JPH03128567A - Picture reader - Google Patents

Abstract

PURPOSE:To always read a picture area accurately by comparing a picture signal obtained through readout of the picture area with a preset value and detecting the relative position in the read area or the size of a picture medium so as to set the read range. CONSTITUTION:A CPU 28 reads a data from a line memory and continues to carry a film in the subscanning direction till the maximum value reaches 25, that is, 0.1 of density or over in a digital value. Succeedingly, the film is stopped at a position advanced by 15mm further from the film tip at that time. The CPU 26 reads the content of a line memory sequentially and compares it with a preset threshold level and memory addresses A, B in crossing with the threshold level are stored. Since the A,B are recognized as the addresses, the film size is obtained by WF=97[mum]X(B-A). The film size in the main scanning direction is discriminated based on the size and the distance till the end of the film is obtained by a horizontal synchronizing signal.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image reading device that can accurately read an image area with a simple configuration.

(Prior Art) Image reading devices have been known that convert image information into digital signals by scanning an image medium such as an X-ray film with a light beam.

For example, in a medical X-ray film reader, this type of device scans the film in the main scanning direction with a laser beam while transporting the film in the sub-scanning direction along a transport guide. Alternatively, the image signal is obtained by photoelectrically converting the light reflected from the film. A photodetector is installed within the scanning width of the laser beam and outside the film transport path, and an image reading section is set at a predetermined timing after this detector detects the scanning light.

FIG. 11 shows an example of an image reading signal forming circuit in a conventional image reading device, in which 100 is an address counter that counts input pixel clocks and is cleared by a horizontal synchronization signal, 200 is a ROM that stores data, and 300 is a ROM.
This is a latch circuit that holds data read out from 200 and outputs it as an image reading signal.

By writing the data 1it-...1000-11 in the ROM 200 in advance and making it possible to read out the data in synchronization with the pixel clock, the 12th [J If the image reading signal forming circuit that always generates an image reading signal (negative logic in the figure) is configured in this way, in the film reading area, the timing of the image reading signal generated with the horizontal synchronization signal as a reference It can be adjusted. That is, the reading area can be adjusted by rewriting the data in the ROM 200, and once the data in the ROM 200 is determined, the image reading signal will be output at a fixed timing from the horizontal synchronization signal. Therefore, as long as the position of the conveyance guide is constant, images can be read within an accurate range.

However, with conventional devices, there may be looseness in the film transport guide, or the reading position may shift depending on the mounting accuracy, resulting in areas that cannot be read and some image information is missing. Sometimes I just sit back and read things outside of the film. Also, even if you specify the image position using coordinates, the film position will be shifted, so the specified area will not appear accurately.These shifts can be eliminated by adjustment during the manufacturing process, but doing so will increase manufacturing costs. Moreover, even if the adjustment is made, if the device is used for many years, the mechanical parts may become loose to some extent, and the reading position may shift.

Incidentally, in this type of apparatus, the size of the film is detected by microswitches arranged at certain intervals in the main scanning direction, but this method has the following problems.

First, the detection method using microswitches requires a large number of parts, which makes assembly work such as installation and position adjustment complicated.

Next, for example, in medical X-ray photography, the size of the film used is almost standardly determined to be the following five types, and the number of microswitches is only four (Japanese Patent Laid-Open No. 60-46
No. 660).

0 1 4 4 O 2 4 4 7 However, when attempting to read films of other sizes, four microswitches are not enough and more microswitches must be installed, making the mechanism extremely complex.

Furthermore, when using microswitches, the reliability and durability of mechanical contacts and actuators must also be considered.

Therefore, a photointerrupter type or reflective type optical sensor switch can be used in place of the microswitch, but the problems mentioned above still exist.In the case of a reflective type optical sensor, a reflector plate is attached on the opposite side of the sensor. Needless to say, it is necessary.

(Objective and Structure of the Invention) The present invention has been made in view of the above points, and it is possible to read an image area accurately and with a simple configuration according to the transport position of the image medium and the size of the image medium. The purpose is to provide a device that can.

To achieve this objective, in the present invention.

The output signal of a photoelectric conversion means for photoelectrically converting the transmitted light or reflected light of the light beam from the image medium is compared with a preset threshold value to determine the relative position within the reading area of the image medium or the size of the image medium. The reading range of the image medium is set according to the detected value.

(Example> An embodiment of the present invention will be described below.

FIG. 1 shows the overall configuration of an image reading device according to the present invention,
A film am stand 2 is provided at the top of the main body frame, and X &! The film XF is transported by a transport system unit 3 including a pulse motor, and along the way, it passes downward between an optical system unit 4 and a light receiving system unit 5, and the image is read. Thereafter, the X-ray film XF is discharged to the film discharge tray 7 via a film discharge guide. A microswitch MS□ is located just outside the film storage stand 2 along the transport path of the X-ray film XF, and a microswitch MS is located at the lower end of the film unloading guide 6.

are provided respectively, and a micro switch M S
When l is ONL/motor 1 for transporting the film, which will be described later.
6 and turn micro switch MS2 from ON to OFF.
When this happens, it is detected that the film XF has been completely ejected.

FIG. 2 shows the configuration of the optical system unit 4 and the light receiving system unit 5 of the image reading device.

Laser light generated from a laser light source 11 such as a semiconductor laser is shaped by a collimator lens 12, reflected by a mirror 13, and then directed toward a rotating polygon mirror 14 called a polygon mirror that rotates at a predetermined speed in a horizontal plane. It will be done. The laser beam reflected by the rotating polygon mirror 14 is focused on an fθ lens 15 at a distance proportional to the incident angle θ with respect to the optical axis.
Trying to read through X&! Since the film XF is also sent downward by the pulse motor 16 of the transport system unit 3, the entire surface of the X-ray film XF is scanned by these.

The laser beam that has passed through the X-ray film XF is reflected by the reflective surface 17a of the elliptical mirror type condenser 17, condensed, and received by the photodiode 18.

Here, the reflective surface 17a of the condenser 17 forms a part of an ellipse, and a photodiode 18 is arranged at one focal point. Instead of the photodiode 18, an element such as a photomultiplier tube or a photodiode array may be used, and instead of the condenser 17, a plastic fiber bundle, a processed acrylic material, or a lens system may be used. etc. can be used.

The image signal obtained by photoelectric conversion by the photodiode 18 is amplified by an amplifier 19, and is logarithmized by a logarithmic amplifier to be converted into a density signal. After being A/D converted by the A/D converter 20, the image is subjected to shading correction by the reading hardware circuit 21 and stored in the image memory 22. Alternatively, instead of storing it in the image memory 22, an interface circuit (for example, 5CS
I, GPIB, etc.) to a host computer B external to the reading device.

A detailed circuit configuration of the light receiving system unit shown in FIG. 3 is shown.

The laser light that has passed through the Xil film XF is converted into an electrical signal by the photodiode 18, passes through the amplifier 19 and sample hold circuit 23, is converted into a digital signal by the A/D converter 20, and is sent to the reading hardware circuit 21. It will be done.

A synchronization signal obtained from a photodetector 24 that detects scanning light or a processing timing signal is input to this reading hardware circuit 21.

Then, the image data processed here is sent to the host computer B via the parallel signal line 25. The CPU 26 has program storage RO as memory.
It is equipped with an M27 and a RAM 28, and command information is sent and received to and from the host computer B via a serial signal line 29 and a serial interface 30.

The image signal obtained by photoelectric conversion by the photodiode 18 is supplied to the amplifier 19, and first, the current-voltage conversion amplifier 19a converts 'I! After converting the current to current pressure voltage, it is supplied to the log amplifier 19b and linear amplifier 19c, and the switch 1
Either one selected at 9d is supplied to the sample hold circuit 23 and the A/D converter 20 to obtain a digital signal. Here, both the log amplifier 19b and the linear amplifier 19c are used, and either one can be selected by the switching signal from the tying control circuit 21g, but when there is no need to switch, the log amplifier 19b and the linear amplifier 19c are used.
There is no need to use the unnecessary one of the g amplifier 19b and the linear amplifier 19c, and especially when only the log amplifier 19b is used, there is no need to perform current-voltage conversion.

The digital image data obtained by A/D conversion is sent to the reading hardware circuit 21, where the switching circuit 21a
When an image data request signal arrives from the host computer B, the shading correction data stored in the second line memory 21c and the multiplier 21d or adder 2 are stored in the first line memory 21b for one scan.
1e, shading is corrected, and sent to host computer B. When using the log amplifier 19b, adder 21e and linear amplifier 19
When c is used, the multiplier 21d is controlled to be used.

21g is a timing control circuit that controls the memory and others, and is controlled by an interface control signal (IF signal) from host computer B. 21h is log
This is a switching circuit for selecting one of the amplifier 19b and the linear amplifier 19c.

Now, taking medical X-ray film as an example, the density is lowest when it is not exposed to any X-rays; in this case, only the density of the base material of the film is produced, and this is called the "base density". I'm here.

The base concentration is usually around 0.17.

On the other hand, the state where there is nothing in the reading section, that is, the state where the scanning light directly reaches the condenser 17 (see Figure 2), is defined as "density 0", and if the difference between density 0 and the base density can be detected, the presence or absence of film can be determined. This means that it can be detected.

Consider a case where the photodiode 18 is used for photoelectric conversion and the log amplifier 19b and preamplifier 19c are connected as in this embodiment. Of course, if the ffiog amplifier 19b is a current input type, the photodiode can be directly connected to the log amplifier 19b. On the other hand, it is assumed that the A/D converter 20 connected later converts Ov to IOV into digital values from 0 to 1024, for example.

Now, assuming that the output value of the log amplifier 19b obtained when nothing is inserted into the scanner (the density is 0) is Ov, the output of the log amplifier 19b becomes r2.
The gain and offset value of the log amplifier 19b are set so that the voltage increases by 5VJ.

On the other hand, in order to digitize the image read from the film, it is necessary to supply a clock signal to the A/D converter 20 and the subsequent memory system. This clock signal is used to determine the timing for capturing pixels that are normally read.

It is synchronized with a synchronization signal generated from the photodetector 24.

Therefore, it is convenient to use the count number (pulse number) of this clock signal as the film position and size information.

FIG. 4 is a block circuit diagram of a portion related to the reading operation of the image reading device.

In the figure, numeral 31 is a pixel original clock generation circuit;
A clock is generated to be supplied to the frequency division counter 32 and gate 34. This pixel original clock generation circuit 31 has a PLL.
A circuit or a programmable timer such as Intel 8253 is used. PTCI and PTC2 are programmable timer counters, and for example, JLPD71054 manufactured by NEC Corporation can be used. The clock for the pulse motor 16 for transporting the film is usually several hundred.
~ several KHz, programmable timer counter PT
The basic clock frequency of the pixel original clock generation circuit 31 is determined in consideration of the maximum operating frequency of C1 and PTC2 and the number of frequency division counter bits. NEC mentioned above, 71
Since the 054 has a 16-bit counter, an input clock of 5 MHz is appropriate.

The divide-by-8 counter 32 connected after the pixel original clock generation circuit 31 is cleared in synchronization with the horizontal synchronization signal (H-SYNC), and the deviation of the pixel clock output with respect to the horizontal synchronization signal is always within 1/8 clock. It can be suppressed. This clock is used as a pixel clock 50, gated by the image reading signal from the RAM sequencer and gate 34, and supplied to the A/D converter 20 as a sample clock.

The RAM sequencer 33 has an address counter 33a and an R
It is composed of an AM 33b and a latch circuit 33c, and determines the timing of image reading in the main scanning direction, that is, generates an image reading area signal 51. Since the scanning light scans the film at a constant speed, the timing with respect to the horizontal synchronizing signal is equal to the physical image reading area in the main scanning direction, and the address counter 33a is 8.
The pixel clock from the frequency division counter 32 is used for a long time, and the horizontal synchronization signal is used as a clear signal to operate.

By rewriting it to exit using the RAM 33bf) data and CPU 26 (see FIG. 3), any timing can be generated. The buffers 41 and 42 are for the CPU 26 to read and write the contents of the RAM 33b, and are controlled by the CPU 26 controlling the control circuit 40 to generate an enable signal and a DIR (direction) signal.

PTC2 is a counter that counts the number of read lines. Since main scanning always starts with a horizontal synchronization signal as a reference, by counting the number of horizontal synchronization signals, it can be determined how many in-reads have been performed. The flip-flop 35 is set by a read start signal generated by an external circuit (such as a CPU).

It is reset by the count end signal of PTC2.

While the flip-flop 35 is set, it indicates that the image is being read, and an image reading bubble signal 52 is output. The sample clock to the AD converter 20 uses a pixel clock 50, an image reading area signal 51, and a signal gated by a reading raw signal 52.

FIG. 5 is a flowchart showing the reading operation of the image reading device. The following will explain the process according to the flowchart.

In step (S-1), a set value for setting the feed speed is set as CPU data in the programmable frequency division counter PTC1 that counts the basic clock. In step (S-2), it is determined whether or not the starting switch has been turned on, and when it has been turned on, the pulse motor 16 for transporting the X-ray film is turned on. Specifically, the programmable frequency dividing counter PTC1 is set to a count enable state, a basic clock is generated from the counter PTC1, and the pulse motor 16 is driven via the driver 30 by this clock. As a result, conveyance of the X-ray film XF is started (S-3).

Next, the initial position setting operation (shown surrounded by a broken line) (S-4
)to go into.

That is, by setting PTC2 to 1 (S4-1) and outputting a reading start signal.

The reading circuit starts reading (S4-2) and stops after writing l main scanning data into the line memory 21b or 21c (S4-3).

The CPO 26 reads this data from the line memory (S4-4), and continues to transport the film in the sub-scanning direction until the maximum value is 25, that is, the digital value reaches a density of 0.1 or more (S4-5). When the maximum value of the data exceeds 25, it means that the leading edge of the X-ray film has approached the scanning line.

At this time, is it okay to set an appropriate value in the pixel original clock generation circuit 31? If it is set to a low frequency, the accuracy of position detection will be poor, and if it is set to a low frequency, the required line memory capacity will be large. Become. Now, f of the fθ lens 15
value, the rotational speed of the polygon mirror 14 [rpm], the pixel original clock frequency aF, and the physical pixel size P [ml
The relationship is as follows.

- On the other hand, when scanning with the rotating polygon mirror 14, it is divided into a section where the image area is actually scanned and a retrace section where it is not, but in the retrace section, no scanning light is incident on the condenser 17. Since the signal output from the photodiode 18 is not concentrated, the signal output from the photodiode 18 is similar to a very high concentration.

Therefore, as shown in FIG. 6, if the one-image reading area signal 51 is set at the maximum reading area or more and sent out at a timing that reaches the retrace section, the signal of the high density area will be read (sampled). ), making accurate size detection impossible.

Now, the maximum image reading area is approximately 400 mm in the case of a medical X-ray film reader.

Assuming that the capacity of the line memory is 4 words (l word depends on the number of bits of the AD converter 20, here it is lO bits), the size of one pixel is substituted into both equations (1), and here So f=380°R=2000
Then, the image original clock frequency F=13 [MHz
]. Therefore, the oscillation frequency of the pixel original clock generating circuit 31 is set to 13 MHz.

Then, the RAM sequencer 33 has addresses a, ~a2.
By writing a value that is "true" only in the section, the maximum reading width can be read with the maximum density (accuracy), and the detected position accuracy will be the highest.

Using the above-mentioned setting values, sampling is performed every line, and the CPU 26 or the line memory 21b performs sampling.

2 Look at the Lc data and determine whether the maximum value of the data exceeds 25 (density 0.1). If it does, it means that the leading edge of the film has reached the scanning line at that point.

The above is the initial position setting operation.

Then, when the film has advanced 15 mm further from the leading edge (S-S), the film is stopped (S-6).
This step (S-5) is performed as a countermeasure against round corners. That is, the corners of the xg film are usually rounded. This depends on the specifications of the film manufacturer, but it is usually a radius of 10 mm (this is often the case. If you scan this area to determine the film position, the position will be different from the actual position. Therefore, be sure to detect the tip and then
The film position is detected after two films are transported in the sub-scanning direction by ~30 mm (15 mm in this embodiment).

Next is the film size detection operation (indicated by a broken line) (S
-7) However, when the film exists within the reading area, the image signal becomes as shown in FIG. 7(a). moreover,
The data in the line memory when one scanning sentence is read (one line sample) is as shown in FIG. 7 (b).

The CPU 26 sequentially reads the contents of the line memory, compares them with a preset threshold value (usually written as a program in the program storage ROM), and stores the crossed address as position information. It will look like this:

Sampling of only one line of data is performed again (S7-1), the sampled data is digitized and stored in the line memory 21b, and its contents are stored in the CP
is scanned by U26 and set to a predetermined threshold (in this example, 2).
．． 5V) (S7-23.Then, the memory addresses A and B that cross the threshold are stored.The storage location is usually RAM2B directly connected to the CPU bus.
The above is the size detection operation.

Since A and B are known as address values.

At this time, the film size is WF=97[μm1x(B-
A). From this value, the film size in the main scanning direction can be determined, and the distance from the horizontal synchronizing signal to the edge of the film can also be determined as shown in Figure 8, LFl = 97 [
ILm]
bt ) (farthest from the horizontal synchronization signal).

Now, when it is desired to read 2048 words of X-ray film, the size of one pixel is determined by the pixel original clock frequency F. Also, the values that should be set in the RAM sequencer 33.

What is necessary is to make it "true" only in the interval from LFI to LF2. In other words, in terms of addresses of the RAM sequencer 33, (a□+b1) to (a, +b2) are "true".
, and the rest can be set as "false". Further, as described above, the pulse motor 16 is driven via the driver 30 by a clock obtained by dividing the basic tarock by 1/P when the programmable frequency dividing counter PTCl is in the count enable state, and the phase speed by the pulse motor 16 is corresponds to the frequency of the clock from the programmable frequency division counter PTC1, thereby changing the read pixel size in the sub-scanning direction, which depends on P2.

Now, returning to the flowchart in FIG. 5 again, in step (S-S), the film that has been advanced to prevent round corners is returned to its original position, and then reading is started from the leading edge of the film (S-9). . The part surrounded by the broken line is the reading operation.

First, set the main scanning direction setting value Pl in the pixel original clock generation circuit 31 as the specified value of the reading pixel size 5-9)
, Next, set the sub-scanning direction set value P1 in the programmable frequency division counter PTCl (S9-2), and then set the read line aP3 in the programmable frequency division counter PTC2 (S9-3).

Next, set the reading circuit to a reading operation enabled state (S9-4),
It is determined whether or not a reading start command has been written from the host computer B (S9-5), and when the command is received, reading is started (sending a set signal to the flip-flop 35), and the conveying pulse motor 16 is turned on (S9-5). S9-
6). In this way, image information is read line by line from the X-ray film. During this time, it is determined whether the programmable frequency division counter PTC2 has counted the horizontal periodic signal by a preset count value P3 or not (S9-7).
When the count is counted, it is assumed that the reading of the reading area has been completed and the conveyance pulse motor 16 is stopped (S9-8). This is the reading operation.

After that, set the setting value for setting the feed speed as CPU data in the programmable frequency division counter PCTI.
-10) Turn on the conveying pulse motor 16 and start discharging the X-ray film XF (S-11)
.

It is determined whether or not the film detection microswitches MS and MS2 provided along the conveyance path are turned off (S-12), and when all of them are turned off (S-12),
At the discharge completion stage), the conveyance pulse motor 16 is stopped (S-13).

With the above method, even if there is an error in the mounting position of the film transport guide, the actual film position is detected and data is read accordingly, making it possible to accurately read the image area.

Furthermore, since the actual film position is detected, there is no need to adjust the reading position as in the prior art.

Furthermore, the film size can be detected with a simple configuration without the need for multiple microswitches as in the conventional method.

In the above embodiment, the position of the film is first detected, and then reading is performed according to the detected position. However, if the film meanderes, the image positions will be different between the leading and trailing parts of the film. Therefore, it is possible to detect the tilt of the film and read the image according to this tilt. For example, when the film is tilted as shown in FIG. 9, α and β in FIG. It is sufficient to detect the film position at two locations. The angle at which the film is inserted can be calculated from the difference in the distance between α and β and the position of the film edge.

The starting point for reading the film can be corrected and read for each scan. At this time, the main scanning can only be tilted, so the shaded area in Figure 9 must be read when scanning.However, the meandering is usually quite regulated by the precision of the physical mechanical parts, and the person inserting the film , unless the film is inserted at an intentional angle, the meandering angle is 5@
It is as follows. Therefore, there is no practical problem even if the reading area is as shown by diagonal lines in Figure 9.Such a mechanism is suitable for use when an autofeeder device is installed, in which film is automatically fed without an operator. Particularly effective. The slight tilt of the automatically fed film is corrected and read using the method described above.

Note that when a tilt of the film is detected, instead of correcting the reading position as described above, the film may be returned and some kind of warning display may be displayed to urge the operator to correctly insert the film.

Alternatively, it is possible to issue something like a warning signal or status message to the host computer. At this time, normal reading operation may be performed instead of tilt correction reading.

By the way, the signal for film position or size detection is the third one.
Either the output of the fLog amplifier 19b or the output of the linear amplifier 19c shown in the figure may be used. For example, when the concentration output characteristic of the linear amplifier 19c is as shown by track 6c in FIG.
When the voltage changes to 0, the output value changes from 0 to about 3v.

Looking at this in terms of a value after A/D conversion, it is a change from 0° to about 300, which is a significantly large change compared to the change from 0 to 25 in the case of the log amplifier 19b.

In other words, the linear amplifier 19c has a larger rate of change within the dynamic range, and is advantageous for detecting the position/size of the film. Therefore, the output of the linear amplifier may be used when detecting the position/size of the film, and the output may be switched to the 10g amplifier during normal image reading.

(Effects of the Invention) As explained above, in the present invention, an image signal obtained by reading an image medium is compared with a preset value to determine the relative position within the reading area of the image medium or the size of the image medium. Since the reading range of the image medium is set according to this detected value, the image area can always be read accurately and with a simple configuration regardless of the transport position of the image medium or the size of the image medium. be able to.

Further, in the present invention, by providing the image reading area designation means and the reading pixel size designation means, it is possible to read a desired image region with a desired pixel size.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram of an embodiment of an image reading device according to the present invention, FIG. 2 is a configuration diagram of main parts of an image reading device according to the present invention, and FIG. The circuit block diagram which shows the part in detail. FIG. 4 is a block diagram of the circuit portion related to the reading operation of the image reading device according to the present invention, FIG. 5 is a flowchart showing the reading operation in the image reading device according to the present invention, and FIG. 6 is the image signal and image reading area signal. 7 (A) is a timing chart of the image signal obtained by the present invention, (B) is a diagram showing data in the line memory, FIG. 8 is a diagram showing memory addresses for image signals, FIG. 9 is a diagram illustrating reading when an X-ray film is conveyed at an angle, FIG. 10 is a diagram of the output characteristics of the linear amplifier and log amplifier used in the image reading apparatus according to the present invention with respect to film density, and FIG. A block diagram showing an example of an image reading signal forming circuit in a conventional image reading device,
FIG. 12 is a timing chart of image reading signals obtained from the circuit shown in FIG. 11. 11-... Laser, 14... Rotating polygon mirror, 16...
Pulse motor, 17-... condenser, 18... photodiode, 19 b = log amplifier, l 9 c
-Linear amplifier, 21-...Reading hardware circuit. 21b, 21c... line memory, 22-... image memory, 26-CPU, 31-... pixel original clock generation circuit, 33-RAM sequencer

Claims (6)

[Claims] (1) An irradiation unit that irradiates an image medium with a light beam in the main scanning direction and the sub-scanning direction, a reading unit that reads transmitted light or reflected light of the light beam from the image medium in the main scanning direction, and the reading unit photoelectric conversion means for converting the transmitted light or reflected light read by the means into an image signal;
storage means for storing a preset threshold; and comparison means for comparing the output signal of the photoelectric conversion means and the threshold;
determining means for determining the relative position of the image medium with respect to the reading means or the size of the image medium based on the output signal of the comparing means; and setting a reading range of the image medium based on the output signal of the determining means. An image reading device comprising a reading range setting means. (2) irradiation means for irradiating a light beam onto an image medium in the main scanning direction and sub-scanning direction; a reading means for reading transmitted light or reflected light of the light beam from the image medium in the main scanning direction; a reading control means for prohibiting the reading means from reading the transmitted light or the reflected light while the means illuminates a predetermined distance from the leading end of the image medium in the sub-scanning direction; a photoelectric conversion means for converting transmitted light or reflected light into an image signal; a storage means for storing a preset threshold value; a comparison means for comparing an output signal of the photoelectric conversion means with the threshold value; determining means for determining the relative position of the image medium with respect to the reading means or the size of the image medium based on an output signal; and a reading range setting for setting a reading range of the image medium based on the output signal of the determining means. An image reading device comprising: means. (3) The image according to claim 2, further comprising a transport means for moving the image medium to a position where the image medium can be irradiated from the tip again after the irradiation device irradiates the image medium a predetermined distance in the sub-scanning direction from the tip thereof. reading device. (4) an irradiation means for irradiating a light beam onto an image medium in the main scanning direction and a sub-scanning direction; a reading means for reading transmitted light or reflected light of the light beam from the image medium in the main scanning direction; photoelectric conversion means for converting the transmitted light or reflected light read by the means into an image signal, storage means for storing a preset threshold value, and comparison means for comparing the output signal of the photoelectric conversion means with the threshold value. a determining means for determining the relative position of the image medium with respect to the reading means or the size of the image medium based on the output signal of the comparing means; reading control means for reading transmitted light or reflected light in the main scanning direction; tilt determining means for determining the tilt of the image medium with respect to the sub-scanning direction based on an output signal of the reading control means; the determining means and the tilt. An image reading device comprising: reading range setting means for setting a reading range of the image medium based on an output signal of the determining means. (5) an irradiation means for irradiating a light beam onto an image medium in the main scanning direction and a sub-scanning direction; a reading means for reading transmitted light or reflected light of the light beam from the image medium in the main scanning direction; photoelectric conversion means for converting the transmitted light or reflected light read by the means into an image signal, storage means for storing a preset threshold value, and comparison means for comparing the output signal of the photoelectric conversion means with the threshold value. and determining means for determining the relative position of the image medium with respect to the reading means or the size of the image medium based on the output signal of the comparing means, and the reading range of the image medium based on the output signal of the determining means. reading control means for reading transmitted light or reflected light of the light beam in the main scanning direction at different positions in the sub-scanning direction of the image medium, based on an output signal of the reading control means; a tilt determining means for determining the tilt of the image medium with respect to the sub-scanning direction; and a settable determining means for determining whether the reading range of the image medium can be set based on output signals of the determining means and the tilt determining means. and warning means for issuing a warning when it is determined that the setting is not possible based on the output signal of the settable determining means. (6) irradiation means for irradiating a light beam onto an image medium in the main scanning direction and the sub-scanning direction; a reading means for reading transmitted light or reflected light of the light beam from the image medium in the main scanning direction; photoelectric conversion means for converting the transmitted light or reflected light read by the means into an image signal;
storage means for storing a preset threshold; and comparison means for comparing the output signal of the photoelectric conversion means and the threshold;
determining means for determining the relative position of the image medium with respect to the reading means or the size of the image medium based on the output signal of the comparing means; and setting a reading range of the image medium based on the output signal of the determining means. The image reading device has a reading range setting means for setting the image medium, and the image reading device has a linear amplifier and a log amplifier as the photoelectric conversion means. A use state determining means for determining whether the image medium is being used for reading; and a linear amplifier is used as the photoelectric conversion means when setting a reading range of the image medium based on an output signal of the use state determining means, and a linear amplifier is used as the photoelectric conversion means to read the image medium. 1. An image reading device comprising: switching means for switching to use a log amplifier as the photoelectric conversion means.