JPS61269460A - Picture reader - Google Patents

Abstract

PURPOSE:To prevent a moire phenomenon and to obtain an intermediate picture free from noise by providing a defocusing device that makes a picture line information a defocused state and a defocusing device that makes the defocusing device the defocused state when reading a dot original. CONSTITUTION:The picture line information of an original 6 is photoelectric converted by an image sensor 20. Output signal of the image sensor 20 is amplified by a dotting circuit 38, digitalized by an A/D oscillator and shading corrected, and then converted to the dot picture in binary or half tone by using a pattern ROM. When reading a dot original, reading in a dot mode is instructed from a console panel. On receiving the dot signal, A CPU 30 operates a focusing motor 26, and shift the image sensor 20 by a specified distance from the focus position. Thus, reading is performed in the defocused state.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a document reading device equipped with an image sensor and a reduction optical system using a lens.

(Prior Art and Problems to be Solved by the Invention) A halftone image is an image in which each pixel is expressed in binary values of white and black, and is widely used in newspapers and printing. Halftone originals are usually expressed by halftone dots.

When halftone dot expression is read by an image sensor and halftone processing such as dithering is performed, image disturbances (stripes) called moiré appear. Moiré occurs when the dot period of the original image is close to the pixel pitch or dither period of the image sensor.

Since moire does not exist in human images, it is not desirable for image reproduction.

Various methods have been tried in the past to suppress moire. For example, Takashima et al.
-67) uses a pattern density method for halftone dot originals in rehalftone dot processing for images containing halftone dot images. There is also a method of using a "blur foot" screen when performing halftone dot processing during printing.

If the pixel pitch of the image sensor is larger than the halftone dot period of the halftone document, moiré does not occur, but the resolution decreases. Furthermore, if the pixel pitch of the image sensor is smaller than the halftone dot period of the halftone original, the resolution will be high, but the occurrence of moiré will be noticeable.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image reading device that can prevent the occurrence of moiré phenomena when reading halftone originals.

(Means for Solving the Problems) A document reading device according to the present invention includes an image sensor that detects the density of a document, a lens disposed in an optical path between the document and the image sensor, and an output signal of the image sensor. a halftone processing means for carrying out halftone processing; a defocusing means for putting the image information incident on the image sensor through the lens into a defocused state; The present invention is characterized by comprising a defocus control means for controlling the defocus state.

(Function) When reading a halftone original where moire occurs, the halftone original is defocused and read in a state where it does not have any apparent periodicity, thereby suppressing the occurrence of moire.

FIGS. 1(a) to 1(C) show the occurrence of moiré.

FIG. 1(a) shows the halftone dot pitch in the focused state. When this pattern is read by an image sensor arranged as shown in FIG. 1(b), the output signal of each pixel 20a of the image sensor becomes as shown in FIG. 1(c).

Therefore, although not shown, an image different from the pattern shown in FIG. 1(a) is output by the halftone conversion (binarization) process. In this example, moiré with a period of 14 pixels occurs during halftone dot processing due to the beat between the period of the document pattern and the sampling period of the image sensor.

In the case of a photographic original, such a phenomenon does not occur because the size of the pixels of the photograph is sufficiently small compared to the pixels of the image sensor, and there is no periodicity in the arrangement thereof.

Next, the document in which moiré occurs is defocused to be in a state as shown in FIG. 1(d), and is made to have no halftone dot periodicity as in the case of a photo document. When this state is read by an image sensor, image=3- The output signal of each pixel 20a of the sensor becomes as shown in FIG. 1(e).

In this case, unlike the case of the focus state, moiré does not occur during the halftone processing of the output signal.

(Example) Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 is a sectional view of the mechanism of the image reader according to this embodiment. A halogen lamp 2 serving as an exposure source irradiates an original 6 placed on an original glass 4''. The halogen lamp 2 is equipped with a reflecting mirror 8 and a book mirror 10.

The reflected light from the original 6 is transmitted to the first mirror 12 and the second mirror 1.
4 and the third mirror 16, and passes through the lens I8 to the image sensor 2 consisting of a one-dimensional array of CCDs.
0.

The image sensor 20 is held by an image sensor holding section 22,
Additionally, the position and angle are adjusted. Further, the image sensor holding section 22 and the lens I8 are attached to a movable table 24.

Adjustment of the magnification is performed using the movable base 2 using the magnification adjustment motor M2.
4 in the optical axis direction.

Focus adjustment is performed by moving the image sensor 20 in the optical axis direction using a focus adjustment motor 26 attached to the moving table 24.

When scanning the original 6, the light source 2 and mirrors 12 to 16 are moved in the scanning direction, as is well known.

FIG. 3 is a block diagram of an electrical system for reading image information. A halftone mode signal, a magnification signal, and a start signal set on an operation panel (not shown) are input to the CPtJ 30 that controls reading. Further, a lens position signal, a slider position signal, and a document leading edge signal indicating the status of the scanning system are input.

On the other hand, the CPU 30, via drivers 32, 34, and 36, respectively operates a motor M1 for moving the scanning system and a motor M2 for magnification adjustment. The focus adjustment motor 26 is driven.

Further, the halogen lamp 2 is turned on by the exposure lamp signal.

The image information of the original 6 goes up to the image sensor 20 and is photoelectrically converted. The output signal of the image sensor 20 is amplified in the halftone conversion circuit 38, digitized by an Al1) converter, subjected to Zuding correction, and then
The image is converted into a halftone image using a pattern ROM in binary or halftone. The output circuit 40 outputs the output signal of the halftone circuit 38 to an output device (for example, a printer) in response to an output control signal from the CPU 30.

When reading a halftone document, first, an instruction is given to read in halftone mode from the operation panel. When the CPU 30 receives the dot mode signal, it operates the pinto motor 26 to move the image sensor 20 by a predetermined distance from the focus position. In this way, reading is performed in a defocused state.

In the embodiment described below, a halftone dot mode is provided, and switching of the mode is instructed from the operation panel.

In another embodiment, as shown in FIG. 4, a defocusing means 44 is provided, and when the image signal, once stored in the line memory 42, is determined to be a halftone image by halftone detection means (not shown). Then, the lens 18 is moved to a defocused state, and the document 6 is read again. Determination of whether or not the image is a halftone dot image by the halftone dot detection means (J1) This may be performed using various conventionally known methods.

In addition, in the embodiment described below, the image sensor 20 is moved to bring it into a defocused state, but the fifth
Various methods as shown in Figures (a) to (c) may be used. As shown in FIG. 5(a), the lens 18 may be moved, or as shown in FIG. 5(b), the original 6 may be moved to adjust the distance MA between the original 6 and the lens 18. It may be shifted. Furthermore, these may be combined. Further, as shown in FIG. 5(C), the lens I8 and the image sensor 20
Alternatively, a filter 46 may be inserted between the lens 18 and the document 6 to change the distance B or the apparent distance.

(Effects of the Invention) According to the present invention, it is possible to prevent a moiré phenomenon when reading a halftone image, and to obtain a noise-free halftone image.

[Brief explanation of drawings]

FIGS. 1A to 1E are diagrams for explaining reading in a defocused state. FIG. 2 is a schematic cross-sectional view of the image league. FIG. 3 is a schematic block diagram of the internal configuration of Image League. FIG. 4 is a block diagram showing a defocusing method in another embodiment of the present invention. FIGS. 5(a) to 5(C) are diagrams each showing a method for achieving a defocused state. 2. Exposure source, 6. Document, 18. Lens, 20. Image sensor, 26. Focus adjustment motor, 30. CPU. 38 Halftone circuit. Patent Applicant: Minolta Camera Co., Ltd. Agent: Patent Attorney: Mr. Mae and 2 others Figure 3 Figure 4 Figure 5 Σ (b) (C)

Claims (1)

[Claims] (1) An image sensor that detects the density of the original, a lens disposed in the optical path between the original and the image sensor, a halftone processing means that halftones the output signal of the image sensor, and a lens. The apparatus is characterized by comprising a defocusing means for defocusing image information incident on the image sensor through the image sensor, and a defocusing control means for causing the defocusing means to be in a defocused state when reading a halftone original. Image reading device.