JP4547102B2 - Electronic camera - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electronic camera that electronically captures a subject image, and more particularly, to correction of smear that occurs as unnecessary charges in a transfer path of a solid-state imaging device (CCD) and degrades image quality.
[0002]
[Prior art]
Smear is generated as unnecessary charges in the transfer path of the CCD due to strong incident light, and becomes an error factor for charges due to exposure that is originally generated by a photodiode. Specifically, the charge generated in the photodiode in the exposure operation by the CCD is output data from the vertical transfer path through the horizontal transfer path, but smear which is an unnecessary charge is mixed with the generated charge from the photodiode. That is a problem.
[0003]
Therefore, a conventional technique is known in which smear charges mixed in the output are corrected by reading the CCD output twice. In the first CCD readout, the exposure data is read out under a desired exposure condition, and in the second CCD readout, the data is read out without transferring the photodiode charge to the transfer path. The smear amount is eliminated by subtracting the second read data from the first read data.
[0004]
Further, for example, an electronic still camera described in Japanese Patent Application Laid-Open No. 5-7335 performs pre-photometry scanning to detect smear information, and removes smear components based on smear information previously detected during main photometry scanning. I have to.
[0005]
These conventional techniques have the following problems. In other words, special hardware (such as a TG (timing generator) for driving the CCD) needs to be provided in order to realize CCD empty readout for smear correction and pre-photometry scanning, leading to system limitations and increased costs. There was a problem.
[0006]
[Problems to be solved by the invention]
The present invention has been made in view of such circumstances, and an object thereof is to provide an electronic camera capable of performing effective smear correction without requiring a special hardware configuration.
[0007]
[Means for Solving the Problems]
In order to solve the above problems and achieve the object, the present invention is configured as follows.
[0008]
An electronic camera according to the present invention is obtained by an image sensor that captures an image of a subject to obtain image information, a photometric unit that obtains photometric data from the image sensor at an exposure time based on a set shutter speed, and the photometric unit. Luminance lower limit determination means for comparing photometry data with a photometry lower limit threshold, and when the photometry data obtained by the photometry means is smaller than the photometry lower limit threshold, the photometry data is set with an exposure time set longer than the exposure time. Re-obtain dark photometry means, and brightness upper limit determination means for comparing the photometry data obtained by the photometry means with the photometry upper limit threshold when the photometry data obtained by the photometry means is larger than the photometry lower limit threshold If the photometry data obtained by the photometry means is larger than the photometry upper limit threshold, the first exposure time set shorter than the exposure time is used. Smear detection photometry means for obtaining second photometry data for smear detection with a second exposure time set shorter than the first exposure time, and photometry data of the second exposure time And correction means for obtaining photometric data excluding the amount of smear based on the photometric data of the first exposure time .
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0011]
FIG. 1 is a block diagram showing a circuit configuration of an electronic camera according to an embodiment of the present invention. In the figure, 101 is a lens system composed of various lenses, 102 is a lens driving mechanism for driving the lens system 101, 103 is an exposure control mechanism for controlling the diaphragm of the lens system 101, 104 is a mechanical shutter, and 105 is color. CCD color image pickup device incorporating a filter, 106 a CCD driver for driving the image pickup device 105, 107 a preprocess circuit including an A / D converter, 108 a color signal generation process, a matrix conversion process, and other various types A digital process circuit for performing digital signal processing, 109 is a card interface, 110 is a memory card such as CF, and 111 is an LCD image display system.
[0012]
In FIG. 1, 112 is a system controller (CPU) for comprehensively controlling each unit, 113 is an operation switch system including various SWs, 114 is an operation display system for displaying an operation state, a mode state, and the like, 115. Is a lens driver for controlling the lens driving mechanism 102, 116 is a strobe as a light emitting means, 117 is an exposure control driver for controlling the strobe 116, 118 is a non-volatile memory (EEPROM) for storing various setting information, etc. ).
[0013]
In the electronic camera of this embodiment, the system controller 112 controls the exposure control mechanism 103, the mechanical shutter 104, and the drive of the CCD image sensor 105 by the CCD driver 106 to perform exposure (charge accumulation) and signal readout, and pre-process them. After being taken into the digital process circuit 108 via the process circuit 107 and subjected to various signal processing, it is recorded on the memory card 110 via the card interface 109. The CCD image pickup device 105 is assumed to be, for example, an interline type with a vertical overflow drain structure and a progressive (sequential) scanning type.
[0014]
FIG. 2 is a plan view showing the element structure of the CCD image pickup element 105. Photodiodes 201 are arranged in a matrix as light receiving elements, a plurality of vertical transfer paths 202 are arranged between the photodiodes 201 in the column direction, and one horizontal transfer line is arranged at the end of the vertical transfer path 202 in the row direction. A transfer path 203 is arranged. The signal charge accumulated in the photodiode 201 is read out to the vertical transfer path 202 by the charge transfer pulse TG, and transferred in the downward direction on the paper in the transfer path 202. The signal charge transferred through the vertical transfer path 202 is then transferred to the horizontal transfer path 203, transferred in the horizontal transfer path 203 to the left in the drawing, and finally output via the read amplifier 204. Yes.
[0015]
Smear that is generated as unnecessary charge in the vertical transfer path 202 due to strong incident light on the photodiode 201 becomes an error factor for the charge due to exposure that is inherently generated by the photodiode 201.
[0016]
This embodiment is an electronic camera that uses a general-purpose TG (timing generator) that is easy to obtain and advantageous in terms of cost, and that corrects smear without requiring additional hardware. The present embodiment is based on the knowledge that the amount of smear does not depend on the electronic shutter speed, and without performing CCD readout by a special driving method as in the prior art, a plurality of times at the time of photometry before the main photographing. The smear correction data is calculated by this exposure.
[0017]
FIG. 3 is a diagram illustrating the relationship between different photometry and brightness (Bv) ranges, and the smear detection range. For example, when the range of brightness (Bv) (darkest to brightest) is divided into three, for example, photometry 1 to photometry 3 correspond to the respective brightness ranges. Each photometry has different shutter speed and sensitivity conditions. Note that photometry 3 is photometry corresponding to the smear detection range.
[0018]
FIG. 4 is a timing chart showing execution of photometry according to the dynamic range of brightness (Bv).
[0019]
In the present embodiment, photometry 2 is first performed. In photometry 2, the shutter speed is T2, and the ISO sensitivity is S2. The brightness value is determined based on the data obtained by the photometry 2. That is, if this luminance value is smaller than the photometric lower limit threshold value, photometry 1 is executed (see FIG. 4A). In photometry 1, the shutter speed is T1 (exposure time increase), and the ISO sensitivity is S1. On the other hand, when the luminance value is larger than the photometric lower limit threshold value, it is determined whether the luminance value of the photometry 2 is further larger than the photometric upper limit threshold value.
[0020]
First, when the luminance value of the photometry 2 does not become larger than the photometric upper limit threshold value, the data obtained by the photometry 2 is used as it is for calculating the luminance value (see FIG. 4B).
[0021]
On the other hand, if the luminance value of photometry 2 is larger than the photometric upper limit threshold value, photometry 3 is executed. This photometry 3 includes two photometry (photometry 3-1 and photometry 3-2) including smear detection (see FIG. 4C).
[0022]
Here, the shutter speed in photometry 3-1 is T3 (exposure time reduced from T2; first exposure time), the shutter speed in photometry 3-2 is T4 (second exposure time), and T4 = nT3. To do. n is an arbitrary positive number, and is 2 here as an example. The ISO sensitivity of photometry 3-1 is S3, and the ISO sensitivity in photometry 3-2 is S4, where S4 = S3. In each of the photometry 1 to 3, the aperture (Av) is fixed.
[0023]
The photometry 3-2 is for smear detection, and smear correction is performed using the exposure data obtained by the photometry 3-2 and the exposure data obtained by the photometry 3-1. This will be specifically described with reference to FIG.
[0024]
FIG. 5A shows exposure data D1 related to photometry 3-1, and FIG. 5B shows exposure data D2 related to photometry 3-2 for smear detection.
[0025]
As described above, the shutter speed in photometry 3-1 is T3 (for example, 1/2500 seconds), the shutter speed in photometry 3-2 is nT3 (for example, 1/5000 seconds; n = 2), and the shutter speed is different. Therefore, the total exposure amounts of the exposure data D1 and D2 are different. However, since the smear amount does not depend on the electronic shutter speed, the same amount exists in both the exposure data D1 and D2. Therefore, when the net exposure (out) amount excluding the smear amount is A, this A is obtained by (D1-D2) × 2. Needless to say, n is not limited to 2.
[0026]
6 and 7 are flowcharts showing the processing operation during photometry in the electronic camera of the present embodiment with the smear correction as described above.
[0027]
First, when ON of the first release is detected (step S1), exposure for photometry 2 is set (step S2), and then photometry 2 is executed (step S3). Exposure data for the photometry 2 is acquired (step S4), and brightness determination based on the acquired exposure data is performed (step S5).
[0028]
That is, in step S5, it is determined whether or not the luminance value calculated from the exposure data for photometry 2 is smaller than the photometric lower limit threshold value. If YES, the process proceeds to step S6. If NO, step S6 is performed. Proceed to S10.
[0029]
If the process proceeds to step S6, the exposure for photometry 1 is set, and then photometry 1 is executed (step S7). After acquiring exposure data for photometry 1 (step S8), a luminance value is calculated based on the acquired exposure data (step S9), and the process of the entire photometry operation is completed.
[0030]
As shown in FIG. 7, when the process proceeds from step S5 to step S10, it is further determined whether or not the luminance value calculated from the exposure data for photometry 2 is greater than the photometric upper limit threshold value. If the determination in step S10 is No, the brightness determination result for photometry 2 is within the upper and lower limits of the possible threshold value, so that the brightness using the exposure data obtained by execution of photometry 2 is used. A value is calculated (step S11).
[0031]
On the other hand, if the determination in step S10 is Yes, it is necessary to perform photometry 3. Since this photometry 3 corresponds to a smear detection range, smear detection is also performed.
[0032]
As described above, photometry 3 includes photometry 3-1 and photometry 3-2. First, in step S12, exposure setting for photometry 3-1 (Tv3-1 = Tv1) is performed. Photometry 3-1 is executed under this exposure condition (step S13), and exposure data of photometry 3-1 is acquired (step S14). In step S15, exposure setting for photometry 3-2 (Tv3-1 = Tv1 + 1) is performed. Photometry 3-2 is executed under this exposure condition (step S16), and exposure data of photometry 3-2 is acquired (step S17). Then, a smear amount is detected from the exposure data acquired in each of the photometry 3-1 and 3-2 (step S18), and a luminance value obtained by correcting the smear amount based on this is calculated (step S19).
[0033]
After the photometric operation as described above is finished, a main exposure (photographing) operation is executed.
[0034]
The smear correction of the electronic camera of the present embodiment as described above is based on the knowledge that the amount of smear does not depend on the electronic shutter speed, and the smear correction is performed by multiple exposures (photometry) with different conditions. Even if a general-purpose TG (timing generator) that is easy to obtain and advantageous in terms of cost is applied because necessary data is obtained and CCD reading by a special driving method is not required as in the prior art. No additional hardware is required, and can be realized by a normal CCD drive circuit and sensor specifications. Moreover, the exposure performance at high brightness can be remarkably improved. Since the calculation of the smear amount in the present embodiment is performed based on a preset accumulation time, this can be easily realized. In addition, it is one of advantageous effects that the performance of smear correction is not affected by the brightness (Bv). Furthermore, it is possible to effectively use the smear information obtained in this embodiment for processing other than photometry, which will contribute to improving the performance of the entire electronic camera.
[0035]
Note that the configuration illustrated in the embodiment of the present invention is an example, and is not intended to exclude other configurations, and a part of the illustrated configuration may be replaced with another or one of the illustrated configurations. Other configurations obtained by omitting a part, adding another function or element to the illustrated configuration, or combining them are also possible. Also, another configuration that is logically equivalent to the exemplified configuration, another configuration that includes a portion that is logically equivalent to the exemplified configuration, another configuration that is logically equivalent to the main part of the illustrated configuration, and the like are possible. is there. Further, another configuration that achieves the same or similar purpose as the illustrated configuration, another configuration that achieves the same or similar effect as the illustrated configuration, and the like are possible.
In addition, various variations of various components illustrated in the embodiment of the present invention can be implemented in appropriate combination.
Further, the embodiment of the present invention is an invention of an invention as an individual device, an invention of two or more related devices, an invention of the entire system, an invention of components within an individual device, or a method corresponding thereto. The invention includes inventions according to various viewpoints, stages, concepts, or categories.
Therefore, the present invention can be extracted from the contents disclosed in the embodiments of the present invention without being limited to the exemplified configuration.
[0036]
【The invention's effect】
As described above, according to the present invention, an electronic camera capable of performing effective smear correction without requiring a special hardware configuration can be provided.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a circuit configuration of an electronic camera according to an embodiment of the present invention. FIG. 2 is a plan view showing a structure of a CCD image sensor of the electronic camera according to the embodiment. FIG. 4 is a diagram showing a relationship between different photometry and brightness (Bv) ranges, and a smear detection range. FIG. 4 is a timing showing execution of photometry according to the dynamic range of brightness (Bv) according to the embodiment. FIG. 5 is a diagram showing exposure data D1 related to photometry 3-1, and FIG. 5 (b) is exposure data D2 related to photometry 3-2 for smear detection according to the above embodiment. 7 is a flowchart showing a part of an operation example during smear correction of the electronic camera according to the embodiment. FIG. 7 is a flowchart showing another part of the operation example during smear correction of the electronic camera according to the embodiment.
DESCRIPTION OF SYMBOLS 101 ... Lens system 102 ... Lens drive mechanism 103 ... Exposure control mechanism 104 ... Mechanical shutter 105 ... CCD color image sensor 106 ... CCD driver 107 ... Pre-process circuit 108 ... Digital process circuit 109 ... Card interface 110 ... Memory card 111 ... LCD image display System 112 ... System controller (CPU)
113 ... Operation switch system 114 ... Operation display system 115 ... Lens driver 116 ... Strobe 117 ... Exposure control driver 118 ... Non-volatile memory

Claims (3)

An image sensor that captures a subject and obtains image information;
Photometric means for obtaining photometric data from the image sensor at an exposure time based on a set shutter speed;
Luminance lower limit determining means for comparing the photometric data obtained by the photometric means with a photometric lower limit threshold;
When the photometry data obtained by the photometry means is smaller than the photometry lower limit threshold, dark photometry means for re-acquiring photometry data with an exposure time set longer than the exposure time, and
When the photometric data obtained by the photometric means is larger than the photometric lower limit threshold, the luminance upper limit determining means for comparing the photometric data obtained by the photometric means with the photometric upper limit threshold,
When the photometry data obtained by the photometry means is larger than the photometry upper limit threshold, the first photometry data is obtained with the first exposure time set shorter than the exposure time, and the first exposure time is further obtained. Smear detection photometry means for obtaining second photometry data for smear detection with a second exposure time set shorter than
An electronic camera comprising: correction means for obtaining photometric data excluding a smear amount based on the photometric data of the second exposure time and the photometric data of the first exposure time .   2. The electronic camera according to claim 1, wherein an exposure time of the second exposure data is n times (where n ≠ 0) an exposure time of the first exposure data. The photometric data obtained by the photometric means is output as photometric data before photographing operation including main exposure when it is larger than the photometric lower limit threshold and smaller than the photometric upper limit threshold. Item 3. The electronic camera according to Item 1 or 2.

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