JP3109855B2 - Electronic camera, image signal compression apparatus and method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic camera for electrically processing an image signal obtained by an image sensor and recording the image signal on a recording medium, an image signal compression apparatus for compressing the image signal, and a method therefor.

[0002]

2. Description of the Related Art Recently, there has been proposed a digital electronic camera which uses a memory card having a semiconductor memory as a recording medium and records a still image signal on the memory card.

[0003] In this method, after a video signal converted into an electric signal by a solid-state imaging device such as a CCD is digitally processed, it is recorded on a memory card, and a digital image signal is read out from the memory card by a reproducing machine to process the reproduced signal. After performing, it is a system that outputs to the monitor.

When an image is digitally recorded, the amount of data increases. Specifically, calculating the amount of data required for one screen,
Assuming that the number of pixels of the image sensor is 768 in the horizontal direction (sampled at 4 fsc) and 480 in the vertical direction, the quantization bit number of each pixel is 8 bits, and each color difference information is a data amount of 輝 度 of the luminance information, the data of one screen. The amount will be about 6 Mbits.

For example, if the memory capacity of a memory card is 12
If M bits are used, the number of images that can be taken is two. Therefore, image compression techniques such as DCT (Discrete Cosine Transform) are used to reduce the amount of data. By utilizing this image compression technique, the data amount per screen is compressed to 1/2 to 1/8 the data amount at the time of non-compression, thereby increasing the number of photographed images.

[0006]

However, as is well known, the compression ratio and the image quality are in a reciprocal relationship. If the compression ratio is increased, the number of stored images can be increased, but the compression ratio cannot be increased unnecessarily because the image quality deteriorates. It is not possible, and depending on the shooting scene, the compression limit is considered to be about 1/4 to 1/8.

Under such a background, the present invention provides an electronic camera and an image signal compression device capable of reducing the amount of data for one screen and reproducing an image satisfactory to a photographer. It is an object.

[0008]

An electronic camera according to the present invention captures a subject image and generates an image signal, and a subject distance detection unit detects a distance between the subject captured by the imaging unit. A focal length detecting unit that detects a focal length of the imaging unit; a compressing unit that compresses an image signal generated by the imaging unit; and an output of the subject distance detecting unit and the focal length detecting unit. Control means for controlling a compression ratio of the compression means. Further, the image signal compression device according to the present invention includes: an input unit that inputs an image signal obtained by capturing a subject image; a determination unit that determines a contour of the subject image in the image signal; Compression means for compressing the image signal input by the means, and control means for controlling a compression ratio of the compression means, wherein the control means comprises an interior surrounded by a contour determined by the determination means. The image signal of the area is determined, and the compression ratio of the image signal of the internal area is controlled to be lower than that of other areas. Further, the image signal compression method according to the present invention is such that an image signal obtained by imaging a subject image is input, a contour portion of the subject image is determined in the image signal, and the contour portion is surrounded by the determined contour portion. Determining the image signal of the internal region obtained, and compressing the input image signal so that the compression ratio of the image signal of the internal region is lower than that of the other regions.

[0009]

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment according to the present invention will be described below in detail with reference to FIGS.

First, the basic concept of this embodiment will be described.

Considering a general photographing scene, (1) a scene in which a subject (person, car, house, flower, etc.) that the photographer intends to photograph exists in the background (back); Scenes that are subjects (landscapes and the like) intended by the photographer are roughly classified into two scenes.

In the case of the shooting scene (1), there is a portion in the shooting screen that does not need to be recorded and reproduced so precisely. That is, there is no problem because the image quality of the main subject does not deteriorate even if the compression ratio is increased, except for the portion corresponding to the main subject that the photographer intends to take. Further, by performing the above processing, the data amount can be reduced.

FIG. 1 is a block diagram of an electronic still camera according to the present embodiment, FIG. 2 is a block diagram for reproducing an image signal stored by the apparatus of FIG. 1, and FIG. 3 is a diagram for explaining a compression operation. FIG. 4 is a diagram for explaining a compression mode determination method.

In FIG. 1, reference numeral 1 denotes an object, 2 denotes an optical system having a focus lens, a zoom lens, etc., 3 denotes a focus control motor for moving the focus lens of the optical system 2, and 4 denotes a zoom lens of the optical system 2. A zoom control motor for moving, a subject distance detecting unit 5 for measuring a distance of the subject 1 from the camera, 6 an image sensor such as a CCD, 7
Denotes an image signal processing unit which performs visibility correction of image signals (R, G, B for a pure color filter and Ye, Mg, Gr signals for a complementary color filter) output from the image sensor 6,
It is converted into a luminance / two-color difference (Y, RY, BY) signal.

A / D converters 8a, 8b and 8c corresponding to the Y, RY and BY signals respectively convert analog image signals into digital image signals.

Reference numerals 9a, 9b and 9c denote buffer memories corresponding to the Y, RY and BY signals, respectively. Reference numeral 10 denotes a switch, which has contacts 10a, 10b and 10c. Have been.

Reference numeral 11 denotes an image compression unit, which converts one screen into 8 × 8.
, And further divide each block by DCT (Di
A well-known image compression is performed by using a "crate cosine transform".

Reference numeral 12 denotes a memory card, 13 denotes a system control unit, and 14 denotes an outline extraction unit, which detects a sharp change point of the luminance signal and extracts the outline of the subject 1 formed on the image sensor 6.

Reference numeral 15 denotes a focal length detecting unit for detecting a focal length, 16 denotes a release switch for photographing by a camera, 1
Reference numeral 7 denotes a switch that is turned on by the first stroke of the release switch 16, and reference numeral 18 denotes a switch that is turned on by the second stroke of the release switch 16.

The recording operation of the electronic camera configured as described above will be described in detail.

When the release switch 16 is pressed to the first stroke, the switch 17 is turned on, and in response to this, the system control unit 13 supplies power to various parts of the internal device of the camera.

The image of the subject 1 is formed on the subject distance detecting section 5 via the optical system 2, and the detecting section 5 converts the optical image of the subject 1 into an electric signal, and performs a predetermined arithmetic processing on the signal. Then, distance information to the subject is calculated. The distance information is input to the system control unit 13, and the control unit 13 controls the focus control motor 3 to perform focusing based on the input information.

Next, a zoom control motor 4 is operated by operating a zoom switch (not shown) provided on the camera.
To change the focal length to change the angle of view of the image of the subject 1 (wide to tele), thereby creating a shooting scene intended by the photographer. When the focal length is changed, there are cases where focus control must be performed depending on the structure of the optical system 2 and cases where it is not necessary to perform focus control. I have.

Next, when photographing and recording the subject 1 at the angle of view determined by the photographer, the release switch 16 (not shown) is pressed to the second stroke. When the switch 18 is turned on in conjunction with this, the system control unit 13 controls each unit of the camera as follows.

The image pickup element 6 outputs an optical image of the subject 1 as an electric signal, and the signal is subjected to luminosity correction, color balance control, and the like by a signal processing section 7 to obtain a luminance signal (Y).
And two color difference signals (RY, BY) are generated and output.

The generated video signal is supplied to an A / D converter 8
a, 8b and 8c are video signals Y, RY and BY, respectively.
The signal is converted to a corresponding digital signal, and the output is Y
The signal is stored in the buffer memory 9a, the RY signal is stored in the buffer memory 9b, and the BY signal is stored in the buffer memory 9c.

Next, the signals stored in the buffer memory are sequentially read out by switching a switch 10 controlled by the system control unit 13 and input to the image compression unit 11.

The image compression section 11 performs a well-known image compression process using DCT based on information on a compression ratio from a system control section 13 described later.

The image signal compressed by the compression processing is recorded on the memory card 12.

In the contact switching of the switch 10, first, in an initial state, the switch 10 is connected to the contact 10a.
The compression processing of the Y signal is performed, and when the processing of storing the compressed Y signal in the memory card 12 is completed, the contact is switched from the contact 10a to the contact 10b. Next, the compression processing of the RY signal is performed, and when the processing of storing the compressed RY signal in the memory card 12 is completed, the contacts 10b to 1
0c. Next, when the same process is performed on the BY signal, the contact is switched from the contact 10c to the contact 10a when the process is completed, and the above-described process is sequentially repeated.

Information on the compression ratio is also output from the system control unit 13 and recorded on the memory card.

Next, compression in this embodiment will be described in detail.

The shooting scene has been described above. (1) A scene in which a subject (person, car, house, flower, etc.) that the photographer intends to shoot exists in the background (back). Scenes that are objects (landscapes, etc.) that the user intends to take are roughly divided into two scenes.

In the case of the shooting scene of (1), there is a portion which does not need to be recorded and reproduced so precisely in the shooting screen. In other words, even if the compression ratio is increased except for the portion corresponding to the main subject (for example, a person) that the photographer intends to take, there is no problem because the image quality of the main subject does not deteriorate, and the data amount can be reduced.

Therefore, the compression mode is (A) a mode in which one screen is compressed at a certain compression ratio (corresponding to the shooting scene (2)), and (B) one screen is divided into a plurality of areas (groups). A mode in which the average compression ratio is changed for each of the regions to perform compression, specifically, a mode in which the subject portion is subjected to low compression and the other portions are subjected to high compression (corresponding to the shooting scene (1)). Divided into

The method of determining the compression mode will be described below.

FIG. 4 is a diagram for explaining a method of determining the compression mode. If the relationship between the focal length and the subject distance is indicated by the hatched portion in FIG. 4, the compression in the mode (A) is performed.
Also, the white portion in FIG. 11 performs the compression in the (B) mode.
The range between f0 and f1 in FIG. 4 is the focal length range of the camera.

The boundary between the hatched portion and the white portion where the subject distance is between D0 and D1 corresponds to the line where the size of the desired subject is the same. On this boundary line, f = kD → D / The relationship of f = 1 / k = const (k: coefficient) is established.

That is, (a) when the subject distance is equal to or more than D1, (b) when the focal length is equal to or less than f0, (c) f ≦ kD
If the relationship of D / f ≧ 1 / k holds, the compression in the (A) mode is performed in the above three cases, and the compression in the (B) mode is performed in other cases.

The values of f0, f1, D0, D1, and k differ depending on the optical system mounted on the camera.

Next, a compression control method will be described.

4 is stored in the system control unit 13. The subject distance data from the subject distance detection unit 5 and the focal length data from the focal length detection unit 15 are input to the system control unit 13. Therefore, the system control unit 13 determines the compression mode based on the subject distance and the focal length data.

If it is determined that any one of the conditions (a), (b) and (c) is satisfied, the system controller 1
3 causes the image compression unit 11 to perform the above-described (A) mode compression.

Next, if none of the conditions (a), (b) and (c) is satisfied, the system control unit 13 performs the above-mentioned (B) mode compression.

On the other hand, the digitized luminance signal output from the A / D converter 8a in FIG.
4 to extract a sharp change point of the digital signal. That is, an area (block group) of the contour portion of the subject 1 is extracted, and the data is transmitted to the system control unit 13.

The system control unit 13 determines the contour area of the subject 1 and its internal area based on the contour extraction data, and issues a command to lower the compression ratio in these areas and to increase the compression rate in other areas. The information is transmitted to the image compression unit 11.

This will be described more specifically with reference to FIG.

In FIG. 3, the image of the subject 1 formed on the image pickup device 6 in FIG. 1 is divided into a total of 64 areas of 8 vertical divisions and 8 horizontal divisions.

The compression mode is determined for each of the 64 areas, and the compression itself is (8 × 8) in each area.
8) Performed in units of pixel blocks.

Based on the data obtained by the contour extraction unit 14, the system control unit 13 selects the contour part and all the regions inside the contour.

That is, taking FIG. 3 as an example, the regions to be extracted are 0D, 0E, 1D, 1E, 1F, 2D, 2E, 2F, 3
B, 3D, 3E, 3F, 4A, 4B, 4c, 4E, 5
A, 5B, 5C, 5E, 6A, 6B, 6C, 6E, 7E
25 areas in total.

Accordingly, the system control unit 13 controls the image compression unit 11 so as to lower the average compression ratio of the 25 regions and increase the average compression ratio of the other regions.

The data of the compression ratio corresponding to each area is stored in the memory card 12 by the system control unit 13.

When the average compression ratio of the 25 regions is 1/8 with little image quality degradation and the compression ratio of the other regions is 1/16, the total number of compressed bits is about 0.5 Mbit.

On the other hand, when one screen is compressed to 1/4 at a uniform compression ratio, the total number of bits is about 0.75 Mbit, and the data amount is reduced to about 2/3 in comparison with this. .

Further, considering a general photographing scene, the main subject (the subject that the photographer wants to take the most) is located at the center of the screen. In FIG. 3, a person is considered as the main subject.
The system control unit 13 is operated based on the detection data of the contour detection unit 14.
Are areas where no person exists (3B, 4A, 4B, 4C, 5
A, 5B, 5C, 6A, 6B, and 6C) are also detected. Therefore, when the data amount is to be further reduced, the contour detection unit 14 detects an area other than the main subject (the area detected near the center of the angle of view). When an area is detected, the compression of the main subject portion is reduced (for example, 1/4 of the time of non-compression), and the compression ratio is increased for other areas where the contour is detected (for example, 1/4 of the time of non-compression).
8) By further increasing the compression ratio (for example, 1/16 of the uncompressed state) in other areas, it is possible to suppress the image quality deterioration of the main subject as much as possible.

FIG. 2 is a block diagram of an apparatus for reproducing an image signal stored in the apparatus of FIG. 12 is a memory card in which image signals are stored in the apparatus of FIG. 1, 20 is a system control section for controlling each section of the apparatus, 21 is a decompression processing section, 22 is a switch, which has switching contacts 22a to 22c and has a system control. It is controlled by the unit 20.

Reference numerals 23a to 23c denote buffer memories which are a luminance signal (Y) and two color difference signals (RY, BY).
It is a memo.

Reference numerals 24a to 24c denote D / A converters corresponding to the Y, RY and BY signals, respectively.

Reference numeral 25 denotes a video encoder for synthesizing the signals output from the D / A converters 24a to 24c and outputting the synthesized signal to a video output terminal 26 as a video signal.

The reproducing operation of the reproducing apparatus configured as described above will be described in detail.

When the reproduction switch 19 is operated, the system control section 20 supplies power to each section, and the compressed data of the image signal and the compression rate data for each area stored in the camera apparatus of FIG. 12 and input to the system control unit 20.

The system control unit 20 transmits the data to a decompression processing unit 21, and the decompression processing unit 21 performs a decompression process on the video signal read from the memory card 12 based on the data. Here, the expansion order is Y, RY, B-
The processing is performed in the Y signal order, and the switch 2
2 is switched. As a result, the expanded Y,
The RY and BY signals are stored in the buffer memories 23a and 23a, respectively.
3b and 23c.

Each signal stored in the buffer memory 23 is input to each of the D / A converters 24a to 24c and converted from a digital signal to an analog signal.

After that, each Y,
The RY and BY signals are input to a video encoder 25. Since a video synchronization signal is input to the video encoder 25 from the system control unit 20, Y, RY, and BY are based on the synchronization signals. The signals are combined and output to the video output terminal 26 as a video signal.

If a television monitor (not shown) or the like is connected to the video output terminal 26, a reproduced image can be viewed.

[0068]

As described above, according to the present invention,
Since the compression ratio is set adaptively by judging the shooting scene, etc., the data amount for one screen can be reduced. Improvement can be achieved.

[Brief description of the drawings]

FIG. 1 is a block diagram of an electronic still camera according to an embodiment.

FIG. 2 is a block diagram of a device for reproducing an image signal photographed and recorded by the device of FIG. 1;

FIG. 3 is a diagram for explaining a compression operation according to the embodiment;

FIG. 4 is a diagram for explaining a compression mode determination method according to the embodiment;

[Explanation of symbols]

 Reference Signs List 5 subject distance detection unit 8a, 8b, 8c A / D converter 11 compression processing unit 12 memory card 13, 20 system control unit 14 contour detection unit 15 focal length detection unit 21 extension processing unit 24a, 24b, 24c D / A conversion 25 Video encoder

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 5/91-5/956 H04N 1/41-1/419 H04N 5/225-5/243 H04N 7 / 24-7/68

Claims (5)

(57) [Claims] An imaging unit configured to capture a subject image and generate an image signal; a subject distance detection unit configured to detect a distance from the subject captured by the imaging unit; and a focus configured to detect a focal length of the imaging unit. Distance detecting means; compressing means for compressing an image signal generated by the image pickup means; control means for controlling a compression ratio of the compressing means according to outputs of the subject distance detecting means and the focal length detecting means; An electronic camera comprising: 2. An input unit for inputting an image signal obtained by capturing a subject image, a determining unit for determining a contour of the subject image in the image signal, and an image signal input by the input unit And a control unit for controlling a compression ratio of the compression unit. The control unit determines an image signal of an internal region surrounded by the contour determined by the determination unit. An image signal compression apparatus for controlling a compression ratio of an image signal in the internal area to be lower than that in another area. 3. The image signal compression apparatus according to claim 2, further comprising recording means for recording the image signal compressed by said compression means on a recording medium. 4. An image signal obtained by capturing an image of a subject is input, a contour of the subject image is determined in the image signal, and an image signal of an internal area surrounded by the determined contour is provided. And compressing the input image signal so that the compression rate of the image signal in the internal area is lower than that of the other areas. 5. The image signal compression method according to claim 4, wherein the compressed image signal is recorded on a recording medium.