JPH0783440B2 - Non-linear enhancement device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a non-linear enhancement apparatus that compensates for image quality deterioration due to band limitation of a filter output image signal by selective enhancement of signal band components.

(Prior Art) The most suitable technical field to which the present invention is applied is a field image of a wide band high-definition television image signal and an inter-frame multiple offset sub-sampling transmission system. In this multiple offset sub-sampling transmission method, high-definition television image signals with a signal band of 34 MHz are subjected to multiple offset sub-sampling between fields and frames by sampling at a frequency of 24.3 MHz that makes a cycle of two frame cycles, and band-compressed and transmitted. On the receiving side, inter-frame interpolation and inter-field interpolation are performed, and in principle, the original image signal is almost completely restored.

Therefore, for a still image signal that does not change with time, it is possible in principle to restore an almost complete original image signal.
Since inter-field or inter-frame interpolation cannot be performed on moving image signals having different pixel information over time, the original image signal is restored by spatial field interpolation. Also, with sampling, so-called aliasing distortion occurs in which the component of the difference between the sampling frequency and the high-frequency signal component is mixed into the low-frequency signal component, so the image signal band to be transmitted is limited, and aliasing distortion occurs in the sampling frequency. It is necessary to avoid the above and select appropriately, or to appropriately convert in the process of signal processing.

Therefore, in the multiple offset sub-sampling transmission of the high-definition television image signal, the still image signal and the moving image signal are separately processed in consideration of the above-mentioned point, and the visually required fineness is lowered. For the moving image signal, the signal band to be transmitted is previously reduced to about 12 to 16 MHz, which is much narrower than 24 MHz of the still image signal, and the subsequent signal processing is performed.

(Problems to be solved by the invention) However, even if the transmission signal band is limited to the above-mentioned allowable range based on the result of the visual evaluation experiment for the moving image signal, for example, when the image motion is small. In some cases, the so-called blurring of the image due to lack of definition may be felt. For example, in the paper entitled "New Transmission System for High-Definition Television" published in the NHK STRL Monthly Report and July 1984 issue by the present inventor. As described, the response in the signal passing area close to the cutoff area of the pre-filter to limit the signal band prior to signal processing on the transmission side in order to reduce the feeling of blurring in moving images as much as possible. It has been conventionally practiced to use a non-linear filter response so as to be about 3 to 4 dB, which is small for a large amplitude signal and large for a small amplitude signal.

However, even if the processing is performed as described above, the moving image reproduced and displayed on the receiving side is still displayed when the still image is switched to the moving image, or when the still image area and the moving image area are on the same screen. When both can be viewed in direct contrast with each other in terms of time or space, the image quality deteriorates to the extent that it cannot be overlooked as a high-definition television due to visual blurring. There was a problem.

As a result of various studies made by the present inventors on the cause of the blurring effect on the reproduced moving image, the field interpolation performed on the receiving side for the moving image signal transmitted by the multiple offset sub-sampling is, in principle, substantially effective. It acts as a low-pass filter, and for this reason, it has been clarified as a new problem that the moving image reproduced and displayed has the above-mentioned blurring feeling, even though the transmitting side performs appropriate processing.

(Means for Solving Problems) An object of the present invention is to solve the above-mentioned problems of the related art and to provide a low interposition on the receiving side of band compression transmission of a wideband image signal such as a high-definition television image signal. It is an object of the present invention to provide a non-linear enhancement apparatus which is remarkably improved as compared with the conventional one as a means for easily eliminating the image deterioration of a reproduced image due to the use of a band pass filter with a simple structure.

That is, the non-linear enhancement apparatus of the present invention branches and inputs a television image signal into a plurality of signal paths each having a different bandwidth, performs separate signal processing on each of the signal paths, and then outputs the signal paths. A nonlinear enhancement device configured to mix signals and output as a single television image signal, comprising a first low-pass filter and a medium-high band in a pass band of the filter connected in series. A first signal path having a non-linear enhancement circuit that enhances only the intermediate level signal component without enhancing the low signal level signal component and the high signal level signal component of the first low pass signal, and the first low pass signal. The television image signal is preceded by at least one other signal path having a low-pass filter with a higher cut-off frequency than the filter. A circuit that branches and supplies the signal to the first signal path and the other signal path and each output signal from the first signal path and the other signal path are mixed, and the signal obtained thereby is mixed into the single signal path. And a mixing circuit for outputting as one television image signal.

(Operation) According to the present invention, it is possible to easily prevent the deterioration of the definition of the reproduced moving image without changing the configuration of the transmitting / receiving device in the transmission of the high-definition television image signal.

(Example) Hereinafter, the present invention will be described in detail with reference to the drawings.

First, a schematic configuration of a transmitter and a receiver used in a high-definition television image signal multiple offset sub-sampling transmission method, which is optimum for applying the present invention, is briefly described with reference to FIGS. 1 (a) and 1 (b), respectively. To do.

In the transmitter shown in FIG. 1 (a), an AD converter 1S digitizes an input image signal of a band of 24 MHz at a frequency of 48.6 MHz, and a still image signal component is a signal component in an oblique direction obtained by an inter-field prefilter 2. Then, the 24.3 MHz sub-sampler 5a performs inter-field offset sub-sampling at a frequency of 24.3 MHz, and the 24.3 MHz-32.4 MHz conversion circuit 6a converts the sampling frequency to lead to the linear mixing circuit 7S. On the other hand, the moving image signal component is 24.3MHz after limiting the signal band to 16MHz by the 14MHz filter 3.
The sampling frequency is converted by the −32.4 MHz conversion circuit 5b and is further led to the linear mixing circuit 7S via the intra-field pre-filter 6b. The conversion of the sampling frequency is for improving the degree of completion of motion detection.

Further, the output digital image signal of the AD converter 1S is guided to the motion detection circuit 4S and the amount of motion of the image is detected by the non-linear processing of the absolute value of the inter-frame difference to detect both the still image and moving image signal components in the linear mixing circuit 7S. Control the mixing ratio. The mixed output image signal is frequency 1 by the 16.2MHz subsampler 8.
6.2MHz inter-frame offset sub-sampling is applied, the obtained multiple offset sub-sampling transmission signal is controlled by the transmission path filter 9S to control the waveform transmission characteristics on the transmission path, and is converted to an analog image signal by the DA converter 10 before transmission. Send to the road.

In the receiver shown in FIG. 1 (b), the input analog image signal is digitized by the AD converter 1R at a frequency of 32.4 MHz, and the still image signal component is interframe interpolation filter.
The offset signal of 2 frame periods is collected by 11 to restore the original signal almost completely, and the 32.4-24.3MHz conversion circuit 13a
After the sampling frequency is converted by, the aliasing component is removed by the inter-field interpolation filter 14 to lead to the linear mixing circuit 7R. On the other hand, the moving image signal component is subjected to spatial interpolation for each field by the field interpolation filter 12 to remove the aliasing component, and the 32.4MHz-24.3MHz conversion circuit 13
The sampling frequency is adjusted to the still image component by b, and then the same is led to the linear mixing circuit 7R. Furthermore, AD converter 1R
Output digital image signal to the motion detection circuit 4R, and controls the mixing ratio of both still image and moving image signal components in the linear mixing circuit 7R according to the amount of motion of the detected image in the same manner as on the transmission side, and mixes The output image signal is converted back to an analog image signal by the DA converter 9R and taken out as a reproduction output image signal.

Therefore, as described above, the field interpolation filter 12 in the receiver shown in FIG. 1 (b) substantially limits the signal band of the moving image signal component as a low-pass filter having a cutoff frequency of 16 MHz, The blurred image in the above-described manner is visually generated in the reproduced and displayed moving image area.

In the present invention, in order to visually remove or reduce the blurring feeling, for example, as shown in FIG. 2, a part of the configuration of the receiving device can be easily modified to visually remove the blurring feeling. To do so. In the configuration example shown in FIG. 2, the field interpolation filter 12 and 32.4 MHz shown in FIG.
Cutoff frequency 1 at which the z → 24.3 MHz conversion circuit 13b operates substantially
A 6 MHz moving image low-pass filter 15 (see FIG. 2) output signal is guided to a nonlinear enhancement circuit 16 (see FIG. 2), and a signal having this moving image low-pass filter 15 and nonlinear enhancement circuit 16 In the road, the response of the mid-high range signal component centered at a frequency of 12 MHz, for example, in the output signal band for the moving image is increased by about 3 to 6 dB compared to the response of the low range signal, and the nonlinear enhancement is appropriately performed. Then, the linear mixing circuit 7R (Fig. 1 (b))
And FIG. 2).

On the other hand, the interframe interpolation filter 1 shown in FIG.
1,32.4MHz → 24.3MHz conversion circuit 13a and the inter-field interpolation filter 14 substantially cutoff frequency 24MHz output signal of the low-pass filter for still image 17 (see FIG. 2), that is, the above-mentioned video Low-pass filter 17 for still images with a cutoff frequency higher than that of the image low-pass filter 15
The output signal from the other signal path having the signal delay amount of the signal delay amount is adjusted so that the still image signal system and the moving image signal system have the same timing at the input side of the linear mixing circuit 7R. It is led to the linear mixing circuit 7R (see FIGS. 1 (b) and 2) via the delay circuit 18 (see FIG. 2) having a delay amount, and the timings of both are aligned to obtain the still image signal component and the moving image signal. As shown in FIG. 1 (b), the components are mixed and extracted according to the amount of movement of the image (the output of the motion detection circuit 4R in FIG. 1 (b)). The signal thus taken out is converted into an analog image signal by the DA converter 9R shown in FIG. 1 (b) and output as a reproduction output image signal.

The above-described non-linear enhancement circuit 16 performs the required non-linear mid-high range enhancement configured as shown in FIG. 3, for example. That is, the input filter output moving image signal component is guided to the band pass filter 19, and only the middle and high band signal components of 3.3 MHz are extracted with a 3 dB bandwidth centered at 12 MHz, for example, and guided to the non-linear circuit 20. In the non-linear circuit 20, for example, an appropriate level of about 3 to 6 dB is suitable only for an intermediate signal level portion within the range of 10/255 to 60/255 for an 8-bit image signal of the input mid-high range signal component. A non-linear process is applied to the portions of low signal level and high signal level to provide zero response. That is, since the signal frequency band to be enhanced in the non-linear enhancement circuit 16 is relatively high, enhancing a low level signal portion emphasizes a signal with a low SN ratio, so that noise in the relevant portion of the reproduced image increases and stands out. In addition, when the high-level signal portion is enhanced, the high-level signal portion is originally emphasized further, so that an unnatural feeling occurs in the relevant portion of the reproduced image.
Therefore, no enhancement is applied to the low signal level and high signal level parts, and visual experiments show that the effect of improving the definition can be visually obtained for the reproduced image. Enhance only the ingredients. If the enhanced output signal of the non-linear circuit 20 is guided to the adder circuit 21 and added to the filter output moving image signal component whose timing is aligned via the delay circuit 22, a moving image signal in which the signal band is low-passed to the necessary minimum is obtained. Even if multiple-offset sub-sampling transmission and field interpolation are applied, a moving image with small motion that is reproduced and displayed does not suffer from the conventional visual blurring, and the signal processing of moving image signal components is complicated. It can be spoofed without being transformed.

The nonlinear enhancement device of the present invention is not limited to the above-described example of band compression transmission of high-definition television image signals, but limits the signal band of a certain signal path (first signal path) according to some other need. Therefore, when the reproduced image visually deteriorates due to another signal path, the degree of the restriction is weakened to expand the signal band to prevent another signal processing, or the visual quality is not increased. The deterioration of image quality can be eliminated, and it can be widely applied to other image information transmission.

In the present invention, a certain signal path (first signal path)
Since the signal band of the image signal is limited by the above, it is intended to relieve the occurrence of visual image quality deterioration (blur) in comparison with other signal paths having a wider signal band than that. There is no reason why it must be one,
Therefore, the present invention can be applied even when there are a plurality of other signal paths.

(Effects of the Invention) As is apparent from the above description, according to the present invention, a television image signal is branched and input into a plurality of signal paths each having a different bandwidth, and in each of these signal paths, separate signal processing is performed. When the bandwidth of a certain signal path is the narrowest and the output is displayed as an image, it can be remedied if the output from another signal path wider than that is uncomfortable. One example thereof is the band limitation effect which substantially acts on the moving image reproduced by performing field interpolation on the moving image signal component band-compressed and transmitted by the above-described multiple offset subsampling described in the embodiment. It is possible to obtain a special effect that the blurred image can be visually removed by a simple circuit configuration while keeping the signal bandwidth.

The non-linear enhancement apparatus of the present invention branches and inputs a television image signal into a plurality of signal paths each having a different bandwidth, performs separate signal processing on each of the signal paths, and then outputs the integrated signal again. Since the apparatus is further structurally limited, the apparatus of the present invention has the above-mentioned configuration even if it is configured in any part of the television image signal transmission system (for example, the transmission side, the reception side, or the transmission path). Since the above-mentioned effects due to the limitation of the present invention are exerted, it is not necessary to particularly specify the portion in which the device of the present invention is configured.

[Brief description of drawings]

1 (a) and 1 (b) are block diagrams respectively showing a schematic configuration of a transmission device and a reception device in multiple offset subsampling transmission of a high-definition television image signal, and FIG. FIG. 3 is a block diagram showing an example of a partial configuration of the receiving device shown in FIG. 1 (b) when the nonlinear enhancement of the invention device is applied, and FIG. 3 is a block diagram showing a configuration example of a nonlinear enhancement circuit according to the invention device. It is a figure. 1S, 1R AD converter 2 Interfield prefilter 3 16MHz filter 4S, 4R Motion detection circuit 5a 24.3MHz subsampler 6a 5b 24.3MHz-32.4MHz conversion circuit 6b Field Inner pre-filter 7S, 7R …… Linear mixing circuit 8 …… 16.2MHz subsampler 9R, 10 …… DA converter 9S …… Transmission line filter 11 …… Interframe interpolation filter 12 …… Field interpolation filter 13a, 13b …… 32.4MHz-24.3MHz conversion circuit 14 …… Inter-field interpolation filter 15 …… Moving image filter 16 …… Nonlinear enhancement circuit 17 …… Still image filter 18,22 …… Delay circuit 19 …… Band pass filter (BPF) 20 …… Nonlinear circuit 21 …… Adding circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Seiichi Koshi 1-10-11 Kinuta, Setagaya-ku, Tokyo Inside the Japan Broadcasting Corporation Broadcasting Technology Laboratory (72) Inventor Yuichi Iwadate 1-10 Kinuta, Setagaya-ku, Tokyo No. 11 Inside the Japan Broadcasting Corporation Broadcasting Technology Research Laboratory (56) References JP-A-57-24173 (JP, A) JP-A-61-96877 (JP, A) Actually developed 59-125174 (JP, U)

Claims (2)

[Claims] 1. A television image signal is branched and input into a plurality of signal paths each having a different bandwidth, each of the signal paths is subjected to separate signal processing, and then the output signals of the signal paths are mixed. A non-linear enhancement device configured to output as a single television image signal by a first low-pass filter and a signal component in a middle-high range in a pass band of the filter connected in series to the first low-pass filter. A first signal path having a non-linear enhancement circuit that does not enhance low-level and high-level signal components, but enhances only intermediate-level signal components, and a higher cutoff than the first low-pass filter. At least one other signal path having a low pass filter in frequency, and the television image signal as the first signal path and the other signal path. A circuit branched and supplied to the signal path and each output signal from the first signal path and the other signal path are mixed, and the signal obtained thereby is output as the single television image signal. A nonlinear enhancement device comprising a mixing circuit. 2. A first low-pass filter, and a low-pass filter having a cut-off frequency higher than that of the first low-pass filter when the number of the other signal paths is one.
A field interpolation filter used for reception of inter-field and inter-frame multiple offset sub-sampling transmission methods of high-definition television image signals, and inter-field and inter-field interpolation filters, respectively. The nonlinear enhancement device according to item 1.