HP Lp2480zx User Guide

							each of the three channels (that is, exactly what will be output, in terms of light, for the given values of
red, green, and blue). This may be expressed by the following diagram:
Figure A-2  Model of Standard Display Device
Here, the input RGB values are first modified by the appropriate transfer function (γR, γG, or γB); this
operation may be viewed as being performed by three look-up tables (LUTs) of the appropriate width
and depth. The modified RGB values (R′, G′, and B′) are then mapped to the resulting output light levels
of the correct intensity and color. This may be viewed as a matrix multiplication operation (A) involving
the R′G′B′ values and the appropriate XYZ tristimulus values for the specific display device primaries,
luminance, and white point in question:
Figure A-3  Matrix Multiplication of Input Values
In essence, the R′, G′, and B′ values may be seen as “gain controls” on three light sources whose peak
outputs are described as (X
R,YR,ZR), (XG,YG,ZG), and (XB,YB,ZB). The display device itself – in this case,
the LCD module used in the LP2480zx monitor – of course has its own native characteristics which may
be modeled as described above. The problem of emulating a different (presumably, standard) output
device characteristic is then one of adding a “transform” block (T, in the diagram below) which will modify
this native characteristic such that the overall system emulates the desired performance. In terms of the
above diagram, if the combination of γ
S and AS represent the desired standard characteristic, it is the
function of the transform block T to correct the native display characteristics (γ
D and AD) such that the
output (TD) of this system matches that of the standard device, for the same input values:
Color Space Emulation 35
 
						

							Figure A-4  Correcting Native Display Characteristics
It can be shown that the required transform (T) may be implemented as a pair of appropriately-sized
look-up tables (LUTs), on either side of a 3 x 3 matrix multiplication. The LUT preceding the matrix
multiplication (the “pre-LUT”) implements the desired standard transfer function or gamma response
curve, such that input values are correctly mapped per that standard into a “linear light” space. The
required matrix for the color remapping (which is referred to as R) is a combination of the matrix that
transforms R′G′B′ to X′Y′Z′ values under the target standard (A
S), and the inverse of the corresponding
matrix for the existing display device (A
D). In other words,
R = A
D-1AS
This stage must then be followed by a second look-up table (the “post-LUT”), which linearizes the
existing display device; specifically, it contains the inverse of the display’s transfer functions γ
D(R,G,B).
The complete transform block (plus the LCD module) as implemented in the LP2480zx monitor is then:
Figure A-5  Color Space Conversion Hardware in the LP2480zx
36 Appendix A   Advanced Color Management Features and Usage
 
						

							Note that since the look-up tables for the three channels (R, G, and B) are independent, differences in
the display device’s transfer function across these three, along with any minor errors in the display white
point, may be “nulled out” using the look-up tables, in addition to the operations required for the color
space emulation as described above. In the LP2480zx, these functional blocks are implemented as part
of the “front end” electronics, in addition to the usual scaler/controller functions of a standard monitor.
Due to the limitations imposed by the components used in the LP2480zx front end, full color space
emulation functionality is not available on the analog composite, component, or S-Video inputs*; it is,
however, fully supported when using the DVI-I (both analog and digital sections), HDMI, and DisplayPort
inputs IF the input video is provided using RGB encoding. Color space emulation is not provided on any
input for video using YUV/YC
BCR encoding. The complete matrix of feature support for the various inputs
and signal encodings is provided in the table on the following page.
NOTE:* These inputs connect between the pre-LUTs and the 3x3 matrix multiplier; therefore, re-
mapping of the input values per the desired output device transfer function is not possible.
Selection of the desired standard color space, or selection of a user-defined custom color space setting,
may be achieved through the on-screen display (OSD) menus, the HP Display Assistant software, or
the optional HP/X-Rite calibration software. These provide the correct programming of the color
management hardware described above as needed for the desired color space characteristics.
NOTE:Refer to the monitor’s DDC/CI and USB communication specification for more details.
Summary of Color Space Selection Availability
As noted, the selection of output device color space presets and the resulting emulation of the desired
display characteristics, is not available for all LP2480zx inputs or all color encodings. Basically, this
functionality is available only when a progressive-scanned RGB input is provided by the video source.
YUV (which is considered here as including YC
BCR, et cetera) encoding cannot be used, nor can color
space emulation be supported for interlaced video (as the LP2480zx must convert any interlaced video
to YUV, if not in this form already, in order for the built-in de-interlacing to operate correctly). When
support for the standard or user-defined color space presets cannot be provided, these options will be
“grayed out” on the OSD, and adjustments for image Hue and Saturation will be provided instead.
Table A-2  Supported Signal Inputs and Color Space Matrix
Input usedColor encodingScan formatResult
DVIRGB (YUV not supported on
these inputs)ProgressiveColor Space presets: enabled
Hue/Saturation controls:
disabled
HDMI or DisplayPort RGBProgressiveColor Space presets: enabled
Hue/Saturation controls:
disabled
InterlacedColor Space presets: disabled
Hue/Saturation controls:
enabled
YUV Either Color Space presets: disabled
Hue/Saturation controls:
enabled
Color Space Emulation 37
 
						

							Input usedColor encodingScan formatResult
Component, CVBS, S-Video YUV (RGB not supported) Either Color Space presets: disabled
Hue/Saturation controls:
enabled
10 bits/color LCD Module
As noted earlier, the LCD module in the LP2480zx monitor provides a 10 bits/color (30 bits/pixel) input,
with true 10-bit drivers within the LCD itself. This means that each primary (red, green, and blue) may
be controlled over 1,024 steps (input codes 0 to 1023) from the black level to the white (peak luminance
for that color). This results in over 1.07 billion separate colors available within the display’s gamut, versus
approximately 16.7 million for a conventional 8 bits/color display.
This increase in dynamic range is required for the accurate display of color within the wide gamut
provided by the LP2480zx’s LCD, and especially for achieving the necessary degree of color accuracy
within the more restricted gamuts that this monitor is capable of providing when emulating various
standard output devices. Increasing a display’s color gamut – the area covered by the display when the
primaries are plotted on a standard chromaticity diagram – would result in a greater difference between
adjacent colors if the degree of control (bits per color) for each primary were not also increased.
Increasing the bit depth of the display drivers achieves this without the possibility of undesirable image
artifacts which may result from temporal or spatial dithering as may sometimes be used with an LCD of
lower inherent accuracy. (The LP2480zx’s “front-end” electronics are also, however, capable of
providing temporal dithering, if needed, to increase the delivered accuracy beyond the 10 bits/color level.
By default, this is used only between the pre-LUT and the 3x3 matrix multiplier stage; temporal dithering
is possible but normally disabled at the 30-bit connection between the post-LUT and the LCD module
itself.)
With most video sources (which typically provide video information at the standard 8 bits/color or 24
bits/pixel), and across all of the LP2480zx’s various inputs, the increased accuracy of the LP2480zx
LCD module is used to provide more accurate color within the selected standard color space. However,
30-bit sources may also be directly supported using the DisplayPort 1.1 and HDMI 1.3 inputs only. This
will be of greatest benefit when the LP2480zx is used in the wider-gamut modes (such as Full, Adobe
RGB, DCI).
LED Backlight Unit
As noted earlier, the LP2480zx monitor employs a backlight consisting of an array of red, green, and
blue light-emitting diodes (LEDs) rather than the more typical cold-cathode fluorescent lamps (CCFLs)
on most LCD monitors. This provides several significant advantages, in addition to the obvious benefit
of a wider color gamut (that is, more saturated primaries) than can currently be achieved using CCFLs.
In the LP2480zx, the red, green, and blue LED arrays are controlled both collectively and separately by
a dedicated backlight controller, which permit both very accurate setting of the display luminance as
well as control of the white point of the unit. Color sensors in the backlight unit feed color information
back to the controller constantly, permitting an accurate white point to be maintained.
Compared with CCFLs, which have only a limited range of brightness control available and a fixed
emission spectrum, the LED backlight used here provides a very wide range of both brightness and
color control. The white point may be adjusted over a range corresponding to a correlated color
temperature (CCT) of 4,000K to 12,000K, including support for all standard white points with CCTs within
this range. In addition, the white luminance may be adjusted from a maximum of approximately 250 cd/
m
2 down to 50 cd/m2, making the LP2480zx suitable for use in low-light environments; at the lower
Table A-2  Supported Signal Inputs and Color Space Matrix (continued)
38 Appendix A   Advanced Color Management Features and Usage
 
						

							brightness settings, both its white luminance and black level compare favorably with those of traditional
CRT displays. (At the low end of this range, the monitor’s black level will typically be approximately 0.05
cd/m
2.)
As with several other parameters set in the color space presets, the programming of the backlight
controller is managed either through the LP2480zx’s on-screen display (OSD), or by using the HP
Display Assistant software.
Transfer Function (Gamma)
As noted briefly in the previous section on Color Space Emulation on page 34 in this Appendix, display
devices typically impose a non-linear transfer function on the input video data, in terms of how the
intensity of the light output by the device varies versus these inputs. This is often referred to as the
display’s “gamma” response characteristic, as one simple model for this behavior is a power-function
curve (in which the exponent is typically represented by the Greek letter gamma, γ) as follows:
Figure A-6  Gamma Curve Response Characteristic
This model, with a “gamma” value of about 2.2 – 2.5, describes the actual response of a standard CRT
display fairly well,* and so was assumed for years to be the typical response curve of an electronic
display device. As it turns out, encoding image information under the assumption of an output device
response of this nature has other advantages, and so it remains very common for standard output device
specifications to require a transfer function or response curve which is of this general nature. The most
common modification to this simple model as seen in many current output device or image encoding
standards is the addition of a linear region at the lower end of the response curve, as shown in the
following diagram. This linear region avoids problems, which otherwise would result from applying the
inverse of the response curve (in image encoding), as otherwise the slope of the curve would be
changing very rapidly in the low-luminance regions of the image.
NOTE:* The biggest shortcoming of the simple gamma curve model as given, with respect to CRT
displays, is that the black level of the input signal (assumed to be zero) does not generally result in
exactly zero luminance for a properly-adjusted CRT. This requires the addition of an offset term into the
model. However, the basic model as shown here remains an adequate description for most non-critical
work.
Transfer Function (Gamma) 39
 
						

							Figure A-7  Low Linear Region Response Curve
A generalized model for the display response curve accommodating the addition of a linear section as
shown above thus requires the specification of four parameters in addition to the “gamma” exponent
value:
For input values (I) ≤ A
0:
Y = I/A
1
For input values (I) > A0′
Y = [(I + A
2)/(1 + A3)]γ
The response of the LP2480zx is automatically set to the correct standard as part of the color-space
selection, using either the on-screen display (OSD) or using the HP Display Assistant software, or using
the optional HP/X-Rite color calibration tools. Independently programming a custom response (as in the
case of the user-defined custom color space preset) requires use of the HP/X-Rite calibration tools.
Using the software provided with this calibration product, the display response may be programmed
using the four-value-plus-gamma model described above.
Several of the standard color space specifications supported by the LP2480zx require the use of the
“four-value” model, as they include a linear section in the response curve as described above. Of course,
even the simple “gamma-only” model may be accommodated within the four-value model, by setting
the A
0, A2, and A3 parameters to zero, and A1 to a value of 1.0. The values used to describe the response
for the standard color spaces or output device specifications supported by the LP2480zx are listed in
the table below.
Table A-3  Response Curve Constants for Various Color Spaces
Color spaceA0A1A2A3gamma (γ)
sRGB0.0404512.920.0550.0552.4
ITU-R BT.7090.0814.500.0990.0992.22222
SMPTE-C0.0814.500.0990.0992.22222
Adobe® RGB01002.19922
DCI-P301002.6
40 Appendix A   Advanced Color Management Features and Usage
 
						

							Color spaceA0A1A2A3gamma (γ)
Full01002.2*
* Note that in “full gamut” mode, the color space emulation capabilities of the LP2480zx monitor are used to correct any
deviations in the LCD’s native performance from its nominal specified values. The color gamut, white point, and response curve
seen in this mode are therefore those of the LCD panel itself, but corrected to their nominal values as accurately as possible.
References:
●Adobe® RGB (1998) Color Image Encoding, Version 2005-05, May 2005, Adobe Systems, Inc.
http://www.adobe.com/digitalimag/pdfs/AdobeRGB1998.pdf
●Digital Cinema System Specification, Vers. 1.1, April 12, 2007 Digital Cinema Initiatives, LLC
http://www.dcimovies.com
●IEC 61966-2-1:1999 Colour Measurement and Management in Multimedia Systems and
Equipment – Part 2-1: Default RGB Colour Space – sRGB, International Electrotechnical
Commission, TC 100
http://tc100.iec.ch/index_tc100.html
●ITU Recommendation BT. 709: Parameter values for the HDTV standards for production and
international programme exchange, April 2002, International Telecommunications Union
http://www.itu.int/net/home/index.aspx
●SMPTE Recommended Practice 145-2005, SMPTE-C Color Monitor Colorimetry
●SMPTE Standard 431-2, Reference Projector and Environment for Display of DCDM in Review
Rooms and Theaters, Society of Motion Picture and Television Engineers
http://www.smpte.org
Table A-3  Response Curve Constants for Various Color Spaces (continued)
Transfer Function (Gamma) 41
 
						

							B Troubleshooting
Solving Common Problems
The following table lists possible problems, the possible cause of each problem, and the recommended
solutions.
ProblemPossible CauseSolution
Screen is blank.Power cord is disconnected.Connect the power cord.
Power button on front panel of the
monitor is turned off.Press the front panel power button.
NOTE:If pressing the power button has no effect, press
and hold the power button for 10 seconds to disable the
power button lockout feature.
Video cable is improperly
connected.Connect the video cable properly. Refer to Setting Up theMonitor on page 7 for more information.
Screen blanking is active.Press any key on the keyboard or move the mouse to
inactivate the screen blanking utility.
Monitor will not turn on.Master power switch on rear panel
of the monitor is turned Off.Turn the master power switch to On.
Image appears blurred,
indistinct, or too dark.Brightness is too low.Press the – (minus) button on the front panel. If this does
not correct the image, press the Menu button to open the
OSD Menu, and adjust the brightness scale as needed.
Image is not centeredPosition may need adjustment.Press the Menu button to access the OSD menu. Select
Image Control/Horizontal Position or Vertical Position to
adjust the horizontal or vertical position of the image.
Check Video Cable is
displayed on screen.Monitor video cable is
disconnected.Connect the appropriate video signal cable between the
computer and monitor. Be sure that the computer power is
off while connecting the video cable.
Input Signal Out of Range,
Change Settings to 1920 x
1200 – 60Hz is displayed on
screen.Video resolution and/or refresh rate
are set higher than what the monitor
supports.Restart the computer and enter Safe Mode. Change the
settings to a supported setting (see Recognizing Preset
Display Resolutions on page 46). Restart the computer
so that the new settings take effect.
The monitor is off but it did
not seem to enter into a low-
power sleep mode.The monitors power saving control
is disabled.Check the monitors OSD menu setting for power saving
enable/disable controls. The control should be set to
enable to allow the monitor to enter into low-power modes.
OSD Lockout is displayed.The monitors OSD Lockout
function is enabled.Press and hold the Menu button for 10 seconds to disable
the OSD Lockout function.
Power Button Lockout is
displayed.The monitors Power Button
Lockout function is enabled.Press and hold the power button for 10 seconds to unlock
the power button function.
42 Appendix B   Troubleshooting
 
						

							Using the Worldwide Web
For the online access to technical support information, self-solve tools, online assistance, community
forums of IT experts, broad mutlivendor knowledge base, monitoring and diagnostic tools, go to
http://www.hp.com/support
Preparing to Call Technical Support
If you cannot solve a problem using the trouble shooting tips in this section, you may need to call
technical support. Have the following information available when you call:
●The monitor
●Monitor model number
●Serial number for the monitor
●Purchase date on invoice
●Conditions under which the problem occurred
●Error messages received
●Hardware configuration
◦Video card
◦Type of computer
◦Cable input used (for example, HDMI, VGA, DVI, or DisplayPort)
●Calibration system used
●Hardware and software you are using
Using the Worldwide Web 43
 
						

							C Technical Specifications
NOTE:All performance specifications are provided by the component manufacturers. Performance
specifications represent the highest specification of all HPs component manufacturers typical level
specifications for performance and actual performance may vary either higher or lower.
HP LP2480zx Model
Table C-1  HP LP2480zx Model Specifications
Display
Type61 cm
TFT LCD24 inches
Viewable Image Size61 cm diagonal24–inch diagonal
Tilt Adjustment-5 to 35°
Swivel Adjustment-45 to 45°
Height Adjustment100 mm range3.94–inch range
PivotClockwise 
Maximum Weight (Unpacked)12.5 kg27.5 lbs.
Dimensions (include base)
Height
Depth
Width42.5 cm
25.4 cm
56.5 cm16.7 inches
10.0 inches
22.2 inches
Optimum Graphic Resolution1920 × 1200 (60Hz) analog input
1920 × 1200 (60Hz) digital input
Text Mode720 × 400
Dot Pitch0.270 (H) × 0.270 (W) mm
Horizontal Frequency24 to 76 kHz
Vertical Refresh Rate47 to 61 Hz
Environmental Requirements Temperature
Operating Temperature
Storage Temperature
5 to 35° C
-20 to +60° C41 to 95° F
-4 to 140° F
Relative Humidity 20 to 80%  
44 Appendix C   Technical Specifications