JPH04233373A - Image processor - Google Patents

Abstract

PURPOSE:To efficiently control the data quantity of compressed data. CONSTITUTION:By using control coefficients Q1, Q2 given in advance by an encoding part (1) 3 and an encoding part (2) 4, data quantities B1, B2 at the time when image data is compressed are derived, and by primary approximation based on this value, an arithmetic part 5 derives a control coefficient Q for giving a data quantity B0 of target compressed data, and an encoding part (0) 7 executes encoding of the image data by using Q0.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus, and more specifically to an image processing apparatus that compresses an analog-to-digital converted image and outputs compressed data to a transmission medium, a storage medium, or the like.

0002

2. Description of the Related Art FIG. 7 shows a conventional image encoding device in which an image is inputted from a terminal 101 and is converted into an analog-to-digital signal (hereinafter referred to as A/D) by an A/D converter 102, and then encoded. In section 103, variable length compression encoding is performed. The variable length compressed encoded data is temporarily stored in the transmission buffer memory 104 and sent to the transmission path 106. At this time, the occupied amount of the buffer memory 104 and the transmission line 1
Based on the transmission rate of 0.06, a control coefficient for controlling the data generation amount of the variable length compression code of the encoding section 103 is generated, and is fed back to the encoding section 103 through the filter 105. Thereby, compressed image data can be transmitted at an average rate of the transmission path. The data received from the transmission path 106 is temporarily stored in the reception buffer memory 107.
It is sent to the decoding unit 108 together with the sent control coefficients,
As a result, the variable length compression encoded data is decompressed and decoded, and D
A /A converter 109 performs digital-to-analog conversion, and the image is output from a terminal 110.

[0003] Many methods have been proposed for the color image compression method of the encoding unit 103 in FIG. 7, and the so-called ADCT method has been proposed as a typical color image encoding method.

FIG. 8 shows a conceptual diagram of the configuration of an image encoding apparatus using the ADCT method. The input image is data converted into 8 bits, that is, 256 gradations/colors by the A/D converter 102 in FIG. 7, and the number of colors is RGB.
, YUV, YPbPr, YMCK, etc., 3 or 4 colors
Color. The input image is immediately subjected to a two-dimensional discrete cosine transform (hereinafter referred to as DCT) in subblock units of 8×8 pixels, and then linear quantization of the transform coefficients is performed. The quantization step size differs for each transform coefficient, and the quantization step size for each transform coefficient is a value obtained by multiplying the 8×8 quantization matrix element by K, which takes into account the difference in visibility for each transform coefficient with respect to quantization noise. shall be. Here, K is called a control coefficient. The value of K controls the image quality and the amount of compressed data generated. Table 1 shows an example of quantization matrix elements. In other words, as K becomes larger, the quantization step becomes smaller, resulting in poorer image quality and smaller amount of data.

[0005]

[Table 1]

After quantization, the DC transform component (hereinafter referred to as DC component) is one-dimensionally predicted between neighboring subblocks, and the prediction error is Huffman encoded.

Then, the quantized output of the prediction error is divided into groups, and the identification number of the group to which the prediction error belongs is first Huffman encoded, and then the value within the group is represented by an equal-length code.

[0008] AC conversion components other than DC components (hereinafter referred to as AC
It is written as an ingredient. ) encodes this quantized output while scanning it in a zigzag manner from low frequency components to high frequency components as shown in FIG. In other words, transform coefficients whose quantized output is not 0 (hereinafter referred to as significant coefficients) are classified into groups according to their values, and the quantized coefficients sandwiched between the group identification number and the immediately preceding significant transform coefficient are classified into groups according to their values. Huffman encoding is performed by pairing with the number of transform coefficients whose output is 0 (hereinafter referred to as invalid coefficients),
Next, the value within the group is expressed using an equal-length code.

[0009]

[Problems to be Solved by the Invention] However, in such conventional image encoding devices, the amount of compressed information generated for each image is not constant, so it is difficult to estimate the amount of buffer memory shown in FIG. Images can cause failures, and too many images increase the amount of hardware, making it difficult to design a stable system and leading to high costs. Furthermore, since the control coefficients are fed back, even for the same image, the control coefficients differ depending on the previous image, and the image quality changes over time, resulting in the appearance of unsightly images. In addition, the transmission line can be made of magnetic tape or
When considering recording media such as optical discs, there are many problems such as connection,
It has been extremely difficult to realize such functions, such as search and editing, because the image breaks do not match the recorded data management area.

[0010] Furthermore, when this technology is applied to a still image system that does not have a buffer memory, has a constant control coefficient, and does not provide feedback, it may not be possible to specify the time it takes to transmit one image, or the time required to record it may be The drawback was that it was unclear how much capacity was required for each sheet.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image processing apparatus that can effectively control the amount of compressed data.

0012

[Means and Effects for Solving the Problems] In order to solve the above problems, the image processing device of the present invention compresses the frequency conversion coefficient of image data and uses a control coefficient to make the amount of compressed data variable. An image processing device that controls the amount of data, wherein a control coefficient that provides a target amount of data is linearly approximated by an amount of data generated by a first control coefficient and an amount of data generated by a second control coefficient. It is characterized by asking for.

[0013]

[Embodiment] In the embodiment of the present invention described below, N is set as a plurality of consecutive integers, and the Nth control coefficient is compressed for each image data to obtain the desired amount of information. Multiple trials are performed so that the coefficient is small and the N+1th control coefficient is large, and the desired amount of information is determined by the amount of information trial-generated by the N-th control coefficient and the trial-generated information by the N+1-th control coefficient. The method is characterized in that it has means for performing first-order approximation based on the amount of information obtained.

[0014] With the above means, by making the amount of compressed and generated information for each image constant, the amount of buffer memory is minimized, and it is easy to design a stable system that will not be corrupted by any image. In addition, the image quality is constant for the same image without feedback of control coefficients, and when considering a recording medium such as a magnetic tape or optical disk as a transmission path, functions such as splicing, searching, editing, etc. to make it easier to realize, and
When this technology is applied to a still image system that does not have a buffer memory and does not feed back control coefficients, the time required to transmit one image is kept constant, and the capacity required for each image is It is possible to provide an image processing device that keeps the constant value.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a block diagram of the configuration of an image processing apparatus according to the present invention. An image inputted from a terminal 1 is A/D converted at 2, and converted into a variable length image by an encoding section (1) at 3 using the so-called ADCT method. encoded. At this time, the control coefficient K is compressed as a constant Q1 for one image frame, thereby obtaining the compressed information amount B1 and sending it to the calculation unit 5.

At the same time, the encoder (2) of No. 4 performs variable length encoding using the so-called ADCT method. At this time, the control coefficient K is a constant Q2 for one frame of the image.
As a result, the compressed information amount B2 is obtained and sent to the calculation section 5. Further, 6 is an image data delay unit which delays the A/D converted image by approximately one image frame.

[0017] The encoding unit (0) of No.
The optimum control coefficient K=Q0 calculated by linear approximation of 2, B1, and B2 is compressed and encoded, and the compressed encoded data is stored in the transmission buffer memory of 8.

Reference numeral 9 denotes a transmission path, and for instantaneous transmission, it is a transmission medium such as optical fiber, satellite, microwave, terrestrial radio waves, optical space, etc., and for storage transmission, it is a transmission medium such as a digital VTR or D
Storage media include tape-shaped media such as AT, disk-shaped media such as floppy disks and optical disks, and solid media such as semiconductor memory.

The transmission rate is determined by the amount of information of the original image, the compression rate, and the required transmission time, and varies from several tens of kilobits/second to several tens of megabits/second.

On the other hand, the data received from the transmission path 9 is 10
The compressed encoded data read out from the 10 reception buffer memories is decompressed and decoded at 11 using the optimal control coefficient Q0 received at the same time, digital-to-analog converted at 12, and then sent from terminal 13. Output the image.

The present invention will be explained in more detail using FIGS. 2 and 3. Figure 2 shows an example of an image to be transmitted. One image has 1280 pixels horizontally and 1088 pixels vertically, each with 8 bits.
It is assumed that the image is D-converted. The data capacity per sheet here is 1, 280 x 1, 088 x 8 = 11, 141, 1
20 bits, and if this is transmitted as 30 videos per second, 11, 141, 120 x 30 = 334, 2
A high-speed transmission line of 33,600 bits/second is required.

On the other hand, the transmission rate of a transmission path is usually fixed in most cases, and an amount of information exceeding this transmission rate will cause a breakdown and cannot be transmitted. Now, assuming a transmission path of 36.0000 Mbit/sec, and assuming that the redundancy other than image information such as sync code, ID code, and parity is 5%, the transmission rate at which image information can be transmitted is 34.2000 Mbit/s.
M bits/second, and the amount of compressed information for one image (one frame) is 1.1400 M bits/frame. Therefore, it is sufficient to compress each frame of image to 10.23% or less, and the remaining 1,140,000-(11,141,
120 x 0.1023) = 263.424 bits/frame, or 263.424 x 30 = 7,902.7
It is sufficient to insert dummy data of 2 bits/second.

[0023] If the control coefficient is a certain value and as a result, the compressed information amount of a certain image is 10%, the image information capacity is 334, 233, 600 x 0.1 = 33, 423
, 360 bits/sec, 34,200,000-(33
It is sufficient to insert dummy data of 4,233,600×0.1)=776,640 bits/sec.

[0024] If the control coefficient is a certain value and as a result, the compressed information amount of a certain image is 11%, the image information capacity is 334, 233, 600 x 0.11 = 36, 76
34,200,000-(33
4, 233, 600 x 0.11) = -2, 565, 69
This becomes 6 bits/second, which exceeds the transmission rate of the transmission path and causes failure.

[0025] Therefore, the target compression ratio is set to 10.23%,
In order to obtain a close value without exceeding this value, the optimal control coefficient Q0 may be given to the encoding (0) of 7 in FIG.

FIG. 3 shows an explanatory diagram for determining the optimum control coefficient Q0. Here, we will explain the case where the data is compressed and encoded to about 1/10 by the so-called ADCT method and then transmitted.

The encoding method is the same as that shown in FIG.
After performing DCT transform in units of DCT subblocks, linear quantization of transform coefficients is performed. The quantization step size differs for each transform coefficient, and the quantization step size for each transform coefficient is the 8×8 quantization matrix element shown in Table 1, which takes into account the difference in visibility for each transform coefficient with respect to quantization noise. is multiplied by the control coefficient K. The image quality and amount of generated data are controlled by this value of K, and are reduced to approximately 1/10. After quantization, for the DC component, one-dimensional prediction is performed between adjacent subblocks as a difference value from 0 in the first DCT subblock, and the prediction error is Huffman encoded. Then, the quantum output of the prediction error is divided into groups, and first the identification number of the group to which the prediction error belongs is Huffman encoded, and then, which value within the group is represented by an equal-length code. The AC component is encoded while scanning this quantized output in a zigzag manner from low frequency components to high frequency components. That is, the significant coefficients are classified into groups according to their values, and the group identification number and the number of invalid coefficients sandwiched between the immediately preceding significant conversion coefficients are combined and subjected to Huffman encoding. Now 2
Select two control coefficients Q1 and Q2, Q1<Q0, Q0<Q
Condition 2 shall be satisfied.

FIG. 3 shows the relationship between the control coefficient K and the compressed information amount Y in one general image frame. This Y and K
The relationship is expressed by the function g, that is, Y=g(K),
This function g is Y=g(K)=plogK+q(p, q are constants)...(1
) is said to be extremely close to the 1og curve.

[0029] Therefore, the control coefficient Q1 is encoded by the encoder (1) shown in 3 in FIG. 1 to obtain the compressed information amount B1.

The control coefficient Q2 is encoded by the encoder (1) shown in FIG. 1 to obtain a compressed information amount B2.

In the calculation section 5 in FIG. 1 (Q1, B1)
A straight line connecting the two points of (Q2, B2), Y=aK+b(a,
b is a constant). Result, (Math 1)

[0032]

[Outside 1]

[0033] Transform (Math. 2)

[0034]

[Outside 2]

Therefore, in FIG. 3, if B0 is the target compression ratio (10.23%), B0 is substituted for Y in Equation 2 to obtain the optimum control coefficient Q0. (Number 3)

[0036]

[Outer 3]

In reality, the amount of compressed information generated by the optimal control coefficient Q0 is on Y=g(K), so it becomes B0. Equation (1) is a 1og curve, which is a downwardly convex curve, and a straight line connecting two points on this downwardly convex curve is always located above, as shown in FIG. This always shows that B0>B0, and under no circumstances will the target compression ratio be exceeded and no breakdown will occur in the transmission path.

In Equation 3, Q1, Q2, and B0 are fixed known values in the device, and are constants, and it is sufficient to obtain only B1 and B2 in an encoding trial. Therefore, the encoders (1) and (2) shown in numbers 3 and 4 in FIG. 1 need only generate the compressed information amount.

Further, in FIG. 1, the calculation unit 5 calculates the above equation 3, but a CPU or the like may be used for the calculation, or a ROM, RAM, or the like may be used. A lookup table may also be used.

[0040] In the above example, the relationship between the control coefficient and the amount of compressed information was explained as a log curve, but in reality it may differ from this, for example, it may be approximated by a quadratic curve or a cubic curve. In some cases, it is a curved line. This differs depending on the method of quantization in the encoding section, the type of encoding, etc. However, in both cases, the curve is downwardly convex (the tangent line is always below the curve), and the method for determining the control coefficient as described above is effective based on this characteristic.

FIG. 4 shows a block diagram of the configuration of an image encoding apparatus according to a second embodiment of the present invention, in which an image inputted from a terminal 20 is A/D converted at 21, and an encoding section (1 ) is subjected to variable length encoding using the so-called ADCT method described above. At this time, the control coefficient K is compressed as a constant Q1 for one image frame, thereby obtaining the compressed information amount B1 and sending it to the comparison/calculation section 26. At the same time 2
The encoder (2) of No. 3 performs variable length encoding using the so-called ADCT method. At this time, the control coefficient K is
The frame is compressed to a constant Q2, thereby obtaining a compressed information amount B2, which is sent to the comparison/calculation section 26. Further, 24 encoding units (3) perform variable length encoding using the so-called ADCT method. At this time, the control coefficient K is compressed as a constant Q3 for one image frame, thereby obtaining a compressed information amount B3, which is sent to the comparison/calculation section 26. Furthermore, the so-called AD
Variable length encoding is performed using the CT method. At this time, the control coefficient K is compressed as a constant Q4 for one image frame, thereby obtaining a compressed information amount B4, which is sent to the 26 comparison/calculation section.

An image data delay unit 27 delays the A/D image by about one frame. 28 is an encoding unit (0) which compresses and encodes the optimal control coefficient K=Q0 obtained by the comparison/calculation unit 26, and converts the compressed encoded data into 2
9 is stored in the transmit buffer memory.

30 is a transmission line, and data received from the transmission line 30 is stored at once in a reception buffer memory 31.
The compressed encoded data read out from the reception buffer memory is decompressed and decoded at 32 using the optimal control coefficient Q0 received at the same time, and digital-to-analog converted at 33.
The image is output from the terminal 34.

The second embodiment of the present invention will be explained in more detail using FIGS. 5 and 6.

Furthermore, as shown in FIG. 2, the image to be transmitted is the same as in the first embodiment, and a case will be described in which one frame of image is similarly compressed to 10.23% or less.

That is, similarly, the target compression ratio is set at 10.23%, and optimal control is applied to the 28 encoders (0) in FIG. 4 in order to obtain a close value without exceeding this target. It is only necessary to give the coefficient Q0.

FIG. 5 shows an explanatory diagram for determining this optimum control coefficient Q0.

The encoding method is the so-called ADCT method shown in FIG. 8, as in the first embodiment.

Now the four control coefficients Q1, Q2, Q3, Q4
, and satisfy the conditions Q1<Q0 and Q0<Q4.

FIG. 5 shows the relationship between the control coefficient K and the compressed information amount Y in one general image frame. As mentioned above, the relationship between Y and K is expressed by the function g, that is, Y=g(K).

Here, Y=g(K) is extremely close to a log curve.

Therefore, for the control coefficient Q1, 22 in FIG.
The encoding unit (1) performs encoding to obtain a compressed information amount B1. 23 encoders (2
) to obtain the compressed information amount B2. The control coefficient Q3 is encoded by the encoder (3) 24 in FIG. 4 to obtain the compressed information amount B3. The control coefficient Q4 is encoded by the encoder (4) 25 in FIG. 4 to obtain the compressed information amount B4. Next, the flow of the comparison/calculation section in FIG. 426 will be explained with reference to FIG.

In comparison/calculation 26 in FIG. 4, B0≦B1, B2, B3, and B4 obtained by the above compression encoding trial are sequentially determined with respect to the target compressed information amount B0.
Compare B1, B0≦B2, B0≦B3, and B0≦B4 to find N (N is a positive integer) such that B0 satisfies BN≦B0≦BN+1.

When this N is known, compare 26 in FIG. In the calculation section (QN, BN) (QN+1, BN+1
), calculate the straight line connecting the two points, Y = aK + b (a and b are constants), and the result (Equation 4)

[0055]

[Outside 4]

Therefore, if B0 in FIG. 5 is the target compression ratio (10.23%), then in Equation 4, Y is
0 is substituted to obtain the optimal control coefficient Q0. (Number 5)

005
7]

[Outer 5]

In reality, the amount of compressed information generated by Q0 is on Y=g(K), so it becomes B0. That is, B0
>B0, and under no circumstances will the target compression rate be exceeded and no breakdown will occur in the transmission path.

[0059] Of the above number 5, Q1, Q2, Q3, Q4
, B0 is a constant known value in the device, and is a constant;
It is sufficient if only B1, B2, B3, and B4 are obtained in the encoding trial. Therefore, the encoding units 22, 23, 24, and 25 (1
), (2), (3), and (4) need only generate the compressed information amount.

In addition, in the comparison/calculation section 26 in FIG. I do not care. In addition, in this second embodiment, the number of encoders that generate only the encoded information amount is 4.
As explained above, by increasing this number, the optimal control coefficient approaches the target amount of compressed information as much as possible without exceeding it, and efficient encoding becomes possible. Therefore, the present invention is not limited to this. Further, for convenience, the encoding section has been described using a general encoding method as shown in FIG. 8, but another encoding method may be used. Furthermore, in this example, since the DCT portion in FIG. 8 is common to each encoding section, it is not necessary to have a plurality of them as in this embodiment, and it is possible to combine them into one.

According to the above-described embodiments of the present invention, it is possible to make the amount of compressed information constant for each image by determining the optimal control coefficient from the linear approximation of a plurality of encoding trials, thereby saving the buffer memory. It is easy to design a stable system that minimizes usage and does not break down with any image, has constant image quality for the same image without feedback of control coefficients, and When considering a recording medium such as a magnetic tape or an optical disk, this makes it easy to realize functions such as linking, searching, and editing. In addition, when this technology is applied to a still image system that does not have a buffer memory and does not feed back control coefficients, the time required to transmit one image is fixed, and the time required for each image to be recorded is It becomes possible to provide an image encoding device with a constant capacity.

Note that the frequency transform is not limited to DCT, and other orthogonal transforms such as Hadamard transform may be used.

Furthermore, the block size is not limited to 8×8 pixel blocks.

Furthermore, the encoding method after quantization is not limited to Huffman encoding, but may be other methods such as arithmetic encoding or run-length encoding.

Furthermore, it is not necessarily a linear approximation itself, but any approximation similar to a linear approximation is within the scope of the idea of the present invention.

[0066]

As described above, according to the present invention, the amount of compressed data can be well controlled.

[Brief explanation of the drawing]

FIG. 1 is a configuration block diagram of a first embodiment of the present invention.

FIG. 2 is a diagram showing an image to be transmitted in an embodiment for explaining the present invention.

FIG. 3 is a diagram showing a calculation method according to a first embodiment of the present invention.

FIG. 4 is a diagram showing a configuration block diagram of a second embodiment for explaining the present invention.

FIG. 5 is a diagram showing a calculation method according to a second embodiment of the present invention.

FIG. 6 is a diagram showing a calculation flow of a second embodiment to explain the present invention.

FIG. 7 is a configuration block diagram of a conventional example.

FIG. 8 is a diagram illustrating a general variable length encoding method.

FIG. 9 is a detailed explanatory diagram of a general variable length encoding method.

[Explanation of symbols]

3 Encoding unit (1) 4 Encoding unit (2) 5 Arithmetic section 6 Delay section 7 Encoding unit (0)

Claims (3)

[Claims] Claim 1. An image processing device that quantizes and compresses frequency transform coefficients of image data and controls the amount of compressed data using a control coefficient that makes the amount of compressed data variable, the apparatus comprising: An image processing apparatus characterized in that a control coefficient to be applied is determined by linear approximation using an amount of data generated by a first control coefficient and an amount of data generated by a second control coefficient. 2. The image processing apparatus according to claim 1, wherein the first control coefficient is small and the second control coefficient is large with respect to the control coefficients that provide the target data amount. 3. For the control coefficients that provide the target data amount, N is a plurality of consecutive integers, and the Nth control coefficient is small and the N+1th control coefficient is large.
A claim characterized in that a plurality of trials are performed, and the target data amount is determined by linear approximation using the data amount trial-generated by the N-th control coefficient and the data volume trial-generated by the N+1-th control coefficient. Item 1. Image processing device according to item 1.