JPH01165264A - Image reader - Google Patents

Abstract

PURPOSE:To perform a dimmer operation normally and to realize the high picture quality of a reader by providing a shading correction circuit to correct nonuniformity in the light quantity of an illumination means and dispersion in the sensitivity of the image element of an image sensor, and a dimmer circuit to adjust the luminance of the illumination means so as to set the output of the image sensor within a prescribed range. CONSTITUTION:On an analog picture signal 61 from the image sensor 4, A/D conversion and shading correction are applied at the sheding correction circuit 50. At a time when the image sensor 4 reads a white reference plate 7 and the shading correction circuit 50 fetches white reference data, a dimmer state detection circuit 52 detects whether or not the dimmer operation is performed normally. A CPU54 reads the dimmer state detected by the dimmer state detection circuit 52 via a data bus 32, and sends a command to control the light quantity to a light quantity control circuit 53. In such a way, it is possible to perform the dimmer operation normally even when the partial lowering of the limit quantity 19 generated in a light source or a temperature characteristic is attached on the sensitivity of the image sensor.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an image reading device used for copying machine document files and the like.

Conventional technology In recent years, image reading devices are required to have higher image quality.

Conventionally, the dimming of an image reading device has been controlled by monitoring a portion of the luminous flux of an illumination lamp with a photodetector so that the output of the photodetector becomes a predetermined value.

An example of a conventional image reading device will be described below with reference to FIG. FIG. 2 is a schematic cross-sectional view of a sub-scanning unit of a conventional image reading device.

l is the document table, 2 is the fluorescent lamp, 3 is the Rondo lens array, 4
5 is a line image sensor, and 5 is a photodetector. The photodetector 5 outputs a voltage proportional to the amount of incident light. 6 is a fluorescent light 2. This is a sub-scanning unit including a Rondo lens array 3° image sensor 4, which moves parallel to the document table in the direction of arrow S in the figure, and sub-scans the document placed on the document table. Fluorescent light 2
The dimming is performed by controlling the light amount of the fluorescent lamp so that the output of the photodetector 5 becomes a predetermined value.

Problems to be Solved by the Invention However, with the above configuration, the photodetector only monitors a part of the luminous flux of the fluorescent lamp, so when the light intensity at both ends of the fluorescent lamp decreases, There has been a problem in that normal dimming cannot be performed when the sensitivity of the image sensor changes due to temperature.

In view of the above-mentioned problems, the present invention normally performs dimming even when the light intensity of the light source partially decreases or the sensitivity of the image sensor has temperature characteristics, and if the light intensity of the light source decreases so drastically that dimming is impossible. provides an image reading device that has a function of displaying this to the operator and prompting the operator to replace the light source.

Means for Solving the Problems: A manuscript table on which the manuscript is placed; a lighting means for illuminating the manuscript;
An image sensor that converts an optical signal into an electrical signal, an optical system that focuses reflected light or transmitted light from a document onto the image sensor, and a shading correction circuit that corrects unevenness in light amount of the illumination means and variation in pixel sensitivity of the image sensor. , a white reference plate, and a dimming circuit that adjusts the brightness of the illumination means so that the output of the image sensor when reading the white reference plate falls within a predetermined range, and the dimming circuit includes a comparator and a microprocessor. , further comprising display means for warning an operator when the dimming circuit becomes incapable of dimming, and characterized in that the shading correction circuit does not perform shading correction when reading a white reference plate. shall be.

According to 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 a range in which shading correction can be performed normally.
If adjustment is not possible, the operator is notified through the display.

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

FIG. 3 is a schematic cross-sectional view of the sub-scanning unit of the image reading device of the present invention. 1 is an original table, 2 is a fluorescent lamp, 3 is a rod lens array, 4 is a digital image sensor, and 7 is a white reference plate. 6 is fluorescent light 2, rod lens array 3
．． This is a sub-scanning unit including an image sensor 4, which moves parallel to the document table in the direction of arrow S in the figure, and sub-scans the document placed on the document table.

FIG. 1 is a block diagram of an image reading device according to 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, 53 is a fluorescent lamp light amount adjustment circuit , 54 is c
pu.

32 is a data bus for the CPU 54. An analog image signal 61 from the image sensor 4 is subjected to AD conversion and shading correction in a shading correction circuit 50. The output 4 of the shading correction circuit 50 is input to an image processing circuit 51 when reading an image of a document, and undergoes signal processing such as binarization processing. When the image sensor 4 is reading the white reference plate 7 and the shading correction circuit 50 is taking in the white reference data, the dimming state detection circuit 52 detects whether the dimming is being performed normally.

The CPU 54 detects the dimming state B detected by the dimming state detection circuit 52.
is read via the data bus 32, and a command for adjusting the light amount is sent to the light amount adjustment 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 an image sensor, 62 is an AD converter, 63 is a power supply that generates a reference high level voltage (voltage ERT) for the AD converter 62, and 64 is an AD
This is the reference low level voltage of 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 voltage ERH, 6 is Xi of voltage ERB + 0.5 (ERT-ERB)
, 67 is the reference low level voltage 64 of the AD converter 62
This is a switch that changes the 68 is AD converter 6
2 digital output, 70 is a RAM that stores 1547 worth of white reference data, 71 is data read from RAM 7Q, 69 is a division ROM that stores division table data.
, 72 is output data of the division ROM 69, 73 is a selector, and 74 is an output of the selector 73.

The flow of image signals when the image sensor reads the white reference plate and the shading correction circuit takes in the white reference data will be explained. Analog image signal 6 from image sensor
1 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 is ERB+0.5 (ERT
-ERB). When scanning images of normal originals,
Since the switch 67 is connected to the power supply 65, the quantization step of the AD converter when taking in the reference white data is reduced to 1/2, increasing 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 image signals when performing shading correction, that is, when reading an image of a document will be explained. Switch 67 connects to power supply 65. The AD-converted image signal 68 is divided by the white reference data 71 read out for each pixel by a division ROM 69. The selector 74 selects the output of the division ROM and outputs the shading-corrected image signal 14.

Next, the dimming state circuit will be explained using FIG. 5. FIG. 5 is a block diagram of the dimming state detection circuit. 74 is an output signal of the shading correction circuit, 20.21 is a comparator, 24.25 is an output signal of comparators 20 and 21, 22 is an upper limit value of white reference data, and 23 is a lower limit value of white reference data.

26 and 27 are D flip-flops, 35 is a line enable signal (LENBL), and when this signal is at low level, the output signal 74 of the shading correction circuit 50 is
is valid. 34 is a shading ready signal (SHRDY) indicating that the shading correction circuit 50 is taking in white reference data and is active low. 36 is the OR gate, 31 is the I10 port and the CPU
It is accessed from the CPU via the 54 data buses 32.

The operation of the dimming state detection circuit will be explained. LRNBL 3
When 5 and 5HRDY 34 are 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 5HRDY34 are active means that the shading correction circuit 50
The output signal 74 from is white reference data. The output 24 of the comparator 20 is the white reference data 7.
When 4 is equal to or larger than the white reference data upper limit value, it becomes high level. The D input of the D flip flop 26 is at a high level. When the output 24 of the comparator 20 goes high, this rising edge causes the Q output 2 of the D flip-flop to go high.

The output 25 of the comparator 21 becomes high level when the white reference data 74 is equal to or smaller than the white reference data lower limit value. The D input of D flip-flop 27 is at a high level. When the output 25 of the comparator 21 goes high, this rising edge causes the Q output 29 of the D flip-flop to go high. 30 is a recent signal of the D flip-flop 26.27 outputted from the I10 port 31 via the data bus 32 of the CPU, and when this signal becomes low level, the D flip-flop 26.27
The Q outputs 28 and 29 of are at low level. The CPU 54 determines whether the amount of light from the fluorescent lamp is too bright or too dark by reading whether the Q output 28.29 of the D flip-flop is at a high level or a low level via the I10 boat 31. can do. For example, D flip
The output 28 of the flop 26 is high level, and the D flip
When the output 29 of the flop 27 is at a low level, the fluorescent lamp is too bright and the white reference data for shading correction is overflowing. Also D flip
The output 28 of the flop 26 is low level, and the D flip
When the output 29 of the flop 27 is at a high level, the fluorescent light is too dark and the white reference data for shading correction is underflowing. When the outputs 28 and 29 of the D flip-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 must reset the D flip-flop 26.27 before reading the state of the dimming detection circuit, ie, the Q output of the D flip-flop 28.29. The CPU reads the status of the dimming detection circuit and
Change the amount of light from the fluorescent lamp so that the Q outputs 28 and 29 of the D flip-flop are both at low level. C
If both the Q outputs 28 and 29 of the D flip-flop do not become low level even if the light intensity of the fluorescent lamp is changed to the limit of the adjustable range, the PU24 lights the LE038 through the I10 port 31 and dims it. Informs you that something is not working properly.

Using Figure 6, light aiI! The I adjustment circuit 5 will be explained below. FIG. 6 is a block diagram of the light amount adjustment circuit.

32 is the data bus of the CPU54, 40 is the I10 boat,
41 is the output of I10 port 40, and the data width is 8 bits. 45 is a PWM clock having a period of 1/256 of the light amount integration time of the image sensor. 44 is an 8-bit counter, 47 is the output of the 8-pin counter 44, and 42
is an 8-pin comparator, 43 is the output of the comparator 42, and 46 is a fluorescent lighting circuit. CPU54 is I1
The light amount setting data 41 of the fluorescent lamp is set via the 0 port 40. The counter 44 receives the PWM clock 45 as a clock input. The comparator 42 compares the counter output 47 and the light intensity setting data 41, and when the counter value 47 is larger than the light intensity setting data 41, the signal 4 becomes high level.
Outputs 3. The fluorescent lamp lighting circuit 46 turns on the fluorescent lamp when the comparator output 43 is at a low level. By changing the light amount setting data 41, the lighting time of the fluorescent lamp can be changed and the light amount can be adjusted.

Next, the flow of the CPU program will be explained.

The sub-scanning unit 6 is normally on standby at the position of the white reference plate 7. When there is a request to read a document, initial data for setting the amount of light of the fluorescent lamp is set in the I10 boat 40, and the fluorescent lamp 2 is turned on. Next, after resetting the D flip-flops 26 and 27, the shading correction circuit 50 is placed in the white reference data acquisition mode. The shading correction circuit 50 is 1
After the time has elapsed to capture more than one line of data, CPt
1 is a D flip-flop 26 of the dimming state detection circuit 51
．． The Q outputs of the D flip-flops 26 and 27 of the am light state detection circuit 51 read the Q outputs 28 and 29 of the AM light state detection circuit 51 and adjust the light intensity setting data of the light intensity adjustment circuit 53 so that the Q outputs 26 and 27 are both at low level. Read output 28.29 Q
When both outputs 26 and 27 are not at low level, after changing the light intensity setting data of the light intensity adjustment circuit 53,
After the D flip-flop 26.27 is reset and the shading correction circuit 50 takes in one or more lines of data, the CPU again outputs the Q output 28.29 of the D flip-flop 26.27 of the dimming state detection circuit 51. The light amount setting data of the light amount adjustment circuit 53 is adjusted so that both the Q outputs 26 and 27 become low level. Repeat this procedure to dim the fluorescent light. If both the Q outputs 28 and 29 of the D flip-flop do not go to low level even if the light intensity of the fluorescent lamp is changed to the limit of the adjustable range, the LED 38 is turned on via the I10 boat 31 to ensure that the dimming is normal. Let them know what they can't do.

Effects of the Invention As described above, the present invention can reduce the local light intensity of the light source,
Even if the sensitivity of the image sensor has temperature characteristics, it is possible to perform normal dimming and to operate shading correction normally. The light source is so bright that it cannot be dimmed! If the decrease is severe, it is possible to display this to the operator and prompt the operator to replace the light source.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the image reading device of the present invention, and FIG.
3 is a schematic sectional view of the sub-scanning unit of the image reading device of the present invention, FIG. 4 is a block diagram of the shading correction circuit, and FIG. 5 is a schematic sectional view of the sub-scanning unit of the conventional image reading device. Block diagram of dimming state detection circuit,
FIG. 6 is a block diagram of the light amount adjustment circuit. 1... Document table, 2... Fluorescent light, 3...
... Rondo 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 RO
M. Name of agent: Patent attorney Toshio Nakao

LL+4-seasonal

Claims (4)

[Claims] (1) A document table on which a document is placed, an illumination device that illuminates the document, and an image sensor that converts optical signals into electrical signals;
An optical system that focuses reflected light or transmitted light from the original onto the image sensor, a shading correction circuit that corrects uneven light intensity of the illumination means and variation in pixel sensitivity of the image sensor, a white reference plate, and a white reference plate that reads the white reference plate. 1. An image reading device comprising: a dimming circuit that adjusts the brightness of illumination means so that the output of the image sensor falls within a predetermined range when the image sensor is in use. (2) The image reading device according to claim (1), wherein the dimming circuit includes a comparator and a microprocessor. (3) The image reading device according to claim (1), further comprising display means for warning an operator when the dimming circuit becomes incapable of dimming. (4) The image reading device according to claim (1), wherein the shading correction circuit does not perform shading correction when reading a white reference plate.