JPH0740718B2 - Image processing device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image processing apparatus such as a facsimile machine and a digital copying machine, which electrically processes an original image, and particularly, a read signal obtained by reading the original image with an image sensor. The present invention relates to an image processing device that corrects nonuniformity.

[Prior art]

Conventionally, there are known devices that electrically perform various image processings such as facsimile machines and copiers, but most of these devices use an image sensor such as a CCD sensor to illuminate a document with a light source and reflect the reflected light. It is reading. However, it is difficult for a light source such as a fluorescent lamp to obtain a uniform amount of light over its entire length, and vignetting (vignet
In some cases, a uniform read signal may not be output due to a difference in the light transmittance of the lens due to ting), uneven sensitivity of the light receiving element, or the like. In this description, the nonuniformity of the read signal is called shading distortion. Therefore, in order to obtain a good read signal, a mechanism for electrically correcting this shading distortion has been proposed.

FIG. 1 shows an example of the structure of a conventional image processing apparatus that performs shading distortion correction.

In FIG. 1, reference numeral 1 denotes a CCD sensor as a photoelectric conversion element. Reflected light of a document exposed by a light source is transferred onto the CCD sensor 1 via an optical system (not shown) such as a lens and a prism. It is imaged. The CCD sensor 1 has a plurality of light receiving elements arranged in a line, and each light receiving element reads an image in pixel units.

The timing of reading image data from the CCD sensor 1 is controlled by the reading control unit 7. The output of the CCD sensor 1 is amplified to a predetermined level by the amplifier 3 and then binarized by the comparator 11 and output. At this time, changing the reference voltage of the comparator 11 corrects the sheating distortion.

The reference voltage of the comparator 11 is determined based on the shading distortion data stored in the memory 9 including a random access memory or the like. That is, the reading control unit 7 outputs the data output from the CCD sensor 1 and the memory 9
The reading of the shading distortion data stored in is linked, and the A / D, D corresponding to the reading position of the CCD sensor 1
The binarized reference voltage of the comparator 11 is changed via the / A converter 5, and the shading distortion is corrected according to the light amount distribution of the light source.

The shading distortion data is input by scanning a standard member such as a standard white plate before the original image is read by the CCD sensor 1. The analog output of the CCD sensor 1 obtained by scanning the reference member is converted into a digital value of a plurality of bits for each pixel by the A / D, D / A converter 5 and, for example, a memory for one line corresponding to the reading position 9 is stored.

When it is desired to increase the reading speed, the image processing apparatus having the above-described configuration requires the A / D and D / A converters 5 to operate at high speed. Generally, a high-speed A / D and D / A converter has a drawback that the structure is complicated, the cost is high, and the price of the image processing apparatus as a whole is increased.

Further, in order to store a plurality of bits of digital data for each pixel in a memory that stores shading distortion data, for example, a considerable storage capacity is required, and there is a cost problem.

Further, Japanese Patent Laid-Open No. 56-157576 discloses a technique for reproducing a shading waveform by using an up / down counter. In Japanese Patent Laid-Open No. 56-157576, it is detected whether the output level of each pixel obtained by reading the reference member having the reference density is higher or lower than the output level of the previous pixel, and the data is stored in the memory. When reading the original image, the data stored in the memory is read, the up / down counter is driven, and the voltage waveform corresponding to the output of the up / down counter is reproduced to perform shading correction.

However, in the technique disclosed in Japanese Patent Laid-Open No. 56-157576, since the shading waveform is stored and reproduced by using the up / down counter, a sudden level change occurs at the rising portion of the waveform at the head of the shading waveform. Has a drawback that the up / down counter cannot follow. Therefore, when the shading waveform is stored, the count value of the up / down counter is increased by performing several reading operations until the voltage level according to the output of the up / down counter matches the voltage level of the rising portion of the shading waveform. . During reproduction of the shading waveform, the up / down counter for giving the voltage level of the rising portion of the shading waveform is controlled, and then the up / down counter for reproducing the shading waveform is controlled.

Therefore, the technique disclosed in Japanese Patent Laid-Open No. 56-157576 has a problem that the control for storing and reproducing the shading waveform is complicated.

Further, in the one using an up-down counter for storing and reproducing the shading waveform described in Japanese Patent Laid-Open No. 56-157576, the up-down counter can accurately store and reproduce the waveform at a portion where the level change between pixels is abrupt. Can not. Further, in order to make the count value of the up-down counter follow a sudden level change between the pixels, it is necessary to drive the up-down counter using a clock faster than the drive clock of the image reading sensor, If an up-down counter that can be driven by such a high-speed clock is used, the cost of the entire device will increase.

〔Purpose〕

The present invention has been made in view of the above points, and an object thereof is to provide a simple, inexpensive, and high-speed image processing apparatus capable of surely correcting shading distortion, and to read an original image photoelectrically in pixel units. Means, a reference member for reference density, a detection means for detecting whether the output level of each pixel obtained by reading the reference member by the reading means is higher or lower than the output level of the previous pixel, and the detection means Memory means for storing data indicating whether the output level of each pixel of the reading means is higher or lower than the output level of the previous pixel based on the detection result; and the reading means reading the reference member in synchronization with the memory means. An address for storing the data in the memory means is designated, and an address for reading the data from the memory means is designated in synchronization with the reading of the original image by the reading means. A response counter, charging / discharging means for charging or discharging a capacitor according to the data read from the memory means in synchronization with reading of an original image by the reading means, and a voltage value charged in the capacitor It is an object of the present invention to provide an image processing apparatus including: a correction unit that corrects an output obtained by reading an original image by the reading unit.

〔Example〕

Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings. However, in the following, the same or corresponding members as those in the conventional example of FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted.

FIG. 2 is a simplified block diagram of a document reading apparatus to which the present invention can be applied.

A document placed on the document table 59 with its reading surface facing downward is illuminated by a fluorescent lamp 52, and a document image is formed on the CCD sensor 1 through the reflection mirrors 53 and 55 and an optical lens 56. The dotted line in the figure indicates the optical path of the reflected light from the document. Fluorescent lamp 52, reflective mirror 53,5
An optical system motor (not shown) 5 moves along a guide rail 58 to scan an original on an original table 59. CCD sensor 1
Then, the intensity of the reflected light from the document is converted into an electric signal of a predetermined pixel unit for each line, and the document image is read. In this embodiment, the uneven emission of the fluorescent light 52, the reflection mirrors 53, 5
The shading distortion caused by the uneven density of 5 and the uneven distribution of the height of the optical lens 57 is collectively removed electrically. That is, in this embodiment, the reference member 51 for measuring shading distortion data, which is provided outside the document placement area, is used.
Is read by the CCD sensor 1 prior to the original scanning, and then the original scanning is performed to correct the shading distortion for the original reading signal. The reference member 51 for measuring the shading strain data is a plate serving as a measurement reference for the shading strain data, and the entire surface thereof is uniformly painted in white or gray, for example.

FIG. 3 shows a CC provided in the document reading device shown in FIG.
FIG. 3 is a block diagram of a circuit configuration example for executing shading distortion correction on a read signal output from the D sensor 1.

As shown in FIG. 3, the output of the CCD sensor 1 is amplified by the amplifier 3 and then input to the outside of the comparator 11 and to the negative input terminals of the peak hold circuit 23 and the comparator 41.
The output signal line 23a of the peak hold circuit 23 is connected to one of the contacts of the analog switch 35. The other contact of the analog switch 35 is grounded, and a charge / discharge circuit including a resistor 37 and a capacitor 39 is connected to the common contact of the analog switch 35. The output of the charging / discharging circuit is connected to the + input terminal of the comparator 41 and divided by the resistors 43 and 45 to be the binarized reference voltage of the comparator 11. That is, the binarized reference voltage corresponding to the charging voltage of the capacitor 39 is supplied to the comparator 11.

On the other hand, the output signal line 41a of the comparator 41 is connected to the AND gate 2
It is connected to a gate circuit composed of 9,31 and OR gate 27. That is, the output of the comparator 41 is connected to one input terminal of the AND gate 29, and the output data of the memory 9 is input to one input terminal of the AND gate 31. The AND gates 29 and 31 are adapted to be gated by the signal line 7b of the reading control section 7. At this time, since the gate input of the AND gate 31 is inverted, when one of the AND gates 29 and 31 is open, the other is closed. The outputs of the AND gates 29 and 31 are input to the OR gate 27, and the logical sum thereof is used as the data input of the D flip-flop 25.

Therefore, when the output 7b of the read control unit 7 is at high level, the output 41a of the comparator 41 is selected and the OR gate 27 is selected.
On the contrary, when the output 7b is at the low level, the output 9a of the memory 9 is selected and output from the OR gate 27. The reading control unit 7 reads the reference member 51
That is, the output 7b is set to the high level when the shading distortion data is measured, and the output 7b is set to the low level when the document is read.

The D flip-flop 25 is latched by the read clock 7a that is output in synchronization with each read of one bit of the CCD sensor 1 by the read control unit 7 via the signal line 7a. The output signal line 25a of the D flip-flop 25 is connected to the input terminal IN of the memory 9 and the control terminal of the analog switch 35. Here, it is assumed that the analog switch 35 is connected to the upper signal line 25a when the signal line 25a is at the low level. The read / write timing control of the memory 9 is performed by the read control unit 7 via the signal line 7c. The read / write address control of the memory 9 is performed by an address counter that counts the clock 7d output from the read control unit 7 in synchronization with the read clock 7a.
Performed by 33.

That is, when the CCD sensor 1 reads the reference member 51, the signal line 7
Set the memory to write mode by pressing c and set the address counter 3
The output of the D flip-flop 25 is stored in the memory 9 according to the address value of 3. On the other hand, when reading the original, the memory is set to the read mode by the line 7e and the shading distortion data stored in the memory 9 is read in synchronization with the reading operation of the CCD sensor 1 according to the address value of the address counter 33.

Thus, the shading distortion data stored in the memory 9 is a binary signal output from the D flip-flop 25. Therefore, the configuration of the present embodiment can greatly reduce the memory capacity as compared with the configuration of storing a plurality of bits of shading distortion data for each pixel as in the conventional example.

Next, the operation of the above configuration will be described in detail with reference to the timing chart of FIG. FIG. 4 shows changes in the signal lines 7a and 41a, the connection points 3a, 25a and 41b, and the memory address 7e of the memory 9 in FIG.

When reading the shading distortion data, the voltage charged in the capacitor 39 via the heat hold circuit 23 shown at the bottom of FIG. 4, that is, the voltage at the connection point 41b and the signal line 3a.
The output of the amplifier 3 is compared by the comparator 41.

Therefore, the comparator 41 can detect the fluctuation of the output of the CCD sensor 1 via the amplifier 3 with respect to the charging voltage of the capacitor 39. Since the charging voltage of the capacitor 39 changes following the output of the CCD sensor 1 as described later, the comparison operation of the comparator 41 causes the CCD sensor 1 to operate.
It is possible to determine whether or not the current output of the above has changed with respect to the output corresponding to the immediately preceding pixel. This makes it possible to detect nonuniformity of the output of the CCD sensor 1 due to shading distortion.

The waveform of the output signal line 41a of the comparator 41 becomes high level when the output of the amplifier 3 is lower, as shown in the third stage of FIG.

At this time, that is, when measuring the shading distortion data, the signal line 7b is set to the high level, and the data of the signal line 41a is launched into the D flip-flop 25 in synchronization with the read clock of the signal line 7a. As a result, the signal line 25a
The waveform of is the waveform shown in the fourth row of FIG.

If the voltage of the signal line 3a is higher than the connection point 41b, the signal line 2
5a becomes low level in synchronization with the clock, whereby the analog switch 35 is connected to the signal line 23a side. Therefore, the amplifier 3 held by the peak hold circuit 23
The capacitor 39 is charged through the resistor 37 due to the output peak value of, and as a result, the voltage at the connection point 41b rises.

On the other hand, when the voltage of the signal line 3a is lower than the connection point 41b, the analog switch 35 is switched to the ground side by the operation opposite to the above, so that the capacitor 39 is discharged through the resistor 37 and the voltage of the connection point 41b. Can be lowered.

Thus, depending on the output of the comparator 41, the capacitor
By increasing or decreasing the charging voltage of 39, the charging voltage of the capacitor 39 can be made to follow the output of the CCD sensor 1.

By the above operation, a waveform corresponding to the output of the CCD sensor 1 appears at the connection point 41b as shown in the bottom of FIG. In the above operation, the data of the connection point 25a is stored and saved in the memory 9 for one line for each pixel by the address control of the signal line 7e of the address counter 33.

In this manner, the output 25a for one line is stored in the memory 9 as data indicating a change point for approximately representing a change in the output obtained by reading the reference member 51 by the CCD sensor 1.

On the other hand, when the shading distortion correction processing is performed on the image signal obtained by reading the original image, the reading control unit 7 sets the signal line 7b.
Is set to a low level so that the output signal of the memory 9 is input to the D flip-flop 25. Then, the read address is set to the signal line corresponding to the read position of the CCD sensor 1.
Give to 7e. As a result, the analog switch 35 is switched according to the data read from the memory 9 in the same pattern as when reading the shading distortion data, and the capacitor 39 is charged and discharged. At this time, the output (23a) of the peak hold circuit 23 is white (background or background) of the document.
Since the voltage varies depending on the density of the portion, the voltage at the connection point 41b in this white region changes in substantially the same manner as when scanning the reference member 51. That is, at the connection point 41b, a voltage waveform substantially similar to that at the bottom of FIG. 4 is reproduced.

Therefore, the voltage change at the connection point 41b according to the shading distortion data is given to the comparator 11 via the voltage dividing resistors 43 and 45, and the threshold level is changed.

As a result, the threshold value used for binarizing the read output of the original image by the CCD sensor 1 becomes a value according to the shading distortion, and accordingly, the image data correction according to the shading distortion is performed and the comparator 11 Can obtain a binary signal from which shading distortion has been removed.

Since the configuration using the charge / discharge circuit as described above can be speeded up relatively easily compared to the configuration using the conventional D / A or A / D converter, it is possible to perform the shading correction process at a lower cost and faster than the conventional one. . Therefore, it is possible to perform the image processing including the shading distortion correction processing at a higher speed with a lower manufacturing cost than the conventional one.

Also, in the conventional A / D and D / A conversion configuration, several bits (often 8 bits) are assigned to each pixel bit of the CCD as shading distortion data to express the density level, and this is stored in the memory. However, according to the present embodiment, since it is sufficient to secure a 1-bit memory per 1-bit pixel of the CCD as described above, the required memory capacity can be reduced to a fraction of that of the conventional one. is there. In addition, since the amount of data is small, the time required for memory access can be greatly reduced, so there is no need to use a high-speed memory element.
There is an advantage. However, one CCD pixel corresponds to multiple clocks of 25 D flip-flops, and the clock rate is increased so that more accurate shading distortion waveforms can be stored and reproduced, and more accurate shading distortion waveforms can be stored and reproduced. May be performed.

Further, in the present embodiment, the method of fixing and reading the original is described, but it goes without saying that the original may be moved by a roller or the like to read the entire surface of the original. In this document moving type configuration, a reference member for measuring shading distortion may be provided in the moving path along which the document is moved.

Further, in addition to the reflected light from the original, it is also applicable to a configuration in which the transmitted light of an image of a microfilm or the like is read by a CCD sensor.

〔effect〕

As apparent from the above description, according to the present invention, the capacitor is charged or discharged according to the data indicating whether the output level of each pixel obtained by reading the reference member is higher or lower than the output level of the previous pixel. Since the output obtained by reading the original image is corrected according to the voltage value charged in the capacitor, the circuit configuration can be simplified and an inexpensive image processing apparatus can be provided. Further, by using the charge / discharge characteristics of the capacitor, it is possible to follow a rapid change in the data obtained by reading the reference member at high speed, and in particular, by using the rising characteristics of the charging voltage when charging the capacitor, It is possible to quickly follow up the storage and reproduction of the waveform in which the voltage level of the rising portion of the shading waveform changes suddenly.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating the configuration of a conventional image processing apparatus, FIG. 2 is a simplified configuration diagram of a document reading apparatus to which the present invention is applied, and FIG. 3 is a configuration of the image processing apparatus of the present invention. 4 is a waveform diagram showing signal waveforms at respective connection points in FIG. 1 …… CCD sensor, 7 …… reading control section 9 …… memory 11,41 …… comparator 23 …… peak hold circuit 25 …… D flip-flop 27 …… OR gate, 29 …… AND gate 35 …… analog switch

Claims (1)

[Claims] 1. A reading unit that photoelectrically reads an original image in pixel units, a reference member having a reference density, and an output level of each pixel obtained by reading the reference member by the reading unit is an output level of a previous pixel. Detection means for detecting whether the output level of each pixel of the reading means is larger or smaller than the output level of the previous pixel based on the detection result of the detection means; and memory means for storing the data. And specifying an address for storing the data in the memory means in synchronization with the reading of the reference member by the reading means, and reading the data from the memory means in synchronization with the reading of the original image by the reading means. An address counter for designating an address, and a controller for reading data from the memory means in synchronization with reading of an original image by the reading means. Image processing, comprising: a charging / discharging unit that charges or discharges the sensor; and a correction unit that corrects the output obtained by reading the original image by the reading unit according to the voltage value charged in the capacitor. apparatus.