JPS62195980A - Picture reader - Google Patents

Abstract

PURPOSE:To correctly correct the shading in the offset of an image sensor by providing a control circuit for proportionally correcting and converting a black and white comparison level, reading plural reference values to make correction reference density data and proportionally correcting and converting based on the reference density data according to the command of the reading density. CONSTITUTION:The image sensor 23, before reading an original 21, reads respectively the density of a reference density original 20, black B, gray G and white W, converts into digital values by an AD converter 13 and inputted to a RAM 14. Then, when the reading density command D0 is applied to the control circuit 17, the control circuit proportionally correcting and converting according to the values of the RAM memory 14 corresponding to the black B, the gray G and the white W density and the black and white comparison level is set to the RAM memory 14 again. For instance, the RAM memory 14 is set to V0 correspondingly to the reading density command value D0. Generally, a picture density value and the value of the image sensor are not primarily proportionated but proportional to a logarithmic value. The control circuit 17 can apply the black and white comparison voltage level corrected correspondingly to the reading density command.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an image reading device that converts a document image into an electrical signal using an image sensor and reads the electrical signal.

2. Description of the Related Art In recent years, image reading devices have been widely used as input devices for image signals to personal computers and word processors. In particular, an image sensor in which a plurality of image sensors or chips are connected can be made into a high-speed reading device by simultaneously reading each sensor chip in parallel.

An example of the conventional image reading device described above will be described below with reference to the drawings.

FIG. 5 shows a schematic configuration diagram of a conventional image reading device. In Fig. 5, 1 is an image sensor, 2 is an image sensor, a chip, 3 is an AD converter, and 4 is a RAM.
5 is a DA converter, 6 is a comparison circuit, and 7 is a read concentration voltage generator.

The operation of the image reading device configured as described above will be described below.

First, the image signal output read from the image sensor 1 is converted into black and white binary values by a comparator circuit. This black-and-white comparison level is set by the DA converter 5. On the other hand, the output from the image sensor 1 of the one-sided image reading device has variations in sensitivity, and variations between sensor chips and outputs within the sensor chips are different. In addition, uneven illumination on the document surface due to the light source is added. Therefore, it is necessary to correct these variations in read output (referred to as shading correction). In FIG. 5, before reading the original, a standard density original placed in front of the original is read 9, and the AD converter 3 converts the reading output variation into a digital value and inputs it into the RAM memory 4. Next time you read the manuscript, RAM memory 4
is read out and converted into an analog voltage by the DA converter 5, and this value is used as the black and white comparison level.

The state of shading correction at this time is shown in FIG.

FIG. 6 shows the correction within the sensor chip, and the comparison level 8 is corrected and set in correspondence with the sensor output level 9. It is reliable if the sensor output can be corrected in units of 1 bit within the sensor, but in this case, a high-speed AD converter and a DA-y inverter are required, which increases the cost. In reality, sensitivity variations within the sensor do not change rapidly, so there is a method (16 to 3) that corrects multiple focuses at once.
2 bits) is sufficiently practical.

A density voltage generator 7 in FIG. 6 is used to set the density for reading an image. The reading density can be set by changing the value of the black and white comparison level 8 using the density voltage generator 7.

Problems to be Solved by the Invention However, with the above configuration, when the reading density setting is changed, the black and white comparison level is corrected at a fixed magnification, so the black and white density may change suddenly or the offset voltage of the image sensor may change. As a result, an accurate black-and-white comparison level cannot be obtained, resulting in the problem of density unevenness occurring during image reading.

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides an image reading apparatus that prevents uneven reading density by setting an accurate black and white comparison level for reading density setting.

Means for Solving the Problems In order to solve the above problems, the image reading apparatus of the present invention reads a plurality of reference density originals of different densities and data in a RAM memory read from the reference density originals. The control circuit includes a control circuit that proportionally corrects and converts the black and white comparison level in accordance with the reading density command.

Operation The present invention uses the above-described configuration to read a plurality of reference densities as corrected reference density data, and performs proportional correction conversion based on the reference density data in accordance with a read density command. A comparison voltage proportional to the density can be set, and changes in the offset of the image sensor can be corrected to obtain accurate shading correction.

Embodiment Hereinafter, an image reading apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration diagram of an image reading device according to an embodiment of the present invention. 1st
In the figure, 11 is an image sensor, 12 is an image sensor and a chip, 13 is an AD converter, 14 is a RAM memory, 15 is a DA converter, 16 is a comparison circuit, and 17 is a control circuit.

18 is analog switch 1, 19 is analog switch 4
It is 2.

Regarding the image reading device configured as above, the following is the first part.
The operation will be explained using FIG. FIG. 2 shows the arrangement of reference density originals in the image reading device. In Figure 2, 20 is black (B).

21 is a reading document, 22 is a fluorescent lamp, 23 is an image sensor, and 24 is a focusing fiber lens.

Before reading the document 21, the image sensor 23 reads the density, black (B), gray (q, and white) of the reference density document 2o, converts them into digital values by the AD converter 13, and stores them in the RAM memory 14.

Next, when the reading density command D0 is given to the control circuit 17,
The control circuit performs proportional correction conversion using the values in the RAM memory 14 corresponding to the black (B), gray q, and white W densities.
The black and white comparison level is set in the RAM memory 14 again. FIG. 3 shows the operation of correction conversion.

In FIG. 3, Db, Dg, and Dw are black, gray, and white density values, respectively, and vb, v9. vw is the value of the corresponding AD converter 13. From FIG. 3, the RAM memory 14 is set to vo corresponding to the read density command value D0. Generally, the image density value and the image sensor value are not linearly proportional, but are proportional to the logarithm value of the density. The control circuit 17 can provide a black and white comparison voltage level corrected in accordance with the reading density command. The black and white level of the RAM memory 14 is converted into an analog voltage value by the DA converter 16.

In FIG. 1, analog switches 18 and 19 are circuits that switch according to the respective sensor chips.
The cost is reduced so that only one shading correction circuit consisting of a converter 1s, a RAM memory 14° and a DA converter 15 is required.

C1 and C2 are capacitors, and analog switch 19
When switching, the comparison level is maintained.

In the above description, the black of the reference density original 20 may be approximated by measuring with the fluorescent lamp 22 turned off, and the black density original may be omitted. Image sensor 1 that supports black density
By measuring the output voltage of image sensor 11
Therefore, even if the offset voltage varies over time, it will be corrected by the shading correction operation of the present invention every time.

FIG. 4 is a diagram showing the state of shading correction for each image sensor. Since an inexpensive AD converter or the like is used, several bits within the sensor are corrected at once.

Since the sensor output does not change suddenly, there is no problem in practical use.

If the output level of the image sensor 11 becomes too low, even if shading correction is performed, the S/N ratio will be poor, resulting in poor accuracy and uneven density in the read image.

In this case, by preheating the fluorescent lamp, the amount of light from the fluorescent lamp increases and the S/N ratio can be improved.

In FIG. 2, the standard density original 2o, which is a white density original, is also used to position the beginning of the original to be read. By detecting the value of the AD converter 13 when the density changes from gray to white, the beginning of the document can be found.

Furthermore, black and white can be automatically determined according to the density of the original 21. - As an example, the original 21 is randomly read once using the AD converter 13. The analog switch 18 is sequentially switched and read, and the background density level of the original 21 is read into the RAM memory 14. Next, the control circuit 17 sets the brightest part as the background density of the document 21, and automatically sets the black and white comparison level so that this density is determined to be white. Through the above operations, the black and white comparison level is set according to the density of the original 21, and by reading the original 21 again, the reading density level of the original 21 is automatically set.

As described above, according to this embodiment, shading correction can be performed accurately and the offset of the image sensor can also be corrected.

On the other hand, in this image reading device, when a fluorescent lamp is used as an illumination light source, the amount of light decreases when the temperature of the fluorescent lamp is low. Therefore, when the device is powered on, the fluorescent lamps are preheated and turned on. At the same time, this device reads the reference density document and detects the change in the light amount of the fluorescent lamp during preheating, and when the change in light amount decreases, it is assumed that the temperature has become high enough and the light is turned off. Furthermore, since the fluorescent lamp gradually cools down over time, it is also possible to turn on the fluorescent lamp again after a certain period of time and detect the amount of light. Here, it is convenient to place the reference density original separately at the origin position so that it can be read without moving the image sensor.

Effects of the Invention As described above, the present invention is equipped with a reference density document having multiple densities and a control circuit that corrects and converts the black and white comparison level of the comparator circuit in accordance with the reading density command, thereby accurately performing shading correction and adjusting the density. An image reading device with less unevenness can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic circuit configuration diagram of an image reading device according to an embodiment of the present invention, FIG. 2 is a schematic configuration diagram showing the reading of a reference original, and FIGS. 3 and 4 are corrections for the black and white comparison level of the image sensor. FIG. 6 is a schematic circuit diagram of a conventional image reading device, and FIG. 6 is an explanatory diagram of shading correction operation. 11... Image sensor, 12... Sensor chip 7", 13... AD converter, 14...
-RAM memo IJ, 15-DA converter, 16...
... Comparison circuit, 17 ... Control circuit, 18.19.
・・Analog switch, 2o・・−Reference density original, 21
...Manuscript, 22--Fluorescent lamp, 23--Image sensor, 24--Focusing fiber lens. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 3
Figure 11 LOL Cell X Figure 4

Claims (5)

[Claims] (1) Multiple image sensors that scan and read images;
A reference density original with a plurality of different densities placed in front of the original, an AD converter that converts the read signal into a digital signal, a RAM memory that stores the output of the AD converter, and an analog signal that converts the output of the RAM memory. a comparison level generation circuit composed of a DA converter that converts the data into a DA converter; a comparison circuit that compares the level of the comparison level generation circuit with the output signal of the image sensor; An image reading device characterized in that it is equipped with a control circuit that proportionally corrects and converts a comparison level in accordance with a reading density command. (2) The image reading device according to claim 1, wherein the comparison level generation circuit includes an analog switch that switches and operates the comparison level generation circuit corresponding to each image sensor. (3) The image reading device according to claim 1, wherein the reference density original is composed of black, gray, and white density originals. (4) Image reading according to claim 1, characterized in that a fluorescent lamp is used as a light source for illuminating the original, and the fluorescent lamp is turned on and preheated when the reading output value of the reference original is lower than a specified value. Device. (5) A fluorescent lamp is used as a light source for illuminating the original, and when the power is turned on, the fluorescent lamp is turned on and preheated, and during preheating, the time for turning off the fluorescent lamp is controlled according to changes in the reading output value of the standard density original. An image reading device according to claim 1, characterized in that: