Color correction device for a color image forming apparatus

A color image processing apparatus including an image-reading device for reading a color image on an original to obtain first color image data, an image memory which stores the first color image data, and a factor memory which stores a predetermined correction factor. A color correction system corrects the first color image data with the correction factor. An image-producing apparatus produces a color copy image on the basis of the corrected first color image data, where the image-reading device reads the color copy image to obtain second color image data. The image-processing apparatus further includes a processing member which performs a comparison between the first color image data stored and changes the correction factor on the basis of the comparison.

BACKGROUND OF THE INVENTION 
The present invention relates to a color image forming apparatus that forms 
a color image by sequentially forming toner images on an image carrying 
member, and that is used in the industrial fields of electrostatic 
recording and electrophotography. 
It has been conventional practice, in forming a color image by 
electrophotography, to repeat electrifying, imagewise exposing, 
developing, and transferring for every independent color component and 
form the respective color toner images that are aligned in an overlapping 
manner on a copying sheet. More specifically, to form a color image, that 
is, to form respective color toner images of yellow (Y), magenta (M), cyan 
(C), and black (BK) toners using the light modulated based on the color 
information data derived from a color document, the above-mentioned 
process is repeated four times. Such a color image forming system, 
however, requires that every toner image should be transferred onto a 
transfer member every time the independent toner image has been developed. 
Thus, such an image forming system has problems, including a larger 
copying apparatus, a complicated recording process, and disadvantageously 
long copying time. Other disadvantages include an inferior color image 
formed due to misalignment of transferred toner images, since the 
respective color toner images are independently transferred onto a 
recording sheet in independent transferring processes. 
To overcome such disadvantages, there is a color image forming method 
wherein a plurality of toner images formed on a common photosensitive 
member are simultaneously developed in order to perform a transferring 
process at once. This method, however, still has disadvantages; a toner 
image previously developed is spoiled when another toner image is 
developed, or, color balance on a final image is deteriorated because a 
toner of a former image is blended with a developer for an image later 
formed. 
To overcome such disadvantages, there is proposed a method in Japanese 
Patent Publication Open to Public Inspection (hereinafter referred to as 
Japanese Pat. O.P.I. Publication) No. 144452/1981, wherein developing 
performed while a photosensitive member is not allowed to come into 
contact with the turf of a developer layer. In this developing method, the 
operation of an AC bias applied allows a toner contained in a developer to 
jump to the photosensitive member, whereby developing is performed on the 
non-contactive basis. 
The principle of image forming method according to the developing method 
disclosed as above is hereunder described. The flowchart in FIG. 19 shows 
the change in surface potential on a photosensitive member where positive 
polarity charging is performed and developing is also performed using a 
toner of positive polarity. PH represents an exposing area on the 
photosensitive member; DA, a non-exposing area on the photosensitive 
member; DUP, an increase in potential caused because the positively 
charged toner T has been deposited on the exposing area PH in the first 
developing; CUP, an increase in potential on the exposing area PH due to 
the second electrifying. 
The photosensitive member is subjected to uniform electrifying using a 
Scorotron electrifier, and endowed with a uniform surface potential E. The 
surface potential E in the exposing area PH drops to near-zero level by 
the first image exposing using irradiation of an exposing light source 
such as a laser, cathode ray tube, and light-emitting diode. The positive 
bias, of which DC component being virtually equal to the surface potential 
E on an unexposed area, is applied onto a developing unit, and developing 
is performed, whereby the positively charged toner in the same developing 
unit adheres onto the exposing area PH that has a relatively low 
potential, and, as a result, a first positive image is formed. The 
potential on the area where the positive image has been formed rises by a 
DUP due to the positively charged toner adhering thereon. Next, when the 
second electrifying is performed on the Scorotron electrifier, the surface 
potential further rises by a CUP, thereby the surface potential E reaches 
a level approximately same as that of the non-exposing area DA. The 
surface of photosensitive member endowed with the uniform surface 
potential E is subjected to the second imagewise exposing to form an 
electrostatic latent image which is developed in a manner previously 
mentioned to form the second positive image. 
When the above procedure is repeated it forms overlapping forms toner 
images on the photosensitive member, and a single color toner image is 
obtained. The color toner image is then transferred onto a recording 
sheet, thereby fixed by pressure or by heating, to form a color image. At 
this time, the toner and potential present on the photosensitive member 
are removed and neutralized correspondingly, in order to prepare next 
color image forming. In addition, the previously mentioned color image 
forming method can incorporate the neutralizing process prior to the 
electrifying process. Furthermore, a common exposure light source or 
different light sources may be used for respective image exposing. 
Incidentally, in a color image forming method, when reproducing color tones 
by overlapping three primary colors, namely, Y, M and C, the BK component 
is theoretically deemed unnecessary based on the principle of subtractive 
color reproduction. However, when reproducing a sharp image such as a 
character or line drawing, it is necessary to enhance black compared to 
the three primary colors. For such a purpose, forming black by overlapping 
the three primary colors is insufficient. This problem is attributable to 
the fact that the three primary color toners in practical application do 
not have an ideal absorption wavelength region, and that a minor 
misalignment is inevitable since strictly aligning toner images of three 
primary colors is impossible. Additionally, in the additive color 
reproducing process, there is problem such as insufficient image density 
attributable to the same reasons. Accordingly, in forming a color image, a 
developing unit containing a black toner is usually incorporated. 
In forming a color image according to electrophotography, two methods are 
generally available: a normal developing method where developing is 
performed on an electrostatic image on a photosensitive member using a 
toner having a polarity reverse to that of the electrostatic image, and a 
reverse developing method where an electrostatic image is developed using 
a toner having a polarity common with that of the electrostatic image. The 
reverse developing method is advantageous in that unlike the normal 
developing method that necessitates a background of image which is 
continuously exposed, this method only requires the area where a toner 
adheres solely exposed. Therefore, strict mechanical precision is not 
required of the associated optical system and the service life of 
photosensitive member tends to be longer since the member is less 
frequently subjected to fatigue, and since the electrical potential on the 
photosensitive member and the toner adhering thereon are of a common 
polarity. 
Accordingly, a recording apparatus having an exposing light source such as 
a laser, cathode ray tube, and light-emitting diode often incorporates the 
reverse developing method. However, forming a color toner image on a 
photosensitive member in compliance with the reverse developing method 
incurs the following problem. An area where a toner adhered by a prior 
developing does not readily allow the imagewise exposing light to be 
transmitted. Even if such light has been transmitted, the surface 
potential on the photosensitive member does not decrease because of the 
potential on the toner image. Accordingly, a toner does not readily adhere 
onto the member in development later performed. In the additive color 
reproducing method, similar problems occur since perfect alignment, as 
well as perfect developing in compliance with the nature of independent 
latent image, are difficult. Accordingly, a desirable color image is not 
formed when intending to reproduce various color tones, because of 
deteriorated color balance or since the image is disturbed around the edge 
portions. 
In summary, in image reproducing the need exists for image processing that 
eliminates the previously mentioned effects regarding the toner images. 
However, in electrophotography, the charge potential on a photosensitive 
member, charge level on a toner, and amount of a toner adhering onto the 
member vary depending on ambient conditions or in the course of service 
life. Accordingly, it is quite difficult to control these factors 
satisfactorily. 
Because of these reasons, a user had to manually adjust color balance among 
Y, M and C color components by comparing an original document with a 
resultant duplicate. Accordingly, the user has had to make several 
duplicates while seeking optimum color balance. 
SUMMARY OF THE INVENTION 
The object of the present invention is to achieve color reproduction of 
high fidelity, or to achieve color reproduction of high fidelity in a 
designated area. More specifically, the object of the invention is to 
provide a color image forming apparatus that forms a vivid color image 
with good color balance and free from imaging failure, by comparing an 
original image with a duplicated image to correct and modify the tone and 
gradation in image data, and by using the modified data to form a color 
image. 
This object of the invention is attained by a color image forming apparatus 
comprising image reading means, means for performing color correction on 
image data including information on a plurality of colors, means for 
forming a latent image on an image carrying member based on the results of 
color correction performed by the aforesaid means, and a plurality of 
developing means for developing, by the using color toners, the latent 
image formed by aforesaid means, whereby a color image is formed by 
sequentially forming a plurality of independent toner images on the image 
carrying member, wherein the above-mentioned color correction means has an 
arithmetic processing portion for changing tone and gradation in the 
above-mentioned image data by the comparing the image data of the 
duplicate with those of the original document. 
The color image forming apparatus of the invention is a copying apparatus 
comprising image reading means and color image output means, wherein both 
the data of original document and those of duplicate are input by the 
image reading means, and both sets of image data are compared with each 
other for color correction. The color correction feature is used in the 
following manner: 
(i) A specific area on a document is entered by area designating means, 
whereby color reproduction on the designated area is given a priority of 
attaining color balance to other areas, or, otherwise, image correction is 
performed solely on an independently designated area; 
(ii) Using a color control chart as a document allows correction on overall 
color balance. Deliberately selecting a color control chart can perform 
correction as intended. For example, when correcting colors on characters 
or illustration, a chart containing Y, M, C, B (blue), G (green), R (red), 
and BK (black) is used; when performing gradation correction for a 
photograph, for example, a chart including a gray scale and varied 
densities is used. 
(iii) In these correction procedures, correction parameters obtained by 
arithmetic operations are stored in a memory.

DETAILED DESCRIPTION OF THE INVENTION 
The preferred embodiments according to the invention are hereunder 
described. 
In the image forming apparatus in FIG. 1(a), numeral 1 represents a 
drum-shaped image carrying member comprising a photoconductive 
photosensitive layer made, for example, of Se and rotatable in the arrow 
direction; 11 and 12, electrifiers for uniformly electrifying the surface 
of the image carrying member 1; 21 and 22, imagewise exposing areas for 
independent color toner images; 31 through 34, developing units, 
respectively, having differently colored toners, i.e, toners of cyan (C), 
magenta (M), yellow (Y), and black (BK); 13 and 41, respectively, a 
pre-transfer electrifier and a pre-transfer exposing lamp each provided in 
compliance with a specific requirement in order to allow a color image, 
that comprises a plurality of color toner images in an overlapping formed 
on the image carrying member, to be readily transferred onto a transfer 
member P, or to allow the transfer member P to be readily separated from 
the image carrying member; 14, a transferring unit; 61, a fixing unit that 
fixes a toner image having been transferred onto the transfer member P; 42 
and 45, neutralizing lamps or neutralizing corona dischargers, one type of 
which may be used, or both types of which may be used in combination. 
Numeral 16 represents a neutralizing electrode for sheet separation; 51, a 
cleaning unit having a cleaning blade on fur brush that comes in contact 
with the surface of the image carrying member 1 in order to remove a toner 
remaining on the same surface from which the color image has been 
transferred, and that leaves from the surface of the image carrying member 
1 by the time the area which has undergone the first developing reaches 
the area corresponding with the same unit. 
If the electrifiers 11 and 12 are of a type that additionally electrify the 
already electrified surface on the image carrying member 1, it is 
particularly favorable to use a Scorotron discharger, for example as shown 
in the figure, which is less affected by previous electrification and 
capable of providing stable electrification. Additionally, in such an 
image forming apparatus as shown here and having the drum-type image 
carrying member 1, the imagewise exposing lights 21 and 22 can be those 
formed by separating slit exposing light into independent color components 
using a filter as used in the case of a conventional monocolor 
electrophotographic copying apparatus. However, to reproduce a vivid color 
image, it is preferable that the imagewise exposing lights be laser beam 
scanners shown in FIGS. 4(a), (b) and (c) where imagewise exposing is 
performed and a resultant latent image is reverse-developed. When using 
the laser beam scanners shown in FIGS. 4(a) and (b) for forming the 
imagewise exposing light 104, it is possible to readily form a plurality 
of latent images of different colors at different timing, and, therefore, 
to reproduce a vivid color image. 
The apparatus in FIG. 1(b) is different from that of FIG. 1(a) in that in 
the former apparatus, infrared LEDs 71 and 72 are used to perform uniform 
exposing. This arrangement is effective for a photosensitive member of 
greater light memory property. 
The infrared LEDs 71 and 72, respectively, have a characteristic wavelength 
allowing the light emitted to pass through the already deposited toner. 
In the laser beam scanner of FIG. 4(a), a laser beam is emitted from laser 
121, such as a He--Ne laser. The laser beam is thereby intermittently 
transmitted by an acoustic optical modulator 122 and deflected by a mirror 
scanner 123 that is rotated by a driving motor 130 and comprises an 
octahedral rotatable polygon mirror, and is thereby directed through a 
focalizing f-.theta. lens 124. The beam comprises an imagewise exposing 
light 104 that scans the surface on the image carrying member 1 at a 
constant velocity. Numerals 125 and 126 represents mirrors; 127, a lens 
that optimizes the diameter of beam directed to the focalizing f-.theta. 
lens 124. A laser beam scanner having the arrangement in FIG. 4(b) is also 
advantageous, wherein a laser beam generated by a semiconductor laser 221 
is reflected by a polygon mirror 223 that is rotatably driven by a driving 
motor 230. The beam transmitted via a f-.theta. lens 224 is thereby 
deflected by a reflector mirror 237, and projected onto the surface of the 
image carrying member 1 and forms an emission line. Numeral 234 represents 
an index sensor that detects the beam position in order to control the 
initiation of beam-scanning; numerals 235 and 236 are cylindrical lenses 
for correcting inclination angles. Numeral 238a, 238 b, and 238c represent 
reflector mirrors that compromise both a beam scanning path and a beam 
detection path. When using the laser beam scanner described in Japanese 
Pat. Application No. 239469/1986 filed by the present applicant, as well 
as an insulating plate, such as a optical deflector 223' processed by 
etching a crystal plate, the bidirectional scanning is enabled, unlike the 
scanning with a rotating polygon mirror. When performing such 
bidirectional scanning, the optical scanning system can have an 
arrangement for example, shown in FIG. 4(c). 
More specifically, by disposing index sensors 234 and 234' in the forward 
and rear zones on scanning direction, the start and end (the "end" may be 
deemed the "start" of scanning, since the beam starts return pass) of one 
forward scanning pass using a laser beam can be detected, and, 
accordingly, the relevant image information is recorded on the image 
carrying member 1. 
In FIG. 4(c), numerals 238c and 238c' respectively represent a reflector 
mirror. 
Once scanning starts, the beam is detected by the index sensor 234 or 234', 
and an unshown modulator starts modulating the beam based on the first 
color signal. The modulated beam scans the surface of the image carrying 
member 1 that has been already uniformly electrified with the electrifier 
11 or 12. Then, a latent image corresponding with a first color is formed 
on the surface of the drum with the main scanning by the laser beam 104 
and with the sub-scanning by rotation of the image carrying member 1. 
Additionally, the imagewise exposing light 104 is not limited only to the 
above-mentioned dot exposing using a laser beam, and can be one using, for 
example, an LEd, CRT, liquid crystal, or fiber optics. The image forming 
apparatus according to the invention can be a recording system having a 
belt-configured image carrying member. 
In the image reader on FIG. 2, numeral 37 represents a document presser 
that presses a document 1 against a platen; 38a, 38b, and 38c, 
respectively, a reflector mirror that reflects light L obtained when 
subjecting the document 1 to imagewise exposing using an exposing lamp 2. 
The light L reflected by the group of reflector mirrors is converged by a 
lens 3 and directed to a linear image sensor 4, and is thereby converted 
into an electrical signal. The arrow indicates a direction along which a 
light source 2, the group of mirrors 38a, 38b, and 38c are shifted for 
sub-scanning. The light L.sub.1 converged by the lens 3 projects a reduced 
image onto the surface of the CCD image sensor 4 shown in FIG. 3 and 
having a mosaic filter layer 42 comprising B, G and R elements. The light 
L.sub.1 irradiates sensor elements 41 disposed linearly and densely on the 
CCD image sensor 4, and is thereby converted into an electric signal. 
Being driven by two phase pulses 43 (.phi..sub.1, and .phi..sub.2) at the 
velocity corresponding with the pulse frequency of transfer gate pulse 44, 
the photoelectrically obtained electrical signal is transferred along the 
main scanning direction shown by the arrow X on the transfer portion (CCD 
shift register) and is output from an output 46. The resultant output 
signal is being input to the modulator of the laser beam scanner in FIG. 4 
via a signal system in the image forming system in FIG. 11 described 
later. The color image reader of the invention may incorporate a method 
where three primary color components so-separated by a dichroic mirror are 
independently fed into the CCD or a method where a document is optically 
scanned using a color contact image sensor. 
Developing units 31 through 34 each preferably have a structure illustrated 
in FIG. 5. 
In FIG. 5, numeral 131 represents a development sleeve comprising a 
non-magnetic material such as aluminum or stainless steel; 132, a magnetic 
member disposed within the development sleeve 131 and circumferentially 
having a plurality of magnetic poles; 133, a developer layer thickness 
regulating blade that regulates the thickness of developer layer formed on 
the development sleeve 131; 134, a scraper blade that removes a developer 
layer remaining on the development sleeve 131 once developing is complete; 
135, an agitating rotary member that agitates the developer in a developer 
reservoir; 137, a toner hopper; 138, a toner supply roller having recesses 
and supplying a toner from the toner hopper 137 to the developer reservoir 
136; 139, a power supply that applies a bias voltage sometimes including a 
vibrating voltage component onto the development sleeve 131 via a 
protective resistor in order to form an electric field for controlling the 
behavior of toner which moves between the development sleeve 131 and the 
image carrying member 1. In this figure, the development sleeve 131 and 
the magnetic member 132 rotate in the directions of the respective arrows. 
However, the development sleeve 131 may be of a fixed type, or the 
magnetic member 132 may be of a fixed type, or both the development sleeve 
131 and the magnetic member 132 may rotate in a common direction. When a 
fixed type magnetic member 312 is used, in order to increase the magnetic 
flux density of a magnetic pole facing the image carrying member 1 to 
greater than that of another magnetic pole, magnification is usually 
enhanced for this specific pole, or a pair of magnets of the same polarity 
or of different polarities is disposed in this area wherein the pair of 
magnets is positioned in close proximity with each other. 
In such developing units, the magnetic pole on the magnetic member 132 
usually has a magnetism of a 500 to 1500 Gauss magnetic flux density. The 
developer in the developer reservoir 136 is thereby attracted to the 
surface of the development sleeve 131 by the magnetic force, and the 
thickness of developer deposited on the sleeve 131 is regulated by the 
layer thickness regulating blade 133 to form a developer layer. The 
developer layer travels in a direction in common with or reverse to the 
direction of rotation of the image carrying member 1 indicated by the 
arrow (in this figure, to the common direction. Thus in the developing 
area facing the surface of the image carrying member 1, the developer 
develops an electrostatic latent image on the image carrying member, and 
remaining developer is removed from the surface of the development sleeve 
131 by the scraper blade 134 and collected into the developer reservoir 
136. In the second developing onwards which is recurringly performed to 
form color toner images in an overlapping manner, on a non-contactive 
basis is preferred, so as not to put the toner already deposited on the 
image carrying member in the preceding developing. In a non-contactive 
developing system, the developer layer on the development sleeve 131 is 
not in contact with the image carrying member when the developing bias is 
not applied, and, once a D.C.-A.C. composite bias is applied onto the 
development sleeve 131, a toner is allowed to jump and adhere to the image 
carrying member 1 in the presence of an alternating electric field. 
FIG. 5 illustrates a state where developing is performed according to the 
non-contactive developing system. 
The respective developing units 31 through 34 preferably use the so-called 
two component developer comprising a non-magnetic toner and a magnetic 
carrier. With this type of developer, the toner does not need black or 
brown magnetic material, whereby a vividly colored toner can be obtained, 
and potential on a toner is easily attained. Such a magnetic carrier is 
preferably an insulative carrier of which resistivity being not less than 
10.sup.8 .OMEGA.cm, preferably, not less than 10.sup.13 .OMEGA.cm, wherein 
carrier particles independently comprise a resin, e.g., a styrene resin, 
vinyl resin, ethylene resin, rosin modified resin, acrylic resin, 
polyamide resin, epoxy resin, or polyester resin, which contains dispersed 
fine particles of ferromagnetic or paramagnetic material, i.e., triiron 
tetraoxide, Y-ferric salt, chromium dioxide, manganese oxide, ferrite, or 
manganese-copper based alloy; or wherein the carrier particles 
independently comprise a particle of any of these magnetic materials, and 
the surface of the particle is coated with any of the above-mentioned 
resins. If this resistivity is excessively small, an electrical potential 
is injected into carrier particles once a bias voltage is applied onto the 
development sleeve 131, whereby the carrier particles disadvantageously 
tend to adhere onto the surface on the image carrying member 1 too 
strongly, or the bias voltage fails to be satisfactorily applied onto the 
image carrying member 1. The carrier particles too strongly adhering onto 
the image carrying member 1 adversely affect the tone reproduction of a 
color image. 
The resistivity is a value obtained as follows: carrier particles are 
loaded and tapped in a container having a cross-section of 0.50 cm.sup.2, 
thereby a load of 1 kg/cm.sup.2 is applied onto the compacted particles, 
and then, a current value corresponding with a voltage that generates an 
electric field of 1000 V/cm between the load and the bottom electrode is 
read. 
A carrier of average particle size of not larger than 5 m will result in 
too small a magnification; a carrier of not smaller than 50 .mu.m fails to 
improve image quality and readily causes breakdown and discharge, 
resulting in difficulty in applying a high voltage. To sum up, the 
preferred average particle size is not less than 5 .mu.m and nor more than 
50 .mu.m. In compliance with a specific requirement, to the carrier 
particles is added an additive such as a fluidity improving agent made of 
anhydrous silica or the like. 
The preferred toner comprises particles, of average size of 1 to 20 .mu.m, 
that incorporate various pigments, and, in compliance with a specific 
requirement, a triboelectricity controlling agent or the like. The 
preferred toner also has an average electrification level of 3 to 300 
.mu.c/g, in particular, 10 to 100 .mu.c/g. A toner of average size of not 
larger than 1 .mu.m does not readily leave carrier particles; a toner of 
not smaller than 20 .mu.m decreases resolution of an image. 
Using such a developer comprising an insulative carrier and toner allows a 
bias being applied onto the development sleeve 131 in FIG. 3 to be 
determined so that a toner is sufficiently adhered to an electrostatic 
latent image and fog is eliminated, while the possibility of leak current 
is also eliminated. In order to allow the toner to be more readily 
transported in the course of developing in the presence of a bias voltage 
being applied, a toner may contain a magnetic material that can be used in 
a magnetic carrier in an amount that does not deteriorate the vividness of 
toner color. 
The arrangement of the developing units, as well as the composition of 
developer advantageously used in the practice of the invention are as 
above described. However, the scope of the invention is not limited only 
to these descriptions. In the practice of the invention, other useful 
developing units and developers are described in Japanese Pat. O.P.I. 
Publication Nos. 30537/1975, 18656/1980 through 18659/1980, 144452/1981, 
116553/1983 through 116554/1983. More specifically, the arrangement of an 
image forming apparatus is preferably in compliance with the 
non-contactive developing conditions using a two-component developer as 
specified in Japanese Pat. O.P.I. Publication Nos. 57446/1983, 96900/1983 
through 96903/1983, 97973/1983, 192710/1985, 192711/1985, 14537/1985, 
14539/1985, and 176069/1985, each filed by the present applicant. The 
developing unit disclosed in Japanese Pat. O.P.I. Publication No. 
176069/1985 is particularly advantageous in that a magnetic member within 
a development sleeve is of a fixed type, and developing is performed in an 
area between magnetic poles where the thickness of developer layer is 
smaller. The developing gap is resultingly smaller, and it is thus 
possible to form sufficiently great developing electric field and to 
achieve high developing performance. A magnetic member of a fixed type is 
advantageous in realizing an image forming apparatus that has a plurality 
of developing units. 
Every imagewise exposure must be performed on an exact specific position of 
an image carrying member. Designation of an imagewise exposing area is 
readily and accurately achieved by detecting the position and controlling 
the imagewise exposure timing with an index marker for registration 
(unshown, one or plurality of markers based on a requirement) for 
registration disposed on a specific location on the image carrying member, 
or using a conventional photosensor that detects, every time the image 
carrying member turns, a pulse or the like generated by an encoder 
rotating in conjunction with the image carrying member. Such an 
arrangement eliminates a color image of misaligned toner images. 
The laser optical systems below especially accurately eliminate a 
misaligned image: a polygon mirror used in conjunction with, as optical 
scanning means, position controlling methods disclosed in Japanese Pat. 
O.P.I. Publication Nos. 161566/1981, 64718/1982, and 53866/1984; a method 
for forming a plurality of laser beams with a polygon mirror as described 
in Japanese Pat. O.P.I. Publication No. 150066/1985; and a method for 
forming a plurality of laser beams using an optical modulator. 
Additionally, as mentioned previously, according to the above-mentioned 
recording system a toner image formed on the image carrying member 1 is 
directly transferred onto a transfer member P with a transferring unit 14, 
without using a transfer drum. This arrangement eliminates misaligned 
toner images and enables a smaller copying apparatus. 
Using any of the above-mentioned recording apparatus, a color image forming 
method as illustrated in FIG. 6 can be performed. This figure covers up to 
the second developing. 
FIG. 6 illustrates one preferred embodiment of the reverse developing 
system according to the invention, wherein an electrostatic latent image 
is formed according to an electrostatic latent image forming method with 
this method the imagewise exposed portion constitutes an electrostatic 
latent image which has a potential level lower than that of background 
portion. In the course of developing, a toner electrified to have a 
polarity identical with that of the background portion potential adheres 
to the latent image. 
In the embodiment in FIG. 6 using the recording apparatus of FIG. 1(a), the 
surface of the image carrying member 1 which has undergone initialization 
is subjected during the first turn to uniform electrifying by the 
electrifier 11. The electrified surface is thereby subjected to the first 
imagewise exposure by irradiating with relevant imagewise exposing light 
generated by the laser beam scanner in FIG. 4 so that the potential on the 
electrostatic latent image portion is approximately zero. The resultant 
electrostatic latent image is subjected to the first developing by a 
developing unit selected from the developing units 31 and 32, i.e., the 
developing unit that contains a toner (in this case, unlike the example in 
FIG. 6, a toner is electrified to have a polarity same as the image 
carrying member) of which has color corresponding with that of the 
imagewise exposing light 21. In the next latent image forming onward, once 
the electrifier 12 is used, the second imagewise exposure is performed by 
projecting the imagewise exposing light 22 of another color onto a 
position different from the position where the preceding imagewise 
exposing light 21 was projected, or by projecting the similar light 22 of 
a different color onto the same position. The resultant electrostatic 
latent, images of approximately zero potential are thereby developed by 
either developing unit 33 or 34 containing a developer of color, toner 
corresponding to the color of the latent image. Then, in the second turn 
of the image carrying member, the third and fourth electrifying, latent 
image forming, developing are performed, as described referring to FIG. 6, 
and tone cycle of color image recording is complete. In the above example, 
the potential on an exposing area drops to approximately zero level, even 
when a toner T is electrified to have a polarity the same as the image 
carrying member 1, because a laser beam is allowed to pass through the 
toner T. Accordingly, in developing for adhering a toner T' of another 
color onto an electrostatic latent image formed later, the toner T' 
adheres in an overlapping manner onto the electrostatic latent image where 
the toner T has already been deposited and is subjected to exposure i.e., 
writing. Therefore, it is possible to form a vivid monocolor or multicolor 
image based, on a feature that a new toner image is formed in an 
overlapping manner on a previously formed toner image without being 
adversely affected by the latter image. 
Next, the arrangement of a color image forming system according to the 
invention is hereunder described referring to FIG. 7. This image forming 
method employs the process of FIG. 6, wherein the control signal from a 
CPU controllingly drives a recorder, dot pattern memory and image forming 
process. In conjunction with the travel of the exposing system (lamp 2, 
mirrors 38a, 38b, and 38c) as shown in FIG. 2, a CCD image sensor 4 that 
is one type of color scanner longitudinally reads color information of B, 
G, and R components on a document 1, and outputs an analog video signal. 
This signal is subjected to A/D conversion, then to shading rectification 
in order to remove distortion derived from color information and/or 
optical system, and is temporarily input to a buffer memory so as to align 
the respective B, G, and R components on a common image position. 
FIG. 3 illustrates a CCD color image sensor. Instead, a contact color image 
sensor may be used. 
To improve the color separation characteristics of a color separation 
filter, a notch filter may be incorporated; this filter eliminates light 
of bands between B and G, and G and R. As the notch filter, an 
interference filter is preferably used, and, for example, a notch filter 
having spectral characteristics as shown in FIG. 11 is used. This notch 
filter 171 is located in front of or behind lens system or between lenses, 
when incorporated into a lens system 170 shown in FIG. 12. When 
incorporated into a contact color sensor, the filter 171 is located in 
front or behind a light converging element. FIG. 13 illustrates an image 
reader using a light converging element 181. In this figure, numeral 182 
represents an exposing lamp for exposing an image; 183, a reflector 
mirror; 184, a slit; 185, a contact image sensor. The B, G, and R signals 
from the buffer memory are converted into complementary colors Y, M, and 
C, and subjected to tone rectification. Next, a black component is sampled 
(UCR) from the respective Y, M, C data groups. Chromatic components and an 
achromatic component are thereby separated from each other. Then, the 
chromatic components, i.e., Y, M, and C components are subjected to color 
rectification, and together with a black component (BK) subjected to toner 
rectification and input to a pattern generator (PG). In this example, the 
color components are converted into digital dot pattern signals based, for 
example, on the dither method, and stored onto a page memory for 
independent colors. These groups of image data are being output, in 
conjunction with the rotation of the image carrying member, to a recorder, 
via a line memory that is needed as a buffer. Writing and image forming 
are thereby performed. In FIG. 7, during the first turn of the image 
carrying member, a C dot pattern is output by the first latent image 
forming means via a selector that selects color information; a Y dot 
pattern is output by the second latent image forming means via a delay 
circuit that incorporates a delay between two times of toner image forming 
respectively by the first and second image forming means. In the second 
turn, when the rotating image carrying member resumes the position of the 
preceding image forming, an M dot pattern is output by the first latent 
image forming means via the page memory based on the writing timing. After 
a specific delay, a BK dot pattern is similarly output by the second 
,latent image forming means. 
FIG. 8 shows an arrangement with a significantly reduced image memory. Like 
the arrangement in FIG. 7, image data are input to a pattern generator 
(PG) in the course of the first scanning by a color scanner. In this 
example, the image data are converted into digital dot pattern signals 
based, for example, on the dither method, wherein a C dot pattern signal 
that is the first signal is subjected to writing is, transferred via a 
line memory that is needed as a buffer. Writing and image forming are 
performed as virtually synchronized with the reading. At the same time, a 
Y dot pattern signal that is the second signal subjected to writing is 
output to a recorder via a delay circuit that coordinates two image 
forming means. An M dot pattern is, during the next turn of the image 
carrying member, retrieved in conjunction with the writing timing based on 
re-scanning by a color scanner, and after a specific delay, a BK dot 
pattern is similarly retrieved via a delay circuit. The color scanner is 
driven in conjunction with the rotation of the image carrying member. 
In FIGS. 7 and 8, the delay circuit is an image memory and also functions 
as a shift register. This image memory compensates the difference of 
writing timing that lies between the two image forming means. 
In an ordinary color mode, a developing unit containing a toner of a color 
that corresponds with image data is actuated. In the image forming 
apparatuses in FIGS. 1(a) and (b), the developing units 31 and 32, 
respectively, have a cyan toner and magenta toner perform developing of 
image data that are output without being transmitted via a delay circuit. 
The developing units, respectively, having a yellow toner and black toner 
perform developing of image data that are output via a delay circuit. The 
image forming means 21 corresponds with the first image forming means, and 
the image forming means 22 corresponds with the second image forming 
means. The position, on the photosensitive drum, of the first latent image 
forming means differs from that of the second one. Accordingly, the timing 
for transmitting data from the delay circuit must be precisely delayed 
after another group of data has been similarly transmitted. The delay for 
transmitting the second group of data is controlled by counting the first 
horizontal synchronizing signal (pulses), and once a predetermined 
counting number is reached, the second image information (color 
information) is transmitted. Alternately, similar timing can be set by 
using the status of drum rotation that is detected by a drum encoder or 
the like, or based on the time elapsed. 
The method in FIG. 8 requires that the reading system be reset prior to the 
initiation of the next writing, and further requires that toner images be 
aligned on the image carrying member. Satisfying these requirements using 
mechanical means is extremely difficult, and, therefore, it is 
recommended, that a line member serving as a buffer be incorporated for 
each color screen. More specifically, precisely aligning images is 
achieved by: for designating a document position, in the course of 
shifting of a light source (initiation of document reading), a reference 
point on a platen, or a reference point on a specific position in the 
shifting path of the light source, or a document end as a reference point 
is being read and stored in a buffer memory; and at the same time, by 
performing the second writing onwards based on the writing timing 
dependent on the signal that indicates the reference M toner image formed 
on the drum. The so-overlapped toner images are subjected to a 
pre-transfer electrifier 13 and exposing lamp 41 which both promote easy 
transfer, and then, by the operation of a transfer electrode 14, are 
transferred onto a transfer sheet P being fed from a cassette. The 
transfer sheet P is separated by the operation of a separation electrode 
16, and heated by a fixer 61 to fix the toner image. Once transfer is 
completed, the toner remaining on the surface of image carrying member 1 
is cleaned by a neutralizing unit 15 and a cleaning unit 51 having a 
cleaning blade in order to prepare the next image forming. 
FIGS. 9 and 10 are timing charts, respectively, illustrating the timing of 
image forming in FIGS. 7 and 8. The reference signals Ey.sub.1, Em.sub.1, 
Ec.sub.1, and Ek.sub.1, are reference density patterns, for toner 
concentration control, electrifying potential, exposure intensity, and for 
feedback of developing bias, and are capable of providing a color image of 
greatly improved reproduction. 
According to the invention, once a memory registering button 301 on a panel 
of the image forming apparatus in FIG. 14(a) is pressed, a reference 
document shown in FIG. 14(b) is being read. This step hereinafter is 
called the first step. In advance, all of or a specific region in an area 
intended for precise reproduction is designated by document position 
designating means 302. For example, when either or both of a tone pattern 
area using tone patterns 403 and/or a color tone pattern using color toner 
patterns 404 is (are) scanned by reading means that designates a specific 
position on these patterns, thereafter the original image read from a 
specified area or the whole screen is, as shown in the flowchart in FIG. 7 
or 8, subjected to color tone rectification by the complementary color 
conversion portion and to tone rectification by the tone rectification 
portion next to the conversion portion. Rectification for each color is 
processed based on the correction factor stored in each corresponding 
memory, and the original image data is stored in a reference image memory 
and is printed out. Next, the second mode is started so that the printed 
(duplicated) document is placed on the platen, and read by a color image 
reader. The copy image data having been read is re-subjected to the same 
process and to data processing based on the correction factor stored in 
each corresponding memory, and then the copy image data is outputted from 
pattern generator. 
The copy image data for each color are compared with the original image 
data stored at the first mode in reference image memory, and then the 
differences between them are calculated. The correction factors are newly 
determined on the basis of the result of the calculation. In usual copy 
mode for copying various original documents, image data will be rectified 
by using the correction factors currently determined by above first and 
second modes, and then the rectified image data will be printed out. 
This image forming apparatus is provided with a surface potentiometer and a 
reflective densitometer in order to prevent fluctuation in color 
reproduction and density on the printer portion. By detecting the surface 
potential and density, and by correspondingly adjusting the voltage being 
applied to electrifiers, laser intensity, and developing bias, the 
reference patch image of each independent color is positively allowed to 
have a constant specific toner density. Naturally, this arrangement alone 
is not sufficient in accurately reproducing colors. Additionally, the 
image data read by the scanner is not necessarily always constant. 
Furthermore, the total color tone and gradation are not always reproduced 
accurately. Therefore, in the case that accurate color is requested, the 
color reproduction condition may be determined by performing above 
correction. 
FIG. 15 illustrates a flowchart representing the abovementioned the first 
and second modes. Namely, in the first mode, the reference document is 
read and the read original image is subjected to the color separation and 
the rectification process. The obtained original image data is thereby 
stored in the reference image memory and a copy image is printed out on 
the basis of the data. In the second mode, the copy image printed out at 
the first mode is read and the read copy image is subjected to the color 
separation and the rectification process, and then the obtained copy image 
data are processed by comparing with the original image data stored in the 
reference image memory. The correction factors are newly determined on the 
basis of the processing result and the determined correction factors are 
stored in the corresponding factor memory. 
The area that is subjected to the above-mentioned comparison is set within 
the previously mentioned designated image area. More specifically, the 
separated independent color components Y, M, and BK are subjected to 
differentiation based on the respective image densities. Arithmetical 
integration is thereby performed on each designated area. In the case of a 
larger image area, sampling intervals are set larger in compliance with a 
memory capacity, and in order to make the difference smaller, the 
previously mentioned correction factor is determined. The correction 
factor is stored in the factor memory, which is a RAM, and re-used as a 
correction factor for copying. The memory in the RAM can be backed up, so 
that it can be maintained even when a power switch is turned OFF. 
The above-mentioned arithmetic operation for image data is defined by the 
following expressions. 
A complementary color conversion that performs color tone rectification 
performs the following conversion, i.e., linear masking operation. 
##EQU1## 
Bi, Gi, and Ri are independent-color data representing logarithmically 
converted values of densities that have been input by scanner and 
undergone shading rectification; Yi, Mi, and Ci are independent-color data 
representing values of densities undergone complementary-color conversion. 
The factor {aij} is a factor determined by an experiment, and is in advance 
stored in the factor memory A. 
Next, tone rectification is effected as indicated by and input data curve 
and a rectified output curve in FIG. 18, wherein input data indicated with 
a dotted line are corrected to a .gamma.-rectified curve indicated with a 
solid line. More specifically, data stored in the factor memory B are 
corrected to the data on the rectified curve based on the backup table 
method. The factor memory B is selectively driven based on the developing 
characteristics and dither pattern. 
Next, a black component is singled out. The black component differentiation 
is performed based on the following expressions. 
EQU B.sub.0 =.alpha..sub.1 Bi+.beta..sub.1 min (Yi, Mi, Ci) 
EQU Y.sub.0 =.alpha..sub.2 Yi+.beta..sub.2 min (Yi, Mi, Ci) 
In these expressions, Bi, Yi, Mi, and Ci, represent independent-color input 
data each representing density values independent color components BK, Y, 
M, and C, each being input into an arithmetic processing portion; B.sub.0, 
Y.sub.0, M.sub.0, and C.sub.0, represent densities values of independent 
color components BK, Y, M, and C, each being converted on the arithmetic 
procession portion; min (Yi, Mi, and Ci) represents data corresponding 
with a minimum density value in three primary color data Yi, Mi and Ci; 
and .alpha..sub.1, .alpha..sub.2, .alpha..sub.3, .alpha..sub.4, 
.beta..sub.1, .beta..sub.2, .beta..sub.3, and .beta..sub.4, represents 
parameters capable of being modified by external instructions. 
The histogram showing the respective color density levels Yi, Mi, Ci, and 
Bi, is shown in FIG. 16(a); and FIG. 16(b) shows the respective color 
density levels of data Y.sub.0, B.sub.0, C.sub.0, and M.sub.0 each 
obtained by arithmetic operation based on the assumption that parameters 
.alpha..sub.1 through .alpha..sub.4 and .beta..sub.1 through .beta..sub.4 
are commonly 1. 
FIG. 16(a) shows unchanged input data, while FIG. 16(b) shows data 
converted in the arithmetic processing portion. Comparing FIG. 16(a) with 
(b) demonstrates that the converted data shown in (b) mean significantly 
smaller amounts of toners adhering onto the photosensitive member 1. In 
other words, performing UCR with .beta..sub.2 through .beta..sub.4 each 
slightly greater than zero is advantageous in that, in an image forming 
method where a plurality of toner images are formed in an overlapping 
manner on the image carrying member, a new toner image is formed as less 
affected by an already formed toner image. .beta..sub.2 through 
.beta..sub.4 are preferably within a range of 0 to 1. 
If a memory registering button 301 has been pressed for color tone 
adjustment, the data which have undergone black-component separation are 
not subjected to data correction in a chromatic signal masking portion and 
a tone rectification portion. Such data correction is performed only if a 
independent-color density adjustment button 303 or tone adjustment button 
307 has been pressed in a normal copy mode in order to vary color tone or 
gradation. 
Next, image data converted into a dither pattern by a pattern generator are 
stored in the reference image memory at the first mode. Additionally, the 
image data is outputted to the printing device, and the printed sample is 
then prepared based on such image data. At the second mode, the data of 
the printed sample are re-fed by the color scanner. Such copy image data 
are subjected to the similar image processing, and sequentially outputted 
via the pattern generator. The difference between such copy image data and 
the data in the corresponding location in the dot reference image memory 
are calculated for each color. 
The calculations are performed by the following expressions: 
##EQU2## 
wherein B.sub.O, Y.sub.O, M.sub.O, and C.sub.O are respectively image data 
having been input based on the reference document; B.sub.c, Y.sub.c, 
M.sub.c, and C.sub.c, are respectively image data having been input based 
on a copy sample of the reference document. (X, Y) represents coordinates 
in the document subjected to sampling. The arithmetic results 
(.DELTA..sub.B, .DELTA..sub.Y, .DELTA..sub.M, .DELTA..sub.C) correspond 
with the color difference between the document and the copy sample. 
In this arithmetic operation,, the difference in information of gradation 
for each color. However, it is possible to detect which density portion on 
a specific color image is deviated from a counterpart on a document, by 
subdividing the above arithmetic operation into sub-operations 
corresponding to specific density ranges for each color. Each sub-divided 
area is thereby subjected into the arithmetic sub-operation. 
By using the resultant difference data, for example, the 
complementary-color conversion factor and the tone rectification factor 
may be newly determined by referring to a table prepared by experiment. 
FIG. 17(a) illustrates 4.times.4 dither matrix used on a pattern generator 
for processing rectified image data, wherein the matrix has threshold 
values for each of Y, M, C and BK image components, and accordingly, the 
respective images are formed on a common position. More specifically, the 
respective pixels of the respective colors are alloted to specific common 
positions, and image forming by writing and depositing toners is performed 
on these specific common positions. FIG. 17(b) shows an operation where M, 
C, and BK components are written as respectively staggered by .tbd..sub.1, 
.tbd..sub.2, .tbd..sub.3, and .tbd..sub.4. 
Additionally, in an arithmetic operation based on the above algorithm, any 
input data can be used as far as the similar data include color 
information. For example, when transmitting a TV image, blue, green, and 
luminance levels are displayed as the primary three colors of the additive 
color process based on the Y, I, and Q signals, whereby the similar 
luminance levels may be converted into density levels of the three primary 
colors of the subtractive color process, i.e., Y, M, and C. The analog Y, 
M, and C output signals from an image pick-up tube or the like can be used 
unchange as input data for an arithmetic operation, or these signals may 
be used as input signals by digitization or by incorporating other data. 
The algorithm as the previously mentioned arithmetic operation is hereunder 
described in detail by referring to FIGS. 16 and 17. FIG. 16 shows the 
respective total sums of the respective color density levels of the 
respective colors. As in the case of input data in FIG. 16(a), the levels 
in FIG. 16(a) are converted into those in (b) using the three primary 
colors Y, M, and C of a common density level makes BK when blended 
together. More specifically, the level equal to Ci that has a minimum 
density level among input data is reduced from the above data Yi, Mi, and 
Ci, thereby the level is replaced with the BK component. By processing 
image data in this way, i.e., by processing the difference, advantageously 
enables accurate detection of fluctuation in Y, M, C, and BK components in 
input data. 
According to the present embodiment, it is possible to designate a 
parameter externally. Also, it is possible to incorporate a method for 
feeding back data to the developing bias. According to the invention, 
designating a specific image area may be performed with a digitizer. Based 
on a signal corresponding with the designated area, the area being 
processed is determined, and an arithmetic processing portion (in FIGS. 7 
and 8, this portion corresponds with the achromatic signal masking portion 
and the next tone rectification portion) designates a parameter only for 
the designated image area. Accordingly, it is possible to designate a tone 
in a specific area. 
Next, when comparing a density level of each pixel in a document data 
processed as shown in FIGS. (a) and (b) with the similar level in printed 
image data, the comparison may be performed on the whole pixels in a 
designated image area or on sampled pixels. Otherwise, levels of several 
pixels may be averaged, then subjected to differentiation. Such 
arrangements allows a smaller capacity differentiation data memory to 
perform differentiation satisfactorily. 
The so-determined parameter is registered in a memory. Document scanning 
may be repeated in determining the parameter, and parameter values are 
thereby converged to a specific value. This arrangement enables highly 
appropriate parameter determination. Color tone may be likewise given 
higher priority. 
The present invention provides a color image forming apparatus comprising 
image reading means and color image output means, wherein a vivid color 
image of good color balance is obtained by comparing an original document 
with a duplicated document in order to correct color tone and gradation. 
Additionally, sometimes, there is a need for reproducing a specific area in 
document having a specific color which must be reproduced correct in tone 
and gradation. In this case, a user has been conventionally supposed to 
reproduce the specific area with good color balance at the cost of 
imbalanced colors in an area other than the specified area or in the whole 
document area. In contrast, the document position designating means of the 
present invention gives priority to the specified area as well as 
maintains the color balance in the whole document area.