1、 Rec. ITU-R BT.1439-1 1 RECOMMENDATION ITU-R BT.1439-1 Measurement methods applicable in the analogue television studio and the overall analogue television system (Question ITU-R 86/6) (2000-2006) Scope This Recommendation defines measurement methods and test signals used in analogue television syst
2、ems programme verification. The ITU Radiocommunication Assembly, considering a) that proper operation of analogue television studios and of other analogue parts of the television chain requires accurate monitoring of the correct performance of individual sections of the overall system; b) that such
3、monitoring is best performed on analogue video equipment using appropriate analogue video test signals; c) that the methods to measure the correct performance of sections of the analogue television chain, based on the use of analogue video test signals, should desirably be standardized; d) that ITU-
4、T Recommendation J.61 recommends nomenclature and measuring methods for analogue video test signals at baseband, for use on analogue video transmission links; e) that most of the test signals and measuring methods recommended in ITU-T Recommendation J.61 are also applicable and are indeed already wi
5、dely applied to the measurement of the performance of analogue video production chains; f) that, whenever possible, the same measurement signals and measurement methods should desirably be applied throughout the analogue television chain, including both the production sections and the transmission s
6、ections, recommends 1 that the definitions of video parameters at baseband, as given in Part 1 of this Recommendation, should be applied where appropriate to measurement of video baseband parameters in analogue television studios and the overall analogue television system; 2 that the measuring metho
7、ds and test signals, as given in Part 2 and Annex 1 to this Recommendation, should be used where appropriate to perform measurements at video baseband in analogue television studios and the overall analogue television system; 3 that the design for filters, as given in Annex 2 to this Recommendation,
8、 for application to specific measuring methods should be used where appropriate, when performing similar measurements at video baseband in analogue television studios and the overall analogue television system; 2 Rec. ITU-R BT.1439-1 4 that, when it is desired to perform on-line measurements of perf
9、ormance at video baseband in the overall analogue television system in the presence of programme signals, the measurement methods and insertion test signals given in Annex 3 to this Recommendation should be applied where appropriate; 5 that the K-rating methods of assessment given in Annex 4 to this
10、 Recommendation for the measurement of short-term waveform distortion may also usefully be applied to measurements in the analogue television studio and the overall analogue television system, if desired. NOTE 1 Measurement methods for digital television equipment with analogue input and output are
11、defined in Recommendation ITU-R BT.1204. Measuring methods and test signals are the same as in ITU-T Recommendation J.61. PART 1 Definitions of video parameters 1 Waveform terminology The following terms concerning the components and values of a composite colour video signal are illustrated in Fig.
12、1: A : the non-useful d.c. component B : the useful d.c. component, integrated over a complete frame period C : the picture d.c. component, integrated over the active line period, TuD : the instantaneous value of the luminance component E : the instantaneous signal value with respect to the bottom o
13、f the synchronizing pulses F : the peak signal amplitude (positive or negative with respect to blanking level) G : the peak amplitudes of chrominance components H: the peak-to-peak signal amplitude J : the difference between black level and blanking level (set-up) K : the peak-to-peak amplitude of t
14、he colour burst L : the nominal value of the luminance component M : the peak-to-peak amplitude of a monochrome composite video signal (M = L + S) S : the amplitude of the synchronizing pulses Tsy: duration of line synchronizing pulse Tlb: duration of line blanking period Tu: duration of active line
15、 period Tb: duration of breezeway Tfp: duration of front porch Tbp: duration of back porch. The amplitudes L, S and M are used as reference amplitudes for the video signal. The amplitudes defined by B, C, D, E, F, G, H and J above, may be expressed as percentages of the value L. Rec. ITU-R BT.1439-1
16、 3 Average picture level (APL) is the mean value of C over a complete frame period (excluding blanking periods) expressed as a percentage of L. 2 Definitions of signal parameters 2.1 Nominal impedance, Z0The input and output impedance, Z0of each device should be specified, as either unbalanced or ba
17、lanced with respect to earth. 2.2 Return loss The return loss, relative to Z0, of an impedance Z is, in the frequency domain: dB)()(log2000fZZfZZ+In the time domain, it is expressed by the symbolic formula: dBlog2021AA4 Rec. ITU-R BT.1439-1 where A1is the peak-to-peak amplitude of the incident signa
18、l and A2is the peak-to-peak amplitude of the reflected signal. Numerically, the result is the same as that obtained by the frequency domain method if the return loss is independent of frequency. 2.3 Polarity and d.c. component The polarity of the signal should be positive, that is to say, such that
19、black-to-white transitions are positive-going. The useful d.c. component, B in Fig. 1, which is related to the average luminance of the picture, may or may not be contained in the signal and need not be transmitted or delivered at the output. A non-useful d.c. component, A in Fig. 1, may be present
20、in the signal (for example, due to d.c. supplies). Limits for this component need to be specified for the terminated and unterminated conditions. 2.4 Nominal signal amplitude The nominal signal amplitude is the peak-to-peak amplitude of the monochrome video signal that includes the synchronizing sig
21、nal and luminance signal component set to peak-white (M in Fig. 1). 3 Definitions of performance parameters The definitions in 3.2 and the subsequent sub-sections assume that the equipment has nominal insertion gain as defined in 3.1. 3.1 Insertion gain Insertion gain is defined as the ratio, expres
22、sed in decibels, of the peak-to-peak amplitude of a specified test signal at the receiving end to the nominal amplitude of that signal at the sending end, the peak-to-peak amplitude being defined as the difference between the amplitudes measured at defined points of the signal used. 3.2 Noise 3.2.1
23、Continuous random noise The signal-to-noise ratio for continuous random noise is defined as the ratio, expressed in decibels, of the nominal amplitude of the luminance signal, L in Fig. 1, to the r.m.s. amplitude of the noise measured after band limiting. A signal-to-weighted-noise ratio is defined
24、as a ratio, expressed in decibels, of the nominal amplitude of the luminance signal, L in Fig. 1, to the r.m.s. amplitude of the noise measured after band limiting and weighting with a specified network. The measurement should be made with an instrument having, in terms of power, a defined time cons
25、tant or integrating time. 3.2.2 Low-frequency noise The signal-to-noise ratio for low-frequency noise is defined as the ratio, expressed in decibels, of the nominal amplitude of the luminance signal, L, in Fig. 1, to the peak-to-peak amplitude of the noise after band limiting to include only the spe
26、ctrum 500 Hz to 10 kHz. 3.2.3 Periodic noise The signal-to-noise ratio for periodic noise is defined as the ratio, expressed in decibels, of the nominal amplitude of the luminance signal, L in Fig. 1, to the peak-to-peak amplitude of the noise. Rec. ITU-R BT.1439-1 5 Different values are specified f
27、or noise at a single frequency between 1 kHz and the upper limit of the video frequency band and for power-supply hum including lower-order harmonics. 3.2.4 Impulsive noise The signal-to-noise ratio for impulsive noise is defined as the ratio, expressed in decibels, of the nominal amplitude of the l
28、uminance signal, L in Fig. 1, to the peak-to-peak amplitude of the impulsive noise. 3.3 Non-linear distortion In television equipment the transmission may not be completely linear. The extent of the non-linear distortion which is produced will depend primarily on: the APL, as defined in 1; the insta
29、ntaneous value of the luminance component (D in Fig. 1); the amplitude of the chrominance signal (G in Fig. 1). There would, in general, be little purpose in defining completely the non-linear characteristics of a television equipment chain. It is necessary, therefore, to limit the number of measure
30、d quantities by restricting them to those which are recognized as being directly correlated with picture quality. Additionally, the test conditions should be restricted by introducing a systematic classification in the definition of the quantities to be measured. The nature of the video signal is su
31、ch that, in terms of picture quality, the impairment due to the effect of circuit non-linearity on the synchronizing signal is different from the effect of circuit non-linearity on the picture signal. Furthermore, the non-linearity may affect the luminance and chrominance signals individually or cau
32、se interaction between them. This leads to the following system of classification of non-linear distortions: 6 Rec. ITU-R BT.1439-1 The above classification applies for steady-state conditions during a time span which is long in relation to the field period. In this case, the concept of average pict
33、ure level has a precise significance. If these conditions are not fulfilled, for example, if a sudden change in the APL is introduced, additional non-linear effects may be produced, the extent of which will depend on the long-time transient response of the circuit. Additional non-linearity may also
34、occur if a sudden change in signal amplitude occurs. 3.3.1 Picture signal 3.3.1.1 Luminance signal For a particular value of APL, the non-linear distortion of the luminance signal is defined as the departure from proportionality between the amplitude of a small step function at the input to the circ
35、uit and the corresponding amplitude at the output, as the initial level of the step is shifted from blanking level to white level. 3.3.1.2 Chrominance signal Gain For fixed values of luminance signal amplitude and APL, the non-linear gain distortion of the chrominance signal is defined as the depart
36、ure from proportionality between the amplitude of the chrominance sub-carrier at the input to the circuit and the corresponding amplitude at the output, as the amplitude of the sub-carrier is varied from a specified minimum to a maximum value. Phase For fixed values of luminance signal amplitude and
37、 APL, the non-linear phase distortion of the chrominance signal is defined as the variation in the phase of the chrominance sub-carrier at the output, as the amplitude of the sub-carrier is varied from a specified minimum to a maximum value. 3.3.1.3 Intermodulation from the luminance signal into the
38、 chrominance signal Differential gain If a constant small amplitude of chrominance sub-carrier, superimposed on a luminance signal, is applied to the input of the circuit, the differential gain is defined as the change in the amplitude of the sub-carrier at the output as the luminance varies from bl
39、anking level to white level, the APL being maintained at a particular value. Differential phase If a constant small amplitude of chrominance sub-carrier without phase modulation, superimposed on a luminance signal, is applied to the input of the circuit, the differential phase is defined as the chan
40、ge in the phase of the sub-carrier at the output as the luminance varies from blanking level to white level, the APL being maintained at a particular value. 3.3.1.4 Intermodulation from the chrominance signal into the luminance signal If a luminance signal of constant amplitude is applied to the inp
41、ut of a circuit, the intermodulation is defined as the variation of the amplitude of the luminance signal at the output resulting from the superimposition on the input signal of a chrominance signal of specified amplitude, the APL being maintained at a particular value. Rec. ITU-R BT.1439-1 7 3.3.2
42、Synchronizing signal 3.3.2.1 Steady-state distortion If a video signal of specified APL and containing synchronizing pulses of nominal amplitude (S in Fig. 1) is applied to the input of the circuit, the steady state non-linear distortion is defined as the departure from nominal of the mid-point ampl
43、itude of the synchronizing pulses at the output. 3.3.2.2 Transient distortion If the APL of the video signal is stepped from a low value to a high value, or from a high value to a low value, the transient non-linear distortion is defined as the maximum instantaneous departure from the nominal value
44、of the mid-point amplitude of the synchronizing pulses at the output. 3.4 Linear distortion Linear distortions are those which can be caused by linear equipment. Such distortions do not depend on the APL, or the amplitude, or the position of the test signals. In the case of equipment which is affect
45、ed by a small amount of non-linearity, measurements can still be carried out. However, as the results can be somewhat affected by the APL and the amplitude and position of the test signals, it is good practice, when presenting the results, to specify the measurement conditions. Linear distortions ca
46、n be measured either in the time domain or in the frequency domain. The quantities which can be measured in the two domains may be classified as shown below. 3.4.1 Waveform distortion of the luminance signal The distortion of the video waveform due to a television circuit will in general be represen
47、ted by a continuous function in the time domain. 8 Rec. ITU-R BT.1439-1 In practice, however, the form of the video signal and the effects on a displayed picture are such that the resulting impairments may be classified by considering four different time-scales which are comparable to the durations
48、of many fields (long-time waveform distortion), one field (field-time waveform distortion), one line (line-time waveform distortion), and one picture element (short-time waveform distortion). In considering each of these time-scales, therefore, impairments appropriate to the other three are excluded
49、 by the measurement method. 3.4.1.1 Long-time waveform distortion If a video test signal, simulating a sudden change from a low APL to a high one or a high average picture level to a low one, is applied to the input of a circuit, long-time waveform distortion is present if the blanking level of the output signal does not accurately follow that of the input. This failure may be either in exponential form or, more frequently, in the form of damped very low-frequency oscillations. 3.4.1.2 Field-time waveform distortion If a square-wave signal with a period of the sa
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