Chrominance processing arrangement having immunity to colorstripe encoding

A video system (100) includes a chrominance processing arrangement (200). The chrominance processing arrangement (200) includes a burst accumulator (240) operative to detect a polarity inversion within a burst interval associated with a horizontal line of video information, and generate at least one output signal that compensates for the detected polarity inversion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to video systems, and more particularly, to a chrominance processing arrangement for use in video systems that provides, among other things, immunity to colorstripe encoding.

2. Background Information

Techniques such as colorstripe encoding are often utilized to discourage the unauthorized reproduction of video recordings by degrading the quality of the resultant copies. Although colorstripe encoding is not intended to degrade playback of authorized video recordings, some picture degradation typically occurs. Colorstripe encoding software is commercially available from companies, such as Macrovision.

Colorstripe encoding generally involves inverting the polarity of a portion of the colorburst (i.e., “burst”) interval associated with a horizontal line of video information. Such encoding may be applied to a given number of horizontal lines that comprise a video frame. For example, colorstripe encoding may be applied to 4 out of every 20 lines, or to 2 out of every 17 lines, etc. The polarity inversion of colorstripe encoding causes the gain of automatic color control (“ACC”) circuitry of a video system to be modulated, thus resulting in horizontal stripes of oversaturated chrominance on the display.

A traditional approach for reducing the visibility of artifacts associated with colorstripe encoding is to make the ACC time-constant sufficiently large so that the amplitude of the modulation is reduced. This approach, however, is not completely satisfactory since it does not completely eliminate the artifacts, but simply reduces their amplitude. Moreover, this approach necessitates an ACC time-constant that may be larger than is otherwise preferred for optimum signal acquisition behavior.

Another approach for reducing the visibility of artifacts associated with colorstripe encoding is to utilize a burst replacement technique. In general, burst replacement involves stripping colorstripe encoding from video information by removing a burst packet and replacing it with an artificially generated burst packet. Burst replacement, however, is not ideal since removal of an original burst packet may cause valuable information within that burst packet to be lost, and thereby create operational problems within a video system. For example, removal of an original burst packet may cause chrominance synchronization problems to occur.

Accordingly, there is a need for a chrominance processing arrangement that avoids the aforementioned problems, and thereby provides improved immunity to colorstripe encoding. The present invention addresses these and other issues.

SUMMARY OF THE INVENTION

In accordance with the present invention, a video system includes a chrominance processing arrangement. The chrominance processing arrangement includes means for detecting a polarity inversion within a burst interval associated with a horizontal line of video information, and for generating at least one output signal that compensates for the detected polarity inversion.

The exemplifications set out herein illustrate preferred embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, and more particularly toFIG. 1, a diagram of an exemplary video system100including a chrominance processing arrangement200according to principles of the present invention is shown. Video system100ofFIG. 1may be embodied, for example, as a television signal receiver, a set-top box, a video cassette recorder (“VCR”), a digital versatile disk (“DVD”) player, a video game box, a personal video recorder (“PVR”) or any other system having a video processing function.

InFIG. 1, video system100includes chrominance processing arrangement200for receiving and processing a modulated chrominance subcarrier input signal (“Chroma”), to thereby generate and output baseband chrominance signals (“Cr” and “Cb”). According to an exemplary embodiment, the Cb and Cr signals may represent demodulated chrominance signals such as B-Y and R-Y color difference signals, as used in video systems such as television signal receivers or other systems. Chrominance processing arrangement200may, for example, be included on one or more integrated circuits (“ICs”). Although not expressly shown inFIG. 1, video system100may also include other components, such as other ICs and other electrical and non-electrical components. As will be explained herein, chrominance processing arrangement200provides video system100with immunity to colorstripe encoding.

Referring toFIG. 2, a diagram providing further exemplary details of chrominance processing arrangement200ofFIG. 1is shown. InFIG. 2, chrominance processing arrangement200comprises a variable-gain amplifier210, a chrominance demodulator220, a filter230, a burst accumulator240, a quadrature oscillator250, and an ACC detector and filter260.

According to an exemplary mode of operation, amplifier210receives a modulated chrominance input signal (“Chroma”) having a nominal subcarrier frequency of 3.58 MHz. Amplifier210adjusts the gain (e.g., amplitude) of the modulated chrominance input signal to thereby generate and output a gain-adjusted chrominance signal. Chrominance demodulator220receives the gain-adjusted chrominance signal from amplifier210and, according to an exemplary embodiment, multiplies the gain-adjusted chrominance signal by quadrature phase sinusoid signals provided from quadrature oscillator250to thereby generate and output demodulated chrominance signals.

Filter230performs a filtering operation (e.g., low pass filtering operation) upon the demodulated chrominance signals generated by chrominance demodulator220to thereby generate and output baseband Cb and Cr signals. As previously indicated herein, the baseband Cb and Cr signals may represent demodulated chrominance signals such as B-Y and R-Y color difference signals, as used for example in television signal receivers or other systems.

Burst accumulator240receives and samples the baseband Cb and Cr signals output from filter230to thereby generate output signals representative of the average Cb and Cr amplitude values for each burst interval. There is one such burst interval associated with each horizontal line of video information. According to an exemplary embodiment, burst accumulator240takes thirty-two (i.e., 32) amplitude samples of each of the baseband Cb and Cr signals during a burst interval, and averages these amplitude samples to thereby generate average Cb and Cr amplitude values for the burst interval. A different number of samples may, of course, be taken in accordance with the present invention. Burst accumulator240provides output signals representative of the average Cb and Cr amplitude values for the burst interval to quadrature oscillator250and ACC detector and filter260, to thereby control their respective operations. For example, quadrature oscillator250uses the output signals from burst accumulator240to control its oscillation phase, and thereby control the phase of the sinusoidal signals provided to chrominance demodulator220. According to an exemplary embodiment, ACC detector and filter260includes amplitude detection and filtering circuitry, and uses the output signals from burst accumulator240to generate and output a control signal that controls the amplitude gain of amplifier210.

InFIG. 2, colorstripe encoding introduces errors into the output signals of burst accumulator240. In particular, the average Cb amplitude value generated by burst accumulator240is especially susceptible to errors due to the polarity inversion introduced through the colorstripe encoding process. For example, without colorstripe encoding, the baseband Cb signal may normally exhibit a constant amplitude value of −448 during a burst interval when video system100is in a steady-state condition (e.g., not during a signal acquisition state such as following a channel change). Accordingly, the average Cb amplitude value is −448 during this burst interval. However, when colorstripe encoding is present, a portion of the burst interval is subject to a polarity inversion that causes the average Cb amplitude value to change. For example, if colorstripe encoding is applied to one-fourth of a burst interval, then one-fourth of the samples taken during this burst interval have inverted polarities. That is, assuming 32 samples per burst interval, and a normal average Cb amplitude value of −448, the average Cb amplitude value for the burst interval having colorstripe encoding is:
[(8)(448)+(24)(−448)]/[32]=−224
As indicated in the foregoing equation, when colorstripe encoding is applied to one-fourth of a burst interval, one-fourth of the samples (i.e., 8 out of 32) taken during this burst interval have inverted polarity and thereby cause the average Cb amplitude value to differ from its normal value of −448.

According to an exemplary embodiment, the baseband Cr signal may normally exhibit a constant amplitude value of zero (i.e., 0) during a burst interval when video system100is in a steady-state condition. Accordingly, during a steady-state condition of video system100, the average Cr amplitude value is not particularly susceptible to errors due to the polarity inversion introduced through colorstripe encoding, since the inverse of 0 is 0. However, the average Cr amplitude value is not typically 0 during a signal acquisition state, such as following a channel change. Accordingly, when video system100is in a signal acquisition state, the average Cr amplitude value is likewise susceptible to errors due to the polarity inversion introduced through colorstripe encoding.

Errors in the output signals of burst accumulator240may be addressed by simply increasing the time constant in ACC detector and filter260, and thereby “smoothing” the errors and making them less visible. However, even with the use of a relatively large time constant, some artifacts are still visible with certain video material. Even with perfect smoothing, a less than desirable amount of chrominance oversaturation (e.g., up to 13 percent) may occur. As will be explained herein, the present invention addresses these problems by canceling errors attributable to colorstripe encoding in the output signals of burst accumulator240, prior to any filtering by ACC detector and filter260.

Referring now toFIG. 3, a diagram providing further exemplary details of burst accumulator240ofFIG. 2is shown. As indicated inFIG. 3, burst accumulator240includes components for processing the baseband Cb signal, and components for processing the baseband Cr signal. In particular, the components for processing the baseband Cb signal include accumulators305and310, a sign comparator315, a multiplier320, a multiplexer325, and a subtractor330. The components for processing the baseband Cr signal include accumulators335and340, a multiplier345, a multiplexer350, and a subtractor355.

According to an exemplary mode of operation, accumulators305and310receive and sample the baseband Cb signal to thereby generate accumulated Cb amplitude values in accordance with enabling burst gate (“BG”) signals BG1and BG2, respectively. In particular, the BG1and BG2signals are activated to respectively enable accumulators305and310to sample the baseband Cb signal and generate accumulated Cb amplitude values. The BG1and BG2signals may, for example, be generated by a processor or other device (not shown) of video system100.

According to an exemplary embodiment, the BG1signal has a pulse width duration that is equal to, or approximately equal to, the duration of a burst interval, which is typically about 1.78 milliseconds. For example, the pulse width duration of the BG1signal may be slightly longer than, or shorter than, the duration of a burst interval. Moreover, the BG1signal is activated to coincide with each burst interval. In this manner, the activated BG1signal enables accumulator305to sample the baseband Cb signal and generate accumulated Cb amplitude values during each burst interval.

According to an exemplary embodiment, the BG2signal has a pulse width duration that is less than the duration of the burst interval. For example, the pulse width duration of the BG2signal may be equal to one-fourth the duration of a burst interval, or some other fractional portion thereof. In particular, the pulse width duration of the BG2signal preferably corresponds to the portion of the burst interval where colorstripe encoding is expected to be present. Accordingly, if colorstripe encoding is present during the initial one-fourth of the burst interval, then the BG2signal has a pulse width duration equal to one-fourth the duration of the burst interval. Moreover, the BG2signal is activated during this portion of the burst interval where colorstripe encoding is present. In this manner, the activated BG2signal enables accumulator310to sample the baseband Cb signal and generate accumulated Cb amplitude values during the portion of each burst interval where colorstripe encoding is expected to be present.

Sign comparator315receives the accumulated Cb amplitude values generated by accumulators305and310, and performs a sign comparison operation thereon. In particular, sign comparator315determines whether the sign of the accumulated Cb amplitude value generated by accumulator305is the same as the sign of the accumulated Cb amplitude value generated by accumulator310. That is, sign comparator315determines whether the accumulated Cb amplitude values are both positive (+) or both negative (−). In the event that the accumulated Cb amplitude values are different (i.e., one being positive and the other negative), then sign comparator315generates a switching (“SW”) signal in a predetermined logic state that controls the switching state of multiplexer325. As will be explained later herein, the accumulated Cb amplitude values have different signs when colorstripe encoding is present within a given burst interval, and have the same sign when colorstripe encoding is not present within a given burst interval.

Multiplier320receives the accumulated Cb amplitude value generated by accumulator310, and multiplies the same by a predetermined value to generate a multiplied value. Multiplier320further generates an output signal representative of the multiplied value. According to an exemplary embodiment, the predetermined value utilized by multiplier320is two (i.e., 2). As will be illustrated later herein, this value of 2 enables any error to be cancelled and corrected.

Multiplexer325receives the output signal generated by multiplier320, and also receives an input signal having a value of 0. This input signal to multiplexer325may, for example, be generated by a processor or other device (not shown) of video system100. Multiplexer325is switched in dependence upon the SW signal generated by sign comparator315so as to selectively output either the output signal of multiplier320, or the input signal having a value of 0. According to an exemplary embodiment, multiplexer325outputs the output signal of multiplier320when the SW signal is in one logic state (e.g., logic high), and outputs the input signal having a value of 0 when the SW signal is in the other logic state (e.g., logic low).

Subtractor330receives the accumulated Cb amplitude value generated by accumulator305, and subtracts therefrom the value represented by the output of multiplexer325to thereby generate a burst signal (“Burst Cb”). In this manner, subtractor330subtracts either a value of 0 or the multiplied value of multiplier320from the accumulated Cb amplitude value of accumulator305. As will be explained later herein, subtractor330subtracts the multiplied value of multiplier320from the accumulated Cb amplitude value of accumulator305when colorstripe encoding is present within a given burst interval. Conversely, subtractor330subtracts a value of 0 from the accumulated Cb amplitude value of accumulator305when colorstripe encoding is not present within a given burst interval. The burst signal generated by subtractor330is then normalized (by circuitry not shown inFIG. 3) to generate the output signal of burst accumulator240which represents the average Cb amplitude value for the given burst interval. For example, this average Cb amplitude value may be generated by dividing the value represented by the burst signal by the number of samples taken within the burst interval.

The components of burst accumulator240for processing the baseband Cr signal are substantially identical in structure and function to certain components for processing the baseband Cb signal. In particular, accumulators335and340are substantially identical to accumulators305and310, respectively. Moreover, multiplier345is substantially identical to multiplier320, multiplexer350is substantially identical to multiplexer325, and subtractor355is substantially identical to subtractor330. Accordingly, for clarity of explanation, these identical components will not be described again except where applicable. Note, however, that the components of burst accumulator240for processing the baseband Cr signal do not include a sign comparator since the SW signal generated by sign comparator315is used to control the switching state of multiplexer350.

For a better understanding of the present invention, a more detailed explanation of burst accumulator240will now be provided with reference toFIG. 3. In particular, the following explanation describes an exemplary operation in which burst accumulator240detects colorstripe encoding within a burst interval associated with a horizontal line of video information, and compensates for such encoding in its output signals so as to provide improved chrominance processing in video system100. The following explanation is intended as an example only, and does not limit the present invention in any manner. In the following example, assume: (i) that colorstripe encoding is present in the initial one-fourth of a burst interval, and (ii) that 32 samples are normally taken during a burst interval.

Accumulators305and310receive and sample the baseband Cb signal to thereby generate accumulated Cb amplitude values in accordance with the enabling BG1and BG2signals, respectively. Accordingly, accumulator305generates an accumulated Cb amplitude value for the entire burst interval (or at least most of the burst interval) while accumulator310generates an accumulated Cb amplitude value for the portion of the burst interval where colorstripe encoding is expected to be present (i.e., the initial one-fourth of the burst interval). In this manner, accumulator305takes 32 samples of the baseband Cb signal, while accumulator310takes 8 samples of the baseband Cb signal. Since colorstripe encoding is present in the initial one-fourth of the burst interval, the first 8 samples taken by accumulator305and all 8 samples taken by accumulator310have inverted polarities.

Assuming a normal baseband Cb value of −448, the accumulated Cb amplitude value generated by accumulator305is:
(8)(448)+(24)(−448)=−7,168
Note that without colorstripe encoding, the accumulated Cb amplitude value generated by accumulator305would be:
(32)(−448)=−14,336
The accumulated Cb amplitude value generated by accumulator310is:
(8)(448)=3,584
The accumulated Cb amplitude values generated by accumulators305and310(i.e., −7,168 and 3,584) are provided to sign comparator315which compares the signs of the two values and determines them to be different. As a result of this sign difference, sign comparator315generates the SW signal.

The accumulated Cb amplitude value generated by accumulator310is also provided to multiplier320which multiplies the accumulated Cb amplitude value by 2 to generate an output signal having a value of:
(2)(3,584)=7,168

Multiplexer325receives the output signal generated by multiplier320, and is switched in response to the SW signal generated by sign comparator315so as to pass the output signal of multiplier320to subtractor330. Subtractor330receives the accumulated Cb amplitude value (i.e., −7,168) generated by accumulator305, and subtracts therefrom the value represented by the output of multiplexer325to thereby generate the burst signal (“Burst Cb”) having a value of:
(−7,168)−(7,168)=−14,336
Note that this value of −14,336 is the same value that accumulator305would have generated if colorstripe encoding was not present. The burst signal generated by subtractor330is then normalized (by circuitry not shown inFIG. 3) to generate the output signal of burst accumulator240which represents the average Cb amplitude value for the given burst interval. In particular, the average Cb amplitude value for the burst interval is:
(−14,336)/(32)=−448

The baseband Cr signal is processed in a similar manner to the baseband Cb signal, as described above, to generate a burst signal (“Burst Cr”). This burst signal is likewise normalized (by circuitry not shown inFIG. 3) to generate the output signal of burst accumulator240which represents the average Cr amplitude value for the given burst interval. As previously indicated herein, the baseband Cr signal may normally exhibit a constant amplitude value of 0 during a burst interval when video system100is in a steady-state condition. Accordingly, during a steady-state condition of video system100, the average Cr amplitude value is not particularly susceptible to errors due to the polarity inversion introduced through colorstripe encoding since the inverse of 0 is 0. However, the average Cr amplitude value is not typically 0 during a signal acquisition state, such as following a channel change. Accordingly, when video system100is in a signal acquisition state, the average Cr amplitude value is susceptible to errors due to colorstripe encoding, and such errors are corrected by the Cr signal processing components of burst accumulator240shown inFIG. 3.

Referring toFIG. 4, a flowchart400summarizing exemplary steps for carrying out the present invention is shown. For purposes of example and explanation, the steps ofFIG. 4will be described with reference to chrominance processing arrangement200ofFIG. 3. Note that the steps ofFIG. 4are merely exemplary, and do not limit the present invention in any manner.

InFIG. 4, process flow begins at step401where burst accumulator240receives one or more demodulated chrominance signals, such as the baseband Cb and Cr signals provided from filter230. At step402, burst accumulator240processes the one or more demodulated chrominance signals so as to detect a polarity inversion within a burst interval associated with a horizontal line of video information. As previously indicated herein, a detected polarity inversion indicates that colorstripe encoding is present within the given line. Next, at step403, burst accumulator240generates one or more output signals that compensate for the polarity inversion detected at step402. As previously described herein, burst accumulator240performs such compensation by canceling the errors in its output signals introduced by the polarity inversion. Then, at step404, the one or more output signals from burst accumulator240are used to control chrominance processing. For example, quadrature oscillator250uses the one or more output signals from burst accumulator240to control its oscillation phase, and thereby control the phase of the sinusoidal signals provided to chrominance demodulator220. Moreover, ACC detector and filter260uses the one or more output signals from burst accumulator240to generate and output a control signal that controls the amplitude gain of amplifier210.

As described herein, the present invention advantageously provides artifact-free demodulated chrominance in a video system. The present invention described herein is particularly applicable to various video systems, either with or without display devices. Accordingly, the phrase “video system” as used herein are intended to encompass various types of systems or apparatuses including, but not limited to, television sets or monitors that include a display device, and systems or apparatuses such as a set-top box, VCR, DVD player, video game box, PVR or other video system that may not include a display device.

While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. For example, while a preferred embodiment of the present invention uses a burst accumulator to detect a polarity inversion within a burst interval and generate a compensating output signal, it will be intuitive to those skilled in the art that devices other than a burst accumulator may be used to perform these functions. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.