JPH06141293A - Dc offset elimination television signal processing circuit - Google Patents

Abstract

PURPOSE:To eliminate the effect due to a DC offset when a signal multiplexed on upper and lower non-picture portion signals of a signal of the letter box system is reproduced on a receiver side. CONSTITUTION:An auxiliary signal to be sent by picture upper and lower portion signals in the letter box system is sent from a sender side on the picture upper and lower portion signal through a system comprising a 4 2 converter 14, a vertical shift circuit 20, an adder 21, a 1H delay device 22, a nonlinear compressor 23, a time compressor 15, and a rearrangement circuit 16 and also through an emphasis circuit boosting a low vertical spatial frequency. When the auxiliary signal has no vertical DC component, the auxiliary signal receives nonlinear amplitude compression through the emphasis circuit without other modification and sent at the picture upper lower portion. On a receiver side, the signal passes through a nonlinear amplitude expansion circuit in inverse characteristic with the sender side and a de-emphasis circuit and when the signal is subject to vertical frequency shift processing, the signal is subject also to vertical frequency shift on the receiver side and when the signal is not subject to vertical frequency shift processing, the signal is not subject to vertical frequency shift and the signal passes only through a nonlinear amplitude expansion circuit and a de-emphasis circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC offset canceling television signal processing circuit used in a transmitter encoder and a receiver decoder for transmitting a landscape screen television signal compatible with a current receiver.

[0002]

2. Description of the Related Art Television signals are obtained by scanning a screen. For example, in the NTSC system, effective scanning lines are about 48
One screen is composed of 0 [book / frame].

When an image is taken by a horizontally long screen camera having an aspect ratio of 16: 9 and displayed on a display having an aspect ratio of 4: 3, the circularity cannot be maintained and a circular object becomes a vertically long ellipse. That is, if it is left as it is, compatibility with the current receiver of the landscape screen broadcast cannot be obtained. In order to display a circle as a circle on a display with an aspect ratio of 4: 3 without losing the landscape screen, it is necessary to perform compression processing to 3/4 in the vertical direction. In this way, the encoding method for displaying the camera signal of the horizontally long screen with the current receiver having the aspect ratio of 4: 3 while maintaining the circularity is accompanied by the non-image part at the top and bottom of the display (there are black bars at the top and bottom of the screen, The image is displayed in the center of the screen), so it is called the letterbox method. In the letterbox method, if the number of effective scanning lines of the original image is 480 [lines / frame], the number of scanning lines is converted to 360 [lines / frame] to vertically compress it to 3/4 and to output 120 [ Book / frame] is a non-image portion. On the other hand, if the letter-box type signal is displayed as it is on the display having the same horizontal aspect ratio of 16: 9 as that of the camera, a circular object becomes a horizontal elliptical shape. Therefore, it is necessary to decode the signal transmitted as a signal compatible with the current receiver into the original horizontal screen signal. For this purpose, it is necessary to perform 4/3 decompression processing of the transmitted signal in the vertical direction and convert it into 480 [lines / frame].

As described above, in the letterbox system, compression / expansion in the vertical direction is required, and the scanning line conversion technique is indispensable. The scan line conversion technique is known as an application of the sample point conversion technique using an interpolation filter.

However, even in the scanning line conversion technique, an important problem occurs when handling interlaced television signals which are generally widely used. In the interlaced scanning signal, one image (hereinafter referred to as frame) is composed of two field images. The field image is composed of ½ of the scanning lines of the frame image, and the scanning lines have a positional relationship of offset between successive fields. At present, the field storage type is mainly used in the interlaced scanning camera. That is, in reality, imaging is performed by sampling in the time direction for each field.
Therefore, in a still image, a correct frame image can be obtained by superimposing two consecutive first and second fields.
In the case of a moving image, a correct frame image cannot be obtained because the image shift occurs.

In order to solve such a problem, in the scanning line conversion technique in which an interlaced scanning signal is input, a still image is processed as (between fields), and in the case of a moving image, an intra-field error does not occur. The motion adaptive processing technology that performs signal processing is adopted. However, the inventor of the present invention has noticed that there is a further problem when the above-described motion adaptive processing technique is adopted in the letterbox method.

That is, in the intra-field processing, since the number of scanning lines forming the field is only half of the frame, in principle, only half the vertical resolution can be realized as compared with the frame processing (inter-field processing). At the same time, if the input signal contains a vertical high-frequency component that exceeds the expressible vertical resolution, aliasing distortion occurs and the image quality is significantly degraded.

In the letterbox system, since the number of scanning lines is further reduced by the vertical compression processing, the reduction in resolution of interlaced scanning and the theoretical deterioration of image quality due to aliasing distortion become more remarkable. In particular, when constructing a system based on the current NTSC system, it is necessary to convert 240 lines in the field to 180 lines (or 180 lines to 240 lines), but it is very inconvenient in terms of visual characteristics and just deteriorates. This is the most easily detected area. For example, 1125
In the [book / frame] HDTV, the number of effective scanning lines in the field is about twice that of NTSC, so it does not cause a serious deterioration, whereas in the NTSC system, 240 scanning lines are used for in-field processing of moving images. Since it will be converted into 180 scanning lines, the vertical resolution is 180 [lines /
Only screen height] or less can be realized. At the same time, the vertical high frequency components of 180 [lines / screen height] or more of the input signal become aliasing distortion.

[0009]

As described above, in the letterbox system, an encoder and a decoder capable of handling progressive scanning signals have been satisfactory in performance, but an encoder capable of handling interlaced scanning signals. And no decoder has been implemented.

Therefore, the inventor of the present invention, even if an interlaced scanning signal is input, performs frame synthesis on the interlaced scanning signal, converts the interlaced scanning signal into a progressive scanning signal in advance, and then converts the number of scanning lines so as to conform to the letterbox method. The present invention proposes a system that can improve the resolution and reduce the aliasing distortion on the current receiver side.

Further, in this case, in the letterbox system, the transmitting side performs vertical compression to transmit a 360 [line / frame] signal, and the receiving side performs vertical expansion, but in this state, it is theoretically 360. [Book / Screen height]
The above vertical resolution cannot be obtained. Therefore, of the effective number of scanning lines of NTSC system of about 480 [lines / frame], 360 [lines / frame] is used as the letterbox main screen and 120 [lines / frame] on the upper and lower parts of the screen are improved in vertical resolution. It is used as a multiple area of the auxiliary signal for Here, the signals multiplexed in the upper and lower parts of the screen have important information in the low frequency component. However, in general, even the DC component cannot be completely transmitted. Therefore, in reality, a DC regeneration circuit is used on the receiving side to reproduce the DC component and then perform decoding processing.

However, the DC reproducing circuit cannot remove some imperfections because it is affected by the offset of the circuit, the fluctuation of the average luminance level of the signal, or the sag characteristic. This incompleteness is a matter of degree, and sufficient characteristics are obtained for reproducing a normal television image. However, this is a problem when configuring the letterbox receiver. The signal transmitted in the upper and lower parts of the screen is an auxiliary signal and is transmitted at a level much smaller than that of the main screen signal. Therefore, since the imperfections of the DC reproducing circuit have a relatively large influence, they cannot be ignored and become a major factor in the deterioration of the quality of the reproduced image in the letterbox system. As described above, when the signal multiplexed in the upper and lower non-image parts of the letterbox system is reproduced on the receiving side, deterioration of quality occurs due to DC offset.

Therefore, in the present invention, in the letterbox system, the DC offset which is inevitably generated on the receiving side is removed, that is, when the signal multiplexed on the upper and lower non-picture parts of the letterbox system is reproduced on the receiving side, the DC offset is generated. It is an object of the present invention to provide a television signal processing circuit capable of removing the influence of.

[0014]

According to the present invention, when the auxiliary signal to be transmitted at the upper and lower portions of the screen has a vertical DC component on the transmitting side, frequency shift is performed to a vertical high frequency region and a vertical spatial frequency is reduced to a low frequency region. It is transmitted at the top and bottom of the screen after passing through the boosting emphasis circuit. If the auxiliary signal to be transmitted in the upper and lower parts of the screen does not have a vertical DC component, pass through an emphasis circuit that boosts the low frequency at the vertical spatial frequency,
After passing through the non-linear amplitude compression circuit, it is transmitted at the top and bottom of the screen.

On the receiving side, a non-linear amplitude expansion circuit and a de-emphasis circuit having characteristics opposite to those on the transmitting side are passed, and when the transmitting side is vertically frequency shifted, the receiving side also performs vertical frequency shift. When the vertical frequency shift is not performed on the transmitting side, only the non-linear amplitude expansion circuit and the de-emphasis circuit are passed.

[0016]

On the transmitting side, when the auxiliary DC signal to be transmitted contains the vertical DC component, the frequency is shifted to the vertical high band, so that the vertical DC component is removed. Therefore, the amplitude level does not become infinite even if the emphasis for boosting the vertical low range is performed. Further, the amplitude can be suppressed to a value that can be transmitted by the non-linear amplitude compressor.

On the receiving side, after non-linear expansion, it is passed through a de-emphasis circuit having a vertical DC gain of "0". Although the DC recovery circuit on the receiving side has some imperfections, it is possible to reduce the relative DC offset between adjacent scanning lines to an almost negligible level. Therefore, if, for example, a differential circuit between scanning lines is adopted as the de-emphasis circuit of the vertical DC gain "0", the DC offset can be almost completely removed. When the vertical frequency shift is performed on the transmitting side before the emphasis, the auxiliary signal can be reproduced by performing the frequency shift on the receiving side.

[0018]

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

As a typical embodiment, a processing block diagram of a letterbox type encoder for inputting interlaced scanning signals is shown in FIG. Further, in FIG. 3, for the purpose of explanation of the operation, the vertical spatial frequency f concerning the signal of each node of the embodiment is shown.
The figure shows the two-dimensional spectrum of v and the temporal spatial frequency ft.

The number of effective scanning lines having the spectrum shown in FIG. 3 (1a) at the input terminal 1 is 480 [lines / frame], the frame frequency is 30 [Hz] (the field frequency is 60 [H]).
z]) 2: 1 interlaced scanning signal is input. Figure 3
The signals in the shaded areas A and B in (1a) are characteristic of interlaced scanning. The vertical high-frequency component and the temporal high-frequency component overlap due to the interlacing of the interlaced scans, and are indistinguishable in terms of signal. For example, in a picture having a vertical high frequency component in a still image, a flicker called interline flicker, that is, a temporal high frequency component occurs as aliasing. Further, even if the pattern has only the vertical low-frequency component, when the pattern moves, it appears in the vertical high-frequency region as a turn. In interlaced scanning, the areas A and B in FIG. 3 (1a) have the same information and cannot be distinguished. The frame synthesizing circuit 2 synthesizes the first and second fields.
It becomes the spectrum of (1b). That is, it is converted into a progressive scanning signal having a frame frequency of 30 [Hz]. Interlaced scanning → sequential scanning conversion between the same frame frequency is easily realized by alternately rearranging the scanning line signals in the first field and the scanning line signals in the second field using the buffer memory and outputting them as the same frame signal. it can. The output of the frame synthesis circuit 2 is a vertical low pass filter (V-LP
F) 4 is input and band-limited to the spectrum shown in FIG. Further, the 4 → 3 scanning line conversion circuit 11 36
It is converted into 0 [book / frame], and the spectrum of FIG. 3 (1d) is obtained. The input / output signal of the V-LPF 4 is input to the subtractor 5 and the difference calculation is performed to obtain the spectrum of FIG. 3 (1g). This signal has an important meaning as information representing the motion in a moving image.

The output of the subtractor 5 is a vertical frequency shift (V-
The shift circuit 6 converts the spectrum into that shown in FIG. In the vertical frequency shift circuit 6, the vertical frequency shift can be easily realized by inverting the polarity for each scanning line. next,
The horizontal / vertical low pass filter (HV-LPF) 7 limits the band horizontally / vertically. As will be described later, this signal is finally multiplexed and transmitted to the upper and lower non-image area, but this area has a transmission capacity of 120 [lines / frame] which is 1/3 of the main screen 360 [lines / frame]. Not not. Therefore, the amount of information has to be reduced to 1/3, and components having a low visual contribution are deleted in advance. For this reason
HV-LPF7 is inserted. An example of this characteristic is shown in FIG.

The output of the HV-LPF 7 is input to two systems of a 4 → 3 converter 8 and a 4 → 2 converter 14. One system is to improve the resolution of the moving image when the main signal is reproduced by the current receiver, and the other system is used to reproduce the original signal. The 4 → 3 converter 8 of one system converts an input signal into a sequential scanning signal of 360 [lines / frame], and the 4 → 2 converter 14 of the other system converts an input signal of 240 [lines / frame] in sequence. Convert to scan signal.

The signal converted into the progressive scanning signal of 360 [lines / frame] by the 4 → 3 converter 8 is converted by the vertical frequency shift (V-shift) circuit 9 into the spectrum of FIG. The output of the vertical frequency shift circuit 9 is multiplied by K (K = 0 to 1) in the multiplier 10. K is the motion detection circuit 3
Given as the output of K, K = 0 for still images, K for moving images
= 1 is defined. Therefore, when the signal having the spectrum of FIG.
The signal having the spectrum of FIG. 3 (1d), which is the output of the conversion circuit 11, is added to form a signal having the spectrum of FIG. 3 (1e). The output of the adder 12 is a progressive scanning signal having a frame frequency of 30 [Hz] of 360 [lines / frame], and the frame frequency of 30 [Hz] (field frequency of 60 [H
z]) 2: 1 interlaced scanning signal. Similar to the frame synthesizing circuit 2 described above, the sequential scanning → interlaced scanning conversion between the same frame frequencies uses the buffer memory to alternately output the scanning line signals in the frame for each scanning line as the first field signal and the second field signal. This can be easily achieved. The spectrum of the output of the progressive scan → interlaced scan converter 13 is shown in FIG. 3 (1f), and the information indicating the motion of the moving image is stored in the interlaced scan signal of 360 [lines / frame] as shown by the shaded area. Compatibility with current letterbox receivers is ensured.

The output of the 4 → 2 scanning line converter 14 is input to the vertical frequency shift (V-shift) circuit 20 and the vertical DC component is suppressed. The output of the vertical frequency shift circuit 20 is input to the adder 21. The output of the adder 21 is input to the other input terminal of the adder 21 through a 1-line delay device (1HDL) 22 to form a cyclic filter that boosts the low frequency band of the vertical frequency. The output of the adder 21 is set through the non-linear amplitude (NL) compressor 23 so that the amplitude does not become excessive. Although the output of the non-linear amplitude compressor 23 is 240 [lines / frame], it is input to the time compression circuit 15 and time-compressed to ⅓ and ⅔ for each scanning line, and 120 [] is output by the data rearrangement circuit 16. Book / frame]
Is converted into an interlaced scanning format signal and becomes a screen upper and lower part multiplexed signal.

The switch 17 switches between the main screen signal and the screen upper and lower signals, and a letterbox type 480
[Book / frame] The interlaced scanning signal is output from the output terminal 18. FIG. 2 shows an embodiment of the receiving side of the present invention.

The encoded signal at the input terminal 50 is subjected to direct current regeneration by the direct current regeneration circuit 65 and input to the switch 51 and the motion detector 64. The switch 51 supplies the main screen signal to the frame synthesizing circuit 52 and the screen up / down signal to the rearrangement circuit 53. From the interlaced scanning of the main screen signal of 360 [lines / frame] to 360 by the frame synthesis circuit 52
It is converted into the sequential scanning with the frame frequency of 30 [Hz] of [book / frame], and the spectrum of FIG. The signals multiplexed on the upper and lower parts of the screen are rearranged by the rearrangement circuit 53,
The time compression circuit 1 described in FIG. 1 passes through the time expansion circuit 54.
It is returned to a signal similar to the output of 5. Further, the output of the time expansion circuit 54 is input to the non-linear expansion device 69. The nonlinear decompressor 69 is set to have an inverse characteristic to the nonlinear compressor 23 on the transmission side. The output of the nonlinear expander 69 is a 1-line delay device (1
(HDL) 66 and subtractor 67 are connected to one input terminal. The output of the 1-line delay unit 66 is supplied to the other input terminal of the subtractor 67. Therefore, a difference signal between lines is obtained at the output of the subtractor 67, and de-emphasis on the receiving side is formed. Since the relative level between DC offset lines is negligibly small, the output of the subtractor 67 can eliminate the influence of DC offset. The signal from which the DC offset has been removed is returned to the original spectrum by the vertical frequency shift circuit 68, and the 2 → 3 scanning line converter 55 and the 2 → 4 scanning line converter 6 are provided.
Input to 0. The output of the 2 → 3 scan line converter 55 is 36
The vertical frequency shift register circuit 56 converts the frame frequency of 30 [Hz] into sequential scanning at 0 [lines / frame].
Entered in. In the vertical frequency shift circuit 56, the input signal is converted into the spectrum of FIG. 3 (1j) and supplied to the multiplier 57. The output K of the motion detection circuit 64 is connected to the other input terminal of the multiplier 57, and K = 1 is output in the case of a moving image. Therefore, in the case of a moving image, the vertical frequency shift circuit 5
The output of 6 is added to the subtractor 58 through the multiplier 57,
The vertical / temporal folding components included in the interlaced scanning of 360 [lines / frames] are removed, and the result shown in FIG.
It becomes the spectrum of d).

The frame frequency is 30 [Hz] at 360 [books / frames] that have been cleaned by removing aliasing components.
The progressive scanning signal of 48 is output by the 3 → 4 scanning line converter 59.
It is converted into a progressive scanning signal having a frame frequency of 30 [Hz] at 0 [lines / frame], and the spectrum shown in FIG. 3 (1 c) is obtained and sent to the adder 62. In addition, the frame frequency of 3 at 480 [lines / frame] by the 2 → 4 scanning line converter 60.
The signal converted into the progressive scan signal of 0 [Hz] has the spectrum of FIG. 3 (1 g) by the vertical frequency shift circuit 61 and is sent to the adder 62. 3 by adder 62
→ 4 scan line converter 59 output and vertical frequency shift circuit 6
The outputs of 1 are added to obtain the spectrum of FIG. 3 (1b). The output of the adder 62 is a progressive scanning signal having a frame frequency of 30 [Hz] of 480 [lines / frame], but the progressive scanning → interlaced scanning conversion circuit 63 causes the frame frequency to be 30 [Hz] (field frequency 60 [Hz]). Of 2:
Converted to one interlaced scanning signal. As described above with reference to FIG. 1, in order to perform the sequential scanning → interlaced scanning conversion between the same frame frequencies, if the scanning line signals in the frame are alternately output as the first field signal and the second field signal for each scanning line using the buffer memory. Easy to implement.

In the above embodiment, an example in which the interlaced scanning signal is transmitted in the letterbox system and converted into the interlaced scanning signal on the receiving side has been described, but the present invention is limited to a system which handles the interlaced scanning signal. Instead, it can be applied to a letter box system that handles progressive scanning signals.

[0029]

As described above, according to the present invention,
For the upper and lower multiplexed signals, the line difference calculation is performed on the receiving side, so that the DC offset component is removed. Since the transmission side performs the difference characteristic between the lines on the reception side and the processing with the reverse characteristic, the frequency characteristic of the total transmission and reception becomes flat, and the predetermined signal is reproduced on the reception side. On the transmitting side, the vertical DC component is suppressed in advance, then the vertical low band is boosted, and the nonlinear amplitude compression is performed, so that the amplitude can be set to an optimum level at which transmission is possible without becoming excessive.

[Brief description of drawings]

FIG. 1 is a diagram showing a transmitting side according to an embodiment of the present invention.

FIG. 2 is a diagram showing a receiving side according to an embodiment of the present invention.

FIG. 3 is a two-dimensional spectrum diagram in the vertical / temporal spatial frequency domain shown for explaining the operation of the embodiment of the present invention.

[Explanation of symbols]

2 ... Frame synthesis circuit, 3 ... Motion detector, 4 ... Vertical low-pass filter, 5 ... Subtractor, 6 ... Vertical shift circuit, 7 ...
Horizontal / vertical low pass filter, 8 ... 4 → 3 converter, 9 ...
Vertical frequency shift circuit, 10 ... Multiplier, 11 ... 4 → 3 converter, 12 ... Adder, 13 ... Sequential scan → Interlaced scan converter, 14 ... 4 → 2 converter, 15 ... Time compression circuit, 16
... rearrangement circuit, 17 ... switch, 20 ... vertical shift circuit, 21 ... adder, 22 ... 1H delay device, 23 ... nonlinear amplitude compressor, 51 ... switch, 52 ... frame synthesizing circuit,
53 ... Rearrangement circuit, 54 ... Time expansion circuit, 57 ... Multiplier, 58 ... Subtractor, 59 ... 3 → 4 converter, 60 ... 2 → 4
Converter, 61 ... Vertical shift circuit, 62 ... Adder, 63 ...
Sequential scanning → interlaced scanning conversion circuit, 64 ... Motion detector,
66 ... 1H delay device, 67 ... Subtractor, 68 ... Vertical shift circuit.

Claims (7)

[Claims] 1. A television signal processing circuit for transmitting an image as a main signal using a partial scanning line of the number of effective scanning lines and transmitting an auxiliary signal on the remaining scanning lines, wherein the auxiliary signal is transmitted in a vertical direction. A DC offset elimination television signal processing circuit having an emphasis processing means for boosting a low frequency range. 2. A television signal processing circuit for transmitting an image as a main signal using a partial scanning line of the number of effective scanning lines and transmitting an auxiliary signal on the remaining scanning lines, wherein a vertical low frequency band of the auxiliary signal is used. A DC offset elimination television signal processing circuit having means for suppressing a component and means for performing an emphasis processing for boosting a low frequency band in a vertical direction. 3. The DC offset removing television signal processing circuit according to claim 2, further comprising vertical frequency shift means as means for suppressing the vertical low frequency component of the auxiliary signal. 4. A television signal processing circuit for transmitting an image as a main signal using a partial scanning line of the number of effective scanning lines and transmitting an auxiliary signal on the remaining scanning lines, wherein a vertical low frequency band of the auxiliary signal is used. DC offset removal television signal processing circuit having means for suppressing a component, means for performing an emphasis process for boosting a low frequency band in the vertical direction, and non-linear amplitude compression means for performing a non-linear processing on the output of this means. . 5. A television processing circuit for receiving a transmitted signal in which an image is included as a main signal using a part of the effective scanning lines and an auxiliary signal is included in the remaining scanning lines. A television signal processing circuit for eliminating DC offset, comprising vertical de-emphasis means for making the gain of vertical DC zero for signals transmitted by scanning lines other than the main signal. 6. An image is included as a main signal using a partial scanning line of the number of effective scanning lines, an auxiliary signal is included in the remaining scanning lines, and the auxiliary signal is transmitted. In a television processing circuit for receiving a signal in which the vertical frequency shift is suppressed and the vertical frequency is further shifted, a vertical de-emphasis means for making the gain of the vertical direct current 0 with respect to the signal transmitted by the scanning line other than the main signal, and this means. And a vertical frequency shift means for vertically shifting the output of the DC offset television signal processing circuit. 7. An image is included as a main signal using a partial scanning line of the number of effective scanning lines, an auxiliary signal is included in the remaining scanning lines, and the auxiliary signal is transmitted. In a television processing circuit that receives a signal whose components have been suppressed, then is boosted in the low frequency range in the vertical direction to undergo emphasis processing, and then nonlinearly compressed, a signal transmitted by a scanning line other than the main signal. With respect to the above, a vertical de-emphasis means for processing so that the vertical DC gain of the output of this means becomes zero, and a vertical frequency shift means for vertically shifting the output of this means. A television signal processing circuit for eliminating DC offset, which is characterized in that