JPH11122511A - Image quality correction circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the image quality correction circuit by which image quality is improved more by reducing a degree of emphasis of contour in the case that an image whose contour is clear is received and increasing a degree of contour emphasis in the case that an image whose contour is not clear is received. SOLUTION: The correction circuit is provided with one filter circuit that extracts a specific frequency component of input image data, an accumulation circuit 2 that accumulates absolute values of image data extracted by the one filter circuit 1, a comparator circuit 3 that compares the accumulation result of the accumulation circuit 2 with a threshold level and controls a limit value of a limiter circuit 6, the other filter circuit 4 that extracts the specific frequency component of the input image data, an up-sampler 5 that applies up- conversion to a sampling frequency of the image data extracted by the other filter circuit 4 by an optional multiple, the limiter circuit 6 that limits output data of the up-sampler 5, a down-sampler 7 that restores the sampling frequency of the limited data to a sampling frequency before the up-conversion, and an adder 8 that adds output data of the down-sampler 7 and the input image data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image quality correction circuit suitable for use in an image reproducing apparatus, and more particularly to an image quality correction circuit for varying the degree of edge enhancement in accordance with the frequency component of an input image. Things.

[0002]

2. Description of the Related Art As a conventional technique, an image quality correction circuit used in a DVD (Digital Versatile Disc) reproducing apparatus will be described as an example with reference to FIGS. Here, FIG. 3 shows a DV using a conventional image quality correction circuit.
FIG. 4 is a schematic configuration diagram showing a reproduction signal processing system of the D reproduction device, FIG. 4 is a waveform diagram of a main part in a conventional image quality correction circuit, and FIG. 5 is an explanatory diagram showing limiter characteristics of a limiter circuit in the conventional image quality correction circuit.

Referring to FIG. 4, a reproduction signal processing system of a conventional DVD reproduction apparatus includes a disk 11 on which an image and an audio signal are recorded, an RF amplifier 12 for amplifying a reproduction signal reproduced by a pickup, and A digital demodulation / error correction circuit 13 for digitally demodulating the signal amplified by the RF amplifier 12 and for correcting an error of the demodulated data;
MPEG2 for expanding data compressed by the PEG2 method
A decoder 14, a Y / C separation circuit 15 for separating the expanded data into luminance data and color difference data, and a filter circuit 1 for extracting a specific frequency component of the separated luminance data
6 is provided.

An upsampler 17 for up-converting (raising) the sampling frequency of the luminance data extracted by the filter circuit 16 to an arbitrary multiple, and a limiter circuit 18 for limiting the output data of the upsampler 17 in amplitude.
A down-sampler 19 for returning the sampling frequency of the amplitude-limited data to the sampling frequency before the up-conversion, and an adder 20 for adding the output data of the down-sampler 19 and the output luminance data of the Y / C separation circuit 15
And the output luminance data of the adder 20 and the Y / C separation circuit 15
And a Y / C mixing circuit 21 for mixing the output color difference data.

Here, the filter circuit 16, upsampler 17, limiter circuit 18, downsampler 19, and adder 20 constitute an image quality correction circuit.

Next, the operation of the reproduction signal processing system of the DVD reproduction apparatus will be briefly described. A reproduction signal reproduced from the disk 11 is amplified by the RF amplifier 12. The amplified signal is output to a digital demodulation / error correction circuit 13 where it is digitally demodulated, the error of the demodulated data is corrected, and the output is output to an MPEG2 decoder 14. It should be noted that this data is data compressed by the MPEG2 method at the time of recording.

The output data is expanded by the MPEG2 decoder 14 and decoded into data before compression. The decoded data is supplied to the Y / C separation circuit 1
5 to be separated into luminance data and color difference data.

The separated luminance data is output to an image quality correction circuit, which will be described in detail later, becomes data in which the outline is emphasized, and is output to the Y / C mixing circuit 21. Also, the separated color difference data is output to the Y / C mixing circuit 21 and
The C mixing circuit 21 mixes the input luminance data and color difference data, and outputs image data with an enhanced edge to the next stage.

Next, the above-described image quality correction circuit will be described. The luminance data shown in FIG. 4A separated by the Y / C separation circuit 15 is supplied to the filter circuit 16, the upsampler 17, the limiter circuit 18, and the downsampler 1 described above.
9, is input to an image quality correction circuit composed of an adder 20, one of which is input to the adder 20, and the other is input to the filter circuit 16.

First, the luminance data input to the filter circuit 16 is supplied to a filter circuit 16 generally using a BPF (band-pass filter) or LPF (low-pass filter) at a specific frequency shown in FIG. The components are extracted.

The extracted data is output to an upsampler 17 composed of a zero interpolation circuit 17a and an LPF 17b, subjected to zero interpolation processing, and up-converted (increased) to an arbitrary multiple of the sampling frequency to reduce aliasing noise. The signal is output to the limiter circuit 18. The output waveform from the upsampler 17 is shown in FIG. This output waveform is shown in FIG. 4 if the LPF 17b is an ideal filter.
As shown in (c), the waveform is the same as the output waveform of the filter circuit 16, but in practice there is no ideal filter, and the waveform is actually output as a slightly dull waveform.

The data input to the limiter circuit 18 is limited in amplitude to a predetermined level and output to the downsampler 19. The limiter characteristic of the limiter circuit 18 is shown in FIG.
As shown in (1), it has a non-linear characteristic, and outputs as it is when the input amplitude does not exceed L, outputs L when it exceeds L, and outputs as it is when the input amplitude does not exceed -L. , -L, the output is -L. The output waveform of the limiter circuit 18 is shown in FIG.

The data whose amplitude has been limited by the limiter circuit 18 is output to a down sampler 19 comprising an LPF 19a and a thinning circuit 19b, and is returned to the sampling frequency before the up-conversion of the sampling frequency. Is output. In addition, down sampler 19
Is not a rectangular wave, as shown in FIG. 4E, because the waveform is slightly dull by the LPF 19b.

The adder 20 adds the output data of the downsampler 19 and the output luminance data of the Y / C separation circuit 15, and outputs the image data whose outline is enhanced as shown in FIG. I do.

As described above, by providing the image quality correction circuit, it is possible to obtain image data in which the outline is emphasized and improve the image quality.

[0016]

However, in the conventional image quality correction circuit, the contour of the input image is sharp because the enhancement level of the outline is constant regardless of the frequency component of the input image. Regardless of the image or the unclear image, the contour enhancement level is constant. Therefore, if the contour is emphasized too much, a glare-like screen is displayed on the display screen. In particular, when the input image is a bright image, there is a problem that the image is noticeably recognized.

That is, in the conventional setting of the contour emphasis level, the contour of the input image is clear, and the level is set so that the screen is not glaring when the image is bright. However, with such a setting, there is a problem that the enhancement of the outline is weakened when an image having an unclear outline of the input image is input.

[0018]

An image quality correction circuit according to the present invention includes one filter circuit for extracting a specific frequency component of input image data and an absolute value of the image data extracted by the one filter circuit. An accumulation circuit for calculating, a comparison circuit for comparing an accumulation result of the accumulation circuit with a threshold value, and controlling a limiter value of a limiter circuit, and another filter circuit for extracting a specific frequency component of input image data, An upsampler for up-converting the sampling frequency of the image data extracted by the other filter circuit to an arbitrary multiple, a limiter circuit for limiting the output data of the upsampler, and a sampling frequency of the amplitude-limited data. A downsampler for returning to a sampling frequency before up-conversion, and an adder for adding output data of the downsampler and input image data It is intended to be equipped with.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. Here, FIG. 1 is a block diagram showing an image quality correction circuit of the present invention, and FIG. 2 is an explanatory diagram showing a specific example of limiter value control of a comparison circuit in the image quality correction circuit of the present invention.

Referring to FIG. 1, an image quality correction circuit according to the present invention includes one filter circuit 1 for extracting a specific frequency component of input image data, and an absolute value of the image data extracted by one filter circuit 1. And a comparison circuit 3 that compares the output accumulation result of the accumulation circuit 2 with an internal threshold value and outputs a control signal for controlling a limiter value of a limiter circuit 6 described below. Is provided.

The other filter circuit 4 for extracting a specific frequency component of the input image data, and an upsampler for up-converting (raising) the sampling frequency of the image data extracted by the other filter circuit 4 to an arbitrary multiple. 5
A limiter circuit 6 for limiting the amplitude of the output data of the upsampler 5, a downsampler 7 for returning the sampling frequency of the amplitude-limited data to the sampling frequency before the up-conversion, and output data and input image data of the downsampler 7 And an adder 8 for adding.

Next, the operation of the image quality correction circuit of the present invention will be described. Here, the description will be made based on the background that the input image data is the luminance data separated by the Y / C separation circuit, corresponding to the above conventional example.

First, input image data is input to one filter circuit 1 and the other filter circuit 4, and
It is input to the adder 6. From the image data input to one filter circuit 1, a specific high frequency component is extracted by one filter circuit 1 generally using a BPF (band pass filter) or HPF (high pass filter). .

The extracted high frequency component is output to the accumulating circuit 2, the absolute value of the high frequency component is added, and the added accumulation result is output to the comparing circuit 3. The comparison circuit 3 compares the input accumulation result with a built-in threshold value, and when the input accumulation result is lower than the threshold value, increases the limiter value as shown by L1 in FIG. If the input accumulation result is higher than the threshold value, a control signal for lowering the limiter value (increase the amplitude limit) is output to the limiter circuit 6 as indicated by L2 in FIG.

That is, when an image having a sharp outline of the input image data is input, the comparison circuit 3 increases the amplitude limit of the limiter circuit 6, and an image having an unclear outline of the input image data is input. In the case, the limiter circuit 6
Is controlled to reduce the amplitude limitation of

In this embodiment, the description has been made on the assumption that the data of the threshold value is built in the comparison circuit 3 in advance.
Needless to say, threshold data may be provided outside the comparison circuit 3, and the threshold data may be taken in and compared with the input accumulation result.

Next, the luminance data input to the other filter circuit 4 is generally represented by a BPF (bandpass filter).
Alternatively, a specific high frequency component is extracted by a filter circuit 4 using an HPF (high pass filter).

The above-described one filter circuit 1 and the other filter circuit 4 may be filter circuits having the same characteristics, or the characteristics of one filter circuit 1 may be changed from the characteristics of the other filter circuit 4 to extract a high-frequency signal. The frequency component of the frequency range may be slightly changed, and the frequency component may be compared with a threshold.

The extracted high frequency components are output to an upsampler 5 comprising a zero interpolation circuit 5a and an LPF 5b, subjected to a zero interpolation process, and up-converted (increased) to an arbitrary multiple of the sampling frequency. The aliasing noise is reduced and output to the limiter circuit 6. The high-frequency component data input to the limiter circuit 6 is controlled to limit or increase the amplitude based on the control signal from the comparison circuit 3 described above, and is output to the downsampler 7.

The data whose amplitude has been controlled by the limiter circuit 6 is output to a down sampler 7 composed of an LPF 7a and a thinning circuit 7b, and is returned to the sampling frequency before the up-conversion of the sampling frequency. Output to The adder 8 adds the output data of the down-sampler 7 and the input image data, and outputs image data having more or less outlines emphasized to the next stage.

In the above description, when the image quality correction circuit is applied to the image reproducing apparatus, the description has been made of the luminance signal processing system of the reproduction processing system, but it may be used for the chroma signal processing system. Not even.

As described above, the image quality correction circuit of the present invention changes the limiter level for the high frequency component according to the frequency component of the input image data, so that the outline of the input image is clear. For an image, the degree of edge enhancement is low, and for an image in which the outline of an input image is not clear, the degree of edge enhancement is controlled to increase the image quality.

[0033]

According to the image quality correction circuit of the present invention, the limiter level is varied according to the case where the outline of the input image data is clear and the case where the outline is not clear, and the degree of outline enhancement. , It is possible to solve the problem that the outline enhancement is weakened when an image whose input image has an unclear outline is input, and the image quality can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an image quality correction circuit according to the present invention.

FIG. 2 is an explanatory diagram showing a specific example of limiter value control of a comparison circuit in the image quality correction circuit of the present invention.

FIG. 3 is a schematic configuration diagram showing a reproduction signal processing system of a DVD reproduction device using a conventional image quality correction circuit.

FIG. 4 is a main part waveform diagram in a conventional image quality correction circuit.

FIG. 5 is an explanatory diagram showing limiter characteristics of a limiter control circuit in a conventional image quality correction circuit.

[Explanation of symbols]

 Reference Signs List 1 filter circuit 2 accumulation circuit 3 comparison circuit 4 filter circuit 5 upsampler 6 limiter circuit 7 downsampler 8 adder

Claims (1)

[Claims] A filter circuit for extracting a specific frequency component of the input image data; an accumulator circuit for accumulating an absolute value of the image data extracted by the one filter circuit; A comparison circuit that compares the accumulation result with a threshold value and controls a limiter value of a limiter circuit; another filter circuit that extracts a specific frequency component of input image data; and image data extracted by the other filter circuit An upsampler for up-converting the sampling frequency of the upsampler to an arbitrary multiple, a limiter circuit for limiting the amplitude of the output data of the upsampler, and a downsampler for returning the sampling frequency of the amplitude-limited data to the sampling frequency before the upconversion. An image quality correction circuit comprising an adder for adding output data of the downsampler and input image data. .