1. Black-level (Brightness) Calibration
Correct black-level calibration
is critical to achieving a picture with full contrast and subtle
details in dark shadow regions. Black-level is calibrated by adjusting
a display's Brightness control (funny name for a black-level control
isn't it?) using a PLUGE (Picture Line-Up Generator Equipment) pattern.
The HDG-3000 provides a variety of PLUGE patterns to make the most
accurate black-level adjustment possible.
HDTV standards specify that black corresponds to a video signal level
of 0 volts (0-IRE). The display's black-level circuits must be adjusted
to produce minimum light output for a 0-IRE input signal. If the
Brightness control is set too high, the display will not be able to
produce black at all. The darkest areas of the picture will only be
dark-gray and the picture will appear washed-out, lacking in vivid
contrast.
If the display's Brightness control is set too low, portions of the
picture that should be dark-gray will be produced as black, and
everything darker in the picture will also appear as black. In other
words, several levels of dark gray in the picture will be crushed into
black and the picture will look overly harsh; lacking in dark shadow
details.
0% APL PLUGE
One measure of display quality is
how well the black-level remains fixed as the average picture
(brightness) level (APL) of the incoming video changes. Only
fixed-pixel and the finest CRT-based displays maintain a constant
black-level with large changes in APL. In the majority of CRT-based
displays the black-level adjustment must be a compromise over a range
of APLs. The HDG-3000 provides PLUGE patterns with 0%, 25% and 50% APL
to make the best setting.
Properly calibrated CRT-based displays should be able to produce fully
black picture areas; i.e. a complete absence of light output. But
fixed-pixel display technologies like LCD (Liquid Crystal Display) and
DLP (Digital Light Processing) projectors have not been able to produce
total black. It is even more important that the black-level in those
display devices be accurately adjusted to minimize light output for
black video signals.
HDG-3000 Black-level Adjustment Patterns:
25% APL PLUGE
The HDG-3000 has three dedicated
PLUGE patterns for adjusting black-level. Each pattern is divided into
two-halves. The left half of the pattern contains two vertical stripes
against a 0 IRE (black) background. The stripe on the left is at a
video signal level of -4 IRE. This is below (darker than) black and
should not be visible after the display is properly adjusted. The
stripe on the right is at a video signal level of +4 IRE. This is
slightly brighter than black and should be visible after the display's
black-level is correctly adjusted.
50% APL PLUGE
The right side of each PLUGE
pattern is at a different brightness level. The right side of one PLUGE
pattern is at 0 IRE, making the entire background of the frame 0 IRE.
This is a 0% APL PLUGE pattern. The right side of another PLUGE pattern
is at 50 IRE, which creates a 25% APL pattern. The 50% APL PLUGE
pattern has a right-side background of 100 IRE (peak white).
Black-level Calibration Procedure:
Black-level should be adjusted at
the beginning of a complete display calibration. It must also be
monitored and re-adjusted during the display calibration process. The
Black-level adjustment often interacts with the Contrast adjustment and
will change during the Color Temperature and Grayscale Tracking
adjustments. The HDG-3000 provides unique calibration patterns to
monitor and re-adjust black-level while making those adjustments.
Adjust the Brightness (or Black-level) control of the display until the
below-black stripe can not be seen and the above-black stripe is
visible on each of the three APL PLUGE patterns. If a satisfactory
setting can not be found that works on all three PLUGE patterns, then
adjust using the 25% APL PLUGE pattern as the best compromise.
2. Contrast (Peak-White) Calibration
The Contrast control adjusts the
gain of the video amplifier, which determines the peak-white brightness
level. In many products the Contrast control and Brightness
(black-level) controls interact and must be adjusted interactively.
There is no absolute brightness level that is correct for a video
display, but 30 fL (foot-Lamberts) is considered an acceptable level
for a direct-view display in a dimly-lit room. In a brightly lit room
50 fL or more may be necessary. In a totally dark front-projection
theater 12 fL is the SMPTE digital projection standard, but 10 fL is a
more realistic target for CRT front projectors.
As picture brightness is increased in CRT-based displays several
performance tradeoffs occur. In many direct-view and rear-projection
CRT displays the high-voltage power supplies are too weak to maintain a
constant CRT anode voltage with the large changes in CRT beam current
that occur as a picture changes from very dark to very bright. The CRT
anode voltage may temporarily drop in bright areas of the picture. A
drop in anode voltage causes the picture to expand in bright areas.
Short-term high-voltage stability refers to picture behavior within a
frame. For instance, a bright white rectangle, in an otherwise dark
picture, may widen across the top because the high-voltage dips from
the sudden increase in beam current. The sides of the rectangle return
to their normal width as the high-voltage stabilizes and returns to its
normal voltage. This produces a trapezoidal shape with the top of
the rectangle being wider than the bottom. The higher the contrast
setting, the brighter the white areas, and therefore the more likely
and apparent the short-term stability problems.
Long-term stability problems occur between frames when the picture
suddenly changes from high to low APL, or visa-versa. The entire
picture may appear to momentarily expand or contract before returning
to normal size. In extreme cases the picture size may even oscillate
briefly. An excellent example of this problem can be found in pictures
that depict lightning storms. The entire picture may pulse in size as
bright lightning bolts suddenly and dramatically raise the APL of the
picture.
Another problem that occurs in CRT displays at high Contrast settings
is a loss of picture resolution. The CRT spot size increases with
increasing beam current because of space-charge effects in the electron
beam. The electrons repel each other, which causes the beam to
increasingly spread apart as the beam current is increased. This is
particularly a problem for HDTV displays where CRT spot size is a
limiting factor in picture resolution.
For these reasons a brighter picture is not necessarily a better
picture.
Fixed-pixel projectors use a lamp with a fixed light level and picture
brightness is varied on a pixel basis by changing the transmissive
(LCD) or reflective (LCoS or DLP) property of each pixel. But the
maximum brightness level is limited by the lamp. If the Contrast level
is set too high the brightness will clip below the 100 IRE (peak-white)
level of the incoming signal. The picture will be harsh with excessive
contrast because brightness differences will not be visible in the
brightest areas.
CRT-based displays can produce small regions of peak-white brighter
than a full-screen of peak-white because of limited available beam
current. The difference between the peak brightness levels in small
regions and full-fields may be 4:1 or more. Since video, unlike
computer graphics, is largely composed of dynamically changing areas of
peak brightness, a small area measurement of peak-white is more
representative of the apparent picture brightness than is a full screen
measurement. Most fixed-pixel projection systems produce the same
brightness in full fields as small areas because they have fixed
brightness sources provided by projection lamps.
HDG-3000 Contrast Adjustment Patterns:
The HDG-3000 has several patterns
that can be used together to determine the best operating point for the
Contrast control. These include the 100 IRE Grayscale Window with 98
IRE PLUGE, the 50/100 IRE Split Window, the B/W Multi-burst, the Dual
Needle Pulse, and the Overscan patterns. The 50% APL PLUGE pattern can
also be used to ensure that the peak white level is not clipped below
100 IRE on fixed-pixel displays. The 100 IRE Gray Field can be used to
measure the full-field brightness compared to the peak brightness using
the 100 IRE Window pattern.
Contrast Calibration Procedure:
100 IRE Grayscale Window
with 98/100 IRE Stripes
The Contrast control can be
initially set to the desired target level by using a Color Analyzer to
measure the brightness of the white rectangle in the 100 IRE Grayscale
Window pattern. The black-level can be re-checked using the PLUGE
stripes on the left side of that pattern. Two 100 IRE window patterns
are provided. One pattern includes a peak-white PLUGE pattern to the
right of the window that consists of two adjacent vertical stripes at
98 IRE and 100 IRE. If those stripes appear as only a single bright
stripe then the Contrast control is too high and the peak-white level
is clipping below 98 IRE. The 50% APL PLUGE pattern also has a 98 IRE
stripe in the middle of the 100 IRE right side to check for peak-white
clipping. After ensuring that the black-level and 100 IRE white levels
are simultaneously correct check for any of the undesirable side
effects discussed below.
Luma Multiburst
Use the Multiburst pattern to
check CRT-based displays for a loss of resolution at the desired
Contrast level. If the upper bands of the Multiburst pattern become
significantly more distinct at a lower Contrast level, then a lower
brightness level may be warranted.
50/100 Window
If the Contrast control is turned
up too high a CRT spot may bloom, or expand excessively. Use the 50/100
IRE Window pattern to check for spot blooming. If the 100 IRE rectangle
is wider than the 50 IRE rectangle below it, then spot blooming is the
likely cause. Reduce the Contrast control until the rectangles are the
same width. Spot blooming can damage CRTs.
Dual Needle Pulse
Short-term high-voltage stability
problems may be evident on the 100 IRE Grayscale Window pattern. Look
for trapezoidal distortion of the white rectangle. The Dual Needle
Pulse pattern is a more sensitive indicator of short-term stability
problems. The upper half of the pattern is black with a narrow white
vertical line on both sides. The bottom half of the pattern is
reversed. As a CRT beam moves from the top half of the frame to the 100
IRE bottom half of the frame, a large increase in CRT beam current is
suddenly required. The thin black lines in the bottom half of the frame
will bend outward if the high-voltage drops and in most cases will
return to their normal position before the bottom of the frame as the
high-voltage supply recovers. The amount of line deflection and the
length of time it takes the line to return to normal are measures of
the high-voltage performance. In extreme cases the line may wiggle in
an "S" pattern as the supply attempts to recover. In some products,
with excellent high voltage supplies, the line may show minimal or no
short-term stability effects.
Overscan Bounce Test
The Overscan Bounce pattern can
be used to observe long-term high-voltage stability. The Overscan
Bounce pattern changes repeatedly from a low to high APL. As the
picture APL changes the picture size may momentarily expand and
contract. The amount of change can be measured by observing the
percentage shift in overscan as the high-voltage supply settles. Each
of the lines on the borders of the Overscan Bounce pattern represents a
1% change in size.
If high-voltage stability problems appear excessive it may be desirable
to reduce the Contrast control setting and settle for somewhat less
picture brightness.
3. Geometry Calibration
Geometry calibration is the
process of adjusting the display for the correct picture size, while
ensuring that horizontal and vertical lines in the picture remain
straight and parallel to the edges of the picture and evenly spaced
from one another when using an appropriate calibration pattern.
CRT-based displays may have an array of adjustments for this purpose
including horizontal and vertical position, size, linearity, tilt, bow,
keystone, pincushion and others. Many CRT projectors permit the green
CRT to be turned on by itself to adjust geometry and then the remaining
red and blue CRTs are adjusted later for the best convergence.
HDG-3000 Geometry Adjustment
Patterns:
Inverse 16:9 Crosshatch
The HDG-3000 includes a 16:9
Crosshatch with vertical and horizontal white lines against a black
background. There is also an Inverse 16:9 Crosshatch pattern with
vertical and horizontal black lines against a gray background. The 16 x
9 grid pattern produces square cells for easy adjustment or measurement
of horizontal and vertical linearity. The pattern is also marked with
single-pixel wide guide lines that are approximately 3% from the edges
of the display (2.8% from the top and bottom and 3.1% from the sides).
These lines can be used to identify the outer cells of the Crosshatch
pattern, and as a rough guide of acceptable overscan. Additional
Overscan and Inverse Overscan patterns marked in 1% increments are also
included for more exact setting or measurement of overscan.
Geometry Adjustment Procedure:
Use the available adjustment
controls to fit the 16:9 Crosshatch calibration pattern to the display
screen size and to optimize the straightness and spacing of the grid
pattern lines. Many CRT-based direct-view and rear-projection TVs will
work best when adjusted for about 3% overscan using the 16:9 pattern
guidelines. This allows for some change in picture size with changes in
APL, and also allows for some variation in geometry at the edges of the
picture so that no portion of the screen is without picture coverage.
In some cases more overscan may be required to cover these variations.
It may be possible to adjust high-performance front projectors for
satisfactory performance with less overscan. Use the Overscan patterns
to adjust for specific values. The Overscan pattern also has narrow
crossed lines in each corner that are useful for adjusting geometry in
those difficult locations.
4. Convergence Calibration
Convergence calibration is the
process of aligning the separate red, green and blue CRT beams in
direct-view monitors, or the projected red, green and blue images from
separate CRTs in projection systems, so that they precisely overlap
everywhere in the picture. This is particularly crucial in HDTV
displays in order to maximize resolution and avoid color fringing on
fine lines or edges in the picture. It is normally not necessary to
adjust convergence in fixed-pixel projection devices such as LCD and
DLP projectors because their convergence is mechanical in nature and
should have been permanently adjusted at the factory.
HDG-3000 Convergence Adjustment Patterns:
The 16:9 Crosshatch pattern is the
ideal pattern for adjusting convergence. Each of the three primary
colors should overlap the others without color fringing. With all three
colors turned on the grid pattern should be completely white against
the black background.
Convergence Adjustment Procedure:
Different displays provide a wide
range of electronically adjustable convergence controls. In many
projectors these controls duplicate the function of the geometry
adjustment controls, but are individually adjustable for each red,
green and blue primary color. It is good practice to only adjust green
when doing the geometry adjustment. Then turn off the blue CRT beam
(this function is provided in most display calibration menus) and
adjust the convergence of the red CRT beam to match the green beam
using the red convergence controls. It is then easiest to adjust the
blue CRT beam with only the red and blue beams turned on. Finally turn
on all three beams to verify the convergence adjustments.
5. Color Temperature and Grayscale Calibration
Accurate color depends on
calibrating the display for the proper grayscale color temperature of
6500 degrees Kelvin, which is called D65 or D6500. The color
temperature must remain constant over the entire range of the grayscale
from near black to peak-white (100 IRE). It is somewhat ironic that
accurate color is dependent on accurate shades of gray. If the color
temperature of gray is too high, the picture will have a blue tint. If
the color temperature is too low, the picture will have a red tint. If
the color temperature varies from dark to bright the color tint will
also vary throughout the picture. An electronic instrument called a
Color Analyzer is required to measure the color temperature over the
range of grayscale values from about 10 IRE to 100 IRE to ensure it is
accurate and remains constant.
Direct-view CRT monitors and fixed-pixel projectors tend to have the
best grayscale tracking behavior when properly calibrated. The color
temperature can usually be adjusted to remain within a few hundred
degrees Kelvin of D65 over the entire grayscale range. CRT projectors
tend to have a wider variation in color temperature even with best
possible calibration. A total variation of about 1000 degrees Kelvin is
not uncommon. CRT projectors tend to become more red at brightness
levels above 75 IRE because the beam current of the blue CRT is
stressed the most.
Display products provide two (red and blue) or three (red, blue, and
green) controls to adjust the color temperature at the dark end of the
grayscale. These are usually called the Bias or Cutoff controls and
they adjust the offset level of the appropriate video amplifiers. They
have the largest effect at the darker end of the grayscale between 10
and 50 IRE. Two (red, blue) or three (red, blue, green) Gain or Drive
controls are provided to adjust the gain of the video amplifiers. They
affect the color temperature over the entire grayscale so the Bias and
Gain controls interact over the grayscale range. The Bias controls also
directly affect the black-Level, which must be readjusted as the Bias
controls are adjusted. The Gain controls affect the 100 IRE brightness,
so the Contrast control will also have to be re-adjusted as the Gain
controls are changed (particularly the green gain).
HDG-3000 Grayscale Calibration
Patterns:
75 IRE Grayscale
The HDG-3000 includes Grayscale
Window patterns that consist of a gray rectangle at 25, 50, 75 and 100
IRE against a black background. These four values are convenient to use
for adjusting the grayscale color-temperature controls (see below for
other levels in 10 IRE increments). As these controls are adjusted the
black level may shift. The left side of each Grayscale Window pattern
has PLUGE stripes so that the Black-Level (Brightness control) can be
adjusted if necessary as the grayscale adjustments are made. There is
also an additional 100 IRE window that has 98 IRE and 100 IRE stripes
on the right side. This can be used with DLP and LCD projectors to
verify that the peak-white level is not clipped while adjusting the
Gain controls. If that happens use the Contrast control to reduce the
peak-white level so that both stripes are distinctly visible again.
30/40 IRE Split Window
The HDG-3000 also includes 10,
20, 30, 40, 50, 60, 70, 80, 90 and 100 IRE Window patterns to measure
and verify the grayscale accuracy at 10 IRE increments from 10-100 IRE.
These can also be used for adjusting grayscale in place of the 25, 50,
75, and 100 IRE windows if desired. The HDG-3000 also includes 1-10 IRE
Window patterns in 1 IRE steps for verifying grayscale at dark levels.
Vertical Luma Linearity
The HDG-3000 provides Horizontal
and Vertical Luma Linearity patterns with 10-IRE steps from 0 to 100
IRE, and 1 IRE steps from 0-10 IRE, to verify the color temperature at
other luminance values. These patterns should appear to have a constant
color temperature. Displays can also have hot spots that might affect
the color temperature in some portions of the screen. The Split
Vertical Luma Linearity pattern is particularly useful to separate
hot-spotting problems from actual color temperature variations with
grayscale level.
Grayscale Adjustment Procedure:
Split Vertical Luma Linearity
The Gain and Bias controls will
interact when used to set the color temperature over the entire
grayscale range. A Color Analyzer must be used to ideally set the color
temperature to D65 (x=0.3127, y=0.3290) at 25, 50, 75, and 100 IRE
using the Grayscale Window calibration patterns. Be sure to adjust
Black-Level (Brightness control) using the PLUGE patterns and the
100-IRE white reference brightness using the 50% APL Dual PLUGE pattern
or the 100 IRE Window Dual PLUGE pattern before beginning the grayscale
adjustment.
A good initial procedure is to adjust the Bias controls for D65 using the 25 IRE Grayscale Window pattern and then adjust the Gain controls for D65 using the 75 IRE Grayscale Window. The adjustments will interact and it will be necessary to move back and forth between the calibration patterns several times before both patterns can be set to D65. Use the PLUGE stripes at the left side of the Window patterns to ensure that the Black-level remains set correctly, especially when adjusting the Bias controls. Readjust the Brightness control as necessary to maintain the proper black-level.
After initially setting the color
temperature to D65 at 25 IRE and 75 IRE measure the color temperature
at 50 IRE and 100 IRE using the appropriate Window patterns. The
objective is to be as close to D65 as possible at all grayscale levels.
In direct-view CRT monitors the grayscale can usually be maintained
within about +/- 200 degrees Kelvin of D65 from 25 to 100 IRE. In CRT
and fixed-pixel projectors the grayscale can usually be adjusted within
+/- 500 degrees Kelvin and sometimes much better with careful
adjustment. The flatter the grayscale temperature the more accurate
will be the picture color.
with 98/100 IRE Stripes
Use the 98/100 IRE stripes on the right side of the 100 IRE Window Dual PLUGE pattern to ensure that the peak-white level is not clipped while adjusting the Gain controls of DLP or LCD projectors. Use the Contrast control to maintain the desired brightness level in the 100 IRE Window.
The grayscale is often too blue (higher than 6500K) at 50 IRE and too red (below 6500K) at 100 IRE because the blue CRT beam current is driven harder and may not track the output of the other CRTs. Some projectors have additional gamma adjustments that can be used to adjust the tracking to flatten a blue hump in the grayscale color-temperature curve at 50 IRE. The blue CRT beam current also limits first at high drive levels, which may cause the color temperature to rapidly become too red at 100 IRE. To solve this problem, and reduce a blue hump at 50 IRE, it is usually necessary to reduce the maximum brightness at 100 IRE, either by reducing the green Gain control (and then the other Gain controls to achieve the correct color temperature) or to reduce the Contrast control, if no green Gain control is provided.
Use the Bias, Gain, and Contrast
controls to obtain the best 100 IRE brightness while achieving the
flattest grayscale color temperature. If the grayscale color
temperature varies excessively, and particularly when it becomes too
red, skin-tones will become unrealistic and other colors will be
inaccurate.
6. Color Saturation & Hue Calibration
Displays with YPbPr component
video inputs include a Color saturation control. This changes the
amplitude of the Pb and Pr (color-difference) signals with respect to
the Y (luminance) signal, which affects the sensation of color depth or
vividness of color. Deep colors are highly saturated and pastel colors,
or shades of white, have minimum color saturation. A few displays may
also provide a Hue control that adjusts the shade of the colors. It is
critical to have color saturation and hue properly calibrated to
achieve accurate picture color. When using an RGB interface the color
saturation and hue are normally not adjustable, but their accuracy can
be verified using the same calibration pattern procedure given below.
HDG-3000 Color Saturation & Hue
Calibration Patterns:
75% Tri-Split Color Bars
The HDG-3000 provides 75% and
100% Tri-Split Color Bars to visually adjust color saturation and hue.
The 75% Color Windows and 100% Color Flat Fields can be used to adjust
color saturation and hue, or to measure color accuracy using a color
analyzer.
Color Saturation Adjustment
Procedure:
The Split Color Bars are used in
the same way that SMPTE color bars are used to adjust color saturation
and hue in NTSC systems. Display the 75 IRE Split Color Bars and use
blue, red, and green filters to view one color component of the pattern
at a time. Many CRT displays allow only a single red, green or blue CRT
beam to be individually turned on, which is easier and more accurate
than using filters. Adjust the Color saturation (and Hue) control while
viewing only one primary color at a time. When viewing using the blue
primary only, the white, blue, cyan, and magenta colors will form four
vertical blue bars that should be the same intensity from the top to
the bottom of the display. When viewing with the red filter or CRT
beam, the red, white, yellow and magenta colors should all appear as
the same intensity of red. And when viewing with the green filter or
green CRT beam, the green, white, yellow and cyan colors should appear
to be the same intensity of green.
7. Verifying/Adjusting Color Accuracy
75% Red Window
100% Red Field
Color accuracy depends on the
display's primary colors matching the Rec. 709 standard for HDTV
(SMPTE-C/Rec. 601 standard for SDTV), the color saturation (and hue)
calibration, and the accuracy of the grayscale color-temperature
tracking. If the primary colors do not exactly match the standards the
overall picture color accuracy may sometimes be improved by slightly
compromising the grayscale color temperature. (The tracking must still
be maintained at a constant color temperature.)
To verify color accuracy a Color Analyzer can be used to
measure the color coordinates of the primary and complementary display
colors and compare them to the standard colors. It is important to make
measurements using the same intensity level and screen area for the
colors measurements as are used for making white (grayscale)
measurements. This is particularly true when measuring or adjusting
CRT-based displays. When measuring full screen color fields the CRTs
are required to provide much more beam current, which shifts the
measured and visual colors. The HDG-3000 provides 75% color windows
that match the 75 IRE Grayscale Window's size, location and intensity
for making adjustments and verifying performance. The larger 100% full
field color patterns are provided for measuring color shifts and chroma
noise, and also for evaluating color uniformity over the screen.
HDG-3000 Color Accuracy
Verification/Adjustment Patterns:
75% Magenta Window
The 75% Color Window patterns include color windows of the primary (red, green and blue) and complementary (cyan, magenta and yellow) colors and a 75% gray window.
Color Accuracy Verification/Adjustment Procedure:
Use a Color Analyzer to measure the CIE x,y coordinates of each of the primary and complementary Color Windows, and the 75% gray Window. Plot the position of each color on a simple x,y graph. Also mark the position of the standard SMPTE 274M (ITU-Rec. 709) high-definition primary and complementary colors on the graph. The accuracy of the colors can be seen directly from the graph by comparing the measured values of each color to the high-definition standard colors.
CIE x,y Colorimetry
Rec. 709 for 720p, 1080i
White (D65) = 0.3127, 0.3290
Red = 0.640, 0.330
Green = 0.300, 0.600
Blue = 0.150, 0.060
Yellow = 0.419, 0.505
Cyan = 0.225, 0.329
Magenta = 0.321, 0.154
Rec. 601 (SMPTE C) for 480i, 480p
White (D65) = 0.3127, 0.3290
Red = 0.630, 0.340
Green = 0.310, 0.595
Blue = 0.155, 0.070
Yellow = 0.421, 0.507
Cyan = 0.231, 0.326
Magenta = 0.314, 0.161
Notice that a straight line drawn
from each primary through the reference white point should pass through
the complementary color point.
75% Green Window
To optimize the color accuracy of
a display that does not have the correct primaries you can use the
following procedure. First draw a color gamut triangle using the
measured primary color values as the vertices of the triangle. Then
pick a proposed new color temperature near the D65 standard. Draw a
line from each primary color through the proposed new color temperature
and extend it until it intersects the primary triangle. The
complementary colors should lie at the intersections with the color
gamut triangle. Select the best new color temperature that
simultaneously minimizes the color accuracy errors of the three
complementary colors. Measure the complementary colors to verify the
results.
8. Sharpness/Detail Enhancement Calibration
If the display includes Sharpness or Detail Enhancement controls they should be calibrated to maximize apparent picture resolution, but avoid any excessive edge-enhancement that creates outlining artifacts.
HDG-3000 Sharpness/Detail Enhancement
Calibration Patterns:
Luma Multi-burst
Initially adjust Sharpness or
Detail Enhancement controls such that each of the black and white line
bursts (except the last burst) in Luma Multiburst pattern appear to
have the same black/white contrast ratio. The 37 MHz burst at the right
end of the pattern is at the limit of HDTV horizontal resolution (the
black and white lines are each 1-pixel wide) and most displays will not
produce it at full contrast, if at all. If the sharpness or detail
enhancement control is set to an excessively high level to increase the
contrast of the final burst, it is likely to exaggerate the contrast of
the mid-frequency bursts and create outlining artifacts on edges of
lines or objects. So do not increase the controls to the point that the
mid-frequency bursts start to appear brighter than the low frequency
bursts, regardless of the appearance of the 37 MHz burst.
Sharpness
After the initial adjustment of
the Sharpness or Detail Enhancement controls, use the Sharpness pattern
to look for edge outlining artifacts. The Sharpness pattern has 1, 2,
3, 4 and 5 pixel-wide vertical and horizontal black lines against a
gray background that reveals edge-outlining artifacts. (The horizontal
lines are 2, 4, 6, 8, and 10 pixels high in the 1080i and 480i formats
to avoid interlace line flicker.) Look for ghost-like line images on
either side of the lines. They may appear as brighter or darker halo
lines, or both. Reduce the Sharpness or Detail Enhancement control from
its initial settings until any edge-outlining artifacts disappear. If
edge outlining can not be reduced with Sharpness or Detail Enhancement
controls, it may reveal problems with poorly terminated cables,
particularly when long cables are connected to the display. If
outlining artifacts are present without Sharpness or Detail Enhancement
controls, and cables are not at fault, it is possible that the display
has Scan Velocity Modulation (SVM) (CRT only), or other non-adjustable
enhancement circuits that will be detrimental to picture quality.
9. Other Performance Checks
Checkerboard
A Checkerboard pattern with black and white squares is included for measuring the amount of light leakage in the black areas of the picture. There are 16 rectangular (16:9) blocks in a 4x4 pattern. The black blocks are at 0 IRE and the white blocks are at 100 IRE. You can also use this pattern to make simple contrast-ratio measurements in different areas of the display.
A full-field 0-IRE (totally black) frame is also included for measuring light leakage in DLP or LCD projectors.
A Color Multiburst pattern is provided to observe the bandwidth of the Pb and Pr color-difference signal paths compared to the Y luminance path.
A special pattern is included for sizing and positioning a 16:9 HDTV picture inside a 4:3 TV screen. Adjust the display's vertical size and position controls until the height of the black border above and below the 16:9 picture is equal to the black border width on the sides of the calibration pattern.
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