JPH0695240B2 - Image forming device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image forming apparatus such as an original copying apparatus that photoelectrically reads and copies an original.

(Prior Art) Conventionally, as an image forming apparatus of this type, for example, an image reading device (hereinafter, referred to as a reader) that photoelectrically reads a color original, and an image that outputs an image read by the image reading device There is a combination of output devices (hereinafter referred to as printers).

By the way, it is difficult to always keep the characteristics of the reader and the printer in a constant state due to environmental changes, changes over time, etc., and it is necessary to appropriately change the parameters for determining the reading characteristics of the reader each time. In order to do this simply, a method has been considered in which a predetermined test chart is output by a printer, the test chart is read by a reader to determine the characteristics of the printer and the reader, and the above parameters are automatically determined.

(Problems to be Solved by the Invention) However, such a conventional technique has the following problems. That is, the reader spatially samples and reads an input document, exchanges it for an electrical signal and sends it to a printer, and the printer outputs an image in accordance with the spatially sampled electrical signal. By the way, an MTF (Modified Transfer Function) 41 that determines the transfer characteristic depending on the wavelength of the optical system of the reader has a large value in the output spatial frequency fp of the printer, as shown in FIG. Therefore, when the image output by the printer is read by the reader, interference occurs between the spatial frequencies of the two to cause moire, and an error occurs in the read signal of the reader, and the characteristics of the reader cannot be accurately adjusted. There was a problem.

Therefore, the present invention has been made in order to solve the above-mentioned problems of the prior art, and an object of the present invention is to accurately read a chart output from an image output device with an image reading device and read the image reading device. An object of the present invention is to provide an image forming apparatus capable of accurately adjusting the characteristics of the apparatus and the like.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides an image reading unit having a plurality of photoelectric elements arranged in a straight line, and an image reading of a document image placed on a document table. In an image forming apparatus having an image forming optical means for forming an image on the means and an image output means for outputting an image based on a digital signal corresponding to an image read by the image reading means, the image output means performs a predetermined test. An image is output based on the chart, and the image is read by the image reading means to have an adjustment mode for adjusting the image forming characteristics of the image output means. In this adjustment mode, the image is output based on a predetermined test chart. When the image is read by the image reading means, the image forming state of the image forming optical means on the image reading means is set to a defocus state. In the present invention, when the test chart is read by the image reading device, the optical path length of the image forming optical system of the image reading device is made different from the optical path length when reading a normal document, so that the image reading device To prevent interference with the spatial frequency of the image output device.

(Example) Below, this invention is demonstrated based on the Example shown in figure.

FIG. 1 is a schematic configuration diagram showing an embodiment of an image forming apparatus according to the present invention. This image forming apparatus is a color image forming apparatus, and includes a color image reading apparatus 100 that photoelectrically reads a color original and a color image output apparatus 101 that outputs a color image based on a signal from the color image reading apparatus 100. Has become. The color image reading apparatus 100 illuminates the color original 1 placed on the original placing glass 2 with the light source 3, and reflects the reflected light image from the color original 1 with the small image forming element array 4 by the infrared cut filter. An image of the same size is formed on the color image reading sensor 6 through 5. As shown in FIG. 2, the color image reading sensor 6 is configured by linearly arranging pixels R, G, and B corresponding to red, green, and blue. , Is connected to the correction circuit 7.

The correction circuit 7 includes a color correction circuit 24 as shown in FIG.
And a logarithmic conversion circuit 25 and a color correction circuit 26. The signal output from the color image reading sensor 6 is
Through the color correction circuit 24 and the logarithmic conversion circuit 25, the three primary colors of printing are yellow (Y), magenta (M), and cyan (C).
Is converted into an electric signal. The Y, M, C signals are further processed by a color correction circuit 26 to generate Y ', M', C'signals and a black signal BK in addition to them in the case of four-color printing. It is output to 101.

Here, in the color correction circuit 26, color correction called masking that optimizes the spectral characteristics, color mixture characteristics, gradation characteristics, etc. of the color materials of the color image output device 101 and the black component are extracted.
Calculation processing such as UCR (under color removal) subtracted from the primary color signal is performed. The specific operation contents of the masking and UCR are as shown in, for example, equations (I) and (II).

BK = a ₁ min (Y, M, C) Y ″ = Y−a ₂ min (Y, M, C) (I) M ″ = M−a ₃ min (Y, M, C) C ″ = C −a ₄ min (Y, M, C) Here, min (Y, M, C) is an operation that takes the minimum value of Y, M, C. The parameters of a _i and b _ij are controlled according to the characteristics of the color image reading device 100 and the color image output device 101.

The correction circuit 7 configured as described above has a predetermined Y, M, C,
A pattern generator 14 that outputs a BK signal to the color image output device 101, and an output test chart by the pattern generator 14 is read by the color image reading device 100, and the read signal and the predetermined Y, M, C, and BK signals From
An arithmetic processing circuit 15 for operating and determining the parameters a _i and b _ij of the equations (I) and (II) is connected.

In the present embodiment, in addition to the above configuration, when the output test chart 300 (FIG. 4) is read by the color image reading device 100, the optical path length of the image forming optical system of the color image reading device 100 is set to a normal value. It is configured to be different from the optical path length when reading the color original 1. That is, a colorless and transparent filter 16 in the visible wavelength region is arranged above the small image-forming element 4 of the color image reading apparatus 100 so as to be able to enter and leave the optical path.

On the other hand, as shown in FIG. 1, the color image output device 101 includes a semiconductor laser 8 connected to the correction circuit 7 of the color image reading device 100, and Y, M sequentially output from the semiconductor laser 8 are provided. Beam B corresponding to C, C and BK
Is exposed on the photosensitive drum 9 through a scanning unit (not shown). The images exposed on the photosensitive drum 9 are
The image is developed by a rotary developing device 10 corresponding to four colors of Y, M, C, and BK, and the developed image is sequentially transferred and superposed on a transfer paper 12 wound around a transfer drum 11. Then, the image formed on the transfer paper 12 is fixed by the fixing device 13,
Output a color image.

In the color image forming apparatus according to the present embodiment having the above configuration, the characteristics are adjusted as follows. First, Y, which is predetermined by the pattern generator 14,
The M, C, and BK signals are output to the color image output device 101, and a specific test chart is formed on the transfer paper 12. As shown in FIG. 4, this test chart outputs colors 301 to 356 corresponding to Y, M, C, and BK signals with various brightness. Next, this output chart is placed at a predetermined position on the original placing table glass 2, and the filter 16 is inserted into the optical path of the imaging optical system to change the optical path length of the imaging optical system. In this state, the color image sensor 6 reads the colors at a plurality of specific positions to read the characteristics of the test chart, that is, the gradation characteristics and the color mixture characteristics of the color image output device 101, and the well-known least-squares method and the like. The coefficient of each of the formulas (I) and (II) is calculated and determined by the method of.

At that time, since the filter 16 is inserted in the optical path of the imaging optical system, if the refractive index of the filter 16 is n and the thickness is t, the optical path length is Changes, and it becomes a defocused state. Therefore, if the output spatial frequency of the color image output device 101 is fp, the image forming optical system is in the defocused state, so that the MTF4
2 can be made sufficiently small in fp as shown in FIG. Thus, the refractive index n and the thickness t of the filter 16 are determined. Therefore, the output spatial frequency of the color image reading sensor 6 is different from the output spatial frequency fp of the color image output device 101, and the color on the test chart can be accurately read without causing moire. Then, the respective coefficients of the expressions (I) and (II) can be calculated based on the signals obtained by reading the colors on the test chart, and the image forming characteristics can be adjusted accurately.

In the illustrated embodiment, the case where the filter 16 is inserted in the optical path in order to change the optical path length of the imaging optical system has been described. However, the present invention is not limited to this, and the original platen glass is used as a machine. Alternatively, the positions of the small image forming element and the color image reading sensor may be moved up and down.

Further, in the above-mentioned embodiment, the case where the colorless and transparent filter 16 is used has been described, but it is also possible to set parameters for the purpose of special color reproduction by using a colored filter.

(Effects of the Invention) The present invention has the above-described configuration and operation, and when the test chart output from the image output device is read by the image reading device, the optical path length of the imaging optical system of the image reading device is set. Since the optical path length when reading a normal document is made different and the image forming state is set to the defocused state, the spatial frequency of the image reading device is changed to prevent interference with the spatial frequency of the image output device. be able to. Therefore, the test chart can be accurately read by the image reading device, and the characteristics can be adjusted accurately. Also,
Since the adjustment of the characteristics does not depend on the spatial frequency of the image output apparatus, the automatic adjustment of the characteristics can be performed even in the case where various image output apparatuses having different spatial frequencies such as a thermal transfer method and an inkjet method are used. .

[Brief description of drawings]

1 is a schematic configuration diagram showing an embodiment of a color image forming apparatus according to the present invention, FIG. 2 is a partial front view showing a color image reading sensor, FIG. 3 is a block diagram showing an image signal correcting circuit, FIG. 4 is a plan view showing a test chart, and FIG. 5 is a graph showing the relationship between MTF and spatial frequency. Explanation of symbols 1 …… Color original, 16 …… Filter 100 …… Color image reading device 101 …… Color image output device 300 …… Test chart

Claims (1)

[Claims] 1. An image reading means having a plurality of photoelectric elements linearly arranged, an image forming optical means for forming an image of a document placed on a document table on the image reading means, and an image read from the image reading means. In an image forming apparatus having image output means for outputting an image based on a digital signal corresponding to, an image based on a predetermined test chart is output by the image output means and the image is read by the image reading means. The image output means has an adjustment mode for adjusting the image forming characteristics, and when the image read out by the image reading means outputs an image output based on a predetermined test chart in this adjustment mode, the image by the image forming optical means. An image forming apparatus, wherein an image forming state on a reading unit is set to a defocus state.