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TECHNICALLY SPEAKING...

12 ExtroNews 14.3 Fall 2003

Don’t you agree? If you’re a “dyed-in-the-wool”

A/V techie, you are now envisioning those rare

experiences. If you aren’t an A/V techie, you’re

undoubtedly thinking that this author should

“get a life”.

It’s been some time since we’ve talked about

video test signals and their uses. The exciting

launch of the Extron VTG 300 extends the VTG

product heritage and brings along with it support

for audio testing as well. Today, we’re here to

talk test signals. For some, my discourse will be

review. For others, it will be new. If you will now

push the Power On button of your VTG 300,

I’ll get started.

Creating Your Own Video Memories

First, take a look at Table 1 below to see the

application of the 10 unique visual test patterns.

Available pattern types are grouped around

speciﬁc operating formats: computer graphics,

NTSC/PAL television, high deﬁnition television,

or 16:9 widescreen graphics. I’ll start discussion

on all patterns appropriate for computer graphics,

high deﬁnition, and 16:9 widescreen graphics.

Then we’ll look at patterns tailored for NTSC

and PAL.

The Graphics Group

White Field

The white field pattern historically demon-

strated the uniformity of a white raster

generated by a CRT display. Since CRT display

uniformity depends on accurate convergence

of three electron beams (direct view) or three

light beams (projection), the white ﬁeld pattern

will exhibit nonlinear color variations where

beam landing is not accurate. It is routinely

used to measure light fall-off and efficiency of

the optics.

This pattern is still useful for digital

projectors since optical performance is still

an issue. For projectors using reﬂective liquid

crystal technology, it displays the quality of

white uniformity most often called “shading”.

White uniformity is still a challenging

performance characteristic regardless of the

display technology.

On the electrical side, this pattern represents

full video excursion. On a scope, the video level

will be full reference (0.7 volt p-p). This facilitates

a quick check of balance between R, G, and B

outputs with a scope. Comparing one channel

to the other in the invert-and-add mode allows

very accurate evaluation of video level and

channel balance.

Alternating Pixel Pattern

This pattern is a full-ﬁeld alternation of 100%

white and 0% black levels at the primary

operating clock rate (pixel rate) of the selected

graphics line rate. This pattern is commonly

used to evaluate the speed of a graphics source

because the pattern exercises the system at its

by Steve Somers, Vice President of Engineering

VTG 300 Video and Audio Test Signals — As Good As It Gets

here’s something about crisp, bright, clean color bars and the wonderment of a ﬂat multi-

burst response that just makes the hair stand up on my arms. Yet, a chance encounter with

perfect black level and gray scale near extreme white…is as infrequent as a full solar eclipse.

And, ultimately, witnessing a perfect, undistorted scope response of a square wave as it passes

through an audio system…well, that’s about as good as it gets. Test patterns driving systems…

scopes tracing waveforms, one after the other…all is as engineers intended it to be…somehow

establishing the order of all things electronic.

Crosshatch

32 x 24

Crosshatch

32 x 18

SMPTE Bars

EBU Bars

Color Bars

H Pattern

16-Level Split

Grayscale

Multiburst

Alternating

Pixels

White Field

Test

Pattern

Signal

Range

VIDEO

HDTV

16:9 HR

NTSC

480p and

576p only

Except 480p

and 576p

PAL NTSC/PAL

Table 1: Video/Graphics test pattern groups.

1 2 ... 7 8 9 10 11 12 13 14 15 16 17 ... 23 24

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