JPH0650902B2 - Image reader - Google Patents

Description

The present invention relates to an image reading apparatus using a solid-state image sensor.

[Conventional technology]

As an image reading device of this type, as shown in JP-A-58-202662, a white diffusion plate that can be arranged at an image reading position, a light source that illuminates the image reading position, and an image reading position by the light source are provided. An optical sensor such as a solid-state image sensor that detects reflected light from the placed document or the white diffuser and a memory device that temporarily stores the output signal of the optical sensor are provided, and the output signal from the memory device and the It is known that a binary signal is obtained by comparing the output signal from the optical sensor with a binary circuit.

In the image reading device described in JP-A-58-202662, the output signal from the memory device is converted into an analog signal by a digital-analog converter, and then the analog signal and the analog signal obtained from the optical sensor are combined. To obtain a binarized signal.

Further, as a conventional image reading apparatus, there is Japanese Patent Laid-Open No. 59-18978.
As shown in Japanese Patent Publication No. 3, a means for detecting the background density level in the scanning line of the original image area is provided, and in the scan before the scanning of the predetermined scanning line, the threshold level of the predetermined scanning line is sequentially determined based on the detected background density. It is known that a binary signal is obtained by changing the binary signal.

The image reading apparatus described in Japanese Patent Laid-Open No. 59-189783 does not require a memory for storing image signals and preliminary scanning, but it requires three latches and two comparators. is there.

[Problems to be Solved by the Invention]

The image recording apparatus described in Japanese Patent Laid-Open No. 58-202662 uses a binarization circuit for comparing analog signals with each other, that is, an analog comparator, and thus requires a digital-analog converter. Because
In addition to being easily affected by external environmental conditions, stable operation is difficult, and it is difficult to perform highly accurate and high speed shading correction.

Further, in the image recording apparatus described in Japanese Patent Laid-Open No. 59-189783, it is necessary to perform the threshold level calculation for each line of the original scanning, so that it is not possible to reduce the calculation time loss and the three It requires a latch and two comparators, and cannot avoid cost increase.

An object of the present invention is that it is not easily affected by external environmental conditions, can perform stable operation, and can perform fine shading correction for each pixel at high speed without using a high-speed multiplier. , To provide a low-cost image recording device.

[Means for Solving the Problems]

The above object is to provide a reference reflector, a solid-state image sensor having a photoelectric conversion element corresponding to a pixel of a document reading scanning line, and one line of a reference analog signal from the reference reflector read by the solid-state image sensor. An analog-digital converter for converting the reference digital signal in units, a read / write memory for storing reference digital signals obtained from the analog-digital converter as reference data, having an address capacity corresponding to the pixels of the original scanning line A microprocessor for digitally calculating the comparison data based on the reference data and the density setting value, and replacing the calculated comparison data with the reference data of the read / write memory for storage; and an analog signal for reading an original read from an original. Dizzy It is achieved by an image reading device including a digital comparator for obtaining a binary signal by comparing the comparison data stored as original reading digital data converted into a digital signal to the read-write memory by Le converter.

[Action]

First, one line of the reference analog signal read by the solid-state image sensor from the reference reflection plate is converted into a reference digital signal by an analog-digital converter on a pixel-by-pixel basis and then stored in the read / write memory as reference data.

Next, the result of digital calculation in the microprocessor based on the reference data and the density setting value is stored as the comparison data in the read / write memory in place of the reference data.

Thereafter, a digital comparison circuit compares the read original digital data read from the original by a solid-state image sensor into a digital signal by an analog-digital converter with the comparison data stored in the read / write memory, and a binary output is obtained. can get.

〔Example〕

 An embodiment of the present invention will be described in detail below.

FIG. 2 shows the structure of the image reading apparatus, in which an original 7 is placed on a glass plate 6 fixed to the apparatus. Reference numeral 1 denotes a solid-state image sensor (hereinafter, referred to as CCD) having a photoelectric conversion element corresponding to one line of pixels. Reflected light from the light source 3 passes through the reflection mirrors 4a, 4b, 4c and the imaging lens 2 and is reflected by the CCD 1. Form an image (original image) on the light-receiving surface. The light source 3 and the reflection mirror 4a are an integral movable part, which moves in the direction of the arrow shown in the drawing during the reading operation and returns to the home position shown in the drawing after the reading is completed at the right end. The reflection mirrors 4b and 4c form an integral movable part, and move at half the speed of the reflection mirror 4a so that the length between the document surface and the CCD 1 becomes constant in conjunction with the movement of the reflection mirror 4a. .

Reference numeral 5 is a white reference reflector for performing shading correction described later.

In FIG. 1, the read signal of the CCD 1 described in FIG. 2 is an analog signal, which is amplified to a desired voltage by an amplifier 11 and then converted to an analog-digital converter (hereinafter referred to as A
It is converted into a 7-bit digital signal by a signal 12 called DC.

Reference numeral 18 is a clock pulse generator (hereinafter referred to as CPG), which generates a timing signal necessary for a reading operation. Reference numeral 13 denotes a read / write memory (hereinafter referred to as RA, which has an address capacity corresponding to one line of pixels of the CCD 1.
(Referred to as M), and the selector 16 allows the ACD 12
Data write from Microprocessor (hereinafter MP
The read / line from U) 20 and the lead 3 for outputting to the digital comparison circuit 15 perform three operations.
Reference numeral 14 is an address counter for giving the address of the RAM 13, and the MPU 20 is made
To read / write 3, read / write the MPU20.
Operates by the write signal, otherwise CPG1
Operates with a clock from 8.

The MPU 20 is an 8-bit microprocessor and also controls the start and stop of motors of other devices shown in the figure.
Reference numeral 21 is a reading density setting switch, which sets in 16 steps.

A digital comparison circuit 15 compares the value output from the RAM 13 with the original reading signal from the CCD 1 to give a binary output.

The operation of the above configuration will be described with reference to FIG.

The light source 3 is turned on by the reading start signal, and the reflected light of the reference reflection plate 5 is read into the RAM 13 corresponding to the pixels of the CCD 1. The read reference data is D ₀ shown in FIG.
~ D ₂₀₄₇ . This value is the light source 3, the optical systems 4a to 4c,
The values are different due to the characteristics of No. 2 and the variation of each pixel of the CCD 1. Next, the RAM 13 is connected to the selectors 16 and 17
To switch to the MPU20 side, and 2 based on the density setting value.
Calculate comparative data for quantification. 5th detail
Figure and Figure 6 show. For the binary comparison data Rn, if the value of the reference data obtained by the reference reflector 5 is Dn and the set value is m, Should be calculated.

However, there is no cheap MPU 20 that has a division instruction, and if the division is performed by a program, the calculation time becomes long. Therefore, in this embodiment, the density setting value is set to "16". By doing so, the calculation equivalent to the division is performed by the multiplication and the shift operation of the register as shown in FIGS. 5 and 6. This gives 20
The calculation of 48 pixels could be performed in about 60 ms.

Next, scanning for reading the original image is started, the original for one page is read, and the moving unit returns to the home position. When the reading is continuous, no new calculation is performed using the comparison data Rn, and the next page scan is performed to reduce the calculation time loss.

〔The invention's effect〕

As described above, according to the present invention, (1) comparison data is obtained as a result of digital calculation in the microprocessor based on the reference data and the density setting value stored in the read memory corresponding to the pixels of one line of the original document. Since the original is read after the document is stored in the read / write memory as described above, a dedicated high-speed arithmetic unit is not required, and the cost can be reduced.

(2) Since shading correction for binarization is performed by a digital circuit in each pixel unit, it is possible to perform shading correction with high accuracy and at high speed while being less affected by external environmental conditions. It is possible.

(3) Digital calculation in the microprocessor for making the comparison data only needs to be performed once when the reference reflector is read, and it is possible to save the calculation time loss.

And so on.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention, FIG. 1 is a diagram showing a signal processing section, FIG. 2 is a structural diagram of an image reading device, FIG. 3, and FIG.
FIG. 5, FIG. 5 and FIG. 6 are diagrams for explaining the operation. 1 ... Solid-state image sensor, 5 ... Reference reflector, 7 ...
Manuscript, 12 ... Analog-to-digital converter, 13 ...
... Read / write memory, 14 ... Address counter, 1
5 ... Digital comparator, 20 ... Microprocessor.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Matsumoto 3-2-1, Saiwaicho, Hitachi, Ibaraki Hitachi Engineering Co., Ltd. (72) Inventor Osamu Kikuchi 3-2, Saiwaicho, Hitachi, Ibaraki No. 1 within Hitachi Engineering Co., Ltd. (56) Reference JP-A-58-202662 (JP, A) JP-A-59-189783 (JP, A) JP-A-59-219070 (JP, A)

Claims (1)

[Claims] 1. A reference reflector, a solid-state image sensor having a photoelectric conversion element corresponding to a pixel of a scanning line for reading an original, and one line of a reference analog signal from the reference reflector read by the solid-state image sensor. An analog-digital converter that converts a reference digital signal in pixel units, a read-write memory that has an address capacity corresponding to the pixels of the original scanning line and stores the reference digital signal obtained from the analog-digital converter as reference data, A microprocessor for digitally calculating the comparison data based on the reference data and the density set value, replacing the calculated comparison data with the reference data of the read / write memory, and storing the read analog signal read from the document. Analog Digi Le converter image reading device including a digital comparator for obtaining a binary signal by comparing the converted original reading digital data with the comparison data stored in said read-write memory to the digital signal by.