Extron Electronics VTG 400D_400 DVI User Guide - Manual (Page 76)

Appendix, cont’d
VTG 400D/400 DVI • Appendix A-12
each step above 100% is just visible ensures that peak video changes and details
near white are preserved.
Conversely, the shallow ramps near black at the bottom of the pattern show
performance near black. The shallow ramp extends downward below black (0%) by
eight steps to -5.5% and upward to +5.5% in eight steps. Each step represents a
0.685% change. Adjusting brightness (black level) so that each of the steps below
0% is just visible ensures that peak video changes and details in the shadows are
preserved.
The center of the pattern includes a regular 15 step split grayscale for convenience
and serves the same function as the split grayscale pattern described earlier.
12. Ramp
The ramp pattern is commonly used to evaluate display performance
in the area of pixel depth capability. Since the creation of image test
patterns using digital technology, the industry acknowledges that a
minimum pixel depth of 8 bits per pixel (256 levels) is the minimum
pixel depth requirement for perception of continuous tones in colors and grayscale
for each of the primary colors (i.e. red, green, and blue). The VTG utilizes 10-bit
pixel depth for creation of all its test patterns. This provides four times more
resolution for shades of colors or levels of gray than 8-bit systems.
The gradual change in light output across the ramp should appear smooth without
any noise, banding, or other inconsistencies. Displays and processors having less
than 8 bits per pixel per color may exhibit periodic vertical bands along the ramp
pattern, commonly called contouring. The ramp pattern, due to its gradual level
change, can be used to highlight specific points where image processing noise may
become visible.
13. Color Bars (8-color split)
For graphics line rates, this color bar pattern is helpful in verifying
correct cable connections for red, green, and blue signals. It may be
used to facilitate setting of video levels and check for low frequency
crosstalk between the color channels. General uses include
verification of relative color timing, saturation, and level adjustment.
SMPTE Color Bars (with PLUGE pattern)
Designed for NTSC video systems, this pattern was standardized by
the Society of Motion Picture and Television Engineers for proper
alignment of the NTSC color transmission system. This color bar
pattern is used to evaluate NTSC color decoding systems and assist in
proper setup of the color and tint (hue) controls in an NTSC television monitor or
receiver. The PLUGE pattern contained in the lower right section of the pattern is
used to set proper black level as described for the dedicated PLUGE pattern
available from the VTG 400.
The small complimentary color rectangles at the bottom of the larger color bars are
used to facilitate color and tint calibration. In order to properly calibrate the color
and tint controls, some method of suppressing the red and green channels is
necessary so that only the blue content of the color bar signal is in use. This may be
done by viewing the test pattern through a blue filter, by switching to the “blue
only” mode available on some monitors, or by removing the red and green cables
from the display input if the decoding process is being handled in an external video
processor.