JPH06268961A - Digital electronic still camera - Google Patents

Abstract

PURPOSE:To attain quantization matching the 4 characteristic of a picture when picture data subject to orthogonal transformation is quantized. CONSTITUTION:A block activity calculation section 108 obtains a degree of a high frequency component included in each block, that is, a block activity from picture data subject to block processing. An evaluation function generating section 110 obtains an evaluation function such as a variance from the block activity of plural blocks and gives the result to a quantization table setting section 116. A total activity calculation section 112 obtains a total activity and gives it to the setting section 116. The quantization table setting section 116 selects a quantization coefficient based on both the evaluation function representing a characteristic of the picture and the entire characteristic of the picture and sets the result to a quantization section 104. Thus, even when the picture has the same value of the total activity but the distribution of the high frequency component differs, the quantization is executed by a different quantization coefficient and then the quantization matching the picture characteristic is executed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital electronic still camera and, for example, to a digital electronic still camera which two-dimensionally orthogonally transforms image data of a photographed object scene image and records it on a recording medium.

[0002]

2. Description of the Related Art As is well known, in a digital electronic still camera, an image signal representing an image of an imaged object field is converted into digital data and recorded. In order to perform recording efficiently, these digital image data are compressed into a data amount less than a desired amount by a conversion method such as two-dimensional orthogonal transform coding, and the image of a semiconductor memory, a magnetic disk, an optical disk, or the like is compressed. It is recorded on the data recording medium.

As such an electronic still camera, for example, there is a digital electronic still camera such as a pending patent application by the same applicant as the present application, Japanese Patent Application No. 63-309870. In such an electronic still camera, image data of one screen imaged and digitized is divided into blocks of a predetermined number and a predetermined size, and the image data of each block is converted into a frequency domain image by a two-dimensional orthogonal transformation. It is converted into data, that is, a conversion coefficient.

The transform coefficient is divided by a quantizing coefficient according to the characteristics of the photographed image to be quantized. In this case, the quantization coefficient has been determined based on the total number of block activities representing the degree of high frequency components included in each block, that is, the total activity of the captured image. A plurality of quantized coefficients are prepared in the look-up table, which is selected and read based on the total activity of the image data, and the transform coefficient is divided. The quantized transform coefficient is then Huffman encoded and recorded in an image data storage medium such as a memory card.

[0005]

However, as described above, in the conventional technique, the quantization coefficient is determined based on the degree of the high frequency components included in the entire image, that is, the total activity. Quantization is performed with the same quantization coefficient even for images with different characteristics having the total activity, which is not necessarily quantized as data according to the characteristics of the image.

For example, when a high frequency component is uniformly distributed in an image as a whole, and in another image, a high frequency component is included in a large amount in some parts and distributed. The characteristics of the image are completely different from those in the case where it is present. But,
When the total activity is calculated by both sides, the same value may be obtained for the entire image, and even if the characteristics of the image are different, the same quantization coefficient is used for the calculation. In these cases, for example, when the quantization coefficient is set low at the same value and the high frequency components are evenly distributed, the influence of the quantization is small at the time of reproduction, but the high frequencies are partially In an image containing a large number of frequency components, the deterioration of that portion becomes noticeable. Therefore, even if the total activity has the same value, it is necessary to change the quantization coefficient to perform the quantization more suited to the characteristics of the image.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a digital electronic still camera which solves the problems of the prior art and can obtain data more suitable for image characteristics.

[0008]

In order to solve the above-mentioned problems, the present invention digitizes an image signal obtained by picking up an object field, orthogonally transforms this image data, and further quantizes and codes. In a digital electronic still camera for recording in digitized form, the camera divides the digitized image data into blocks of a predetermined number and a predetermined size, and a block of the image data from the blocking unit. Orthogonal transform means for transforming by the orthogonal transform method, quantizing means for quantizing the image data from this orthogonal transform means by quantizing coefficients according to the characteristics of the image, and quantized image data And a coding means for coding with a desired coding method. Further, the camera calculates the degree of high frequency components included in the blocked image data. Block activity calculating means, an evaluation function calculating means for calculating an evaluation function representing a frequency characteristic in each part of the image based on the block activity from the block activity calculating means, and an evaluation function from the evaluation function calculating means. Quantized coefficient setting means for selecting a quantized coefficient based on the above and setting it in the quantizing means.

In this case, the block forming means divides the image data vertically and horizontally to form a block of several pixel data, and the block activity calculating means calculates the block activity based on the divided pixel data of each block. The evaluation function calculation means may calculate the variance value of the activity for every several blocks as the evaluation function.

Further, the block activity calculating means may calculate the activity for each line, and the evaluation function calculating means may calculate the variance value of the block activity for every several lines as the evaluation function.

Further, the camera has a total activity calculating means for adding the respective block activities calculated by the block activity calculating means to calculate the total activity of the image, and the quantization coefficient setting means is an evaluation function. Quantization coefficients may be selected based on both and total activity.

In this case, this camera may have a bit allocation calculating means for determining the code amount of each block based on the total activity and the block activity.

[0013]

According to the digital electronic still camera of the present invention, the image data representing the digitized object scene image is divided into blocks by the block forming means, and the degree of the high frequency component of the image data contained in each block. The so-called block activity is obtained by the block activity calculating means, and the evaluation function expressing the characteristic in each part of the image is obtained by the evaluation function calculating means from these block activities. The quantized coefficient selecting means selects a quantized coefficient based on this evaluation function. As a result, the quantizing means quantizes the image data of each block that has been orthogonally transformed by using the quantized coefficient according to the characteristic of the block. Further, the encoding means encodes and records each quantized data.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a digital electronic still camera according to the present invention will be described in detail with reference to the accompanying drawings.
FIG. 2 shows an embodiment of the digital electronic still camera according to the present invention. This electronic still camera
An object scene incident through the lens 10 is photographed by the imaging device 12, and an image signal representing this object scene image is sent to the compression unit 30 in the form of digital data, whereby the image data is compression-encoded and stored in the memory. This is a device that stores data in the card 40. In particular, in this embodiment, the two-dimensional orthogonally transformed digital data is quantized and compressed by a quantization step according to the characteristics of the image.

The image pickup device 12 will be described in detail.
Is advantageously applied to a solid-state imaging device such as a CCD, and captures a scene image input through the imaging lens 10.
Outputs an RGB color image signal that represents the scene. In addition,
Other functional units such as an exposure mechanism and a focusing mechanism necessary for photographing are not directly related to the understanding of the present invention, and thus the description thereof will be omitted.
In addition, the memory card 40 may be, for example, an SRAM (static
A memory device in which a semiconductor device such as RAM) or EEPROM (electrically erasable and rewritable ROM) is carried on a card-shaped substrate, and is preferably detachably attached to the device.

The output of the imaging device 12 is connected to an analog / digital (A / D) converter 14. The converter 14 is a signal conversion circuit that converts an analog image signal supplied from the imaging device 12 into corresponding digital data and outputs the digital data. For example, the image signal from CCD12 is 10
Digitized into bit data. This A / D converter
The digital data output of 14 is connected to the signal processing section 16. In this embodiment, the signal processing unit 16 performs preprocessing such as white balance adjustment and gradation correction, and converts each color data obtained in RGB into image data of a luminance signal (Y) and a color difference signal (C). It is a processing circuit.

The output of the signal processing unit 16 is connected to the frame memory 24. The frame memory 24 is controlled by the memory controller 18, the image data from the signal processing unit 16 is sequentially stored, and the stored data is read and supplied to the data compression unit 30. The memory controller 18, the data compression unit 30 and the like are controlled by the control unit 20 having a main control circuit (CPU). Further, the data compression section 30 records and reads data to and from the memory card 40 in response to an external input from the input operation section 22.

Next, the internal structure of the data compression section 30, which is a characteristic part of this embodiment, will be described with reference to FIG. The data compression unit 30 includes a blocking unit 100, a two-dimensional orthogonal transform (DCT) unit 102, a normalization unit 104, and a Huffman coding unit 106, and further, a quantization coefficient of the normalization unit 104. α
As a coefficient setting unit that determines the bit allocation value of the encoding unit 106, a block activity calculation unit 108, an evaluation function creation unit 110, a total activity calculation unit 112, a bit factor calculation unit 114, and a quantization table setting unit 116.
And a bit allocation calculation unit 118.

Each section will be further described. The blocking section 10
Reference numeral 0 denotes a circuit which includes a frame buffer and outputs the image data for one image input to the frame buffer by dividing it into a plurality of blocks, for example, blocks each having 8 × 8 pixels.

The two-dimensional orthogonal transformation unit 102 is a circuit for performing two-dimensional orthogonal transformation on the image data of each block. Well-known orthogonal transforms such as discrete cosine transform and Hadamard transform can be considered as the two-dimensional orthogonal transform, and discrete cosine transform (DCT) is advantageously used in this embodiment. The image data for each block that has been subjected to the two-dimensional orthogonal transformation is arranged vertically and horizontally so as to be changed from low-order data to high-order data, and is sequentially output. The DC component data is output first. That is, the image data as a result of the two-dimensional orthogonal transformation, that is, the transform coefficient is sent to the normalization unit 104 in order of the DC component and the AC component in the order from the low frequency component to the high frequency component.

The normalizing section 104 performs quantization and coefficient truncation on the transform coefficient. The quantization is performed by dividing the transform coefficient by a quantization step value corresponding to the quantization coefficient α. The coefficient truncation is to compare the quantized coefficient with a predetermined threshold value, and round off the portion below the threshold value. Quantization coefficient α of this embodiment
Is calculated based on a value calculated from a plurality of block activities by an evaluation function such as their variance and the total value of the entire image, that is, the total activity, and the quantization coefficient α is set in the quantization table. It is supplied from the unit 116 to the normalization unit 104.

The data quantized by the quantizer 104 is
Each block is scanned in a zigzag pattern in order from a low frequency to a high frequency AC component and supplied to the encoding unit 106. The encoding unit 106 encodes the transform coefficient input from the quantization unit 104. Since the AC component of the conversion coefficient is often continuous with zeros, a continuous amount of zero-value data, that is, a run length of zeros and a non-zero amplitude are obtained, and these are two-dimensionally Huffman-encoded. The image data for each block output from the encoding unit 106 is recorded on a recording medium such as the memory card 40 in a desired bit allocation for each block. The bit allocation value for each block is calculated by the bit allocation calculation unit 11
The encoding is stopped based on the code stop signal S from 8.

The block activity calculation unit 108 calculates the extent to which each of the data divided into blocks by the blocking unit 100 contains a high frequency component. In this embodiment, the block activity is obtained by obtaining and adding the absolute value of the difference between the respective values of the pixel data forming one block and the average value of the pixel data of the block. The activity of each block includes an evaluation function creation unit 110 and a total activity calculation unit 11
2 and the bit factor calculation unit 114.

The evaluation function creating unit 110 calculates an evaluation value peculiar to the image from the value of the block activity. In the present embodiment, for example, the activity is calculated from the block activity for every several blocks from the activity calculator 108, and the evaluation value of each block is obtained. Thereby, the evaluation function f (X1) peculiar to the image is calculated. For example, as shown in FIG. 3, the image A has a high activity value in the central part, and a variance value with a large gradient showing low values on both sides is obtained, and the image B has a slightly high activity value in the central part. A gentle variance value is obtained that shows a slightly lower value on both sides. In this way, the evaluation function creation unit 110 obtains the evaluation function f (X1) peculiar to the image from the block activity and outputs it to the quantization table setting unit 116. For example, for a line with a large variance value, it is better to increase the quantization coefficient to increase the number of quantization steps and reduce the coefficient truncation to make the conversion coefficient in each block clearer.
Further, in a line having a small variance value, the quantization coefficient may be reduced to average each data.

The total activity calculating unit 112 is an addition circuit for adding the block activities for one screen and calculating the total value thereof, that is, the total activity of the entire image. This total activity represents the degree of high frequency components included in the entire image. The calculated total activity is output to the quantization table setting unit 116 and the bit factor calculation unit 114.

The bit factor calculating unit 114 calculates the weight of the bit distribution in each block when determining the bit distribution value for each block. This is calculated from the total activity and the block activity.

The bit allocation calculation unit 118 receives the block activity, and based on the bit factor of each block calculated by the bit factor calculation unit 112,
The bit allocation value for each block is calculated. The bit allocation calculating unit 118 supplies the code stop signal S to the encoding unit 106 when the bit allocation value calculated in each block is exceeded, and controls the code amount in each block.

The operation of the electronic still camera of this embodiment having the above-mentioned structure will be described. First, the operator presses a release button (not shown) to photograph a desired object scene image. As a result, when the field of view is imaged by the imaging device 12 of the camera to form analog RGB color video signals, these are converted into digital data by the analog-to-digital conversion unit 14.

The RGB digital data is converted into image data such as a luminance signal and a color difference signal by the signal processing unit 16 and is passed through the memory controller 18 to the frame memory.
Stored in 24 respectively. When the desired image data is stored in the frame memory 24, the operator presses a predetermined button of the input operation unit 22 to record the image data in the memory card. At this time, the control unit 20 controls the memory controller 18 to transfer the image data from the memory 24 to the data compression unit 30 to perform the recording process.

The data compression unit 30 which has received the image data for one image sequentially stores the image data representing the subject image in the frame buffer of the block unit 100. Receiving this, the block unit 100 divides the block into 8 × 8 pixel blocks and sequentially outputs the blocks to the two-dimensional orthogonal transformation unit 102 and the block activity calculation unit 108. Two-dimensional orthogonal transformation unit that received this
102 sequentially performs a two-dimensional orthogonal transformation on each block. At this time, the block activity calculation unit 108 obtains the degree of high frequency components in each block, that is, the activity from the pixel data of each block,
These block activities are evaluated function creation unit 110,
The total activity calculation unit 112 and the bit allocation calculation unit 118 are supplied to each.

As a result, the evaluation function creating unit 110 calculates the variance value from the block activity for each line and sends it to the quantization table setting unit 116 as the image evaluation function F (X1). On the other hand, the total activity calculation unit 11
In 2, when the block activity is added and the block activity for one screen is received, the total activity value is supplied to the quantization table setting unit 116 and the bit factor calculation unit 112, respectively. The quantization table setting unit 116 that has received the total activity and the evaluation function selects a quantization coefficient according to the image from these values and sets it in the normalization unit 104. For example, in a block having a large variance value, the quantization coefficient is increased to increase the number of quantization steps and the coefficient truncation is decreased to make the transform coefficient in each block clearer. In a block with a small variance value, the quantization coefficient is reduced and each data is averaged.

Next, when the data orthogonally transformed from the low-order data to the high-order data are sequentially supplied from the two-dimensional orthogonal transformation unit 102 to the normalization unit 104, the normalization unit 104 sets the setting unit 116.
These are sequentially divided by the quantized coefficients from and quantized. The quantized result data is sequentially output to the Huffman coding unit 106. Receiving this, the encoding unit 106 sequentially Huffman-encodes the quantized data and sequentially outputs these to the memory card 40 for recording.

On the other hand, the bit factor calculation unit 112 and the bit allocation calculation unit 118 calculate for each block which bit and how much bit should be allocated to which block from the total activity of the entire image and the block activity. There is. As a result, when the coding unit 106 exceeds the bit distribution of the calculated value, the bit distribution calculating unit 118 sends a code stop signal to the coding unit 106 to control the code amount in each block to control the entire image. The code amount of is limited to a predetermined amount of data or less. As a result, the encoding unit 10
The recording efficiency of the memory card 40 is increased by prohibiting the output of the extra encoded data in 6 to the memory card 40.

As described above, according to the electronic still camera of this embodiment, at the time of quantization in the data compression unit 30,
Since the quantization is performed by selecting the quantization coefficient according to the characteristic of the image using the evaluation function indicating the characteristic of each part of the image together with the total activity of the entire image, for example, as shown in FIG. Quantization can be performed more accurately even when the same value is used but the image characteristics are different.

In the above embodiment, the variance is obtained from the block activity of every several blocks and used as the evaluation function. However, in the present invention, for example, the activity of each line is obtained and evaluated from the activity of every several lines. The value may be calculated.

[0036]

As described in detail above, according to the digital electronic still camera of the present invention, an image evaluation function is obtained from the block activity of blocked image data, and quantization is performed based on this evaluation function. Since the coefficient is set, it is possible to perform the quantization more accurately according to the characteristics of the image. Especially, in the case of different images in which the total activity of the entire image has the same value and the distribution of high-frequency components is different, the quantization step is changed by changing the quantization coefficient to obtain a more faithful quantization. There is an excellent effect that can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a main part of a digital electronic still camera according to the present invention.

FIG. 2 is a block diagram showing a functional configuration example of an electronic still camera according to the embodiment.

FIG. 3 is a diagram showing an example of activity distribution in different images.

[Explanation of symbols]

 30 data compression unit 100 blocking unit 102 two-dimensional orthogonal transformation unit 104 normalization unit 106 Huffman coding unit 108 block activity calculation unit 110 evaluation function creation unit 112 total activity calculation unit 116 bit factor calculation unit 118 quantization table setting unit 118 Bit allocation calculator

Claims (5)

[Claims] 1. A digital electronic still camera for digitizing an image signal obtained by picking up an image of a field, orthogonally transforming the image data, further quantizing and encoding, and recording the digital signal. Blocking means for dividing the converted image data into blocks of a predetermined number and a predetermined size, an orthogonal transformation means for transforming the image data from the blocking means by a predetermined orthogonal transformation method, and the orthogonal transformation Quantizing means for quantizing the image data from the means by a quantizing coefficient according to the characteristics of the image, and encoding means for encoding the quantized image data by a desired encoding method. Further, the camera further comprises block activity calculating means for calculating the degree of high frequency components included in the blocked image data, and the block activity calculating means. Evaluation function calculating means for calculating an evaluation function representing the frequency characteristic in each part of the image based on the block activity from the lock activity calculating means, and selecting a quantization coefficient based on the evaluation function from the evaluation function calculating means. And a quantizing coefficient setting means for setting the quantizing means. 2. The digital electronic still camera according to claim 1, wherein the block forming unit divides the image data vertically and horizontally to form pixel data for every several pixels, and the block activity calculating unit divides the image data into divided blocks. A digital electronic still camera characterized in that a block activity is calculated on the basis of pixel data for each of the blocks, and the evaluation function calculating means calculates a variance value of the activity for each of several blocks. 3. The digital electronic still camera according to claim 1, wherein the block activity calculating means calculates an activity for each line, and the evaluation function calculating means calculates a variance value of the block activity for every several lines. A digital electronic still camera characterized in that. 4. The digital electronic still camera according to claim 1, wherein the camera adds the respective block activities calculated by the block activity calculating unit to calculate a total activity of an image. The digital electronic still camera, wherein the quantization coefficient setting means selects a quantization coefficient based on both the evaluation function and the total activity. 5. The digital electronic still camera according to claim 4, wherein the camera has a bit allocation calculating means for determining the bit allocation of each block based on the total activity and the block activity. Electronic still camera.