FULL FIELD RED TEST CHART

TRANSPARENCY

The test chart is designed for measuring the behaviour of the chrominance channel expressed

as the signal-to-noise ratio. The equipement has to be arranged as shown in Fig. 1.

Fig. 1

Conditions of shooting

• The luminance of a transparent test chart, at peak white, shall be 636 cd/m² +/- 5%

   (= 2000lx)

• The white balance shall be set manually or autmatically to 3200K +/- 100 K

• The test chart shall be shot by the camera so that the frame limited by the arrows

  exactly coincides with the edges of the picture displayed on the video monitor in

  underscan mode

• The camera shall be adjusted out of focus

• Gain control shall be set to "0 dB" gain

• Optical filter shall be set to "open position"

The AM chrominance signal-to-noise ratio and the PM chrominance signal-to-noise ratio

shall be measured as follows. The method applies to NTSC and PAL color video signals.

The chrominance signal-to-noise ratio (S/N) is separated into amplitud-modulated (AM)

chrominance S/N ratio (ratio of reference signal level to amplitude-modulated noise

component) and phase-modulated (PM) chrominance S/N ratio (ratio reference signal

level to phase-modulated noise component). The reference signal is the voltage (V_ref) 

of the chrominance signal to 100% amplitude of the non-composite video signal.

Each ratio is defined as follows

AM chrominance S/N = 20 lg (Vref(p-p)) / (AM noise r.m.s.)

PM chrominance S/N = 20 lg (Vref(p-p)) / (PM noise r.m.s.)

where:

V_{ref (p- p)}  = chrominance voltage corresponding to 100% amplitude on non-composite video

                   signal

AM noise r.m.s. = r.m.s. voltage of the amplitude-modulated component of the

                             noise in the chrominance band width.

PM noise r.m.s. = r.m.s. voltage of the phase- modulated component of the

                             noise in the chrominance band width

The AM and PM noise indications shall be isolated from the influence of PM and AM noise,

respectively, by 30dB minimum. The AM detector shall be an averaging detector type that

measures power in the AM sidebands.

Chrominance noise measurement circuit

Fig. 2 shows a typical circuit configuration for the measurement of the chrominance noise.

Fig. 2

The noise measuring apparatus shall contain electronic gatin circuits capable of excluding

horizontal (H) and vertical (V) blanking intervals from the voltmeter. The duty cycle shall be

such as to essentially measure the entire television field. Suitable compensation for the duty

cycle of the gating process shall be incorporated in the apparatus to ensure accuracy.

The changes in the color subcarrier are separated into amplitude and phase components and

are measured. The color burst shall not be employed as reference for the phase detection since

there is no direct relationship to the picture contents due to the frequently used separate

processing of the burst.

The demodulated signals are then band-limited by the high-pass and low-pass filters to

achieve the overall measuring system having cut-off frequencies as indicated below. The

components are converted into r.m.s. voltage by the r.m.s. converter and the value is indicated

with the meter.

The ratio between the noise voltage (V _ms) and the reference (V_ref(p-p)) is expressed in

decibles. The PM detector in the PAL system is designed so that it is capable of detecting

the disturbance components created when the phase is switched to coincide with the PAL phase.

High-pass fc100 Hz, 1 kHz, 10 kHz, 100 kHz

Low-pass fc100 kHz, 500 kHz, 1 MHz