JPH04239880A - Original reader - Google Patents

Abstract

PURPOSE:To input a picture without damaging picture information possessed by an original. CONSTITUTION:A stray light correcting plate 5 is buried on the contact glass 1 near an original to be read so as not to prevent the traveling of an original. It is a plate long in a main scanning direction, having uniform known reflectance. A photoelectric conversion element 4a reads the original to be read and a photoelectric conversion element 4b reads the stray light correcting plate. The influence of a secondary light source and the influence of shading generated on an original face can be removed from the reading signal of the correcting plate 5.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a document reading device, and more particularly to an image reading device capable of capturing image information with high precision. For example, it is applied to copying machines, facsimile machines, image file devices, and the like.

0002

8(a) and 8(b) are diagrams for explaining straight light generation. In the figures, 31 is an original, 32 is a contact glass, 33 is a light source, 34 is an opposing reflector, and 35 is a The CCD light receiving element, 36 is a housing.

[0003] Stray light refers to reflected and diffused light from the peripheral casing 36, the document itself, and its multiple reflection light, and is a bundle of light rays that enters the document 31 or the imaging surface from a path other than the original optical path. It has been observed that the signal of the image area of interest changes due to stray light due to the influence of surrounding image signals, and that the MTF of the read image deteriorates, but this is necessary for a high-quality document reading device. It becomes a big problem in some cases. In contrast to the original reading signal when the original is a solid black image, in the configuration shown in Figure 8, the black image signal in the center is affected by the white image in the periphery, resulting in a phenomenon in which the density decreases. It has been observed. This is because, as shown in FIG. 8, the light beam reflected and diffused on the document surface is re-reflected by the surrounding casing 36, especially the light source itself, and affects the nearby image area as stray light. be.

Conventionally, in order to prevent this, a method has been proposed in which light shielding plates are arranged in the longitudinal direction of the linear light source at right angles thereto to cut off the light beams that are reflected and diffused in the longitudinal direction of the linear light source (for example, Japanese Patent Laid-Open No. -182864). This is called a louver. Although this is not intended to directly prevent stray light, it is a method used in practice.

[0005] In addition, for example, Japanese Patent Application Laid-Open No. 1-267531
The publication proposes a method in which light transmission or non-transmission is controlled in synchronization with an image information detection means such as a CCD using a mechanical shutter or a liquid crystal shutter adjacent to a document loading means. However, in reality, it is difficult to align the reading pixels and the shutter and to drive the shutter at high speed, and the device itself becomes large, which is not practical.

[0006] Also, the previously proposed patent application No. 2-2124
No. 70 obtains a sensor output by blocking the reflected light from pixels that are normally read in a certain way, only the components detected by the sensor by a secondary light source, stores this in memory, and performs normal reading. Stray light is corrected by subtracting it from the read output (that is, the output obtained by adding the influence of the secondary light source to the information of the regular pixels).

[0007] When an image reading device reads a document, there is a phenomenon that the reading level is changed due to the actual brightness of a certain point. This is because the illumination for reading the document is applied to an area having a certain area including the point where the document is to be read, and the diffused reflected light from the surrounding document surface becomes a secondary light source. The light from this secondary light source mixes into the optical path from the normal reading point to the sensor and is sensed by the sensor as a level change. Therefore, a small black area within an entirely white area is read brighter than it actually is.

For example, as shown in FIG. 8, black characters in a white document are affected by the white background, and the black becomes lighter and the edges become duller, making it impossible to read the characters as clearly black characters. Also, an area of a certain size goes from white to black (from black to white)
Even during transition, the edges are not clear and blurred, resulting in a read image that lacks fine image information.

[0009] Also, a shading correction error is a factor of variation in the reading level. Shading correction is
Before reading starts, a reference white board is read and stored, and each read signal is multiplied by the reciprocal of this to correct non-uniform illuminance. However, since reading of the document starts soon after the light source is turned on, the light source is in a very unstable state. As a result, the illuminance distribution fluctuates during reading of the document, resulting in an error in shading correction.

0010

[Object] The present invention was made in view of the above-mentioned circumstances, and an object of the present invention is to provide a document reading device that can input an image without damaging the image information of the document.

[0011]

[Structure] In order to achieve the above objects, the present invention provides (1)
In an image reading device that obtains an electric signal according to the density of a document as an image signal using a photoelectric conversion element, a correction plate with a known density provided on a document mounting means substantially close to a pixel of the document to be read, a document reading pixel and the The correction plate has an optical arrangement in which an image is formed by an imaging element onto a photoelectric conversion element placed adjacent to the correction plate; It consists of a correction plate with a known density, and an optical arrangement that images the original reading pixels and the correction plate onto an adjacent photoelectric conversion element using an imaging element, and the photoelectric conversion element adjusts the density of the original. In the image reading device which obtains a corresponding electric signal as an image signal, the correction plate is arranged on the light source side with respect to the original reading position. Hereinafter, the present invention will be explained based on examples.

First, the concept of the present invention is illustrated in FIGS. 2(a) and 2(b).
). Even if the reflectance of the original to be read is the same, the level of the signal read will vary depending on the brightness of the ground (reflectance of the surrounding image) and variations in the brightness distribution of the light source. The former is an effect of the luminous flux from the above-mentioned secondary light source (hereinafter referred to as stray light), and the latter is an effect of shading. If we now consider ideal reading characteristics that are not affected by these influences, a proportional relationship as shown in FIG. 2 holds between the actual reading characteristics and the ideal reading characteristics. Therefore, when the reflectance of the pixel to be read is r, a signal (output signal from an ideal reading system) d0 that is not affected by "secondary light source" and "shading" is:
It can be calculated using the following formula. d0=d・(1-(y-y0)/y)=d・y0/
y (1)

00
13] At this time, y is the actual read signal when a document with a known reflectance r0 is placed on the pixel of interest, y0 is the ideal read signal that is not affected by the secondary light source and shading, and d is the reflectance This is an actual reading signal for the r document. (y-y0)/y in the above equation (1) indicates the stray light rate that is occurring. If the stray light rate can be considered to be equal between the reading pixels on the document surface and the correction plate, the above (1)
The formula holds true.

FIG. 1 is a configuration diagram for explaining one embodiment of a document reading device according to the present invention. In the figure, 1 is a contact glass, 2 is a light source, 3 is an imaging element, and 4a and 4b are photoelectric conversion devices. 5 is a stray light correction plate, and 6 is an original. The stray light correction plate 5 is a main part of the present invention, and the stray light correction plate is embedded in the contact glass 1 near the document reading area on the contact glass 1 so as not to obstruct the travel of the document 6. , a plate (stray light correction plate) that is long in the main scanning direction and has a uniform and known reflectance. The photoelectric conversion element 4a is configured to read an original, and the photoelectric conversion element 4b is configured to read a stray light correction plate. Here, the depth of the groove for embedding the correction plate 5 in the contact glass 1 is set to a level that can be sufficiently ignored compared to the depth of field of the imaging system.

The correction plate 5 does not necessarily need to be embedded in the surface of the contact glass 1 unless scanning of the original to be read can be prevented, and a sufficiently thin sheet may be pasted on the glass surface or paint with uniform density may be applied thereto. Further, the effect is the same whether the imaging element is of the same magnification type or the reduced type. When illuminating the original with a diffuse light source such as a fluorescent lamp, Figure 3
As shown in , the peak of the illuminance distribution on the document is not necessarily located at the reading position, but tends to shift toward the light source. This tendency becomes more noticeable when the document is moved closer to the light source in order to increase the illuminance on the document surface. Therefore, a lot of stray light is generated from areas with high illuminance other than this reading position. Therefore, by placing a correction plate on the document on the light source side with respect to the document reading position, and blocking unnecessary light flux that illuminates areas other than the reading position, the level fluctuation of the read signal depending on the document ( The effect of secondary light sources) can be reduced, and the burden of correction can be reduced. This allows for higher precision reading.

The output signal from the photoelectric conversion element 4a corresponds to d in FIG. 2, and the output signal from the photoelectric conversion element 4b corresponds to y. Here, by measuring and storing in advance the output signal from the photoelectric conversion element 4b in a state where there is no influence of the secondary light source and shading corresponding to y0 (for example, a state where no document is placed), the above ( Using equation 1), it is possible to obtain an ideal read signal that is not affected by the secondary light source and shading.

FIG. 4 is a circuit diagram for explaining signal processing of the document reading device according to the present invention, and in the figure, 10 and 11 are C
CD sensor, 12 and 13 are sample and hold circuits (S&
H), 14 and 15 are A/D converters, 16 and 17 are correction memories, 18 and 19 are shading correction circuits, 20 is a removal circuit, 21 is a correction memory (y0), and 22 is a multiplication circuit.

This is an embodiment of signal processing in which a signal obtained by the image reading device shown in FIG. 1 is processed according to the above equation (1). Photoelectric conversion element (CCD sensor)
After the output signal is A/D converted, shading correction is performed. The difference from the signal from the ideal reading that remains without shading correction is the stray light component. Figure 4
is an example of correcting this signal. Signal di from the first pixel of photoelectric conversion elements 4a and 4b in FIG.
Di/yi is calculated by a division circuit for yi, and the product is calculated by the signal y0, which is not affected by the secondary light source and which is measured at a certain illuminance and stored in memory before reading the image. , this is taken as the i-th pixel reading signal output of the document.

FIG. 5 is another circuit diagram for explaining the signal processing of the document reading device according to the present invention, and the reference numerals in the figure correspond to those shown in FIG.
The same reference numerals are given. As shown in FIG. 2, the actual reading characteristics include fluctuation components due to shading and stray light compared to the ideal reading characteristics. The signal processing system shown in FIG. 4 performs the stray light correction process of the present invention on the reading characteristics after shading correction. However, shading and stray light can be considered to be the same component that changes the output. Therefore, by making the reflectance of the stray light correction plate shown in FIG. 1 equal to that of the shading correction plate and setting the signal y0, which is not affected by the secondary light source and stored in the memory, for each pixel, , variations in the light source and variations due to the secondary light source can be corrected together.

This makes it possible to omit the shading correction that was performed on the output signals from the two CCD sensors in the example of FIG. 4, and to simplify the configuration of the signal processing circuit. Furthermore, according to the present invention, a standard white plate (shading correction plate) for performing shading correction is read and corrected for each line, and the light source fluctuates and the shape of the illuminance distribution changes over time. No shading correction error occurs.

FIG. 6 is still another circuit diagram for explaining the signal processing of the original reading device according to the present invention. In the figure, 23 is a line memory, and other parts having the same functions as those in FIG. 4 are designated by the same reference numerals. is attached. In FIG. 1, since the image reading position and the stray light correction plate reading position are separated by several lines in the sub-scanning direction, the influence of the secondary light source on both is also different by several lines. Therefore, FIG. 6 shows the output signal from the stray light correction plate of the signal processing system in FIG.
Corresponding lines are stored, delayed, and stray light components corresponding to the same reading position are subtracted from the image reading signal by the method of formula (1).

FIG. 7 shows still another circuit for explaining the signal processing of the document reading apparatus according to the present invention, and the same reference numerals as in FIG. 6 are used in the figure. A line memory 23 is added to the signal processing system shown in FIG. 5 in order to perform the above correction by delaying the deviation of the stray light component due to a difference in reading position by a corresponding line.

[0023]

[Effects] As is clear from the above description, the present invention has the following effects. (1) Effect corresponding to claim 1: A correction plate with uniform density is installed near the reading position on the contact glass surface,
Since the reflected light from the original and the correction plate is read by an imaging element and a different photoelectric conversion element, it is possible to determine the effects of secondary light sources and shading occurring on the original surface from the read signal of the correction plate. As a result, it is possible to perform highly accurate document reading by removing these influences from the document reading signal. (2) Effect corresponding to claim 2: In the document reading device of claim 1, since the correction plate is arranged on the light source side, a large amount of secondary light source (stray light) is generated from the document on the light source side. can reduce the impact of Therefore, the above (
The burden of correction shown in equation 1) is reduced, and as a result, highly accurate reading becomes possible.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram for explaining an embodiment of a document reading device according to the present invention.

FIG. 2 is a diagram for explaining the concept of the present invention.

FIG. 3 is a diagram showing the relationship between light source position and illuminance distribution.

FIG. 4 is a circuit diagram for explaining signal processing of the document reading device according to the present invention.

FIG. 5 is another circuit diagram for explaining signal processing of the document reading device according to the present invention.

FIG. 6 is yet another circuit diagram for explaining signal processing of the document reading device according to the present invention.

FIG. 7 is still another circuit diagram for explaining signal processing of the document reading device according to the present invention.

FIG. 8 is a diagram for explaining stray light generation.

[Explanation of symbols]

1 Contact glass 2. Light source 3 Imaging element 4a, 4b Photoelectric conversion element 5 Stray light correction plate 6 Manuscript

Claims (2)

[Claims] 1. An image reading device that obtains an electrical signal according to the density of a document as an image signal using a photoelectric conversion element, comprising: a correction plate with a known density provided on a document mounting means substantially close to a pixel of the document to be read; What is claimed is: 1. A document reading device comprising: a document reading pixel and an optical arrangement for forming an image of the correction plate on an adjacent photoelectric conversion element using an imaging element. 2. A correction plate with a known density provided on a document mounting means substantially close to a pixel of a document to be read, and a photoelectric conversion element placed adjacent to the document reading pixel and the correction plate by an imaging element. In the image reading device, the correction plate is arranged on the light source side with respect to the original reading position. The document reading device according to claim 1, characterized in that: