JPS63292763A - Picture reader - Google Patents

Abstract

PURPOSE:To generally correct the unevenness in the characteristic of a light source or a photoelectric conversion element and a change in the elapse of a time of the characteristic by controlling the quantity of light of the light source at the time of scanning the original of a reference and matching an output signal from the photoelec tric conversion element to a presecribed set value. CONSTITUTION:A control means for controlling the quantity of the light of the light source at the time of reading the original to the prescribed quantity of light based on the output signal of the photoelectric conversion element (light receiving element array) 11 when the light from the light source 8 in which many light emitting elements are arranged in the form of a string is projected on the prescribed reference original is provided. The quantity of the light of the light source is controlled and the output signal from the photoelectric conversion element is matched to the prescribed set value to carry out a general shading correction including the light source and the photoelectric conversion element. Accordingly, the light energy efficiency of the light source is enhanced, the unevenness in the characteristic of the light source or the photoelectric conversion element, the deterioration in a reading picture quality resulting from the change in the lapse of the time of the characteristic are generally corrected and the picture quality can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image reading device installed in, for example, a facsimile machine, and more particularly to an image reading device using a plurality of light emitting elements such as an LED array as a light source.

(Prior art) In general, in image reading devices, due to factors such as variations in the illuminance distribution of the light source and variations in the conversion characteristics of the photoelectric conversion elements, the image signal level in the scanning width direction of the document becomes uneven and the read image quality deteriorates. do.

Therefore, conventionally, so-called shading correction has been performed to deal with this problem.

Conventional image reading devices that perform this type of shading correction, for example, measure the light/voltage characteristics of a photoelectric conversion element before shipping, store the measured data as correction data in the device, and ship it to the user. There are known devices that perform shading correction based on the correction data during use. That is, the photocurrent from each photoelectric conversion element during document reading is corrected to an appropriate level based on correction data corresponding to each photoelectric conversion element,
The photocurrent in the main scanning direction is made uniform to improve image quality. On the other hand, in recent years, there has been a trend to use LED arrays as shown in Figure 6 as light sources instead of conventional fluorescent lamps due to their superior durability. Since it is composed of light emitters, it has the disadvantage of large variations in illuminance distribution. Therefore, when selecting each element constituting the array, the above-mentioned variations in illuminance distribution are resolved by performing strict pre-shipment adjustments such as matching the characteristics and setting the current limiting resistor to an appropriate value.

However, in such conventional image reading devices, the illuminance distribution of the LED array can be made uniform at the time of shipment, but even if the illuminance distribution varies due to changes in each element over time, this is not the case. It was impossible to deal with it. In addition, although conventional shading correction can deal with the above-mentioned changes over time to some extent, it is difficult to attenuate the read photocurrent to a predetermined reference level (for example, 50% level of the photocurrent peak value before correction). Therefore, the photocurrent corresponding to this attenuation was wasted. In other words, the light energy of the light source is wasted and the efficiency of light energy utilization is low.Furthermore, the light source has to be driven around its maximum output, which increases power consumption and reduces durability. decline,
Another problem is that heat generation has an adverse effect on the surrounding areas.

(Purpose of the Invention) Therefore, the present invention has been developed to control the light intensity of the light source when scanning a reference document and to match the output signal from the photoelectric conversion element to a predetermined setting value, so that the light source and the photoelectric conversion element can be controlled. We perform comprehensive shading correction including the above, and collectively correct for variations in characteristics of light sources and photoelectric conversion elements, as well as changes in characteristics over time, while increasing the efficiency of light energy utilization.
The purpose is to improve the read image quality.

(Structure of the Invention) In order to achieve the above object, the present invention uses a photoelectric conversion element to receive reflected light of light projected onto a document from a light source in which a large number of light emitting elements are arranged in a row, and convert it into an electrical signal. In an image reading device that reads an image of an original document, the light amount of the light source is controlled to a predetermined light amount when reading the original document based on an output signal of a photoelectric conversion element when light from the light source is projected onto a predetermined reference original document. The present invention is characterized in that it is provided with a control means for controlling.

Hereinafter, the present invention will be specifically explained based on examples.

1 to 5 are diagrams showing an embodiment of the present invention, which is applied to a facsimile machine.

In FIG. 1, 1 is a facsimile machine, and 2 is an image reading device installed in the facsimile machine 1. In FIG. The document set in the image reading device 2 is guided and fed by rollers 3, which activates the document detection sensor 4 provided in the middle of the feed to prompt the output of a detection signal, and then further feed the document. The target glass 5 and the holding plate 6 having a uniform reflective surface are passed through at a predetermined speed, and are discharged to the outside by a roller ruff.

The presser plate 6 or original plate is irradiated with light from a light emitting element array (light source) 8 that has passed through the target glass 5, and the irradiated light is reflected by the presser plate 6 or the original plate. Note that the holding plate 6 has a function as a reference document.The light emitting element array 8 has a large number of light emitting elements (for example, light emitting diodes (LEDs)).
diodes) are arranged in rows in the reading direction of the document tray. FIG. 2 is a diagram showing an example of the light emitting element array 8. As shown in FIG. In the figure, the light emitting element array 8 includes light emitting diodes L, ~L1, resistors R1 ~ R1, and a driver LDI.
-LD.

For example, the light emitting diode LI, the resistor R3, and the driver LD form one set, and n sets (for example, 32 sets) are provided. Since these groups have the same configuration, one group will be explained below. A power supply +EV is applied to the driver LD via a resistor R, and a plurality of bits (for example, 4 bits) of control data B1 to B and LED selection data A1 are input. Driver LDI is LED selection data A
.

is selected as described later, imports control data B, -B, and reads this control data B, -
Based on the light amount correction value PH (described later) indicated by B, the amount of current to the light emitting diode L is controlled to vary the light amount (that is, a correction operation is started). In this control method, for example, a predetermined setting value SL corresponding to the target illuminance distribution is determined in advance, and this SL and the above-mentioned light amount correction value PH are
When the light amount correction value PH is smaller than SL, the amount of current is increased according to the difference, or when the light amount correction value PH is larger than SL, the amount of current is decreased. . Therefore, the amount of light of each of the light emitting diodes Ll to L is controlled by the LED selection data A, -A so that it always matches SL each time it is selected, and the distribution state of the amount of light in the arrangement direction of the light emitting element array 8 is set as the target. The illuminance distribution is controlled. In addition, L
When ED selection data A1 is not selected, driver L
D, is a light emitting diode L that passes a constant current.

The light emitting diode L emits light without correction.

In FIG. 1 again, the light reflected by the presser plate 6 is reflected by the presser foot F.
The uniform reflection surface of Ii6 reflects the illuminance distribution as it is (hereinafter referred to as reference reflected light), and the light reflected from the original paper is reflected with a light intensity that includes the density information of the original paper (hereinafter referred to as reference reflected light).
The reference reflected first-come-first-served or image information reflected light (hereinafter referred to as image information reflected light) enters an optical system consisting of a mirror 9 and a lens 10, and after the optical axis is bent by the mirror 9, it is focused by the lens 10. Photodetector array (photoelectric conversion element) 1
The light is received at 1. The light-receiving element array 11 is made up of a large number of light-receiving elements (array) corresponding to the number of pixels to be read, and like the light-emitting element array 8, these light-receiving elements are aligned in the main scanning direction corresponding to the reading width of the document. arranged in columns. The light receiving element array 11 converts the received light into a photocurrent Va for each pixel that changes according to the amount of light, and also scans each photocurrent Va in accordance with a main scanning signal HK in the reading width direction and converts it into a serial string. and output. The preamplifier 12 amplifies the photocurrent Va of the serial series at a predetermined amplification factor, and the DC regenerator 13 regenerates the DC component lost due to the amplification and outputs an analog image signal Vo for one read line. The A/D converter 14 converts the analog image signal Vo into a digital image signal Vi, sends it to a known circuit (for example, a data compression circuit via a buffer memory) of the facsimile device 1, and generates the brightness control described above. The light is outputted to the light emitting element array 8, and the amount of light from the light emitting element array 8 is controlled. Therefore, the A/D converter 14 has a function as a light amount control means.

FIG. 3 is a diagram showing an example of the A/D converter 14.

In the figure, the A/D converter 14 is an A/D converter circuit 15.
, a memory circuit 16, and an LED selection signal generation circuit 17.

The A/D conversion circuit 15 includes an A/D converter 18, a peak hold circuit 19, a voltage dividing circuit 20, and a switch 21.
The A/D converter 18 has two reference values (upper reference value Refl
, lower limit reference value Ref2) and the analog image signal VO, and compare the analog image signal VO in the range satisfying Refl>Vo>Ref2 with a plurality of weighted bits (for example,
4 bits) and converted into a digital image signal Vi of digital values, which is output. The details will be explained later, but
The upper limit reference value Refl is the peak value of the analog image signal Vo, and the lower limit reference value Ref2 is either the peak value divided by a predetermined partial pressure ratio (for example, 50%) or Ov. is entered. Therefore, when a divided voltage of the peak value is selected as the lower limit reference value Ref2, the range from approximately the peak value of the analog image signal VO to about 50% thereof is subject to digital conversion; When Ov is adopted as the value Ref2, almost the entire range of the analog image signal Vo is subject to digital conversion. That is, the lower limit reference value Re
By setting f2 appropriately, it is possible to extract and digitally convert only the fluctuations around the peak value of the analog image signal Vo, which is largely affected by the illuminance distribution, or to convert the fluctuations from the peak value of the analog image signal Vo to Ov. The entire range can be digitally converted to support multi-tone processing.

The peak hold circuit 19 holds the peak value of the analog image signal vO, and outputs this held peak value to the A/D converter 18 as the upper limit reference value Refl.

Note that the held peak value is reset at a predetermined timing by two reset signals R3I 5Rsz input to the OR circuit, and these reset signals R3, 5Rsz
, R3z are generated by a timing circuit not shown.

The reset signal RS t is generated at the timing of the detection signal D3 that detects the feeding of the document sheet, and the reset signal RS z is generated at (1) the timing just before reading the document sheet, and (2) the timing at the beginning of reading. The timing (2) is obtained by setting a predetermined timer time t using the detection signal 1 as a reference point, and the timing (2) is obtained by an arbitrary sub-scanning signal VK after the timer time t has elapsed. That is,
The peak value held in the peak hold circuit 19 is
(I) Based on the reference reflected light (peak value of the analog image signal Vo) in the period from when the original is detected to just before reading (corresponding to timer time t), (II) From just before reading to the beginning of reading start There are three types: (III) the peak value of the analog image signal vO based on the image information reflected light, and (III) the peak value of the analog image signal vO based on the image information reflected light in the reading period after the initial reading start.Therefore, the peak hold circuit The magnitude of the upper limit reference value Refl outputted from the voltage dividing circuit 19 also corresponds to the peak values of (I) to (III) above.
0 divides the peak value from the peak hold circuit 19 at a predetermined voltage division ratio (for example, 50%), and divides this into the switch 21.
output to the contact. When the write/read signal W/R, which will be described later, indicates the write timing, the switch 21 switches the contact to the illustrated position and adopts the output of the voltage dividing circuit 20 as the lower limit reference value Ref2, while the write/read signal W/R indicates the write timing. When /R indicates readout, switch the contact in the opposite position to the illustrated position to set the ground potential (Ov) to the lower limit reference value Ref2.
The lower limit reference value Ref2 is adopted as the above A/
Output to D converter 18.

The memory circuit 16 includes a frequency divider 22, an AND 23, an address counter 24, and a RAM 25.
The frequency is divided by N corresponding to the number of elements to generate a frequency-divided signal 1/N. Note that the value of N when generating the frequency-divided signal 1/N is:
It is determined from the ratio of the number of elements in the light receiving element array 11 and the light emitting element array 8. For example, the light receiving element array 11 is 1728
If the light emitting element array 8 has 32 elements, N=54. AND23 ANDs the initial signal S (a signal that continues from the output timing of the detection signal D1 until just before the document reaches the reading position) generated by a timing circuit (not shown) and the frequency-divided signal 17N, and this AND is established. A write/read signal W/R is generated which serves as a write timing during the above period and as a read timing during other periods. The address counter 24 sequentially counts the frequency divided signal 1/N,
The count value is sent to the address signal AD to the RAM 25.
Output as S. The RAM 25 is a random access memory, and its storage capacity is equal to the number of elements in the light emitting element array 8 x
The number of bits of the digital image signal Vi is secured. For example, in the above example, the number of elements in the light emitting element array 8 is 32 elements, and the number of bits of the digital image signal Vi is 4 bits, so
This RAM 25 only needs to have a storage capacity of at least 32X 4 = 128 bits.
Accordingly, the write/read mode is switched, the current digital image signal Vi is written to the bit specified by the address signal ADS from the address counter 24, or the written digital image signal Vi is read, and the control data B, ~B1 data bus and output to the above-mentioned light emitting element array 8.

The LED selection signal generation circuit 17 counts the frequency-divided signal 1/N and outputs a plurality of output lines (A,
~A,) are selected in sequence. That is, the output lines are connected to the aforementioned light emitting element array 8, and each output line is connected to a driver LD.

~LD, is connected to one of them. Therefore, when one of the output lines, for example A, is selected, the driver LD starts the correction operation described above.

Note that the frequency divider 22, address counter 24, and LED selection signal generation circuit 17 described above are reset and returned to the initial state each time the sub-scanning signal VK is input.

Next, the operation of the circuit will be explained with reference to the signal waveform diagrams of each part shown in FIGS. 4(a) to 4(i). First, the document detection sensor 4 detects a document being fed while the document is being fed, and a detection signal is emitted.
is output (see figure (c)), this detection signal D3
The initial signal S is set at the timing of the sub-scanning signal VK immediately after being output.

As described above, the initial signal S is a timer signal having a predetermined timer time t, and is reset when the timer time t has elapsed (see (e) in the same figure). Since the timer time t is set corresponding to the period from the detection of document flaw to just before the start of reading, the document flaw has not yet been read while the initial signal S is set. therefore,
The light received by the light receiving element array 11 becomes reference reflected light reflected by the presser plate 6. When the initial signal S is sent in this way, the AND23 of the memory circuit 16 outputs the divided signal 1/
The write/read signal W/R is output at timing N, and R
The AM 25 is switched to the write mode, and a write/read signal W/R is output to the switch 21 to switch its contact to the position shown in FIG.

As a result, the A/D converter 18 receives a lower limit reference value Re, which is the voltage divided (for example, 50%) of the peak value of the analog image signal Vo held by the peak hold circuit 19.
f2 is added, and furthermore, the upper limit reference value R of the peak value is
efl can also be added. The A/D converter 18 compares these upper limit reference value Reft and lower limit reference value Ref2 with the analog image signal Vo, and calculates the value near the peak value of the analog image signal Vo (more precisely, from the maximum value to the maximum value, for example, 50 %to)
digitally converted into weighted bits.

That is, since the analog image signal VO at this time is generated based on the reference reflected light, variations in the characteristics of each element of the light emitting element array 8 and the light receiving element array 11 or mounting accuracy, mirror 9, lens 10, etc. It is observed including all the error factors of the image signal such as peripheral light intensity unevenness due to the optical system, and the error, that is, the non-uniformity of the signal level in the main scanning direction, appears as a variation around the maximum value of the analog image signal vO. ing. Therefore, as described above, the lower limit reference value Ref2 is set to 5, for example, the upper limit reference value Refl.
By setting it to 0%, the non-uniformity of the image signal is digitally converted with high resolution, and this is converted into the digital image signal V.
It can be output as i (see (h) i in the same figure).

Note that 50% shown in the example is the voltage division ratio of the voltage dividing circuit 20, but depending on the predicted error factor, this may be set to 50% or more to further improve the resolution. The digital image signal Vi indicating the non-uniformity of the image signal is generated in the RAM which has already been switched to the write mode by setting the initial signal S.
25, and this storage is performed sequentially for each predetermined bit assigned to each element of the light emitting element array 8 according to the designation of the address signal ADS. As a result, 1547 minutes of digital image signals Vi based on the reference reflected light are divided and stored in the RAM 25 for each element of the light emitting element array 8, and this is repeatedly executed during the setting period of the initial signal S. Hereinafter, the stored digital image signal Vi for each element of the light emitting element array 8 will be referred to as a light amount correction value PH.

When the timer time t has elapsed and the initial signal S is reset, a reset signal R8 is output, the peak value held in the peak hold circuit 19 is cleared, and the RAM 25 is switched to the read mode. R.A.
The light amount correction value PH read from M25 is sent to the driver LD of the light emitting element array 8 as control data B, -B.
I to LD, and in parallel with this, any of the LED selection selection data A7 is output. For example, when the LED selection data AI is output, the light amount of the light emitting diode L is controlled based on the light amount correction value PH at this time, and further, in the LED selection data A2, the light amount of the light emitting diode L is controlled.
,, In the LED selection data A3, correction is performed over the entire illumination width based on the light amount correction value PH that is successively produced, such as for the light emitting diode 3. Therefore, after the correction, as shown in FIG. 5(b), the light amount of the light emitting element array 8 is corrected to match the set value SL corresponding to the target illuminance distribution, and the light amount in the main scanning direction is made uniform. The uniform irradiated light from the light emitting element array 8 becomes the reference reflected light again, and a digital image signal V is output based on this reflected light.
All errors are corrected and i becomes flat, as shown by the opening in FIG. 4(h). After that, the document tray reaches the reading position, and an analog image signal V is generated based on the image information reflected light from the document tray.

is output, the peak value (
In other words, the background level of the original is determined by the reset signal R8.
The signal is newly held in the peak hold circuit 19 cleared by 2. Therefore, after the start of reading the document, the A/D converter 18 performs quantization according to the newly held peak value, and the quantization level is varied according to the paper quality of the document and the color tone of the background. Ru. Also,
Even during reading of the document, the RAM 25 remains switched to the read mode, and the light emitting element array 8 is constantly receiving control of the light amount by the light amount correction value PH. That is, since the light emitting element array 8 emits light with the same light intensity distribution as when the digital image signal Vi shown in FIG. In this case, this amount of change corresponds to the shading information of the document.

In this way, in this embodiment, the irradiated light from the light emitting element array 8 when the light amount is not controlled is reflected by the presser foot 6, and this is used as the reference reflected light, and the digital image signal Vi is generated by this reference reflected light. is stored as a light amount correction value PH, and the light amount of the light emitting element array 8 is controlled based on the light amount correction value PH so as to have a target illuminance distribution when reading a document. Therefore, variations in the characteristics of the light emitting element array 8 and the light receiving element array 11, peripheral unevenness of the optical system,
Alternatively, it is possible to correct all of these fixed factors such as one error in installation position and fluid factors associated with changes over time at once, and the light emitting element array 8 and the light receiving element array 11
It is possible to improve the read image quality by performing comprehensive shading correction including the following. Furthermore, since the quantization level of A/D conversion is made to match the peak value of the analog image signal Vo, the light energy of the light emitting element array 8 is not wasted, resulting in excellent energy efficiency.

(Effects) According to the present invention, by controlling the light amount of the light source and making the output signal from the photoelectric conversion element match a predetermined setting value,
Comprehensive shading correction including light sources and photoelectric conversion elements can be performed. Therefore, while increasing the light energy efficiency of the light source, it is possible to collectively correct deterioration in read image quality due to variations in characteristics of the light source and photoelectric conversion elements, changes in characteristics over time, etc., and improve image quality. Can be done. Furthermore, by controlling the light intensity of the light source, it is possible to avoid driving for a long time near the maximum output, and it is possible to reduce power consumption, improve durability, and suppress heat generation.

[Brief explanation of drawings]

1 to 5 are diagrams showing an embodiment in which the image reading device according to the present invention is applied to a facsimile machine. A circuit diagram showing the element array, FIG. 3 is a circuit diagram showing the A/D converter section of the facsimile machine, and FIGS. 4(a) to (i) explain the circuit operation of the A/D converter section in FIG. 3. FIGS. 5(a) and 5(b) are graphs showing illuminance distribution to explain the operation, and FIG. 6 is a circuit diagram showing a conventional LED array. 1...Facsimile machine, 2...Image reading device, 3...Roller, ゛4...Document detection sensor, 5...Target Glass, 6...Press plate (reference document), 7...Roller, 8...Light emitting element array (light source), 9...
・Mirror, 10... Lens, 11... Light receiving element array (photoelectric conversion element), 1
2...Preamplifier, 13...DC regenerator, 14...A/D conversion section (light amount control means), 15
...A/D conversion circuit, 16... Memory circuit, 17... LED selection signal generation circuit, 18...
...A/D converter, 19...Peak hold circuit, 20...
・Voltage divider circuit, 21... Switch, 22... Frequency divider, 23... AND. 24...Address counter, 25...RAM.

Claims (3)

[Claims] (1) In an image reading device in which a photoelectric conversion element receives reflected light of light projected onto a document from a light source in which a large number of light emitting elements are arranged in a row, converts it into an electrical signal and reads an image of the document. An image reading device comprising a control means for controlling the light amount of the light source to a predetermined light amount when reading a document based on an output signal of a photoelectric conversion element when light from the light source is projected onto a predetermined reference document. Device. (2) the light source is divided into a plurality of light emitting element groups;
2. The image reading device according to claim 1, wherein the light amount control means controls the light amount for each light emitting element group. (3) The light emitting element of the light source is a light emitting element whose light amount changes depending on the current value, and the light amount control means has a storage means for storing the output value of the photoelectric conversion element at the time of reading the reference document, 3. The image reading device according to claim 1, wherein the current value supplied to each light emitting element of the light source is controlled based on the stored value.