JPH03216072A - Picture reader - Google Patents

Abstract

PURPOSE:To reduce the job time and to simplify the constitution by applying shading correction with a shading waveform stored in a storage means storing plural changes in shading waveforms in advance. CONSTITUTION:A storage means B storing plural number of shading waveforms of a fluorescent light is provided and the shading waveforms stored in advance in the storage means B are selected sequentially with a selection means C attended with a change in the shading waveform of the fluorescent light to correct a change in the shading waveform. At application of power or for a prescribed time, a reference white level representing the absence of an original is read and a change in the shading waveform of the fluorescent light is stored in the storage means B. Thus, even when the shading waveform is subject to change attended with the change in the tube wall temperature of the fluorescent light, the change is sequentially corrected properly by the stored shading waveform in advance and without lighting for a prescribed time before reading, accurate shading correction is attained without need of a heater.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image reading device that forms an image of reflected light from an original image and converts it into an electrical signal.

[Prior Art] Conventionally, image reading devices (also referred to as original reading devices)
The original is illuminated by a light source such as a fluorescent lamp or a halogen lamp, and the reflected light is focused through an optical lens onto a photoelectric conversion unit such as an image sensor using a COD (charge coupled device). It is configured to take out an analog electrical signal and perform A/D conversion on this analog electrical signal using an A/DC (analog/digital) converter to obtain a digital image signal. At this time, a fluorescent lamp is often used as the light source in consideration of heat generation and amount of light.

However, when a fluorescent lamp is used as a light source, there are the following problems.

As shown in Figure 3, the shading waveform of the fluorescent lamp changes rapidly in the initial stage of lighting, so when reading the reference white background at the home position and performing shading correction from this read data, The waveform changes suddenly. Therefore, at the start of image reading, accurate shading correction is performed, but as reading progresses, errors occur in shading correction and accurate shading correction is not performed. This is caused by the fact that the mercury vapor pressure inside the glass tube of the fluorescent lamp changes due to changes in the tube wall temperature, so generally the fluorescent lamp is turned on for a certain period of time to stabilize the tube wall temperature before reading is started. Alternatively, a heater was attached to the fluorescent light to keep it at a temperature that would have the least impact (see Figure 4).
.

[Problems to be Solved by the Invention] However, in the conventional example described above, when starting image reading after turning on a fluorescent lamp for a certain period of time before starting reading, the throughput of image reading is The problem was that there was no

Additionally, when keeping fluorescent lamps warm with a heater, it is necessary to install a sensor that detects the temperature of the tube surface of the fluorescent lamp, and control the temperature of the tube surface of the fluorescent lamp to an appropriate temperature based on the temperature detected by that sensor. , a power supply for the heater, a heater control circuit, a sensor, etc. are required, making it difficult to downsize.
There was a problem in that manufacturing costs increased.

In view of the above-mentioned points, an object of the present invention is to provide an image reading device that does not require lighting for a certain period of time before starting reading and can perform accurate shading correction without requiring a heater or sensor.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a fluorescent lamp for illuminating an original, a reference density object for measuring the shading waveform of the fluorescent lamp, and a light source from the original and the reference density object. In an image reading device having an image sensor that receives reflected light and converts it into an electrical signal, a plurality of pieces of shading waveform data of the fluorescent lamp corresponding to changes in tube wall temperature of the fluorescent lamp are stored in advance before reading the document. a storage means for detecting a level change of the shading waveform obtained from the image sensor when reading a document, and detecting a level change of the shading waveform data stored in the storage means in accordance with the change;
The present invention is characterized by comprising a selection means for selectively reading one of the two, and a shading correction means for performing shading correction based on the shading waveform data read from the storage means.

Further, as an aspect of the present invention, the selection means compares data read from the reference density object via the image sensor before reading the document with the plurality of shading waveform data stored in advance in the storage means. shading waveform data having the closest waveform is read from the storage means, and the shading correction means changes the waveform of the output signal of the image sensor using the read shading waveform data to perform shading correction. It is characterized by

Further, as another aspect of the present invention, the storage means is configured to store a change in a shading waveform of a fluorescent lamp when the reference density object in a state without an original is read through the image sensor when the power is turned on or for a certain period of time after the power is turned on. is stored as shading correction data.

[For use] In the present invention, a storage means for storing a plurality of shading waveforms of fluorescent lamps is provided, and the shading waveforms stored in advance in this storage means are sequentially switched in accordance with changes in the shading waveform of the fluorescent lamps. Furthermore, when the power is turned on or for a certain period of time, a reference white background with no original is read, and changes in the shading waveform of the fluorescent lamp are stored in the above-mentioned storage means. Therefore, even if the shading waveform changes due to changes in the tube wall temperature of the fluorescent lamp, it can be corrected sequentially and accurately using the shading waveform stored in advance. In addition, accurate shading correction is possible without the need for a heater or the like.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

■ Figure 1 shows the basic configuration of an embodiment of the present invention. Here, A is the reference density object (
This is an image sensor that receives the reference white (reference white) and reflected light from the original and converts it into an electrical signal. Reference numeral B denotes a recording means for storing in advance a plurality of fluorescent lamp shading waveform data corresponding to changes in tube wall temperature of the fluorescent lamp before reading the document. C is a selection means that detects a change in the level of the shading waveform obtained from the image sensor A when reading a document, and selects and reads out one of the shading waveform data stored in the storage means B in accordance with this change. D is a shading correction means that performs shading correction based on the shading waveform data read out from the storage means B.

In one embodiment, the selection means C compares the data read from the reference density object via the image sensor A before reading the document with a plurality of shading waveform data stored in advance in the storage means B, and selects the closest waveform. The shading waveform data of the state is read from the storage means B, and the shading correction means D performs shading correction by changing the waveform of the output signal of the image sensor A using the read shading waveform data.

In one aspect, the storage means B stores changes in the shading waveform of a fluorescent light when the reference density copy is read without an original at the time the power is turned on or for a certain period of time after the power is turned on, and is used for shading correction. Store as data.

■ ヱ。。。。。。。。。。。。。。。。。。。。。。。。 Here, 101 is a platen glass on which the original is placed, 102 is an imaging lens that collects reflected light from the original on the platen glass 101 and a white reference plate (described later), and 103 is an optical image formed by the lens 102. It is an image sensor that converts into an electrical signal, and is, for example, a solid-state image sensor array (hereinafter referred to as CCU) such as a COD. Also, 104
10 is a shading correction circuit that performs shading correction on the 8 signals (image signals) of CCDI03.
5 is an AGC (automatic gain control) circuit that adjusts the output level of the image signal that has undergone shading correction to a predetermined value; 106 is an A/D converter that converts the output of the AGC circuit 105;
/D converter.

A selector 107 selectively sends the input signal from the A/D converter 106 to one of two paths. 10
g is a CPυ (central processing control unit) which controls the entire apparatus, and is a microprocessor which controls each component circuit based on the control procedure (program) shown in FIG. Furthermore, this CP010g has a built-in ROM for programming. 109 is a shading waveform storage memory (for example, RAM) that stores in advance a plurality of seeding waveforms supplied via the selector 107;
(The shading waveform can be selectively switched by the control signal of PtJ108.

Further, 110 is an image processing circuit that performs predetermined image processing;
11 is an interface (F/F) circuit that sends and receives signals to and from an external device (for example, a printer, a display, a personal computer, etc.) to the image processing circuit 110 and the CPIJ108; and 112 is a fluorescent lamp that illuminates the original.

FIG. 3 shows changes in the shading waveform at a temperature of 5° C., and FIG. 4 shows the temperature characteristics of the relationship between temperature, brightness, and elapsed time of a fluorescent lamp.

FIG. 5 shows the state of connection between an image reading device (hereinafter referred to as a scanner) according to an embodiment of the present invention and an external device (eg, a laser beam printer, a personal computer). Here, 301 is a scanner having the circuit configuration shown in FIG.
02 is a personal computer, 303 is a laser beam printer, and 304 is a CRT (cathode ray tube) display device.

FIG. 6(A) shows the internal structure of the above-described scanner 301, and FIG. 6(B) shows the original loading position of the scanner 301. Here, reference numeral 10 denotes a reference density object (A) for shading correction, which is arranged along the main scanning direction of the CCD 103 and read immediately before image reading. 11 is a control unit, 13 is a CCD driver (drive circuit), 15 is a fluorescent lamp unit for document illumination, and 16 is a reflection mirror. l7
is the reference density object (B). This standard density subject (
B) 17 is disposed near the original stacking position along the sub-scanning direction of the CCD 103, and is read during document reading and used for shading correction. 18 is a document, and 19 is a platen cover.

α hill j 11% First, as shown in FIGS. 2 and 6 (A), the original l8 on the platen glass (original platen glass) 101 is illuminated with the fluorescent lamp 112 in the original illumination fluorescent lamp unit 15. Then, the reflected light from the original 18 is guided onto the CCD 103 by the imaging lens 14 to form an image of the original. At this time, the original 18 is placed on the platen glass 101 so that the right end becomes the leading edge of the original as shown in FIG. 6(B). In addition, in FIG. 6(A), the original illumination fluorescent lamp unit 15, which is a scanning optical system, has an initial value at the right end, and an optical position sensor (
(not shown) confirms its initial position.

In addition, instructions for various processing modes are input to the scanner 301 from an external device (personal computer) 302 while the original 18 is placed on the platen glass 101.

For example, the instruction for this mode is to set the pixel density to 300 dpi.
(dots/inch), 200dpi, 150dpi
, 75 dpi, or whether to make the image signal binary or multivalued. These instructions are sent to C via the interface circuit ill.
Decoded by P0108, CP0108 is image processing circuit 1
10, according to the instructions, send a control signal for mode switching in advance, and set the pixel density and image signal processing.

Next, when a manual reading start command is input from the external device 302, the fluorescent lamp unit 1-1 is activated under the control of the CPU 108.
5 is scanned in the sub-scanning direction by a motor (not shown), and when it reaches the leading edge position of the document, the CPU 108
outputs a control signal for permitting image signal output to the interface circuit 111, and sends the image signal read by the CCD 103 by scanning the original to the external device 302.

The scanning length of the optical system is uniquely determined by the number of pulses that CPUlO8 drives the optical system drive motor (not shown), so CPUlOg calculates the necessary number of pulses according to the size of the document by driving the motor (not shown). When the image signal is not output), it is determined that the document reading is completed, the fluorescent lamp 112 is turned off, and a control signal indicating that the image signal cannot be output is sent to the interface circuit 1.
11, and performs reversal control of the motor (not shown).

The document illumination fluorescent lamp unit 15 moves in the direction of arrow IA in FIG. 6(A) under the motor reversal control of the CPU 108, and the fluorescent lamp unit 15 is brought to the initial position (home position) by an optical position sensor (not shown). It will stop when it is detected that it has been reached. If the next document reading start command does not come from the external device 302 during the return section of the optical system, the fluorescent lamp unit 15 stops at the initial position and the current reading operation ends.

Next, the flowchart in Figure 7 and Figures 2 to 6 will be explained.
Control operations regarding the shading correction circuit 104 and the shading waveform storage memory 109 will be described with reference to the drawings.

Figure 3 shows the reference density subject of the fluorescent lamp 112 used this time (
A) It shows the change in the shading waveform at 10. At this time, it changes in the order of ■, ■, ■, ■《.

First, the power is turned on (step S1), the document illumination fluorescent lamp unit 15 is moved below the reference density object (A) to (step S2), and the fluorescent lamp 112 is turned on (step S3). At this time, the shading correction circuit 104 is in a through state and does not perform shading correction, and the video signal is sent to the A/D converter 105 in the AGC circuit 105.
The level is controlled so that it becomes the optimal input value (step S4).

Next, the A/D converter 106 converts the reference density object (
The video signal of A) is multivalued and stored in the shading waveform storage memory 109 at regular intervals by the selector 107 (step S4). At this time, the constant interval is C
It is controlled by the shading waveform switching signal from Ptll08. For example, four waveform patterns shown in FIG. 3 are stored in the shading waveform storage memory 109 at regular intervals, for example, at intervals of 20 seconds. Here, the shading waveform changes as ■→■→■→■, and the shading waveform of ■ is considered to be the shading waveform in a stable state.

After storing the shading waveform in the shading waveform storage memory 109 (step S6), the fluorescent lamp 112
(step S7), and the personal computer 3
Waits for an image reading command from 02 (step S8).

When an image reading command is input manually from the personal computer 302, the CP010g turns on the fluorescent lamp 112, measures the level of the current shading waveform at points A and B in FIG. 3, and calculates the slope of the point A and point B. The state of the shading waveform is determined based on the data (indicated by the broken line in FIG. 3), and the data of that waveform is controlled to be output from the shading waveform storage memory 109 (step S9). The shading correction circuit 104 uses the shading data supplied from the memory 109 to perform shading correction before image reading is started. At this time, the switching direction of the selector 107 is the direction of the image processing circuit 110 (
Step S10).

At this time, if the stopped state continues for a long time due to the processing of the host device, for example, if it stops for 20 seconds, and if image reading is started with the shading waveform ■ (step S13), it changes to the shading waveform ■. Therefore, the CPU 108 switches the read address of the shading waveform storage memory 109 using the shading waveform switching signal, and inputs the data of the shading waveform (2) to the shading correction circuit 104 for correction (step S14).

In addition, the light intensity of the reference density object (B) 17 is determined by the CPU 108.
When the amount of light changes, the AGC circuit 105 is controlled to maintain the optimum value (steps Sll and S).
12).

In this embodiment, the number of shading waveforms is four, but if this number is increased, the accuracy of shading correction will further improve.

Also, R is used as the shading waveform storage memory 109.
Although AM is used, the shading change data may be calculated in advance and stored in the ROM.

[Effects of the Invention] As explained above, according to the present invention, when the shading waveform changes due to a change in the tube wall temperature of a fluorescent lamp, a plurality of changes in the shading waveform are stored in advance in the storage means. Since shading correction is performed using the shading waveform, shading errors can be reduced, and as a result, there is no need to turn on the light for a certain period of time before scanning the document, and accurate shading correction can be made without the need for a heater. Effects can be obtained. Therefore, according to the present invention, it is possible to shorten working time, simplify the configuration, downsize the device, and reduce manufacturing costs.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the basic configuration of an embodiment of the present invention, FIG. 2 is a block diagram showing the circuit configuration of an image reading device according to an embodiment of the present invention, and FIG. 3 shows changes in the shading waveform of a fluorescent lamp. 4 is a graph showing the temperature characteristics of a fluorescent lamp, FIG. 5 is a block diagram showing the connection state between an image reading device and an external device according to an embodiment of the present invention, and FIG. 5 is a sectional view showing the internal configuration of the image reading device, FIG. 6(B) is a top view of the device shown in FIG. 6(A), and FIG. 7 is a flowchart showing the operating procedure of an embodiment of the present invention. be. ...Platen glass, ...Lens, ...CCD, ...Shading correction circuit, ...AGC (automatic gain control), ...A/D converter, ...Selector, ...CPU , ...Memory for storing shading waveforms, ...Image processing circuit, ...I/F circuit, ...Fluorescent lamp. A D Figure 1 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1) A fluorescent lamp for illuminating an original, a reference density object for measuring the shading waveform of the fluorescent lamp, and receiving reflected light from the original and the reference density object and converting it into an electrical signal. an image reading device having an image sensor, comprising: a storage means for storing in advance a plurality of pieces of shading waveform data of the fluorescent lamp corresponding to changes in tube wall temperature of the fluorescent lamp before reading a document; a selection means for detecting a level change of the obtained shading waveform and selectively reading out one of the shading waveform data stored in the storage means according to the change; and shading waveform data read out from the storage means. An image reading device comprising: shading correction means for performing shading correction based on. 2) The selection means compares the data read from the reference density object via the image sensor before reading the document with the plurality of shading waveform data stored in advance in the storage means, and selects the data having the closest waveform. 4. A state shading waveform data is read from the storage means, and the shading correction means changes the waveform of the output signal of the image sensor using the read shading waveform data to perform shading correction. 1. The image reading device according to 1. 3) The storage means stores, as shading correction data, a change in the shading waveform of a fluorescent lamp, which is obtained by reading the reference density object without a document through the image sensor when the power is turned on or for a certain period of time after the power is turned on. The image reading device according to claim 1 or 2, characterized in that: