JPS644092Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Field of Industrial Application) The present invention relates to an optical filter that can be applied to optical devices such as photolithographic cameras or image scanning recording devices (hereinafter simply referred to as color scanners). , relates to a low-pass filter that cuts high frequency components of the spatial frequency components of an image and passes low frequency components.

(Prior art) The low-pass filter 6' is also called a high-frequency cut filter. For example, as shown in FIG. 6a
A large number of vapor deposition small circular portions 6a are provided in a random arrangement, and the area of the vapor deposition small circular portions 6a occupies approximately half of the total area. The thickness of the vapor deposited film is adjusted so that the light passing through the small vapor-deposited circular portion 6a has a phase shift of approximately half a wavelength with respect to the light passing through the non-evaporated portion. This filter is known as a phase filter.

When this low-pass filter 6' is installed before (or after) the lens of a prepress camera or the pick-up lens of a color scanner, the aperture of the lens is set to the same size as the small circle 6a due to the phase shift of the light. The same effect as narrowing down appears,
The image will be blurred. For example, if the original image is a halftone dot print, the halftone dots can be blurred to prevent moiré during re-halftone photography.

Further, as another example, the random small circular portion 6a
When the small circular portion 6a is made of a highly light-diffusing material, such as blackened silver particles, the small circular portion 6a scatters the light and shifts the amplitude. This filter is known as an amplitude filter and is also used as a low-pass filter.

(Problem to be solved by the invention) In these low-pass filters, the smaller the diameter of the small circular portion 6a, the more pronounced the blurring of the image becomes. Therefore, a large number of filters with different diameters are prepared to obtain the desired degree of blurring. You must use different filters depending on the situation.

As mentioned above, the present invention eliminates the troublesomeness of appropriately selecting a large number of low-pass filters with different diameters of the small circular part (hereinafter referred to as the light modulation part) 6a, and can achieve the desired blur using a single filter. The purpose is to provide an adjustable low-pass filter.

(Means for Solving the Problems) In order to achieve the above object, the present invention, for example, as shown in FIG.
This is a low-pass filter in which a large number of light modulating parts 6c are alternately arranged in a radial pattern that converges on one point 0, and the sum of the areas of the light modulating parts 6c occupies approximately half of the total area.

(Function) The present invention having the above-mentioned configuration can be used for example as shown in FIG.
As the low-pass filter 6 shown in FIG. 1 is moved and adjusted in the direction of arrow P relative to
By arbitrarily changing the arrangement pitch of the light modulating section 6b and the light modulating section 6c, it is possible to select a desired degree of blur without preparing a large number of low-pass filters.

(Example) Hereinafter, an example of the present invention will be described based on FIGS. 1 to 5.

FIG. 3 is a schematic diagram of the case where the low-pass filter of the present invention is applied to a color scanner to prevent moire.

The light emitted from the light source 1 is reflected by a mirror 2 at a substantially right angle, and a color transparency 4 (hereinafter referred to as the original image) is wrapped around a transparent drum 3.
After passing through a small area (for example, 1 mmφ), the light passes through a pick-up lens 5 and a low-pass filter 6, and its optical path is branched by a branching mirror 7. A reduction lens 8 is provided on one of the branched optical paths for reducing the image enlarged (for example, 10 times) by the pick-up lens 5 (although it is not necessarily necessary to reduce the image, it is often easier to observe if the image is reduced). A grating 9, which will be described later, is disposed on the image forming surface of the reduction lens so that it can be observed in advance with the naked eye whether or not moire occurs on the grating surface.

The other branched optical path includes a reversing mirror 10,
Aperture 11 and blue B, green G, red R, respectively.
Three photoelectric converters 13 corresponding to two dichroic mirrors 12, 12 and a total reflection mirror 12' for color separation into three color components are provided to obtain color-separated scanning image signals of the original image. It's like this.

According to the inventor's research results, the low-pass filter 6 shown in FIG. 1 was found to have excellent effects, and will be described in more detail below.

According to this, the amplitude filter 6 is formed by alternately arranging a large number of light transmitting parts 6b and light diffusing parts 6c in a radial pattern, and by moving the amplitude filter 6 in the direction of arrow P relative to the pick-up lens 5. Therefore, by changing the arrangement pitch of the light-transmitting part 6b and the light-diffusing part 6c (there is no limitation on the direction of movement and there is no problem in moving in any direction), it is possible to obtain the desired degree without preparing a large number of filters. You can select blur.

The light transmitting portions 6b and the light diffusing portions 6c are arranged radially to converge to one point 0, and are formed so that the sum of the areas of the light diffusing portions 6c occupies approximately half of the total area of the amplitude filter 6. The light diffusing part is formed of a material such as blackened silver particles that can provide higher light diffusion than the light passing through the light diffusing part. Note that it is more preferable to form the light diffusing portion with a light-transmitting material than with a light-absorbing material.

In addition, in the above, instead of the light diffusion part 6c, a light modulation part 6c with the required vapor deposition film thickness adjusted,
Can be applied as a phase filter.

As an example, as shown in Fig. 1, the distance d from one end of the filter 6 on which a radial pattern is densely formed to the point 0 outside the filter is 15 mm, and the size of the filter 6 is vertical e = 15 mm, horizontal f =90mm
When the angular pitch θ of the radial pattern is 0.15° as shown in FIG. 2, the arrangement pitch of the light transmitting portion 6b and the light modulating portion 6c can be continuously changed from about 50 μm to 300 μm.

In the above example, only an example of the pitch size between the light transmitting portion 6b and the light modulating portion 6c has been described, but the present invention is not limited to this.

Furthermore, although the transparent portion 6b and the light modulating portion 6c are shown to have the same size (area), they do not necessarily have to be the same size. That is, it may be changed depending on the degree of image quality to be reproduced. For example, if it is desired to cut out higher frequency components among the spatial frequency components of the image, the light modulation section 6c may be changed.
In the opposite case, the portion of the light modulating section 6c may be decreased.

In FIG. 3, light from the original image that has passed through the pick-up lens 5 is modulated by a low-pass filter 6 consisting of the above-mentioned phase filter or amplitude filter, and the light from the original image after modulation is branched by a branching mirror 7. and is projected via the reduction lens 8 onto the grating 9 disposed in one of the branched optical paths as described above.

As shown in FIGS. 4 and 5, the grid 9 is formed in a grid-like checkerboard pattern, and the arrangement pitch of the checkerboard pattern is determined by the shape of the aperture 11 and the pitch of the scanning lines. A large number of predetermined ones are prepared in advance so that they can be selected depending on the pitch of the screen forming the halftone image. That is, (a) the combination of the above-mentioned synchronicity pattern included in the original image 4 and the aperture placed in the other branched optical path, (b) the combination of the synchronicity pattern and the scanning line, and (h) ) The mode of moire that occurs due to the combination of the synchronization pattern and the pitch of the screen, etc. is the mode of moire that occurs due to the combination of the synchronization pattern included in the original image 4 and the grid 9 of the specific pitch. It has been experimentally confirmed that there is a substantial approximation.

Therefore, the grid 9 of a predetermined pitch is created by taking into consideration the synchronicity pattern included in the original image 4, the aperture 11 to be used, the screen pitch, the pitch of the scanning lines, and the enlargement ratio of the image to be scanned and recorded.
is selected, and the low-pass filter 6 is adjusted so as to eliminate the moiré caused by the reduced image projected on the grid and the grid, so that an image recording signal is obtained by the light from the original image modulated thereby. It's okay.

As a specific example, (1) The pitch of the synchronization pattern between the screen pitch and the pattern is both 145 μm.
(equivalent to a 175 line/inch screen), (2) the aperture 11 is 1.5mm x 1.5mm and the pattern is 1.5mm pitch, or (3) the scanning pitch and pattern are 72μ
In either case of m or 64μm, the pitch of the low-pass filter is
A thickness of about 70 μm to 140 μm was effective. Of course, if the magnification changes, the pitch of the low-pass filter 6 must also be changed.

The grid 9 is not limited to a grid-like checkerboard pattern, but may simply be composed of grid-like thin lines.

(Effect of the invention) Since the present invention is a low-pass filter 6 in which a large number of light-transmitting parts 6b and light modulating parts 6c are arranged in a radial manner so as to converge on one point, the low-pass filter 6 is By moving and adjusting the light transmitting section 6, the arrangement pitch of the light transmitting section 6b and the light modulating section 6c can be arbitrarily changed. This has excellent effects such as being able to arbitrarily obtain a desired blurred image.

[Brief explanation of the drawing]

1 and 2 show the low-pass filter of the present invention, FIG. 1 is a plan view thereof, FIG. 2 is a plan view showing the angular pitch of its radial pattern, and FIG.
The figure is a schematic diagram of the low-pass filter 6 of the present invention applied to a color scanner, Figure 4 is a plan view of the grid 9 in Figure 3, Figure 5 is an enlarged view of its main parts, and Figure 6 is a conventional technology. FIG. 3 is a perspective view of such a low-pass filter. 6, 6'...Low pass filter, 6b...Transparent section, 6c...Light modulation section, 0...Origin where the radial pattern converges.

Claims (1)

[Claims for Utility Model Registration] 1. A low-pass filter in which a large number of light transmitting parts 6b and light modulating parts 6c are arranged alternately and radially so as to converge to one point 0. 2. The low-pass filter according to claim 1, wherein the area of the light modulating section 6c occupies approximately half of the total area. 3. The low-pass filter according to claim 1 or 2, in which the light modulating section 6c is provided with a vapor-deposited film. 4. The low-pass filter according to claim 1 or 2, in which a light-diffusing material is arranged in the light modulating section 6c.