Display control apparatus with independent information receivers

Color conversion processing is enabled in accordance with the color characteristics of the display panel. A display control device displays images using a display panel with one picture element consisting of four pixels of red (R), green (G), blue (B) and white (I). A color converter generates R, G, B, I signals from an input signal, and a color characteristic discrimination signal changes the characteristics of the color converter.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a display control apparatus for a display 
panel with one picture element constituted of four pixels of, for example, 
R (red), G (green), B (blue) and I (white), wherein the display control 
apparatus generates R, G, B and I signals from an input signal. 
2. Related Background Art 
Recently, display systems on the computer have been put to practical use, 
wherein display contents are represented not only by characters or lines 
but also natural images with characters and lines synthesized. This means 
that the feature of halftone display is important for the display panel 
(CRT, liquid crystal, plasma, EL) which is the display means in the 
display system. However, in display apparatuses except for CRT, the 
halftone display is not a simple matter. In the following, the halftone 
display on a liquid crystal display, particularly with a ferroelectric 
liquid crystal display panel will be exemplified. 
Conventionally, display elements using a ferroelectric liquid crystal (FLC) 
are well known, wherein ferroelectric liquid crystal is injected into a 
liquid crystal cell having two sheets of glass substrate disposed 
opposedly with a cell gap of about 1 to 3 .mu.m held, its opposed faces 
being formed with transparent electrodes and subjected to orientation 
treatment, as disclosed in Japanese Patent Application Laid-Open No. 
61-94023. 
The features of such a display element using ferroelectric liquid crystal 
include the fact that a bonding strength between an external electric 
field and spontaneous polarization can be used for switching, and that the 
switching can be effected with the polarity of the external electric 
field, as the longitudinal directions of ferroelectric liquid crystal 
molecules corresponds one-to-one to the spontaneous polarization 
directions thereof. The ferroelectric liquid crystal is utilized mainly 
for the binary (white, black) display elements by making two stable states 
of light transparent and interrupting. 
Further, typically, color display apparatus are well known wherein color 
filters of red (R), green (G) and blue (B) corresponding to the size of an 
electrode are provided on the glass substrate, one picture element being 
constituted of three pixels of R, G and B. Also, in order to improve the 
color characteristic of a panel, by providing two G pixels, one picture 
element may be constituted of four pixels of R, G, B and I. Further, in 
order to compensate for decreased brightness of the panel which may be 
caused by the low light transmittance of color filter and liquid crystal 
itself, a color display apparatus has been proposed in U.S. patent 
application Ser. No. 968,402 (filing date Oct. 29, 1992) wherein, by 
providing a white (I) pixel by means of a white color filter, one picture 
element is constituted of four pixels of R, G, B and I. This I pixel acts 
to increase the number of display colors. 
FIG. 2 shows the relationship between the switching pulse amplitude of a 
ferroelectric liquid crystal element and the transmittance. This is a 
graphic representation in which the quantity of transmitted light after 
applying a single pulse with one polarity to a cell (element) in a 
complete light interrupted state (black) is plotted as the function of the 
amplitude V of a single pulse. When the pulse amplitude is equal to or 
less than a threshold V.sub.th (V&lt;V.sub.th), no quantity of transmitted 
light will arise, in which the transparent state of the pixel after 
applying the pulse as shown in FIG. 3B is not different from that of FIG. 
3A indicating a state before applying the pulse. If the pulse amplitude V 
exceeds the threshold (V.sub.th &lt;V&lt;V.sub.sat), a part of the pixel 
transfers to the other stable state, resulting in a light transparent 
state as shown in FIG. 3C indicating a halftone of transmitted light as a 
whole. If the pulse amplitude V is further increased, exceeding a 
saturation value V.sub.sat (V.sub.sat &lt;V), the whole pixel is placed in a 
light transparent state as shown in FIG. 3D, with the quantity of 
transmitted light being fixed. 
As can be seen from FIG. 2 to FIG. 3D, it is requisite that the pulse 
amplitude V be controlled to be V.sub.th &lt;V&lt;V.sub.sat in order to effect 
halftone display in the ferroelectric liquid crystal element. However, 
owing to a steep slope in a range from V.sub.th to V.sub.sat, it is 
difficult to control the halftone correctly with the pulse amplitude V. 
This problem has been described in connection with FLC, but the same thing 
can be said if more halftone levels are to be obtained for a TN liquid 
crystal having no active elements. 
In order to resolve the above problem, a method has been proposed in which 
pseudo-halftone display is enabled by using only two states as shown in 
FIGS. 3B and 3D. At present, most color display systems are constituted by 
CRT as the display apparatus, but when they are constituted by FLC which 
is difficult to make halftone display, instead of CRT, a pseudo-halftone 
display function, as previously mentioned, may be provided within the 
display apparatus for the purpose of providing the compatibility with the 
CRT and the general utilization as the display system, as described in 
U.S. patent application Ser. No. 968,402, cited previously. 
However, the color characteristic of a panel as display means may greatly 
change by the area ratios of pixels such as R, G, B and I, the wavelength 
of backlight or its distribution, but as the display means itself outputs 
no information concerning the color characteristic to the outside, it was 
necessary to change the digital processing for pseudo-halftone display 
depending on the panel to prevent the color tint of an image from varying 
when the display means was changed. 
Also, depending on the display panel such as FLC in particular, the display 
characteristic, particularly the color characteristic sometimes changed 
with the change in temperature caused by the use. 
Further, the display characteristic changed with the filter arrangement or 
dot density of the display panel. 
SUMMARY OF THE INVENTION 
The present invention has been achieved in the light of the above-described 
problem, and its object is to provide a display controller which can 
generate display data in accordance with the condition of display means. 
To accomplish such object, according to the present invention, there is 
disclosed an apparatus for controlling display means comprising, 
receiving means for receiving information relating to a condition of the 
display means, 
generating means for generating image data in accordance with the condition 
of the display means received by said receiving means, and 
supplying means for supplying the image data generated by said generating 
means to the display means as display data. 
Also, it is another object of the present invention to provide a display 
control device which can make the color conversion processing in 
accordance with the color characteristic of the display panel. 
To accomplish such object, according to the present invention, there is 
disclosed an apparatus for controlling display means comprising, 
input means for inputting first color image data, 
converting means for converting the color image data into second color 
image data, 
supplying means for supplying the second color image data to the display 
means as display data, and 
setting means for setting the color converting characteristic of said 
converting means suitable for the display means. 
Further, it is another object of the present invention to provide a display 
system excellent in color reproducibility. 
It is still another object of the present invention to provide excellent 
reproduction of halftone images. 
Other objects and forms of the present invention will be apparent from the 
following description based on the drawings, and the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 is a block diagram of the entire display device. 
In the same figure, 1 is a display control device of an information 
processing system to which the present invention is applied. 
2 is an information supply and image generation source of the information 
processing system 1, including a computer and a personal computer. 
3 is a display panel unit (comprising a ferroelectric liquid crystal as 
mentioned above), one picture element being constituted of four pixels of 
R, G, B and I. Also, a color characteristic discrimination signal 18 is 
output so that the color characteristic determined by the pixel 
configuration (shape, array) of the panel can be discriminated externally. 
The display panel unit 3 includes a drive circuit for driving the panel, a 
control circuit for controlling the panel to be driven in the optimal 
condition, a panel backlight, a power source and so on. 
4 is a CRT signal (display signal) reception unit for receiving a CRT 
signal (image signal or synchronizing signal) and having a feature of 
converting it into a signal suitable for a subsequent processing unit. 
Since the CRT signal of a typical computer is an analog video signal, the 
reception unit 4 includes an A/D converter and a sampling clock generation 
unit for the A/D conversion. 
5 is a color converter which is a main part of the present invention. By 
using R, G, B signals which are converted from a CRT signal into digital 
form, R, G, B and I signals are generated. 
6 is a pseudo halftone processing unit for outputting binary or multi-level 
data, and having a feature of generating a binary or multi-level halftone 
signal from the image signal converted into digital form by the CRT signal 
reception unit 4 and color converted by the color converter 5. An example 
of pseudo halftone display as referred to herein will be shown in the 
following. 
&lt;Error Diffusion Method&gt; 
Binarization or multi-level generation errors arising in converting 
peripheral pixels around a pixel of interest (which are processed before 
the pixel of interest) into binary or multi-level value are weighted, and 
then added to the pixel of interest, so that a threshold is determined at 
which value the binarization or multi-level generation is performed. 
&lt;Average Density Reserve Method&gt; 
Threshold is not constant, but is determined by a weighted average value 
obtained from already converted binary or multi-level data around the 
pixel of interest in the error diffusion method, so that the threshold is 
variable depending on the state of the pixel. 
Besides, a dither method and a density pattern method are provided, 
including a multi-level dither method at multi level, but not limited to 
binary level. 
7 is an image area separation unit (including a simple binarization or 
multi-level generation unit) which separates a portion which should be 
excluded from pseudo halftone display such as characters or fine lines in 
the image information transmitted via the color converter 5 from the CRT 
signal reception unit 4. Also, the image area separation unit 7 includes a 
simple binarization or multi-level generation unit for effecting simple 
binarization or multi-level generation when not performing the pseudo 
halftone processing. An example of an image area separation method in this 
embodiment will be shown below. 
&lt;Luminance Discrimination Separation Method&gt; 
One example of separating means is a separation method based on the 
luminance of a CRT image signal. Typically, the characters and fine lines 
on the computer containing important information on the screen have 
relatively high luminance. Thus, separation is effected by discriminating 
the high luminance portion in the CRT signal. 
8 is a synthesis unit (including switch priority) for synthesizing the data 
obtained in the pseudo halftone processing unit 6 and the simple 
binarization data obtained in the image area separation unit 7. The 
portion discriminated by the image area separation unit 7 is 
preferentially subjected to simple binarization. The user of the display 
system can switch on or off the practice of this priority feature. 
9 is a compression unit, and 10 is an expansion unit. The compression unit 
9 has a function of compressing the amount of information to reduce the 
capacity of the frame memory when storing binary data in binary pseudo 
halftone into the frame memory 12. Also, the expansion unit 10 has a 
function of restoring compressed data, when reading data from the frame 
memory 12. 
11 is a partial write control unit having a function of, in a display 
device having a memory such as FLC, detecting only a rewritten portion of 
the image data in the frame memory, and outputting data of the rewritten 
portion to the display device preferentially. It can also preferentially 
paint the rewritten portion by this function, and is effective for an FLC 
requiring some time to rewrite. 
12 is a frame memory for storing image data necessary for the partial 
rewrite detection. 
13 is a CPU for controlling the computer 2. 
14 is a CPU system memory for controlling the computer 2 comprised of RAM 
and ROM. 
15 is a frame memory for storing image information generated by the 
computer 2. 
16 is a CRT controller for controlling the frame memory 15 for the CRT 
signal. 
17 is a CRT interface for converting image data from the frame memory 15 
into the CRT signal (analog signal). 
Referring now to FIG. 1, the operation will be described below. 
First, the computer 2, which is an image information source, outputs image 
information stored in the frame memory 15 via the CRT interface 17 to the 
CRT under the control of the CRT controller 16 which is controlled by the 
CPU 13. A CRT signal is subdivided into a video signal (three types of 
analog signal of R, G, B provided in the color display, one type of analog 
signal provided in the monochrome display) and a synchronizing signal 
(signals for delimiting the video signal for each line and each frame, 
which are referred to as a horizontal synchronizing signal and a vertical 
synchronizing signal, respectively). The CRT signal is input into the CRT 
signal reception unit 4, the video signal being converted into digital 
signals of R, G and B (each consisting of plural bits). The sampling clock 
at this time is generated by multiplying the horizontal synchronizing 
signal. A digitized video signal is input into the color converter 5. The 
color converter 5 generates and outputs R, G, B and I signals from input 
R, G and B signals. The generated R, G, B and I signals are input into the 
pseudo halftone processing unit 6, and converted into a binary or 
multi-level value. Conversion procedure at this time relies on a 
non-interlace conversion in order to convert a transmitted CRT signal at 
any time, whereby the halftone reproducibility is enhanced as the pseudo 
halftone processing can conduct error distribution and the calculation of 
threshold on principle. 
On the other hand a digital signal with I signal added via the color 
converter 5 from the CRT signal reception unit 4 is input into the image 
area separation unit 7 at the same time, where a portion of the signal 
unsuitable for the pseudo halftone such as characters and fine lines is 
discriminated as previously described in a paragraph of function 
description and converted into binary form with a single threshold or 
multi-level form with a fixed threshold, without being subjected to pseudo 
halftone processing. 
The binary or multilevel signals obtained in the pseudo halftone processing 
unit 6 and the image area separation unit 7 are appropriately switched by 
the synthesis unit 8 to be output to the compression unit 9. This 
switching is made to preferentially output the simple binary or 
multi-level signal obtained in the image area separation unit 7. The 
priority can be compulsorily changed upon a request from the user of the 
display system. This processing is effective when displaying characters 
and fine lines preferentially or when displaying a natural image such as a 
photograph preferentially. 
The compression unit 9 compresses a signal from the synthesis unit 8 and 
stores it in the frame memory 12. The compression method is preferably a 
line unit compression method such as MH as the partial write control is 
for each line. 
The signal from the compression unit 9 is transmitted at the same time to 
the partial write control unit 11. The partial write control unit 11 reads 
a compressed signal at least one frame before from the frame memory 12, 
and compares it with the line transmitted from the compression unit 9. The 
partial write control unit 11 controls the frame memory 12 to detect the 
line containing the different pixel and outputs its line signal to the 
expansion unit 10 preferentially. 
This embodiment may be configured to exclude the compression unit 9 and the 
expansion unit 10. In this case, the signal from the synthesis unit 8 is 
directly written into the frame memory 12, and the signal in the frame 
memory 12 is directly output to the display panel unit 3 under the control 
of the partial write control unit. 
The color converter 5 which is a main portion of the present invention will 
be described below in detail. FIG. 4 is a color converter to which the 
features of the present invention are applied most appropriately. 
The color characteristic discrimination signal 18 is a signal output from 
the display panel unit 3 in FIG. 1, consisting of three bits in this case. 
The color characteristic of the display panel unit is obtained 
theoretically or by measurement, and set at 0 if the color characteristic 
is F.sub.0, or at 1 if it is f.sub.1. In the following, the same rule is 
applied for 2, 3, . . . and with three bits, the panel having up to seven 
kinds of color characteristics can be dealt with. 
The color converter 5 is constituted of a ROM herein. The input (address) 
into the color converter 5 is R, G, B signals output from the CRT signal 
reception unit 4, each consisting of four bits, and a color characteristic 
discrimination signal 18 output from the display panel unit 3, as shown in 
FIG. 1. And R, G, B and I signals are output as the output data. Each 
output signal consists of four bits. 
The internal data of the color converter 5 (ROM) will be described below. 
First, where the color characteristic of the display panel unit is 
f.sub.0, look-up data groups for all the groups of input signal (R, G, B) 
are obtained theoretically or by measurement for the panel display color 
designated by the input signal group and the signal group (R, G, B, I) 
which can approximate most closely or optimally the panel display color or 
desired color among the reproducible colors in the display panel unit. 
Likewise, for f.sub.1 to f.sub.7, the look-up data groups are obtained. 
Obtained data is stored in ROM, and corresponding data is selected by the 
input R, G, B and the color characteristic discrimination signal 18 is as 
the address. 
With the configuration as described above, R, G, B, I signals can be 
reproduced from R, G, B signals. Also, even for a display panel unit 
having different color characteristics, it is possible to deal with the 
display panel unit by using the color characteristic discrimination signal 
output from the display panel unit as the data has been already stored in 
the color converter 17 (ROM). Further, by changing the data in the ROM (or 
replacing the ROM), the color conversion processing can be made 
programmable. And by using a ROM having high speed access time with the 
look-up table method, the color conversion processing can be simply 
implemented in real time. 
While in this embodiment the color converter is constituted of a single 
ROM, it will be appreciated that the color converter may be constituted of 
a separate ROM for each look-up data group of the display panel unit 
having different color characteristics, wherein the ROM is selected by the 
color characteristic discrimination signal 18. 
It will be also appreciated that instead of selecting the ROM, the CPU in 
the display control unit may discriminate the look-up table group in 
accordance with the color discrimination signal 18, wherein the data is 
set in RAM. 
Also, the color characteristic discrimination signal only needs to indicate 
the color characteristic of the display panel, as mentioned above. For 
example, when the color characteristic of the display panel varies with 
the temperature, the temperature information may be used as the 
discrimination signal. 
As described above, according to the embodiment of the present invention, I 
signal can be generated from R, G, B signals, whereby it is possible to 
exploit the feature of display means containing I signal simply by using 
the conventional CRT signal without any change. Also, to cope with the 
change in color characteristic of the display means, the look-up table can 
be used programmably and in real time. 
As described above, according to the present invention, the color 
conversion processing is allowed in accordance with the color 
characteristic of the display panel. 
It should be noted that the image area separation method is not limited to 
that of the above embodiment, but may be implemented by utilizing the 
spatial frequency component. 
Also, the color component conversion is not limited to a conversion from 
RGB into RGBI, but may be effected from RGB to R'G'B', or from YIQ to RGB, 
for example. 
The image processing may be changed depending on the temperature 
characteristic of the display panel, as well as the color decomposition 
filter arrangement, the array of display elements or its density. 
The present invention is not limited to the above embodiment, but various 
variations and modifications can be made within the scope of the claims.