Video signal processing circuit

Abstract: A video signal output circuit used in a TV set to sample the frequency level of an input video signal so that monitored pictures are automatically optimized in quality. A luminance signal is separated from the input video signal by a Y/C separator. A plurality of band-pass filters whose passing frequencies are f₁, f₂, f₃, ..., f n detect the frequency spectrum of the luminance signal through sampling. The detected values are sent to a controller attached to an equalizer. The equalizer is controlled so that monitored pictures based on the output video signal are optimized in quality.

Description: Recent years have seen numerous kinds of apparatus developed and marketed as video signal sources. Illustratively, ordinary television sets are equipped with many video input terminals for receiving video signals from, e.g., a video tape recorder (VTR) and optical disk players in addition to broadcast program signals. The characteristics of the video signal of VTR's sometimes differ from those of optical disk players (commonly known as laser disk players). For example, the frequency characteristic of the video signal may vary depending on the performance and property of the video apparatus in question. Furthermore, recordings are sometimes made on the medium in such a manner that special visual effects are provided to enhance the contents of the program recorded. Given these parameters of variation, video apparatuses with fixed video circuit characteristics such as conventional television sets may not cope adequately with diverse video signals coming from external video sources. For example, the screen may turn high-resolution pictures into scenes of unnatural glare, or the screen may show "dulled" pictures lacking visual sharpness. US-A-4,882,623 discloses a signal processor for enhancing outlines in image signals produced by endoscopes. The form of the processing applied to the image signal is set manually by the user. GB-A-2,142,501 discloses a video signal processing apparatus in which the luminance signal is scaled responsive to its peak magnitudes. EP-A-0,150,098 discloses two video signal processing apparatus. One applies a predetermined equalisation process to the video signal, the other one of two different processes. In the latter apparatus no detail is given as to how the two processes are selected between. It is therefore an object of the present invention to overcome the above-described drawbacks and disadvantages of the prior art and to provide a video signal output circuit that improves the prior art. According to the present invention, there is provided a video signal output circuit comprising: detecting means for detecting a plurality of specific frequencies of the frequency spectrum of an input video signal; signal processing means for averaging the outputs of said detecting means using a predetermined time constant to obtain respective frequency level values for each detected frequency; and an equalizer circuit for receiving the frequency level values of said input video signal obtained from said signal processing means; wherein said equalizer circuit performs either one of the two operations of: a) equalising the level values of the respective specific frequencies of said input video signal to be substantially equal, and b) modifying the level values of the respective specific frequencies of said input video signal to have a predetermined frequency spectrum pattern. In operation, the video signal output circuit according to the invention detects the tendency of the frequency spectrum of the luminance signal component in an input video signal to check the characteristic of the input video signal and thereby flattens that characteristic through equalizing. This scheme averages monitored pictures in terms of quality so that optimum pictures are always obtained from video signals of different input video sources. The invention will become more apparent upon a reading of the following description and appended drawings of an illustrative embodiment. In the drawings:- Fig. 1 is a block diagram of a video signal output circuit incorporated in a television set and embodying the present invention; and Fig. 2 is a set of views showing output frequency spectrum examples of input video signals together with control signal and output frequency characteristics. One preferred embodiment of the invention will now be described with reference to the accompanying drawings. Fig. 1 is a block diagram of a video signal output circuit embodying the invention, the circuit being applied to a television set. In Fig. 1, reference numeral 1 is a tuner (front-end type); 2 is an intermediate amplifier including an intermediate frequency amplifier and a demodulator; 3 is a switching circuit that selects a demodulated video signal or an externally input video signal; and 4 is a Y/C separator that separates the video signal into a luminance signal and a chrominance signal. The luminance signal is fed to a video amplifier 5 and the chrominance signal is supplied to a chrominance signal processing circuit 6. Reference numeral 7 is an equalizer which, under control of external signals, automatically performs equalizing operation in response to the characteristic of the input video signal, as will be described later in more detail. The output video signal of the equalizer 7 and the color difference output signal of the chrominance signal processing circuit 6 are supplied to a matrix circuit 8. In turn, the matrix circuit 8 generates primary color signals R, G and B. The luminance signal separated by the Y/C separator 4 is fed to detecting means 9 that detects the frequency spectrum of the signal. The detecting means 9 comprises a plurality of band-pass filters (BPF) 9A whose passing center frequencies are f 1 , f 2 , f 3 , ..., f n ; a plurality of detectors 9B that detect the outputs of the band-pass filters 9A and hold the peak values (mean values) of these outputs for a predetermined period of time; and a plurality of A/D converters 9c that subject the outputs of the detectors 9B to A/D conversion for input to a controller 10 made of a microcomputer or the like. The passing frequency band of each band-bass filter may be selected as desired. For ordinary video signal bands, the number of center frequencies may range from three to seven (n = 3 - 7). The controller 10 has a changeover switch S1 used to select either automatic or manual control of the frequency characteristic of the video signal. In manual control mode, visual sharpness control is effected using UP and DOWN keys. In automatic control mode, D/A converters 11 are supplied with the level control data corresponding to the output levels of the A/D converters 9C. Analog control signals after conversion by the D/A converters 11 are fed to the equalizer 7. The inventive video signal output circuit of the above construction operates as follows: When a video signal is input illustratively following reproduction from a laser disk, the detection levels of the spectrum frequencies f 1 , f 2 , f 3 , ..., f n passing through the band-pass filters 9A and sampled at predetermined intervals are fed to the controller 10, as shown in Fig. 2 (A). On receiving the sampled detection levels, the controller 10 supplies the D/A converters 11 with control data D 1 , D 2 , D 3 , ..., D n indicated by envelope-like two-dot chain line in Fig. 2 (B). Given the output signals of the D/A converters 11, the equalizer 7 amplifies and expands the input video signal for each of the frequency bands involved. As a result of this, the video signals output by the equalizer 7 are levelled off, as depicted in Fig. 2 (C). The above-mentioned video signal input is primarily concerned with input sources having numerous high-pass frequency signal components. If part of the high-pass frequency signal components have been lost through dubbing or like operation, the controller 10 outputs control data D 1 , D 2 , D 3 , ..., D n whose levels are expanded on high-bands, as indicated by dashed line in Fig. 2 (B). This also provides suitable averaging of the video signal levels. Where the sharpness characteristic is controlled manually, the video signal levels may be controlled in such a manner that a frequency band of about 2.7 MHz is established as shown by dashed line B or by two-dot chain line C in Fig. 2 (C). The controller 10 may incorporate a memory device that outputs predetermined equalizing characteristics. With this arrangement, a given input video signal source when selected will prompt control data of the necessary pattern to be output. The above-described embodiment corrects the frequency characteristic of the luminance signal component in the video signal. An alternative embodiment may also be devised to correct the frequency characteristic of a composite signal. As described and according to the invention, the video signal output circuit detects frequency components of the input video signal and controls the equalizer in its video circuitry based on these frequency components. This makes it possible automatically to monitor optimum pictures derived from the video signals supplied by diverse video sources. While a preferred embodiment of the invention has been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the scope of the following claims.

Claims: A video signal output circuit comprising: detecting means (9) for detecting a plurality of specific frequencies of the frequency spectrum of an input video signal; signal processing means (10) for averaging the outputs of said detecting means using a predetermined time constant to obtain respective frequency level values for each detected frequency; and an equalizer circuit (7) for receiving the frequency level values of said input video signal obtained from said signal processing means (10); wherein said equalizer circuit (7) performs either one of the two operations of: a) equalising the level values of the respective specific frequencies of said input video signal to be substantially equal, and b) modifying the level values of the respective specific frequencies of said input video signal to have a predetermined frequency spectrum pattern. A video signal output circuit according to claim 1, wherein said detecting means includes: a plurality of band-pass filters (9A) having different respective pass bands; and analog-to-digital converter means (9E) for converting the output of said band-pass filters from an analog to a digital format. A Video signal output circuit according to claim 2, wherein the number of said band-pass filters (9A) is in the range of from three to seven. A video signal output circuit according to claim 1, 2 or 3 wherein said signal processing portion comprises a central processing unit (10). A video signal output circuit according to claim 1, 2, 3 or 4 wherein said equalizer circuit (7) varies the frequency characteristic of a luminance signal of the input video signal. A television incorporating a video signal output circuit according to any one of the preceding claims.

Inventors: AMANO TOSHIO, ODA OSAMU, SAITOH MITSUMASA, AMANO, TOSHIO, ODA, OSAMU, SAITOH, MITSUMASA
Applicants: SONY CORP, SONY CORPORATION
Application year: 1992
Main classification: H04N5
IPC codes: H04N5