JP2004180151A - Digital camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digital camera which provides clear images on a scene where the main object largely moves and contributes to power saving. <P>SOLUTION: when a photographing mode is selected, this digital camera starts to obtain through images at a standard frame rate. While the through images are displayed, a CPU calculates an integrated value of difference data between two former and latter frames, compares the integrated value with a reference value, and switches a frame rate to a low frame rate when the integrated value is smaller than the reference value. Thereby, it makes the images clear to look at in the scene where the main object moves largely and suppresses power consumption in a scene where the main object makes little movement. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a digital camera provided with an electronic viewfinder.
[0002]
[Prior art]
Digital cameras that record captured images as digital data on a memory card are known. Many digital cameras are provided with an electronic viewfinder that reproduces a frame captured by a CCD image sensor in real time and displays it as a through image during framing. When the photographing mode is selected, the CCD image sensor captures a through image at a frame rate of about 30 frames per second, for example.
[0003]
If the frame rate is high, the number of frames reproduced per unit time is large, so that the quality of the through image is improved, but the operating frequency of the CCD image sensor is high, and the power consumption is large. On the other hand, if the frame rate is lowered, power consumption can be suppressed, but the image quality of the through image is lowered.
[0004]
In view of this, there has been proposed a digital camera that normally captures a through image at a low frame rate and switches to a standard frame rate when the shutter button is pressed halfway (see, for example, Patent Document 1). According to this, since the number of times of normal image capture can be reduced, power saving can be achieved, and the subject can be confirmed with good image quality by switching to the standard frame rate immediately before shooting.
[0005]
[Patent Document 1]
Japanese Patent Laid-Open No. 2000-67039
[Problems to be solved by the invention]
However, in the above-described digital camera, the frame rate is not switched to the standard rate unless the shutter button is half-pressed regardless of the shooting scene. The shooting scene includes various scenes such as a scene in which the main subject hardly moves, such as a shooting scene in which the main subject is a landscape, and a scene in which the main subject moves intensely, such as an athletic meet scene. In a scene where the movement of the main subject is intense, if the frame rate is low, the movement of the main subject is not displayed smoothly and the screen is difficult to see.
[0007]
SUMMARY OF THE INVENTION An object of the present invention is to provide a digital camera that makes it easy to see a screen in a scene where the movement of a main subject is intense and contributes to power saving.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the digital camera of the present invention reproduces in real time an imaging means for photoelectrically converting a subject image formed by a photographing lens to obtain a photographed image, and a frame captured by the imaging means. A digital camera including an electronic viewfinder that displays a through image on a display is provided with a frame rate adjusting unit that adjusts a frame rate of the through image based on difference data between two frames before and after.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
In the digital camera 10 shown in FIG. 1, a battery 15 for supplying power is detachably set on a camera body 11. A lens barrel 12 incorporating a photographing lens is provided on the front surface of the camera body 11, and a power button 13 and a shutter button 14 are provided on the upper surface. Further, on the rear surface of the camera body 11, a zoom button 16, a general-purpose key 17 in which four buttons are arranged in a cross, a mode selection lever 18, and an LCD (Liquid Crystal Display) panel 19 are provided.
[0010]
The mode selection lever 18 selects various modes such as a shooting mode for shooting, a playback mode for playing back a shot image, and a setup mode for making various settings. The general-purpose key 17 is displayed on the menu screen and is used for moving a cursor for selecting various items, selecting items, and the like. The LCD panel 19 is used for playback display of a captured image in the playback mode, is used for displaying a menu screen for performing various settings in the setup mode, and is a through image that is a subject confirmation image in the shooting mode. Is used as an electronic viewfinder.
[0011]
The zoom button 16 includes an enlargement button 16a and a reduction button 16b. By operating these buttons, the optical photographing magnification of the photographing lens 26 (see FIG. 2) is switched. When the shooting mode is selected, the capturing of the through image is started and the through image is displayed on the LCD panel 19.
[0012]
FIG. 2 is a block diagram showing the configuration of the digital camera 10. A memory card 23 is detachably set on the camera body 11. In the memory card 23, the main image data is converted into, for example, an image file in a JPG (Joint Photographic Expert Group) format and stored.
[0013]
The CPU 21 controls each part of the main body of the digital camera 10 in accordance with an operation signal input from the operation unit 22. In the lens barrel 12, a photographing optical system including a photographing lens 26 and a diaphragm 27 is incorporated.
[0014]
The photographing lens 26 is driven by a lens driving mechanism 28 including a motor, and the optical photographing magnification is changed and the focus is adjusted. The aperture 27 is driven by an aperture drive mechanism 29 including a motor to switch the aperture diameter. The lens driving mechanism 28 and the aperture driving mechanism 29 are driven by motor drivers 31 and 32 controlled by the CPU 21.
[0015]
Behind the photographic optical system, a CCD image sensor 33 is arranged as an image sensor. As is well known, the CCD image sensor 33 includes a photoelectric surface in which a large number of light receiving elements are arranged in a matrix. The CCD image sensor 33 photoelectrically converts subject light that passes through the photographing optical system and forms an image on the photoelectric surface. In front of the photocathode, a microlens array for condensing light on each pixel, and a color in which filters of each color are regularly arranged so that each pixel corresponds to one of R, G, and B, respectively. A filter array is arranged.
[0016]
The CCD image sensor 33 outputs the charge accumulated for each pixel as a serial imaging signal line by line in synchronization with the vertical transfer clock and horizontal transfer clock supplied from the CCD driver 36. The charge accumulation time (exposure time) of each pixel is determined by an electronic shutter drive signal given from the CCD driver 36.
[0017]
The analog imaging signal captured from the CCD image sensor 33 is input to the analog signal processing circuit 38. The analog signal processing circuit 38 includes a correlated double sampling circuit (CDS), an auto gain controller (AGC), and an AD converter (ADC). The CDS removes noise from the analog signal, and the AGC automatically adjusts the gain of the analog signal. The ADC generates image data by digitally converting an analog signal. This image data is CCD-RAW data having R, G, and B density values for each pixel, and this CCD-RAW data is input to a DSP (Digital Signal Processor) 41. The analog signal processing circuit 38 is also supplied with a timing signal from the timing generator 31 and is synchronized with the timing at which charges are taken in from the CCD image sensor 33.
[0018]
When the shooting mode is selected, the CCD image sensor 33 starts capturing a through image. When the shutter button 14 is fully pressed and a main shooting instruction is issued, the CCD image sensor 33 temporarily stops the capturing of the through image. Import images. When the main shooting ends, the capturing of the through image is resumed.
[0019]
The captured through image is reproduced in real time and displayed on the LCD panel 19. The frame rate for capturing and displaying can be adjusted in two stages: a standard frame rate and a low frame rate lower than the standard frame rate. At the standard frame rate, 30 frames are captured per second, and at the low frame rate, half of the frames are captured per second. Compared to the low frame rate, the standard frame rate has a larger number of captures per unit time, so that smooth image quality can be obtained, but power consumption is larger.
[0020]
These frame rates are adjusted according to the intensity of movement of the main subject. The movement of the main subject is detected by obtaining difference data between two frames before and after the capturing time is different. The through image capture is started at the standard frame rate, and when the obtained difference data is smaller than a preset reference value, it is switched to a low frame rate.
[0021]
The frame memory 39 is a working memory that is used when a DSP (Digital Signal Processor) 41 performs various signal processing on image data. The frame memory 39 is connected to each part of the CPU 21 and the DSP 41 via the data bus 55. As the frame memory 39, for example, an SDRAM (Synchronous Dynamic Random Access Memory) that performs data transfer in synchronization with a bus clock signal having a fixed period is used. The image written in the frame memory 39 is subjected to various image processing by the DSP 41.
[0022]
The DSP 41 is an IC chip including an AF circuit 43, an AE / AWB circuit 44, an image input controller 46, an inter-frame difference integration circuit 47, an image processing circuit 48, a compression processing circuit 49, a media controller 50, and a video encoder 51. Various types of signal processing are performed on the image data input from the signal processing circuit 38, and a live view is displayed on the LCD 19 and the memory card 23 is accessed to read and write image files.
[0023]
The image input controller 46 takes in the CCD-RAW data from the analog signal processing circuit 38 and writes it in the frame memory 39. The AF circuit 43 detects the focal position based on the image captured by the CCD image sensor 33 and performs focusing. The AE circuit measures subject brightness and determines an aperture value, a shutter speed, and the like. The AWB circuit is an auto white balance circuit, and automatically adjusts the white balance at the time of shooting.
[0024]
The compression processing circuit 49 performs compression processing on the main image data that has been subjected to various types of image processing by the image processing circuit 48 to generate an image file. The media controller 50 accesses the memory card 23 to write and read image files. In the reproduction mode, the compressed image data is read from the memory card 23 and is decompressed by the compression processing circuit 49 and then output to the LCD 19.
[0025]
The image processing circuit 48 performs image quality correction processing such as gamma correction, sharpness correction, and contrast correction on the image data, CCD-RAW data is Y data that is a luminance signal, Cb data that is a blue color difference signal, and a red color difference signal. YC processing for converting into YC data composed of Cr data is performed.
[0026]
The inter-frame difference integration circuit 47 reads the through image written in the frame memory 39, compares the two frames, and obtains an integrated value of the difference data obtained by the comparison. As illustrated in FIG. 3A, a scene in which the main subject 55 moves from the left to the right on the screen will be described as an example. Difference data between the latest frame 56 and the previous frame 57 captured before that is the difference data. It is represented by an area 58a indicated by hatching in the frame 58. The integral value of the difference data corresponds to the area of this region 58a. Compared to FIG. 3A, when the moving speed of the main subject 55 is faster (the movement is intense), the area 58a becomes larger as shown in FIG. 3B.
[0027]
The CPU 21 switches the frame rate to a low frame rate when the integrated value of the difference data obtained by the inter-frame difference integrating circuit 47 becomes smaller than a preset reference value. If the integral value of the difference data is equal to or greater than the reference value, the standard frame rate is restored. This comparison is performed, for example, every time one frame is captured, and the frame rate is adjusted. By adjusting the frame rate of the through image in this way, the main frame has a standard frame rate in the case of a main subject that moves rapidly, so that the motion is displayed smoothly. On the other hand, when the motion is small, the frame rate is switched to a low frame rate, which contributes to power saving.
[0028]
The VRAM 40 is a memory for image output to the LCD 19. The through image once written in the frame memory 39 is subjected to image quality correction processing and YC processing and then written in the VRAM 40. The through image written in the VRAM 40 is sent to the video encoder 51. The video encoder 51 converts the digital data into an analog composite signal and outputs it to the LCD 19. Since the through image is rewritten at high speed, the VRAM 40 is provided with areas 40a and 40b for two frames so that data can be written and read in parallel.
[0029]
Hereinafter, the operation of the above configuration will be described with reference to the flowchart shown in FIG. When the power is turned on and the shooting mode is selected, the digital camera 10 starts capturing a through image and displaying the captured through image on the LCD panel 19 at a standard frame rate. The photographer performs framing while viewing the through image displayed on the LCD panel 19.
[0030]
When one frame of a through image is captured, the inter-frame difference integration circuit 47 compares the previous frame captured before that with the latest frame to determine difference data between the two frames, and calculates an integral value thereof. The CPU 21 compares the integral value with the reference value, and switches to a low frame rate when the integral value is smaller than the reference value. Capture is performed at a low frame rate, and when the integral value again exceeds the reference value, the standard frame rate is restored. The frame rate adjustment is repeated in this procedure until the through image capture is completed.
[0031]
In this way, the frame rate is adjusted according to the movement of the main subject. Contributes to power saving.
[0032]
In the above embodiment, the example in which the frame rate is adjusted in two stages has been described. However, three or more frame rates may be set, and the frame rate may be adjusted between them.
[0033]
In addition, the comparison between the two frames before and after is performed every time one frame is captured, but the comparison interval is not performed every time one frame is captured, for example, every time a plurality of frames of about 2 to 3 are captured. It may be performed at predetermined time intervals.
[0034]
In addition, although the present invention has been described as an example in which the present invention is applied to a digital still camera, the present invention can also be applied to a digital camera capable of shooting a moving image.
[0035]
【The invention's effect】
As described above in detail, the digital camera of the present invention is a digital camera including an electronic viewfinder that reproduces a frame captured by an imaging unit in real time and displays it on a display as a through image. Since the frame rate adjustment means for adjusting the frame rate of the through image based on the difference data is provided, it is possible to provide a digital camera that makes it easy to see the screen in a scene where the movement of the main subject is intense and contributes to power saving. it can.
[Brief description of the drawings]
FIG. 1 is a rear perspective view of a digital camera.
FIG. 2 is a block diagram showing an electrical configuration of the digital camera.
FIG. 3 is an explanatory diagram of a main subject motion detection method;
FIG. 4 is a flowchart illustrating a procedure for adjusting the frame rate of a through image.
[Explanation of symbols]
10 Digital Camera 19 LCD Panel 21 CPU
33 CCD image sensor 47 Inter-frame difference integration circuit

Claims (1)

An image pickup unit that photoelectrically converts a subject image formed by a shooting lens to obtain a shot image, and an electronic viewfinder that reproduces a frame captured by the image pickup unit in real time and displays it on a display as a through image In digital cameras,
A digital camera comprising a frame rate adjusting means for adjusting a frame rate of a through image based on difference data between two frames before and after.

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