JPH0678992B2 - Image reader - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image reading device that reads an image using a plurality of filters that transmit visible light and light other than visible light.

[Prior Art] In a conventional film image information reading apparatus of this type (hereinafter, referred to as a film scanner), generally, from behind a film original such as a microfilm or a photographic film,
The film original is illuminated by the illumination optical system, the transmitted light is projected and imaged on the image forming surface of the photoelectric conversion element via the projection optical system, and the photoelectric conversion element photoelectrically converts the image information of the film original. It was converted into an electric signal.

However, since such a conventional device is configured, dust adhering to the illumination optical system and the projection optical system, scratches and dust on the film original appear as black dots on the read image data, and as a result, However, there was a problem that the image quality deteriorates.

2 (A) and 2 (B) schematically show the influence of the above-mentioned dust and scratches on the image data and the output image. In the case of a reversal film, FIG. 2 (A) and FIG. ) Is the case of a negative film. As shown in FIGS. (A) and (B), regardless of whether the film is a reversal film or a negative film, when a film original is converted into an image signal and read by a film scanner, the above dust and scratches are
It appears as a black dot on the image signal.

As a result, as shown in FIG. 3A, in the case of a reversal film, the above-mentioned image signal is directly subjected to image processing such as gamma correction and output to an output device such as a printer.
There is a problem that the above-mentioned influence of dust and scratches directly appears as black dots in the output image.

On the other hand, in the case of a negative film, as shown in this figure (B), the negative image is converted into a positive image by subtracting the image signal read by the film scanner from the image signal read at the full level. Therefore, there is a problem that the above-mentioned influence of dust and scratches appears in the output image as white bright spots.

Therefore, focusing on the transmittance characteristics of the film with respect to infrared light, only the dust and scratches that cause the above-mentioned image quality deterioration are detected by the infrared light that passes through the original, and the image data read by the detected dust information is used. Film scanners have already been proposed to make corrections.

[Problems to be Solved by the Invention] However, in such a proposed apparatus, a sensor for detecting dust and scratches and a sensor for reading image data are separately provided, so that both sensors are required because of the necessity of screen matching. It requires very high precision for alignment, but in reality, the exact alignment is impossible.

Therefore, the proposed device uses a complicated processing system such as electrically expanding the information of the dust detected by the dust detection sensor to make it apparently large and correcting the image data based on this extended data. There was a drawback that it cost.

An object of the present invention is to provide a good optical path length when reading a common target image using a first filter that transmits visible light of a specific wavelength and a second filter that transmits light other than visible light of a specific wavelength. The object is to provide an image reading device that can be controlled in a uniform manner.

[Means and Actions for Solving Problems] In order to achieve the above object, the image reading apparatus of the present invention is a photoelectric conversion unit (corresponding to the linear sensor 11 in the embodiment) for converting optical information into an electric signal. And a first filter (also corresponding to color separation filters 35c, 35d, 35e) that transmits visible light of a specific wavelength, and a second filter (also IR filter 35f) that transmits non-visible light of a specific wavelength. A case where visible light from the target image is formed on the photoelectric conversion unit via the first filter, and a light other than visible light from the target image on the photoelectric conversion unit via the second filter. The optical path length correcting means (also the drive mechanism 13) for making the optical path length different from that for forming an image.

Embodiments Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows the basic configuration of the embodiment of the present invention.

In the figure, a is a wavelength selecting means, which is arranged so as to be insertable in the optical path of the illumination optical system or the projection optical system. b
Is a displacement means, which displaces the photoelectric conversion element substantially from the image forming position of the projection optical system when the wavelength selection means a is inserted in the optical path.

Reference numeral c is a detection unit that detects the position of dust and scratches on the optical system and the film original based on the image information read from the photoelectric conversion element displaced by the displacement unit b.

FIGS. 3 (A) and 3 (B) show the respective spectral transmittances of a typical negative film and reversal film. This figure (A) shows the spectral transmittance characteristics of a negative film without exposure, and this figure (B) shows the spectral transmittance characteristics of a reversal film without exposure. Here, the horizontal axis represents wavelength and the vertical axis represents transmittance. In the infrared region, as shown in FIGS.
For example, at wavelengths above 800 nm, it is understood that both negative and reversal films have high transmission.
In addition, it has been experimentally confirmed that the transmittance in the infrared region is high and hardly changes depending on the size of the transmittance in the visible region (about 350 to 700 nm). Ie 80
By paying attention to the wavelength in the infrared region of 0 nm or more, it is possible to measure the illuminance unevenness on the light receiving surface regardless of the film image information. The embodiment of the present invention utilizes this principle to perform the shading correction described in detail below.

FIG. 4 shows a schematic structure of the film scanner of the embodiment of the present invention.

In the figure, 1 is an illumination lamp for illuminating a film original,
Reference numeral 2 is a condenser lens that collects illumination light, and 3 is a heatproof filter. The lamp 1, the condenser lens 2 and the heatproof filter 3 constitute an illumination system. Reference numeral 4 is a filter changing mechanism described later in FIG.
A shutter mechanism described later in the drawing. Reference numeral 6 denotes a sub-scanning system, which will be described later in FIG. 5, which scans the film original, and sequentially scans the film original in the vertical direction (sub-scanning direction) of the drawing substantially perpendicular to the optical axis. A projection lens 7 forms an image of the transmitted light of the film original on the sensor 11, and has a zoom function capable of changing the projection magnification.

Numeral 8 is a total reflection mirror rotatable about a pivot, which is in the optical path (observed solid line position in the figure) when the finder is observed, and a known drive mechanism, such as a rotary mechanism, is located at the position indicated by the alternate long and short dash line in the figure during film scanning. It is driven by a plunger or the like to evacuate. Reference numeral 9 denotes a focus plate of the finder, which is used by the user to observe the film original. 10 is a photometric sensor patterned on a transparent glass substrate.

The sensor 11 is a line sensor of a self-scanning type such as CCD, and is arranged at a right angle to the optical axis and in a direction perpendicular to the drawing (main scanning direction) which is 90 ° offset from the scanning direction of the sub-scanning system 6 (sub-scanning direction). There is. Reference numeral 12 denotes a light amount adjusting mechanism such as a diaphragm mechanism and an ND filter that controls (adjusts) the light receiving surface illuminance of the line sensor 11 based on the photometric output of the photometric sensor 10. In this example, the position of the projection lens 7 is set. It is arranged.
Reference numeral 13 denotes a drive mechanism for displacing the sensor 11 by a small amount in the optical axis direction.
It is possible to change the order. In addition, l-l shows an optical axis.

FIG. 5 shows a detailed configuration example of the sub-scanning system 6 of FIG. In this figure, 21 is a scanning unit (carriage) supported so as to be movable in the direction of the arrow (sub-scanning direction), and 22 is a scanning unit 21.
A guide rail that supports the arrow in the moving direction of the arrow (sub-scanning direction), 23 is a feed screw that drives the scanning unit 21 by being rotated by a drive motor (26) described later, and 24 and 25 are rails 22 and 23. Is a support portion that supports the base at both ends with respect to a base (not shown).

Reference numeral 26 denotes a drive motor that rotates the feed screw to drive the scanning unit 21 in the direction of the arrow in the figure.
It is a step motor that is driven stepwise according to the reading pitch of. 27 is fixed on the scanning unit 21
It is a film original holder that moves together with.
27a and 27b are a pair of glasses of the holder 27, and sandwich the film original between them to enhance the flatness of the film original. In particular, dust on the surface of the glass 27a, 27b and on the surface of the film original sandwiched between the glass 27a, 27b is captured as a part of the image signal because it is in an image-forming relationship with or in the vicinity of the light-receiving surface of the sensor 11 by the projection lens. The problem is big.

Reference numerals 28, 29, and 30 denote switches for detecting the scanning start position, the center position, and the scanning end position of the scanning unit 21, respectively, and corresponding protrusions 21a, 21b, which are integrally provided on three sides of the scanning unit 21. It is turned on and off (opened and closed) by 21c. That is, when the first switch 30 is ON, the scanning unit 21 is in the start position, when the second switch is ON, the scanning unit 21 is in the center position, and when the third switch 28 is ON, scanning is performed. Department
21 is at the scan end position. The detection of the central position by the switch 29 is used when observing the entire screen by the finder 9.

FIG. 6 shows the detailed structure of the shutter mechanism 5 of FIG.
In this figure, 31 and 32 are light-shielding plates that are rotatably supported around rotation shafts 31a and 32a, and 33 and 34 are rotary plans that rotate and drive the light-shielding plates 31 and 32 through the rotation shafts 31a and 32a, respectively. It's a jar. A range AA indicated by a chain double-dashed line in the figure is a screen range of a film original.

When observing the viewfinder, the light blocking plates 31 and 32 are driven outwardly by the rotary plungers 33 and 34,
At the opening position shown by the broken line in this figure, when reading the film original data, the light shielding plates 31 and 32 are driven inward by the rotary plungers 33, 34 and are at the light shielding position shown by the solid line. When the light shielding plates 31 and 32 are in the light shielding position, they are closed except for the slit portion 31b having the width a so that only a part of the film original facing the light receiving portion of the sensor 11 is illuminated. The original part is the light shield plate 31, 32
The light is shielded from light by this, and thereby deterioration of the image quality of the read image data due to ghost flare or the like is minimized. l-l is the same optical axis as in FIG.

FIG. 7 shows a detailed structure of the filter exchange mechanism 4 of FIG. In the figure, 35 is a filter holder for holding a color filter or the like inserted in the optical path l-l, which is rotatably supported by a support shaft 35g. The filter holder 35 has a transparent part 35b for observing the viewfinder.
And R (red), G (green), and B (blue) color separation filters 35c, 35d, and 35e, respectively, and further cut visible light for detecting dust and scratches on film originals and optical systems. An IR filter (infrared filter) 35f having characteristics is provided.

Reference numeral 35a is a gear (gear) formed on the circumference of the semicircular filter holder 35. A small-diameter gear 36 is driven by the motor 37, and the large-diameter gear 35 that meshes with the gear 36.
Rotate the filter holder 35 via a and
5b and one of the R, G, B and IR filter sections 35c, 35d, 35e and 35f are selectively inserted in the optical path l-1.

In addition, on the side surface of the filter holder 35, the optical path l-l
Pattern electrodes 38a, 39a, 40a, 41a, 42a, 43a for detecting the position of a filter inserted therein are provided. That is, the electrode 43a is associated with the position of the transparent portion 35b, the electrode 39a is associated with the position of the R filter 35c, and the G filter 35d.
The electrode 40a is provided corresponding to the position of, the electrode 41a is provided corresponding to the position of the B filter 35e, and the electrode 42a is provided corresponding to the position of the IR filter 35f. To be done.

Further, brushes 38b, 39b, 40b, 41b, 42b, 43b are arranged corresponding to the electrodes 38a, 39a, 40a, 41a, 42a, 43a, respectively. Now, assuming that the brush 38b, which is always in contact with the electrode 38a, is at the ground level (ground potential), the brush 43b is at the low level when the transparent portion 35b is inserted in the optical path as shown in FIG. , R filter 35c is inserted, the brush 39b becomes low level and G
When the filter 35d is inserted, the brush 40b becomes low level, when the B filter 35e is inserted, the brush 41b becomes low level, and when the IR filter 35f is inserted, the brush 42b becomes low level. It becomes a level.
l-l is the same optical axis as in FIG.

FIG. 8 shows the total spectral sensitivity including the spectral sensitivity of the linear sensor 11 for the spectra of the R, G, B and IR filters 35c, 35d and 35f of the filter holder 35. Here, the horizontal axis represents wavelength and the vertical axis represents sensitivity. As shown in the figure, during use of the IR filter 35f, the linear sensor 11 performs photoelectric conversion particularly at a wavelength in the infrared region of 800 nm or more.

In FIG. 9, B indicates an output example of the visible light filter (for example, B filter 35e), and IR indicates an output at the same film position of the IR filter 35f. That is, B and IR in FIG. 9 respectively indicate the output of one line of the linear sensor 11, and in FIG. 9B, the light and shade of the image on the transparent color film original is clearly shown as the output of the sensor 11 being large and small. Has been reproduced. However, in the waveform B, the lack of image information due to dust indicated by the arrow in the figure is difficult to distinguish from the image signal.

On the other hand, the sensor output when using the IR filter 35f indicated by IR is a constant output regardless of the size of the image output when using the B filter 35e shown in B, and the signal level is low at only the dust and scratches. It Therefore, the dust position can be detected by comparing and judging the magnitude of the sensor output signal (IR image data) of the IR filter with an appropriate slice level.

When reading IR image data with this IR filter,
The above-mentioned drive mechanism 13 shown in FIG. 4 slightly displaces the sensor 11 in the optical axis direction (direction of arrow X in FIG. 4) to displace the sensor 11 from the image forming position of the projection lens 7.
As a result, the image of the dust of the optical system and the scratch on the film projected on the sensor 11 is out of focus and appears as an image larger than the actual size at the output of the sensor 11.

FIG. 10 shows the circuit configuration of the film scanner of the embodiment of the present invention shown in FIG. In this figure, 101 is a control unit for controlling each motor and sensor according to the control procedure as shown in FIG. 11 and FIG. Reference numeral 102 denotes a mirror drive unit that controls the drive of the rotary plunger 8a that opens and closes the mirror 8.
Is a shutter controller for driving and controlling the rotary plungers 33, 34 of the shutter mechanism 5, 104 is a filter controller for driving and controlling the motor 37 of the filter exchanging mechanism 4, and 105 is driving and controlling the motor 26 of the sub-scanning system 6. It is a scanning control unit. A sensor driver 106 drives and controls the linear sensor 11. Reference numeral 108 denotes an A / D (analog / digital) converter that sequentially performs analog / digital conversion of the output of the self-scanning type linear sensor 11 such as a CCD.

Reference numeral 109 denotes a drive unit that controls the drive of the drive mechanism 13 that slightly displaces the sensor 11.

Next, the operation of the embodiment of the present invention will be described in detail with reference to the flowcharts of FIG. 11 and FIG.

Now, when observing the film original with the naked eye through the finder, the mirror 8 is in the optical path of l-1, the center of the film original holder 27 of the sub-scanning system 6 is at the center position of the optical path, and the shutter mechanism 5 is used. The light-shielding plates 31 and 32 are open, and the transparent portion 35b of the filter exchanging mechanism 4 is inserted into the optical path. In this state, the user (operator) confirms the image state of the film original by the image on the focus plate 9 of the finder.

Next, when the start button 110 is pressed and a scanning start signal (start signal) 211 is generated (step S1), the control unit 101
First outputs a mirror drive signal 201 to the mirror drive unit 102, retracts the mirror 8 from the optical path by the rotary plunger 8a (step S2), and then outputs a shutter drive signal 202 to the shutter control unit 103, and a pair of The rotary plungers 33 and 34 drive the shading plates 31 and 32 of the shutter mechanism 5 to the shading positions to shade harmful light such as ghost flare (step S3).

At the same time, the control unit 101 outputs a filter control signal 203 to the filter control unit 104 to selectively insert a color separation filter in the optical path. If the image data is read in order of R, G, B, and IR, the filter control unit 104 first responds to the filter control signal 203 until the R filter 35c is inserted in the optical path, that is, the brush 39b The motor 37 is driven until it becomes low level (step S4).

When the brush 39b becomes low level, the filter control unit 104
Is a filter replacement end signal that means the end of filter replacement
204 is returned to the control unit 101. In the subroutine of FIG. 12 of step S5, when the control unit 101 receives the filter exchange end signal 204 (step S101), it sends the scan start signal 205 to the scan control unit 105. When the scanning control unit 105 receives the scanning start signal 205, first, the sub-scanning system (carriage) 6
To the scanning start position, that is, until the switch 30 is turned on, the step motor 26 is driven (step S10).
2). When the switch 30 is turned on, the scanning control unit 105 determines that scanning has ended, and returns a scanning end signal 206 to the control unit 101. At this point, the preparatory operation for scanning the filter document ends.

The control unit 101 receives the scan end signal 206 (step S10
3), the reading start signal 207 is output to the sensor driver 106, and the driver 106 drives the sensor 11 according to this starting signal 207 (step S104). The output signal (image signal) 209 of the sensor 11 is sequentially converted into a digital signal by the A / D converter 108 and sent to an image processing circuit (not shown), and the sensor 11 outputs the output signal 209 by a predetermined number of pixels,
Finish reading one line.

Upon completion of reading this one line (step S10
5), the control unit 101 sends the scan control signal 2 to the scan control unit 105.
05 is output, and the scan control unit 105 drives the pulse motor 26 by a predetermined pitch in response to the scan control signal 205 to end the sub-scanning for one line of the sub-scanning system 6 (step S106).

After that, returning to step S104, the sensor 107 is driven in the same manner as described above, and the image signal (R signal) of one line is read. When the read processing operation of steps S104 to S106 described above is repeated for a predetermined cycle (for one screen) (step S10
7) The reading of R image data is completed.

Then, return to the main routine and proceed to step S6,
The control unit 101 uses the filter control signal 2 to replace the filter.
The filter control unit 104 is operated by 03 to drive the motor 37 until the G filter 35d is positioned in the optical path l-1, that is, the brush 40b becomes low level (step S6).

After the G filter 35d is selected in this way, the process proceeds to step S7, and the G screen data is read by repeating the same processing cycle (steps S101 to S107 in FIG. 12) as the above R screen reading.

The B screen data is also read from the linear sensor 11 in the same manner as described above (steps S8 and S9).

After reading the B screen data, the control unit 101 inserts the IR filter 35f into the optical path by the filter control signal 203 (step S10), and at the same time, by the control signal 212, the driving unit 109.
The drive mechanism 13 is driven via the
Is displaced in the optical axis direction to complete the preparation for reading out the IR screen (step S11). Next, proceeding to step S12, the IR screen data is read by the processing of steps S101 to S107 of FIG. 12 in the same manner as described above.

After the completion of this one-screen reading, the process returns to the main routine of FIG.
The sub-scanning system 6 is moved to the center position of the sub-scanning by operating the motor 105 by the rotation of the motor 26 (step S13), and after the driving is completed, that is, after the switch 29 is turned on, the filter control signal
The motor 37 is operated via the filter control unit 104 by 3 to insert the transparent portion 35b into the optical path (step S14), and the mirror drive unit 201 is operated by the mirror drive signal 201 to return the mirror 8 to the optical path ( Simultaneously with step S15), the shutter drive signal 202 operates the rotary plungers 33, 34 via the shutter controller 103 to open the light shielding plates 31, 32 (step S16). Through the above processing, a series of screen reading processing operations for film originals are completed.

Next, detection of dust adhering to the optical system and scratches on the film original and image signal correction processing will be described.

FIG. 13 shows a schematic configuration of the above-mentioned dust and scratch detection and image signal correction processing unit in the embodiment of the present invention. In this figure, 301, 302, 303, 304 respectively represent the respective read image data 210 of R, G, B, IR according to the control procedure of FIG. 11 described above.
An image memory that is received from the / D converter 108 and stored. A detection unit 305 detects the position (address) of dust or scratches on the screen based on the image data in the IR image memory 304. A correction unit 306 performs image signal correction processing, which will be described later, on the image data of the R, G, and B image memories 301, 302, 303 based on the data (address data) of the dust and scratch positions detected by the detection unit 305. It is a processing unit.

Next, processing operations such as detection of dust and scratches will be described with reference to the flowchart of FIG. First, the image data Sij (i is the line direction, j is the read line address) is sequentially read from the IR image memory 304 (step S301).
Based on the principle described in FIG. 9 above, step S301
It is determined whether or not the image data Sij read out in step 1 is smaller than a predetermined slice level defined as a criterion for determining dust or scratches (step S302), and the address (i, j) of image data below the slice level is sequentially detected. The data is stored in the internal memory of the unit 305 (steps S303 to S305).

After that, the correction processing unit 306 corrects the image data of the R, G, and B image memories 301, 302, 303 based on the address information indicating the position of the dust or scratch stored in the detection unit 305, for example Processing is sequentially performed (steps S306 to S3
08).

Here, it is assumed that Sij is the image data of the R, G, B image memories 301, 302, 303, and the image data corresponding to the address detected by the detection unit 305.

Sij = Si _-1 , j ... Replaces the garbage image data with the previous image data.

Sij = (Si _-1 , j + Si, j _-1 + Si, j ₊₁ + Si ₊₁ , j) / 4 ... Replaces the garbage image data with the average data of the upper, lower, left and right image data.

However, n = 1 to m ... When the dust image data is continuous with a plurality of pixels, a series of dust image data is interpolated by the image data immediately before and immediately after.

These methods shown by are examples of the correction processing of dust image data. The R, G, and B image data subjected to these processes are output to the outside as R, G, and B output signals (step S310).

In the present embodiment, the sensor is displaced in the optical axis direction in order to blur the focus, but the present invention is not limited to this, and the same effect can be obtained by positively utilizing the infrared aberration of the projection lens. To be

As described above, according to the embodiment of the present invention, the visible light image data and the dust and scratch detection infrared image data are read and processed using the same image sensor. It is possible to eliminate the positional deviation between the image data and the infrared light image data, and at the time of reading the infrared image data, the sensor position is displaced in the optical axis direction to blur the focus and provide a low-pass filter effect. Therefore, it is possible to enlarge the projected image of dust and scratches,
It is possible to obtain an effect that it is possible to suppress a detection error due to an edge portion of dust or a scratch.

[Effects of the Invention] As described above, according to the present invention, it is possible to favorably control the optical path length when reading a common target image by using a plurality of filters that respectively transmit visible light and light other than visible light.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing the basic structure of an embodiment of the present invention, FIGS. 2 (A) and 2 (B) are schematic diagrams showing the influence of dust and scratches on a conventional device, and FIG. FIGS. 4A and 4B are characteristic diagrams showing the spectral transmission characteristics of the film in the unexposed state, FIG. 4 is a schematic diagram showing a schematic configuration of the film scanner of the embodiment of the present invention, and FIG. FIG. 6 is a perspective view showing a configuration example of the sub-scanning system 6, FIG. 6 is a perspective view showing a configuration example of the shutter mechanism 5 of FIG. 4, and FIG. 7 is a perspective view showing a configuration example of the filter exchange mechanism 4 of FIG. , Fig. 8 is a characteristic diagram showing the spectral sensitivity of each R, G, B, IR filter, and Fig. 9 is an output waveform diagram showing an output example of the sensor 11 at the same film position of the visible light filter and the IR filter. FIG. 10 is a block diagram showing the circuit configuration of the reading unit of the color film scanner of FIG. 4, FIG. 11 and FIG. 2 is a flow chart showing the control procedure of the control unit 101 of FIG. 10, FIG. 13 is a block diagram showing the circuit configuration of the detection / correction unit of the embodiment of the present invention, and FIG. 14 is the detection unit and correction processing of FIG. It is a flow chart which shows operation of a part. 1 ... Lamp, 2 ... Condenser lens, 3 ... Heat-proof cut filter, 4 ... Filter replacement mechanism, 5 ... Shutter mechanism, 6 ... Sub-scanning system, 7 ... Projection lens, 8 ... Total reflection mirror , 9: focus plate, 10: photometric sensor, 11: sensor, 12: light intensity adjustment mechanism, 13: drive mechanism, 26, 37 ... motor, 27 ... film document holder, 31, 32 ... … Shading plate, 35… Filter holder, 101… Control unit, 102… Mirror drive unit, 103… Shutter control unit, 104… Filter control unit, 105… Scan control unit, 106… Sensor driver, 108 …… A / D converter. 109 ... Drive unit, 301-304 ... Image memory, 305 ... Detection unit, 306 ... Correction processing unit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Makoto Katsuma 770 Shimonoge, Takatsu-ku, Kawasaki-shi, Kanagawa Canon Inc. Tamagawa Plant (72) Inventor Shigeki Yamada 770 Shimonoge, Takatsu-ku, Kawasaki-shi, Kanagawa Canon Inc. In Tamagawa Plant (72) Inventor Tsuyoshi Kobayashi 770 Shimonoge, Takatsu-ku, Kawasaki City, Kanagawa Canon Inc., Tamagawa Plant (56) References JP-A-60-194660 (JP, A) JP-A-49-1280 (JP) , A) JP-A-57-24808 (JP, A) JP-B-53-5830 (JP, B2)

Claims (1)

[Claims] 1. A photoelectric conversion means for converting optical information into an electric signal, a first filter which transmits visible light of a specific wavelength, and a second filter which transmits light other than visible light of a specific wavelength. When visible light from the target image is formed on the photoelectric conversion unit via the first filter, and when light other than visible light from the target image is connected to the photoelectric conversion unit via the second filter. An image reading apparatus, comprising: an optical path length correcting unit for making an optical path length different from that when an image is formed.