JP3012655B2 - Digital camera - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a digital electronic still camera, and more particularly, to a digital electronic still camera.
The present invention relates to a digital electronic still camera capable of saving power consumption.

2. Description of the Related Art A digital electronic still camera is an image capturing apparatus that captures an object scene using a solid-state imaging device such as a CCD and stores an image signal representing the captured image in a memory in the form of digital data. As a memory, for example, a memory card in the form of a memory card mounted with a RAM, such as a semiconductor memory, is often used. In that case, data compression such as orthogonal transform coding is often performed in order to efficiently use the storage area of the memory.

In particular, two-dimensional orthogonal transform coding is widely used because it can perform coding at a large compression rate and can suppress image distortion due to coding.

In such two-dimensional orthogonal transform coding, image data is divided into a predetermined number of blocks, and image data in each block is subjected to two-dimensional orthogonal transform. The orthogonally transformed image data, that is, the transform coefficient, is compared with a predetermined threshold, and a portion below the threshold is truncated (coefficient truncation).
Is performed. As a result, the conversion coefficient equal to or smaller than the threshold value is thereafter processed as 0 data. Next, the transform coefficient subjected to coefficient truncation is divided by a predetermined quantization step value, that is, a normalization coefficient, and quantization by a step width, that is, normalization is performed. Thereby, the value of the conversion coefficient, that is, the dynamic range of the amplitude can be suppressed.

The comparison with the threshold value and the normalization process are often performed simultaneously. That is, when the conversion coefficient is normalized by a predetermined normalization coefficient and the result is converted into an integer, the conversion coefficient having a value lower than the normalization coefficient becomes zero.

The normalized transform coefficients are then Huffman coded and stored in memory.

In such two-dimensional orthogonal transform coding, since the amount of operation is large, the circuit scale of the orthogonal transform unit and the coding unit becomes large, and accordingly, the IC chips constituting these functional units are usually used. Power consumption is higher than that of ICs. Therefore, the power supplied from the battery is insufficient depending on the number of pictures taken by the electronic still camera and the battery capacity that can be mounted, and it is desired to reduce power consumption.

Aims of the present invention are to solve such a problem of the prior art and to provide a digital electronic still camera capable of suppressing unnecessary operation in compression encoding and saving power.

DISCLOSURE OF THE INVENTION According to the present invention, a digital electronic still camera for photographing an object field and storing image data representing the object field in a memory includes a block dividing unit for dividing the image data represented by the image data into a plurality of blocks. And orthogonal transform means for performing two-dimensional orthogonal transform on digital image data divided into a plurality of blocks, encoding means for encoding data orthogonally transformed by the orthogonal transform means, and operations of the orthogonal transform means and the encoding means Operation control signal supply means for supplying an operation control signal for controlling the orthogonal transform means and encoding means,
The operation time is controlled by the operation control signal supplied from the operation control signal supply means.

Description of Embodiments Next, embodiments of a digital electronic still camera according to the present invention will be described in detail with reference to the accompanying drawings.

Referring to FIG. 1, an embodiment of a digital electronic still camera is shown. This camera has an imaging device 12, which captures an object scene, compresses and encodes an image signal representing the image in the form of digital data by an orthogonal transform unit 28 and an encoding unit 26, and stores the image data in a memory card 40. It is a device that accumulates in.

For the imaging device 12, for example, a solid-state imaging device such as a CCD is advantageously applied, and an imaging field is photographed by the imaging lens 10,
A color image signal representing the object scene is, for example, red (R),
The imaging device outputs green (G) and blue (B) color component signals. This color component signal is output in the same raster scanning format as the TV signal. Other functional units such as an exposure mechanism and a focusing mechanism required for photographing are not directly related to the understanding of the present invention, and thus description thereof is omitted. The memory card 40 is, for example, RA
A semiconductor memory device such as M is a storage device carried on a card-like substrate, and is advantageously detachably mounted on the device.

The output of the imaging device 12 is connected to an analog-to-digital converter (AD) 14, which is a signal conversion circuit that converts an input analog image signal into corresponding digital data and outputs it. This digital data is quantized to, for example, 8 bits for each of the color component signals RGB. This digital data output is sent to the signal processing unit 16
It is connected to the.

In this embodiment, the signal processing unit 16 performs a pre-processing such as a white balance adjustment and a gradation correction, and a luminance / color difference processing for converting the color component signal data into a luminance signal and a two-phase color difference signal to the image data. Perform processing.

The output of the signal processing unit 16 is connected to the memory controller 18. The memory controller 18 is connected to the memory 24, and controls storage of the output from the signal processing unit 16 in the memory 24 and reading from the memory 24. The image signal output from the imaging device 12 is in the form of a normal raster scanning sequential signal. The memory controller 18 blocks image data. That is, as shown in FIG. 2, the screen 50 of one frame represented by the image signal is divided into a plurality of areas of a predetermined size, that is, blocks 52, and each block 52
The image data is read every time.

Each block 52 may have a size of, for example, 8 pixels in the horizontal scanning (H) direction and 8 pixels in the vertical scanning (V) direction, or may have a different number of pixels in the vertical and horizontal directions. The image data read in units of the blocks 52 is sent from its output to the encoding unit 26 and the orthogonal transformation unit 28.

Image data for each block read from the memory 24 by the memory controller 18 is sent to the encoding unit 26,
Activity is calculated. After that, the data is again sent to the orthogonal transform unit 28 for each block and subjected to orthogonal transform, and then sent to the encoding unit 26 and encoded.

The orthogonal transformation unit 28 has a function of performing orthogonal transformation on image data input from the memory controller 18 in units of blocks and outputting the result. As the orthogonal transform, for example, a two-dimensional discrete cosine transform (DCT) is advantageously applied.
As a result, the image data of each block 52 is
Is converted into data in the frequency domain every time, and the data is arranged from the lower frequency in the horizontal (H) direction and the vertical (V) direction of the screen 50.

The image data for each block subjected to the two-dimensional orthogonal transformation in the orthogonal transformation unit 28 is arranged vertically and horizontally, low-order data is arranged in the upper left part, and becomes higher-order data in the lower right direction. DC component data is arranged at the upper left. The output of the orthogonal transform unit 28 is sent to the encoding unit 26.

The encoding unit 26 performs normalization after performing coefficient truncation on the image data that has been subjected to the two-dimensional orthogonal transformation in the orthogonal transformation unit 28, that is, the transform coefficients. The coefficient truncation is to compare the orthogonally transformed transform coefficient with a predetermined threshold value and to cut off a portion below the threshold value. In the normalization, the transform coefficient after the coefficient truncation is divided by a predetermined quantization step value, that is, a normalization coefficient α, and quantization is performed using the normalization coefficient α. The normalization coefficient α is obtained from the fixed length parameters K1 and K2 based on the value obtained by summing the activities of the blocks, as described later.

The normalization coefficient α is set according to the total activity of the image data, that is, the total value of the activities. The setting of the normalization coefficient α is performed according to the equation α = K1 · (total activity) + K2, for example, by the conversion shown in FIGS. 3A and 3B. According to the conversion shown in FIG. 3A, the normalization coefficient α changes in proportion to the total value of the activities. No.
In the conversion shown in FIG. 3B, the increase in the normalization coefficient α with respect to the increase in the total value of the activities is small, and high-precision encoding can be performed.

In this embodiment, the normalization is performed by multiplying the data stored in the weight table T as shown in FIG. 4 by the above-mentioned normalization coefficient α.

In the orthogonally transformed transform coefficients, low-frequency components are important as data, and high-frequency components are less important than low-frequency components. Therefore, the weight table T as shown in FIG. A small value is assigned to the component, and a large value is assigned to the high frequency component. The coefficient truncation was performed by the value α · T obtained by multiplying the data of this table T by the above-mentioned normalization coefficient α. Normalization is performed by dividing the transform coefficient. The product α · T of the normalization coefficient and the table is set for each of the luminance signal Y and the color difference signals Cr and Cb.

The encoding unit 26 encodes a DC component of data for each block input from the memory controller 18 and an AC component of data for each block input from the orthogonal transform unit 28. The normalized transform coefficients are arranged in blocks in the same manner as the pixel data shown in FIG. 5, and their AC components are scanned in a zigzag manner in order from the low-frequency components as shown in FIG. Encoded at 26.

The encoding unit 26 encodes the normalized transform coefficients scanned in a zigzag manner. Since the AC component of the conversion coefficient is often continuous with zeros, the amount of continuous data of zero value,
That is, a zero run length is detected, a zero run length and a non-zero amplitude are obtained, and these are subjected to two-dimensional Huffman coding. The amount of encoded data output from the encoding unit 26 is limited according to the previously calculated activity of each block. That is, the output of the coded data of each block is limited according to the ratio of the activity of each block to the total activity obtained by summing the activities of each block, and the length is fixed.

The orthogonal transform unit 28 and the encoding unit 26 perform various types of compression encoding by inputting various parameters from the control unit 20 as described later, and are formed by, for example, one IC chip.

The output of the encoding unit 26 is sent to the memory card 40 via a connector (not shown). Memory card 40 is, for example, SRA
A semiconductor memory device such as an M or an EEPROM is a storage device carried on a card-like substrate, and is advantageously detachably mounted on the device.

An example of data recorded on the memory card 40 is shown in FIG. As shown in the figure, in the recording area of the memory card 40, as will be described later, normalized table data TY · αY of the luminance signal Y, compressed luminance signal data Y,
Data is recorded in the order of the normalized table data Tr · αr of the color difference signal Cr, the compressed color difference signal data Cr, the normalized table data Tb · αb of the color difference signal Cb, and the compressed color difference signal data Cb. Normalized table data TY / αY, Tr / α
r and Tb · αb are used when decoding the compressed signals Y, Cr, and Cb.

The parameter setting unit 30 sets parameters necessary for compression encoding for each of the luminance signal Y, the color difference signals Cr, and Cb in the case of color image data, and outputs the parameters to the encoding unit 26.

An input operation unit 22 is connected to the parameter setting unit 30, and an instruction for setting various parameters used for compression coding is input from the input operation unit 22. The parameter setting unit 30 selects a desired parameter from parameters stored in a storage unit (not shown) according to an instruction from the input operation unit 22, and outputs the selected parameter to the encoding unit 26.

The parameters include, for example, the number of blocks constituting an image, the code amount, fixed length parameters K1, K2, code transfer speed, quantization tables TY, TCr, TCb, and the like.
The number of blocks constituting the image is sent to notify the encoding unit 26 of the number of blocks, since the number of divided blocks varies according to the size of the image captured and stored in the memory, that is, the number of pixels. . As the code amount, the total bit number, that is, the code amount is transmitted because the total number of bits allocated to the compression-encoded data varies depending on the image quality mode of the compressed image data and the capacity of the memory card 40. As described above, the fixed length parameters K1 and K2 are used as coefficients for obtaining a normalization coefficient α used in normalization. Code transfer speed is memory card 40
The transfer speed of data to a recording medium such as
Sent to inform. Quantization tables TY, TC
r and TCb are the luminance signal Y and the color difference signal C as described above.
Used in r, Cb normalization.

The control unit 20 is a control unit that controls the entire apparatus.In particular, the orthogonal conversion unit 28 is configured to stop the orthogonal transform operation and reduce the power consumption by a standby signal or an active signal for causing the orthogonal transform operation to be performed. And outputs to the encoding unit 26 a standby signal for stopping the encoding operation to reduce power consumption or an active signal for causing the encoding operation. Further, it outputs a control signal for controlling reading of image data from the memory 24 to the memory controller 18. Orthogonal transform unit 28 and coding unit
The standby unit 26 receives the standby signal and the active signal output from the control unit 20, respectively, and enters a standby state in which the orthogonal transform and the encoding operation are stopped in response thereto, or an operation state in which the operation can be performed. The control unit 20 can control the operation or stop of the operation by stopping the operation clock signals for the orthogonal transformation unit 28 and the encoding unit 26, for example. As described above, the orthogonal transform unit 28 and the encoding unit 26 are configured to stop the orthogonal transform operation and the encoding operation in response to the standby signal, and the orthogonal transform unit 28 and the encoding unit 26 are controlled to the standby state. When the orthogonal transform operation and the encoding operation are stopped, the power consumption during the period in which the operation is stopped is reduced.

1 will be described with reference to the timing chart of FIG. 8 and the flowchart of FIG.

First, the operator inputs instructions of various parameters according to the size of an image captured from the input operation unit 22, the quality of an image to be compressed, the capacity of the memory card 40, and the like (100). The instruction input to the input operation unit 22 is sent to the parameter setting unit 30, and the parameter setting unit 30 selects the designated parameter from a plurality of parameters stored in a storage unit (not shown) in accordance with the instruction.

When the photographing is instructed, the imaging device 12 photographs the scene and outputs a one-frame image signal representing the scene. This image signal is output from the imaging device 12 to the analog / digital converter 14, where it is converted into corresponding digital data (102). This image data is subjected to preprocessing and luminance / color difference processing in the signal processing unit 16, and is temporarily stored in the memory 24 under the control of the memory controller 18 (104).

As shown in FIG. 8, at time t1, a standby signal for stopping the orthogonal transform operation from the control unit 20 to the orthogonal transform unit 28 to save power consumed by the orthogonal transform unit 28 is transmitted, and An active signal is sent to the unit 26. Thereby, the orthogonal transform unit 28 enters the standby state and operates in the low power consumption mode, and the encoding unit 26 changes from the standby state to the operating state. By the control signal from the control unit 20, from the parameter setting unit 30 to the encoding unit 26, the number of image blocks,
Parameters such as a code length fixed length parameter and a code transfer speed are transferred (106). When these parameters are sent to the encoder 26, a bus switching signal is sent from the control unit 20 to the memory controller 18, and the image data for each block is read from the memory 24 under the control of the memory controller 18 (108). The read image data for each block is sent to the encoding unit 26, where the total activity is obtained, and the normalization coefficient α is obtained using the fixed length parameters K1 and K2. Also, the bit allocation of the encoded data for each block is determined from the activity of each block with respect to the total activity. In accordance with the bit allocation, the output of the data to be encoded later is fixed in length (110).

The parameter setting unit is controlled by a control signal from the control unit 20.
From 30, the quantization table TY for the luminance signal Y is
Is sent to the memory card 40 from the encoding unit 26 and recorded (112). As a result, the luminance signal Y can be compressed and encoded.

Here, the control unit 20 outputs an active signal to the orthogonal transformation unit 28 as shown at time t2 in FIG. As a result, the orthogonal transform unit 28 enters a state where the orthogonal transform of the luminance signal can be performed.

The image data for each block of the luminance signal Y is read out from the memory 24 and sent to the orthogonal transformation unit 28.
The DC component of the image data of each block, that is, the average value of each pixel, is sent to the encoding unit 26. The image data for each block sent to the orthogonal transformation unit 28 is subjected to orthogonal transformation and sent to the encoding unit 26.

In the encoding unit 26, the luminance signal Y is normalized using the table α · TY, then Huffman encoding is performed, and the luminance signal Y is fixed according to the previously calculated bit allocation of the encoded data for each block. Lengthening is performed (114). As shown in FIG. 7, the fixed-length luminance signal data Y is recorded in the memory card 40 in the area next to the table α · TY.

Next, as shown at time t3 in FIG. 8, the control unit 20 outputs a standby signal to the orthogonal transform unit 28. As a result, the orthogonal transform unit 28 enters the standby state again. According to the control signal from the control unit 20, the color difference signal from the parameter setting unit 30
The quantization table for Cr Cr is sent to the encoding unit 26, and the table α · TCr is recorded from the encoding unit 26 to the memory card 40 (116).

Here, the control unit 20 outputs an active signal to the orthogonal transform unit 28, as shown at time t4 in FIG. Thus, the orthogonal transform unit 28 is in a state where the orthogonal transform of the color difference signal Cr can be performed.

The image data for each block of the color difference signal Cr is read from the memory 24 and sent to the orthogonal transform unit 28.
The DC component of the image data of each block, that is, the average value of each pixel, is sent to the encoding unit 26. The image data for each block sent to the orthogonal transformation unit 28 is subjected to orthogonal transformation and sent to the encoding unit 26.

The encoding unit 26 normalizes the color difference signal Cr using the table α · TCr, and thereafter performs encoding and fixed length (118). As shown in FIG. 7, the data Cr of the compression-coded chrominance signal is recorded in the area next to the table α · TCr of the memory card 40.

Further, as shown at time t5 in FIG. 8, the control unit 20 outputs a standby signal to the orthogonal transform unit 28. As a result, the orthogonal transform unit 28 enters the standby state again. According to the control signal from the control unit 20, the color difference signal from the parameter setting unit 30
The quantization table TCb for Cb is sent to the encoding unit 26, and the table α · TCb is recorded from the encoding unit 26 to the memory card 40.

Here, the control unit 20 outputs an active signal to the orthogonal transform unit 28 as shown at time t6 in FIG. As a result, the orthogonal transform unit 28 enters a state where the orthogonal transform of the color difference signal Cb can be performed.

The image data for each block of the color difference signal Cb is read from the memory 24 and sent to the orthogonal transform unit 28, and the color difference signal Cb
The DC component of the image data of each block, that is, the average value of each pixel, is sent to the encoding unit 26. The image data for each block sent to the orthogonal transformation unit 28 is subjected to orthogonal transformation and sent to the encoding unit 26.

The encoding unit 26 normalizes the color difference signal Cb using the table α · TCb, and thereafter performs encoding and fixed length (122). The compression-coded color difference signal data Cb is recorded on the memory card 40 as shown in FIG.

When the compression encoding of the color difference signal Cb ends, a compression end signal is output from the encoding unit 26 to the control unit 20, and the compression encoding ends. When the compression encoding process is completed, at time t7 in FIG.
As shown in (5), a standby signal is sent to each of the orthogonal transformer 28 and the encoder 26, and the orthogonal transformer 28 and the encoder 26 return to the standby state, respectively, and operate with low power consumption.

According to the present embodiment, a parameter selected from various parameters is sent to the encoding unit 26, and thereby encoding can be performed. Then, at the time of these parameter transfer, the orthogonal transform unit 28 is set to a standby state by sending a standby signal to the orthogonal transform unit 28, and the orthogonal transform operation is stopped.

Therefore, since the power consumption of the orthogonal transform unit 28 requiring large power is suppressed at the time of parameter transfer, power consumption can be reduced. This makes it possible to prevent the battery from running short during shooting, and to smoothly perform shooting and compression encoding processing.

Furthermore, since the quantization tables TY, TCr, and TCb are transferred for each of the luminance signal Y and the chrominance signals Cr and Cb, appropriate encoding can be performed for each of the luminance signal Y and the chrominance signals Cr and Cb. The memory area for storing the quantization table of the unit 26 can be reduced.

In the case of compression encoding of a black-and-white signal, it is possible to easily perform encoding for a black-and-white signal by omitting the processing of the color difference signals Cr and Cb and performing only compression encoding of the luminance signal Y. Yes, and does not require special equipment and sequences for black and white signals.

When the orthogonal transform unit or the encoding unit that performs the compression encoding of the luminance signal Y is a separate IC from these functional units that perform the compression encoding of the color difference signals Cr and Cb, these ICs are individually Power consumption can be saved by controlling to enter a standby state in which the orthogonal transform operation or the encoding operation is stopped. In particular, in the present embodiment, the operation of the orthogonal transform unit 28 is stopped in the first pass until the quantization table TY is transferred after obtaining the total activity, the normalization coefficient α, and the bit allocation for each block. In a second pass for actually encoding and outputting the image data read out for each block, the image data for each block is encoded based on the calculated parameters such as the bit distribution, and the amount of code is controlled. Output from the encoding unit 28.
In this case, also when the parameters for the color difference signal are transferred, the operation of the orthogonal transform unit 28 is similarly stopped, and the power consumption is reduced.

Effect As described above, according to the present invention, when the orthogonal transforming means and the encoding means requiring large power do not need to operate, by putting them into a standby state, the power consumption required for compression encoding can be reduced. . Therefore, it is possible to prevent occurrence of a trouble due to a shortage of power supplied from the battery.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing one embodiment of a digital electronic still camera according to the present invention, FIG. 2 is an explanatory diagram showing an example of a block configuration of a screen in the embodiment shown in FIG. 1, FIGS. 3A and 3B. The figure shows an example of a look-up table for converting the total value of the activity into a normalization coefficient. FIG. 4 shows an example of weight table data. FIG. 5 shows an example of pixel data constituting a block. 6, FIG. 6 is a diagram showing the order of performing run-length and non-zero encoding, FIG. 7 is a diagram showing an example of data recorded on the memory card of FIG. 1, and FIG. 8 is an operation of FIG. FIG. 9 is a flow chart showing the operation of the apparatus shown in FIG. Explanation of Signs of Main Parts 12 ... Imaging Device 18 ... Memory Controller 24 ... Memory 26 ... Encoding Unit 28 ... Orthogonal Transformation Unit 30 ... Parameter Setting Unit 40 ... Memory Card

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Mikio Watanabe 2-26-30 Nishiazabu, Minato-ku, Tokyo Fuji Photo Film Co., Ltd. (56) References JP-A-63-122392 (JP, A) JP-A Sho 61-135286 (JP, A) JP-A-55-147073 (JP, A) JP-A-1-165283 (JP, A)

Claims (3)

(57) [Claims] 1. A digital camera for photographing an object scene and outputting image data representing the object scene to a recording medium,
A camera configured to store the image data in a readable manner; and performing a storage control on the storage unit to vertically and horizontally store the image data stored in the storage unit in each of a first stage and a second stage. First control means for dividing the data into a plurality of blocks each including a plurality of pixels in the direction and reading data for each block; setting means for setting a first parameter for code amount control and a quantization table; An orthogonal transformation means which is controlled to an operation stop state in the first step and is controlled to an operation state in the second step in response to an operation control signal supplied to the input; Orthogonal transform means for orthogonally transforming the data in an operating state to calculate a transform coefficient; and a second controlling a compression encoding process on the image data.
Control means for supplying, to the control input, the operation control signal for controlling the operation of the orthogonal transform means to an operation stop state and an operation state, and the first control means Encoding means for encoding a DC component of data read from the storage means and an AC component of the transform coefficient, the encoding means based on the data read from the storage means in the first step Calculating means for calculating an activity and a total activity of each block; and, in the first stage, setting a normalization coefficient based on the first parameter and the total activity, and setting the normalization coefficient and the quantization A normalization means for generating a normalization table corresponding to the table, wherein in the second step, the AC component of the transform coefficient supplied from the orthogonal transform means is normalized. A normalizing unit that normalizes the data by a table, and a limiting unit that limits the amount of encoded data of each block according to the activity. The encoding unit in the first step stores the normalization table in the recording medium. The second control means supplies an operation control signal to the orthogonal transformation means for controlling the orthogonal transformation means to an operation stop state in the first stage prior to compression-encoding the image data. When the operation of the orthogonal transform means is stopped and the normalization table is obtained, an operation control signal for controlling the orthogonal transform means to an operation state is supplied to the orthogonal transform means, and the first and second steps are performed. The encoding unit in the second stage encodes a DC component of data read from the storage unit by the first control unit, and in the operation state in the second stage, The AC component of the transform coefficient calculated by the orthogonal transform means is normalized and encoded according to the normalization table, and encoded data whose data amount is limited to a predetermined length according to the activity is output to the recording medium. A digital camera. 2. The camera according to claim 1, wherein, when the image data is color image data, the setting unit supplies a second parameter for each signal component of the color image data to the encoding unit. And the second control means supplies the second parameter to the encoding means, and generates the normalization table for each signal component by the encoding means. A digital camera, wherein an operation control signal for controlling the means to be in an operation stop state is supplied to the orthogonal transform means, and the orthogonal transform means stops the orthogonal transform operation in response to the operation control signal. 3. The camera according to claim 1, wherein said second control means sends a second operation control signal for controlling the operation of said encoding means to an operation stop state or an operation state to said encoding means. The encoding means, in response to the second operation control signal,
A digital camera controlled to an operation stop state for stopping an encoding operation or an operation state for encoding image data converted by the orthogonal transformation means.