JPS6134142B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical mask used for emphasizing the sharpness of a reproduced image in an image scanning recording device such as a plate-making scanner or a facsimile, and in particular, a relief mask used for emphasizing sharpness. This invention relates to an optical mask that prevents the appearance of images.

2. Description of the Related Art Conventionally, in image scanning recording apparatuses such as plate-making scanners, the sharpness of a reproduced image is generally improved by emphasizing the detail or contrast of the image to be reproduced.

As an optical method for improving the sharpness of such an image, a method using an unsharp mask or a differential mask is generally used.

FIG. 1 shows the principle of contrast enhancement by a differential mask, where A is the main signal and E is the blur signal. This blur signal is a so-called blurred image signal in which the change in signal level with respect to changes in image density is slower than that of the main signal.
Such a blur signal is produced by making the aperture of the aperture installed in the incident optical path larger than the aperture of the main signal aperture during photoelectric scanning of the original image, and the light intensity of the light beam passing through the aperture is reflected on the circumference of the aperture of the aperture. It is well known that this can be achieved by providing an annular semi-transparent part that gradually attenuates outward from the vicinity of the center.

Therefore, by subtracting the blur signal B from the main signal A, a contrast enhanced signal such as C is obtained.
When this contrast enhancement signal C is added to the main signal A, the density difference is expanded in a portion of the original image where the density changes, as shown in D, and a contrast enhancement effect is produced in the duplicated image, thereby improving the sharpness.

However, in an actual image scanning recording device such as a plate-making scanner, the photoelectrically converted main signal A and blur signal B are first processed by a logarithmic amplifier as shown in FIG.
The signals A' and B' are logarithmically transformed, and then the blur signal B' is subtracted from the main signal A' to obtain a contrast-enhanced signal C'. Here, the reason why both the main signal A and the blur signal B are input to the logarithmic amplifier is to improve the sharpness in the entire density range of the reproduced image. be.

Contrast enhancement signal formed in this way
C' is added to the main signal A' to form a main signal D' with enhanced contrast in the part where the density of the original image changes, and when a duplicate image is recorded with this signal D', the second
A relief image is generated in the part corresponding to a in Figure D′,
Visually, there was a drawback that gave an unnatural sense of discomfort.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical mask that does not generate a relief image when enhancing the sharpness of an image reproduced in an image scanning recording device.

FIG. 3A shows an embodiment of the optical mask 1 according to the present invention, which has an aperture 3 having a larger diameter than the aperture of the main signal mask plate and a concentration gradient around the aperture 3. It consists of an annular gradation section 2. The density slope of this gradation portion 2 is such that the density increases gradually as it moves away from the opening 3, as shown in FIG. Rather, the density value at the center of the gradation portion 2 has a curved density slope higher than that in the case of a logarithmic curve. The outer part of the gradation part 2 is a light-shielding part having a density value that is at least equal to or higher than the maximum density value of the gradation part 2.

When such an optical mask 1 is used in place of a conventional mask plate for creating a blur signal, the obtained blur signal is as shown in FIG. 4B. That is, the waveform of the portion corresponding to the opening 3 is similar to that when using a conventional mask plate (FIG. 1B),
The waveform of the portion corresponding to the gradation portion 2 has a shape opposite to the concentration gradient of the gradation portion 2.

Therefore, even if the blur signal formed by the optical mask 1 is logarithmically converted using an appropriate logarithmic conversion means such as a logarithmic amplifier as in the past, the rise and fall of the blur signal will be gradual as shown in FIG. 4C. The contrast enhancement signal D is formed by subtracting the blur signal C from the logarithmically converted main signal A, or is formed by adding the contrast enhancement signal D to the main signal A. The contrast-enhanced main signal E does not have a sudden change in density around it that causes a relief image like a in FIG. 2D.

What is shown in FIG. 5 is another embodiment of the optical mask according to the present invention. In this method, linear transparent parts are formed radially, and the number of transparent lines is gradually increased from the outer edge of the transparent part to the center. It can be made by increasing the amount of transmitted light in the opposite direction, and can achieve the same effect as the optical mask shown in FIG. 3.

Further, FIGS. 6 and 7 show other embodiments of the optical mask according to the present invention, which require the optical formation of a gradation portion having a predetermined concentration gradient as in the case of FIG. This embodiment has the advantage that it can be manufactured more easily than the above-mentioned embodiments because it can be manufactured by making the outer peripheral shape of the protruding portion of the light-transmitting portion 4 more concave than the logarithmic curve.

In the above description, the optical mask according to the present invention is provided at a position equivalent to the main signal mask plate, but it can also be provided on the optical path before that, for example, near the scanning light source. As a result, it is possible to increase the shape of the optical mask used, which is particularly advantageous when using an optical mask as shown in FIG. 5 because it is easy to manufacture.

Furthermore, in the above embodiment, the explanation was given using a differential mask that enhances the contrast of a duplicate image to improve sharpness. Exactly the same effect can be achieved with an unsharp mask.

As described above, when the optical mask according to the present invention is used to create a blur signal for improving the sharpness of a reproduced image, it is possible to completely prevent the occurrence of relief images that give an unnatural and unnatural feeling to the reproduced image. .

[Brief explanation of the drawing]

FIG. 1 is a signal waveform showing the principle of image contrast enhancement by a differential mask, FIG. 2 is an actual signal waveform processed by an image scanning recording device, and FIG. 3 is a signal waveform according to the present invention. An example of an optical mask, FIG. 4 shows a signal waveform when the optical mask of FIG. 3 is used to improve the sharpness of a reproduced image, and FIGS. Other examples of masks are shown. 1... Optical mask, 2... Gradation section,
3...Opening.

Claims (1)

[Claims] 1. Adding and subtracting the main signal and blur signal obtained by photoelectrically converting the light beam that scanned the original image through main signal and blur signal mask plates having different aperture sizes. In an image scanning recording device that improves the sharpness of a reproduced image by a sharpness emphasis signal formed by
In the blur signal mask plate, the density value is small at the center, and the density value gradually increases toward the periphery, and the density value at the center of the density slope is higher than that in the case of a logarithmic curve. By providing a curved density distribution, when logarithmically converting the blur signal obtained by the light beam transmitted through the blur signal mask plate, the curved density distribution is transparent so that the rise and fall of the converted signal waveform are gentle. An optical mask having a light beam transmission part with a light intensity distribution. 2. Claim 1, characterized in that the light beam transmitting section is composed of an aperture and an annular gradation section around the aperture in which the concentration increases as the distance from the aperture increases. optical mask. 3. A patent characterized in that the light beam transmitting portion is formed radially by a plurality of image-shaped transmitting portions, and the number of light transmitting lines is gradually increased from the outer edge to the center of the light transmitting portion. The optical mask according to claim 1. 4. The optical mask according to claim 1, wherein the light beam transmitting portion is formed by an opening whose outer peripheral shape is more concave than a logarithmic curve.