JPH0129346B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dotted original input device, and relates to a negative or positive reflective or transparent original (hereinafter referred to as a dotted dot) that reproduces the tone of an image using halftone dots.
The present invention relates to a device for scanning and inputting information.

Conventionally, when scanning a document using a scanner or a direct engraving machine using a gravure cylinder, as shown in FIG. The light is received by a phototube 7 through an aperture 5 and a lens 6, and the intensity of the light is converted into the intensity of an electric current.

However, when the original is a halftone original, moire occurs between the halftone dots of the original and the scanning line. In order to avoid this moiré, the only options were to increase the aperture until it was the average value of several halftone dots, or to shift the focus when scanning the original and enter it in a so-called blurred state. In either method, the resolution is significantly lower than that of the original.

The present invention relates to a halftone original input device for a scanner or the like that does not cause moire or decrease in resolution when a halftone original is used as a document, and will be explained in detail below with reference to the drawings.

FIG. 2 is an explanatory diagram of the screen pitch and halftone dot b of the halftone original, and the screen pitch of the halftone original is a
In this case, in order to input a halftone original without recognizing each halftone dot as a halftone dot and without reducing resolution, input the halftone original into a square c whose side corresponds to the screen pitch a. If you pick up pixels and input them as average density, you can obtain exactly the same effect as inputting continuous tone pixels without reducing the resolution of a halftone original. If such input is obtained, it may be outputted as continuous tone or net positive and negative using a normal scanner,
Alternatively, the gravure cylinder may be directly engraved.

In order to obtain this desired effect, a square aperture 5 may be inserted in the scanning head so that the phototube 7 can receive light from a pixel equal to one side of the screen pitch of the screen original.

However, in the case of halftone originals, the screen angles are changed for each color to prevent moire from occurring due to each other's screens when overprinting is performed. Note that d indicates the arrangement of halftone dots.

FIG. 3 is an explanatory diagram showing an example of pixel information pick-up when scanning a screen original with a square aperture and a screen angle of 30 degrees.
As can be seen here, even though a halftone original with a uniform halftone dot b area is being scanned, the density of each pixel e information clearly varies greatly (black dots within each pixel e). (This becomes clear when comparing the total area of .

In such a case, the output halftone dot area will vary and a moire phenomenon will occur. As a result of various studies to solve this problem, it was discovered that the problem could be solved by setting a square aperture to match the angle of the mesh original.

FIG. 4 shows an example in which a screen original with a screen angle of 30° is arranged with apertures matching the screen angle of 30°.

As is clear from Figures 4a and b, no matter what pixel pick-up interval is scanned, by using a square aperture that matches the screen angle of the halftone original, the average of one halftone dot is always obtained. It becomes possible for the phototube to capture the image as a density, and it becomes possible to input it without reducing the resolution of the original mesh original.

That is, as long as the screen angle of the screen original and the angle of the square aperture match, the same effect can be obtained whether the pixels are picked up apart or overlapped.

By the way, as shown in FIG. 5, in a net positive used as a net original, patterns 10 and 11 having different screen angles in the scanning direction of the original (direction of the arrow in the figure) are combined. There is also. In this case, if the angle of the aperture 5 is made to match the screen angle of the pattern 10, moiré will occur between the halftone dot pattern of the screen angle of the pattern 11 and the scanning line.

Taking these points into consideration, the present invention provides a screen original input method that does not cause moiré between the halftone dot pattern of the screen original and the scanning line, even if the screen original is a screen original in which patterns with different screen angles are combined. The aim is to provide equipment.

That is, according to the mesh original input device of the present invention, the screen angle of the mesh original image can be detected in advance, and the angle of the aperture can be changed to match the detected screen angle.

According to the apparatus of the present invention, when scanning a mesh original, the mesh original is scanned by a line sensor prior to the square aperture 5, and the screen angle of the mesh original is determined based on the signal from the line sensor. can be detected.

6a and 6b are explanatory diagrams of the principle of screen angle detection by the device of the present invention, and assume that the screen original moves relatively in a direction perpendicular to the length direction of the line sensor 40. . Further, the screen pitch a of the screen original is known in advance. In this case, the following relational expression holds between the distance x in the scanning direction between halftone dots A and halftone dots B of the halftone original, the screen angle Θ, and the screen pitch a.

Θ=sin ^-1 x/a Here, since the screen pitch a is known, the screen angle Θ can be found by knowing the distance x. In order to find the distance x, the present invention utilizes electrical signals obtained by scanning the halftone dots A and B of the halftone original by the line sensor 40.

FIG. 7 is for explaining how the distance x is determined using the electric signal obtained by scanning the halftone dots of the halftone document using the line sensor 40.

First, the line sensor 40 scans the halftone dot A and binarizes the obtained electrical signal. FIG. 7 shows the signal 21 of the halftone dot A thus obtained, and also shows the signal 22 obtained by scanning the halftone dot B.

Here, a constant pulse signal 23 as shown in FIG. 7 is generated from a pulse generator such as an encoder, and the pulse signal is generated within a period t from when the signal 21 becomes high level until when the signal 22 becomes high level. Count the number of pulses of signal 23.
If the number of pulses counted at this time is Y, and the distance the screen original moves per pulse is X, the relational expression x=X・Y is established, and therefore Θ=sin ^-1 X・Y/a. Become.

Note that the value of X is appropriately determined depending on the required resolution.

As described above, the screen angle of the screen original is determined, and the angle of the square aperture 5 is determined to match this angle.

If the aperture angle determined in this way is different from the currently set aperture angle, the aperture is rotated by an aperture driving means such as a pulse motor so as to reach the determined aperture angle.

FIG. 8 is a schematic explanatory diagram of the mesh original input device of the present invention as described above, in which a mesh original 33 is illuminated by a reflection or transmission light source 31 and a lens 32, and the reflected or transmitted light is transmitted to a lens 34. The light is received by a phototube 37 through an aperture 35 and a lens 36, and the intensity of the light is converted into the intensity of an electric current.

On the other hand, a line sensor 40 for scanning the mesh original 33 is attached prior to the scanning of the mesh original 33 by the aperture 35. A screen original 33 is illuminated by a light source 41 for reflection or transmission and a lens 42, and the reflected or transmitted light is received by the line sensor 40 via the lens 43. As the line sensor 40 scans the halftone dot image of the halftone document, it outputs electrical signals 21, 22, etc. as illustrated in FIG. 7, and these signals are input to the arithmetic unit 44.

On the other hand, a pulse signal 23 shown in FIG. 7 is generated from a pulse generator 45 such as an encoder, and this pulse signal is input to an arithmetic unit 44. Furthermore, data preset by a parameter input device 46 for inputting parameters such as screen pitch that vary depending on the screen original can be input to the arithmetic device 44.

The arithmetic unit 44 calculates the screen angle Θ of the screen original based on the previously described relational expression based on preset data, the signal from the line sensor, and the pulse signal from the pulse generator. The value of the screen angle Θ of the screen original thus obtained is used to change the angle of the aperture by the aperture driving means. That is, the difference Θ' - Θ between the screen angle Θ of the mesh original and the previously obtained screen angle Θ' of the mesh original is determined, and a pulse signal corresponding to Θ' - Θ is sent to the pulse motor drive device 47 as an angle signal. The pulse motor drive device 47 drives the pulse motor 4 so that the screen angle of the screen original and the angle of the aperture 35 match.
Drive 8. A pulse motor gear 49 is attached to the pulse motor 48, and the pulse motor gear 49 meshes with an aperture gear 50 attached to the aperture 35, so that the rotation of the pulse motor 48 allows the aperture 35 to rotate. ing. Note that since the scanning of the mesh original by the line sensor 40 precedes the scanning of the mesh original by the phototube 37 via the aperture 35, the portion of the mesh original 33 measured by the line sensor 40 is the position to be input by the phototube 37. In order for the angle signal to be input to the pulse motor drive device 47 when the angle signal is reached, the arithmetic unit 44 should have a function of applying a time delay, or a time delay circuit should be added next to the arithmetic unit. .

Next, to explain the halftone dot detection by the line sensor in more detail, it is determined whether the halftone dot detected by the line sensor is to be halftone dot A or halftone B as follows. That is, what is between the starting point i and the midpoint j of the line sensor 40 is taken as the measuring target for halftone dot A, and what is between the midpoint j and the ending point k is taken as the measuring target for halftone dot B. In this way, the counting period of the pulse signal 23 for halftone dots A and B can be obtained. Also, under the above measurement conditions, the halftone dot A
If halftone dot A under the above conditions is detected again after halftone dot B is detected, the count value of the pulse signal 23 is cleared and counting is restarted from that halftone dot A.

Alternatively, the screen angle Θ of the mesh original may be determined by repeating the measurement of the screen angle of the mesh original a plurality of times and having data of a majority or more of the same value.

In addition, the screen angle for screen manuscripts is generally 15°,
Since it takes discrete values such as 30°, 45°, and 60°, it can also absorb variations in the measured value of the screen angle Θ.

As described above in detail, according to the apparatus of the present invention, when inputting a screen original into a scanner for plate making, etc., the difference between the halftone dots of the screen original and the input scanning line can be adjusted without impairing the sharpness of the screen original. Moiré can be prevented. Furthermore, even when inputting mesh originals with different screen angles, the aperture angle and the screen angle of the mesh original can always be made to match. Even in the case of inputting an original, it is possible to prevent moiré between the halftone dots of the halftone original and the input scanning line without impairing the sharpness of the halftone original.

[Brief explanation of drawings]

Figure 1 is an illustration of scanning a document using a normal scanner or direct engraving machine with a gravure cylinder. Figure 2 is an illustration of screen pitch and halftone dots. Figure 3 is an illustration of scanning a document with a square aperture and a 30° screen angle. Figure 4 is an explanatory diagram showing the information density of a pixel in scanning a mesh original. Figure 4 is an explanatory diagram showing the information density in scanning when the square aperture is made to match the screen angle of the mesh original (30°C). FIG. 6 is an explanatory diagram of the principle of screen angle detection by the device of the present invention. FIG. 7 is an explanatory diagram of electric signals and pulse signals by the line sensor. A schematic explanatory diagram of the apparatus shown in FIG. 1...Light source, 2...Lens, 3...Original, 4...
...lens, 5...aperture, 6...lens,
7... Phototube, 10, 11... Pattern, 21... Signal of halftone dot A, 22... Signal of halftone dot B, 23... Pulse signal, 31... Light source, 32... Lens, 33
... Net manuscript, 34 ... Lens, 35 ... Aperture, 36 ... Lens, 37 ... Phototube, 40 ...
...Line sensor, 41...Light source, 42, 43...
... Lens, 44 ... Arithmetic device, 45 ... Pulse generator, 46 ... Parameter input device, 47 ...
...Pulse motor drive device, 48...Pulse motor, 49...Pulse motor gear, 50...Aperture gear.

Claims (1)

[Claims] 1 In an original scanning input device having a light source, a lens, an aperture, and a phototube, there is a square aperture that allows square pixels corresponding to the screen pitch of a screen original to be input to the phototube, and a screen original is scanned in advance of the aperture. a line sensor for determining the screen angle data of the screen original based on the signal from the line sensor; A screen original input device comprising: an aperture drive means for driving the screen to match the screen angle of the screen original.