JPH01196960A - Color picture processing unit - Google Patents

Abstract

PURPOSE:To decrease the deviation of an image forming position in case of using a lens with color aberration by providing an infrared ray cut-filter before a spectrum system and specifying the transmission characteristic. CONSTITUTION:An object 2 is lighted by a light source 110 and an infrared ray cut-filter 100 is arranged in front of the lens 3 constituting the optical system. The filter whose range of 50% of transmittivity is within a wavelength of 600-660nm is used as the transmission characteristic of the filter 100. As a result, the long wavelength area of the light source 110 is attenuated by the filter 100, the color aberration is decreased and the deviation of the relative image forming position with respect to CCDs 5-7 is made slight. Thus, even when the lens 3 having the color aberration is used, the color aberration is corrected substantially.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a color image processing device suitable for application to a plain paper recording color copying machine, etc., and particularly to a color image processing device using an infrared cut filter.

[Background of the Invention] In a color image processing device, such as a color copying machine using a laser beam, a color original is separated into a plurality of color separated lights, and each of them is converted into an image signal using a different photoelectric conversion element. Later, various image signals were processed.

FIG. 5 is a block diagram of essential parts of an example of such a color image processing apparatus 1, in which an optical image of the document 2 irradiated by the light source 110 is guided to the spectroscopic system 4 via the optical system 3.

The spectroscopic system 4 can be constructed using three prisms as shown in the figure.

By using this spectroscopic system 4, in this example, R,
The light is separated into three primary color lights, G and B, and images are formed on the corresponding photoelectric conversion elements 5 to 7, respectively.

As the charging conversion elements 5 to 7, semiconductor elements such as CCDs are used.

The image signals obtained from the CCDs 5 to 7 are supplied to the image processing means 9 and subjected to various image processing such as color ghost correction, resolution correction, and multi-value processing, and are then led to the output device 90 via the interface 80. It will be destroyed.

As the output device 90, a copying machine or the like that uses a laser beam as a light source is used, and color image information is developed here, and this is transferred onto recording paper (W recording paper, etc.) to record a color image. .

[Problem to be solved by the invention] By the way, in this way, it is possible to
When capturing images with D5-7 and trying to record characters or line drawings, if the CCDs 5-7 are not aligned accurately, pixel misalignment will occur and the image will be incompletely recorded with degraded image quality. Put it away.

Therefore, in such a device, it is necessary to adjust the deviation between the CCDs 5 to 7 to within at least 1/4 pixel.

On the other hand, even if the CCDs 5 to 7 are aligned accurately, the lens 3 has chromatic aberration, as is well known, so it is necessary to solve the problem caused by this.

An example of the relationship between the spectral characteristics of the spectroscopic system 4 (particularly the spectral characteristics of the dichroic mirror) and the chromatic aberration characteristics is shown in FIG.

Due to such chromatic aberration of lens 3, C0D of the color separation image
The imaging positions for images 5 to 7 are shifted.

For example, a lens 3 having chromatic aberration characteristics as shown in FIG.
When a lens 3 is used and no optical filter is placed in front of the lens 3, as shown in FIG. It will shift.

When measuring the pixel pitch, it was found that there was a shift of up to 4 pixels. If the imaging position is relatively shifted by as much as 4 pixels, the magnification will be different between each element, which will cause a practical problem.

On the other hand, as the light source 110, a halogen lamp or the like is used. As is well known, halogen lamps have a light emission characteristic (
Figure 2 La) is shown.

As is clear from the curve La, the halogen lamp emits a lot of infrared light. When there is a lot of infrared light, the resolution (MTF
) deteriorates, so when using a halogen lamp, it is necessary to cut off infrared rays from the halogen lamp. Therefore, an infrared cut filter is placed in front of the lens 3.

When measuring the deviation of the imaging position when using a filter with the trade name HA30 (its spectrum is shown in Figure 2 Lb) as an infrared cut filter, the amount of deviation is the same on both the left and right sides as shown in Figure 8. .

However, the amount of deviation is almost the same as in Fig. 7.

Therefore, this case is also a problem.

If a lens with less chromatic aberration is used, this shift in the imaging position can be reduced, but lenses with less chromatic aberration are expensive.

In view of this, the present invention proposes a color image processing device in which the deviation of the imaging position is reduced even if a lens having the same chromatic aberration as the conventional one is used.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a spectroscopic system that converts image information into a plurality of color-separated lights, and a plurality of color-separated lights that convert each color-separated light into an image signal. It has a photoelectric conversion element of ~6
It is characterized in that the wavelength is selected to be within a wavelength range of 60 nm.

[Function] As the light source 110, one having spectral characteristics such as a halogen lamp whose relative value increases in a long wavelength region is used. Therefore, the characteristics of the optical spectrum are as shown in FIG. 2 La.

An infrared cut filter 100 is arranged in front of the lens 3. The spectrum (transmission characteristics) of this filter 100 has a transmittance of 50% in the range of 600 to 660.
Filters are used that are in the nm wavelength range.

Specifically, FIG. 2 L1. As shown in L2, a filter is used that has a spectroscopic spectrum in which the relative value decreases to 0.5 or less in the long wavelength region (infrared region) from 600 to 700 nm.

When the filter 100 having such a spectrum is used, the long wavelength region of the light source 110 is
Attenuated by 00.

When the long wavelength region is attenuated, the center of gravity of the R spectral characteristic curve moves toward the G spectral characteristic curve in FIG.

Then, the amounts of chromatic aberration r, g, b determined from the relationship between the imaging characteristic Lr of the lens 3 and the position of the center of gravity of each spectral characteristic of R-B.
becomes smaller. As a result, the amount of deviation of the imaging position with respect to C0D5-7 becomes so small that it can be ignored in practical terms.

[Embodiment] Next, an example of a color image processing apparatus according to the present invention will be described in detail with reference to FIG. 1 and subsequent figures.

Color image information Wl (optical image) of a subject 2 such as a document is divided into three color separated images i in a spectroscopic system 4 via an optical system 3'z.
be done. In this example, the light is separated into three primary color lights: red, R, green, and blue. Therefore, the spectroscopic system 4 consists of three prisms and two
It consists of dichroic mirrors.

The R-B color separation images are formed on photoelectric conversion elements 5 to 7, which function as image reading means. A CCD can be used as the photoelectric conversion element. Therefore, by supplying the image signals (expressed as R to B for convenience) from each of C0Ds 5 to 7 to the A/D converters 10 to 12, a predetermined number of bits,
In this example, it is converted into a 6-bit digital signal. A/
Shading correction is performed simultaneously with D conversion. 14 to 16 indicate shading correction circuits.

The digital image signal subjected to the shading correction is extracted in gate circuits 17 to 19 only for the signal corresponding to the maximum original size. When the maximum document width to be handled is 84 size, the size signal B4 generated by the timing signal forming means of the system is used as the gate signal.

The image data from which only the predetermined area has been extracted is supplied to the next stage density conversion circuit 120, where it undergoes density conversion processing (logarithmic conversion processing).

The image data R-B that has undergone density conversion is sent to the color correction circuit 3.
0, undergoes color correction and undercolor removal processing, and is converted into Y, M, C, and K density data in this example.

A color conversion table or the like in a ROM is used for conversion to density data.

The color correction circuit 30 roughly encodes the color information (R to B) of the image data.

Therefore, the color correction means 30 outputs density data (6 and dot data) and color code data (3 and dot data) corresponding to the input image data.

The density data and color code data are supplied to the color ghost correction circuit 40 and are
Also, color ghosts in the sub-scanning direction (drum rotation direction) are corrected.

Color ghost processing applies only to color code data.

After color ghost correction, the image data (color code data and density data) is processed in the subsequent resolution correction circuit 50, where only the density data of the input data is processed and its resolution (MTF) is corrected.

This is because the resolution deteriorates due to deformation of the beam shape of the laser beam, deterioration of the development characteristics of the toner onto the photoreceptor drum, and the like.

As the resolution correction circuit 50, a convolution filter using 3×3 pixel image data or the like can be used.

The resolution-corrected density data and color code data are each supplied to the color data selector 60, and image data is selected and output according to the color copy sequence.

For example, in the case of a red copy sequence, image data (density data) based on a red color separation image is used as the image data, so that only the red image data can be extracted at this time.

This is the case when an electrophotographic color copying machine is used as the output device 9o, and one color image is developed with one rotation of the photoreceptor drum, and once development of all colors is completed, one rotation of the photoreceptor drum is performed. This is because a color copying machine is used which records a color image by transferring an image onto recording paper through a transfer process and then performing a separation process.

The image data output from the color data selector 60 (
a degree data) is subjected to multivalue processing in the multivalue conversion means 7o. For example, by using 4 thresholds, 6
The bit-structured density data is converted into 5 values.

Threshold data is set manually or automatically.

In order to automatically determine threshold data, automatic threshold setting means (
EE) 71 is provided, to which concentration data is supplied, and optimal threshold data is set for the input concentration data. Further, manual threshold setting means 72 is provided for manually setting threshold data.

The threshold value data that has been completely set is supplied to a multi-value conversion circuit 73, where the density data is multi-valued.

Multi-value processing may be performed for each color using threshold data set for each color.

The 3-bit multi-value data subjected to multi-value processing is supplied to an output device 90 via an interface circuit 80.

As the output device 150, a laser recording device or the like can be used as described above.

As the developing device, an electrophotographic color copying machine is used. In this example, two-component non-contact jumping development and reversal development are employed. Therefore, the transfer drum used in conventional color image formation cannot be used anymore.

In the color image processing apparatus 1 thus configured, the subject 2 is illuminated by the light source 110, and the infrared cut filter 100 is disposed in front of the lens 3 constituting the optical system.

As described above, the light source 110 used has a light spectrum (see La in FIG. 2) in which the relative value becomes large in the long wavelength region.

Specifically, a halogen lamp, a fluorescent lamp with daylight color or white light, or the like can be used.

On the other hand, the infrared cut filter 100 that has the following characteristics can be used.

That is, as for the spectral spectrum (transmission characteristics) of this filter 100, the range of transmittance of 50% is 600%.
Filters within the wavelength range of ~660 nm can be used.

Specifically, FIG. 2 L1. As shown in L2, a filter is used that has a spectroscopic spectrum in which the relative value decreases to 0.5 or less in the long wavelength region (infrared region) from 600 to 700 nm.

When the filter 100 having such a spectrum is used, the long wavelength region of the light source 110 is
Attenuated by 00.

When the long wavelength region is attenuated, the center of gravity of the R spectral characteristic curve moves toward the G spectral characteristic curve in FIG.

Then, the amount of chromatic aberration r*g+b determined from the relationship between the imaging characteristic Lr of the lens 3 and the position of the center of gravity of each spectral characteristic of R-B.
becomes smaller. As a result, the amount of deviation of the imaging position relative to the CCDs 5 to 7 becomes small.

For example, when an infrared cut filter with the trade name C-5O8 is used as the filter 100, its spectral spectrum is curve L1 in FIG. 2.

If this is used, pixel shifts as shown in FIG. 3 will occur. In other words, the pixel shift is within two pixels. 2
If the pixel shift is on the order of a pixel, there is no risk of causing any practical problems.

The lens 3 used is a lens having chromatic aberration characteristics as shown in FIG. 6, as described above.

Further, when an infrared cut filter with the trade name IEC502 is used as the filter 100, its spectral spectrum becomes curve L2 in FIG. 2.

When this is used, the pixel shift will be within 2 pixels as shown in FIG.

In this way, even when using a lens 3 having the same chromatic aberration as the conventional lens, if the spectral spectrum of the infrared cut filter 100 is appropriately selected, the chromatic aberration can be substantially corrected by the filter 100.

In addition, as the infrared cut filter 100 mentioned above,
The above is just an example, as any filter may be used as long as its transmittance range of 50% is within the wavelength range of 600 to 660 nm.

[Effects of the Invention] As explained above, according to the configuration of the present invention, as an infrared cut filter, the range of transmittance of 50% is 6.
- It uses a filter within the wavelength range of 00 to 660 nm.

According to this, even when a lens having chromatic aberration similar to that of a conventional lens is used, the chromatic aberration can be substantially corrected by this filter.

As a result, the image quality of characters and line drawings can be significantly improved.

Therefore, the present invention is extremely suitable for application to the color image processing apparatus as described above.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing an example of a color image processing device according to the present invention, FIG. 2 is a spectrum characteristic diagram of an infrared cut filter, FIGS. 3 and 4 are explanatory diagrams of pixel shift,
FIG. 5 is a block diagram of a main part used to explain the present invention, FIG. 6 is a characteristic diagram showing the relationship between spectral characteristics and chromatic aberration, and FIGS. 7 and 8 are explanatory diagrams of conventional pixel shift. 1... Color image processing device 2... Original (subject) 3... Lens 4... Spectroscopic system 5-7... Photoelectric conversion elements 10-12... A/D converter 20 ... Density conversion circuit 30 ... Color correction means 40 ... Color ghost correction circuit 50 ... Resolution correction circuit 60 ... Color data selector 70 ... Multi-value conversion means 80 ... Interface circuit 90 ...Output device 100...Infrared cut filter 110...Light source

Claims (1)

[Claims] (1) Includes a spectroscopic system that converts image information into a plurality of color-separated lights, a plurality of photoelectric conversion elements that convert each color-separated light into image signals, and an image processing means that performs image processing on the plurality of image signals. death,
An infrared cut filter is installed in front of the above spectroscopic system,
As for its transmission characteristics, the range of transmittance of 50% is 600 to 660.
A color image processing device characterized in that the color image processing device is selected to have a wavelength within the range of nm.