JPH0720195B2 - Image reader - Google Patents

Description

The present invention relates to an image reading device.

[Prior Art] A conventional image reading apparatus uses, for example, a fluorescent lamp as a light source. When the fluorescent lamp is used, the amount of light may differ between the center and both ends of the fluorescent lamp. Further, when a lens is used in the optical system, the amount of peripheral light decreases due to the cos ⁴ θ rule or the like. In order to correct these light intensity distributions,
Mechanical shading (operation of passing a large amount of peripheral light) and electrical shading (operation of changing a reference voltage according to the output of the fluorescent lamp when binarizing a video signal) are adopted.

The mechanical shading is between the fluorescent lamp and the subject,
Alternatively, a shading plate as shown in FIG. 5 is provided between the subject and the lens so that the peripheral light amount is greater than the central light amount. With this, the distribution of the amount of light by the fluorescent lamp or the lens is corrected.

Next, electrical shading will be described.

FIG. 6 (a) is a diagram showing a waveform of a video signal for one line (a waveform after direct current reproduction) and a slice level when electrical shading is not performed.

As the slice level, for example, about 60% of the peak voltage of the video signal waveform is considered, and the effective reading width is assumed to be the illustrated length. In this case, in the section (a), it is judged that the signal is actually a white signal but a black signal.

FIG. 6 (b) is a diagram showing a waveform of a video signal for one line (waveform after direct current reproduction) and a slice level subjected to electrical shading.

When performing electrical shading, the reference white plate is read before the image reaches the reading position, and the read video signal is stored in the memory. Then, the signal waveform stored in the memory (the signal waveform corresponding to the reference white board) is reproduced at a level of about 60% of the peak voltage of the current video signal waveform, and this is set as a slice level. Thereby, the video signal waveform can be binarized in consideration of the characteristics of the video signal waveform.

Then, when the document is set before the reading position, the reference all-white signal (video signal corresponding to the reference white plate) is read before the document reaches the reading position (this reading will be referred to as "prescan" below). The video signal waveform according to the current light intensity distribution is stored in the RAM or the like. Then, the slice level is determined with reference to the stored video signal waveform.

If the original is set in front of the scanning position,
This is shown in FIG. In this figure, the surface of the reference white plate 1 used when performing the pre-scan is on the side of the hatched portion is white. Reference numeral 2 is a fluorescent lamp, and reference numeral 3
Is a manuscript. In addition, when a plurality of pages of originals are set, the above prescan is repeated each time each page is read.

By the way, as shown in FIG. 7B, when the document 3 is inserted beyond the reading position, prescan cannot be performed. Therefore, it is not possible to obtain an all-white video signal. Therefore, the slice level is determined based on the video waveform stored in advance. The video signal waveform stored in advance is stored in, for example, a ROM or a battery-backed RAM.

Therefore, in the conventional reading device, the prescan is performed when the document is set in front of the reading position, and when the document is inserted beyond the reading position, it is already stored without being prescanned. The slice level is determined based on the waveform of the video signal being generated.

However, it is very rare that a document is inserted beyond the reading position. For this rare case, there is a problem that mounting a ROM or a battery backed up RAM and storing the video signal waveform is not economical in terms of cost and board space.

[Object of the Invention] The present invention has been made in view of the above-mentioned problems, and in a reading device capable of reading a document halfway, the document is set at a normal reading position in order to read the document halfway. When scanning starts when the document is inserted deeply beyond, it eliminates the inconvenience that shading correction cannot be performed because the reference white plate cannot be read immediately before reading the document image, and is only for the rare case where the document is read halfway. Eliminates the inconvenience of increasing costs due to the provision of a memory for storing shading correction data, and eliminates the inconvenience of economic efficiency by securing a space for mounting the memory on the circuit board. It is an object of the present invention to provide an image reading apparatus capable of performing the above.

Embodiment of the Invention FIG. 1 is an explanatory diagram of an embodiment of the present invention.

In this figure, a fluorescent lamp 20, a reference white plate 22 used when performing a prescan, a document 24, a document sensor 26 for detecting whether the document 24 is set,
Document edge sensor 28 that detects the leading edge of the document 24
, Reflection mirror 30, shading plate 32, lens 34
And CCD 36 are provided.

The document sensor 26 outputs a signal of level "0" when the document 24 is not set, and outputs a signal of level "1" when the document 24 is set. The document edge sensor 28 has a level "1" when the document 24 is set (not present) on it.
It outputs a signal of (level "0").

Normally, the document sensor 26 detects whether or not the document 24 is set on the document table, and the document 24 is fed until it reaches the document edge sensor 28. Then, prescan is performed. After that, since the distance from the document edge sensor 28 to the reading position is known,
The document 24 is fed by an amount corresponding to the length, and the reading operation is started.

From the beginning, when the document 24 is set on the sensors 26 and 28, it is not known how far the document 24 is inserted, so it is determined that the document 24 is set at the reading position and prescanning cannot be performed. Also, instead of the CCD 36, another image sensor may be used.

FIG. 2 is a block diagram showing an embodiment of the present invention.

The timing circuit 42 is a circuit that outputs a transfer pulse, a shift pulse, a reset pulse, a sampling pulse, a DC reproduction signal that is active while a dark output is output, and an address signal that specifies a RAM address.

The drive circuit 44 is a circuit that converts a pulse generated at the level of C ² MOS or TTL into a level that can drive the CCD 36 and supplies the pulse to the CCD 36.

The sample-and-hold circuit 48 outputs a signal other than the image signal (optical signal), such as a reset signal or an implied output signal, by the amplifier circuit 46. Therefore, the sample and hold circuit samples and holds the data at the timing when the image signal is output. However, it outputs only an analog optical signal component.

The DC reproducing circuit 50 is a circuit that corrects the DC component so that the output level in the dark is at the ground. Further, an amplifier circuit 46, a peak hold circuit 52, and a shading correction circuit 54 are provided.

Next, the prescan operation and the operation of storing the video signal waveform in the RAM 62 will be described.

The RAM 62 can be stored by a standby power supply, and stores data for reproducing a video signal waveform of an all-white signal.

If the original is, for example, A3 size and is read at 8 lines / mm, a CCD of 2592 pixels is required. If 8-bit data can be stored for each pixel, 256 levels can be set for each pixel. In the above embodiment, the video signal waveform of the all-white signal is reproduced by repeating charging and discharging with a predetermined time constant based on the peak voltage. In this case, RAM62 is 2592 x 1
It may have any bit capacity.

When storing the video signal waveform of the all-white signal, first,
The signal from the control circuit 72 to the shading correction circuit 54 is set to level "1". That is, NONSHD = 0 is set and the mode is set to perform shading correction. Then, the control circuit 72 generates a prescan start pulse toward the delay circuit 60. As a result, the delay circuit 60 first outputs a signal of level "1".

Then, when the timing circuit 42 generates two shift pulses, the delay circuit 60 outputs "0". Here, when the delay circuit 60 outputs "0", data for reproducing the video signal waveform of all white is output from the RAM 62.
When the delay circuit 60 outputs "1", the RAM 62 inputs data for reproducing the video signal waveform of all white.
When the signal from the control circuit 72 to the shading correction circuit 54 outputs “0” (NONSHD = 1),
Prescan cannot be performed.

After the pre-scan pulse is generated from the control circuit 72 and the shift pulse is generated from the timing circuit 42, the data until the next shift pulse is generated (that is, the output signal of the voltage comparison circuit 58) is input to the RAM 62. .

Shading correction circuit 54, at the beginning of the line,
Outputs a ground level signal. That is, at the beginning of the line, the ground level signal is output by the reference voltage output from the timing circuit 42.
The voltage comparison circuit 58 outputs a signal of level “0” when the level of the output signal of the DC reproduction circuit 50 is higher than the level of the output signal of the shading correction circuit 54. At this time, the shading correction circuit 54 performs the charging operation, and the RAM 62 stores the data "0".

Here, the multiplexer 64 outputs the output signal of the RAM 62 when the level of the output signal of the delay circuit 60 is “0”, and outputs the voltage when the level of the output signal of the delay circuit 60 is “1”. The output signal of the comparison circuit 58 is output. Note that, at present, the multiplexer circuit 64 is outputting the output signal of the voltage comparison circuit 58. After that, the same operation is performed, and the RAM 62 stores the data that reproduces the all-white video signal waveform.

FIG. 3 is a diagram showing a DC reproduction waveform at the time of prescan and a waveform stored in the RAM 62.

In FIG. 3, for example, at the point (a), the output signal of the DC regeneration circuit 50 (the signal indicated by the broken line) is
Since it is larger than the output signal of the shading correction circuit 54, the data of "0" is stored in the RAM 62 and the multiplexer 64 outputs the signal of level "0", so that the shading correction circuit 54 performs the charging operation. .

On the other hand, for example, at the point (a), since the output signal of the DC reproducing circuit 50 is smaller than the output signal of the shading correction circuit 54, the RAM 62 stores the data of level “1” and the multiplexer circuit 64 stores the data. Since the signal of level "1" is output, the shading correction circuit
54 discharges.

Here, for example, since the number of bits of the A3 original is 2592 bits, which position among them is “0” (that is, the charging operation is performed) or “1” (that is, the discharging operation is performed). However, the RAM 62 needs to be stored. Address data that counts the number of bits is the timing circuit
42 outputs.

Next, a method of outputting the data stored in the RAM 62 and causing the shading correction circuit 54 to output a similar waveform of the all-white signal waveform stored at the time of the print scan will be described.
Note that here, since the peak value of the image currently being read is considered, the peak value changes.

First, the control circuit 72 outputs a signal of level "1" to the delay circuit 60 and sets the mode to perform electric shading. Then, in order for the delay circuit 60 to output the signal of level “0”, the multiplexer circuit 64
Outputs the output signal of the RAM 62. Then, data "0" and data "1" are output corresponding to each bit of one line. At this time, since the shading correction circuit 54 charges and discharges according to the output signal of the multiplexer circuit 64, the shading correction circuit 54 can output a waveform similar to the all-white signal waveform stored during the prescan. . That is, electrical shading is possible.

Here, when the level of the signal from the control circuit 72 to the delay circuit 60 is "0", electrical shading is not performed. That is, in this case, only the charging operation is always performed.

The voltage dividing circuit 56 outputs about 60% of the output signal of the shading correction circuit 54 and sets this output signal at the slice level.

The voltage comparison circuit 66 is a circuit for inputting the video signal waveform after the DC reproduction outputted by the DC reproduction circuit 50 and the slice level outputted by the voltage dividing circuit 56 to perform binarization. When the level of the output signal of the DC reproducing circuit 50 is higher than the signal level of the voltage dividing circuit 56, that is, when it is a white signal, the voltage comparison circuit 66 outputs a signal of level “0”.
On the contrary, the level of the output signal of the DC regeneration circuit 50 is
When the signal level is smaller than the signal level of, that is, when it is a black signal, the voltage comparison circuit 66 outputs a signal of level "1".

The signal processing circuit 68 is a circuit that performs various kinds of signal processing on the binarized signal output from the voltage comparison circuit 66.

That is, the above-described embodiment is an image reading apparatus that reads an original with a line sensor, performs mechanical shading with a shading plate, and performs electrical shading with shading correction data obtained by reading a reference white plate having a reference density. A first memory for storing the shading correction data obtained by reading the reference white plate, a means for detecting that the AC power supply of the apparatus has changed from the OFF state to the ON state, and an AC power supply of the apparatus from the OFF state to the ON state The image reading apparatus includes a second memory which is cleared when the shift to the (1) is detected and which is set when the first memory stores the shading correction data, and a correction unit which corrects the shading of the image data read by the line sensor. .

Further, when the original is not present at the reading position and the reference white plate can be read at the start of reading the original, the correction means reads mechanical shading and the reference white plate, and electrically reads the shading correction data. Shading is performed, and the shading correction data obtained by reading the reference white board is stored in the first memory.
At the start of reading the original, the original is present at the reading position, the reference white plate cannot be read, and the shading correction data is set to the first shading correction data depending on the stored contents of the second memory.
If it is determined that the original is read, the mechanical shading and the electric shading based on the shading correction data stored in the first memory are performed, and the original is read at the start of reading the original. Is present at the position, and the reference white plate cannot be read,
Further, when it is determined by the stored contents of the second memory that the shading correction data is not stored in the first memory, it is a means for performing mechanical shading and preventing electrical shading.

The control circuit 72 and the shading correction circuit 54 are examples of the correction means.

FIG. 4 is a flowchart showing the control operation of the control circuit 72.

First, the control circuit 72 operates with a standby power supply. For this reason, the flow chart is started when the main power supply and the standby power supply are turned off.

When the main power supply and the standby power supply are turned from the off state to the on state, the data for performing the shading correction is not stored in the RAM 62, so "0" is set to the flag called SHDEND (shading end) (S82). Then, for example, when the reading operation is selected from the operation section (S84), it is determined whether or not a document exists (S84).
86).

If there is no document, error processing (S88) is performed, and then the process returns to S84. If there is a document, it is determined whether the document is set on the document edge sensor 28 (S90). If no document is set on the document edge sensor 28,
The document is cued up to 28 (S92), and when the cued up to the document edge sensor 28 is finished, the control circuit 72
Then, the level of the signal from the shading correction circuit 54 to the shading correction circuit 54 is set to "1" (NONSHD = 0), and the mode is set to the electrical shading. At this time, mechanical shading is also performed.

Then, a prescan pulse is sent to the relay circuit 60 to perform prescan. It is needless to say that the fluorescent lamp is preheated for a predetermined time, and after that, the fluorescent lamp is turned on and a predetermined time has elapsed, and then the prescan is performed.

After performing the prescan operation, the SHDEND flag is set to "1" and the completion of the reading operation is waited (S100).
When the reading operation is completed, the process returns to S84.

When the document is set on the document edge sensor 28 (S90), the prescan is not performed, and the SHDEND flag is "0" (that is, when the data for performing the shading correction is not stored in the RAM 62). (S102), SHDEND flag is set to "1". vice versa,
When the data for shading correction is stored in the RAM 62, the SHDEND flag is set to "0".

In S104, only level "0" is output as a signal from control circuit 72 to relay circuit 60 (NONSHD = 1 is set), and electrical shading is not performed, but only mechanical shading is performed.

Further, in S106, only the level "1" is output as a signal from the control circuit 72 to the relay circuit 60 (NONSHD
= 0) and perform electrical and mechanical shading.

In the above-described embodiment, a very rare case in which a document is inserted beyond the reading position (in the above-described embodiment, the condition that the operation of changing the main power supply from the off state to the on state is performed is also added) This eliminates the need to have a ROM or battery backup circuit, making the image reading device economical.

Even if the image is read only by mechanical shading, a satisfactory image can be obtained at room temperature.

In the above embodiment, the shading waveform is stored.
RAM62 can be stored with standby power, but that RAM
The memory 62 may be stored only by the main power supply.

EFFECTS OF THE INVENTION According to the present invention, when the original is at the reading position at the start of reading the original and the reference white plate cannot be read, and the data obtained by reading the reference white plate is stored in the memory, Since mechanical shading and electrical shading based on the data stored in the memory are performed, when the document starts to be read deeply inserted beyond the normal reading position, the reference white plate is read immediately before reading the document. This has the effect of eliminating the inconvenience of being unable to perform shading correction due to the inability to read.

Further, according to the present invention, when the original is at the reading position at the start of reading the original and the reference white plate cannot be read, and the data obtained by reading the reference white plate is not stored in the memory, mechanical shading is performed. Since electrical shading is not performed, it is possible to eliminate the inconvenience of increasing costs due to the provision of a dedicated memory for storing data for shading correction only in the rare case of reading an original from the middle. Further, by securing a space for mounting the dedicated memory on the circuit board, it is possible to solve the problem that economic efficiency is deteriorated.

Furthermore, according to the present invention, means for detecting that the AC power supply of the apparatus has changed from the OFF state to the ON state, and clearing when detecting the change of the AC power supply of the apparatus from the OFF state to the ON state, the shading correction data. Since the second memory that is set when the first memory stores is provided, it can be surely detected that the AC power supply has changed from the off state to the on state, and the shading correction data can be stored in the first memory. The effect that the stored information can be surely detected and the shading correction operation becomes reliable is achieved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention. FIG. 2 is a block diagram showing the above embodiment. FIG. 3 is a diagram showing a DC reproduction waveform at the time of prescan and a waveform stored in the RAM in the above embodiment. FIG. 4 is a flow chart showing the operation of the above embodiment. FIG. 5 is a view showing a general shading plate used when performing mechanical shading. FIG. 6 is a diagram showing a relationship between a video signal waveform and a slice level in the conventional example. FIG. 7 is a diagram showing a positional relationship between a document and a reading position in the above conventional example. 22 …… Standard white board, 24 …… Original, 36 …… CCD, 32 …… Shading board, 54 …… Shading correction circuit, 56 ……
Voltage dividing circuit, 72 ... Control circuit.

Claims (1)

[Claims] 1. A document is read by a line sensor, and mechanical shading is performed by a shading plate,
In an image reading device that performs electric shading by shading correction data obtained by reading a reference white plate having a reference density, a first memory for storing the shading correction data obtained by reading the reference white plate; A means for detecting the transition of the power supply from the off state to the on state; cleared when the transition of the AC power supply of the apparatus from the off state to the on state is detected, and set when the shading correction data is stored in the first memory A second memory; and a correction unit for shading-correcting the image data read by the line sensor, wherein the correction unit does not exist at the reading position at the start of reading the document, and If the reference white plate can be read, the above mechanical shading and the above reference white plate The shading correction data obtained by reading the reference white plate is stored in the first memory, and the original document is read at the start of reading the original document. In addition, it is not possible to read the reference white plate,
Further, when it is determined that the shading correction data is stored in the first memory based on the stored content of the second memory, the mechanical shading and the first shading data are stored in the first memory. The electric shading is performed by the shading correction data, and the original is present at the reading position when the reading of the original is started, and the reference white plate cannot be read, and the storage of the second memory is performed. If it is determined that the shading correction data is not stored in the first memory, the mechanical shading is performed to prevent the electrical shading. apparatus.