JPS61120579A - Picture reader - Google Patents

Abstract

PURPOSE:To obtain a proper shading correction even when the light intensity of a light source is lowered while being immune to dust and dirt by storing a maximum output as the result of white reference face scanning and reading a white reference value being the storage contents in reading a picture signal on an original so as to apply correction. CONSTITUTION:A digital picture signal 30 of an A/D converter 23 is stored in a white reference memory 41 via a latch 42 and a buffer 34 in the 1st white reference read scanning. Then a control signal 55 is a clock controlling the write of the white reference memory 41 for the 2nd and succeeding scannings, and only when the signal is logical H, a write signal 47 actuates the write of the white reference memory 41. The write on the white reference memory 41 is conducted when a scanning trigger signal 16a is logical H and the write on the white reference memory 41 is inhibited and the reader is brought into the normal picture signal read state. Thus, the shading correction of the picture signal at reading of an original is attained normally with high accuracy by writing the maximum value of white reference on the white reference memory 41 by several times of scanning.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an image reading device used in a facsimile machine or the like.

Conventional configuration and its problems A conventional image reading device will be described below.

FIG. 1 shows a block configuration of a conventional image reading device.

In FIG. 1, 1 is a document, 2 is a document holding plate, 3 is a fluorescent lamp for illuminating the document 1, 4 is a fluorescent lamp cover, S is a lens system, and 6 is a document that is illuminated through a lens system 5. A solid-state image sensor for extracting information as an analog signal, 7 is an A/D
This is the conversion section. 8 is a storage circuit that stores the output of the A/D converter 7, specifically, a random access memory (
RAM). 9 is a storage circuit for storing inverse coefficient sensitivity values, which will be described later; specifically, it is a read-only memory (R
OM). 1o is a multiplication circuit.

Note that the inner surface of the document holding plate 2 is treated to have a uniform white color by means of painting or the like.

In the above configuration, the white reference inner surface of the document holding plate 2 is read before the information on the document 1 is photoelectrically converted into an image signal by the solid-state image sensor 6. Since this photoelectric conversion signal is a signal obtained by scanning a uniform white surface, there are many factors that affect the entire photoelectric conversion system, such as uneven illumination of the original surface, loss of peripheral light from the lens 5, and nonuniform sensitivity of the solid-state image sensor 6. This indicates non-uniformity in sensitivity.

Now, from the photoelectric conversion signal of the white reference plane, the A/D converter 7
The sensitivity coefficient value of each element 6 converted into a digital image signal is stored in the storage circuit 8 via the storage circuit 8. Next, when photoelectrically converting the document surface, the storage circuit 8 The sensitivity coefficient value corresponding to the solid-state image sensor 6 is read from the image signal, and the inverse coefficient sensitivity value corresponding to this image signal is retrieved from the storage circuit 9 which has been tabulated in advance, and this value is multiplied by the photoelectric conversion signal of the document surface in the multiplication circuit 10. Then, the required non-uniformity of the photoelectric conversion system is removed, and a photoelectric conversion signal on the surface of the document can be obtained.

By the way, although the inner surface of the document holding plate 2 is painted white, small dust and dirt may adhere to this white surface during the operation of reading the document.

If there is such dust or dirt, when obtaining a white reference signal, the sensitivity of the photoelectric conversion system will be isometrically low only in the dust or dirt area, which is a disadvantage of not being able to obtain an appropriate white reference signal. It had

Furthermore, if the light intensity of the fluorescent lamp decreases during use, the white reference signal will also decrease, and the ability to remove unevenness in the photoelectric conversion signal obtained by scanning the document will also decrease, making it difficult to output an appropriate image signal. It had the disadvantage that it could not be obtained.

Purpose of the Invention In view of the above-mentioned drawbacks, the present invention provides an image reading system that is not affected by dust or dirt and can obtain an appropriate photoelectric conversion signal of a white reference surface even if the light intensity of the illumination light source decreases. It provides equipment.

Structure of the Invention In order to achieve the above-mentioned object, the present invention scans a white reference surface for non-uniformity correction (hereinafter referred to as Schudeng correction) for a certain period of time by multiple increments during document surface reading.
When the maximum value output is held and the white reference surface is scanned subsequently, the white reference surface scan obtained by changing the amplification factor of the input photoelectric conversion signal is determined by the maximum value output. By memorizing the maximum output value and reading out and correcting the memorized content during photoelectric conversion of the document surface, it is not affected by the dust or dirt mentioned above, and even if the light intensity of the light source decreases, it can maintain the proper level. The configuration is such that a white reference signal can be obtained.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 shows a block configuration of an image reading device in an embodiment of the present invention.

Items 1 to 6 in FIG. 2 have the same structure as those shown in FIG. 1 with the same numbers.

7a is an amplification/A/D conversion section, which includes a variable amplification section 7b composed of a multiplier type D/A converter and an amplifier, an A/D converter 7C, and a latch circuit that detects the maximum value of the white reference value. and a maximum value detection section 7d composed of a comparator circuit and the like. Reference numeral 8a denotes a correction section, which includes a white reference memory control section 8b composed of a white reference memory, a counter for controlling the white reference memory, a comparator circuit for detecting the maximum value of the white reference value for each scan, and a white reference memory control section 8b for detecting the inverse coefficient sensitivity value. R to remember
○ Consists of M8c, multiplier 8d, etc.

Reference numeral 9a denotes a scan counter timing generator that generates a scan timing signal such as a scan start signal.

Hereinafter, more detailed configuration examples of each of the blocks a, 8a, and 9a will be explained using plan views.

FIG. 3 shows a more detailed block configuration of the scan counter timing generator 9a.

In FIG. 3, 11 is a signal representing the reading period in the main scanning direction by the solid-state image sensor 6, and 10 is a drive signal for reading the white reference surface, each of which is a signal sent from an external microprocessor (white reference start signal). It is. 12,13
．． 14 is a clip flop, 15 is a counter for scanning time to obtain the maximum value output of the white reference plane, 15
a is the scan start trigger signal. 16 is a scanning time counter for storing in the ROM 8c the maximum value of the white reference signal obtained by the subsequent white reference plane scanning/Udeng correction, and 1e5a is the scanning start trigger signal.

Next, the amplification A/D conversion section 7a will be explained.

FIG. 4 shows the block configuration of the amplification/A/D conversion section Ryoa.

In FIG. 4, 20 is an analog image signal obtained from the solid-state image sensor 6, 21 is a multiplication type D/A converter, 22 is an amplifier, 23 is an A/D converter, and 24 is a multiplication type signal obtained by the output of the latch 26. 26 is a flip-flop, 27 is a gate section, and 28 is a comparator. 29 is the analog image signal output of the amplifier 22, 3o is the digital image signal output obtained from the A/D converter 23, 31 is the sample manual clock for A/D conversion, 32 is the sampling output clock, and 33 is the digital image signal 3o. is the image signal output 3 from the latch section 25
34 is a trigger signal to the latch unit 26, and 36 is a digital level signal to the multiplication type D/A converter 21.

Next, the correction section 8a will be explained.

FIG. 6 shows a detailed block configuration of the correction section 8a.

In FIG. 6, 40 is a counter that generates an address for a storage circuit 41 (hereinafter referred to as white reference memory), 43 is a buffer, 42, 44 is a latch, 46 is a ROM for Schuden correction coefficients, 46 is a comparator, and 47 is a flip-flop, 48a to 48c are gate sections, 4-wire flip-flops, and the father is a digital multiplier.

The operation of the image reading apparatus configured as shown in FIGS. 3, 4, and 5 will be described below.

First, in FIG. 3, when a white reference start signal 1o is input from a microprocessor (not shown), the flip-flops 12 and 13 are turned on, and the scan start trigger signal 15a becomes "H" state.

At this time, the counter 15 counts a predetermined cycle in the main scanning direction, and when it ends, the flip-flop 12 is reset and the scan start trigger signal 16a also becomes "L" state. Since this scan start trigger signal 16a is connected to the gate section 27 in FIG. 4 and the ROM 24 that stores coefficients for varying the gain of the multiplier type D/A converter 21, when it is in the "H" state, the ROM 24 The level 36 indicating the output data of is set to be XaO in hexadecimal notation. At this time, if the gain of the amplifier 22 is set to double, the level of the input analog image signal 29 to the A/D converter 23 becomes equal to the level of the input analog signal 20.

By the way, at this time, the input digital image signal 3 of the latch 26
By comparing the input digital image signal 30 with the previously captured digital image signal 35 in the comparator 28, a comparison signal 33 is output when the input digital image signal 30 has a higher output level, and via the gate 27, the 7 ripple drop 2θ join. On the other hand, since the sampling output 32 for A/D conversion is always applied to the clock input of the flip 70 knob 26, the input digital image signal 30 of the latch 25 is updated and stored only when the comparison signal 33 mentioned above is present. In this way, the latch 25 operates so that the white reference value from the A/D converter 23 is held at its maximum value. At this time, the level of the input analog image signal 29 is
It goes without saying that the voltage must be adjusted to below the reference voltage of the voltage.

On the other hand, when the level of the white reference value is set and the scan start trigger signal 15a goes to the L state, the flip-flop 14 is set and the scan start trigger signal 16a goes to the "H" state. At this time as well, the counter 16 counts a predetermined period in the main scanning direction, and when it ends, the 7-rip 70-tub 14 is reset and the scan start trigger signal 16a also goes to the "L" state. When this scan start trigger signal 16a becomes "H" state, the scan start trigger signal 15a goes low.
In this state, the ROM 24 comes to output a gain control coefficient value corresponding to the maximum value of the digital image signal 35 from the latch 25. That is, the level of the digital image signal of the latch 25 is expressed as "A I+", the coefficient value of the ROM 24 at this time is set as "B", and the coefficient value is A-B= so that the output level 36 is controlled by the following formula. If the settings are set constant, even if the value of the input analog level 20 is insufficient during the white reference period, the gain of the multiplier type D/A converter 21 will be RO according to the maximum value output from the latch 26.
Since it is controlled by the coefficient value output 36 of M24, the A/D
The input analog level 29 of the converter 23 is always the A/D
The amplitude is adjusted to the reference voltage of the converter 23.

For example, when the scan start trigger signal 15a is in the H" state,
When the maximum value output of the latch 25 is stored as "KO" in hexadecimal notation, when the scan start trigger signal 16a is in the H state, it is R
Since 91" is output to 36 in hexadecimal notation by OM 24, the gain of multiplication type D/A converter 21 is multiplied by 1.13.

Therefore, the A/D converter input level of the input analog image signal 2o is amplified to an amplitude up to the reference voltage value of the A/D converter 23.

As a result, even if the light intensity of the light source decreases, the multiplication type D/A
The converter 21 automatically corrects the decrease, making it possible to read the appropriate white reference value.Furthermore, when the scan start trigger signal 16a is in the "H" state,
The white reference value is stored in the white reference memory 41, and the operation at this time will be explained with reference to FIGS.

First, in the first white reference reading scan, the A/D converter 23
The digital image signal 30 is stored in a white reference memory 41 via a latch 42 and a buffer 43.

At this time, a counter 40 counts using a clock pulse 54 synchronized with the sampling output clock 32, and the address of the white reference memory 41 is specified based on its output.

Next, in the second white reference reading, the reading lock 53,
Using the latch clock 62 synchronized with this, the digital image signal 3o after A/D conversion passes through the latch 42, and an input digital signal 56 to the comparator 46 is generated. On the other hand, the contents of the white reference memory 41 addressed by the clock pulse 64 are read out via the lunch 44 as the other digital signal 67 of the comparator 46 .

At this time, the aforementioned data is compared by inputting the comparison clock 48 whose phase is slightly delayed from the latch clock 52,
If the input digital signal 66 is large, the comparison output 58 will rise, thereby operating to provide the white reference memory write state 4 completed.

As a result, the buffer 43 is opened, and the maximum value of the white reference signal is updated and rewritten in the white reference memory 41 every scan synchronization.

The control signal 66 is a clock that controls writing to the white reference memory 41 for the second and subsequent scans, and this signal is set to "H".
Only in this state, writing to the white reference memory 41 is performed by the write signal 47 described above.

As mentioned above, the writing operation to the white reference memory 41 is as follows:
When the scanning trigger signal 16a is in the "H" state, the signal is activated.
When the state is set to L'', writing to the white reference memory 41 is prohibited and the image signal reading state becomes normal. Therefore, by writing the maximum value of the white reference value as the white reference memory 41 by scanning several times, Normally, the schudeng correction of the image signal is performed with high precision when reading a document.

As in the conventional case, this Schuden correction is performed by reading the signal level from the white reference memory 41 and using the ROM 45 in which the inverse coefficient sensitivity values for the white reference value are previously tabulated.
A uniform digital image signal can be obtained by multiplying the digital image signal obtained by reading the content and the surface of the document using the multiplication circuit 5o.

Effects of the Invention The maximum value of the white reference plane for performing Schuden correction is held by scanning multiple lines for a certain period of time, and the maximum value output is used as input for the subsequent scanning and reading of the white reference plane several times. The maximum value output of white reference plane scanning obtained by changing the amplification factor of the analog signal is memorized,
By reading out and correcting the white reference value of the forelight memory contents when reading the image signal on the document surface, it is not affected by dust or dirt, and even if the light intensity of the light source decreases, appropriate shoden correction can be achieved. The effect is great.

[Brief Description of the Drawings] Fig. 1 is a block wiring diagram of a conventional image reading device, Fig. 2 is a block wiring diagram of an image reading device according to an embodiment of the present invention, and Fig. 3 is a scanning counter in Fig. 2. 4 is a block wiring diagram of the timing generation section, FIG. 4 is a block wiring diagram of the amplification/A/D conversion section in FIG. 2, FIG. 5 is a block wiring diagram of the multiplication section in FIG. 2, and FIG. 6 is a block wiring diagram of the multiplication section in FIG. 2 is a timing chart of the main parts of . 1... Original, 5... Lens system, 6...
...Solid-state image sensor, 7a...Amplification/A/D
Conversion section, 7b...Variable amplification section, 7C...
...A/D conversion section, 7d... Maximum value detection section, 8
a: Correction unit, 8b: White reference memory control unit, 8C: ROM, 8d: Multiplier, 9a: Scanning counter timing generator.

Claims (1)

[Claims] a reading means for reading image information of a document and reading white reference information on a white reference surface provided near the document during first and second scanning periods; and a variable amplification of the read information read by the reading means. and determining the maximum value of the white reference information read by the reading means within the first scanning period, and adjusting the amplification factor of the amplifying means according to the maximum value of the white reference information. an amplification factor control means for controlling outside the scanning period, and determining the maximum value for each pixel of the white reference information sent from the amplification means within the second scanning period, and determining the maximum value of the white reference information for each pixel according to the maximum value. An image reading device comprising: a correction means for correcting image information of the document read by the reading means.