JPH06334817A - Original reader - Google Patents

Abstract

PURPOSE:To suppress difference in picture quality of readers due to dispersion in luminance of an LED and sensitivity dispersion in a CCD by blinking an LED array synchronously with a read time of a CCD one-dimensional image sensor and deciding a lighting time for one reading based on a read level of a white reference board to have a proper time. CONSTITUTION:A standard lighting time set in advance is set to a register 19 and a white reference board 3 is read in this state and received by a picture processing DSP 7 to detect a maximum value A. When whether or not the maximum value A exceeds a preset reference value B is checked and when the value A is in excess, the difference C=B-A is calculated. The excess state as above indicates that the lighting time is too larger with respect to the illuminance of an LED array 1, then the lighting time is reduced corresponding to the difference C. Since the relation between the difference C and the proper lighting time D is stored in advance in a ROM 13, the data D are set in the register 19 to adjust properly the lighting time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a document reading device in a facsimile machine, a copying machine, an image scanner or the like, and more particularly, it illuminates a document with a linear light source composed of an LED (light emitting diode) array, and CCDs the linear image. (Charge-coupled device) The present invention relates to an improvement of a document reading device configured to take an image with a one-dimensional image sensor.

[0002]

2. Description of the Related Art A document reading apparatus having the following basic structure has been well known. A document and a white reference plate are illuminated with a linear light source composed of an LED array, and a linear image of the illuminated portion is read by a CCD one-dimensional image sensor. An analog image signal output from the image sensor is appropriately amplified by an ABC (automatic background adjustment) circuit or the like, and input to a DSP (digital signal processor) for image processing. The DSP, after A / D converting the image signal, performs various digital operations for image quality improvement such as shading correction, edge enhancement, and noise removal, and stores the processed digital image data in a memory. As we all know,
The read data of the white reference plate is used for shading correction.

In the case of a facsimile machine, the image data stored in the memory is compression-encoded by an encoding / decoding unit, and the compressed data is transmitted via a modem.

[0004]

In the conventional document reading apparatus of this type, the LED array, which is the illumination light source, is continuously turned on during the reading operation so that the illuminance thereof is appropriate. The drive current of the LED array is set appropriately, and the reading cycle is set appropriately to optimize the charge storage time of the CCD.
Since there are variations in the brightness characteristics of the LED array, the sensitivity characteristics of the CCD image sensor, or the characteristics of the reading optical system for each product, it is inevitable that the reading sensitivity of the illumination system also varies. The variation of this characteristic is ABC
It is possible to compensate to some extent by automatic gain control of a circuit or the like and the shading correction.

However, in the conventional correction technique of this type, CC
When the illuminance of the light source was too small for the charge accumulation time of D, the deterioration of the image could not be prevented. In order to shorten the reading time of the document, the reading cycle of the CCD tends to be as short as possible and the illuminance of the LED array tends to be high. The level of the image signal when the white reference plate is read is designed to be the maximum allowable value. Therefore, if the brightness of the LED array is too low and the sensitivity of the CCD is too low due to product-to-product variations, the white reference level decreases and the S / N (signal noise) deteriorates, resulting in image deterioration. In addition to the deterioration of the S / N, the variation in the brightness of the LED light source and the variation in the sensitivity of the CCD cause a difference in the image quality of each device. The degraded image is not improved by automatic gain adjustment or shading correction.

Further, in a facsimile apparatus, a high-resolution document reading apparatus compatible with a fine mode may read a document at a low resolution of ½ according to the standard mode of a communication partner. In this case, the document reading system is operated in the same manner as in high resolution, and the read image data is discarded (invalidated) every other line to obtain image data of 1/2 low resolution.

In the conventional apparatus, when reading a document at a low resolution as described above, the LED is used as in the high resolution mode.
The array is on continuously. Therefore, charges are accumulated in the CCD in response to the image of the invalid line. The data of the invalid line is transferred in response to the line sync signal.
If the white level of the image in the invalid line is too high, the residual charge that remains in the photosensitive cell without being transferred increases, and the residual charge adversely affects the data in the next valid line, resulting in poor image quality. To do. There is also a problem that the illumination power is wasted when the invalid line is read.

The present invention has been made in view of the above-mentioned conventional problems, and a first object of the present invention is to suppress variations in optical systems among products. A second object is to prevent the image of the invalid line from adversely affecting the data of the valid line in the low resolution reading mode.

[0009]

Therefore, in the first invention,
The linear light source consisting of an LED array illuminates the original and the white reference plate, and the linear image of the illuminated portion is CC-illuminated.
D In a document reading device for reading with a one-dimensional image sensor, in synchronization with a reading cycle of the image sensor, blink control means for driving the LED array to light for a lighting time that is appropriately variably set, and under predetermined lighting conditions. The white reference plate is read, a proper value of the lighting time is determined based on the reading level, and a lighting time adjusting means for setting the value as a parameter of the blinking controlling means is provided.

In the second invention, the LED array is turned on by the blinking control means and the blinking control means at the time of reading a valid line in the low resolution reading mode, and at the time of reading an invalid line, the LED array is turned on.
A lighting prohibition control means for controlling the ED array not to light is provided.

[0011]

In the apparatus of the first invention, the LED array is blinked in synchronization with the reading cycle of the CCD one-dimensional image sensor, and the lighting time for one time is determined to be an appropriate value by the adjusting means. As a result, when the reading level of the white reference plate is low, the lighting time is adjusted accordingly, and the white reference level is always kept constant by the CCD.

In the device of the second invention, since the LED array is not turned on when reading the invalid line,
The residual charge due to the image of the invalid line is hardly generated, and the data quality of the next valid line is not deteriorated.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the construction of the essential parts of a facsimile apparatus including the embodiments of the first and second inventions. In the document reading apparatus of this embodiment, the document 2 and the white reference plate 3 are illuminated by the linear light source including the LED array 1, and
The linear image of the illuminated portion is read by the CCD one-dimensional image sensor 4. An analog image signal output from the image sensor 4 is appropriately amplified by an amplifier 5 and an ABC (automatic background adjustment) circuit 6, and input to a DSP (digital signal processor) 7 for image processing. D
The SP7 performs A / D conversion of the image signal, then performs various digital operations for image quality improvement such as shading correction, contour enhancement, and noise removal, and stores the processed digital image data in the RAM8. RAM for fax machines
The image data stored in 8 is compressed and encoded by the encoding / decoding unit 10, and the compressed data is transmitted via the modem 11. Note that, in FIG. 1, other components of the facsimile apparatus not directly related to the present invention are omitted.

In FIG. 1, a CPU 12 that executes a program stored in a ROM 13 performs sequence control and data processing that controls the entire facsimile apparatus. Part of the control according to the first and second aspects of the invention is also performed by the CPU 12 as follows.

The DSP 7 generates a line sync signal c for the CCD image sensor 4 at a constant cycle based on the clock signal from the clock generator 9. In the image sensor 4, every time the line synchronization signal c is generated, the charges accumulated in the photosensitive cells of each pixel up to that time are transferred to the output register section and output in series to the amplifier 5. The period from the generation of a certain line synchronization signal c to the generation of the next line synchronization signal c is the charge accumulation period corresponding to the input image, and the serial analog image signal from the image sensor 4 is synchronized with the line synchronization signal c. It is output one line at a time.

In the device of the present invention, the LED array 1 is not constantly lit during the reading period, but is normally driven by the driver 15 in accordance with the blinking timing signal from the blinking control section 14. As will be sequentially described below, the blinking control unit 14 turns on the LED array 1 in synchronization with the line synchronization signal c, and turns off the LED array 1 before the next line synchronization signal c is generated. That is, the LED array 1 is used for a certain period of time that is appropriately shorter than the reading cycle of the image sensor 4.
Lights up.

The structure and operation of the blinking control section 14 will be described.
In the normal high resolution reading mode, the lighting permission signal a given from the CPU 12 to the AND gate 16 is always "1", the Q output of the flip-flop 17 is input to the driver 15 via the AND gate 16, and the LED array 1 Becomes a lighting drive signal.

As shown in the timing chart of FIG. 4, the flip-flop 17 is set in response to the line synchronizing signal c, its Q output becomes "1", and the LED array 1 is turned on. At the same time, when the Q output becomes "1", the counter 1
8 starts counting the clock signal from the clock generator 9.

The count value of the counter 18 is the comparison circuit 20.
When the count value that is compared with the setting value of the register 19 and is gradually increased reaches the setting value, the comparison circuit 20 outputs the coincidence signal b, and the coincidence signal b resets the flip-flop 17. When the flip-flop 17 is reset and the Q output becomes "0", the LED array 1 is turned off, and at the same time, the count of the counter 18 is stopped and reset.

That is, the LED array 1 is turned on in response to the line synchronization signal c and turned off after a time corresponding to the set value of the register 19. The set value of the register 19 is data that determines one lighting time of the LED array 1, and the lighting time changes in proportion to this set value.

The CPU 12 sets the lighting time data in the register 19. As an initial process when the power of the device is turned on, the CPU 12 executes a lighting time adjustment process shown in FIG.

In the first step 201 in the flow chart of FIG. 2, a preset standard value of the lighting time (for example, a time corresponding to 90% of one line cycle) is set in the register 19. In that state, the white reference plate 3 is read (step 202), the read data is taken in via the DSP 7, and the maximum value A is detected (step 20).
3). Then, it is checked whether or not the maximum value A exceeds a preset reference value B (step 20).
4) If it exceeds, the difference C = BA is calculated (step 205).

The fact that A exceeds B means that the illuminance of the LED array 1 is too large when the lighting time is set to the standard value, and the difference data C indicates that it is too large. . Therefore, when A exceeds B, the lighting time is appropriately shortened according to the difference data C (the larger the difference data C, the shorter the lighting time). The relationship between the difference data C and the appropriate lighting time D is stored in advance in the ROM 13 in the form of a control table. In step 206, the lighting time D corresponding to the detected difference data C is read from the control table, and the next step 20
In step 7, the lighting time data D is set in the register 19. The lighting time is now properly adjusted. If A does not exceed B, steps 205, 20
Skip 6,207.

Next, the second invention will be described. In the low resolution mode in which the original is read at a resolution of 1/2 of the standard resolution, the CPU 12 executes the lighting prohibition control shown in FIG. 3, and the line synchronization signal c as shown in the timing chart of FIG.
The lighting permission signal a is set to "0" every other cycle to prohibit lighting of the LED array 1 when reading an invalid line.

[0025]

As described above in detail, in the device of the first invention, the LED array is blinked in synchronization with the reading cycle of the CCD one-dimensional image sensor, and one lighting time is the white reference plate. A proper value is determined based on the reading level of. That is, when the reading level of the white reference plate is small, the lighting time is adjusted to be long, and the CCD
At, the white reference level is always kept constant. As a result, the white reference level is lowered and it is possible to prevent deterioration of image quality due to deterioration of S / N.

In addition, variations in the brightness of the LED light source, CCD
It is possible to suppress the individual difference in the image quality of the device due to the variation in the sensitivity.

In the device of the second invention, since the LED array is not turned on when reading the invalid line,
The residual charge due to the image of the invalid line is hardly generated, and the data quality of the next valid line is not deteriorated. Further, it is possible to reduce the illumination power when reading the invalid line, and particularly when the present invention is applied to a battery-powered portable device, it is very effective in extending the operating time in the battery.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a document reading device including the first and second inventions.

FIG. 2 is a flowchart of a lighting time adjustment process in the embodiment of the first invention.

FIG. 3 is a flow chart of lighting prohibition control in the embodiment of the second invention.

FIG. 4 is a timing chart showing the main points of the operation in the embodiment of the first invention.

FIG. 5 is a timing chart showing the main points of the operation in the embodiment of the second invention.

[Explanation of symbols]

 1 LED array 2 Document 3 White reference plate 4 CCD one-dimensional image sensor 14 Flashing control section

Claims (2)

[Claims] 1. A document reading apparatus which illuminates a document and a white reference plate with a linear light source composed of an LED array and reads a linear image of the illuminated portion with a CCD one-dimensional image sensor, wherein a reading cycle of the image sensor is set. In synchronization, a blinking control means for driving the LED array to light for a lighting time that is appropriately and variably set, and the white reference plate being read under a predetermined lighting condition, and an appropriate value of the lighting time based on the reading level. Decide
An original reading apparatus, comprising: a lighting time adjusting means for setting the value as a parameter of the blinking controlling means. 2. A document reading apparatus which illuminates a document and a white reference plate with a linear light source composed of an LED array and reads a linear image of the illuminated portion with a CCD one-dimensional image sensor, in which a reading cycle of the image sensor is set. In synchronization, blink control means for driving the LED array to illuminate for a variably set lighting time, and blinking control means for turning on and off the LED array when reading a valid line in the low resolution reading mode. When reading the line, the LED
An original reading apparatus, comprising: a lighting prohibition control unit that controls so that the array is not turned on.