JPH1169226A - Electronic camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce random noise and fixed noise through overlapping processing of a plurality of images. SOLUTION: When a 1st image is written in an arithmetic memory (S1), gradation conversion is made (S2), and a value (n) denoting the number of images is reset to zero (S3). Then data of an even numbered line of the n-th image are written in the arithmetic memory (S4), and the data are added to corresponding data in the arithmetic memory after gradation conversion (S5). Similarly, data of an add numbered of lines of the n-th images are added (S6, S7). The number (n) is counted up (S8), and the sum processing is repeated until the count reaches 15 (S9 → S4). When the number of overlapped images reaches a specified number (S9), processing of eliminating fixed noise is conducted (S10), and various image processings are conducted (S11) and final image data are stored in a recording memory.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic camera,
More specifically, the present invention relates to a technique for reducing noise in an image signal.

[0002]

2. Description of the Related Art In recent years, an optical image of a subject has been captured by an imaging lens,
An image is formed on a two-dimensional solid-state imaging device (photoelectric conversion device) such as a CCD via an optical imaging system such as an aperture, and an electric image signal that is photoelectrically converted and output by the imaging device is converted into digital data and recorded. Electronic cameras configured to store the data on a medium have been put to practical use.

[0003] In addition, an accumulation time in the photographing means is set, and when the accumulation time is longer than a predetermined time, two or more images are continuously photographed, a plurality of images are added and synthesized in a memory, and one image is obtained. An electronic still camera which outputs the image data is disclosed in Japanese Patent Publication No. Hei 7-38701.

[0004]

SUMMARY OF THE INVENTION In the above prior art,
When the shutter speed is a slow shutter of a predetermined time or more, the image is synthesized by performing shooting twice or more consecutively,
Even when shooting can be performed at a normal shutter speed, in a subject including high brightness and low brightness, image data may be saturated in a high brightness portion, and random noise due to dark current may be conspicuous in a low brightness portion. The conventional camera described above cannot handle such a subject.

In a CCD using complementary color (including yellow, cyan, and magenta) color filters, the spectral characteristics of the color filters overlap with each other, resulting in poor color separation, and color noise in a color-converted image. There are noticeable drawbacks. This color noise also occurs in a subject that can be photographed at a normal shutter speed, and cannot be handled by a conventional camera.

Further, when a low light quantity subject is photographed, C
The color balance of the image may be lost due to the variation in the sensitivity characteristic of the CD. The sensitivity characteristic of the CCD is that each color changes linearly in the normal illuminance region, but is not linear in the low illuminance region. Therefore, if the color balance is adjusted in the normal illuminance region, the balance in the low illuminance region is lost. Also,
The above-mentioned conventional camera requires an adder and a plurality of memories in order to access the memory at a high speed, which increases the cost.

Further, when images of the same subject are superimposed, there has been a problem that fixed noise generated at the time of capturing an image becomes relatively large. SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to enable an electronic camera to easily execute a superposition process for reducing random noise.

Another object of the present invention is to make it possible to avoid an increase in fixed noise due to superposition when the superposition processing is performed in an electronic camera.

[0009]

According to the present invention, there is provided an electronic camera configured to convert an optical image of a subject into an image signal by a photoelectric conversion element and record the image signal on a recording medium. The number of images is set, and a plurality of images of the same subject are superimposed and stored as one image.

According to this configuration, the number of images to be photographed is set in advance, the same object is photographed by the set number of images, and these images are superimposed to reduce random noise. According to the second aspect of the present invention, the fixed pattern noise is removed from the image obtained by superimposing the plurality of images. According to such a configuration, fixed noise generated in a fixed pattern is removed from the superimposed images.

According to the third aspect of the invention, the fixed pattern noise is set based on an image signal obtained by photographing a true-dark image. According to such a configuration, for example, an image signal corresponding to a true-dark image is obtained by photographing in a state where light is shielded by a lens cap or a mechanical shutter, and this image signal is used as fixed pattern noise.

When the fixed pattern noise is substantially the same for each line, the fixed pattern noise may be set as one-dimensional data. In the invention according to claim 4,
The fixed pattern noise is removed simultaneously with the black reference setting. According to such a configuration, the fixed pattern noise is removed at the same time when the black reference is set.

[0013] According to a fifth aspect of the present invention, the data bit width of the superimposed image is made wider than the data bit width of the photographed image. According to such a configuration, for example, when the captured image is 10-bit data, the data bit width of the superimposed image is set to, for example, 16 bits, thereby coping with an increase in data due to the addition processing.

According to the sixth aspect of the present invention, one image is read from the photoelectric conversion element in a plurality of times. According to such a configuration, one image is not read at once, but is read a plurality of times. According to the seventh aspect of the present invention, one memory has an area for superimposing an image of one screen and an area for storing an image read from the photoelectric conversion element.

According to this configuration, the storage area for the photographed image and the work area for superimposition coexist in one memory. In the invention according to claim 8, two memories, a first memory and a second memory, are provided, and a header is attached to each image and recorded in the first memory. Transferring the image to the second memory,
It was configured to superimpose images.

According to this configuration, the photographed image is
First, a header is added and recorded in the first memory, and the superposition of images is performed by transferring the contents of the first memory to the second memory. In the invention according to claim 9, the first
When recording to the memory, the image is compressed.

According to this configuration, the photographed image is image-compressed and recorded in the first memory, and then transferred to the second memory during the superimposition processing. According to the tenth aspect of the present invention, the header includes a tag indicating that the image is a superimposed image. According to this configuration, when the captured image is recorded in the first memory, a tag indicating whether the image is a superimposed image is included in the header,
A distinction is made between a normal captured image and an image to be superimposed.

According to the eleventh aspect of the present invention, the number of photographed images is determined from the free space of the first memory. According to this configuration, the number of images to be photographed for the same subject is determined from the size of the free space in the first memory for recording the photographed image. In the invention according to claim 12, the electronic camera is an electronic camera that performs color photographing by combining a photoelectric conversion element and a mosaic color filter, and performs the gradation conversion and superimposition processing of the plurality of images by interpolation. The configuration is such that the image obtained through the mosaic color filter before the processing is performed as it is.

According to this configuration, for example, in an electronic camera that forms an optical image of a subject on a photoelectric conversion element through a color filter in which RGB filters are arranged in a mosaic pattern, an image signal obtained through the color filter is Interpolation is performed to separate image signals for each color based on the image signal. However, tone conversion and superimposition are performed with the image signal in which the data of each color is arranged in a mosaic before the interpolation is performed.

According to a thirteenth aspect of the present invention, the gradation conversion processing is performed on the image signal after the superposition. According to this configuration, after the captured images are superimposed, a gradation conversion process such as gamma conversion is performed on the superimposed images. For example, in an electronic camera or the like using the mosaic color filter, it is necessary to perform gradation conversion processing after performing color separation. However, since the amount of information of an image increases due to the color separation, the gradation conversion processing is performed by superposition processing. In the configuration performed before the above, as a result, the amount of information for performing the superimposition processing is increased. Therefore, the gradation conversion processing is performed after the superposition is performed, and the memory capacity required for the superposition processing is reduced.

According to a fourteenth aspect of the present invention, a gradation conversion process is performed on an image from which the fixed pattern noise has been removed. According to such a configuration, the processing proceeds in the order of image superposition processing, removal of fixed pattern noise, and gradation conversion processing, and gradation processing is performed on the image from which random noise and fixed noise have been removed.

According to a fifteenth aspect of the present invention, a gradation conversion process dedicated to low light quantity is performed before the plurality of images are superimposed. According to such a configuration, tone conversion processing with characteristics suitable for photographing a subject with a small amount of light is performed before superimposition.

[0023]

According to the first aspect of the present invention, since images are superimposed in accordance with the set number, random noise can be reduced even for a subject which can be photographed at a normal shutter speed. In the invention according to claim 2,
Random noise can be reduced by superimposing images with a small memory capacity, and fixed noise can be reduced.

According to the third aspect of the present invention, fixed pattern noise peculiar to each electronic camera can be easily obtained, so that fixed noise can be effectively reduced. Claim 4
In the described invention, the amount of calculation does not increase by removing the fixed pattern noise simultaneously with the black reference setting. According to the fifth aspect of the invention, when the superimposition processing is performed by the addition processing, it is possible to prevent an overflow of the added value and to avoid the gradation deterioration.

According to the sixth aspect of the present invention, even when the memory capacity is small, the area for storing the image read from the photoelectric conversion element is reduced, so that it is possible to perform the calculation without changing the circuit groove configuration. Superposition processing can be performed without having a plurality of memories, and random noise can be reduced. In the invention according to claim 7, since an adder is not required,
There is no need to change the conventional circuit configuration. In addition, since the superimposition processing and the capture of the image from the photoelectric conversion are performed by one memory, the superposition of the images can be performed without increasing the cost.
Random noise can be reduced.

According to the eighth aspect of the present invention, the superimposed image can be divided and written in a plurality of memories, and the superimposed image can be transferred to a computer for processing. . According to the ninth aspect of the present invention, the number of images that can be written to the first memory increases by compressing the images.

According to the tenth aspect of the present invention, it is possible to identify an image to be superimposed by searching for a tag in the header. According to the eleventh aspect of the present invention, since the number of shootable images is managed by the camera, the user does not need to calculate the free space in the memory and set the number of shootable images. Claim
According to the invention described in 12, the superimposition process is performed as it is on the image obtained through the mosaic color filter, so that the amount of information during image processing is rarely reduced.

According to the thirteenth aspect of the present invention, by performing the gradation processing after the superposition, the information amount of the image handled in the superposition processing can be suppressed, and the memory capacity used in the superposition processing can be reduced. . In the invention according to claim 14,
By removing fixed noise and performing gradation processing, there is no need to perform fixed noise gradation processing compared to the method of removing fixed noise after performing gradation processing, so the calculation time can be reduced. it can.

According to the fifteenth aspect of the present invention, it is possible to correct the color balance collapse due to a low light quantity. Further, by performing the gradation conversion before the superposition, it is possible to avoid a decrease in the number of gradations.

[0030]

Embodiments of the present invention will be described below. FIG. 1 is a diagram illustrating a basic configuration of an electronic camera according to an embodiment. In FIG. 1, an optical image from a subject is transmitted through a photographing lens 2 to C as a photoelectric conversion element.
An image is formed on the CD 1, and the CCD 1 photoelectrically converts the optical image of the subject into an electric signal.

The CCD 1 is illuminated with an optical image of a subject through various filters. Examples of the various filters include a low-pass filter that passes only a low spatial frequency band, and an infrared ray cut filter. A mosaic color filter composed of a combination of an infrared cut filter and a color filter such as RGB or CMYG is used.

The electronic camera according to the present embodiment is
This is a so-called single-panel color electronic camera. When a combination of RGB color filters is used as the mosaic color filter, only one of R, G, and B information is provided for each pixel of the CCD 1 (646 × 484 pixels in the present embodiment). Is obtained, R, G, and B data are obtained for each pixel by interpolation, and separated into image signals for each of R, G, and B colors.

The image signal from the CCD 1 is CDS /
After the AGC circuit 3 performs the correlated double sampling process and the amplification process, the A / D converter 4 performs A / D conversion. A
The / D-converted image data is subjected to various types of image processing by software processing by the Main-CPU 5, and is recorded in the recording memory 6. As a memory, a parameter storage memory 7 and an operation memory 8 are provided in addition to the recording memory 6.

The image compression circuit 9 is a circuit for compressing and recording image data, and
, Display of a photographed image and photographing information is performed. Sub
-The CPU 11 is configured to be able to communicate with the Main-CPU 5 while receiving signals from the mode switch 12 and the power switch 13 and receiving the signals from the CCD drive circuit 14, the CDS / AGC.
A timing generation circuit 15 for outputting a timing signal to the circuit 3 and the A / D converter 4;
Control 16

A description will be given of a photographing process in which a plurality of images of the same subject are superimposed and stored as one image in the above configuration. A first aspect corresponding to the invention of claim 7
In the embodiment, first, the number of images to be shot is set by the mode switch 12 in FIG. And take the first image,
All the pixels (710 × 484) of the first image data are written into the operation memory 8. This memory is usually DRA
M is used. As shown in FIG. 2, this image has an optical black area from the 647th pixel to the 710th pixel of each line. The optical black area is shielded from light, and a later-described black reference calculation is performed using the pixel data in this area.

In the following, a case where a subject with a low light quantity is photographed will be described. The image data is subjected to gradation conversion exclusively for low light quantity by the Main-CPU 5. This gradation conversion table is
It is recorded in the parameter recording memory 7. As this memory, an EEPROM, a flash memory, or the like is used. Then, the gradation-converted 10-bit image data is stored in the calculation memory 8 with a 16-bit width per pixel. This memory area is for storing a superimposed image obtained by the addition processing. By making the bit width of the superimposed image wider than the bit width (10 bits) of the image data, the occurrence of overflow due to the addition processing is prevented. In the present embodiment, since the number of superimposed sheets is 16 as described later, the occurrence of overflow is reliably avoided.

Next, the second image is photographed, and only the data of the even-numbered line of this image is read and written in the empty area of the operation memory 8. This image data is stored in Main-C in the same manner as the first sheet.
The gradation is converted by the PU 5 and added to the corresponding pixel in the area where the first image is stored. Next, only the image data of the odd line is read and stored in the area where the image data of the even line has been written. Similar to the image data of the even-numbered line, after the gradation conversion, it is added to the corresponding pixel of the superimposed image.

Then, in the same manner as in the second image, the third and subsequent images are sequentially superimposed on the superimposed images stored in the operation memory. In this way,
In the case of software processing using a CPU, superposition can be performed without using an adder or a plurality of memories. Also,
If there is room in the operation memory 8, a photoelectric conversion element (CCD)
From 1), it is also possible to read the image data at one time. In addition, if image data can be read from the photoelectric conversion element in pixel units or line units, a configuration may be adopted in which only one line of image data is read.

The DRA is internally provided as the Main-CPU 5.
If a RISC-MPU equipped with M is used, image data can be accessed with an internal clock, so that high-speed arithmetic processing is also possible. In the second embodiment corresponding to the invention of claim 8, after the taken image is read into the arithmetic memory 8,
The image data is added to the header and written into the recording memory 6. This memory may be built-in or detachable. For this, a flash memory or a floppy disk is usually used. A tag indicating that the image is a superimposed image is attached to this header, and after all the images have been photographed, image data is called from the recording memory 6 (first memory) to the arithmetic memory 8 and superimposed.

In this configuration, the Sub-CPU 11 manages the capacity of the image data recorded in the recording memory 6. Then, the number of recordable images based on the free space of the recording memory 6 is displayed on the liquid crystal display device 10, and the number of images less than the number is set. The last photographed image is stored in the recording memory 6.
Without recording on a pixel, performs gradation conversion exclusively for low light quantity,
A 6-bit width is stored in an area of the arithmetic memory to be superimposed. Then, the tag of the header of the image data in the recording memory 6 is searched, and the photographed image is read into the arithmetic memory 8 line by line. Then, gradation conversion is performed, and addition is performed with the corresponding pixel of the superimposed image.

By adopting such a configuration, it is possible to perform the superposition even when the area where the image read from the photoelectric conversion element cannot be secured is not secured. The CCD can usually read image data only on the entire screen or in field units. However, since the recorded image data can be read in byte units, the area secured in the arithmetic memory 8 is small. Good.

When writing the captured image data into the recording memory 6, the image data can be compressed by the image compression circuit 9. Since the amount of information needs to be preserved for the image before superimposition, lossless compression such as run-length encoding is performed. Further, in this configuration, it is not necessary to superimpose the photographed image data immediately after photographing. For example, if a detachable memory is used as the recording memory 6, even if one memory becomes full, a plurality of recordings can be performed. It is possible to write data separately for the memory 6. Further, the recording memory 6
Can be transferred to a computer (second memory of the computer), and can be superimposed by software on the computer. By adopting such a configuration, the same processing can be realized by software on a computer even when the overlay processing cannot be performed in the arithmetic memory 8.

For example, in a case where 16 images of the same subject are set to be superimposed, when the process of superimposing the 16th image on the image on the arithmetic memory 8 is completed,
A calculation process is performed to subtract a value corresponding to the fixed pattern noise from each line of the image data on the calculation memory 8 on which the 16 images are superimposed. When a plurality of (16) images of the same subject are superimposed as described above, the random noise is reduced, but the fixed noise becomes relatively large. The noise is removed by subtracting the fixed pattern noise. The removal of the fixed pattern noise can be performed simultaneously with the black reference setting. The black reference setting is a process of subtracting the signal level of the transfer path of the CCD and setting the 0 reference of the image signal. This is usually performed by calculating the average value of the optical black area in FIG. 2 and subtracting the average value from the image data.

Here, the fixed pattern noise corresponds to FIG.
The signal of the CCD driving circuit is superimposed on the image data. This fixed pattern noise is one-dimensional data h
(X), which is stored in the parameter storage memory. Let the coordinates of each pixel be (x, y),
Assuming that the output image data is f (x, y) and the superimposed image data is g (x, y), the arithmetic processing for removing the fixed pattern noise is f (x, y). = G (x, y) −n × h (x) + a. Here, n represents the number of shots, and a represents the average value of the optical black area.

The image data from which the fixed pattern noise has been removed is subjected to color conversion and gamma conversion (gradation conversion processing), and then each pixel is written to the recording memory 6 as 8-bit data for each color. With a configuration in which gradation conversion processing such as gamma conversion is performed after the fixed pattern noise is removed, when the captured image has low contrast, a high-contrast image is obtained without lowering the gradation of the output image. It is possible.

FIG. 7 is a flowchart showing the calculation processing in the first embodiment. When the first image is written into the calculation memory 8 (S1), gradation conversion is performed (S2).
N indicating the number of images is reset to zero (S3). Then, the data of the even-numbered line of the n-th image is written into the calculation memory 8 (S4), and a process of adding the data to the corresponding data in the calculation memory 8 after gradation conversion is performed (S5). Next, the data of the odd-numbered line of the n-th image is written into the calculation memory 8 (S6), and a process of adding the data to the corresponding pixel of the calculation memory 8 after gradation conversion is performed (S7).

When the addition processing of one image is performed, the number n is counted up (S8), and the addition processing is repeated until the counted-up number becomes 15 (S9 → S4). When the number of superimposed images reaches the specified number (S9), a process of subtracting fixed noise from superimposed image data stored in the calculation memory 8 is performed (S10), and further, interpolation processing, color conversion, and gamma Conversion (gradation conversion processing) is performed (S11), and the finally obtained image data is stored in the recording memory 6.

FIGS. 8 and 9 are flowcharts showing the arithmetic processing according to the second embodiment of the present invention, in which the number n of superimposed images is reset to zero (S1).
2) When the first image is written into the calculation memory 8 (S1
3) Insert a tag indicating that the image is a superimposed image with a header (S14). Then, the recording memory 6
(S13), and the number n of images is counted up (S16). The writing is repeated until the counted number reaches 15 (S
17 → S13).

When the number of superimposed images reaches the specified number (S17), the 16th image data is written into the arithmetic memory 8 (S18), and gradation conversion is performed (S19). Then, the number n of images and the number m of lines to be superimposed are reset to zero (S20, S21). Next, the image data of the m-th line of the n-th image is written in the calculation memory 8 (S22), and a process of adding the image data to the corresponding line on the calculation memory 8 after gradation conversion is performed (S23). .

When the addition processing is performed for each line,
The number m of lines is counted up (S24), and the addition process for each line is repeated until the number of lines counted up becomes 484 (S25 → S22). When the addition process for the last line is completed and the number m of lines becomes 484 (S25), the number n of images is counted up in order to superimpose the next image (S25).
26) until the number reaches 15 which is the specified number (S
27 → S22), the process of sequentially adding the image data from the first line (m = 0) to the last line (m = 483) to the corresponding line of the superimposed image up to that point is repeated.

When the number of superimposed images reaches the specified number (S27), a process for subtracting fixed noise from the superimposed image data stored in the operation memory 8 is performed (S27).
28) Further, interpolation processing, color conversion, and gamma conversion (gradation conversion processing) are performed (S29), and the finally obtained image data is stored in the recording memory. In the above description, the number of images to be superimposed is fixed. However, photographing may be interrupted immediately before an overflow occurs due to addition of data to reduce the number of superimposed images, and the number of images to be superimposed can be set arbitrarily. You may do it.

If the memory capacity is small and the calculation cannot be performed for all the pixels with the bit width (8 bits) or more of the output pixel, the image is reduced (pixels are thinned out) and the above processing procedure is executed. You can make it happen. Furthermore, when the memory capacity is small and the calculation cannot be performed with the bit width (8 bits) of the output pixel or more, the calculation is performed with the bit width of the output pixel and the division according to the number of photographed images is performed, thereby superimposing. May be obtained.

When arithmetic averaging is used as a method of superposition, the number of shots is reduced to 2 in order to reduce the calculation time.
Averaging may be performed by a bit shift operation as a power of. On the other hand, the fixed pattern noise corresponds to CC in FIG.
The signal of the D drive circuit 14 is generated by being superimposed on the image data.
This appears as a vertical streak in the image as shown in FIG.

For this noise, at the time of product shipment, means such as taking a picture in a dark room, taking a picture with a cap or a lens barrier on the lens surface, or taking a picture with an electronic shutter with the mechanical shutter closed. To photograph a true-dark image. Then, the Main-CPU 5 performs gradation conversion dedicated to low light quantity. This image data is averaged in the vertical direction, then the average value of the optical black area of the CCD 1 is obtained, and the average value is subtracted from the one-dimensional data. And apply a low-pass filter to this data,
Reduces high frequency noise. This is stored in the parameter storage memory 7 of FIG. 1 as average data of fixed pattern noise.

Further, in order to cope with a change over time, the user can photograph a pure dark image before or after photographing, or periodically, and update the fixed pattern noise. This can be done automatically by the camera when the power switch is turned on. In the case of using a mosaic color filter as in the present embodiment, if the image obtained by the CCD 1 is subjected to a superposition process before color separation by performing an interpolation operation or the like, the superposition process is performed. The amount of data to be processed is reduced, and the memory capacity can be saved. Then, after overlapping, color separation is performed.
Tone conversion processing such as gamma conversion is performed on the color-separated image signal.

The configuration may be such that the gradation conversion processing is performed before the superposition processing. In this case, however, it is necessary to generate the image signal by performing the above-described processing such as color separation before the gradation processing. As a result, the amount of information to be superimposed increases, and the memory capacity used also increases. However, if the configuration is such that the gradation conversion is performed before the superposition processing, it is possible to avoid a decrease in the number of gradations of the captured image data. In the present embodiment, a 10-bit input / output gradation conversion table is used. In a region where the slope of this characteristic is 1 or more (left side of the boundary line in FIG. 10), a sample of the gradation characteristic with respect to the output value is coarse. Therefore, the number of gradations decreases. Therefore, by performing the superposition after the gradation conversion, this image deterioration can be compensated and the decrease in the number of gradations can be avoided.

That is, the tone conversion processing before the superposition causes an increase in the amount of information due to processing such as color separation, so that it is necessary to increase the memory capacity to be used. Conversely, in the gradation conversion processing after the superposition, the superposition is performed before the processing such as the color separation is performed. This causes a decrease in the number of tones.

In the gradation conversion such as the above-mentioned gamma conversion, a gradation conversion table suitable for a subject with a low light quantity is provided in advance. It is preferable that the conversion is performed by using the conversion table dedicated to low light quantity. C
The sensitivity characteristics of the CD have different characteristics for each color, but since the variation is not linear in the low illuminance area as shown in FIG. 4, even if the color balance is adjusted in the normal illuminance area, the sensitivity is lost in the low illuminance area. In addition, as shown in FIG. 5, when a normal gradation conversion table is used, the variation may be large. Therefore, by using a gradation conversion table dedicated to low light quantity as shown in FIG. 6, it is possible to correct variations in the low illuminance area.

The superimposed images may be photographed one by one based on the operation of the release switch by the photographer. When the release switch is operated once, the expected number of images is reduced. A configuration in which an image is automatically taken may be used.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram of an electronic camera according to an embodiment.

FIG. 2 is a diagram showing a mosaic color filter and an optical black area in the embodiment.

FIG. 3 is a diagram illustrating a state of fixed pattern noise.

FIG. 4 is a diagram showing sensitivity characteristics of a CCD.

FIG. 5 is a diagram showing output characteristics of a CCD and characteristics of normal gradation conversion.

FIG. 6 is a diagram showing output characteristics of a CCD and characteristics of gradation conversion dedicated to low light intensity.

FIG. 7 is a flowchart illustrating a state of a superimposing process according to the first embodiment;

FIG. 8 is a flowchart illustrating a state of a superimposing process according to the second embodiment.

FIG. 9 is a flowchart illustrating a state of a superimposition process according to the second embodiment;

FIG. 10 is a diagram illustrating characteristics of a gradation conversion table.

[Explanation of symbols]

 Reference Signs List 1 CCD 2 shooting lens 3 CDS / AGC circuit 4 A / D converter 5 Main-CPU 6 recording memory 7 parameter storage memory 8 operation memory 9 image compression circuit 10 liquid crystal display device 11 Sub-CPU 12 mode switch 13 power supply Switch 14 CCD drive circuit 15 Timing generation circuit 16 Exposure control circuit

Claims (15)

[Claims] An electronic camera configured to convert an optical image of an object into an image signal by a photoelectric conversion element and record the image signal on a recording medium, wherein the number of images to be photographed is set, and a plurality of images of the same object are photographed. An electronic camera wherein images are superimposed and stored as one image. 2. The electronic camera according to claim 1, wherein fixed pattern noise is removed from an image obtained by superimposing the plurality of images. 3. The electronic camera according to claim 2, wherein said fixed pattern noise is set based on an image signal obtained by photographing a true-dark image. 4. The electronic camera according to claim 2, wherein the removal of the fixed pattern noise is performed simultaneously with the black reference setting. 5. A data bit width of the superimposed image,
The electronic camera according to any one of claims 1 to 4, wherein the data bit width is wider than a data bit width of a captured image. 6. The method according to claim 1, wherein the reading of one image from the photoelectric conversion element is performed a plurality of times.
The electronic camera according to any one of the above. 7. The memory according to claim 1, wherein one memory has an area for superimposing an image of one screen and an area for storing an image read from the photoelectric conversion element. An electronic camera according to claim 1. 8. An image processing apparatus comprising two memories, a first memory and a second memory, wherein a header is attached to each image and recorded in the first memory. The electronic camera according to any one of claims 1 to 6, wherein the electronic camera is transferred to a second memory to superimpose images. 9. The electronic camera according to claim 8, wherein an image is compressed when recording to said first memory. 10. The electronic camera according to claim 8, wherein a tag indicating that the image is a superimposed image is included in the header. 11. The electronic camera according to claim 8, wherein the number of photographed images is determined from a free space of the first memory. 12. The electronic camera according to claim 1, wherein the electronic camera performs color photographing by combining a photoelectric conversion element and a mosaic color filter, and performs a gradation conversion and a superposition process of the plurality of images by performing an interpolation process. The electronic camera according to any one of claims 1 to 11, wherein the processing is performed with an image obtained through a previous mosaic color filter. 13. The image processing apparatus according to claim 1, wherein a gradation conversion process is performed on the image signal after the superimposition is performed.
12. The electronic camera according to any one of items 11 to 11. 14. The image processing apparatus according to claim 2, wherein a gradation conversion process is performed on the image from which the fixed pattern noise has been removed.
5. The electronic camera according to any one of 4. 15. The method according to claim 1, wherein a gradation conversion process dedicated to a low light amount is performed before the plurality of images are superimposed.
12. The electronic camera according to any one of items 11 to 11.