JPH03230691A - Digital electronic still camera - Google Patents

Abstract

PURPOSE:To attain compression processing with less picture deterioration in a main object and less memory capacity by dividing a picture into plural blocks and setting a compression rate depending on the degree of focusing in the unit of blocks. CONSTITUTION:A circuit to set a compression ratio in a camera consists of an X-Y address generating circuit 1, a buffer memory 2, a digital video signal processing circuit 3, a zone selection circuit 4, a zone range finder memory 5, a focus setting value memory 6, a compression ratio decision circuit 7 and a compression processing circuit 8. The picked-up picture is divided into plural blocks to detect the focusing state of each block, the compression ratio of the signal processing as to the focused blocks is selected lower and the compression ratio of the signal processing as to the not focused blocks is set higher. Thus, the information quantity is compressed without deteriorating the resolution of the video image of an main object and lots of pictures are picked up with a few memory capacity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a digital electronic still camera that appropriately compresses still image signals and stores them in a memory.

[Prior Art] Conventionally, still images are recorded on magnetic media by processing output signals from two-dimensional photoelectric conversion elements, and the still images are played back on TV! l
Still video cameras such as llIr are known. This still video camera handles images in the form of video signals, so it is attracting attention for its expandability not found in conventional silver halide cameras. However, in order to record on a small magnetic sheet, this still video camera requires highly accurate head position control and highly accurate constant rotation control, so it is not as portable as a conventional silver halide camera. sex,
Ensuring reliability is currently considered difficult.

Therefore, a still video camera using a solid-state memory as a recording medium instead of a magnetic medium has been proposed.

A still video camera using this solid-state memory has fewer mechanically moving parts and is likely to be made smaller and lighter.

However, with the current degree of integration of memory ICs, a large number of memory ICs are required to record a large number of videos, which results in a large cost. As a method to solve this problem, a method can be considered in which the amount of information of the video signal is compressed by some method, recorded in a memory, and then decompressed during playback to obtain the original video signal. This makes it possible to record a large number of videos with limited memory capacity.

However, if we consider the capacity of current memory, we should expect a considerable compression ratio. For example, when one field of video signal is digitized with a sampling frequency three times the color subcarrier frequency, approximately 1.5 Mbit of memory is required. Now, assuming that 50 fields are recorded per unit of recording medium as a standard, if an attempt is made to digitize the video signal of 50 fields in the above example, a memory capacity of 75 Mbit is required.

Here, when considering reversible compression (no deterioration in the quality of information even when compression/expansion processing is performed) and assuming that the compression ratio is limited to about 1/3, a memory of about 25 Mbit is required.

In this case, 25 IMbit SRAMs are required, which is difficult to realize in terms of shape and cost. Considering the irreversible pressure wJ (the quality of information deteriorates when compression/expansion processing is performed), the compression ratio can be expected to be 1/10 or more, so
It only requires about 8 IMbit SRAMs, so it is very likely to be realized. As a method of irreversible compression, predictive encoding method (DPe
M) or one using orthogonal transformation (DCT) can be considered.

However, when high compression is performed, the image quality deteriorates significantly compared to the original image. In the compression using DCT described above, high frequency components for which bit allocation is reduced are lost. Therefore, when compression and expansion processing is performed, there is a problem in that the entire image appears out of focus.

For example, Japanese Patent Application Laid-Open No. 63-286078 discloses that a mode in which video signals are compressed and recorded and a normal recording mode in which video signals are not compressed can be selected depending on the shooting purpose, and the image quality and recording capacity can be selected as appropriate. An electronic still camera is shown. In this camera, the recording mode in which the image was taken is stored in the memory, and when playing back, it is read and played back in the appropriate mode. The video recording compression method disclosed in the publication is based on thinning out of pixel signals, and the resolution within the screen (corresponding to the compression ratio) is all the same. Therefore, the above problem exists.

Furthermore, Japanese Patent Application Laid-Open No. 63-299680 discloses a system that separates background and non-background areas and performs encoding appropriate for each area, with the aim of encoding an image signal with a small amount of information. has been done.

To separate these areas, the screen is divided into blocks, and the difference between the highest and lowest brightness levels of each block is used. The method disclosed in this publication does not change the compression ratio depending on the in-focus state, and the circuit configuration for separating the background and non-background is complicated.

[Problems to be Solved by the Invention] The present invention solves the above-mentioned conventional problems by dividing the screen into a plurality of blocks and setting the compression rate for each block based on the degree of focus or the position of the block. Therefore, it is an object of the present invention to provide a digital electronic still camera that is capable of compression and expansion processing with little image deterioration in the main subject portion, and that requires less memory capacity.

[Means for Solving the Problems] In order to achieve the above object, the present invention includes an image sensor that photoelectrically converts an image taken by exposure, and an A/D converter that converts an image signal read out from the image sensor. D converter and
In a digital recording type electronic still camera that compresses the output signal from the A/D converter and stores it in memory, a focusing state divides the imaging screen into multiple blocks and detects the focused state of each block. Based on the detection means and the detection result of the focus state detection means, the compression rate of signal processing for the block that is in focus is set low, and the compression rate of signal processing for blocks that are not in focus is set high. The compression ratio setting means is also provided.

In addition, in an electronic still camera using the same digital recording method as above, the image capture screen is divided into multiple blocks, and the blocks in the center of the screen have a lower compression rate for signal processing, and the blocks near the periphery of the screen have a lower compression rate for signal processing. It is equipped with compression rate setting means for setting a high compression rate.

[Effects] With the above configuration, the in-focus area, or the center of the screen, is compressed only at a relatively low compression rate, so there is little deterioration in image quality, while the out-of-focus area, or the periphery of the screen, is compressed at a high rate. Therefore, there is less deterioration in image quality as a whole, and for example, it is possible to perform compression/expansion processing with less deterioration in image quality of the main subject. In addition, in portrait photography, etc., the aperture is set wide open to capture the background (periphery of the screen), but by applying high compression/expansion processing to the background part, it is possible to simplify the signal of that part. This makes the main subject stand out, making it desirable for portraits.

[Example] An embodiment of the present invention will be described below with reference to the drawings.

This embodiment compares the subject distance of each zone with the currently set shooting distance, and determines the zone whose subject distance is closest to the currently set shooting distance as the main subject zone. be.

FIGS. 1(a) and 1(b) show an example of the photographic screen 1o, distance information and compression ratio in each zone. In the case of this example, the data was divided into 9 zones and each was measured. As a result, the data for the center and lower center of the screen was 1 m, that for the lower left was 5 m, that for the lower right was 3 m, and the other areas were at infinity. do. Assuming you focus at 1m,
The center and bottom of the screen are 5/10, and the bottom left is 2/10.
, the lower right part is compressed to 3/10, and the other parts are compressed to 1/10. By setting such a compression ratio, if the area of each zone is the same, the captured image data will be approximately 115 in total.

FIG. 2 is a block diagram of a circuit for changing and setting the compression ratio. In the figure, the memory contents of the zone distance measurement value memory 5 are the results of distance measurement in each zone, and the memory contents of the focus setting value memory 6 are the shooting distances set at that time. When compressing the data in the buffer memory 2, a zone is selected in the zone selection circuit 4 based on the address value output from the X-Y address generation circuit 1, and the zone distance measurement value and focus setting value for that zone are These values are input to the compression ratio determination circuit 7, and the compression ratio is determined based on these values, and the compression processing circuit 8 operates based on this compression ratio. In the compression ratio determining circuit 7, the greater the difference between the two values, the higher the in-zone compression ratio is determined.

The buffer memory 2 of this embodiment is a frame memory that stores data obtained by A/D converting the output of the CCD image sensor, and is also connected to the digital video signal processing circuit 3 via a common data bus.

After A/D converting the output of the CCD image sensor, it is stored in the buffer memory 2 as image data.Furthermore, the image data stored in the buffer memory 2 is subjected to color separation, matrix processing, and white processing in the digital video signal processing circuit 3. Balance processing and the like are performed, and the processed, eg, Y, RY, and BY signals are stored in the buffer memory 2 again.

The compression processing circuit 8 performs compression processing on this signal.

A specific example of changing the compression ratio is, for example, two-dimensional discrete cosine transformation. This conversion method changes the degree to which bits are allocated to high frequency components in the two-dimensional frequency plane resulting from the conversion. Alternatively, to delete information on high frequency components, the compression ratio is changed by increasing or decreasing the number of components to be deleted. When the number of bits allocated to high frequency components is reduced as described above, the S/N ratio in the high frequency portion deteriorates. Furthermore, if information about high frequency components is deleted, the resulting image will have low resolution. However, in the present invention, the number of bits of high-frequency components in out-of-focus areas that do not originally contain high-frequency components is deleted, and information is deleted, so the amount of data can be reduced without degrading the overall image quality. This allows for significant compression.

An outline of an embodiment of a still video system using a solid-state memory as a memory for image information will be described below with reference to FIG.

In this figure, the same elements as those explained in FIG. 2 are designated by the same reference numerals. When the user presses the release button (not shown) of the camera 20 halfway, the switch S1 is turned on, and the system controller 31 obtains the distance value of each zone obtained from the zone distance measuring element 39, and performs distance measurement at the center of the screen. The focus drive motor 38 uses the value as the focus setting value.
Outputs a drive signal to. When the release button is further pressed, the switch S2 is turned ON, and the system controller 31 performs calculations based on the light amount value obtained by the photometric element 40, determines the exposure value, and uses the mechanical shutter 33 to determine the exposure value.
The opening/closing time of the shutter 33 is determined and the shutter 33 is driven. The image sensor (CCD image sensor) 34 performs exposure for a predetermined time through the lens 32, and the CCD image sensor 3
4 stores the photoelectrically converted image signal. This image signal is transferred and output according to a clock provided by a timing generator 37, amplified by an amplifier 35, converted into a digital value by an A/D converter 36, and stored in the buffer memory 2. The accumulated video signal is subjected to color separation processing, γ processing, white balance processing, and matrix processing in the digital arithmetic circuit 22.

After converting into an R=Y, BY signal format, compression processing is performed.

The compressed video signal is transferred from the buffer memory 2 to the connector 41.
Image memory 4 in memory card 21 connected by
2 and end the recording. At this time, the compression ratio of each zone is also recorded in the compression ratio storage memory 43 within the memory card 21.

Next, the regenerator 51 will be explained using FIG. 4.

Memory card 21 is connected to regenerator 51 by connector 65. The video signal in the memory card 21 compressed on the camera 20 side is transferred to the buffer memory 62 inside the regenerator 51 according to a timing signal given from a timing generator 64. This transferred compressed video signal is expanded by the digital arithmetic circuit 52.

At this time, the compressed video signal is subjected to two-dimensional inverse orthogonal transformation for each zone according to the signal from the X-Y address generation circuit 61 and the contents stored in the compression ratio storage memory 43 in the memory card 21. Perform processing and expand the signal.

Y obtained by elongation.

The R, -Y, and BY signals are subjected to NTSC encoding processing in the NTSC encoder 63 and transferred to the buffer memory 62 again. The NTSC encoded here is Y, R-Y obtained by decompression.

Of 13-Y, R-Y and B-Y are balanced modulated with color subcarriers, and a burst signal, horizontal synchronization signal, and vertical synchronization signal are added to the signal that overlaps that component and the Y signal. be. When processing for one screen is completed, the buffer memory 62
The NTSC signal within is read out by a clock provided by a timing generator 64, D/A converted by a D/A converter 66 using a synchronized clock, and outputted from a video output 69. Note that the feed switch 70 is an access button for accessing images recorded in the image memory 42, and is an access button for accessing images recorded in the image memory 42.
1. Connected to the timing generator 64. By pressing this button, the contents of the image memory 42 can be newly read into the buffer memory 62 and the next screen can be reproduced.

The above-mentioned embodiment is just an example, and various locations and signal forms for predetermined signal processing are possible. For example, the output of the image sensor is
It is also possible to immediately perform A/D conversion, perform compression processing, record on a memory card, and perform color separation processing, γ processing, white balance processing, matrix processing, and even NTSC encoding processing during playback. There is also a method in which the output of the image sensor is subjected to normal analog signal processing, that is, color separation processing, γ processing, white balance processing, matrix processing, and NTSC encoding processing, and then the NTSC signal is A/D converted and recorded in memory. Conceivable.

Moreover, the compression method can be implemented using any method such as a predictive encoding method or a method using vector quantization.

Further, in this embodiment, the screen is divided into nine blocks, but the number of blocks can be set as desired by the photographer. In addition, a portrait mode is provided, and in this mode, to take Figure 1 as an example, the compression ratio of the center and center r parts of the screen is lowered, or no compression is performed, and the compression ratio of other blocks is It may also be possible to automatically set the value to be higher. This provides the same effect as when shooting with a shallow depth of field by opening the aperture.

That is, the main subject becomes clear and the background appears blurred, making the main subject stand out and making it desirable for portraits.

Furthermore, varying the compression rate based on distance information can be applied to a variety of applications. For example, in the case of compression in the frequency domain, it is considered that the photographing distance and the signal component in the highest frequency range that can exist in the subject have a correlation with each other, so the compression rate may be varied depending on the photographing distance.

[Effects of the Invention] As described above, according to the present invention, it is possible to compress and record image information that reflects the photographer's intentions within the shooting screen, without reducing the resolution of the image of the main subject. ,
The amount of information in one image can be compressed, and many images can be captured with a small memory capacity.

Furthermore, deterioration in image quality due to compression of image information other than the main subject, for example, peripheral images, has the effect of enhancing the main subject, and the same effect as when shooting with the aperture wide open can be obtained.

Furthermore, unlike the conventional example, a complicated configuration for separating the background and non-background is not required, and the configuration can be simplified.

[Brief explanation of drawings]

FIGS. 1(a) and 1(b) are diagrams showing an example of the shooting screen of the digital electronic still camera of the present invention, distance measurement information and compression ratio when the screen is divided into a plurality of zones, and FIG. FIG. 3 is a block diagram of one embodiment of the circuit for setting the compression ratio, FIG. 3 is a block diagram of one embodiment of the overall configuration of the camera, and FIG. 4 is a block diagram of one embodiment of the regenerator. 2... Buffer memory, 3... Digital video signal processing circuit, 4... Zone selection circuit, 5... Zone distance measurement value memory, 6... Focus setting value memory, 7...
- Compression ratio determining circuit, 8... Compression processing circuit, 1o...
Imaging screen, 20... Camera, 21... Memory card, 34... Imaging device, 36... A/D converter,
42... Image memory, 43... Compression ratio storage memory.

Claims (2)

[Claims] (1) An image sensor that photoelectrically converts images captured by exposure;
An A/D converter that A/D converts the image signal read from the image sensor, and a digital recording electronic still camera that compresses the output signal from the A/D converter and stores it in the memory. A focus state detection means that divides the screen into multiple blocks and detects the focus state of each block, and compression of signal processing for the in-focus block based on the detection result of this focus state detection means. 1. A digital electronic still camera, comprising compression ratio setting means for setting a compression ratio low and a compression ratio for signal processing for blocks that are not in focus high. (2) an image sensor that photoelectrically converts images captured by exposure;
An A/D converter that A/D converts the image signal read from the image sensor, and a digital recording electronic still camera that compresses the output signal from the A/D converter and stores it in the memory. A digital device comprising a compression rate setting means that divides a screen into a plurality of blocks, sets the signal processing compression rate lower for blocks in the center of the screen, and sets the signal processing compression rate higher for blocks near the periphery of the screen. Electronic still camera.