JPS63184468A - Color image forming device - Google Patents

Abstract

PURPOSE:To always attain prescribed color reproduction by reading a standard color original and setting a color conversion coefficient so that the output of the color conversion means reaches a prescribed value corresponding to the standard color original thereby forming image. CONSTITUTION:Signals R, G, B of elements 6R, 6G, 6B on a CCD are led to a circuit 14 applying LOG transformation and A/D conversion, and converted into digital signals Y',M, and C,. The Y,, M', C' signals are led to a color processing circuit 15 applying masking processing and background color eliminating processing and the color conversion coefficients are set so as to bring the output signals Y'', M'', C'' and BK'' of the color conversion circuit 15 into a prescribed value corresponding to the standard color original thereby forming an image.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a color image forming apparatus equipped with a color correction function.

[Prior Art] This type of color image forming apparatus, which has been known in the past, performs color correction on signals read from a document based on preset color conversion coefficients, and forms and outputs a color image. Ta.

[Problems to be solved by the invention] However, if changes occur over time in the brightness of the document illumination lamp, the spectral sensitivity of the color photoelectric conversion element array, the gain of the amplifier used to digitize one image signal, etc. ,
If color correction was performed according to preset color conversion coefficients, there was a drawback that colors faithful to the color document could not be reproduced.

In addition to color thermal transfer printers, color inkjet printers, color laser beam printers, etc., display devices such as CRTs are known as devices for forming color images. However, since the color reproduction characteristics of these devices are different from each other, there has been a drawback that color adjustment must be performed again when the printer is replaced.

In other words, because the color reproduction characteristics of the output devices connected to the color image reading device are different, the optimal setting values for color adjustment are different, and if you change the output device, you will have to make adjustments again. did not become.

FIG. 9 shows the reproduction range of solid colors when replacing the printer as an output device, plotted on the CIELIJV axis of the isochromatic space (the case where L''=60 is cut out and shown). In the figure, the solid line (a) indicates the color reproduction range of a thermal transfer printer, and the broken line (b) and the dashed-dotted line (C) indicate the color reproduction range of a color laser beam printer.

These (b) and (C) are the characteristics when the electrostatic latent image contrast is changed in the same device.

In order to output the colors shown in the two points, the thermal transfer printer uses Yellow = 3/3 and Cyan = 3/
3 manpower is required. In addition, in the color laser beam printer shown by the broken line (b), Yellow=2/3
, Cyan-2/3 human power is required, and the color laser beam printer shown by the dashed line (C) requires Ye
Low = 1/3, Cyan = 1/3 manpower is required.

Therefore, in view of the above-mentioned points, a first object of the present invention is to provide a color image forming apparatus that can always reproduce a constant color.

A second object of the present invention is to provide a color image forming apparatus configured to set the color conversion coefficient of a color conversion circuit to an appropriate value in consideration of the characteristics of an image reading device, the type of output printer, and color reproduction factors. It is about providing.

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a reading means for reading a standard color original, a color converting means for introducing the output of the reading means, and an output of the color converting means that is a standard color document. The apparatus includes a control means for setting a color conversion coefficient of the color conversion means to a predetermined value corresponding to a color original, and a color image forming means for forming an image by inputting the output of the color conversion means.

[Function] In the color image forming apparatus according to the present invention, a standard color document whose chromaticity coordinates are known in advance is read, and color conversion coefficients are determined so that the output of the color conversion means becomes a predetermined value. .

[Example] Hereinafter, the present invention will be described in detail based on Examples.

FIG. 2 is a schematic configuration diagram showing an optical reading system of a color image forming apparatus to which the present invention is applied. In this figure, 1 is an original, and 2 is an original table glass on which the original 1 is placed. 3 is an illumination device, and 4 is an imaging element array. 5 is an infrared cut filter, and 6 is a contact type CCD color sensor (hereinafter referred to as
7 is an optical system unit.

First, the process of reading a color original will be explained. When a copy key (not shown) is pressed, the illumination device 3 illuminates the original 1, and the reflected light from the original is reflected by the imaging element array 4. Passes through an infrared cut filter 5.

Then, an original image is formed on the CCD 0, and the optical system unit 7 scans the original in the direction of the arrow. CCD6 has
As shown in FIG. 3, red (R), green (G), and blue (B) filters are regularly attached to each pixel.

As the original is scanned, electrical signals from the CCD 6 are processed by a signal processing circuit shown in FIG.

In Fig. 4, 6R, 6G, and 6B are R and G on CCD6.
, represents the signal from the B capacitive element. Next, R,G with
, B signals are sent to circuit 1 that performs LOG conversion and A/D conversion.
4, Y', M', C in digital signal form
'The signal is converted twice. The Y', M', and C' multiplied signals are introduced into a color conversion circuit 15 that performs masking processing and LICR (undercolor removal) processing. This color conversion circuit 15 is
The calculation process shown in the following equation is performed.

...(i) Here, (Y'1M' + C'Lin is Y', M'
, C' is the smallest signal among the signals of all~a4
41 b 4 are color conversion coefficients, respectively.

Also, 16 is a color printer such as a color laser printer, 17 is a CPU (central processing unit), and 18 is a RAM.
(random access memory), 19 stores the color calculation process (described in detail later) to be executed by the CPU;
OM (Random Access Memory).

These Y″1M″, C″, and aK# signals are visualized by a color image forming apparatus such as a color thermal transfer printer, a color inkjet printer, or a color laser beam printer.

A color image forming apparatus consisting of an image reader and an image printer is required to have the same image output when reading the same color document. Therefore, as an embodiment of the present invention, a feedback system as shown in FIG. 1 is constructed.

In FIG. 1, 25 is a standard color original whose chromaticity coordinates are known. As this standard color original fi 25, a tone pattern (64 colors) printed in the form shown in FIG. 5 is used.

Then, this standard color original 25 is read by the optical system unit 7 shown in the second figure, and the color conversion circuit 15 reads Y"1M".
, C'', BK'' signals to the target values shown in Fig. 6.
The color conversion coefficients of the color conversion circuit 15 are determined.

The above-mentioned Y, M, and C1BK target values (see FIG. 6) are determined by the type of color printer used and color reproduction factors. For example, there is a color P in the color standard document shown in FIG. 5 (this color corresponds to point P on the CIELUV diagram), and this color is used by the printer (a).

In order to faithfully reproduce the printer (b) and printer (C) (see Figure 9), the target reading values are (Y, M, C), respectively.
, BK) = (3/3,0.3/3.0), (2/3
, 0.2/3.0).

(1/3, 0.1/3, 0).

However, if the color conversion circuit 15 is capable of producing 256 gradations of color, °°0°'' shown in FIG. 6 is the 0 level.

3"1°° is 85 level, °"2°° is 170 level
II 31″ should be 255 level. However, N
000 indicates a state in which no toner of any color is printed.

Next, the process of reading the standard color original 25 created in this way will be described in detail.

As shown in FIG. 7, the standard color original 2 is placed at a predetermined position on the original platen glass 2 in the same way as when setting an original.
Set 5. Then, the test mode instruction key (not shown) is pressed again. Then, the optical system unit 7 stops at position A on the standard color original 25, the original is illuminated by the illumination device 3, the mixed color pattern is read by the CCD[i, and the information is stored in the RAM 18. Next, the optical system unit 7 moves to position B and reads the mixed color pattern similarly to position A. Similarly, the mixed color patterns are read at positions C and D and stored in the RAM 18. In this way, output values Yl", Ml', CI' (i is shown in FIG. 6) corresponding to each pattern of 64 colors are obtained.
(representing “NO,”) is obtained.

Furthermore, a standard white board (not shown) is placed at the tip of the document table glass, and the reflected light from the standard white board is read by the CCD 6, and based on the output values Yw, Mw, and Cw of the standard white board, the output values Yl' and Ml are Shading correction is performed on ', Cmu°. Since this shading correction is performed after LOG conversion, for example, processing such as "Y=255-Yw+Y1" can be similarly performed for Mlo, C, and °.

Next, change the value after shading correction to a new output value Y,
',M,',C,', YI according to equation (i)
'', Mlo, C1''+'to'' are obtained. Thereafter, the coefficients of the equation (i1) are determined according to the following equation so as to approach the preset target output values Y, M, C, UK shown in FIG.

The evaluation functions for yellow, magenta, and cyan are each φY
, φM, and φC. Then, for yellow, φ7=Σ(a, □YI'12Myo' 10a
13C1' -Yl)2+(Σ C+'Yt',)a+
3-(ΣY+Yi')=0+(ΣCt'
M+')a+s-(ΣYIMI'))=055+(ΣC1'Ml')a13-(ΣYICi'))
= .

In the same way, for magenta and cyan, the following formula is obtained.

Here, when the above equation is expressed as [C] [A] = [0], A=C-1·D, so the coefficients of all to a33 can be found.

Note that C-1 is the inverse matrix of C.

Next, a44+b4 is φ=Σ(
a44(Y+'+Ml'+CI°)mln"1)4
-BKI) 2 to +Σ(Y+', M, ', CI')b
4-ΣBKI (Yl', Mt', C+')mln
) 5 = 0 - ΣBKI) = 0 Therefore, if the above equation is expressed as [E] [F] = [G], the coefficients of a441 b4 can be found from F = E-'-G. Note that E-1 is the inverse matrix of E.

In this way a l l~a 33+ a44+ b4
CP018 executes the calculation to obtain the following, and then the new coefficients a-th to a33+a44. b4 is input to the color conversion circuit 15.

In this way, the Y, M, C, and BK ratio outputs when reading the standard color original 25 consisting of 64 evaluation colors can be controlled so as to always approach the target values.

Furthermore, by uniformly selecting the evaluation colors in the isochromatic space, it is possible to obtain substantially the same output for all colors. Furthermore, by selecting a specific color in a color document as the evaluation color, the same output can be obtained with high accuracy for that specific color.

Finally, the color reproduction factor signal sent from the color printer 16 (see FIG. 1) will be explained using a color laser beam printer as an example.

FIG. 8 shows a cross-sectional configuration of a color laser beam printer. Laser light modulated by the laser driver 31 is irradiated onto the photosensitive drum 35 (uniformly charged by the charger 34) via the polygon mirror 32 and mirror 33, thereby forming an electrostatic latent image. This photosensitive drum 35 rotates in the direction of the arrow in the figure. Then, the rotary developing device 36 performs development for each color.

The thus obtained toner image is converted into Y (yellow) and 9M (magenta) by the transfer charger 38.

C (cyan) and OX (black) are transferred separately. When the transfer is completed, the paper sheet 39 is separated from the transfer drum 37 by a separating means 40 and fixed by a fixing device 41. The remaining toner after transfer is cleaned by a cleaner 42.

In this type of color laser beam printer, the electrostatic latent image contrast and toner density determine the characteristics of reproduced colors in response to input signals.

Transfer efficiency, fixing temperature, outside temperature and humidity, etc.

Here, the electrostatic latent image contrast can be determined by measuring the potentials of bright areas and dark areas on the photosensitive drum, and can be brought close to the target potential by the potential control unit 44. Furthermore, the toner concentration can be measured by inserting a toner concentration sensor 45 into the developing device, and can be kept constant by controlling the replenishment system. Transfer efficiency can be controlled by measuring the transfer current to the drum side with an ammeter. The fixing temperature can be controlled by inserting a temperature sensor 47 inside the fixing device 41 and measuring the temperature. The outside temperature and humidity can also be controlled using a heater or the like. In this way, factors that influence the characteristics of reproduced colors (color reproduction factors) can be extracted to the outside.

Therefore, if the color reproduction factor of the type of output printer is known, the input signal and the reproduced color can be associated with each other.

Note that the present invention is not limited to electrophotographic methods, but can also be applied to inkjet methods and thermal transfer methods.

[Effects of the Invention] As explained above, according to the present invention, the color conversion coefficients are automatically set, so the user does not have to make complicated color adjustments just by reading a standard color original. You can get the special effect of disappearing.

Further, according to the present invention, color correction characteristics can be automatically adjusted as necessary, so that constant color reproducibility can always be maintained. Furthermore, by implementing the present invention, even if the type of output device or the color reproduction factor changes, there is no need to redo the troublesome color adjustment.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing one embodiment of the present invention, Fig. 2 is a sectional view of a document reading device, Fig. 3 is an enlarged view of the CCD surface, and Fig. 4 is a block diagram showing a part of this embodiment. , FIG. 5 shows an example of a standard color original, and FIG. 6 shows Y and M when reading a standard color original. Figure 7 shows the target values for C and B. Figure 7 shows the operation of this example. Figure 8 shows the cross-sectional configuration of a laser beam printer. Figure 9 shows the color reproduction factors of different printer types. Time Y
, M, C, and BK. 6R, 6G, 6B...CCO sensor, 14...LO
G conversion and to/D conversion circuit, 15...color conversion circuit, 16...color printer, 17...cpu. 18...RAM. 19...ROM.

Claims (1)

[Scope of Claims] Reading means for reading a standard color original; color conversion means for introducing the output of the reading means; A color image forming apparatus comprising: a control means for setting a color conversion coefficient of a conversion means; and a color image forming means for forming an image by introducing the output of the color conversion means.