JPH09187005A - Coder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the coder with an excellent coding efficiency in which deterioration in image quality is suppressed. SOLUTION: An edge detector 3 detects presence of an edge with a prescribed amplitude or over from a blocked input image signal 1. A MAX value detector 9 detects a maximum value from a coefficient signal 4 in a block subject to orthogonal transformation and controls a quantization width to be increased when the maximum value is high and controls the quantization width not so high when the edge is detected. Furthermore, Furthermore, an adaptive filter 6 filters the coefficient signal 4 while revising the filter characteristic in response to the presence of the edge and gives the result to a quantizer 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coding device used in a digital VTR or the like for compressing, transmitting and recording an image signal.

[0002]

2. Description of the Related Art FIG. 5 shows a block diagram of a conventional encoder. In the figure, 1 is a digitized and blocked input image signal, 2 is an orthogonal transformer, 4 is a coefficient signal obtained by orthogonal transformation, 8 is a quantizer for quantizing the coefficient signal 4, and 9 is a block. MAX value detector for detecting the largest coefficient among the coefficients, 10 is a control signal for controlling the quantization width of the quantizer 8 according to the MAX value of the coefficient, 11 is a quantized coefficient signal, and 12 is Quantized coefficient signal 11
Is an encoder for encoding, and 13 is an encoded output signal.

Next, the operation of the above configuration will be described. First, the input image signal 1 is collected by a blocker (not shown) into a block of, for example, vertical 8 pixels × horizontal 8 pixels and input to the orthogonal transformer 2. Discrete cosine transform (DCT) is often used as the orthogonal transform method. The orthogonally transformed image signal becomes a coefficient signal 4 and the quantizer 8 and MAX
It is supplied to the value detector 9. The coefficient signal 4 referred to here generally includes a DC coefficient representing a direct current and an AC coefficient other than that, but most of the data amount is an AC coefficient, and the DC coefficient is encoded by a separate circuit (not shown). Shall be
Hereinafter, the coefficient will be referred to as the AC coefficient.

Next, the quantizer 8 divides the input coefficient signal 4 by a certain quantization width to reduce the data amount.
At this time, the MAX value detector 9 detects the largest coefficient among the coefficients of each block, and controls the quantization width according to the magnitude of the value. Specifically, when the maximum value of the coefficient 4 is large, the quantization width is increased to improve the data amount reduction effect, and when the maximum value of the coefficient 4 is small, the quantization width is decreased to reduce the S of this block. It works to avoid a decrease in / N. The coefficient signal 11 thus adaptively quantized by the quantizer 8 is run-length coded or variable-length coded by the coder 12 to become the output signal 13. In the encoding method by such an encoding device, the tradeoff between the improvement of the compression rate and the image quality deterioration due to the encoding is relatively performed by controlling the quantization width according to the size of the coefficient in the block. It can be said that the method can be easily adjusted.

[0005]

However, in the conventional coding apparatus, since the quantization width is determined by the maximum value of the coefficient, a block including a large coefficient is always quantized with a large quantization width. Depending on the design, image quality deterioration may be noticeable. For example, a block including an edge with a large amplitude tends to show image quality deterioration more easily than a block with a complicated pattern even if quantization is performed with the same quantization width.

The present invention has been made in order to solve the above problems, and an object of the present invention is to provide an encoding device having high encoding efficiency and capable of suppressing image quality deterioration.

[0007]

According to a first aspect of the present invention, an orthogonal transformation means for orthogonally transforming an input image signal and outputting a coefficient signal, and a quantum for quantizing the input image signal transformed by the orthogonal transformation means. And a maximum value detecting means for detecting the maximum value of the coefficient signal and controlling the quantization step of the quantizing means according to the value, and detecting an edge of a predetermined amplitude or more of the input image signal. Edge detection means for adjusting the quantization step control of the maximum value detection means are provided.

According to a second aspect of the present invention, an orthogonal transform means for orthogonally transforming an input image signal and outputting a coefficient signal, a filter means for filtering the coefficient signal, and a quantizing means for quantizing the output of the filter means. And edge detecting means for detecting an edge having a predetermined amplitude or more in the input image signal and adjusting the filtering condition of the filter means.

According to a third aspect of the invention, an orthogonal transformation means for orthogonally transforming an input image signal and outputting a coefficient signal, a filtering means for filtering the coefficient signal, and a quantizing means for quantizing the output of the filtering means. A maximum value detecting means for detecting the maximum value of the coefficient signal and controlling the quantization of the quantizing means in accordance with the value, and the filter means for detecting an edge of a predetermined amplitude or more of the input image signal. And edge detection means for adjusting the quantization step control of the maximum value detection means.

According to a fourth aspect of the present invention, an orthogonal transformation means for orthogonally transforming an input image signal and outputting a coefficient signal, a quantizing means for quantizing the input image signal transformed by the orthogonal transformation means, and the coefficient. The maximum value detecting means for detecting the maximum value of the signal and controlling the quantization step of the quantizing means according to the value, and the maximum value detecting means for detecting the edge of the coefficient signal having a predetermined amplitude or more And edge detection means for adjusting the conversion step control.

According to a fifth aspect of the present invention, an orthogonal transformation means for orthogonally transforming an input image signal and outputting a coefficient signal, a filtering means for filtering the coefficient signal, and a quantizing means for quantizing the output of the filtering means. And edge detecting means for adjusting the filtering condition of the filter means by detecting an edge having a predetermined amplitude or more in the coefficient signal.

According to a sixth aspect of the present invention, an orthogonal transformation means for orthogonally transforming an input image signal and outputting a coefficient signal, a filtering means for filtering the coefficient signal, and a quantizing means for quantizing the output of the filtering means. A maximum value detecting means for detecting the maximum value of the coefficient signal and controlling the quantization of the quantizing means in accordance with the value, and an edge of the coefficient signal having a predetermined amplitude or more for detecting the maximum value of the filter means. Edge detection means for adjusting filtering conditions and quantization step control of the maximum value detection means are provided.

[0013]

1 shows a block diagram according to a first embodiment of the present invention. In the figure, 1 is a digitized and blocked input image signal, 2 is an orthogonal transformer, 3 is an edge detector for detecting edges in a block of the input image signal 1, and 4 is a coefficient obtained by orthogonal transformation. A signal, 5 is an edge detection signal, 6 is an adaptive filter that filters the coefficient signal 4 according to the presence or absence of the edge detection signal 5, 7 is a filtered coefficient signal, 8 is a quantizer that quantizes the coefficient signal 4, 9 Is a MAX value detector that detects the largest coefficient among the coefficients in the block, 10 is a control signal that controls the quantization width of the quantizer according to the MAX value of the coefficient, 11 is a quantized coefficient signal, and 12 Is an encoder for encoding the quantized coefficient signal 11, and 13 is an encoded output signal.

Next, the operation of the above configuration will be described. Similarly to the conventional example, the input image signal 1 is grouped into a block of, for example, vertical 8 pixels × horizontal 8 pixels, and is orthogonally transformed by the orthogonal transformer 2 to obtain a coefficient signal 4. The input image signal 1 is also input to the edge detector 3, it is determined whether or not the image block includes an edge having a predetermined amplitude or more, and the determination result is output as an edge detection signal 5. The coefficient signal 4 and the edge detection signal 5 are the adaptive filter 6 and the MAX, respectively.
It is input to the value detector 9.

The MAX value detector 9 detects the largest coefficient among the coefficients in the block as in the conventional example, and when the value is large, the quantization width is made large, and when it is small, the quantization width is made small. Although the control signal 10 is output, if the edge detection signal 5 is true, that is, if an edge having a predetermined amplitude or more is included, the quantization width is controlled not to be too large even if the MAX value is large. This is because, as described above, in a block including an edge, if the quantization width is increased, the image quality deterioration due to the quantization distortion tends to stand out, and the block distortion or mosquito noise is generally improved. However, simply suppressing the quantization width causes a problem that the compression rate is lowered. Therefore, when the adaptive filter 6 detects an edge having a predetermined amplitude or more, the coefficient signal 4 is reduced in order to reduce the data amount. The filtered signal 7 is supplied to the quantizer 8.

The manner of filtering by the adaptive filter 6 is shown in FIG. FIG. 11A shows an AC coefficient string immediately after orthogonal transformation, the vertical axis represents the gain (absolute value) of the coefficient, and the horizontal axis represents the higher frequency component toward the right.
Although the actual coefficients are arranged two-dimensionally, they are represented here one-dimensionally for simplification. (B) and (c) of the same figure show examples of filter characteristics. (B) is a characteristic that smoothly attenuates high frequencies, and (c) is a characteristic that completely cuts high frequencies. The subsequent results are shown in (d) and (e), respectively. In either case, filtering reduces the gain of the coefficient in the block, so
In the encoding process in the latter stage, the number of code words decreases and the number of code words decreases, and a code having a shorter code length is assigned, which works to reduce the data amount. As a result, it is possible to suppress the amount of data that would increase from the original quantization when the quantization width is suppressed due to the presence of edges.
If no edge is detected (including an edge having a small amplitude), no filtering is performed.

According to this embodiment, the MAX value detector 9 for controlling the quantization width according to the maximum value of the coefficient in the block.
And an adaptive filter 6 for directly filtering the coefficients themselves are controlled by a signal 5 in which an edge having a predetermined amplitude or more in a block is detected, thereby suppressing an increase in data amount and obtaining an encoding device with less image quality deterioration. be able to.

FIG. 3 shows a block diagram according to a second embodiment of the present invention. Since only the input signal of the edge detector 3 is different from FIG. 1, the description of the operation will be limited to this point, and the description of the other operations will be omitted. In the present embodiment, edge detection is performed using the orthogonally transformed coefficient signal 4 instead of the input image signal 1. This is to simplify the circuit configuration of the edge detector 3 by simply performing edge detection.

FIG. 4 shows the coefficient positions for one block after orthogonal transformation. The black part at the upper left is the DC coefficient, and a, b,
The symbol c indicates the position of the low frequency AC coefficient (one or more) near DC, and represents the coefficient in the vertical, horizontal, and diagonal directions, respectively. If there is a large edge in the block, it does not necessarily match exactly, but since the coefficients at the positions of a to c become large, edge detection can be performed simply by comparing with a predetermined value.

In FIG. 3, the edge detector 3 and the MAX value detector 9 receive the same coefficient signal 4 as input, and both have a similar processing content using a comparator or the like. You can also save on scale. According to the present embodiment, the circuit scale of the edge detector 3 can be saved, and an increase in the amount of data can be suppressed to obtain an encoding device with less image quality deterioration as in the first embodiment. it can.

[0021]

As described above, according to the first aspect of the present invention, the quantization step is adjusted by detecting the maximum value of the orthogonal transform coefficient and the edge having the predetermined amplitude or more of the input image signal. It is possible to obtain an encoding device with less number of bits.

According to the second aspect of the present invention, since the filtering condition for filtering the coefficient signal after the orthogonal transformation is detected by detecting the edge of the input image signal having the predetermined amplitude or more, the input image can be constructed with a simple structure. It is possible to obtain an encoding device that suppresses an increase in the amount of data according to the pattern of a signal.

According to the third aspect of the present invention, the filtering condition for filtering edges of the input image signal having a predetermined amplitude or more and filtering the orthogonal transform coefficient, the maximum value of the orthogonal transform coefficient and the predetermined amplitude of the input image signal or more. Since the edge is detected and the quantization step is adjusted, an increase in the amount of data can be suppressed according to the pattern of the input image signal, and an encoding device with less image quality deterioration can be obtained.

According to the inventions of claims 4 to 6, since the edge detection is performed by using the coefficient signal after the orthogonal transformation instead of the input image signal, the circuit can be simplified, and the invention can be simplified. The same effects as those of the inventions of to 3 can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a characteristic diagram showing how a coefficient signal is filtered.

FIG. 3 is a block diagram showing a second embodiment of the present invention.

FIG. 4 is a configuration diagram showing an arrangement of two-dimensional coefficient signals.

FIG. 5 is a block diagram showing a conventional encoding device.

[Explanation of symbols]

 1 Input Image Signal 2 Orthogonal Transformer 3 Edge Detector 4 Coefficient Signal 5 Edge Detection Signal 6 Adaptive Filter 7 Coefficient Signal after Filtering 8 Quantizer 9 MAX Value Detector 10 Quantization Width Control Signal

Claims (6)

[Claims] 1. An orthogonal transform means for orthogonally transforming an input image signal to output a coefficient signal, a quantizing means for quantizing the input image signal transformed by the orthogonal transform means, and a maximum value of the coefficient signal is detected. Then, the maximum value detecting means for controlling the quantization step of the quantizing means according to the value and the edge of the input image signal having a predetermined amplitude or more are detected to adjust the quantization step control of the maximum value detecting means. And an edge detecting means for performing the encoding. 2. An orthogonal transform means for orthogonally transforming an input image signal to output a coefficient signal, a filter means for filtering the coefficient signal, a quantizing means for quantizing the output of the filter means, and the input image signal. And an edge detection unit that adjusts the filtering condition of the filter unit by detecting an edge having a predetermined amplitude or more. 3. An orthogonal transform means for orthogonally transforming an input image signal and outputting a coefficient signal, a filter means for filtering the coefficient signal, a quantizing means for quantizing the output of the filter means, and a quantizing means for quantizing the coefficient signal. A maximum value detecting means for detecting the maximum value and controlling the quantization of the quantizing means in accordance with the maximum value; and a filtering condition of the filter means and the maximum value for detecting an edge having a predetermined amplitude or more of the input image signal. An encoding apparatus comprising: an edge detecting unit that adjusts the quantization step control of the value detecting unit. 4. An orthogonal transform means for orthogonally transforming an input image signal and outputting a coefficient signal, a quantizing means for quantizing the input image signal transformed by the orthogonal transform means, and a maximum value of the coefficient signal is detected. Then, the maximum value detecting means for controlling the quantization step of the quantizing means according to the value and the edge of the coefficient signal having a predetermined amplitude or more are detected to adjust the quantization step control of the maximum value detecting means. An encoding apparatus comprising: an edge detecting unit. 5. An orthogonal transform means for orthogonally transforming an input image signal and outputting a coefficient signal, a filter means for filtering the coefficient signal, a quantizing means for quantizing the output of the filter means, and a coefficient signal for the coefficient signal. An encoding apparatus comprising: an edge detecting unit that detects an edge having a predetermined amplitude or more and adjusts a filtering condition of the filter unit. 6. An orthogonal transform means for orthogonally transforming an input image signal to output a coefficient signal, a filter means for filtering the coefficient signal, a quantizing means for quantizing the output of the filter means, and a coefficient signal for the coefficient signal. A maximum value detecting means for detecting a maximum value and controlling the quantization of the quantizing means according to the value, a filtering condition of the filter means and the maximum value by detecting an edge of a predetermined amplitude or more of the coefficient signal. An encoding apparatus comprising: an edge detecting unit that adjusts a quantization step control of the detecting unit.