Apparatus and method for adjusting image contrast on a display device

An apparatus for adjusting the image contrast of a display device, which includes a memory storing first data representing a predetermined image contrast, a driver for driving the display device, an input device for inputting second data representing the image contrast different from the predetermined one, a data-rewriting device for supplying the first data read from the memory and the second data input from the input device to the second data in the memory. In use, the apparatus is be incorporated within an apparatus having the display device, such as a copying machine. The input device is part of the console panel unit mounted on the outer side of the copying machine. The display device displays both the first data and the second data.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an apparatus and method for adjusting the 
image contrast of a display device, and more particularly, to an apparatus 
and method for adjusting the image contrast of the display device which is 
incorporated in the console panel unit of a copying machine or a facsimile 
device. 
2. Description of the Related Art 
Various apparatuses have a console panel unit. Among these apparatuses are: 
an image processor for processing image information, e.g., characters and 
graphics; an image scanner for reading image information from an original 
and supplying this information to an image processor; a printer for 
printing image data output from a computer or the like, on a recording 
medium; a copying machine for copying an original having image 
information, and a facsimile device for transmitting and receiving image 
information though a communication line. A display device is incorporated 
in the console panel unit of each of these apparatuses, for displaying 
messages showing the conditions of some of the components of the apparatus 
and the instructions as to operate the apparatus. 
It is desirable that the display device incorporated in the console panel 
unit of, for example, a copying machine which performs an 
electrophotography process, should display as many characters, symbols, 
and graphic characters as is possible. Further, it is demanded that the 
display device should display as many messages as is possible, since the 
apparatus has many functions to perform and is required to carry out these 
functions in complex combinations. To display many characters, symbols, 
graphic characters, and messages, the display device used in the copying 
machine or the like is large in size. 
Display devices of various types are known which can be used for the 
purpose described above. Among these are: a light-emitting diode display 
(hereinafter referred to as "LED display" which can display characters, 
graphics, and graphic characters; a cathoderay tube display (hereinafter 
referred to as "CRT display") which can display characters, graphics, and 
graphic characters, and a liquid crystal display (hereinafter referred to 
as "LCD" which ca display the same data items as the CRT display. The LED 
display cannot display as many characters and graphics as are desired. On 
the other hand, although the CRT display may display as many characters 
and graphics as is desired, it is considerably larger. The LCD is not as 
large as the CRT display but can display as many characters, graphics, and 
graphic characters as is desired, and is thus used commonly in console 
panel units. In particular, dot-matrix type LCDs, which have display 
elements arranged in rows and columns, are used in great numbers. 
The LCDs available at present are classified into three types. The first is 
a positive type wherein some of the display elements become opaque when 
driven, thus defining characters, symbols, and graphic characters. The 
second is a negative type wherein some of the display elements become 
opaque when driven, whereby the remaining display elements define 
characters, symbols, and graphic characters. The third is a 
positive-negative type, which functions as a positive type when operated 
in the first operating mode and as a negative type when operated in the 
second mode. With most LCDs available now, it is possible to change the 
image contrast, that is, the ratio in brightness of the data items 
displayed to the background of the screen. 
The image contrast of the LCD is adjusted before the copying machine is 
delivered from the factory. To be more specific, the drive voltage of the 
LCD, i.e., the voltage applied from a LCD drive circuit to the LCD is 
adjusted such that it has a value for which LCDs display images in the 
best contrast. As is generally known in the art, however, the image 
contrast of any LCD greatly varies in accordance with the direction in 
which light is externally applied to the LCD. Hence, the image contrast of 
the LCD must be readjusted in accordance with the intensity and direction 
of external light applied to the LCD after the copying machine has been 
installed in a specific room for use. 
The variable resistor used for adjusting the drive voltage of the LCD is 
incorporated within the console panel unit, and cannot therefore be 
accessed from outside. In order to have access to the variable resistor, 
the cover concealing the variable resistor must be removed from the 
copying machine. After the variable resistor is adjusted, the cover must 
be attached to the copying machine. Removing and attaching the cover is 
time-consuming, and increases the chance of staining and damaging the 
cover. Furthermore, since the variable resistor must be adjusted, with the 
cover removed, while the power switch of the copying machine is on, the 
person who adjusts the variable resistor is exposed to the danger of 
electric shock. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide an apparatus and method 
for adjusting, with ease, the image contrast of a display device, or the 
ratio in brightness of the data items displayed to the background of the 
screen of the display device. 
Another object of the invention is to provide an apparatus which can adjust 
the image contrast of a display device incorporated in a specific 
apparatus without removing covers from the specific apparatus. 
Still another object of the invention is to provide a method of adjusting 
the image contrast of a display device to an optimal value, regardless of 
the direction in which light is applied to the display device, or 
regardless of the position of the person adjusting the image contrast. 
According to a first aspect of this invention, there is provided an 
apparatus for adjusting an image brightness of a display device capable of 
displaying data of first and second brightness radios of what is displayed 
against a background thereof, the apparatus comprising means for 
energizing the display device which displays information, including the 
data, in a desired ratio, means for inputting further data for altering a 
present brightness ratio, and means for supplying the data representing 
the first brightness ratio and the second brightness ratio set by 
inputting means to the display device. The display device includes a first 
display section for displaying data, a second display section for 
displaying the first brightness ratio and a third display section for 
displaying the second brightness ratio. 
According to a second aspect of the invention, there is provided a method 
of adjusting the image contrast in a display device using an apparatus 
which comprises means for storing first data representing a brightness 
ratio of the data displayed by the display device to the background of the 
screen of the display device; means for supplying drive signals to the 
display device in accordance with the first data read from the memory 
means; means for inputting second data different from the first data 
stored in the memory means; and means for supplying the first data stored 
in the memory means and the second data input from the input means, to the 
display device, and altering the drive signals in accordance with the 
second data, thereby to replacing the first data with the second data in 
the memory means, said method comprising the steps of: a) setting the 
apparatus to contrast-adjusting mode in response to a signal input from 
said input means; b) causing the display device to display the first data 
stored in the memory means; c) setting the apparatus to data-inputting 
mode; d) allowing the second data to be input from the input means; e) 
setting the apparatus to the contrast-adjusting mode; f) causing the 
display device to display the second data input from the input means, and 
altering the drive signals in accordance with the second data; g) 
replacing the first data by the second data in the memory means; and h) 
releasing the apparatus from the contrast-adjusting mode. 
Additional objects and advantages of the invention will be set forth in the 
description which follows, and in part will be obvious from the 
description, or may be learned by practice of the invention. The objects 
and advantages of the invention may be realized and obtained by means of 
the instrumentalities and combinations particularly pointed out in the 
appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows a copying machine 2 having a housing 8 and legs 8a protruding 
from the bottom of the housing 8. The legs 8a are hard-rubber legs, lock 
bolts, or spacer bolts. An original table in located on the top of the 
housing 8 An original holder 4 is hinged to the original table, for 
holding an original placed on the original table. 
Two cassettes 20a and 20b are removably inserted in the two slots in the 
right side of the housing 8, respectively. Either cassette contains a 
stack of sheets of paper on which images will be transferred from 
originals. A tray 20c is attached to the left side of the housing 8, for 
receiving copied sheets of recording paper. A front cover 6f, a rear cover 
(not shown), a right side cover 6r, and a left-side cover (not shown) are 
provided on the front, rear, right side, and left side of the housing 8, 
respectively. These covers can be opened to allow access into the interior 
of the housing 8. These covers and the top cover 6u are made of 
self-extinguishing resin. The housing 8 contains an image-forming section 
(not shown), a contrast-adjusting apparatus 70 (shown in FIG. 3), and some 
other components. The image forming section includes a latent image 
forming section for converting the information on a document into an 
electrostatic latent image, and an image transfer section for realizing 
the latent image and transferring the realized image to a sheet of paper. 
An inner cover (not shown) is arranged within the housing 8, covering the 
image-forming section and preventing the user from touching the 
image-forming section. A part of the top surface of the housing 8 is a top 
cover 6u having a console panel unit 14. The LCD 50 is designed to display 
characters and graphics, indicating instruction messages and the 
conditions of some of the components of the machine 2. The console panel 
unit 14 has keys 51 to 59 to input operation commands and numerical data, 
etc. 
The console panel unit 14 will now be described in detail, with reference 
to FIG. 2. The unit 14 has a LCD 50 for displaying the conditions of some 
of the components located within the housing 8, instruction messages, for 
instance, "READY" or "PAPER JAM," and the like. The LCD 50 has a 
magnification-displaying section 50a, a message-displaying section 50b, 
and a data-displaying section 50c, as is best shown in FIGS. 5A, 5B, and 
5C. 
As is shown in FIG. 2, the console panel unit 14 also has a print key 51, 
an interrupt key 52, a energy saver key 53, an all-clear key 54a, a 
clear/stop key 54b, a group of numeral keys 55, and a group of 
magnification-setting keys 56. The print key 51 is depressed to cause the 
machine 2 to start copying an original. The interrupt key 52 is depressed 
to cause the machine 2 to stop the copying operation and start performing 
another operation. The energy saver key 53 is operated to set the machine 
2 to energy-saving mode, or put the machine 2 in preheated condition. The 
all-clear key 54a is depressed to cancel all operation modes set in the 
copying machine 2, and set the machine 2 to predetermined initial 
operation modes. The clear/stop key 54b is pushed to clear numerical data 
items such as the desired number of copies and/or interrupt the operation 
the machine 2 is performing. The group of keys 55 has ten numeral keys "0" 
to "9" which are selectively pushed to enter numerical data such as the 
number of copies to make. The magnification-setting keys 56 are operated 
to input a desired value at which the image of the original will be 
enlarged or reduced. 
The console panel unit 14 also includes a display section 57 for displaying 
the size of the original D and the size of the sheets P being used, an 
alarm display section 58 for displaying graphics instructing the user to 
replenish toner T and/or sheets P or informing the user of a trouble 
occurring within the housing 8, such as paper jamming, a copy-density 
setting switch 59 for adjusting the density in which the image on the 
original is to be copies, function keys, and a mechanical counter designed 
to count the copies made. 
These keys, display sections, and other components of the console panel 
unit 14 are connected to the contrast-adjusting apparatus 70 which is 
contained in the housing 8. 
As is illustrated in FIG. 3, the contrast-adjusting apparatus 70 has a 
nonvolatile memory 74, a D/A converter 76 for changing the voltage applied 
to the LCD 50, and a CPU 72 for supplying data to the memory 74 and 
receiving data therefrom, and for supplying data to the LCD 50 and the D/A 
converter 76. 
A data-reading command signal is supplied from the console panel unit 14 to 
the CPU 72 when one key or several keys among the group of numeral keys 55 
are depressed. In response to this command signal, the CPU 72 reads the 
data stored in the memory 74, and supplies this data (hereinafter referred 
to as "first data") to the LCD 50 and also to the A/D converter 76. The 
D/A converter 76 converts the first data into a first voltage. The first 
voltage is applied to the LCD 50, thus driving the LCD 50. Hence, the LCD 
50 displays the first data in its first and second display sections, in 
the first contrast determined by the first voltage applied from the D/A 
converter 76. 
When another one key or several keys among the group of numeral keys 55 are 
depressed, other data (hereinafter referred to as "second data") is input 
to the CPU 72. The CPU 72 supplies the second data to the LCD 50 and also 
to the D/A converter 76. The D/A converter 76 converts the second data 
into a second voltage, which is applied to the LCD 50. Hence, the LCD 50 
displays the second data in its first display section in the second 
contrast determined by the second voltage, while it displays the first 
data in its second display section in the second contrast determined by 
the second voltage. 
When still another one key or several keys among the group of numeral keys 
55 are operated, thus inputting new data, this new data is supplied to the 
LCD 50 and the D/A converter 76 through the CPU 72, whereby the first 
display section of the LCD 50 displays the new data in the contrast 
determined by the new data, while the second display section displays the 
unrenewed data in the contrast determined by the new data. 
On the other hand, when the interrupt key 52 is depressed, a data-renewing 
command signal is supplied to the CPU 72. In response to the data-renewing 
command signal, the CPU 72 erases the data stored in the memory 74 and 
write the new data thereinto. At the same time, the CPU 72 controls some 
components of the copying machine 2 other than the contrast-adjusting 
apparatus 70, thereby setting the machine 2 to ordinary operation mode. 
A method of adjusting the contrast of the LCD 50 will now be explained, 
with reference to the flow chart of FIG. 4. 
First, in step STP 1, the power switch of the copying machine 2, is turn on 
while at least two keys, e.g., the "0" and "5" keys of the numeral key 
group 55, are depressed simultaneously. Alternatively, the two keys are 
depressed simultaneously when the copying machine 2 remains in operable or 
ready condition. In step STP2, the CPU 72 outputs a test-mode signal in 
response to the signals representing "0" and "5" supplied from the numeral 
key group 55, and the parameters of some components of the machine 2, 
other than the contrast-adjusting apparatus 70, are renewed in accordance 
with the test-mode signal, whereby the copying machine 2 is set to test 
mode. At the same time, the CPU 72 supplies first display data to the LCD 
50. In step STP 3, the LCD 50 displays the message "TEST MODE" in its 
message-display section 50b, the letter "A" in its data-display section 
50c, as is illustrated in FIG. 5A. 
Thereafter, in step STP4, the "9" key of the numeral key group 55 is 
depressed twice, thereby inputting a contrast-setting code, and then the 
print key 51 is depressed, thus inputting a code entry signal. Then, the 
flow goes to step STP5, in which the CPU 72 generates a contrast setting 
signal in response to the contrast-setting code and the code entry signal. 
As a result of this, the copying machine 2 is set to contrast-setting 
mode. Then, in step STP6, the CPU 72 supplies second display data to the 
LCD 50, whereby the LCD 50 displays the message "CONTRAST" in its 
message-display section 50b, as is showing FIG. 5B. Simultaneously, the 
LCD 50 displays the contrast data stored in the memory 74, e.g., "128", in 
its data-display section 50c, and also in a part 50d of the 
message-display section 50b, also as is illustrated in FIG. 5B. 
Here, it will be described the relationship between the data stored in the 
memory 74 and the voltage applied to the LCD 50 from the D/A converter 76. 
The D/A converter 76 divides the voltage applied from a power supply (not 
shown) into 2.sup.n parts, where n is the bit-configuration of the D/A 
converter 76. If the D/A converter 76 is of 8-bit configuration, it 
divides the voltage into 256 parts (=2.sup.8). The D/A converter 74 
thereby converts the input voltage to a voltage determined by the contrast 
data stored in the memory 74. Let us assume that the maximum voltage 
applied to the D/A converter 76 is 5 V, and that the contrast data stored 
in the memory 74 is "128" which is the intermediate of the value of "256", 
i.e., the number of parts into which the power supply voltage is divided 
by means of the D/A converter 76. Then, the output voltage of the D/A 
converter 76 is: 
EQU 5 V.times.128/256=2.5 V 
Whenever the power switch of the copying machine 2 is turned on for the 
first time after the machine 2 has been assembled, the numerical value of 
"128" is read out from the memory 74 and is then displayed by the LCD 50. 
In other words, the LCD 50 displays the contrast data which stored in the 
memory 74 and corresponds to the output voltage of the D/A converter 76. 
In step STP 7, if the contrast data "128" displayed in the data-displaying 
section 50c is too low, keys of the numeral key group 55 are depressed for 
inputting a numerical value greater than "128," i.e., new contrast data. 
Conversely, if the contrast is too high, some keys of the numeral key 
group 55 are depressed, thus inputting a numerical value less than "128," 
or new contrast data. Let us assume that the contrast is too low, and that 
the "1", "3" and "8" keys of the key group 55, are depressed for inputting 
new contrast data "138." 
The flow then goes to step STP 8, in which the following operations are 
performed. First, the new contrast data, i.e., "138", is supplied to the 
CPU 72, which supplies the new contrast data to the LCD 50 and the D/A 
converter 76. Then, the D/A converter 76 converts the new contrast data 
into a voltage, i.e., about 2.7 V (.apprxeq.5 V.times.138/256). Next, the 
voltage of about 2.7 V is applied to the LCD 50. Hence, the LCD 50 
displays, as is illustrated in FIG. 5C, the new contrast data "138" in the 
data-displaying section 50c in a contrast determined by the new contrast 
data "138". In other words, the contrast data displayed in the 
data-display section 50c is changed from "128" to "138," whereas the 
message "CONTRAST" is still displayed in the message-displaying section 
50b. 
The flow advances to step STP9, in which the user determines whether or not 
the new contrast is the best possible. If NO, the flow returns to step 
STP7, in which the user operates the numeral key group 55, thus inputting 
a new numerical data greater or less than "138", and then goes to step 
STP8, in which the new contrast data is displayed in the new contrast 
presented by this new data. Steps STP7 and STP8 are repeated until the new 
contrast is optimal. If YES in step STP9, the interrupt key 52 is 
depressed in step STP10, whereupon the CPU 72 generates a data-rewriting 
signal. The data-rewriting signal is supplied to the memory 74, and the 
initial contrast data of "128" is erased from the memory 74, and new 
contrast data of "138" is written into the memory 74. 
Then, in step STP11, the copying machine 2 is set to the test mode again, 
and the message "TEST MODE" is automatically displayed in the 
message-displaying section 50b of the LCD 50 as is shown in FIG. 5A. 
Needless to say, this message is displayed in the contrast which the user 
think is the best possible. Note that the copying machine 2 returns from 
the test mode to the operable or ready mode by turning off the power 
switch once. 
As has been described above, the apparatus according to the present 
invention is easily adjustable in the image contrast of the LCD of the 
machine, i.e., the ratio in brightness of the displayed characters and 
graphics to the background of the LCD. This is because the contrast data 
determining the image contrast of the LCD stored in the memory can be 
replaced by any new contrast data input by operating the keys of the 
console panel unit. 
Hence, the user need not remove a cover whatever to adjust the image 
contrast as is necessary in the case where the variable resistor for 
adjusting the image contrast of the LCD is located within the housing of 
the copying machine. As a result, the time for removing and attaching such 
a cover is saved, and the risk of damaging or staining such a cover is 
eliminated. 
Moreover, since the LCD displays both the contrast data stored in the 
memory and the new contrast data input by operating the numeral key group, 
the user can easily know the difference between these data and can 
therefore adjust the image contrast of the LCD to the best possible value. 
When it is required of a person to adjust the image contrasts of the LCDs 
of several copying machines, he or she can set them to the same value. 
In addition, since it suffices for such a person to operate the numeral key 
group to adjust the image contrast of the LCD, he or she is not exposed to 
the danger of suffering from electric shock. 
Additional advantages and modifications will readily occur to those skilled 
in the art. Therefore, the invention in its broader aspects is not limited 
to the specific details, representative devices, and illustrated examples 
shown and described herein. Accordingly, various modifications may be made 
without departing from the spirit or scope of the general inventive 
concept as defined by the appended claims and their equivalents.