JPS6128278A - Picture quality compensating device - Google Patents

Abstract

PURPOSE:To obtain an overall picture quality improving effect in matching with a visual characteristic by providing a signal discriminating circuit discriminating a characteristic of an input picture, a compensation signal generating circuit generating a picture quality compensating signal relating to a high frequency signal component and an adder circuit adding the picture quality compensating signal to an input picture signal to generate a picture quality compensation output picture signal. CONSTITUTION:For example, a stepinput picture signal shown in waveform (a) is fed respectively to a low pass filter 1 and a delay line 2 from an input terminal. A linear high frequency compensating differential output signal (d) is fed to a detector 4 to separate a negative polarity component signal shown in waveform (e). The signal (e) is fed to an adder 7 via an attenuator 6 and the differential output signal (d) is fed to the adder 7 via an attenuator 5. A picture quality compensation signal (f) is fed to an adder 8, where it is added to a delayed output original picture signal (c) so as to compensate suitably a bright and dark picture with high contrast in matching with a visual space frequency characteristic thereby obtaining the best visual picture quality.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an image quality compensation device for improving the image quality of a television image signal, and in particular, for compensating for the characteristics of, for example, a luminance signal based on new knowledge regarding the characteristics of visual perception. This is how it was done.

(Prior art) Conventionally, to improve the image quality of television images, aperture compensation circuits and contour compensation circuits have been used to take into account the deterioration of the spatial frequency characteristics of the imaging system and reproduction display system, as well as the psychological effects on viewers. It has been used.

(Problem) Therefore, since this type of conventional image quality compensation device performs linear compensation, when trying to further increase the sharpness of the image, glare occurs in the contours of the image. However, this method has the drawback that it may result in an unnatural image, and in the end, the image quality cannot be sufficiently improved in terms of combination.

(1-1) The purpose of the present invention is to 1- eliminate the above-mentioned conventional drawbacks, 12 and provide image quality compensation that takes into consideration the psychological effects of the viewer and provides a comprehensive image quality improvement effect that matches the visual characteristics. The goal is to provide equipment.

(Configuration of Civilization) The present invention was made based on new knowledge obtained by the inventors regarding the spatial characteristics of visual perception, and the image quality compensation device of the present invention is capable of adjusting the spatial frequency of at least one dimension of an input image signal. a high frequency extraction circuit that extracts high frequency signal components in the region;
From the single polarity amplitude and negative polarity amplitude of the high frequency signal component,
a signal discrimination circuit that discriminates the characteristics of an input image; a compensation signal forming circuit that forms image quality compensation signals related to the high-frequency signal components that are independently adjusted according to visual characteristics based on the discrimination results of the discrimination circuit; The present invention is characterized by comprising an addition circuit that adds the image quality compensation signal to the input image signal to form an image quality compensated output image signal.

(Example) The present invention will be described in detail below with reference to the drawings. Prior to that, we will provide an overview of the spatial frequency characteristics of vision.

First, we will discuss the new findings obtained by the present inventors regarding the spatial frequency characteristics of vision for bright and dark images. When the contrast between the background and the subject is small, there is almost no difference in visual spatial frequency characteristics due to the brightness of the image. On the other hand, in the case of image contrast,
An image with a bright subject against the f+f view (bright image) and an image with a dark subject against the background (llrS image)
A new psychophysical fact has been revealed regarding the spatial frequency characteristics of visual perception, which shows that the way things are seen differs depending on the situation.

The spatial frequency characteristics of vision based on these psychophysical facts can be summarized as follows.

(1) Difference in receptive fields, ie, line spread functions, for bright images and dark images.

Visual spatial frequency characteristics can be expressed, for example, by how a linear image looks, in the same way that circuit characteristics are expressed by their impulse responses.

When the contrast of the linear image is small, the second t4 (
As shown in A) and (B), for the bright line image and dark line image shown in the second row of each figure, as shown in the bottom line of each figure, the polarity is the same as that of each line image. There are responses of opposite polarity before and after the widened response.

On the other hand, when the contrast of the line image is high, the response to the bright line image is similar to the low contrast case shown in FIG. 2(A), but the response to the dark line image is As shown in FIG. 2(C), there is a peculiar phenomenon in which a response of opposite polarity does not appear before and after a response spread with the same polarity.

Therefore, as shown in row 11 of Figure 2 (CD), when two linear images are presented close to each other in parallel and the contrast of the parallel linear images is varied over a wide range of brightness and darkness, The response to the image area between two lines exhibits changing characteristics as shown in the lower part of the figure, and for parallel dark line images, as the contrast changes, the response to the area between two lines exhibits a change characteristic of the opposite polarity. will not occur.

(2) Visual spatial frequency characteristics (MTF) Visual spatial frequency characteristics (MI
F) corresponds to the line spread function of the visual response to low-contrast bright and dark line images described above with respect to Figures 2 (A) and (B), respectively, and corresponds to the bright image area shown in Figure 3. and characteristic curve I for the dark image area, and the visual sensitivity is reduced at low frequencies in both the bright image area and the dark image area.

On the other hand, regarding the spatial frequency characteristic (MIF) of visual perception in response to a stimulus with a high-contrast image, the line spread function of the visual response to a high-contrast dark line image described above in Figure 2 (C) is low Unlike the case in which the characteristic curve I shown in the 1g2 image area of FIG.
Unlike I, there is no reduction in visual sensitivity to dark images at low frequencies, resulting in visual spatial frequency characteristics similar to the pass frequency characteristics of a low-pass filter in an electric circuit.

The image quality compensating device of the present invention is configured to obtain an image quality compensated image that is compatible with the visual spatial frequency characteristics described above. In order to achieve this, we will examine whether or not this type of conventional image quality compensator has an effect on the above-mentioned visual spatial frequency characteristics.

As shown by the dotted line curve (a) or the broken line curve (b) in FIG. This increases the gain 94# in high frequencies.

Therefore, the overall visual response characteristics to the raw image of the image signal processed by the contour compensation circuit are as follows:
For example, it corresponds to the product of the dotted line curve (a) in FIG. 4 and the response characteristic curve shown in FIG. 3.

The response characteristics of vision to both high-contrast and dark images are shown by solid curves in the middle and dark image areas in Figure 5 when no compensation is provided, and the response characteristics of vision to dark images of high contrast 1 are as shown by solid curves in the middle and dark image areas in Figure 5. The response seems to be insufficient at high frequencies. Therefore, in the conventional compensation circuit, the fourth
The illustrated gain-frequency characteristics increased sensitivity at high frequencies, resulting in a compensated visual response as shown by the dotted line in FIG.

Therefore, when the contrast is high, the response to both images becomes excessive at high frequencies, causing glare in the contours of bright areas of the reproduced image, resulting in an unnatural feeling as described above. On the other hand, if the compensation characteristics are kept to a level that does not cause glare in the contours of the two images, the high frequency components of the dark image will tend to be insufficient, and the sharpness will decrease. Depending on the image quality compensation circuit, it is extremely difficult to simultaneously compensate the response characteristics for both images and the dark image during high contrast and obtain an image with good overall quality.
In the image quality compensation device of the present invention, basically, the amounts of contour compensation components added to both image signals and the red bean image signal during high contrast can be adjusted independently in accordance with visual characteristics. That is, as shown by the dotted line in Figure 6 as well as other compensation characteristic curves, the amount of compensation on the positive polarity side and the negative polarity side is adjusted to correspond to the difference in the visual response characteristic due to the brightness of the image described above with reference to Figure 3. By adding high-frequency compensation components that are small on the positive side and large on the negative side to the original image signal, the image characteristics seen through the human eye can be made symmetrical between positive and negative, and both positive and negative can be made symmetrical. The image quality is compensated for just the right amount.

1- FIG. 1(A) shows a configuration example of an image quality compensation apparatus according to the present invention which performs image quality compensation in the above-described manner, and FIG. 1(B) shows an example of signal waveforms of each part thereof.

In the illustrated circuit configuration, for example, a step-like input image signal shown in waveform (a) is supplied from an input terminal to a low-pass filter l and a delay line 2, and a low-pass component signal signal P shown in waveform (b) is supplied. Delayed output image signals shown in waveform (C) corresponding to the delay of the wave output and the p-wave output are respectively extracted. These signals (b) and (C) are respectively supplied to the negative input terminal and positive input terminal of the differential amplifier 3, and a linear high-frequency compensation difference output signal shown in waveform (d) is taken out as the difference output signal.

This difference output signal is supplied to the detector 4 to separate the negative polarity component signal shown in waveform (e). The signal (e) is supplied to the adder 7 via the attenuator 6, and the difference output signal (d) is also supplied to the adder 7 via the attenuator 5. Here, the asymmetrical or A nonlinear image quality compensation signal is taken out from the adder 7 as an output signal.

This image quality compensation signal (f) is led to the adder 8, where it is added to the delayed output original image signal (C) mentioned above, and as shown in the waveform (g), a high-contrast brightness is produced in accordance with the spatial frequency characteristics of visual perception. Then, a compensated output image signal in which the dark image is appropriately compensated and the visually best image quality is obtained is extracted as an addition output.

Note that the low-pass filter 1 in the circuit configuration described above is designed to appropriately change its passband characteristics in accordance with the standard characteristics of the television system targeted for image quality compensation. Since a high frequency component for image quality compensation is extracted based on the difference between the two, it is preferable to use a linear phase characteristic.

Further, since the visual spatial frequency characteristic image is originally two-dimensional, it is desirable that the low-pass filter l is also a two-dimensional filter. As a simple device, a one-dimensional filter can be used instead, but in that case, spatial anisotropy will occur in the contour of the displayed image, that is, contour emphasis only in the horizontal direction will occur.

When the input image signal waveform is a step-like waveform like waveform (a) shown in FIG. 1(B), the compensated output image signal waveform of the image quality compensator of the present invention is as shown in waveform (g) in the same figure. As shown, the compensated output image signal waveform has a positive polarity portion of the step contour slightly increased and a negative polarity portion greatly increased.

FIG. 7 shows an example of the result of image quality evaluation when such image quality compensation is applied to the standard image signal. Compared to the case where conventional linear compensation is applied, that is, the ratio of the compensation amount of (■) is 100%, the image quality compensation according to the present invention in which the negative polarity side is increased, significantly superior evaluation results are obtained. In particular, when the ratio of compensation amount is 10 to 30%, the evaluation is as high as about one rank. This is because, as already mentioned, the image quality compensation according to the present invention does not cause unnaturalness such as glare in the contours unlike the conventional method, and furthermore,
If the present invention is applied to a projection type image display system in which a large amount of flare is likely to occur in displayed images, an even greater effect of improving image quality can be obtained.

(Effects) As is clear from the explanation below, according to the present invention, the high-frequency component of the image signal in the spatial frequency domain is divided into the stop-polarity component and the negative-polarity component, and each independently affects the visual space. Since compensation can be performed in accordance with the frequency characteristics, it is possible to perform image quality compensation that appropriately corresponds to the appearance of both images and dark images during high contrast. Therefore, it is possible to perform sufficient image quality compensation and reproduce and display an image with excellent sharpness without causing any unnatural feeling in both bright and dark areas in the outline of the image.

The image quality compensation device of the present invention can be applied to an imaging system to compensate for any image signal without causing unnaturalness and then send it out, and can also be applied to a playback display system to compensate for image quality with characteristics that match display conditions. is applied to each image signal, and in particular,
It is suitable for application to image compensation in the projection display system described above.

[Brief explanation of drawings]

FIGS. 1A and 1B are block diagrams and signal waveform diagrams showing an example of the configuration and signal waveforms of each part of the image quality compensating apparatus of the present invention, respectively. FIG. 2 (A), (B), (C) and (D) are waveform diagrams and characteristic diagrams showing examples of both images and dark images and visual responses during low contrast and high contrast, respectively. , Fig. 3 is a characteristic curve diagram showing an example of changes in visual spatial frequency characteristics due to brightness and darkness of an image, Fig. 4 is a characteristic curve diagram showing an example of compensation characteristics of a conventional image quality compensation circuit, and Fig. 5 is a characteristic curve diagram showing an example of changes in visual spatial frequency characteristics due to brightness and darkness of an image. A characteristic curve diagram illustrating a comparison of the visual spatial frequency characteristics for images and dark images with the spatial frequency characteristics compensated by a conventional circuit. FIG. FIG. 7 is a characteristic curve diagram showing an example of image quality evaluation results for images subjected to image quality compensation according to the present invention. 1...Low pass filter, 2...Delay line, 3...Differential amplifier, 4...Detector, 5.6...Attenuator. 7.8...Adder. Patent Applicant 11 Broadcasting Association Representative Patent Attorney Yoshi Tani - (A)
<8) (C) Sun/Month (D) Figure 2 Figure 3 Figure 4 Ward °1 Dano - + ('r) Ward 1 Ichikyu Hato Ayu +1 + to ) r \-

Claims (1)

[Claims] a high-frequency extraction circuit that extracts a high-frequency signal component in at least one-dimensional spatial frequency domain of an input image signal; and a signal discrimination circuit that determines characteristics of the input image from positive polarity amplitude and negative polarity amplitude of the high-frequency signal component. a compensation signal forming circuit that forms image quality compensation signals related to the high-frequency signal components that are independently adjusted according to visual characteristics based on the discrimination results in the discrimination circuit; 1. An image quality compensation device comprising: an addition circuit that adds an image signal to an image signal to form an image quality compensated output image signal.