JP3307185B2 - Image signal processing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to compression of an image signal,
The present invention relates to an image signal processing device suitable for a signal processing device that performs a decompression process.

[0002]

2. Description of the Related Art Conventionally, when an image signal is transmitted or stored in a storage device, as disclosed in Japanese Patent Application Laid-Open No. 1-491332, a digitalized signal is used to shorten the transmission time and increase the number of recorded images. On the other hand, a method has been used in which a compression process is performed and then transmitted or stored and decompressed when an image is reproduced.

However, when compressing or decompressing an image, when data such as quantization is decimated, the outline of the image is blurred particularly due to the lack of high-frequency components, thereby deteriorating the image quality. was there. On the other hand, as disclosed in Japanese Patent Application Laid-Open No. 3-119883, a process for preventing image deterioration by performing contour correction after image compression / expansion processing to correct the contour of the image is performed.

[0004]

However, in the above configuration, the frequency at which the contour is emphasized by the contour correction circuit and the degree of contour emphasis are constant regardless of the degree of quantization. However, when the compressed image data is stored in a storage device having a fixed capacity such as an optical disk, it is necessary to suppress the data amount after compression to a fixed value or less. In contrast, the result of compression is generally variable. Therefore, in order to keep the data amount of the compressed image constant, the data amount is often adjusted by changing the degree of quantization. In that case, the ambiguity of the contour and the frequency component of noise generated by quantization change depending on the degree of quantization. Therefore, depending on the degree of quantization, proper contour correction cannot be performed, and in some cases, noise is emphasized, resulting in a problem that image quality is deteriorated.

The present invention has been made in view of the above problems, and has as its object to provide an image signal processing apparatus that performs appropriate contour correction according to the degree of quantization.

[0006]

According to a first aspect of the present invention, there is provided a quantization unit having means for inputting a digital image signal and varying a degree of quantization under control of the microcomputer. An image compression circuit including an encoding unit that encodes the digital image signal quantized by the quantization unit; a decoding unit that decodes the digital image signal compressed by the image compression circuit; and the microcomputer. An image decompression circuit including a dequantization unit having means for varying the degree of dequantization by control of the above, and a signal decompressed by the image decompression circuit is input, and quantization and dequantization are controlled by the microcomputer. And a contour correction circuit having means for varying the degree of contour correction in accordance with the degree of the contour correction.

According to a second aspect of the present invention, there is provided a quantization section having means for inputting a digital image signal and varying the degree of quantization under control of the microcomputer, and a digital image signal quantized by the quantization section. An image compression circuit including an encoding unit that encodes the image data, a decoding unit that decodes the digital image signal compressed by the image compression circuit, and a unit that varies a degree of inverse quantization under the control of the microcomputer. An image decompression circuit including an inverse quantization unit having: And a contour correction circuit.

According to a third aspect of the present invention, the contour correction circuit performs quantization, under control of the microcomputer.
It has a configuration having means for varying the degree of contour correction in accordance with the degree of inverse quantization.

[0009]

With this configuration, high-frequency components lost by quantization during image compression can be appropriately corrected according to the degree of quantization.

Further, by performing contour correction while avoiding the frequency of noise generated by quantization during image compression, contour correction can be performed without emphasizing noise.

Further, by performing contour correction while avoiding the frequency of noise generated by quantization at the time of image compression, it is possible to perform contour correction without emphasizing noise, and to perform quantization at the time of image compression. The high frequency component lost due to this can be appropriately corrected according to the degree of quantization and the frequency at which the contour is emphasized.

[0012]

An embodiment of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 shows the configuration of an image signal processing apparatus according to a first embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes an input terminal for inputting a digital image signal, and reference numeral 10 denotes an image compression circuit, which comprises a quantization unit 11 for quantizing the digital image signal and an encoding unit 12 for encoding. Reference numeral 30 denotes an image expansion circuit, which includes a decoding unit 31 for decoding a compressed image signal and an inverse quantization unit 32 for performing inverse quantization. An outline correction circuit 40 receives an image signal expanded by the image expansion circuit 30 and generates an outline correction signal by an outline correction signal generation unit 41.
The gain control unit 42 controls the gain of the contour correction signal under the control of a microcomputer. Further, the delay circuit 43 matches the phase of the signal expanded by the image expansion circuit 30 with the phase of the contour correction signal output from the gain control circuit 42, and
Add and output.

A microcomputer 50 controls the quantization unit 11, the inverse quantization unit 32, and the gain control unit 42.

The operation of the thus configured image signal processing device will be described below.

A digitized image signal is applied to the input terminal 1. The quantization unit 11 controls the degree of quantization by a control signal of the microcomputer 50 and quantizes the input digital image signal. The encoding unit 12 is a part that compresses the data amount by encoding the quantized data, and a circuit that implements an encoding method such as Huffman encoding is used. Therefore, the image signal is compressed through the quantization unit 11 and the encoding unit 12.

The decoding section 31 decodes the data coded by the coding section 12 using a decoding method corresponding to the coding method of the coding section 12. The inverse quantization unit 32 performs inverse quantization on the image signal decoded by the decoding unit 31 according to a control signal of the microcomputer 50 to a degree corresponding to the degree of quantization by the quantization unit 11. The image signal compressed by the image compression circuit 10 via the decoding unit 31 and the inverse quantization unit 32 is expanded.

The signal expanded by the image expansion circuit 30 is input to a contour correction signal generator 41. The contour correction signal generator 41 generates a contour correction signal as if a specific frequency was extracted from the input image signal. In general, a differentiating circuit that performs twice differentiation is used for the contour correction signal generator 41. The contour correction signal generated by the contour correction signal generation unit 41 is input to the gain control unit 42, and the degree of quantization and inverse quantization in the quantization unit 11 and the inverse quantization unit 32 is controlled by a control signal from the microcomputer 50. The gain is controlled according to. The gain is controlled in such a manner that the gain is increased when the degree of quantization and inverse quantization is large, and the gain is decreased when the degree of quantization and inverse quantization is small. By selecting an appropriate gain according to the degree of quantization and inverse quantization, an optimal contour correction signal can be obtained. If the microcomputer 50 is programmed so that the control signal from the microcomputer 50 changes in accordance with the degree of the quantization and the inverse quantization, the gain control unit 42 outputs the output of the contour correction signal generation unit 41 and the microcomputer. This can be realized using a multiplier that multiplies the control signal from the control signal 50.

The delay circuit 43 receives the signal expanded by the image expansion circuit 30 and delays the same delay amount as the signal generated by the contour correction signal generation unit 41 and the gain control unit 42. The phase is adjusted with the contour correction signal output in step (1).

In the adder 44, the gain control unit 4
By adding the contour correction signal output in step 2 and the image signal whose phase has been adjusted by the delay circuit 43, an image signal whose contour has been appropriately corrected according to the degree of quantization and inverse quantization is obtained.

In this embodiment, the image signal compressed by the image compression circuit 10 is immediately expanded by the image expansion circuit 30, but the image signal compressed by the image compression circuit is stored in a storage device such as a memory or a disk device. Even if the image signal once stored is expanded by the image expansion circuit 30, there is no problem in carrying out the present invention.

(Embodiment 2) FIG. 2 shows the configuration of an image signal processing apparatus according to a second embodiment of the present invention.

In the description, the configuration other than the contour correction circuit 60 is the same as that of the first embodiment and performs the same function, so that the description is omitted.

The image signal expanded by the image expansion circuit 30 is input to a frequency control unit 61. The frequency control unit 61 uses a control signal from the microcomputer so as to avoid the frequency for enhancing the contour in accordance with the quantization and inverse quantization of the quantization unit 11 and the inverse quantization unit 32 and the frequency of the generated noise. And generates a contour correction signal without emphasizing noise.

In the case where quantization is performed by dividing each frequency band using wavelet transform or the like, noise is likely to be generated for a frequency component having a high degree of quantization. Therefore, an outline correction signal is generated so as to avoid the frequency.

FIG. 3 shows an example of the configuration of the frequency control section. An image signal is input to an input terminal 611, and a first differentiating circuit 618 and a second differentiating circuit 619 generate an outline correction signal. The first differentiating circuit 618 and the second differentiating circuit 619 can be realized by calculating a difference between an input image signal and a signal obtained by delaying the input image signal.
A control signal from the microcomputer is input to the control signal input terminal 617, and the delay amount in the first delay control circuit 612 and the second delay control circuit 614 is controlled to control the frequency for enhancing the contour.

FIG. 4 shows a configuration example of the first delay control section 612 and the second delay control section 614. Since the first delay control circuit 612 and the second delay control circuit 614 perform the same function, they may have the same configuration. A control signal from the microcomputer is input to the control signal input terminal 625, and a signal obtained by delaying the signal input from the input terminal 620 by the first delay circuit 621 and the second delay circuit 622 with different delay amounts is used. Is selected by the selection circuit 623 in accordance with the control signal from the CPU and output.

Here, the case where there are two delay circuits has been described. However, it is desirable to provide a large number of delay circuits and set a more appropriate delay amount in accordance with the degree of quantization and inverse quantization.

The contour correction signal whose frequency is controlled by the frequency control unit 61 and generated so as to avoid the frequency of noise is adjusted by the gain adjustment unit 62 and the adder 4
4 is input. The delay circuit 44 receives the image signal expanded by the image expansion circuit 30, delays the same delay amount as that generated by the frequency control circuit 61 and the gain adjustment unit 62, and inputs the same to the adder 44.

The adder 44 adds the contour correction signal output from the gain adjustment unit 62 and the signal output from the delay circuit 43 to obtain an image signal whose contour has been corrected without emphasizing noise.

(Embodiment 3) FIG. 5 shows the configuration of an image signal processing apparatus according to a third embodiment of the present invention. In the description, the configuration other than the gain control unit 42 is the same as that of the above (Example 2) and performs the same function, and thus the description is omitted.

The contour correction signal generated by the frequency control section 61 is input to the gain control section 42.
In the gain control unit 42, the quantization unit 11, the degree of inverse quantization and the frequency of the inverse quantization, and the frequency control unit 6
The gain of the contour correction signal is controlled and output according to the emphasis frequency of the contour correction signal generated in step 1.

In the gain control, not only the degree of quantization and inverse quantization but also the frequency control unit 61
The feature is that the frequency of contour enhancement in the above is considered.
This is because the appropriate value of the gain changes depending on the frequency at which the contour is emphasized.

Therefore, a clearer image can be obtained than when the frequency control section 61 and the gain control section 42 are controlled independently.

[0036]

As described above, according to the present invention, by controlling the degree of contour correction in accordance with the degree of quantization of image compression and performing appropriate contour correction, the high frequency loss lost during quantization of image compression is achieved. The components can be appropriately corrected, and an image with less blur of the contour can be obtained.

Further, by performing contour correction while avoiding the frequency of noise generated during quantization of image compression, contour correction can be performed without emphasizing noise, and an image with less discomfort can be obtained.

Further, according to the present invention, a clearer image can be obtained than in the case where the contour correction frequency and the gain are independently controlled.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an image signal processing device according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of an image signal processing device according to a second embodiment of the present invention;

FIG. 3 is a diagram illustrating a configuration of a frequency control unit illustrated in FIG. 2;

FIG. 4 is a diagram showing a configuration of a delay control unit shown in FIG. 3;

FIG. 5 is a diagram illustrating a configuration of an image signal processing device according to a third embodiment of the present invention;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Image compression circuit 11 Quantization part 12 Encoding part 30 Image decompression circuit 31 Decoding part 32 Inverse quantization part 40, 60 Contour correction circuit 50 Microcomputer

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 1/41-1/419 G06T 3/00 500 H04N 1/409 H04N 5/208

Claims (3)

(57) [Claims] 1. A microcomputer for controlling a digital image signal, a quantization unit for inputting the digital image signal and varying a degree of quantization under control of the microcomputer, and a digital unit quantized by the quantization unit. quantum an image compression circuit and a coding unit, a degree of inverse quantization by the control of the decoding section and the microcomputer for decoding a digital image signal compressed by the image compression circuit for encoding an image signal Same degree as
An image decompression circuit having an inverse quantization unit set in step (a), and a signal decompressed by the image decompression circuit, and the degree of contour correction according to the degree of quantization and dequantization controlled by the microcomputer. An image signal processing device comprising: a contour correction circuit that varies the image signal. 2. A microcomputer for controlling a digital image signal, a quantizer for inputting the digital image signal and varying a degree of quantization under the control of the microcomputer, and a digital image quantized by the quantizer. An image compression circuit including an encoding unit for encoding a signal; a decoding unit for decoding the digital image signal compressed by the image compression circuit; and a quantization unit that quantizes a degree of inverse quantization under control of the microcomputer . To the same degree as
An image expansion circuit having an inverse quantization unit to be set, and a signal expanded by the image expansion circuit is inputted, and the contour emphasis frequency is varied according to the degree of quantization and inverse quantization under the control of the microcomputer. An image signal processing device comprising: a contour correction circuit. 3. The image signal processing apparatus according to claim 2, wherein the contour correction circuit can change the degree of contour correction according to the degree of quantization and inverse quantization under the control of the microcomputer.