A good CRT needs to perform well in all of the tests outlined in the
next section. But to earn the distinction of a Great CRT it
must excel in each of the critical tests below.
Note that all of the test patterns mentioned below are proprietary
DisplayMate test patterns and that most are found only
in the professional DisplayMate Multimedia Editions.
For background information and general guidelines see
How to Test and Evaluate Displays.
1. High Video Bandwidth Index:
The DisplayMate Video Bandwidth Index measures the visibility of
high frequency fine detail in an image.
A value of 100 is perfect and indicates that high and low frequencies,
corresponding to broad and fine detail, are identically reproduced.
Values near 100 are not normally possible because of limitations
in analog electronics and the CRT's finite beam size.
Using one of the recommended Video Boards in the
DisplayMate Best Video Hardware Guide the Index should be in the
85-95 for 1024x768 at 75 Hz
Values lower than the above indicate second-tier performance.
Higher values may indicate over-peaking
in the high frequency compensation for fine image detail.
Values near or greater than 100 indicate substantial over-peaking
and compensation, which is a serious performance flaw.
Perform this test in Green. See item 5, below for White and other colors.
To check for over-peaking and compensation,
see Ringing and Overshoot, item 14, below.
80-90 for 1280x1024 at 75 Hz
75-85 for 1600x1200 at 75 Hz
70-80 for 2048x1536 at 60 Hz
2. Slight Moiré:
With the display's Moiré reduction enabled no more than one test pattern
in DisplayMate's Moiré test suite should show a weak Moiré.
All of the other patterns in the suite should appear Moiré free.
3. Excellent Color Registration:
Mis-registration in the central area of the screen should be less
than 0.1 beam width and less than 0.5 beam width in the corners.
Use DisplayMate's Blinking Color Registration Test patterns.
4. Low Geometric Distortion:
Less than 1.0 mm of distortion anywhere near the edges of the screen.
Any distortion should be smoothly varying with no kinks or bending visible,
so that the distortion is not apparent.
Even when the outer edges are true, there can still be many forms
of interior distortion.
Use any of the DisplayMate Geometry and Distortion test patterns.
For quantitative analysis use the Interactive Screen Distortion
Measurement suite in DisplayMate Professional for DOS.
5. RGB High Frequency Balance:
The Video Bandwidth Index (item 1) for each of the primary Red, Green and Blue
channels should be identical.
If not then there will be a shift in color going from broad
to fine image detail.
An easy way to check this is to view
the Video Bandwidth Index test pattern in White. Adjust the Index
slider so that the high and low frequency blocks are as closely
matched in intensity as possible. There should be no visible
difference in color tinting between the blocks.
6. No Color Tracking Error:
The intensity of the Red, Green and Blue channels should vary identically
with signal level. If that isn't the case then a pure gray-scale will
show color tinting in one or more areas. This often occurs near black at
low intensities and also near peak intensities due to unbalanced saturation
between the RGB channels.
Use the DisplayMate Color Tracking and White-Level Saturation
test patterns. No change in color tint should be visible.
For a more precise determination use the DisplayMate Window Pattern
and a color analyzer.
7. Weak Screen Reflections:
Only very weak internal and external reflections from the screen
should be visible.
This is accomplished with high quality anti-reflection coatings and
The internal reflections within the CRT glass and phosphor layers
reduce the very important local contrast.
Use the DisplayMate Dark Screen, Screen Halos, and Internal Light Scatter
test patterns to search for stray light.
View these patterns in the darkest possible environment.
8. Focus and Sharpness:
CRT image sharpness depends on many factors including
beam size, focus, color registration, and video bandwidth.
Use the DisplayMate Focus Matrix, Resolution Matrix,
Scaled Fonts, Page of Text, and Defocusing, Blooming and Halos test patterns
to evaluate sharpness over the screen.
Sharpness is generally best in the center of the screen
and worst in the corners.
To eliminate the effect of color registration use only one
primary color, typically Green.
9. Accurate Gamma:
The shape of the gray-scale as it increases from black up to peak white is
described in terms of a mathematical power-law function with an index called
Gamma. The Gamma for most CRT displays is in the range of 2.2 to 2.5.
A Gamma of 2.2 is the standard for NTSC TVs and 2.8 for PAL TVs.
The Gamma affects the accuracy of the gray-scale and color mixtures
so specific values are necessary when high accuracy is required.
Use the DisplayMate Gamma Correction Measurement test pattern to
accurately measure the Gamma interactively on-screen.
This pattern requires that the Video Bandwidth Index (item 1) be set first.
For a more detailed analysis, use the DisplayMate Window Pattern
and a photometer to measure the entire brightness curve.
Because of APL Shift, see item 16 below, this will vary with the
size of the Window Pattern. Use both 5% and 100% sizes.
Plot the measurements on log-log graph paper and make sure that
you obtain a perfectly straight line with a slope of the desired Gamma value.
Testing and Evaluating CRTs
To thoroughly evaluate a CRT display you should examine it using all of the
DisplayMate test patterns.
Refer to the Test Information screen for each test pattern for
details on the purpose of the pattern and what to look for in the image.
In addition to the test patterns discussed in What Makes a Great CRT above a
number of important proprietary DisplayMate patterns are also featured below:
10. Screen Uniformity and Color Purity:
The screen is generally brightest at the center, with lower
intensities in the corners. On a high quality display this
will not be apparent visually. Use one of the DisplayMate
Screen Uniformity test patterns to check the uniformity for
both bright and dim intensities using a White screen color.
Use a photometer if measurements are required.
Cycle through Red, Green and Blue to look for intensity and color variations
that indicate Color Purity and Beam Landing errors.
Note that some displays include controls to at least
partially correct these problems.
11. Really Black Black-Level:
The black-level for a properly adjusted CRT should appear to be
true black except in very dark environments. Verify this visually
using one of the DisplayMate Black-Level Adjustment test patterns.
A sensitive photometer may be used to measure the residual brightness
of the black-level.
12. High Peak Brightness:
You can visually compare the relative brightness between two
CRT displays but it's best to use a photometer to measure this value.
Before measuring peak brightness you need to properly adjust the
Brightness and Contrast controls. The Contrast control should be
set as high as possible without producing blooming, halos or
screen regulation problems, see items 8 and 15.
Because of screen regulation the brightness will depend on the area
of the screen being illuminated.
Use the DisplayMate Window Pattern.
Areas of 5% and 15% are frequently used.
Compare those values to that for a 100% area.
The closer the measured values the better.
DisplayMate also includes the ANSI brightness test pattern with target
positions for measuring ANSI standard brightness.
13. High Contrast:
Display contrast is the ratio between the peak white intensity
and the black-level intensity.
The higher the better because visibility and readability depend on contrast.
While contrast can be compared or estimated visually it's best to measure
it with a photometer.
Unfortunately the peak white-level and black-level can be specified
in many different ways. As mentioned in item 12 above the peak
white-level depends on the Window area used: 5%, 15% or 100%.
It will be highest for the 5% window and lowest for the 100% window.
It also depends on the settings of the Brightness and Contrast controls.
The black-level depends on the room lighting and will be lower
in a pitch black room. It will also be lower if the entire screen
is set to black. If portions of the screen are illuminated the
intensity of the black areas of the screen will increase due
to internal reflections within the CRT.
There are two common measures of contrast: full-field sequential and ANSI.
The ANSI method uses a carefully defined procedure and a 4x3 checkerboard
pattern that partially takes into account screen regulation and
internal reflections. The sequential method is non-standard but
generally uses a 5% window with the Contrast control set at maximum
regardless of blooming and regulation effects followed by a
completely black screen in a pitch black room. This is the
contrast that manufacturers generally publish. It can be a
factor of 2 or more greater than the ANSI value.
The DisplayMate Multimedia Edition includes test patterns to measure
the contrast both ways.
14. No Ringing and Overshoot:
Poor signal processing or over-peaking will produce Ringing and
Overshoot, which is visible as extra light or dark edges or waves
around fine image detail.
Use the DisplayMate Ringing and Overshoot and Sharpness with Contrast
test patterns. The Reverse Video Contrast and Color Streaking patterns are
also excellent. No Ringing or Overshoot should be visible.
15. Good Screen Regulation:
The high voltage circuits in the CRT are affected by the beam
current needed to produce the image brightness.
On most CRTs the image expands in areas of the screen that are
bright and contracts in areas that are dim. The entire screen may
be affected or just portions of it. Use the several DisplayMate
Screen Regulation test patterns to check for these effects.
On high quality displays no effect will be visible.
You can measure the peak deflections with a cloth tape measure.
16. No APL Shift:
The brightness in one part of the screen may be affected by the
brightness in another part of the screen and by the average brightness
over the entire screen.
This is due to another form of regulation.
It is evaluated in
terms of the Average Picture Level or APL of the image.
Use the DisplayMate APL Black and Gray-Level Shift test patterns
to visually evaluate this effect.
17. Weak Streaking:
Streaking is visible as positive or negative shadows that trail
image detail on the right.
When there is severe streaking it will wrap around and appear to
precede the image detail.
Streaking is most apparent in high contrast situations.
Use any of the DisplayMate Streaking test patterns to look for this effect.
18. White-Point Color Temperature:
The color temperature of the screen is generally set at the factory
to 9300° for most computer monitors and televisions.
This corresponds reasonably well to the color of "Bright White" paper in
Many monitors include end user presets for other values,
typically 5000° and 6500°, which are
useful for graphic arts and photography respectively.
Use a color analyzer to verify the accuracy of the settings.
Note that measuring correlated color temperature alone is
not sufficient to determine the white-point. The actual Chromaticity
Coordinates must be measured and compared.