Extron Electronics VTG 400D_400 DVI User Guide - Manual (Page 80)

Appendix, cont’d
VTG 400D/400 DVI • Appendix A-16
22. Alternating Pixels (1 on, 1 off)
For computer graphics displays, alternating pixels represent the
highest frequency operation at a given line rate, or resolution. These
one-On, one-Off transitions tax the speed of a graphics system and the
display’s performance as well. Use this pattern to assess the high
frequency performance of the display or a graphics system in total. It may also be
used to align or evaluate pixel timing and phase on fixed pixel displays. As a
source for EMI testing, the alternating pixel pattern represents a worst case scenario
for products that may radiate energy in relation to FCC regulations. Typically, an
oscilloscope is used to measure the true performance of the display system using
this pattern.
Frequency Sweep
Within the NTSC or PAL environment, the frequency sweep pattern
provides a sine wave sweep from near DC to the specified system
bandwidth for the affected broadcast standard. This pattern is used to
evaluate system bandwidth performance and is also used to evaluate
color decoder performance in the region of the chroma subcarrier frequency.
The sweep limit for NTSC is 4.2 MHz and the sweep limit for PAL is
5 MHz. While some visual information can be derived from viewing this pattern on
a display, bandwidth evaluation is most accurately accomplished using an
oscilloscope or waveform monitor.
23. Graphics Multiburst
The graphics multiburst provides groups of digital bursts consisting
of 1/1 (meaning one-On, one-Off) alternating pixels at screen center
flanked by 2/2 alternations, then 4/4 alternations,
8/8 alternations, and a white reference. Perception of grayscale
should remain consistent throughout; otherwise, frequency response differences
will cause color shifts, particularly in the 1/1 burst as compared to the other bursts.
Utilizing an oscilloscope, this pattern may be used to evaluate high frequency
versus low frequency performance of a graphics system. The border area between
bursts is 50% gray. Anomalies of high frequency performance resulting in severe
attenuation of the center burst of 1/1 pixels blend into the middle gray border. In
addition, color shifts are most easily identified against the low frequency nature of
the middle gray level.
Multiburst
The television multiburst is intended to provide rapid evaluation of
system bandwidth over the television channel using a waveform
monitor or oscilloscope. A full bandwidth system reproduces the
multiburst with all bursts having equal amplitude from low
frequency to high frequency. Visually, the pattern may be used to see the relative
quality or effect on bandwidth of the color decoder system and luminance channel.
Each version of the multiburst includes one burst at the system subcarrier
frequency so that luminance channel attenuation due to the quality of the color
decoding system may be observed. Each burst is symmetrical about a 50% (middle
gray) pedestal. Following are the basic specifications for the two multiburst formats
in the VTG 400:
NTSC – White reference bar followed by 0.5, 1, 2, 3, 3.58, and 4.2 MHz bursts
PAL – White reference bar followed by 0.5, 1, 2, 4, 4.43, and 5 MHz bursts.