Browse Prior Art Database

Automated Color Balance for an Inter-Integrated Circuit Display

IP.com Disclosure Number: IPCOM000105354D
Original Publication Date: 1993-Jul-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 6 page(s) / 205K

Publishing Venue

IBM

Related People

Cromar, C: AUTHOR [+3]

Abstract

Disclosed is a process for adjusting color balance, brightness and cut-off automatically on a display which has digital-to-analogue converters (1) ACs, addressable on a serial bus as the adjustment interface.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 31% of the total text.

Automated Color Balance for an Inter-Integrated Circuit Display

      Disclosed is a process for adjusting color balance, brightness
and cut-off automatically on a display which has digital-to-analogue
converters (1) ACs, addressable on a serial bus as the adjustment
interface.

      The embodiment described does not use potentiometers for
adjusting the front of screen parameters.  Instead, a chip set
utilizing an interfacing method termed Inter-Integrated Circuit Bus
(IIC Bus) is used.  The IIC Bus is structured for economy, efficiency
and versatility.  Since the data throughput for control functions is
low, it transfers the data serially in either direction at up to 100
kbits/sec.  Only two wires are needed;  one for data and one for the
system clock, so few IC pins and only simple PCB wiring and
interboard connectors are needed.  The IIC Bus is a true multi-master
bus, so control can be assumed by more than one of the ICs connected
to it.  To avoid loss or corruption of information, a unique address
is allocated to each IC and the bus protocol incorporates an
arbitration procedure to decide control priorities.  When ICs with
fast clocks communicate with ICs with slow clocks, the protocol
effectively synchronises the system clock by defining the clock
source.  The IIC bus supports a wide range of micro-controllers and
peripheral ICs fabricated in many technologies and is accepted as an
industry standard.

     The following adjustments are required to set-up a display.
Geometric parameters, such as height, width and centering, can be set
using average values, since the driver circuitry and cathode ray tube
sub-components are normally a good match.

      Color balance at maximum brightness is controlled by adjustment
of the gain DACs.  The pre-setting described above also applies for
color balance at maximum brightness.

      Brightness override is a DAC which allows automatic adjustment
of the user brightness control.

      Grey scale tracking is adjusted using the cut-off DACs to
ensure that the color balance is pure just before the image
disappears into darkness.  Setting of the cut-offs is a difficult
adjustment for any color display.  Inaccurate setting is
objectionable.  Apart from the fact that great caution is required
for setting the cut-offs, there are restrictions placed due to design
requirements.  At least one of the cut-offs must be left at either
maximum or minimum to ensure that the CRT specification requirements
for G2 voltage are met.  This means that the minimum color point must
be achieved by adjustment of only two cut-offs.  Focus is a manual
adjustment assumed to be set before starting the automated color
balance adjustment.  Equipment used for adjustment is shown in Fig.
1.

Initial Conditions For Automated Color Balance

      First, the video cut-off DACs are preset to their maximum and
the G2 DAC is set to a value which gives a pre-defined low brightness
value as measu...