JPH0352385A - Digital electronic still camera - Google Patents

Abstract

PURPOSE:To prevent the occurrence of a trouble due to power deficiency supplied from a battery by bringing and orthogonal transformation means and a coding means requiring large power into the standby state when the operation of them is disabled to reduce power consumption required for compression coding. CONSTITUTION:The camera is provided with a block processing means 18 dividing a picture data represented from a picture into plural blocks, an orthogonal transformation means 28 applying 2-dimension orthogonal transformation to the digital picture data split into plural blocks, a coding means 26 coding the data subject to orthogonal and an operation control signal supply means 20. Then the operating time of the orthogonal transformation means 28 and the coding means 26 is controlled by an operation control signal supplied from the operation control signal supply means 20. Thus, the unrequired operation for the large circuit scale such as the orthogonal transformation means 28 and the coding means 26 is regulated to save the power and the occurrence of a trouble due to deficient power supplied from the battery is prevented.

Description

[Detailed Description of the Invention] The present invention relates to a digital electronic still camera, and more particularly to a digital electronic still camera that can save electricity. A digital electronic still camera is a photographing device that photographs a subject using a solid-state imaging device such as a CCD and stores an image signal representing the scene in a memory in the form of digital data. Memory is often in the form of a memory card equipped with RAM such as semiconductor memory. In that case, data compression such as orthogonal transform encoding is often performed in order to use the memory storage area efficiently.

In particular, two-dimensional orthogonal transform encoding is widely used because it can perform high compression rate I encoding and suppress image f1 distortion that accompanies encoding. In such two-dimensional orthogonal transform encoding, image data is divided into a predetermined number of blocks, and the image data within each block is subjected to two-dimensional orthogonal transform. The orthogonally transformed image data, that is, the transformation coefficients, are compared with a predetermined threshold, and truncation of the C portion below the threshold is performed (coefficient truncation). As a result, the conversion coefficients below the threshold are then
Processed as OC data. Next, the transform coefficients whose coefficients have been truncated are divided by a predetermined quantization step value, t, that is, a normalization coefficient, and quantization, that is, normalization, is performed by the step width. This gives the value of the conversion coefficient.
In other words, comparison with this threshold and normalization processing, which can suppress the dynamic range of amplitude, are often performed at the same time. That is, when the transformation coefficients are normalized by a predetermined normalization coefficient and the result is converted into an integer, the transformation coefficient having a value lower than the normalization coefficient becomes O. The normalized transform coefficients are then Huffman encoded and
Stored in memory. In such two-dimensional orthogonal transform encoding, since the amount of calculation is large, the circuit scale of the orthogonal transform section and the encoding section becomes large. Along with this, the IC chips that make up these functional units consume more power than normal ICs. Therefore, depending on the number of shots taken by the electronic still camera and the capacity of the battery that can be installed, the power supplied from the battery may be insufficient. It is desired to save power consumption.In order to save power consumption, for example, the orthogonal transform unit and the encoder unit are not operated when these IC chips are not required to operate. It is conceivable to supply a clock signal only when necessary.
However, when the operation is controlled by the clock signal, there is a risk of malfunction due to poor rise characteristics of the clock signal.The present invention solves these problems of the conventional technology. According to the present invention, it is an object of the present invention to provide a digital electronic still camera that can save power by suppressing unnecessary operations in compression encoding. A digital electronic still camera that stores image data representing a scene in a memory has a blocking means that divides the image data represented by the image data into a plurality of blocks, and a digital haze image data 77z? Sencho Tosaiji's direct-to-approach software provides an encoding means for encoding the data orthogonally transformed by the orthogonal transformation means, and an operation control signal for controlling the operation of the orthogonal transformation means and the encoding means. The operating time of the orthogonal transform means and the encoding means is controlled by the operation control signal supplied from the operation control signal supply means.

1 Next, an actual example of a digital electronic still camera according to the present invention will be explained in detail with reference to the accompanying drawings.

Referring to Figure 1, an embodiment of a digital electronic still camera is shown. This camera has an imaging device l2, which photographs a field and converts the image signal representing the scene into a digital data into an orthogonal transform unit 28,
This is a device that compresses and encodes the data using the encoder 26 and stores it in the memory card 40. The imaging device l2 is, for example, C
Solid-state imaging devices such as CDs are advantageously applied, and the imaging lens 10 is used to visualize the subject, thereby producing color images that extend the life of the subject.
Conflict {! Snake 2 For example, red (R). Rim (G) and blue fB1
This is an imaging device that outputs color component signals in the form of color component signals. This color component signal is. It is output in rask scanning format similar to TV signals. Other functional units necessary for photographing, such as an exposure mechanism and a focusing mechanism, are not directly related to the understanding of the present invention, so their explanation will be omitted. The memory card 40 is a storage device in which a semiconductor memory device such as a RAM is supported on a card-like base, and is preferably detachably attached to the apparatus. The output of the imaging device l2 is connected to an analog-to-digital converter (AD) 14, and the converter l4 is a signal conversion circuit that converts a manually input analog image signal into corresponding digital data and outputs it. This digital data is quantized into, for example, 8 bits for each of the color component signals RGB. This digital data output is connected to the signal processing section l6. In this embodiment, the signal processing unit l6 is a signal processing unit that performs preprocessing such as white balance adjustment and gradation correction, and luminance color difference processing that converts color component signal data into a luminance signal and two-phase color difference signals on image data. Process.

The output of the signal processing section l6 is connected to the memory controller l8. The memory controller l8 is connected to the memory 24 and controls storage of the output from the signal processing unit l6 in the memory lJ24 and reading from the memory 24 1B.

The image signal output from the imaging device l2 is . It takes the form of a normal rask scan sequential signal. The memory controller I8 blocks image data. That is, as shown in FIG.
The image data is read out for each block 52. Each block 52 is configured, for example, by horizontal scanning (8 in the old direction).
The size of pixels may be 8 pixels in the vertical scanning tv+ direction, or the size of the number of pixels may be different in the vertical and horizontal directions.
The image data thus read out in units of blocks 52 is output from the encoding unit 26 and the orthogonal transform encoding unit 2.
Sent to 8.

The image data for each block read out from the memory 24 by the memory controller l8 is sent to the encoding unit 26, where the activity is calculated. After that, each block is again sent to the orthogonal transform unit 28 and orthogonally transformed.
The data is sent to the encoding unit 26 and encoded. The orthogonal transformation unit 28 performs orthogonal transformation on the image data input from the memory controller l8 for each block,
It has a function to output. As the orthogonal transformation, for example, a two-dimensional discrete cosine transformation (DCTI) is advantageously applied.Thereby, the image data of each block 52 is transformed into frequency domain data for each block 52, and the image data of the screen 5
Data is arranged in the horizontal (IH) direction of 0 and in the vertical (m) direction starting from the lowest frequency. The image data for each block subjected to two-dimensional orthogonal transformation in the orthogonal transformation unit 28 is arranged vertically and horizontally, with low-order data arranged in the upper left part and higher-order data moving toward the lower right. DC component data is placed at the top left. The output of the orthogonal transform unit 28 is sent to the encoder 26. The encoding unit 26 performs normalization after truncating the coefficients of the image data that has been subjected to the two-dimensional orthogonal transformation in the orthogonal transformation unit 28, that is, the transformation coefficients. Coefficient truncation is to compare the orthogonally transformed transform coefficient with a predetermined Q(a) and truncate the part below the M value. Normalization is to convert the coefficient truncated transform coefficient to a predetermined quantization step value. , that is, divided by the normalization coefficient a, and quantized by the normalization coefficient α.The normalization coefficient α is based on the sum of activities for each block, and is determined by the fixed length parameter Kl, as described later. , κ2. The normalization coefficient a 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 a is given by the formula a=K l · (total activity) + K2 According to the conversion shown in FIG. 3A, the normalization factor tlla changes in proportion to the total activity value. As shown in FIG. 3B, The conversion is such that the increase in the normalization coefficient a is small relative to the increase in the total value of activities, and high-precision encoding can be performed.In this example, the normalization is performed as shown in Fig. 4. This is done by multiplying the data stored in the weight table T by the normalization coefficient α described above.The low-frequency components of the orthogonally transformed transformation coefficients are important as data, and the high-frequency components are the same as the low-frequency components. Since their importance is relatively low, a weighting table T as shown in Fig. 4 assigns a small value to the low frequency component and a large value to the high frequency component, and the data in this table T is assigned a small value to the high frequency component. Normalization is performed by dividing the transform coefficient whose coefficients have been truncated as described above by the value a-T obtained by multiplying the normalization coefficient a.The product a-T of the normalization coefficient and the table is: Luminance These settings are made for each of the signal Y and the color difference signal Cr.Cb.
Encode the AC component of the data for each block input from a. The normalized transform coefficients are arranged in blocks like the pixel data shown in FIG. 5, and the alternating current components are scanned in a zigzag pattern starting from the low frequency component as shown in FIG. 26. The encoding unit 26 encodes the normalized transform coefficients scanned in a zigzag pattern. Since the alternating current component of the conversion coefficient often has continuous zeros, the continuous amount of zero value data, that is, the zero run length, is detected, the zero run length and the non-zero amplitude are determined, and this is converted into a two-dimensional Perform Huffman encoding. The amount of encoded data output from the encoder 26 is limited depending on the activity of each block. That is, the output of the encoded data of each block is limited according to the ratio of the activity of each block to the total activity of each block, and the length is fixed. The orthogonal transform unit 28i5 and the encoding unit 26 perform various compression encodings by inputting various parameters from the iIlto unit 2a, as will be described later, and are each formed by one IC chip, for example. The output of the encoder 26 is sent to the memory card 40 via a connector (not shown). The memory card 40 is a storage device in which a semiconductor memory device such as an SRAM or an EEFROM is supported on a card-like base, and is preferably removably attached to the apparatus. memory card 4
An example of data recorded in 0 is shown in Figure 7. As shown in the figure. In the recording area of the memory card 40, normalization table data TY and αY of the luminance signal Y, compressed luminance signal data Y, and color difference signal C are stored in the recording area of the memory card 40, as described later.
'Normalized table data Tr-ar. Compressed color difference signal data Cr. Data are recorded in the order of normalization table data Tb/αb of color difference signal cb and compressed color difference signal data cb. Normalized table data TY-aY.
Tr-arJ and Tb・αb are. Compressed signal Y. C
r. Used when decoding Cb. The parameter setting N30 includes a luminance signal Y, a color difference signal Cr. Parameters necessary for compression encoding for each Cb are set and output to the encoding unit 26. A manual operation section 22 is connected to the parameter setting section 30.
Instructions for setting various parameters used for compression encoding are input from the manual operation unit 22. In accordance with instructions from the input operation section 22, the parameter setting section 30 selects a desired one from among the variations stored in a storage section (not shown) and outputs it to the encoding section 26. The parameters include, for example, the number of blocks constituting an image, the amount of code, fixed length parameters K1, K2, code transfer speed, quantization table TY. TCr. T.C.
There are b, etc. The number of blocks constituting an image is sent to inform the encoding unit 26 of the number of blocks, since the number of divided blocks differs depending on the size of the image taken and stored in memory, that is, the number of pixels. ．． The total number of bits, that is, the amount of codes, is sent because the total number of bits allocated to compression-encoded data varies depending on the image quality mode of the compressed image data and the capacity of the memory card 40. The fixed length parameters K1 and K2 are
As mentioned above, the normalization factor α used in the normalization
It is used as a coefficient to calculate. The code transfer speed is sent to inform the encoding unit 26 of the data transfer speed to a recording medium such as the memory card 40. Quantization table TV. TCr. TCb is the luminance signal Y and the color difference signal Cr. Used in normalization of Cb. The control section 20 is an Illll section that controls the entire device, and in particular outputs a standby signal or an active signal to the orthogonal transformation section 28 and the encoding section 26. It also outputs a control signal for controlling reading of image data from the memory 24 to the memory controller l8. The operation of the device shown in Fig. 1 will be explained using the timing chart shown in Fig. 8 and the flow chart shown in Fig. 9. First, the operator inputs instructions for various parameters according to the size of the image to be photographed, the quality of the image to be compressed, the capacity of the memory card 40, etc. using the manual operation 8322 (100
1. The instruction input to the input operation section 22 is sent to the parameter setting section 30, and the parameter setting section 30 follows the instruction and selects the instructed parameter from Ifi parameters stored in a storage section (not shown).

When instructed to photograph, the imaging device l2 photographs the scene and outputs an image signal of l frames representing the scene. This image signal is. The image data is outputted from the m-image device l2 to the analog-to-digital conversion 814, where it is converted into corresponding digital data (1021). (1041) As shown in FIG. 8, a standby signal is sent from the control unit 20 to the orthogonal transformation unit 28 and an active signal is sent to the encoding unit 26 at time tl. , orthogonal transformation unit 28
is in a standby state, and the encoding unit 26 is in an operating state.

The control signal from the iill m section 20 causes the parameter setting section 30 to send the . Parameters such as image block size, code amount fixed length parameter, and code transfer speed are transferred (006) When these parameters are sent to the encoder 26, a bus switching signal is sent from the control unit 20 to the memory controller l8. ．． Image data for each block is read out from the memory 24 under the control of the memory controller 18 (l-ro 8). The read image data for each block is sent to the encoding unit 26, the total activity is determined, and the fixed length parameter K
1. The normalization coefficient α is found using K2. Also, the bit allocation of encoded data for each block is calculated from the activity of each block relative to the total activity. According to this bit allocation, the output of encoded data is made into a fixed length (1101!1) The quantization table TY for the luminance signal Y is set from the parameter setting section 30 to the encoded data by the control signal from the control section 20. The table α・TY obtained by multiplying the normalization coefficient α and the quantization table TY is sent from the encoding unit 26 to the memory card 40 and is recorded (1121).
This makes it possible to perform compression encoding processing on the luminance signal Y.

Here, the control section 20 outputs an active signal to the orthogonal transformation section 28, as shown at time t2 in FIG. This puts the orthogonal transform unit 28 in a state where it can perform orthogonal transform of the luminance signal. The image data for each block of the luminance signal Y is read out from the memory 24 and sent to the orthogonal transform section 28, and the DC component of the image data for each block of the luminance signal Y, that is, the average value of each pixel is read out from the encoding section 26. Sent to. Orthogonal transformation unit 2
The image data for each block sent to 8 is orthogonally transformed and sent to the encoding unit 26. In the encoding unit 26, the luminance signal Y is normalized using the table a-TY, and 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 (1141). Data Y of the luminance signal made into a fixed length is recorded in the area next to table α.TY in the memory card 40, as shown in FIG.

Next, as shown at time t3 in FIG. 8, a standby signal is output from the control section 20 to the orthogonal transformation section 28. As a result, the orthogonal transform unit 28 returns to the standby state. In response to a control signal from the control unit 20, the parameter setting unit 30 outputs the quantization table TCr for the color difference signal Cr to the encoding unit 2.
6, and the table a-Tcr is recorded from the encoding unit 26 to the memory card 40 (1161) Here, the control unit 20 outputs an active signal to the orthogonal transformation unit 28, as shown at time t4 in FIG. This puts the orthogonal transform unit 28 in a state where it can perform orthogonal transform on the color difference signal C'.

The image data for each block of the color difference signal Cr is read out from the memory 24 and sent to the orthogonal transform section 28, and the DC component of the image data for each block of the color difference signal Cr, that is, the average value of each pixel is read out from the encoding section 26. Sent to. The image data for each block sent to the orthogonal transform section 28 is orthogonally transformed and sent to the encoder 26.

In the encoding unit 26, the color difference signal Cr is normalized using the table α·TCr, and then encoding and fixed length conversion are performed +1181. The compression-encoded color difference signal data Cr is stored in the memory card 4 as shown in FIG.
0 is recorded in the next area of table α・TCr. Furthermore, as shown at time t5 in FIG. 8, a standby signal is output from the control section 20 to the orthogonal transformation section 28. As a result, the orthogonal transform unit 28 returns to the standby state. In response to a control signal from the control unit 20, the parameter setting unit 30 outputs the signature conversion table TCb for the color difference signal cb to the encoding unit 2.
6, and the table a-TCb is recorded from the encoding unit 26 to the memory card 40.

Here, the control section 20 outputs an active signal to the orthogonal transformation section 28 as shown in IIt6 in FIG. This puts the orthogonal transform unit 28 in a state where it can perform orthogonal transform of the color difference signal cb. The image data for each block of the color difference signal cb is read out from the memory 24 and sent to the orthogonal transform section 28, and the DC component of the image data for each block of the color difference signal cb, that is, the average value of each pixel is read out from the encoding section 26. Sent to. The image data for each block sent to the orthogonal transform unit 28 is orthogonally transformed and sent to the encoder 26. In the encoding unit 26, the color difference signal cb is normalized using the table α・TCb, and then encoded and fixed length is performed (1221. The data cb of the compression encoded color difference signal is As shown in the figure, it is recorded on the memory card 40. When the compression encoding of the color difference signal cb is completed, the encoding unit 26
A compression end signal is output from the controller 20 to the control unit 20, and compression encoding ends. According to this embodiment, parameters selected from various parameters can be sent to the encoding unit 26, thereby allowing encoding to be performed. When transferring these parameters, the orthogonal transform section 28 is placed in a standby state by sending a standby signal to the orthogonal transform section 28.

Therefore, the power consumption of the orthogonal transform unit 28, which requires a large amount of power, is suppressed during parameter transfer, so that power consumption can be saved. This prevents the battery from running out during shooting, and enables smooth shadow and compression encoding processing. Furthermore, i1 childization table T Y . TCr. T.C.
b. Luminance signal Yi5 and color difference signal Cr. Since each Cb is transferred, the Il degree signal Y and the color difference signal Cr. Appropriate encoding can be performed for each Cb, and the memory area for storing the quantization table of the encoding unit 26 can be reduced. Note that in the case of compression encoding of a monochrome signal, the color difference signal Cr. By omitting the processing of Cb and only compressing and encoding the luminance signal Y, encoding for black-and-white signals can be easily performed, and a special device and sequence for black-and-white signals are not necessarily required.

In addition, the orthogonal transform unit or encoding unit that compresses and encodes the Il degree signal Y is connected to the color difference signal Cr. When using a separate IC from these functional units that perform Cb compression encoding, these I
Power consumption can be saved by individually controlling C to put it in a standby state.

According to the present invention, the power consumption required for compression encoding can be reduced by putting the orthogonal transform means and encoding means, which require large amounts of power, into a standby state when they do not need to operate. Therefore, troubles caused by insufficient power supplied from the battery can be prevented.

[Brief explanation of drawings]

FIG. 1 is a functional block diagram showing an embodiment of the digital electronic still camera according to the present invention, FIG. Figure 5 shows an example of weight table data, Figure 5 shows an example of pixel data constituting a block, Figure 6 shows the order of run length and non-zero encoding, and Figure 7 shows an example of the pixel data that constitutes a block. Fig. i is a diagram showing an example of data recorded on the memory card; Fig. 8 is a timing chart showing the operation control IB signal of Fig. 1; and Fig. 9 is a flowchart showing the operation of the device shown in Fig. 1. . main,. Description of 1 Imaging device Memory controller Memory encoding section Orthogonal transformation section Parameter setting section Memory card 2nd figure Figure 8 t1 t2 t) ta tsts t7 Figure 9

Claims (1)

[Claims] 1. In a digital electronic still camera that photographs a subject and stores image data representing the subject in a memory,
The camera includes: a blocking unit that divides image data represented by the image data into a plurality of blocks; and a block dividing unit that divides the digital image data divided into the plurality of blocks into two
orthogonal transformation means for performing dimensional orthogonal transformation; encoding means for encoding data orthogonally transformed by the orthogonal transformation means; and an operation control signal for supplying an operation control signal for controlling the operations of the orthogonal transformation means and the encoding means. supply means, wherein the orthogonal transformation means and the encoding means have operating times controlled by the operation control signal supplied from the operation control signal supply means. 2. The camera according to claim 1, further comprising: when the image data is color image data, parameter supply means supplies parameters for each signal component of the color image data to the encoding means. and the operation control signal supplying means, while the parameter supplying means supplies the parameters to the encoding means,
A digital electronic still camera characterized in that a standby signal is supplied to the orthogonal transformation means.