JP2002290824A - Digital camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a digital camera which has high snapshooting property without inadequately expanding gradations of a photographic scene as a digital camera which has a gradation expanding function of generating image data of gradations exceeding the dynamic range of an imaging device by putting together output signals of the imaging devices taking pictures with different exposure quantities. SOLUTION: A histogram of the intensity values of the output signals of the imaging device is generated and when the number of signals of intensity less than a specific reference value is larger than specified, gradation expansion is not performed. Further, the luminance of an object of photography is detected by a photometric element having a wider dynamic range than the image pickup element and when the luminance of the peripheral part is less than a reference value and the luminance difference between the center part and peripheral part is larger than specified, no gradation expansion is performed. Consequently, unnecessary gradation expansion of a reverse backlight scene wherein the main subject to be photographed is lighter than the background can be avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital camera, and more particularly, to a digital camera capable of providing an image having a difference in brightness exceeding a dynamic range of an image sensor.

[0002]

2. Description of the Related Art A digital camera captures an image by exposing an image sensor that performs photoelectric conversion, and generates image data representing the captured image from an output signal of the image sensor.
The brightness of the image represented by the generated image data is adjusted by adjusting the exposure amount of the image sensor. The adjustment of the exposure amount is performed by changing the photoelectric conversion time, that is, the electronic shutter speed, or by changing the diameter of a light beam guided to the image pickup device by a diaphragm, or by using both of them.

[0003] The image sensor is CCD or CMOS, generally, the dynamic range i.e. the range of the amount of received light intensity of the output signal corresponds well of the imaging device is not very large, about 1: 2 ⁷ is there. Therefore, for example, when the luminance of the photographing target falls within the range of Bv2 to Bv9, an image in which the luminance difference is favorably reflected can be photographed by adjusting the exposure amount. Beyond this range, even if the exposure is adjusted, it is possible to avoid the occurrence of `` blackouts '' in which relatively low-brightness parts become completely black or `` whiteouts '' in which relatively high-brightness parts become pure white. Disappears.

Therefore, the same object to be photographed is photographed a plurality of times by changing the exposure amount of the image pickup device, and the output signals of the image pickup device in each photographing are synthesized so that the difference in signal intensity exceeds the dynamic range of the image pickup device. It has been proposed to generate data (eg, Japanese Patent Laid-Open No. 2000-92378, Japanese Patent Laid-Open No.
000-50151). When synthesizing the signals, the output signal of the image sensor at the time of the exposure with a large amount of exposure is used for a portion with a low luminance, and the output signal of the image sensor at the time of the photographing with a small amount of exposure is used for the portion with a high luminance. In addition, the offset of the signal intensity due to the difference in the exposure amount is corrected.

[0005] The image represented by the image data obtained by this processing has a larger gradation than the image represented by the image data generated by the normal processing, and this processing is called gradation expansion processing. When the gradation enlargement process is performed, S
By improving the / N ratio, it is possible to obtain a high-quality image without blackouts. For example, in the case of shooting a backlight scene in which the main subject is significantly darker than the background, the subtle luminance difference of the subject Can be provided.

[0006]

There are two types of conventional digital cameras that perform the gradation enlarging process, one in which the user instructs whether or not to perform the process, and the other in which the camera itself determines automatically. . However, a camera that automatically determines whether or not to perform the gradation enlargement process uses only the overall luminance difference of the photographing target as a criterion, and performs the gradation enlargement process on the fine luminance distribution of the photographing target. It is not used to determine whether or not. For this reason, if the luminance difference is large, the gradation enlargement process is always performed, which may not be suitable for the shooting target. For example, in shooting a spotlight scene in which only the subject is brightly lit, that is, in a backlight scene (see FIG. 9) in which the background is significantly darker than the subject, even if the user intends to obtain an image with a black background, Contrary to that intention, an image having a bright background can be obtained.

Further, if the gradation enlargement processing is performed, it takes time for photographing a plurality of images and signal processing, and the quick shooting performance is sacrificed to some extent. Therefore, it is desirable to perform the gradation enlargement processing only when necessary. . However, since the conventional digital camera does not use the fine luminance distribution of the photographing target as a criterion for determination, it is not always possible to appropriately determine whether or not the gradation enlargement process is necessary.

Further, in the conventional digital camera, the brightness of the object to be photographed is determined from the intensity of the output signal of the image sensor to determine whether or not to perform the gradation enlarging process. Only afterwards can you make a decision. In this respect also, the quick shooting performance is impaired.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has a function of performing a gradation enlargement process, and does not perform an unnecessary gradation enlargement process, and a digital camera excellent in quick shooting performance. The purpose is to provide.

[0010]

In order to achieve the above object, according to the present invention, there is provided a digital camera which captures an image by exposing an image sensor and generates image data representing the captured image from an output signal of the image sensor. A camera, which captures one image and generates image data from an output signal of an image sensor at the time of capturing the image; and a plurality of images that capture a plurality of images with different exposure amounts. A second function of synthesizing an output signal of the image sensor when capturing the image of the above and generating image data in which a difference in signal intensity exceeds the dynamic range of the image sensor. It is assumed that when the ratio of the portion equal to or smaller than the predetermined value is equal to or larger than the predetermined value, the image data is generated only by the first function.

The first function is a processing function of an ordinary digital camera, and the second function is a function of a gradation enlargement processing. This digital camera performs a normal process without performing the gradation enlargement process when the ratio of the low-luminance portion in the photographing target is large even if the luminance difference of the photographing target is large. Therefore, for a backlight scene in which only a small subject is bright, an image can be provided in which a dark background is black or nearly black. Also, for example, even when a subject illuminated by a spotlight moves, such as in a performance of a play, rapid shooting performance is ensured.

According to the present invention, there is also provided a digital camera for photographing an image by exposing an image pickup device and generating image data representing the photographed image from an output signal of the image pickup device. A first function of generating image data from an output signal of the image sensor at the time of capturing an image, and a plurality of images captured at different exposure amounts, and an output signal of the image sensor at the time of capturing the plurality of images. Synthesize
A second function of generating image data in which the signal intensity difference exceeds the dynamic range of the image sensor, wherein the brightness of a first region located in the periphery of the imaging target is equal to or less than a predetermined value, and Generating image data only by a first function when a luminance difference between a second region and a first region of the photographing object closer to the center than the first region is equal to or greater than a predetermined value. And

This digital camera performs a normal process without performing the gradation enlargement process when the luminance of the peripheral portion of the photographing target is low and the luminance difference between the central portion and the peripheral portion is large. Therefore, even with this digital camera, in a backlight scene, it is possible to provide an image in which the background is blackened or close to black, and quick shooting is ensured.

In any of the above digital cameras, the brightness of the object to be photographed can be obtained from the output signal of the image sensor. In this case, the same output signal may be used for both obtaining the brightness of the shooting target and generating the image data. Alternatively, shooting may be performed before shooting with the first function or the second function. May be used to obtain the brightness of the object to be photographed.

Also, a plurality of photometric elements having a wider dynamic range than the image pickup element may be provided, and the luminance of the object to be photographed may be obtained from the output signal of the photometric element. By providing a plurality of photometric elements, it is possible to obtain the luminance of a plurality of portions of the imaging target necessary for determining the function selection. In addition, since a photometric element having a wider dynamic range than the image sensor is used, it is possible to accurately know the amount of exposure to be set in photographing with the second function. Since the photometry by the photometric element can be performed independently of the photographing, the quick shooting performance is also ensured.

In order to achieve the above object, the present invention also provides a digital camera that captures an image by exposing an image sensor and generates image data representing the captured image from an output signal of the image sensor. Take one image,
A first function of generating image data from an output signal of the image sensor at the time of capturing the image, and an output signal of the image sensor at the time of capturing a plurality of images with different exposure amounts and capturing the plurality of images To generate image data in which the signal intensity difference exceeds the dynamic range of the image sensor.
Which has a plurality of photometric elements having a wider dynamic range than the image sensor, and which of the first function and the second function generates image data based on an output signal of the photometric element. Shall be determined.

By providing a plurality of photometric elements, it is possible to know the luminance distribution of the object to be photographed, and it is possible to avoid unnecessary generation of image data by the second function, that is, gradation expansion processing. In addition, since the photometric element having a wider dynamic range than the image pickup element is used, it is possible to accurately know the exposure amount to be set in the photographing by the second function, and to perform the photometry separately from the photographing. , Quick shooting performance is ensured.

[0018]

Embodiments of a digital camera according to the present invention will be described below with reference to the drawings. The appearance of the digital camera 1 of the first embodiment is schematically shown in a perspective view of FIG. 1 and a rear view of FIG. Digital camera 1
The photographing lens 11, the photometric lens 12 and the front window 13a of the finder are provided on the front, the release button 14, the liquid crystal panel 15 and the operation keys 16a and 16b are provided on the upper surface, the large liquid crystal panel 17, the operation keys 18 and the rear window 13b of the finder are provided on the back. And a recording medium insertion port 19 on the side surface. The digital camera 1 further includes an image sensor 20 inside the photographing lens 11 and a photometer 21 inside the photometric lens 12.

The digital camera 1 forms an image on the image sensor 20 with light from the object to be photographed by the photographing lens 11 and exposes the image sensor 20 to photograph an image. The image sensor 20 has a large number of pixels arranged two-dimensionally, and performs a photoelectric conversion for each pixel to output a signal representing electric charges accumulated. The output signal of each pixel becomes a signal representing the amount of light received from each point of the photographing target, and is used for generating image data representing a photographed image. Each pixel is provided with one of color filters for selectively transmitting red (R) light, green (G) light or blue (B) light, and all pixels are for R light, G light, It is classified into three types for B light. The dynamic range of each pixel of the image sensor 20 is about 1: 2 ^7.

The generated image data is recorded on the recording medium 50 inserted in the insertion slot 19, and the image represented by the image data is displayed on the liquid crystal panel 17. The image data recorded on the recording medium 50 can be read out, and the image can be reproduced and displayed on the liquid crystal panel 17.

The digital camera 1 has a function of automatic focusing (AF) for automatically focusing the photographing lens 11 on a photographing object. The automatic focus adjustment is performed by changing the focus of the photographing lens 11 in a direction in which the contrast of an image formed on the image sensor 20 increases.

The photometric lens 12 is linked to the photographing lens 11, and forms light from a subject to be imaged on the photometric unit 21. FIG. 3 shows a positional relationship between the photometry unit 21 and the imaging device 20 with respect to the imaging target. On the photometric unit 21, an image of a portion having a size of about 2/3 of the center of the image formed on the image sensor 20 is formed. The photometric unit 21 includes thirteen photometric elements 22, and outputs a signal representing the charge accumulated by performing photoelectric conversion for each photometric element 22. Each photometric element 22 is an image sensor 2
Each photometric element 2 has a size several tens of times larger than one pixel.
The output signal of No. 2 is a signal indicating the amount of light received from a wide part of the imaging target, and is used for detecting the luminance of each part.
The dynamic range of the photometric device 22 is about 1: 2 ^10, which is several times or more the dynamic range of the image sensor 20.

The digital camera 1 has an automatic exposure adjustment (AE) function for automatically adjusting the exposure of the image sensor 20 according to the brightness of the object to be photographed. There are two types of light metering methods for automatic exposure adjustment, that is, a method of using the output signal of the light metering unit 21, that is, center-weighted metering and average metering. In center-weighted photometry, the luminance of the object to be photographed is calculated using the output signal of the centrally located one of the photometric elements 22, and in average photometry, the output signals of all the photometric elements 22 are used, and the average intensity of the object to be photographed is calculated from their average intensities. Calculate the brightness.

In the method of adjusting the exposure amount in the automatic exposure adjustment, the aperture of an aperture (not shown) included in the photographing lens 11 is set to a value designated by the user, and the photoelectric conversion time of the image sensor 20, Aperture priority for adjusting the shutter speed, shutter speed priority for adjusting the aperture diameter by setting the electronic shutter speed to the value specified by the user, and program control for adjusting both the electronic shutter speed and the aperture diameter according to the program There are three ways.

The user selects a photometric method or an adjusting method using the operation keys 16a, and specifies an aperture value, an electronic shutter speed, and the like using the operation keys 16b. The specified situation is displayed on the liquid crystal panel 15.

FIG. 4 schematically shows the circuit configuration of the digital camera 1.
Is shown schematically in FIG. The digital camera 1 includes an analog processing unit 31, an A / D converter 32, a white balance (W
B) An adjustment unit 33, a γ correction unit 34, a color interpolation unit 35, a compression unit 36, an interface 37, a CPU 38, an image synthesis unit 39, a RAM 40, and a histogram creation unit 41 are provided.

The analog processing section 31 applies a correlated double sampling (CDS) to the analog signal output from the image sensor 20.
And automatic gain control (AGC) processing to reduce noise and adjust the levels of all signals.
The A / D converter 32 converts the analog signal from the analog processing unit 31 into a 10-bit digital signal,
The adjustment unit 33 individually adjusts the levels of the R, G, and B color component signals converted into digital signals to adjust the white balance. The γ correction unit 34 performs non-linear processing on the signal from the WB adjustment unit 33 so as to be suitable for display.
The color interpolation unit 35 generates an R, G, or B color component signal that will be missing at each pixel position of the image sensor 20 by interpolation processing. Through a series of these processes, image data representing an image captured by the image sensor 20 is generated.

The compression section 36 compresses the image data according to the JPEG system. The interface 37 is a recording medium 5
The image data compressed by the compression unit 36 is recorded on the recording medium 50, and the recorded image data is read from the recording medium 50. The compression unit 36 also has a function of performing reverse processing of compression, and reproduces image data before compression from image data read from the recording medium 50 by the interface 37 for reproduction and display of an image.

The CPU 38 controls the operation of the digital camera 1 as a whole. The CPU 38 is connected to an operation unit 42 including the release button 14 and the operation keys 16a, 16b, and 18, and reflects an instruction given by a user via the operation unit 42 to control. The CPU 38 controls the liquid crystal panel 1
5, 17 and the photometric unit 21 are also connected.

The digital camera 1 performs photographing, that is, exposure of the image pickup device 20 once, and changes the exposure amount of the image pickup device 20 from the first mode in which image data is generated from the output signal of the image pickup device 20 at that time. And a second mode in which output signals of the image sensor 20 in each time of image capturing are combined to generate image data in which a difference in signal intensity exceeds the dynamic range of the image sensor 20. In the second mode, a gradation enlargement process is performed. The first mode and the second
The mode can be switched by the operation keys 18 provided on the back.
The operation is performed. The set mode is displayed on the liquid crystal panel 15.

The principle of the gradation expansion process in the second mode will be described with reference to FIG. FIG. 8A shows the relationship between the brightness of the imaging target, the intensity of the output signal of the image sensor 20, and the electronic shutter speed (ss) at a constant aperture value. S is the intensity of the output signal when the image sensor 20 is saturated. A straight line A indicates that, when the electronic shutter speed is set to tA, the image sensor 20 is saturated when the luminance of the shooting target is YA. A straight line B indicates that when the electronic shutter speed is set to tB faster (shorter) than tA, the image sensor 20 is saturated when the luminance of the imaging target is YB higher than YA. T is the intensity of the output signal corresponding to the luminance YA when the electronic shutter speed is set to tB.

When the electronic shutter speed is tA, a narrower luminance range is made to correspond to the entire dynamic range of the image pickup device 20 than when the electronic shutter speed is tB, so that a low-luminance portion of the photographing object is obtained. The S / N ratio increases. However, when the electronic shutter speed is tA,
For a luminance exceeding YA, the image sensor 20 is saturated.

Therefore, as shown by the bold line in FIG. 8B, an output signal having an intensity lower than S is extracted from an output signal in photographing at the lower electronic shutter speed tA, and the higher electronic shutter speed tB is extracted. From the output signal in the photographing in step (1), the one having an intensity of T or more is extracted, and the extracted signals are combined to generate image data. In synthesizing the signals, the latter signal intensity is increased by the difference (ST) between the intensity S and the intensity T, and the offset of the signal intensity caused by the difference in the shutter speed is corrected. As a result, image data representing an image whose gradation is enlarged can be obtained, and an image can be obtained in which the low-luminance portion of the shooting target is not blackened.

The extraction and synthesis of signals are performed by the image synthesis section 39 (FIG. 4). Further, the output signals of the image sensor 20 in the first and second shootings are obtained after the white balance adjustment processing.
It is stored in the RAM 40.

The above-described automatic exposure adjustment is performed in both the first mode and the second mode. However, in the second mode, a designated one of the aperture priority, the shutter speed priority, and the program control is adopted only in the first shooting, and the aperture value is set to the same as the first in the second shooting. Change the electronic shutter speed. The reason why the automatic exposure adjustment is performed in the first photographing is to make the output signal from the pixel corresponding to the portion where the photometry has been performed be substantially at the center of the dynamic range of the image sensor 20. The reason why the aperture value is fixed in the second photographing is to avoid a change in the image formation state (blur condition) of light on the image sensor 20. The electronic shutter speed in the second shooting is set according to the result of the first shooting.

The first mode and the second mode are the operation keys 1
8 is selected by the user, but even if the second mode is selected, the gradation enlargement processing is not always performed, and the image is captured only by one photographing as in the first mode. In some cases, it generates data. Whether or not to perform the gradation expansion process is determined based on the luminance distribution of the shooting target. The luminance distribution is obtained from a histogram of the output signal intensities of all pixels of the image sensor 20. Histogram is RAM
The histogram creating unit 41 (FIG. 4) creates an image by using the output signal of the first shooting stored in the image processing unit 40.

FIG. 5 shows an example of a histogram. In FIG. 5, (a) shows the case where the luminance of the imaging target is entirely within the dynamic range of the image sensor 20, and (b) shows that the imaging target has many low-luminance parts and the low-luminance part has the dynamic range of the imaging element 20. (C), the object to be photographed has many high-luminance parts, and the high-luminance part is the image pickup device 20.
Are not within the dynamic range.

The CPU 38 determines whether or not to perform the gradation expansion process in the second mode. The CPU 38 determines two reference values SD and H for the signal strength in the determination.
L is used. The reference values SD and HL are small (eg, 10%) and large (eg, 90%) with respect to the intensity of the output signal when the image sensor 20 is saturated.
%). When the ratio of the number of output signals having an intensity equal to or less than the reference value SD to the total number of output signals (the total number of pixels) is equal to or greater than a predetermined value NS (for example, 5%), the CPU 38 does not perform the tone enlarging process. Further, even if the ratio of the number of output signals having the intensity equal to or lower than the reference value SD to the total number of output signals is less than the value NS, the ratio of the number of output signals having the intensity equal to or higher than the reference value HL to the total number of output signals is equal to a predetermined value. The value NH (for example, 5
%), The gradation expansion process is not performed.

For example, in the histogram shown in FIG.
In the case of (b), since the ratio of the number of pixels having the intensity equal to or smaller than the reference value SD is equal to or larger than the value NS, the gradation enlarging process is not performed.
In the case of (c), the ratio of the number of pixels having the intensity equal to or lower than the reference value SD is less than the value NS, and the ratio of the number of pixels having the intensity equal to or higher than the reference value HL is equal to or higher than the value NH. .
In the case of (a), the ratio of the number of pixels having the intensity equal to or less than the reference value SD is less than the value NS, but the ratio of the number of pixels having the intensity equal to or more than the reference value HL is less than the value NH. Not performed.

When the ratio of the number of pixels having the intensity equal to or smaller than the reference value SD is large, the gradation enlargement process is not performed, so that the subject to be mainly photographed is much brighter than the background, as in the case of a backlight scene. When the subject is only a small part of the photographing target, the dark part of the photographing target can be expressed as blackout. In addition, when both the ratio of the number of pixels having the intensity equal to or lower than the reference value SD and the ratio of the number of pixels having the intensity equal to or higher than the reference value HL are small, the gradation enlarging process is not performed. Can be avoided.

The flow of processing from photographing of an image to recording of image data in the digital camera 1 will be described with reference to the flowchart of FIG. First, release button 14
Is determined, that is, whether or not an instruction to start shooting has been given, and if not, it is waited for operation (step # 105). When the release button is operated, the set mode is read from the state of the operation key 18 (# 110), and it is determined whether the mode is the first mode or the second mode (# 115).

When the mode is set to the first mode, the electronic shutter speed (SS) and the aperture value are set according to the above-mentioned method for automatic exposure adjustment (# 120), and the exposure of the image sensor 20, that is, the photoelectric conversion is performed. Perform (# 125). Next, a signal is read from the image pickup device and the processing up to white balance adjustment is performed (# 130), and the processing up to generation and compression of image data is further performed (# 135). Then, the compressed image data is recorded on the recording medium 50 (# 1).
40), and return to step # 105.

If it is determined in step # 115 that the second mode has been set, the electronic shutter speed and aperture value are set according to the above-described method for automatic exposure adjustment (#
145), exposure of the image sensor 20 is performed (# 150). Next, a signal is read out from the image pickup device, and processing until white balance adjustment is performed (# 155).
40 (# 160).

Then, a histogram is created (# 16)
5) Whether there are many low-intensity signals, that is, the reference value SD
It is determined whether or not the ratio of the following luminance signals is equal to or greater than the value NS (# 170). When there are few low-intensity signals,
It is determined whether or not there are many high-intensity signals, that is, whether or not the ratio of the signals having the luminance equal to or higher than the reference value HL is equal to or higher than the value NH (# 175). When there are many low-intensity signals in the determination in step # 170, or when there are few high-intensity signals in the determination in step # 175, the signal stored in the RAM is read out (# 180), and the process up to generation and compression of image data is performed. The processing is performed (# 185), and the compressed image data is recorded on a recording medium (# 190). Thus, similarly to the first mode, the gradation enlargement processing is not performed. After recording the image data, the process returns to step # 105.

When there are many high-intensity signals in the determination at step # 175, the electronic shutter speed is set for the second photographing (# 195). The electronic shutter speed is slower (longer) than the electronic shutter speed in the first photographing, but is slower as the number of signals having a luminance equal to or less than the reference value SD increases. Next, the image sensor is exposed (# 20).
0), a signal is read from the image sensor, and processing up to white balance adjustment is performed (# 205).
It is stored in M (# 210).

Then, the signal stored in step # 160 and the signal stored in step # 210 are read out from the RAM and combined (# 215), and processing up to generation and compression of image data is performed (# 220). This means that the gradation expansion processing has been performed. Finally, the compressed image data is recorded on a recording medium (# 225), and the process returns to step # 105.

Here, after determining which mode the mode is in (# 115), photographing (# 150) is performed to create a histogram (# 165), but before the mode is determined. May be taken to create a histogram. This is suitable when the digital camera 1 is provided with a “live view” function of repeatedly photographing at a fixed cycle and immediately displaying the photographed image on the liquid crystal panel 17.

In this case, the photographing is performed twice in the second mode. However, it is also possible to perform the photographing three or more times to combine the output signals. In this case, the output signals of all the photographing may be combined, or the output signals of the photographing at the highest electronic shutter speed and the photographing signal at the lowest electronic shutter speed may be combined.

Generally, the ratio of the subject to the object to be photographed is small, and most of the object to be photographed is the background. Therefore,
In the backlight scene, the low-luminance portion of the shooting target decreases, and in the backlight scene as illustrated in FIG. 9, the low-luminance portion of the shooting target increases. For this reason, in the second mode of the digital camera 1, the gradation expansion processing is performed in a backlight scene, and the gradation expansion processing is not performed in a backlight scene. In a backlight scene, a user of a camera usually desires an image in which a low-luminance subject is brightly expressed, and in a backlight scene, an image in which a subject having sufficient luminance is directly expressed. 1
Can satisfy both. In addition, unnecessary gradation enlargement processing is not performed in a backlight scene, so that shooting of the next image can be started immediately.

In this embodiment, the luminance distribution of the object to be photographed is obtained from the output signal of the image sensor 20. However, the luminance distribution of the object to be photographed can be obtained from the output signal of the photometric element 22 in exactly the same manner. . In that case, each photometric element 22
Is increased or the number of photometric elements 22 is increased,
It is desirable that 1 corresponds to the entire image pickup device 20.

A digital camera according to the second embodiment will be described. The digital camera 2 of the present embodiment also performs a single shooting operation and generates image data from an output signal of the image sensor at that time, similarly to the digital camera 1 described above. A second mode in which the imaging is performed twice while changing the output signals of the imaging device in each imaging to generate image data in which a difference in signal intensity exceeds the dynamic range of the imaging device. Digital camera 2
Is different from the digital camera 1 only in the method of determining whether or not to perform the gradation enlargement process in the second mode, and the appearance and circuit configuration are the same. Therefore, duplicate description will be omitted. However, since the digital camera 2 does not create a histogram, the histogram creating unit 41 is omitted.

In the digital camera 2, whether or not to perform the gradation expansion process is determined on the basis of the luminance of the peripheral part of the object to be photographed and the luminance difference between the central part and the peripheral part.
When the luminance difference between the central part and the peripheral part is small, the gradation enlargement processing is not performed. For detecting the luminance, the output signals of the photometric elements 22 (see FIG. 3) of the 13 photometric units 21 arranged in three rows in the horizontal direction are used.

Specifically, when the relationship of Expression 1 is satisfied and the relationship of Expression 2 is satisfied, the tone expansion process is not performed. Also, when the relation of Expression 3 is established, the gradation enlargement processing is not performed. Bave ≦ B1 Equation 1 Bcent−Bave ≧ B2 Equation 2 Bmax / Bmin ≦ D Equation 3

Here, Bave is the average of the intensities of the output signals of the six photometric elements located at the left and right ends of each of the 13 photometric elements 22, and Bcent is the photometric element located at the left and right center of the central row. The output signal intensities Bmax and Bmin of
These are the maximum intensity and the minimum intensity of the 13 photometric elements, respectively. Also, D is the dynamic range of the image pickup device 20 1: D is of when expressed as (D is about 2 ⁷ as the above), predetermined the B1 and B2 corresponding to the absolute luminance value Is the value of B2 corresponds to medium brightness (for example, Bv6), while B1 corresponds to low brightness (for example, Bv3).
It is determined to correspond to

When the relationship of Expression 1 is established, the luminance of the peripheral portion of the object to be photographed is low. Also, when the relationship of Equation 2 holds,
The luminance difference between the central part and the peripheral part of the shooting target is large. Therefore, the relationship between Expressions 1 and 2 is satisfied in a backlight scene. That is, the digital camera 2 does not perform the gradation expansion process in the backlight scene. The reason why the gradation expansion process is not performed when the relationship of Expression 3 is satisfied is that the luminance range of the imaging target falls within the dynamic range of the image sensor 20, and there is no need for the gradation expansion. In this case, by the automatic exposure adjustment, an image that sufficiently expresses the range from the lowest luminance to the highest luminance of the photographing target can be obtained.

The flow of processing from photographing of an image to recording of image data in the digital camera 2 will be described with reference to the flowchart of FIG. First, release button 14
It is determined whether or not has been operated, that is, whether or not an instruction to start shooting has been given, and if not, the operation waits until it is operated (step # 305). When the release button is operated, the set mode is read from the state of the operation key 18 (# 310), and photometry is performed by the photometry unit 21 to read out the signal of the photometry element 22 (# 31).
5). Then, it is determined whether the mode is the first mode or the second mode (# 320).

When the mode is set to the first mode, the electronic shutter speed (SS) and the aperture value are set according to the above-described method for automatic exposure adjustment (# 325), and the image pickup device 20 is exposed (# 325). 330). Next, a signal is read from the image pickup device and the processing up to white balance adjustment is performed (# 335), and the processing up to generation and compression of image data is further performed (# 340). Then, the compressed image data is recorded on the recording medium 50 (# 345), and the process returns to step # 305.

When the second mode is set in the determination in step # 320, it is determined whether or not the peripheral portion of the object to be photographed has a low luminance and whether or not the luminance difference between the central portion and the peripheral portion is large. It is determined whether the relationship between the above-described equations 1 and 2 holds (# 350). When the peripheral part has low luminance and the luminance difference between the central part and the peripheral part is large, it is determined whether or not the ratio between the maximum luminance and the minimum luminance of the object to be photographed is large, that is, the above equation
It is determined whether or not holds (# 355).

If the peripheral portion is not low in luminance or the luminance difference between the central portion and the peripheral portion is not large in the determination in step # 350, or if the ratio between the maximum luminance and the minimum luminance is not large in the determination in step # 355, Go to step # 325. Thus, the gradation expansion processing is not performed.

When the ratio between the highest luminance and the lowest luminance is large in the determination at step # 355, the electronic shutter speed and the aperture value are set according to the above-mentioned method for automatic exposure adjustment (# 360), and the image pickup device 20 is exposed. (# 36
5). Next, a signal is read from the image pickup device and the process up to white balance adjustment is performed (# 370), and the signal is stored in the RAM 40 (# 375).

Then, an electronic shutter speed is set for the second photographing (# 380). The electronic shutter speed is set based on a signal having a low intensity among the signals read from the photometric element in step # 315. Next, the image sensor is exposed (# 385), a signal is read out from the image sensor, a process up to white balance adjustment is performed (# 390), and the signal is stored in the RAM (# 3).
95).

Then, the signal stored in step # 375 and the signal stored in step # 395 are read out from the RAM and combined (# 400), and processing up to generation and compression of image data is performed (# 405). This means that the gradation expansion processing has been performed. Finally, the compressed image data is recorded on a recording medium (# 410), and the process returns to step # 305.

In this processing, the electronic shutter speed for the second shooting in the second mode is determined (# 380) based on the result of the photometry (# 315) performed before the start of the shooting, so that the first shooting is performed. Following (# 365), the second shooting (# 385) can be performed promptly. Further, since the dynamic range of the photometric element is wide as described above, it is possible to set the electronic shutter speed (# 380) of the second photographing so as to be appropriate for a low-luminance part of the photographing target. is there.

In the present embodiment, the brightness of the object to be photographed is obtained from the output signal of the photometry unit 21.
The luminance of the object to be photographed can be obtained from the output signal.
In this case, the average of the intensities of the output signals of many pixels located at the center of the image sensor 20 is assumed to correspond to the above-described Bcent, and the intensities of the output signals of many pixels located at the periphery of the image sensor 20 are calculated. The average may be equivalent to Bave described above.

[0065]

According to the digital camera of the present invention in which image data is generated only by the first function when the ratio of the portion of the object to be photographed whose luminance is equal to or lower than the predetermined value is equal to or higher than the predetermined value, When capturing an image of a backlit scene, when it is desired to obtain an image that represents only the brightness difference of the subject, it is possible to provide an image that reflects the intention, and also to ensure a quick shooting property, and to provide a photo opportunity. The risk of missing is reduced.

The luminance of the first region located in the periphery of the object to be photographed is equal to or less than a predetermined value, and the second region and the first region of the object to be photographed which are closer to the center than the first region. The digital camera of the present invention, which generates image data only by the first function when the luminance difference from the region is equal to or more than a predetermined value, has the same effect in shooting a backlight scene.

Further, a plurality of photometric elements having a wider dynamic range than the image pickup element are provided, and it is determined which of the first function and the second function generates image data based on an output signal of the photometric element. With the digital camera of the present invention, it is possible to know the luminance distribution of the object to be photographed, so that unnecessary generation of image data by the second function can be avoided. In addition, by using a photometric element having a wider dynamic range than the image sensor, it is possible to accurately know the amount of exposure to be set in photographing with the second function, thereby reliably achieving the purpose of the second function. Can be. Further, since the photometry can be performed separately from the photographing, the quick shooting performance is secured, and the risk of missing a photo opportunity is reduced.

[Brief description of the drawings]

FIG. 1 is an exemplary perspective view schematically showing the appearance of a digital camera according to first and second embodiments.

FIG. 2 is a rear view schematically illustrating the appearance of the digital camera according to the first and second embodiments.

FIG. 3 is a diagram schematically illustrating a positional relationship between a photometry unit and an image sensor with respect to a shooting target of the digital camera according to the first and second embodiments.

FIG. 4 is a block diagram schematically illustrating an outline of a circuit configuration of the digital camera according to the first embodiment.

FIG. 5 is a view showing an example of a histogram created by the digital camera according to the first embodiment.

FIG. 6 is an exemplary flowchart showing an outline of the flow of processing from shooting of an image to recording of image data in the digital camera of the first embodiment.

FIG. 7 is a flowchart showing an outline of the flow of processing from capturing an image to recording image data in the digital camera according to the second embodiment.

FIG. 8 is a view showing the principle of the gradation enlarging process of the digital camera according to the first and second embodiments.

FIG. 9 is a view showing an example of a backlight scene.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 2 Digital camera 11 Photographing lens 12 Photometric lens 13a, 13b Finder window 14 Release button 15 Liquid crystal panel 16a, 16b Operation key 17 Liquid crystal panel 18 Operation key 19 Recording medium insertion port 20 Image sensor 21 Photometry unit 22 Photometry device 31 Analog Processing unit 32 A / D converter 33 White balance adjustment unit 34 γ correction unit 35 Color interpolation unit 36 Compression unit 37 Interface 38 CPU 39 Image synthesis unit 40 RAM 41 Histogram creation unit 42 Operation unit 50 Recording medium

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // H04N 101: 00 F term (Reference) 5C022 AA13 AB02 AB17 AC03 AC42 AC52 5C024 BX01 CX43 CX47 CX54 CY17 CY45 DX04 EX13 HX28 HX55 HX56 HX57 5C053 FA08 GB21 HA33 KA04

Claims (5)

[Claims] 1. A digital camera that captures an image by exposing an image sensor and generates image data representing the captured image from an output signal of the image sensor. A first function of generating image data from an output signal of the image sensor at the time of image capturing, and capturing a plurality of images with different exposure amounts, and combining the output signals of the image sensor at the time of capturing the plurality of images. A second function of generating image data in which the difference in signal intensity exceeds the dynamic range of the image sensor. When the ratio of the portion of the object to be photographed whose luminance is equal to or less than the predetermined value is equal to or more than the predetermined value, A digital camera that generates image data only by a first function. 2. A digital camera that captures an image by exposing an image sensor and generates image data representing the captured image from an output signal of the image sensor. A first function of generating image data from an output signal of the image sensor at the time of image capturing, and capturing a plurality of images with different exposure amounts, and combining the output signals of the image sensor at the time of capturing the plurality of images. A second function of generating image data in which the difference in signal intensity exceeds the dynamic range of the imaging device, wherein the luminance of a first region located in the periphery of the imaging target is equal to or less than a predetermined value, In addition, when the luminance difference between the second area and the first area, which are closer to the center than the first area, is equal to or more than a predetermined value, image data is generated only by the first function. Specially Digital camera to be. 3. The digital camera according to claim 1, wherein the luminance of the object to be photographed is obtained from an output signal of the image sensor. 4. The digital camera according to claim 1, further comprising a plurality of photometric elements having a wider dynamic range than the image sensor, and obtaining a luminance of an object to be photographed from an output signal of the photometric element. 5. A digital camera that captures an image by exposing an image sensor and generates image data representing the captured image from an output signal of the image sensor, wherein one digital image is captured and the image is captured. A first function of generating image data from an output signal of the image sensor at the time of image capturing, and capturing a plurality of images with different exposure amounts, and combining the output signals of the image sensor at the time of capturing the plurality of images. A second function of generating image data in which the signal intensity difference exceeds the dynamic range of the image sensor, comprising a plurality of photometric devices having a wider dynamic range than the image sensor, based on an output signal of the photometric device. And determining whether the first function or the second function generates the image data.