JPH0834533B2 - Image reading device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading device used for copying machines, document files, and the like.

2. Description of the Related Art In recent years, image reading apparatuses are required to have high image quality.

Conventionally, the dimming of an image reading apparatus has been controlled by monitoring a part of the luminous flux of an illumination lamp with a photodetector and controlling the output of the photodetector to a predetermined value.

An example of a conventional image reading apparatus will be described below with reference to FIG. FIG. 2 is a schematic sectional view of a sub-scanning unit of a conventional image reading device. 1 is a manuscript table, 2 is a fluorescent lamp, 3 is a rod lens array, 4 is a line image sensor, 5
Is a photodetector. The photodetector 5 outputs a voltage proportional to the amount of incident light. Reference numeral 6 denotes a sub-scanning unit including a fluorescent lamp 2, a rod lens array 3, and an image sensor 4, which is indicated by an arrow S in the figure.
And moves in a direction parallel to the document table and subscans the document placed on the document table. The dimming of the fluorescent lamp 2 is performed by controlling the amount of light of the fluorescent lamp so that the output of the photodetector 5 becomes a predetermined value.

Problems to be Solved by the Invention However, in the above configuration, since the photodetector only monitors a part of the luminous flux of the fluorescent lamp, when the amount of light at both ends of the fluorescent lamp decreases. Also, there is a problem that normal light control cannot be performed when the sensitivity of the image sensor changes with temperature.

In view of the above problems, the present invention performs normal light control even if the light amount of the light source is partially reduced or the sensitivity of the image sensor has a temperature characteristic. Provides an image reading device having a function of displaying that fact to the operator and urging replacement of the light source.

Means for Solving the Problems An original table on which an original is placed, an illuminating means for illuminating the original, an image sensor for converting an optical signal into an electric signal, and reflected light or transmitted light from the original on the image sensor. The focusing optical system, the shading correction circuit for correcting the unevenness of the light amount of the illumination means and the pixel sensitivity variation of the image sensor, the white reference plate, and the output of the image sensor when the white reference plate is read fall within a predetermined range. Thus, the dimming circuit for adjusting the brightness of the illuminating means is provided, the dimming circuit includes a comparator and a microprocessor, and when the dimming circuit cannot dimming, a display means is provided to warn the operator of the fact. The shading correction circuit,
Shading correction is not performed when the white reference plate is read.

Effect of the Invention With the above-described configuration, the present invention adjusts the light source so that the image data when the image sensor reads the white reference plate falls within the range in which shading correction can be normally performed. Notify the operator of this through.

Embodiments Embodiments of the image reading apparatus of the present invention will be described below with reference to the drawings.

FIG. 3 is a schematic sectional view of the sub-scanning unit of the image reading apparatus of the present invention. 1 is a document table, 2 is a fluorescent lamp, 3 is a rod lens array, 4 is a line image sensor, and 7 is a white reference plate. Reference numeral 6 denotes a sub-scanning unit including a fluorescent lamp 2, a rod lens array 3, and an image sensor 4, which moves in the direction of arrow S in the figure in parallel with the document table and sub-scans a document placed on the document table.

FIG. 1 is a block diagram of the image reading apparatus of the present invention. 61 is an analog image signal output from the image sensor 4, 50 is a shading correction circuit, 74 is an output of the shading correction circuit, 51 is an image processing circuit, 52 is a dimming state detection circuit, and 53 is a light quantity adjusting circuit of the fluorescent lamp. , 54 is CPU, 32 is CPU5
There are 4 data buses. An analog image signal 61 from the image sensor 4 is AD converted and shading corrected by a shading correction circuit 50. Shading correction circuit 50
The output 74 is input to the image processing circuit 51 when the image of the original is read, and signal processing such as binarization processing is performed. When the image sensor 4 reads the white reference plate 7 and the shading correction circuit 50 takes in the white reference data,
The dimming state detection circuit 52 detects whether dimming is normally performed. The CPU 54 reads the dimming state detected by the dimming state detecting circuit 52 via the data bus 32, and sends a command for controlling the light amount to the light amount adjusting circuit 53 via the data bus 32.

FIG. 4 is a block diagram of the shading correction circuit. 61 is an analog image signal from the image sensor, 62 is
An AD converter, 63 is a power supply that generates a reference high level voltage (voltage ERT) of the AD converter 62, and 64 is a reference low level voltage of the AD converter 62. The AD converter 62 quantizes the range of the reference high level voltage 63 and the reference low level voltage 64. 65 is the power supply of the voltage ERB, 6 is the voltage ERB + 0.5 (ERT-ER
B) power supply, 67 is the reference low level voltage of AD converter 62 6
It is a switch that switches between 4. 68 is a digital output of the AD converter 62, 70 is a RAM for storing white reference data for one line, 71 is data read from the RAM 70, 69 is a division ROM storing division table data, 72 is output data of the division ROM 69, Reference numeral 73 is a selector, and 74 is an output of the selector 73.

The flow of the image signal when the image sensor reads the white reference plate and the shading correction circuit takes in the white reference data will be described. Analog image signal from image sensor
61 is AD converted by the AD converter 62. At this time, the switch 67 is connected to the power supply 66, and the reference low level voltage of the AD converter 62 becomes ERB + 0.5 (ERT-ERB). Since the switch 67 is connected to the power source 65 during normal image reading of an original, the quantization step of the AD converter at the time of capturing the reference white data is halved, which improves the accuracy of AD conversion. The AD-converted white reference data is written into the RAM 70 for one line, and at the same time, the selector 73 selects the output 68 of the AD converter 62 and outputs the white reference data 14.

Next, the flow of the image signal when the shading correction is being performed, that is, when the image of the document is being read will be described. Switch 67 connects to power supply 65. The AD converted image signal 68 is divided by the division ROM 69 by the white reference data 71 read for each pixel. Selector 74 is division ROM
Image signal with shading correction selected.
Is output.

Next, the dimming state circuit will be described with reference to FIG.
FIG. 5 is a block diagram of a dimming state detection circuit. 74 is an output signal of the shading correction circuit, 20 and 21 are comparators, 24 and 25 are output signals of the comparators 20 and 21, 22 is white reference data upper limit value, and 23 is white reference data lower limit value. 26,27
Is a D flip-flop, and 35 is a line enable signal (LENBL). When this signal is at a low level, the output signal 74 of the shading correction circuit 50 is valid. 34 is a shading ready signal indicating that the shading correction circuit 50 is capturing white reference data (SHRD
Y) is active low. 36 is an OR gate, 31 is an I / O
It is a port and is accessed from the CPU via the data bus 32 of the CPU 54.

The operation of the dimming state detection circuit will be described. LENBL35 and SHR
When the DY34 is active, the enable signal 37 of the comparators 20 and 21 becomes active, and the comparators 20 and 21 enter the output enable state. The fact that LENBL35 and SHRDY34 are active means that the output signal 74 from the shading correction circuit 50 at this time is white reference data. The output 24 of the comparator 20 is the white reference data.
High level when 74 is equal to or greater than the upper limit of white reference data. The D input of D flip-flop 26 is high. When the output 24 of the comparator 20 goes high, the Q output 28 of the D flip-flop goes high at this rising edge. The output 25 of the comparator 21 is
High level when the white reference data 74 is equal to or smaller than the lower limit value of the white reference data. The D input of the D flip-flop 27 is high level. When the output 25 of the comparator 21 becomes high level, the Q output 29 of the D flip-flop becomes high level at this rising edge. Reference numeral 30 is a reset signal of the D flip-flops 26, 27 output from the I / O port 31 via the CPU data bus 32. When this signal goes low, the Q output 2 of the D flip-flops 26, 27 is output.
8,29 goes low. CPU54 detects whether the light intensity of the fluorescent lamp is too bright or too dark by reading whether the Q output 28,29 of the D flip-flop is high level or low level through the I / O port 31. can do. For example, when the output 28 of the D flip-flop 26 is high level and the output 29 of the D flip-flop 27 is low level, the fluorescent lamp is too bright and the white reference data for shading correction overflows. become.
Also, the output 28 of the D flip-flop 26 is low level,
When the output 29 of the flip-flop 27 is at high level, the fluorescent lamp is too dark and the white reference data for shading correction is underflowing. D flip
When the outputs 28 and 29 of the flops 26 and 27 are both at high level, it is possible that dust or the like is attached to the white reference plate. The CPU 54 needs to reset the D flip-flops 26, 27 before reading the state of the dimming detection circuit, that is, the Q outputs 28, 29 of the D flip-flops. The CPU changes the light intensity of the fluorescent lamp while reading the state of the dimming detection circuit,
Make sure that the Q outputs 28 and 29 of the D flip-flop are both low level. Even if the CPU24 changes the light intensity of the fluorescent lamp to the limit of the adjustable range, the Q of the D flip-flop
When the outputs 28 and 29 do not go to the low level, the LED 38 is turned on via the I / O port 31 to inform that the dimming cannot be normally performed.

The light amount adjusting circuit 53 will be described with reference to FIG. FIG. 6 is a block diagram of the light amount adjusting circuit. 32 is the data bus of the CPU 54, 40 is the I / O port, 41 is the output of the I / O port 40, and the data width is 8 bits. 45 is a PWM clock having a cycle of 1/256 of the light amount integration time of the image sensor.
44 is an 8-bit counter, 47 is an output of the 8-bit counter 44, 42 is an 8-bit comparator, 43 is a comparator 42
, 46 is a fluorescent lighting circuit. CPU54 is an I / O port
The light intensity setting data 41 of the fluorescent lamp is set via 40. The counter 44 receives the PWM clock 45 as a clock input. The comparator 42 compares the counter output 47 with the light amount setting data 41, and outputs a signal 43 that goes high when the counter value 47 is larger than the light amount setting data 41. Fluorescent lighting circuit
Reference numeral 46 turns on the fluorescent lamp when the comparator output 43 is at a low level. Thus, by changing the light amount setting data 41, the lighting time of the fluorescent lamp changes and the light amount can be adjusted.

Next, the flow of the CPU program will be described. The sub-scanning unit 6 normally stands by at the position of the white reference plate 7. When a document reading request is made, the light intensity setting initial data of the fluorescent lamp is set in the I / O port 40, and the fluorescent lamp 2 is turned on. Then D
After resetting the flip-flops 26 and 27, the shading correction circuit 50 is set to the white reference data acquisition mode. After the time when the shading correction circuit 50 takes in one or more lines of data, the CPU determines the dimming state detection circuit 51.
The Q outputs 28 and 29 of the D flip-flops 26 and 27 are read and the light amount setting data of the light amount adjusting circuit 53 is adjusted so that the Q outputs 26 and 27 are both at the low level. Dimming state detection circuit 51
When the Q outputs 28 and 29 of the D flip-flops 26 and 27 are read and the Q outputs 26 and 27 are not at the low level, after changing the light amount setting data of the light amount adjusting circuit 53, the D flip-flop 26 , 27 is reset, and after the time for the shading correction circuit 50 to take in one or more lines of data elapses, the CPU again reads the Q outputs 28, 29 of the D flip-flops 26, 27 of the dimming state detection circuit 51 and the Q output 26. The light amount setting data of the light amount adjusting circuit 53 is adjusted so that both and 27 become low level. Repeat this procedure to dimming the fluorescent lamp. If the Q output 28,29 of the D flip-flop does not go to the low level even if the amount of light of the fluorescent lamp is changed to the adjustable range limit, the LED 38 is turned on via the I / O port 31 to adjust the dimming. Notify you that you cannot do it normally.

EFFECTS OF THE INVENTION As described above, according to the present invention, even if the light amount of the light source is partially reduced or the sensitivity of the image sensor has temperature characteristics, normal light control can be performed and shading correction can be normally operated. Further, when the light quantity of the light source decreases so much that dimming cannot be performed, it is possible to display the fact to the operator and prompt the operator to replace the light source.

[Brief description of drawings]

FIG. 1 is a block diagram of an image reading apparatus according to the present invention, and FIG.
FIG. 3 is a schematic sectional view of a sub-scanning unit of a conventional image reading apparatus, FIG. 3 is a schematic sectional view of a sub-scanning unit of the image reading apparatus of the present invention, FIG. 4 is a block diagram of a shading correction circuit, and FIG. Block diagram of dimming state detection circuit,
FIG. 6 is a block diagram of the light amount adjusting circuit. 1 ... original table, 2 ... fluorescent lamp, 3 ... rod lens array, 4 ... image sensor, 6 ... sub-scanning unit, 7
...... White reference plate, 50 ...... Shading correction circuit, 54 ...
… CPU, 20,21,42 …… Comparator, 38 …… LED, 62 ……
AD converter, 69 ... Division ROM.

Claims (3)

[Claims] 1. A document table on which a document is placed, illumination means for illuminating the document, an image sensor for converting an optical signal into an electric signal, and an optical system for focusing light from the document on the image sensor. An A / D converter that converts an electric signal from the image sensor into a digital image signal, a quantization step switching unit that switches the quantization step of the A / D converter, a light amount unevenness of the illumination unit, and a pixel sensitivity variation of the image sensor. Shading correction means, a white reference plate for performing shading correction, and a maximum value and a minimum value of the digital image signal within a predetermined range when the image sensor is reading the white reference plate. And a dimming means for adjusting the brightness of the illuminating means, and the quantizing step switching means is configured such that the image sensor reads a document. When the image sensor is reading the white reference plate, a second quantization step smaller than the first quantization step is set. Image reading device. 2. A dimming means, which detects whether the maximum value and the minimum value of the output signal of the image sensor are within a predetermined range, and the brightness of the illuminating means is set based on the output of the comparator. The image reading apparatus according to claim 1, further comprising a microprocessor for performing the above. 3. When it is impossible to adjust the brightness of the illuminating means such that the maximum value and the minimum value of the output signal of the image sensor fall within a predetermined range by the light adjusting means, the operator is warned to that effect. The image reading device according to claim 1, further comprising: