3. 1. Introduction:
In this project, it is intended to build an easy-to-use CRT monitor calibrator, designed to be used by both
technical and non-technical people, and will be both portable and practical in broadcasting environments. It is
essential in broadcasting that monitors used for camera colour controls and post-production are calibrated, to
assure the operator their output colours are the same as what is being broadcast.
In broadcasting, lining up monitors can be time consuming in a very pressurised environment, and requires
skill and technical understanding from the user. Currently, the most common way to calibrate a monitor is by
using various test signals (sawtooth, pluge etc.) and using the eye to adjust. This method can be difficult to
achieve calibration quickly, and can also cause the user a lack of confidence that their reference monitor is
correctly calibrated. This CRT monitor calibrator is intended simply to guide the user step by step to adjust the
contrast, brightness, red, green and blue levels, taking the calibration to the near complete stage quickly,
leaving the user to apply minor tweaks by eye to complete the calibration if necessary.
2. Aims:
It is therefore intended in this project to create a device that will provide the monitor its own PAL test signals to
the CRT monitor, and will have a remote handheld sensor to be held against the monitor that will intelligently
read the luminance values in a specific sequence of test signals. The test signals will have no pattern, and
provide one colour at a time to the full screen, to make circuitry simpler and make easier for the operator to
use, as the handheld sensor can be held anywhere on the monitor display. Using these readings, it will then be
possible to adjust the contrast, brightness and individual red, green and blue pots, ultimately setting the correct
colour temperature of 6500kelvin to match referenced calibrated values. The device will be able to
communicate to the user via an LED display, which will guide the user which pot to tweak and which direction
to tweak it, and when the pot is set correctly. It will also allow feature a next button to take the user to the next
test signal, a restart button to begin a new calibration, and will be able to display when a calibration is
successfully completed. See Figure 1 for a potential user interface of the main control unit.
Figure 1 – Potential User Interface
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4. The design of the handheld sensor is also imperative. As it will be a calibration device, accuracy is essential,
therefore consideration of cable length, photodiode position and filtering external light is critical. It will be
designed for the operator to be held against the monitor display. See Figure 2 for a potential handheld sensor
design.
Figure 2 – Potential Handheld Sensory Design
As it is unlikely any light sensory calibration device will be able to provide 100% accuracy due to a mix of
factors including warm-up time, temperature, cable length etc. it is intended this device will be able to take the
operator to the final stage of calibration quickly, leaving the user to apply minor tweaks by eye to complete the
calibration if necessary. It is intended also for this device to also able to support various monitors, as some
monitors only have simpler contrast, brightness and chroma controls. See Figure 3 for a simplified system
block diagram of the electronic circuitry.
Figure 3 – System Block Diagram
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5. 3. Objectives:
Below is a list of objectives in order to successfully achieve the project aim;
• To create a system that will generate a PAL signal generator with the signals required.
• To design an appropriate handheld sensory device that filters out external light and considers factors
including cable length, temperature and photodiode position.
• To provide a live calibration system that will instruct the operator when the levels are correct and
display in clear form (LED for too high, too low and correct level).
• To conduct extensive research into electronic components required.
• To develop a prototype to test the product functionality, and to develop hardware and software
improvements.
• To conduct extensive testing of photodiode performance.
• To gather accurate readings and calibrate the monitor accurately.
• To design the system to be as ‘easy-to-use’ as possible, suitable for both technical and non-technical
personnel.
• To conduct extensive testing of calibration performance with various monitors.
• To design a suitable and practical electronics and housing design.
These are the key objectives of project, however, they are subject to change during the development of the
project, and may by extended or reduced, influenced by improvement or difficulty decisions.
4. Market Research:
The manufacturers Sony, LaCie and Eizo have various monitor calibrators in the market used for computer
monitor calibration. Personnel in the photography and graphics sector, working with software such as Adobe
Photoshop etc. typically use these calibrators. These calibrators work in a similar design to the design in this
project, with an external USB calibrator to be held against the monitor, however, they use software to provide
test signals to the display using the graphics card, therefore, much simpler. These devices also enable an
operator to calibrate a monitor to various the various colour temperatures used. Devices like these however
were not found for broadcast monitor calibration.
These devices, such as the ColorVision
Figure 4 – ColorVision SpyderPRO Calibrator
(http://www.dansdata.com/images/spyder/spyder640.jpg) SpyderPRO Monitor Calibrator (See Fig 4)
however have a variety of handheld sensor
designs. The design of the remote calibrator is
important to prevent external light entering the
sensor and to prevent damage to the screen.
The spider shape helps distribute weight over
a larger surface area, which is least prone to
damage an LCD if held against the monitor
with too much force.
Although the manufacturers of these devices
haven’t released how exactly these products
work, many claim to work with both CRT and
LCD monitor displays. Although computer
monitors and television monitors have a
considerable difference in contrast ratio’s and
brightness, it opens an investigation whether it
is possible to also include LCD monitor
support in to this product.
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6. In the research process, only very limited information was found regarding a specific monitor calibrator for
broadcast monitors. Sony Broadcast have a monitor calibrator device to work with their BVM-Series monitors,
however, these do not provide the sensor reading functionality to calibrate a monitor, and are typically used for
maintenance and servicing, including advanced geometry controls etc.
In contact with various vision engineers in the broadcasting industry, discussion was made on how monitor
calibration is achieved currently. The most common method currently remains a complete calibration by eye
with the aid of test signals including sawtooth, pluge, colour bars and blue only methods. On average, this
process took an engineer between 5-10minutes per monitor to calibrate. Discussion regarding other calibration
tools on the market for monitor calibration purposes was also conducted, and it was found one tool some
engineers currently used to conduct monitor calibration was used to measure the level of black when using a
pluge test signal.
The response received regarding a broadcast monitor calibrator was very positive, and was suggested a
successful product would be welcomed by vision engineers, lighting directors and editors in post-production
etc.
5. Options Analysis:
At this current stage, production of a prototype test board has begun to design the circuitry required to develop
this product, especially focussing on the calibrator, involving the photodiode, filters and ADC. Various
research into how CRT monitors operate and the issues that might affect the accuracy of calibration of this
product such as scan rate have also been investigated.
The key decision in this project has been whether or not to include an inbuilt PAL signal generator in this
product. An alternative to having an inbuilt PAL signal generator would be using a computer graphics card to
output a PAL signal to the monitor, requiring a RS232 communication link between the calibrator and a
computer. This option would ultimately reduce the circuitry required in making a PAL signal generator, and
could lower the costs of the product. It would also make it possible for instructions to be displayed on the
screen of the monitor being calibrated, making it therefore more user-friendly, and would be much more
achievable within the given timeframe of this project, enabling more time to focus upon development priorities
such as the handheld sensor. Using this option, it would also enable a simple design for a calibrator, consisting
simply of a photodiode, next and restart button, and the required circuitry, which could be directly connected to
a computer and powered via USB (Universal Serial Bus). The intelligence of this calibrator could also be within
the computer software.
With the accuracy of this calibrator being essential, and with the calibration method designed to match monitor
luminance outputs to referenced values in contrast, brightness, red, green and blue using PAL test signals, the
test signal output to the monitor must be accurate. Tests have been conducted to find whether this system
would compromise the accuracy and user-friendliness of the calibrator.
A simple test signals sequence application was
Figure 4 – Visual Basic Test Software
made using Visual Basic, designed to be
mirrored onto a second display on a computer
outputting a PAL signal, allowing testing of the
colour output and the instructions clarity (See
Figure 4). In testing, we found this system would
have major compatibility issues with many
computers, as not all have the facility to output
PAL signals. It was found also in Windows XP
there was no option to output with a PAL colour
temperature as standard, compared to Mac
OSX.
Using a VGA to Video converter, there was still
difficulty outputting a PAL signal. Using a Scan
Rate converter, converting VGA to PAL, it was
then possible to view our calibration software on
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7. a monitor. With this signal looped through to a waveform monitor, the 100% white signal did not line up at 1
Volt. After testing the other test patterns and configurations, the conclusion is that the poor signal accuracy of
this method was unsuitable for calibration purposes. It also requires other expensive equipment and
compromises the user-friendliness of the product. It has therefore been decided to keep the PAL signal
generator within the product.
Another key option was to use a photodiode. With the calibration method being unproven and based on
researched theory, it is required for a light sensor to measure the level of luminance in a range of test signals.
With aid of the PAL signal generator, producing signals such as red, blue and green only, it is expected to find
the luminance value of each red, green and blue value, and therefore adjusting accordingly to produce the
correct colour temperature of 6500kelvin whilst not requiring colour filters in front of the photodiode. The
photodiode is therefore an easy to produce and cheap solution to read luminance values.
6. Extensions/Reductions to Project:
Should the development of the full project appear to not be achievable within the timeframe, a possible
reduction to the project would be to exclude the LED communication interface on the main unit. To
communicate to the operator alternatively, the main unit will connect to a computer via RS232 and the
instructions will appear onscreen via full GUI (Graphical User Interface) software. The main software
intelligence for the calibrator can also be programmed in the computer software rather than in the PIC chip
inside the main unit. This will make development of the calibrator easier and will provide extra expandability
should the calibrator require another feature. This modification will still allow full functionality of the product,
however, it will also require a connection to a computer with software installed and running. Software will
natively be made to run using the Windows operating system, however, if time is available, Mac OSX software
can also be made. Both systems will be able to communicate with the monitor calibrator via a USB to RS232
cable.
Other possible extensions to this project include adjustable colour temperature control and LCD display
support.
7. Budget:
After research of components required to produce the CRT monitor calibrator kit, it is expected to fall within the
£100 budget. With research having been conducted to find the specifications required for the key component
the photodiode, a suitable component was found for £6 excluding postage. The photodiode had the desired
sensitivity ratings, dark level current and visible spectrum wavelength coverage required for this calibrator, and
was an ideal choice. Amongst research via various UK electronic component distributors, this was the most
ideal photodiode within our budget. Should there be concern that this photodiode is not suitable after testing,
there has been budget allocated to invest in an alternative photodiode.
Other equipment that will be required within the budget includes; capacitors, resistors, microchips, LEDs, BNC
connectors, coaxial cable, product casing etc, however, these are all relatively low cost. Facilities required to
develop the project including software and tools are available at no costs.
To keep costs down, it has been decided this device will have a PAL signal generator rather than an SDI
signal generator. PAL has a better compatibility rate within most broadcast monitors in the UK, however, its
disadvantage is that signal levels can reduce over long cable lengths resulting in lower amplitudes which could
cause the calibrator to become inaccurate, however, the calibrator will be set to work with a fixed 5 metre
cable length, which should therefore not affect calibration readings. PAL encoder chips are available for £10,
however, they will also require alternative circuit boards to be able to mount different chips.
Budget has been made available also should replacement components be required. Please see Logbook Page
1 for an ordered component list.
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8. 8. Project Development:
To date, there has been various development into producing a test board to be able to test the performance of
the photodiode. Consideration of monitor scan rates have been made, therefore a 1kHz low pass filter has
been made with the aid of MicroChip FilterLab software to design the circuitry (See Figure 5). Using an
Oscilloscope, it has been possible to see the filter reduce noise in the signal dramatically, and filter out
frequencies above 1kHz using an oscillator.
Figure 5 – Photodiode Low Pass Filter Design
The photodiode has now also been connected to the development
board via the low pass filter and ADC (Analog to Digital
Convertor) for testing (See Logbook Page 6). With data being
sent now directly to a computer via RS232, we are now testing
the photodiode response and ADC readings. (See Logbook Page
8 for circuit diagram).
It is intended to have the PAL signal generator development begin
by early 2008, and have extensive photodiode testing complete
measuring performance against temperature, time etc. to obtain a
full understanding of how to calibrate with optimum performance.
For a full planned development schedule please see attached
Gannt Chart (Figure 6).
Figure 6 – Gannt Chart – Development Schedule
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