Color image forming apparatus

A color image forming apparatus having inputting means for inputting conditions of factors (lighting condition, region, color of eyes, season and date) determining the impression of a color image on an observer. The apparatus further has adjusting means for adjusting at least one of parameters (shading correction data, a reflectance-density conversion characteristic, a UCR/BP characteristic, a masking coefficient, color balance data and .gamma. correction data) of an image processing unit to the input conditions.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a color image forming apparatus which 
forms a full color image on a sheet by electrophotography. 
2. Description of Related Art 
Generally, people have different impressions of a color image depending on 
various factors. The observing conditions (lighting condition, season, 
etc.), the color of the observer's eyes, the observer's sex, the 
observer's age, the observer's psychological conditions, etc. may be the 
factors. For example, a color image which makes a favorable impression on 
Japanese may be reddish and unfavorable to Westerners. Also, it is 
probable that a color image makes a favorable impression on a person in 
summer and an unfavorable impression on the same person in winter. 
In the art of color copying machine and color printer, the relation between 
the factors and the impression of a color image has been studied, and the 
study starts to be used practically. For example, the masking coefficient, 
which is one of the parameters of color correction in making print data 
from image data indicating the three primary colors, is set to a value 
which makes a favorable image to Japanese or to a value which makes a 
favorable image to Westerners according to the destination of the 
apparatus. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a color image forming 
apparatus which forms a favorable color image to the observer in a simple 
process. 
In order to attain the object, a color image forming apparatus according to 
the present invention comprises: inputting means for inputting a condition 
of a factor determining the impression of a color image; and adjusting 
means for adjusting at least one of parameters of image processing means, 
which makes print data from image data indicating the three primary 
colors, to the condition input by the inputting means. 
The factors are the lighting condition (sunlight, incandescent lamp, 
fluorescent lamp, etc.) of a formed image, the region where the color 
image forming apparatus is installed (Asia, Europe, North America, South 
America, Africa, etc.), the color of the observer's eyes (black, blue, 
brown, green, etc.) and the season or the date when the formed image is 
observed. The parameters of the image processing means are shading 
correction data, a reflectance-density conversion characteristic, a UCR/BP 
characteristic, a masking coefficient, color balance data and .gamma. 
correction data. 
Input of a condition of the factor into a control section of the image 
forming apparatus is carried out by use of the inputting means provided on 
an operation panel of the image forming apparatus or by use of a magnetic 
card stored with data about the factor. 
In this way, from the same image data, color images which are favorable to 
different observers in different conditions can be formed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A preferred embodiment of the present invention is hereinafter described 
with reference to the accompanying drawings. In the embodiment, the 
present invention is applied to a digital full color copying machine 
provided with an image reader. 
As shown in FIG. 1, the full color copying machine has an image reading 
section 1 and a laser beam optical scanning system 10 in the upper part, a 
full color image forming section 20 in the middle part and a sheet feeding 
section 50 in the lower part. 
The image reading section 1 comprises an image reader unit 2 which is 
movable in the right and the left in FIG. 1 and an image processing unit 7 
which converts image data read by the image reading unit 2 into print data 
used for image formation. The image reading unit 2 comprises an exposure 
lamp 3 for illuminating a document set on a platen glass 9, a rod lens 
array 4 for converging a light reflected from the document, and a contact 
type CCD color sensor 5 for converting the light into an electric signal. 
The image reading unit 2 stands by at a home position which is in the 
right in FIG. 1 and scans an image of the document while moving in a 
direction indicated with arrow a. During the scanning, the image reading 
unit 2 reads the image as image data of the three primary colors, R (red), 
G (green) and B (blue). The image processing unit 7 converts the image 
data of R, G and B into print data of four colors, C (cyan), M (magenta), 
Y (yellow) and Bk (black). 
The laser beam optical scanning system 10 comprises a laser control unit 
11, a laser source (not shown), a polygonal mirror 12, an f.theta. lens 
13, a mirror 14, etc. The laser source emits a laser beam in accordance 
with the print data of each of the colors C, M, Y and Bk transmitted from 
the image processing unit 7. The laser beam is deflected in a plane by the 
polygonal mirror 12 which rotates at a constant speed. Then, the laser 
beam passes through the f.theta. lens 13 and the mirror 14 and is imaged 
on a photosensitive drum 21 which rotates in a direction indicated with 
arrow b. Thus, an electrostatic latent image is formed on the 
photosensitive drum 21. 
The main components of the full color image forming section 20 are the 
photosensitive drum 21 and a transfer drum 25. Around the photosensitive 
drum 21, there are provided an electric charger 22, a developing unit 23, 
a transfer drum 25, a residual toner cleaner 26 and an eraser lamp 27 for 
erasing residual charge. In the developing unit 23, four developing 
devices 23Y, 23M, 23C and 23Bk which use a developer containing yellow 
toner, a developer containing magenta toner, a developer containing cyan 
toner and a developer containing black toner respectively are arranged one 
upon another. Each time an electrostatic latent image in accordance with 
the print data of each color is formed on the photosensitive drum 21, the 
corresponding developing device 23Y, 23M, 23C or 23Bk operates to develop 
the latent image. The yellow toner, the magenta toner, the cyan toner and 
the black toner are contained in hoppers 24Y, 24M, 24C and 24Bk 
respectively, and when a toner replenishment signal is generated from 
toner density detecting means (not shown), the required toner is 
replenished from the corresponding hopper 24Y, 24M, 24C or 24Bk to the 
corresponding developing device 23Y, 23M, 23C or 23Bk. 
The transfer drum 25 is driven to rotate in a direction indicated with 
arrow c in synchronization with the photosensitive drum 21. Inside and 
outside of the transfer drum 25, there are provided a chuck claw 30 for 
holding the leading edge of a sheet, a sucking charger 31 for sucking the 
sheet onto the surface of the transfer drum 25, transfer chargers 32 and 
33 for transferring toner onto the sheet, erasing chargers 34 and 35 for 
erasing charge, a separation pawl 36 for separating the sheet from the 
transfer drum 25 and a residual toner cleaner 37. 
In order to form a full color image, toner images of Y, M, C and Bk are 
formed on the photosensitive drum 21 and transferred onto a sheet which 
winds around the transfer drum 25 one by one. When all the four images are 
transferred onto the sheet and combined thereon, the separation pawl 36 
operates to separate the sheet from the transfer drum 25. Also, the 
cleaner 37 operates to remove residual toner on the transfer drum 25. 
The sheet feeding section 50 has automatic feed trays 51 and 52 which 
contain sheets of specified sizes respectively. Sheets are fed one by one 
from the tray 51 or 52 which is selected by the operator, and each sheet 
fed from the tray 51 or 52 is transported to the transfer drum 25 by a 
number of rollers. Additionally, the copying machine is provided with a 
manual feed tray 53 such that the operator can manually feed a sheet to 
the image forming section 20. 
The sheet separated from the transfer drum 25 is fed to a fixing device 42, 
where the toner is fixed on the sheet, via a conveyer belt 41. Thereafter, 
the sheet is ejected onto an ejected-sheet tray 45 by an ejection roller 
pair 44. 
Next, referring to FIG. 2, an operation panel 60 of the full color copying 
machine is described. 
The operation panel 60 has the following input means and indication means: 
a copying start key 61 for starting a copying operation; 
a ten-key 62 for setting the number of copies and the magnification; 
a clear/stop key 63 for clearing the set number and stopping a multiple 
copying operation; 
an interrupt key 64 for discontinuing a multiple copying operation to 
handle another copying operation; 
an all reset key 65 for resetting all the input to return the copying 
conditions to initial states; 
a liquid crystal display 66 for displaying pictures shown in FIGS. 3, 4, 
20, 21 and 23 to set copying conditions; 
dials 67 and 68 for making a selection between optional items displayed on 
the liquid crystal display 66, each of the dials 67 and 68 incorporating a 
rotary encoder; 
function keys 71, 72, 73 and 74 for changing pictures on the liquid crystal 
display 66; 
a cancel key 75 for canceling the selection made on the liquid crystal 
display 66; and 
a set key 76 for confirming the selection made on the liquid crystal 
display 66. 
The liquid crystal display 66 displays a picture of FIG. 3 in the initial 
state. In this state, the magnification, the sheet size, the image 
density, etc. can be set. 
The function keys 71 through 74 are used for setting of copying conditions 
to make a color image which will make a favorable impression on the image 
observer. 
When the function key 71 is turned on, the liquid crystal display 66 
displays a picture of FIG. 4. In this state, the lighting condition in 
which the color image is to be observed can be set. On the picture, six 
items "standard", "incandescent lamp", "sunlight", "fluorescent lamp 
(red)", "fluorescent lamp (white)" and "fluorescent lamp (blue)" are 
indicated, and by use of the dials 67 and 68, the operator can select one 
of these. FIG. 4 shows a state that "fluorescent lamp (white)" is 
selected. In the initial state, "standard" is selected, and the image 
processing unit 7 makes print data to make a color image which will makes 
a favorable impression under white light. The light source which 
illuminates a color image influences the color temperature and the 
spectral distribution, and the same color image makes different 
impressions on an observer in different lighting conditions. FIG. 5 shows 
the spectral intensity characteristic of the sunlight (curve A) and that 
of a fluorescent lamp (white) (curve B). Likewise, the other kinds of 
lights each have a peculiar spectral intensity characteristic, and the 
image processing unit 7 adjusts image data to the selected lighting 
condition. 
Referring to FIG. 6, the image processing unit 7 is described in more 
detail. The image processing unit 7 comprises an A/D converting section 81 
which converts image data sent from the CCD color sensor 5, a shading 
correcting section 82, a density converting section 83, a black generating 
section 84, a color correcting section 85, an MTF correcting section 86, a 
magnification changing section 87, a color balancing section 88 and a 
.gamma. correcting section 89. The image processing unit 7 has a ROM 92 
which is stored with shading correction data including adjustment data 
which are used to adjust image data to the lighting condition. The ROM 92 
is controlled by a controller 91 which is driven in accordance with a 
signal sent from the operation panel 60. When the operator sets the 
lighting condition with the picture of FIG. 4 in the above-described 
manner, the controller 91 receives a signal from the operation panel 60 
and commands the ROM 92 to send shading correction data suitable for the 
lighting condition to the shading correcting section 82. Eight-bit data 
(r, g, b) quantized by the A/D converting section 81 are provided with 
shading correction data (R, G, B), and data (R, G, B) are made as follows: 
EQU R=r.times.(R/M) 
EQU G=g.times.(G/M) 
EQU B=b.times.(B/M) 
M: integer 
FIG. 7a shows shading correction data in the standard lighting condition. 
FIG. 7b shows shading correction data to enhance yellow, and these data 
are used when "fluorescent lamp (blue)" is selected. FIG. 7c shows shading 
correction data to enhance blue, and these data are used when 
"incandescent lamp" is selected. These and other correction data suitable 
for the respective lighting conditions are stored in the ROM 92, and the 
data are sent to the shading correcting section 82 in accordance with the 
input with the picture of FIG. 4. 
Also, as shown in FIG. 8, the adjustment of image data to the lighting 
condition may be made in the density converting section 83. In this case, 
a reflectance-density conversion ROM 93 is stored with reflectance-density 
conversion data including adjustment data which are used to adjust image 
data to the lighting condition, and the ROM 93 sends reflectance-density 
conversion data suitable for the lighting condition to the density 
converting section 83 under the control of the controller 91. FIG. 9a 
shows reflectance-density conversion data in the standard lighting 
condition, and these data are indicated by a monotonous decreasing curve 
substantially expressed by Y=-logX. FIG. 9b shows reflectance-density 
conversion data to enhance yellow, and these data are used when 
"fluorescent lamp (blue)" is selected. FIG. 9c shows reflectance-density 
conversion data to enhance blue, and these data are used when 
"incandescent lamp" is selected. These and other reflectance-density 
conversion data suitable for the respective lighting conditions are stored 
in the ROM 93, and the data are sent to the density conversion section 83 
in accordance with the input with the picture of FIG. 4. 
Further, as shown in FIG. 10, the adjustment of image data to the lighting 
condition may be made in the black generating section 84. Generally, in 
forming a full color image from four colors of yellow (Y), magenta (M), 
cyan (C) and black (Bk), a high density region is reproduced by using Bk 
as well as Y, M and C. Originally, any color can be made from three colors 
of Y, M and C. However, in order to improve the reproductivity of a high 
density region, the amounts of Y toner, M toner and C toner are reduced by 
under color removal (UCR) and Bk toner is added. The ratio of the total 
amount of reduced Y, M and C toners (UCR) to the amount of added Bk toner 
(BP) influences the chromaticity of the reproduced image as shown in FIG. 
11. In making the adjustment in the black generating section 84, the 
relation between the ratio of UCR to BP and the chromaticity of the 
reproduced image as shown by FIG. 11 must be considered. In a judging 
section 95, judgment of an achromatic color or a chromatic color is made 
from the data (R, G, B) obtained after the shading correction, and the 
chromaticity is corrected by UCR/BP correction data stored in a UCR/BP 
control ROM 96. The UCR/BP correction data are practically curves C.sub.1, 
C.sub.2 and other curves converted from a standard UCR/BP (%) 
characteristic curve C. With a correction in accordance with the curve 
C.sub.1, the reproduced color shifts to a chromatic side, and with a 
correction in accordance with the curve C.sub.2, the reproduced color 
shifts to an achromatic side. 
Further, in this embodiment, another judging section 97 is provided. The 
judging section 97 judges the chromaticity from the data (R, G, B) 
obtained after the shading correction, and in the black generating section 
84, the chromaticity is corrected by UCR/BP correction data stored in a 
UCR/BP control ROM 98. The correction data stored in the ROM 98 are 
practically a curve D.sub.1 (see FIG. 13a) to make reddish colors clearer 
than a standard characteristic curve D, a curve D.sub.2 (see FIG. 13b) to 
make greenish and bluish colors clearer, and other characteristic curves. 
The UCR/BP control ROMs 96 and 98 are also stored with adjustment data 
which adjust the UCR/BP characteristic curves to the respective lighting 
conditions. The ROM 96 and the ROM 98 are switched for use by a selector 
94 which is controlled by the controller 91. 
FIG. 14 shows a case in which the adjustment of image data to the lighting 
condition is made in the color correcting section 85. A masking operation 
is carried out here. Data of a linear image are processed as follows: 
##EQU1## 
Coefficients of matrices 3.times.3 n (n: integer) are set such that the 
color difference between an original image and a reproduced image will be 
minimized in certain conditions. The coefficients are stored in a masking 
coefficient ROM 101. The ROM 101 is controlled by the controller 91, and 
in accordance with the lighting condition input on the operation panel 60, 
a set of coefficients suitable for the lighting condition is sent to the 
color correcting section 85. 
FIG. 15 shows a case in which the adjustment of image data to the lighting 
condition is made in the color balancing section 88. Regarding the tone, 
the color balancing section 88 reverses the image data of the four colors 
C, M, Y and Bk such that the tone characteristic will be expressed by a 
straight line as shown in FIG. 16, and the reversed data are sent from the 
image processing unit 7 to the laser beam optical scanning system 10 as 
print data. With respect to each of the colors C, M, Y and Bk, the 
reversal of the tone, in the standard condition, is carried out such that 
the tone of the original image and that of the reproduced image will be at 
a ratio of 1:1 as expressed by a line E at an angle of .theta. shown in 
FIG. 17a. A change in color balance is made as follows. For example, if 
the reversal of the tone of yellow is carried out according to a line 
E.sub.1 at an angle of .theta..sub.1 shown in FIG. 17b, yellow will be 
enhanced on the reproduced image. Also, if the reversal of the tone of 
yellow is carried out at the ratio of 1:1 and the reversal of the other 
colors C, M and Bk is carried out with an offset x as expressed by a line 
E.sub.2 in FIG. 17c, yellow will be enhanced on the reproduced image. It 
is possible to change the color balance in any desirable way by combining 
these two methods. 
Color balance correction data suitable for the respective lighting 
conditions are stored in a color balance data ROM 102. The ROM 102 is 
controlled by the controller 91 and sends correction data suitable for the 
lighting condition input on the operation panel 60 to the color balancing 
section 88. 
FIG. 18 shows a case in which the adjustment of image data to the lighting 
condition is made in the .gamma. correcting section 89. .gamma. correction 
is to change the relation between the amount of an output of print data C, 
M, Y or Bk and a target density (tone characteristic). FIG. 19a shows 
.gamma. correction data in the standard condition. With the data, the 
density is proportional to the amount of an output of print data. Both 
FIGS. 19b and FIG. 19c show .gamma. correction data to enhance yellow. 
According to FIG. 19b, with the same amount of output print data, yellow 
is reproduced more densely than the other colors C, M and Bk. According to 
FIG. 19c, the colors C, M and Bk are reproduced more thinly than in the 
standard condition, while yellow is reproduced with the same density as in 
the standard condition. 
.gamma. correction data suitable for the respective lighting conditions are 
stored in a .gamma. correction data ROM 103. The ROM 103 is controlled by 
the controller 91 and sends .gamma. correction data suitable for the 
lighting condition input on the operation panel 60 to the .gamma. 
correcting section 89. 
In this way, in order to make a favorable image, one of the parameters 
(shading correction data, reflectance-density conversion characteristic, 
UCR/BP characteristic, masking coefficient, color balance data and .gamma. 
correction data) of the image processing unit 7 is adjusted to the 
lighting condition of a reproduced image which is set with the picture of 
FIG. 4. Further, two or more of the parameters may be changed for the same 
purpose. 
Additionally, by using the function key 72, the region where the color 
copying machine is installed can be input, and one of the parameters is 
changed in accordance with the input data. When the function key 72 is 
turned on, a picture of FIG. 20 appears on the display 66. The world is 
divided into ten regions, and the regions are provided with numerals 1 
through 10. By use of the dials 67 and 68, one of the regions can be 
selected. The designated number is inversion-indicated. In FIG. 20, 1 
"East Asia" is designated. It is known that people have a characteristic 
feeling about colors in each region of the world. The ROM 101 (see FIG. 
14) is also stored with masking coefficients suitable for the 
characteristic feelings of people in the different regions, and image data 
are corrected with a masking coefficient suitable for the designated 
region. Further, it is also effective to adjust another parameter to the 
region. 
Additionally, by using the function key 73, the season when a reproduced 
image is to be observed can be input, and one of the parameters is changed 
in accordance with the input data. When the function key 73 is turned on, 
a picture of FIG. 21 appears on the display 66. Seasons including 
in-between seasons are indicated on the picture, and one of them is 
selected by use of the dials 67 and 68. The season indicated with a lit 
indication segment is selected. In FIG. 21, "summer" is selected. 
As shown in a chromaticity diagram of FIG. 22, taste in colors in summer is 
in the chromatic side compared with that in winter. The marks "sky in 
summer" and "sky in winter" in the diagram indicate colors to be 
reproduced from the same color of the sky which is read by the CCD color 
sensor 5 such that the reproduced colors will make a favorable impression 
to the observers in summer and in winter respectively. The ROM 101 (see 
FIG. 14) is stored with making coefficients suitable for the seasons, and 
image data are corrected with a masking coefficient suitable for the 
designated season. Further, it is effective to adjust another parameter to 
the season. 
A calendar can be incorporated in the control section of the machine as 
well as or instead of the season input means. The calendar recognizes the 
date, and the date of image formation is automatically transmitted to the 
controller 91. The image processing unit 7 carries out image processing 
with correction data suitable for the season. 
Furthermore, by using the function key 74, one of the parameters can be 
changed in accordance with the color of the observer's eyes. When the 
function key 74 is turned on, a picture of FIG. 23 appears on the display 
66. One of black, brown, green, blue and in-between colors can be selected 
by use of the dials 67 and 68. The color indicated with a lit indication 
segment is selected. In FIG. 23, brown is selected. 
People with eyes of different colors have different sensitivities to 
colors. For example, people with blue eyes are highly sensitive to reddish 
and yellowish colors. The ROM 101 (see FIG. 14) is stored with masking 
coefficients suitable for different colors of eyes, and the image 
processing is carried out with a masking coefficient suitable for the 
input color of eyes. It is effective to adjust another parameter to the 
color of eyes. 
In the embodiment, factors determining the impression of a reproduced image 
are input on the display 66 of the operation panel 60. It is also possible 
to provide the operation panel 60 with magnetic card reading means for 
reading data about the factors stored in a magnetic card 77 (see FIGS. 8, 
10, 14, 15 and 18). 
Although the present invention has been described in connection with the 
preferred embodiment above, it is to be noted that various changes and 
modifications are possible to those who are skilled in the art. Such 
changes and modifications are to be understood as being within the scope 
of the present invention. 
The present invention is applicable not only to a color copying machine 
which directly reads an original image and reproduces the image but also 
to a color printer which makes an image from image data transmitted from a 
host computer. The image processing unit 7 may comprise other components.