JPH11317905A - Digital camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To photograph a picture with a wide dynamic range. SOLUTION: An image with proper exposure, an image with excess exposure and an image with underexposure are recorded by one time photographing. Three image data are weighted depending on luminance recorded at proper exposure so that a heavier weight is given to the image with underexposure at a dark part and a heavier weight is given to the image with excess exposure at a bright part and synthesis data are calculated for each dot. Thus, part of the image with proper exposure having been deformed in black is corrected brighter because a heavier weight is applied to the image with excess exposure so as to reproduce gradation of the dark part, and part of the image with proper exposure having been disappeared in white is corrected darker because a heavier weight is applied to the image with underexposure so as to reproduce gradation of the bright part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital camera for recording a captured image as digital data.

[0002]

2. Description of the Related Art Conventionally, when taking a photograph, a camera has been used in which light taken in from a lens is irradiated onto a film and a chemical reaction occurs to record an image. With the above camera, a photograph can be printed by developing the film and printing it on photographic paper. Since the reaction of silver chloride is generally used as the above chemical reaction, a photograph taken by such a camera is called a silver halide photograph. A silver halide photographic film can record light and dark gradation differences in a wider range than a human can perceive. That is, since it has a wide dynamic range, even when the aperture and the shutter speed are fixed like a film with a lens, it is possible to print properly by adjusting at the time of printing.

On the other hand, in recent years, digital cameras that convert light into an electric signal by an optical sensor such as a CCD, convert the light into a digital signal, and then record the digital signal on a recording medium such as a flash memory have become widespread. With a digital camera,
Using a personal computer or the like, images can be stored and various processes can be easily performed by individuals, and photographs can be printed without developing the film by outputting to a printer. With the improvement of the printing quality of printers, it has become possible to print high-quality photographs that are almost indistinguishable from silver halide photographs.

[0004]

However, CCDs used in the above-mentioned conventional digital cameras generally have a narrow dynamic range as compared with silver halide photographic films.
It is almost equivalent to the range that humans can recognize. Therefore, if you adjust the exposure incorrectly during shooting, the whole image will be white,
Sometimes it turns black. Even if the brightness or contrast of an image is changed using image processing software, it is impossible to extract more information than the information input from the camera, and it is not possible to reproduce the gradation of bright or dark parts. was there.

When the difference in brightness is extremely large, for example, when a person in front of a window and a scene outside the window are simultaneously photographed, if the exposure is adjusted so that the person is properly photographed, the outside scene becomes It becomes too bright and white, and adjusting the exposure to the outside scenery makes the person too dark. This is a problem that also occurs in silver halide photography.

Accordingly, it is an object of the present invention to provide a digital camera capable of recording image data with a wide dynamic range.

Another object of the present invention is to provide a digital camera capable of recording an image in which both a bright portion and a dark portion can be properly viewed even if the difference in brightness is very large.

[0008]

According to a first aspect of the present invention, there is provided a digital camera including a means for recording a plurality of images in the same range with different exposures, so that an image which is overexposed in one photographing operation is provided. And an underexposed image can be recorded. Therefore, the user can select an image with the optimal exposure from a plurality of images. Also, by using an underexposed image for the part that is too bright and flying off white, and combining an overexposed image for the part that is too dark and underexposed, the difference in brightness is extremely small. Even in a very large image, an image in which both bright and dark portions look appropriate can be obtained.

According to the digital camera of the present invention, a plurality of images in the same range are continuously recorded with different exposures. An image with overexposure and an image with underexposure can be recorded in a single photographing without increasing the memory. The exposure can be changed by changing the accumulation time of the CCD for each image or by changing the aperture of the lens.

According to the digital camera of the third aspect of the present invention, a plurality of optical sensors for reading images in the same range are provided, and the exposure is changed for each optical sensor. Images and underexposed images can be recorded. The exposure can be changed by using a plurality of CCDs having different sensitivities as the optical sensors or by making the accumulation times of the CCDs different.

According to the digital camera of the present invention, since there is provided a means for synthesizing one image data from a plurality of image data recorded by changing the exposure, the capacity of the recording medium can be saved. Can be.

According to the digital camera of the present invention, the weight of the overexposed image data is increased in the range of low brightness in the image, and the weight of the underexposed image data is increased in the range of high brightness. The image data is synthesized by increasing the weight. Therefore, an underexposed image is used with a large weight for portions that are too bright and fly white when properly exposed, and overexposed for portions that are too dark and darkened when properly exposed. One image in which the images are used with a large weight can be combined.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below in detail with reference to the drawings using a plurality of examples.

(First Embodiment) FIG. 2 is a block diagram for explaining the structure of a digital camera 1 according to a first embodiment of the present invention. A control device 11, a condenser lens 12, a charge coupled device (CCD) 13 as an optical sensor, an A / D converter 14, a random access memory (RAM) 15 for temporarily recording image data as a recording medium, and recording image data. And an interface 17 for outputting the contents of the flash memory 16 to an external personal computer 20 or the like. The control device 11 is a CP
U, a ROM in which programs for performing various controls of the digital camera 1 are recorded, and input / output means.

Next, the operation of the digital camera 1 of this embodiment will be described.

When the user presses the shutter of the digital camera 1, all the charges accumulated in the CCD 13 are once discharged, and then the light collected by the condenser
The signal is input to the CD 13 and converted into an electric signal. The aperture of the condenser lens 12, the shutter speed, that is, the CCD 1
The storage time of No. 3 is controlled to an appropriate value automatically by the control device 11 or by a user's instruction. The exposure at this time is defined as an appropriate exposure. As the shutter of the digital camera 1, a shutter that physically blocks light or an electronic shutter of the CCD 13 can be used. As the CCD 13, for example, R (Red), G (Green),
By using a CCD 13 in which a plurality of pixels having a primary color filter of B (Blue) are arranged in a matrix,
Color images can be taken. C (Cyan), M
In some cases, a CCD having complementary color filters of (Magenta), Y (Yellow), and G (Green) is used. The complementary color filter may have three colors of C, M, and Y in some cases.

The electric signal output from the CCD 13 is A
The signal is converted into a digital signal by the / D converter 14. A /
The digital data output from the D converter 14 is transferred to the control device 1 by DMA (Direct Memory Access) for speeding up.
The data is recorded by directly specifying the address of the RAM 15 without passing through the address 1. As the RAM 15, a DRAM having a self-refresh function can be used.

Next, by increasing the aperture value of the condenser lens 12 or shortening the accumulation time of the CCD 13, the exposure is made lower than the proper exposure, and the data after A / D conversion is converted in the same manner as described above. The data is recorded in the RAM 15. Further, the aperture value of the condenser lens 12 is reduced, or C
By extending the accumulation time of the CD 13, the exposure is made longer than the proper exposure, and the data after A / D conversion is recorded in the RAM 15 in the same manner as described above. With this, RAM
In 15, three image data are recorded with different exposures.
That is, it is possible to record the image data of the proper exposure, the image data of the underexposure, and the image data of the overexposure in the RAM 15 in one photographing.

Next, the three image data recorded in the RAM 15 are synthesized. An example of a method of combining three image data will be described below.

FIG. 4 shows an example of a histogram of the luminance of the dots of the image data. As shown in (a), the histogram of the image data obtained when an image having a very large difference in brightness is photographed with proper exposure lacks information indicating a gradation difference in both a dark portion and a bright portion. That is,
All dots having a brightness equal to or lower than a certain brightness are the darkest dots, and all dots having a brightness equal to or higher than a certain brightness are the brightest dots. Image data obtained by overexposure is represented by (a) information representing the gradation of a dark part as shown in (b).
More information can be recorded, but there is less information representing the gradation of the bright part. In the image photographed with underexposure, as shown in FIG.
More information can be recorded, but there is less information representing the gradation of dark parts.

In this embodiment, as shown in FIG. 1, the weight of an overexposed image is increased in a dark portion and the weight of an underexposed image is increased in a bright portion according to the luminance recorded at the time of proper exposure. The three pieces of image data are weighted so as to be large, and composite data is calculated for each dot. Thus, in the properly exposed image, the portion of the image that has been crushed to black is over-exposed so that the weight of the overexposed image is used more heavily than at the time of the appropriate exposure, and the gradation of the dark portion is reproduced. The underexposed image is heavily used for the underexposed image, so that it becomes darker than at the time of proper exposure, and the gradation of the brighter portion is reproduced.

Note that there is a time difference in obtaining three image data with different exposures, so that the ranges of the image data may not match due to camera shake or the like. For this purpose, it is possible to cause the control device 11 to perform positioning when combining three pieces of image data using a technique such as feature point detection.

Further, after various image corrections such as white balance adjustment, interpolation processing, and color correction are performed, the image data synthesized in order to increase the number of recordings in the flash memory 16 is converted into a JPEG (Joint Photographic Exper
ts Group) to generate small-capacity image data. JPEG is 256 for each color of R, G, B
It is an irreversible image compression method that can handle an image of about 16.7 million colors in gradation and is a commonly used irreversible image compression method.

The JPEG compression is performed by software by the control device 11, and a dedicated circuit can be used for speeding up. The JPEG-compressed data is recorded in the flash memory 16. Flash memory 1
Reference numeral 6 denotes a rewritable recording medium capable of storing the recorded contents without power supply, and is built in the digital camera 1 or is detachably attached to the digital camera 1. As the flash memory 16, for example, a PC
Memory card conforming to MCIA standard or PCMC
By using a memory card that can be attached to the IA card adapter, the contents of the flash memory 16 can be directly read and written by a personal computer having a PCMCIA card slot. The data recorded in the flash memory 16 is transmitted to the connection cable 1 via the interface 17.
8 to the connected personal computer 20.

In the present embodiment, one image data is synthesized from three image data recorded with different exposures and recorded in the flash memory 16, but all three image data are recorded. It is also possible to record the image in the flash memory 16 and select the most suitable image by the user, or to synthesize the image using the image processing software of the personal computer.

In this embodiment, three image data are recorded in the RAM 15 and then recorded in the flash memory 16. However, after the image data is recorded one by one in the flash memory 16, the next image is stored in the RAM 15. By recording, the capacity of the RAM 15 to be used can be set to one image data.

Further, in this embodiment, three images are recorded in the order of image data of proper exposure, image data of underexposure, and image data of overexposure, but the order is arbitrary in the present invention. Alternatively, two images or four or more images can be recorded and combined.

(Second Embodiment) FIG. 5 is a block diagram for explaining a digital camera 2 according to a second embodiment of the present invention. The substantially same parts as those in the first embodiment are denoted by the same reference numerals.
In the present embodiment, CCDs 131 and 13 are used as optical sensors.
Two light beams 133 and 133 are provided, and light passing through the condenser lens 11 is condensed. Each CCD 131, 132, 13
Reference numeral 3 has the same sensitivity and resolution.

Next, the operation of the digital camera 1 of this embodiment will be described.

When the user presses the shutter of the digital camera 1, all the charges accumulated in the CCDs 131, 132, and 133 are once discharged, and then the light collected by the condenser lens 12 is applied to the CCDs 131, 132, and 133. The signals are distributed and input at the same intensity and converted into electric signals. The aperture of the condenser lens 12 and the accumulation time of the CCD 131 are controlled to appropriate values automatically by the control device 11 or by a user's instruction. The exposure at this time is defined as an appropriate exposure. Also, the accumulation time of the CCD 132 is
1 and the storage time of the CCD 133 is C
It is set shorter than the storage time of the CD 131.

The electric signals output from the CCDs 131, 132 and 133 are A / D converted in the same manner as in the first embodiment.
The three image data recorded in the RAM 15 and recorded in the RAM 15 are synthesized in the same manner as in the first embodiment. Further, various image corrections such as white balance adjustment, interpolation processing, and color correction are performed.

Thereafter, the image data synthesized in order to increase the number of images to be recorded on the image recording medium is compressed by a method such as JPEG to generate small-sized image data.

In this embodiment, one image data is synthesized from three image data recorded with different exposures and recorded in the flash memory 16, but all three image data are stored in the flash memory. 16 and the user can select an optimal image, or the user can combine images using image processing software of a personal computer.

In this embodiment, the light condensed by the condenser lens 12 is distributed to the CCDs 131, 132, and 133 at the same intensity and input. However, the intensity of the light input for each CCD is changed. Thereby, images with different exposures can be recorded.

In this embodiment, the CCDs 131, 13
2 and 133 have the same sensitivity,
By using one having a different sensitivity for each D, images having different exposures can be recorded.

In the above embodiments, a CCD is used as an optical sensor, but other optical sensors such as a CMOS can be used.

In the above embodiments, the flash memory 16 is used as a recording medium for recording image data. However, other recording media such as a floppy disk (FD), a mini disk (MD), and an SRAM are used. It is also possible.

As described above with reference to a plurality of embodiments, according to the present invention, a plurality of images having different exposures can be recorded in one photographing, so that image data can be recorded in a wide dynamic range. it can.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a method for synthesizing a plurality of images by a digital camera according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a digital camera according to the first embodiment of the present invention.

FIG. 3 is a schematic view showing a CCD used in the digital camera according to the first embodiment of the present invention.

FIG. 4 is a diagram illustrating a histogram of luminance of image data recorded by the digital camera according to the first embodiment of the present invention.

FIG. 5 is a block diagram showing a digital camera according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Digital camera 11 Controller 12 Condenser lens 13 CCD (optical sensor) 14 A / D converter 15 RAM (recording medium) 16 Flash memory (recording medium) 17 Interface 18 Connection cable 20 Personal computer

──────────────────────────────────────────────────の Continued on front page (51) Int.Cl. ⁶ Identification code FI H04N 5/91 J

Claims (5)

[Claims] An optical sensor having a plurality of pixels; a unit for converting an output of the optical sensor into image data composed of a digital signal; a recording medium for recording the image data; Means for recording a plurality of images by using a digital camera. 2. The digital camera according to claim 1, wherein a plurality of images in the same range are successively recorded with different exposures. 3. The digital camera according to claim 1, comprising a plurality of said optical sensors for reading an image in the same range, wherein the exposure is changed for each optical sensor. 4. The digital camera according to claim 1, further comprising means for combining one image data from a plurality of image data recorded with different exposures. 5. A method of combining one image data by increasing the weight of high-exposure image data in a range of low brightness in an image and increasing the weight of low-exposure image data in a range of high brightness. The digital camera according to claim 4, wherein: