B signals output from the WB adjustment circuit 30C are output to the gamma correction circuit 30D, where gamma correction for performing gradation correction such as halftone is performed. The gamma corrected R, G, B signals are output to the synchronization processing circuit 30E.

  The synchronization processing circuit 30E performs a process of converting the R, G, B signals into simultaneous equations by interpolating the spatial deviation of the R, G, B signals associated with the CCD color filter array of the single CCD 24. The converted R, G, B signals are output to the RGB / YC conversion circuit 30F.

  The RGB / YC conversion circuit 30F converts the R, G, and B signals into a luminance signal Y and color difference signals Cr and Cb, outputs the luminance signal Y to the contour correction circuit 30G, and outputs the color difference signals Cr and Cb to the color difference matrix circuit 30H. Output to. The contour correction circuit 30G performs processing to emphasize the contour portion (the portion where the luminance change is large) of the luminance signal Y.

  The color difference matrix circuit 30H performs a matrix operation on the color correction matrix coefficients of 2 rows × 2 columns and the input color difference signals Cr and Cb, and performs color correction to realize good color reproducibility.

  The luminance signal Y subjected to the contour correction and the color difference signals Cr and Cb subjected to the color difference matrix conversion are temporarily stored in the RAM 16 and then given to the compression / decompression processing circuit 46, where they are compressed according to the JPEG method. The The compressed image data is recorded on the memory card 50 via the external memory interface 48.

  Next, the transfer efficiency of the horizontal transfer path 24H of the CCD 24 will be described.

  The signal charges of each line of the CCD 24 sent from the vertical transfer path 24V of the CCD 24 to the horizontal transfer path 24H are sequentially transferred in the horizontal direction through the potential well formed in the horizontal transfer path 24H. At this time, the signal charge is not completely transferred to the next transfer element but remains slightly. The ratio of the charge transferred to the next well with respect to the charge in the original well is called transfer efficiency. Further, the transfer efficiency varies depending on the amount of charge (signal amount) in the original well.

  FIG. 4 is a graph showing transfer efficiency characteristics showing an example of the remaining transfer amount with respect to the signal amount. In FIG. 4, assuming that the signal amount in the original well is S0 and the remaining transfer amount after transfer of this signal amount S0 is f (S0), the transfer efficiency can be expressed by the following equation.

[Equation 1]
Transfer efficiency = (1−f (S0) / S0) × 100 (%)
As is apparent from the graph of FIG. 4, the transfer efficiency decreases when the signal amount S0 is small. Also, the transfer efficiency decreases when the CCD driving frequency is high and the CCD temperature is low.

  Since the transfer efficiency varies depending on the CCD, for example, the transfer efficiency is appropriately measured before shipment, or measured by the transfer efficiency calculation function of the camera 1-1 and stored in the ROM 18 or a flash ROM (not shown).

  Returning to FIG. 1, the CCD transfer efficiency detector 52 reads the transfer efficiency of the CCD 24 from the ROM 18.

  The digital signal processing unit 30 performs signal processing based on the transfer efficiency acquired from the CCD transfer efficiency detection unit 52. As the signal processing, for example, the signal processing is performed so as to suppress image quality deterioration that occurs when the transfer efficiency is lower than the standard transfer efficiency (when the transfer efficiency is good).

  That is, in the horizontal transfer path 24H of the CCD 24, signal charges are transferred to GRGBGRGB, so if the transfer efficiency decreases, the color mixture between G and R, G and B increases, and the color reproducibility and resolution deteriorate. .

  In this embodiment, the image quality deterioration is suppressed by changing the color correction matrix coefficients of 3 rows × 3 columns used in the linear matrix circuit 30B (FIG. 3) of the digital signal processing unit 30.

  For example, as shown in FIG. 5A, when the transfer efficiency is good, the color correction matrix coefficients (A11, A12,..., A33) are used, and when the transfer efficiency is bad, the color correction matrix coefficients (B11) are used. , B12,..., B33).

  Further, correction amounts a and c are obtained by the following equations, assuming that the correction amounts for the color correction matrix coefficients (A11, A12,..., A33) are a and c and the transfer efficiency is x (%).

[Equation 2]
a = αx + β
c = γx + λ
However, α, β, γ, λ: coefficients (may be calculated experimentally)
Then, as shown in FIG. 5B, the color correction matrix coefficients (after change) corrected by the correction amounts a and c are used.

  Although the equations for obtaining the correction amounts a and c are linear equations, they may be polynomial equations or exponential logarithmic approximation equations.

  FIG. 6 shows a basic processing flow for storing and holding in order to use transfer efficiency in the signal processing.

  As shown in the figure, R, G, B CCD RAW data is input from the CCD 24 (step S10). Based on the input CCD RAW data, the transfer efficiency is calculated (step S12), and the calculated transfer efficiency is written in the ROM 18 or a memory such as a flash ROM (not shown) (step S14).

  FIG. 7 is a diagram illustrating a processing flow for performing signal processing according to transfer efficiency on a captured image.

  As shown in the figure, the subject of the general scene is photographed (step S20), and R, G, B CCD RAW data is acquired from the CCD 24 (step S22).

  The digital signal processing unit 30 performs various types of signal processing as described with reference to FIG. 3, but reads the transfer efficiency stored in the memory and performs signal processing according to the transfer efficiency (step S24). That is, the linear matrix circuit 30B of the digital signal processing unit 30 changes the color correction matrix coefficient according to the transfer efficiency as shown in FIG. 5, and performs signal processing using the changed color correction matrix coefficient.

  Thereby, even if the transfer efficiency is lowered, it is possible to output a processed image in which deterioration in image quality such as color reproducibility and resolution is suppressed (step S26).

  In this embodiment, the color correction matrix coefficient of the linear matrix circuit 30B is changed according to the transfer efficiency. However, the present invention is not limited to this, and the 22 rows × 2 columns color correction matrix of the color difference matrix circuit 30H is used. The coefficients may be changed, or the color correction matrix coefficients of both matrix circuits may be changed.

[Second Embodiment]
FIG. 8 is a block diagram showing a second embodiment of the imaging apparatus according to the present invention. It should be noted that portions common to the first embodiment of the imaging apparatus shown in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

  The camera 1-2 of the second embodiment shown in FIG. 8 selects the CCD transfer efficiency calculation unit 54 and the transfer efficiency calculation mode in the camera as compared with the camera 1-1 of the first embodiment. Is different in that it further includes mode selection means (not shown).

  The mode dial for selecting the shooting mode may function as a means for selecting the transfer efficiency calculation mode, or the transfer efficiency calculation mode may be selected on the menu screen.

  When the transfer efficiency calculation mode is selected by the mode selection unit, the camera 1-2 performs a processing operation for calculating the transfer efficiency.

  That is, when the subject (for example, a single color chart) is photographed by the camera 1-2 in a state where the transfer efficiency calculation mode is selected, the CCD transfer efficiency calculation unit 54 calculates the pixels in the effective pixel area of the CCD 24 obtained at the time of the photographing. The transfer efficiency is calculated based on the CCD RAW data and the CCD RAW data of the pixels in the optical black (OB) area.

  FIG. 9 is a diagram schematically showing a charge transfer path in the CCD 24. As shown in FIG. 9, the light incident through the optical unit 22 forms an image, and the effective pixel region 24A used for capturing the image and the light shielded around the effective pixel region not used for capturing the image. It is divided into an OB area 24B.

  The charges accumulated in each pixel of the CCD 24 in the transfer efficiency calculation mode are vertically transferred through one vertical pixel through the vertical transfer path 24V and then horizontally transferred through the horizontal transfer path 24H. By repeating this for the number of pixels in the vertical direction, the charges of all the pixels of the CCD 24 are read out.

  The CCD transfer efficiency calculation unit 54 has one pixel (one pixel 27A on the effective pixel region side, one pixel 27A on the effective pixel region side, one on the OB region side) in the boundary region where the effective pixel region 24A changes to the OB region 24B. CCDRAW data for one pixel 27B) is acquired. Here, the CCD RAW data of one pixel 27B on the OB area side corresponds to the transfer remaining amount of the CCD RAW data of one pixel 27A on the effective pixel area side.

  Accordingly, the CCD transfer efficiency calculation unit 54 substitutes the CCD RAW data of the one pixel 27A on the effective pixel region side as S0 and the CCD RAW data of the one pixel 27B on the OB region side as f (S0) in the above-described equation (1). To calculate the transfer efficiency. Note that by using the average value of CCD RAW data of a plurality of pixels in the vertical direction of each pixel, it is possible to calculate an accurate transfer efficiency with little influence of noise or the like.

  The CCD transfer efficiency detection unit 52 acquires the transfer efficiency calculated by the CCD transfer efficiency calculation unit 54 in the transfer efficiency calculation mode from the CCD transfer efficiency calculation unit 54.

  Thereafter, when the general shooting mode is switched from the transfer efficiency calculation mode to the normal shooting mode, the digital signal processing unit 30 acquires the transfer efficiency from the CCD transfer efficiency detection unit 52 as shown in FIG. Then, signal processing according to the transfer efficiency is performed.

[First Embodiment of Transfer Efficiency Calculation Method]
FIG. 10 is a flowchart showing a first embodiment of a transfer efficiency calculation method in the camera 1-2.

  As described above, when the transfer efficiency calculation mode is selected by the mode selection unit, the following processing for calculating transfer efficiency is started.

  That is, in the transfer efficiency calculation mode, for example, a monochrome chart is photographed (step S30), and CCD RAW data of all pixels is acquired from the CCD 24 (step S32). The CCD transfer efficiency calculation unit 54 calculates the CCD RAW data of the one pixel 27A on the effective pixel region side and the CCD RAW data of the one pixel 27B on the OB region side as described in FIG. Capture (steps S34 and S36), and transfer efficiency is calculated based on the CCD RAW data (step S38).

  The calculated transfer efficiency is acquired through the CCD transfer efficiency detection unit 52 for use in signal processing during the main photographing (step S40).

[Third Embodiment]
FIG. 11 is a block diagram showing a third embodiment of the imaging apparatus according to the present invention. Note that portions common to those of the second embodiment of the imaging apparatus illustrated in FIG. 8 are denoted by the same reference numerals, and detailed description thereof is omitted.

  The camera 1-3 according to the third embodiment illustrated in FIG. 11 is further provided with a camera setting detection unit 56 and a temperature detection unit 58 as compared with the camera 1-2 according to the second embodiment. Is different.

  For example, the camera setting detection unit 56 detects camera sensitivity, CCD drive frequency, WB gain, and the like, and the temperature detection unit 58 detects the temperature of the CCD 24. If the temperature of the CCD 24 cannot be directly detected, the temperature detector 58 may detect the temperature inside the camera housing and detect this as a temperature corresponding to the temperature of the CCD 24.

  As is apparent from the graph of FIG. 4, the transfer efficiency decreases when the amount of signal S0 to be transferred is small. Also, the transfer efficiency decreases when the CCD drive frequency is high or when the CCD temperature is low.

  Therefore, when the camera sensitivity is high, since the amount of signal transferred by the CCD 24 is smaller than when the camera sensitivity is low, transfer efficiency is lowered. Similarly, in a captured image under a light source such as a tungsten light bulb, the WB gain for the B signal is much larger than the WB gain for the R signal, and the transfer efficiency is lowered.

  The CCD transfer efficiency calculation unit 54 of the camera 1-3 calculates the transfer efficiency when the shooting setting conditions obtained from the camera setting detection unit 56 and the temperature detection unit 58 are changed from the previous transfer efficiency calculation conditions. A method for calculating the transfer efficiency in this case will be described later.

  The CCD transfer efficiency detection unit 52 acquires the transfer efficiency calculated by the CCD transfer efficiency calculation unit 54 when the shooting setting condition is changed from the CCD transfer efficiency calculation unit 54, and the digital signal processing unit 30 receives the CCD transfer efficiency detection unit 52. The transfer efficiency is obtained from the signal, and signal processing corresponding to the transfer efficiency is performed.

[Second Embodiment of Transfer Efficiency Calculation Method]
FIG. 12 is a flowchart showing a second embodiment of the transfer efficiency calculation method in the camera 1-3. In addition, the same step number is attached | subjected to the part which is common in the flowchart shown in FIG. 10, The detailed description is abbreviate | omitted.

  The shutter button of the operation unit 36 is composed of a two-stroke switch composed of so-called “half-press” and “full-press”. By half-pressing the shutter button, AE (Automatic Exposure), AF (Auto) Focus: Autofocus) is activated, and when it is fully pressed, the image is recorded and recorded.

  In FIG. 12, when the shutter button is half-pressed (step S50), CCD RAW data is acquired from the CCD 24 for AE and AF (step S52). Subsequently, it is determined whether or not the shooting setting conditions obtained from the camera setting detection unit 56 and the temperature detection unit 58 have been changed (step S52). The change in camera sensitivity or the like may be determined based on the setting contents when the camera sensitivity is set in advance by manual operation, or automatically at the time of actual shooting based on the CCD RAW data acquired in step S52. The determination may be made based on the camera sensitivity that is set automatically.

  If it is determined that the shooting setting condition has been changed, the transfer efficiency is calculated in steps S32 to S40 as described with reference to FIG. 10, and then the process shifts to the main shooting when the shutter button is fully pressed (step S56). ).

  On the other hand, if it is determined that the shooting setting condition has not been changed, the transfer efficiency calculated last time can be used, so step S32 to step S40 are omitted (jumped), and the process proceeds to step S56.

  As described above, when the shooting setting condition that causes the transfer efficiency to change is changed, the transfer efficiency is newly calculated prior to the actual shooting.

[Fourth Embodiment]
FIG. 13 is a block diagram showing a fourth embodiment of the imaging apparatus according to the present invention. Note that portions common to those of the second embodiment of the imaging apparatus illustrated in FIG. 8 are denoted by the same reference numerals, and detailed description thereof is omitted.

  A camera 1-4 according to the fourth embodiment shown in FIG. 13 is different from the camera 1-2 according to the second embodiment in that it further includes a time detection unit 60.

  The time detection unit 60 detects the passage of time from the time when the latest transfer efficiency is calculated. The temperature of the CCD 24 varies with time, and the transfer efficiency also varies with this.

  The CCD transfer efficiency calculation unit 54 of the camera 1-3 increases the transfer efficiency when the elapsed time obtained from the time detection unit 60 is equal to or greater than a predetermined threshold value X (a predetermined time when the transfer efficiency varies with time). calculate. A method for calculating the transfer efficiency in this case will be described later.

  The CCD transfer efficiency detection unit 52 acquires the transfer efficiency calculated by the CCD transfer efficiency calculation unit 54 from the CCD transfer efficiency calculation unit 54 every predetermined time, and the digital signal processing unit 30 receives the CCD transfer efficiency detection unit. The transfer efficiency is acquired from 52, and signal processing corresponding to the transfer efficiency is performed.

[Third Embodiment of Transfer Efficiency Calculation Method]
FIG. 14 is a flowchart showing a third embodiment of the transfer efficiency calculation method in the camera 1-4. Note that the same step numbers are assigned to portions common to the flowchart shown in FIG. 12, and detailed description thereof is omitted.

  In FIG. 14, when the shutter button is pressed halfway and CCD RAW data is acquired from the CCD 24 for AE and AF (steps S50 and S52), the time transfer unit 60 calculates the latest transfer efficiency. And whether or not the elapsed time is equal to or greater than a threshold value X is determined (step S60).

  If it is determined that the elapsed time is equal to or greater than the threshold value X, the transfer efficiency is calculated in steps S32 to S40 as described with reference to FIG. Step S56).

  On the other hand, if it is determined that the elapsed time is less than the threshold value X, the previously calculated transfer efficiency can be used, so step S32 to step S40 are omitted (jumped) and the process proceeds to step S56.

  As described above, when the elapsed time that causes the change in transfer efficiency is equal to or greater than the threshold value X, the transfer efficiency is newly calculated prior to the actual photographing.

[Fifth Embodiment]
FIG. 15 is a block diagram showing a fifth embodiment of the imaging apparatus according to the present invention. Note that portions common to those of the second embodiment of the imaging apparatus illustrated in FIG. 8 are denoted by the same reference numerals, and detailed description thereof is omitted.

  A camera 1-5 of the fifth embodiment shown in FIG. 15 is different from the camera 1-2 of the second embodiment in that an AF evaluation unit 62 is further provided.

  Although the camera 1-5 has an AF device, the AF evaluation unit 62 calculates an evaluation value of AF included in the AF device.

  Here, an AF apparatus used for the camera 1-5 will be described.

  This AF apparatus automatically adjusts the lens position of the focus lens (contrast AF) so that the contrast of the subject is maximized, and starts contrast AF when the shutter button is half-pressed.

  That is, when the shutter button is half-pressed, AF search is performed. In the AF search, as shown in FIG. 16, the focus lens is sequentially moved over the focus adjustment range from the near (Near) to infinity (Inf), and the evaluation value is calculated every time the focus lens moves by a predetermined amount.

  The AF evaluation unit 62 takes in a G signal from the AF area (for example, the central region) of the CCD 24, extracts a high frequency component from the G signal through a high-pass filter (HPF), and evaluates by integrating the high frequency component. Calculate the value.

  The CPU 10 obtains the lens position of the focus lens at which the evaluation value reaches the peak (maximum) based on the evaluation value captured during the AF search, and moves the focus lens to this lens position (focusing operation) to perform automatic focus adjustment. Do.

  The CCD transfer efficiency calculation unit 54 of the camera 1-5 calculates transfer efficiency during the AF search. A method for calculating the transfer efficiency in this case will be described later.

  The CCD transfer efficiency detection unit 52 acquires the transfer efficiency calculated by the CCD transfer efficiency calculation unit 54 during the AF search from the CCD transfer efficiency calculation unit 54, and the digital signal processing unit 30 receives the transfer efficiency from the CCD transfer efficiency detection unit 52. And performs signal processing according to the transfer efficiency.

[Fourth Embodiment of Transfer Efficiency Calculation Method]
FIG. 17 is a flowchart showing a fourth embodiment of the transfer efficiency calculation method in the camera 1-5. The parts common to the flowchart shown in FIG. 14 are denoted by the same step numbers, and detailed description thereof is omitted.

  In FIG. 17, when the shutter button is half-pressed (step S50), the AF search is performed as described above. When it is detected that the evaluation value calculated during the AF search is other than the peak value ( In step S70, CCD RAW data is acquired from the CCD 24 (step S72). During the AF search, CCD RAW data is acquired from the AF area of the CCD 24. In step S72, CCD RAW data of all pixels of the CCD 24 is acquired.

  Subsequently, it is determined whether or not the pixel value in the vertical direction of one pixel 27A on the effective pixel region side of the CCD 24 shown in FIG. 9 is a substantially uniform value (step S74). That is, when the evaluation value calculated during the AF search is other than the peak value, the image is out of focus, and particularly at a position greatly deviated from the peak as indicated by the arrow in FIG. 16, the pixel value in the vertical direction of one pixel 27A. Becomes substantially uniform.

  Only when the pixel values in the vertical direction of one pixel 27A are substantially uniform, the CCD RAW data for calculating the transfer efficiency is taken in and the transfer efficiency is calculated and acquired (steps S32 to S40).

  In this embodiment, the color correction matrix coefficients of the linear matrix circuit 30C and / or the color difference matrix circuit 30H are changed according to the transfer efficiency. However, the present invention is not limited to this correction, or is used in combination with this correction. Various signal processes such as a process of changing the frequency band of the low-pass filter (LPF) and a process of changing the contour emphasis of the contour correction circuit 30G may be performed.

FIG. 1 is a block diagram showing a first embodiment of an imaging apparatus according to the present invention. FIG. 2 is a diagram illustrating a configuration example of a CCD image sensor. FIG. 3 is a block diagram showing a detailed circuit configuration of the digital signal processing unit shown in FIG. FIG. 4 is a graph showing transfer efficiency characteristics of the CCD image sensor. FIG. 5 is a diagram showing an example of changing the color correction matrix coefficient in the linear matrix circuit. FIG. 6 is a diagram showing a basic processing flow for storing and holding the transfer efficiency for use in signal processing. FIG. 7 is a diagram illustrating a processing flow for performing signal processing according to transfer efficiency on a captured image. FIG. 8 is a block diagram showing a second embodiment of the imaging apparatus according to the present invention. FIG. 9 is a diagram schematically showing a charge transfer path in the CCD. FIG. 10 is a flowchart showing the first embodiment of the transfer efficiency calculation method in the imaging apparatus according to the present invention. FIG. 11 is a block diagram showing a third embodiment of the imaging apparatus according to the present invention. FIG. 12 is a flowchart showing a second embodiment of the transfer efficiency calculation method in the imaging apparatus according to the present invention. FIG. 13 is a block diagram showing a fourth embodiment of the imaging apparatus according to the present invention. FIG. 14 is a flowchart showing a third embodiment of the transfer efficiency calculation method in the imaging apparatus according to the present invention. FIG. 15 is a block diagram showing a fifth embodiment of the imaging apparatus according to the present invention. FIG. 16 is a graph showing an example of the AF evaluation characteristic of the AF evaluation value at the AF search position. FIG. 17 is a flowchart showing a fourth embodiment of the transfer efficiency calculation method in the imaging apparatus according to the present invention.

Explanation of symbols

  1-1 to 1-5: Imaging device (camera), 10: Central processing unit (CPU), 16: RAM, 18 ... ROM, 20 ... Imaging unit, 22 ... Optical unit, 24 ... CCD image sensor, 24V ... Vertical Transfer path, 24H ... Horizontal transfer path, 26 ... Analog signal processing section, 30 ... Digital signal processing section, 30A ... Offset processing circuit, 30B ... Linear matrix circuit, 30C ... White balance adjustment circuit, 30D ... Gamma correction circuit, 30E ... Synchronization processing circuit, 30F ... RGB / YC conversion circuit, 30G ... contour correction circuit, 30H ... color difference matrix circuit, 36 ... operation unit, 40 ... display unit (LCD), 50 ... memory card, 52 ... CCD transfer efficiency detection unit 54 ... CCD transfer efficiency calculation unit, 56 ... Camera setting detection unit, 58 ... Temperature detection unit, 60 ... Time detection unit, 62 ... AF evaluation unit

Claims (19)

Obtaining an image signal from the image sensor;
A transfer efficiency calculating step for calculating the transfer efficiency of the image sensor;
Processing the acquired image signal based on the calculated transfer efficiency;
A signal processing method for an imaging apparatus.   The imaging according to claim 1, further comprising a step of storing and storing a previously calculated transfer efficiency, wherein the stored transfer efficiency is read and used when the acquired image signal is processed. Device signal processing method.   The signal processing method of the imaging apparatus according to claim 1, wherein the transfer efficiency calculation step calculates the transfer efficiency based on a pixel signal of an effective pixel region of the image sensor and a pixel signal of an optical black region.   The transfer efficiency calculating step includes a signal for each pixel in the front and rear (horizontal direction) across the vertical boundary between the effective pixel region and the optical black region of the image sensor, or a plurality of signals in the vertical direction for each front and rear pixel. The signal processing method of the imaging apparatus according to claim 1, wherein the calculation is performed based on a signal of the pixel.   Including a step of selecting a transfer efficiency calculation mode, wherein the transfer efficiency calculation step calculates the transfer efficiency based on an image signal acquired from the image sensor at the time of shooting in which the transfer efficiency calculation mode is selected. The signal processing method of the imaging device according to claim 1.   Detecting a change in shooting setting condition related to transfer efficiency, and when the change in shooting setting condition is detected, the transfer efficiency calculating step captures an image signal from the image sensor before the main shooting, 5. The signal processing method for an imaging apparatus according to claim 1, wherein transfer efficiency is calculated based on an image signal.   Measuring the passage of time, wherein the transfer efficiency calculating step captures an image signal from the image sensor before the main photographing when the measured passage of time becomes a predetermined threshold or more, and transfers efficiency based on the image signal. 5. The signal processing method of the imaging apparatus according to claim 1, wherein:   The method includes a step of performing automatic focus adjustment based on an image signal from the image sensor before the main photographing, and the transfer efficiency calculating step is performed on the image signal acquired from the image sensor before completion of focus adjustment at the time of the automatic focus adjustment. 5. The signal processing method for an image pickup apparatus according to claim 1, wherein the transfer efficiency is calculated based on the transfer efficiency. Photographic optics,
An image sensor on which a subject image is formed by the photographing optical system;
Image acquisition means for acquiring an image signal from the image sensor;
Transfer efficiency acquisition means for acquiring the transfer efficiency of the image sensor;
Signal processing means for processing the acquired image signal based on the transfer efficiency acquired by the transfer efficiency acquisition means;
An imaging apparatus comprising:   The imaging apparatus according to claim 9, further comprising a storage unit that stores and holds a transfer efficiency calculated in advance, wherein the transfer efficiency acquisition unit reads the transfer efficiency from the storage unit.   The imaging apparatus according to claim 9, further comprising a transfer efficiency calculation unit that calculates a transfer efficiency of the image sensor, wherein the transfer efficiency acquisition unit acquires the transfer efficiency from the transfer efficiency calculation unit. .   The image pickup apparatus according to claim 11, wherein the transfer efficiency calculation unit calculates the transfer signal based on a pixel signal in an effective pixel region of the image pickup device and a pixel signal in an optical black region.   The transfer efficiency calculation means includes a signal for each pixel in the front and rear (horizontal direction) across the vertical boundary between the effective pixel area and the optical black area of the image sensor, or a plurality of signals in the vertical direction for each front and rear pixel. The imaging apparatus according to claim 11, wherein measurement is performed based on a signal of the pixel.   The apparatus further comprises mode selection means for selecting a transfer efficiency calculation mode, wherein the transfer efficiency calculation means is based on an image signal acquired from the image sensor at the time of shooting in the transfer efficiency calculation mode selected by the mode selection means. The imaging device according to claim 11, wherein the imaging device is calculated.   The image capturing device further includes a detecting unit that detects a change in shooting setting condition related to transfer efficiency, and the transfer efficiency calculating unit detects an image from the image sensor before the main shooting when a change in shooting setting condition is detected by the detecting unit. The imaging apparatus according to claim 11, wherein a signal is captured and transfer efficiency is calculated based on the image signal.   Means for measuring the passage of time, wherein the transfer efficiency calculating means fetches an image signal from the image sensor before the actual photographing and transfers based on the image signal when the measured passage of time exceeds a predetermined threshold value; The imaging apparatus according to claim 11, wherein the efficiency is calculated.   The camera further includes an automatic focus adjustment unit that performs automatic focus adjustment based on an image signal from the image sensor before the main photographing, and the transfer efficiency calculation unit acquires from the image sensor before the focus adjustment at the time of the automatic focus adjustment is completed. The imaging apparatus according to claim 11, wherein the transfer efficiency is calculated based on the processed image signal.   18. The signal processing unit includes a matrix circuit that performs color correction, and controls a matrix coefficient of the matrix circuit based on the transfer efficiency acquired by the transfer efficiency acquisition unit. The imaging device described in 1.   The image pickup apparatus according to claim 18, wherein the matrix circuit is at least one of a linear matrix circuit and a color difference matrix circuit.

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