Image reading apparatus with a linear illuminator for reading an image in separated colours using a linear sensor

Abstract: A linear illuminator for image reading by the use of a linear sensor comprises a linear illumination light source, a cylindrical rotational member provided on the circumference of the linear illumination light source, and a plurality of color separation filters installated on the rotational member, and by controlling the rotation of the rotational member, plural kinds of color separation linear illumination light are output in time series; hence making it possible to obtain an extremely miniaturized illuminator for image reading.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an image reading apparatus and an illuminator therefor having a linear illuminating area for reading separated color image using a linear sensor. More particularly, the present invention is applicable to an illuminator for color separated transmitting illumination light used for an image reading apparatus (referred to as film scanner) in which, for example, an original image of a color positive film is converted into separated color analog signals (such as RGB three prime color image signals) by operating a CCD line sensor to scan, and these signals are processed by an A/D converter for storage as digital data. Related Background Art Now, in conjunction with Fig. 1 and Fig. 2, a conventional illuminator for reading color separated image using a linear sensor will be described with a film scanner taken as an example. (A similar arrangement is shown in Japanese patent application laid open No. 64-4166.) Fig. 1 is a cross-sectional view showing the entire structure of a conventional film scanner and Fig. 2 is a perspective view showing the principal part of the structure of the conventional film scanner. In Fig. 1 and Fig. 2, reference numeral 1a designates a halogen lamp with a mirror, and the cross-section of its irradiating beam is substantially circle with a luminous distribution of the so-called Gaussian distribution wherein the intensity is greater in the vicinity of the optical axis of the beam and the intensity becomes less intensified towards the circumference thereof. A reference numeral 21 designates an infrared cutting filter, which is provided between a light source la and the surface of an original 24 to protect a CCD line sensor 12 not to be affected by any infrared light. A reference numeral 22 designates an uneven illumination correcting filter provided between the light source 1a and the surface of the original 24 in order to make the Gaussian distributed circular irradiation beam an even circular illumination. The uneven illumination correcting filter 22 is such that its density changes gradually by the distance from the center of the optical axis; the higher the density in the center (the transmissivity is low), the lower is the density in the circumference thereof (the transmissivity is high). Hence the illuminous intensity in the circular illumination area is made substantially even. A reference numeral 23 designates a condenser lens, the filmed original 24 being supported by a supporting frame 9; 2g, is a filter supporting disc which is a plate substantially circle with color separation filters 3, 4, and 5 installed thereon and rotatively structured with an axis 2h as its center. The rotation of the aforesaid filter supporting disc 2g is controlled by a stepping motor 7. In the case where the original of a color negative film is converted into monochrome, a monochrome conversion correcting filter 6 is provided in order to obtain desirable monochrome image signals by correcting the spectral characteristics of the light source, filmed original, and CCD line sensor. The film supporting frame 9 is movable in the sub-scanning direction by a known transporting mechanism (not shown). A reference numeral 10 designates a mirror and 11, an image formation lens. The illuminating light from the halogen lamp 1a illuminates the filmed original 24 supported by the film supporting frame 9 through the infrared cutting filter 21, color separation filter 3, uneven illumination correcting filter 22, and the condenser lens 23. The optical path is bent by the mirror 10, and the image of the filmed original is formed on the CCD line sensor 12 by the image formation lens 11, and is converted by a photoelectric converter so as to output linear image signals. When the image signals of the filmed original 24 are read using the color separation filter 3 by the relative traveling of the CCD line sensor 12 and the filmed original 24, the filter supporting disc 2g is controlled by a motor 7 to be rotated to enable the next reading using the color separation filter 4. Then, subsequent thereto, the reading is performed using the color separation filter 5 to complete the readings of the filmed color original. If the filmed original in color is converted into monochrome image signals, the filter 6 should be selected to irradiate the light which passes through the aforesaid filter 6 on the filmed original for reading. It is possible to employ a photointerrupter for the detection of the reference position of the filter supporting frame, and if a stepping motor is used, the filter can be selected arbitrarily because the step numbers for each of the filters to enter its optical path from the reference position detected by the aforesaid photointerrupter are predetermined. With a conventional structure such as this, the apparatus becomes large in its size. Particularly, the distance between the light source and the filmed original is long, making it difficult to miniaturize the apparatus. Also, the illumination for the linear reading area should illuminate the other area which is not linear, i.e., the circular area with the aforesaid linearity as its center. Therefore, not only the lighting efficiency is low, but it is also difficult to correct the unevenness of the illumination, and there remains the uneven illumination in the area to be scanned by the line sensor. JP-A-2 103 523 discloses a contact exposure apparatus suitable for forming a proof from a film. The contact exposure apparatus comprises an elongate light source and a set of linear filters mounted on a structure which rotates around the light source such that a linear band of light having a desired colour can be produced by a suitable orientation of the structure about the light source. SUMMARY OF THE INVENTION It would be desirable to eliminate the above-mentioned drawbacks and provide a small linear illumination light source. According to the present invention, there is provided an image reading apparatus having an illuminator comprising a light source and a filter structure as defined in claim 1. In a preferred embodiment, the light source is of such a structure that on the periphery of the linear illumination light source, which is publicly known itself, for obtaining a linear illuminating area, there are provided a diffused band for a quartz rod, a cylindrical rotational member, and a plurality of color separation filters for the aforesaid rotational member to output plural kinds of linear illumination light for color separation in time series by controlling the rotation of the aforesaid rotational member. On the external circumference of the linear illumination light source, color separation filters are provided in a cylindrical supporting tube, and the structure is arranged to rotate the aforesaid cylindrical supporting tube so that the color separation filter can be selected; thus making the miniaturization of the apparatus possible. Also, there is provided an illuminating area which is substantially the same as the reading area for the line sensor to read. Therefore, there is no possibility of illuminating any unnecessary areas; thus making the illuminating efficiency high. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross-sectional view showing the entire structure of a conventional film scanner; Fig. 2 is a perspective view showing the structure of the principal part of conventional film scanner; Fig. 3 is an external perspective view showing the illuminator for reading color separated images using a linear sensor according to the present invention; Fig. 4 is a cross-sectional view showing a principal part of the illuminator for reading color separated images using the linear sensor according to the present invention; Fig. 5 is a cross-sectional view taken along the line A-A in Fig. 4; Fig. 6 and Fig. 7 are external perspective views showing other embodiments for detecting the reference positions of the filter installation cylinder 2. DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 3 is an external perspective view showing the illuminator for reading color separated image using a linear sensor according to the present invention. Fig. 4 is a cross-sectional view showing a principal part of the illuminator for reading color separated image using the linear sensor according to the present invention, and Fig. 5 is a cross-sectional view taken along the line A-A in Fig. 4. In Fig. 3 through Fig. 5, there is shown for the present embodiment an example using the linear illumination light source known by Japanese Utility Model Laid-Open Application No. 63-140519 and Japanese Patent Laid-Open Application No. 63-108332, which obtains the linear illuminating area by providing a diffused band for a quartz rod. In place thereof, however, it may be possible to use a linear illumination light source which obtains the linear illuminating area by covering a luminescent lamp with a cover having slits. In this respect, the members identical to those shown in Fig. 1 and Fig. 2 are described using the same reference marks. In Fig. 3 through Fig. 5, the linear illumination light source is provided with a halogen lamp 1a, a reflection mirror and infrared cutting filter, and at the same time, this light source has a luminous intensity distribution of the so-called Gaussian distribution as described earlier in conjunction with Fig. 1 and Fig. 2. Now, a reference numeral 1b designates a quartz rod; 1c, a diffusion band; and 1d, a cylindrical cover with a slit opening 1e provided on the lower face thereof. Light from the halogen lamp 1a is induced into the inside of the quartz rod 1b from the one end and reflected. Then, the diffused rays of light diffused by the diffused band 1c are output from the slit opening 1e; thus the linear illumination light is obtained. The aforesaid linearly illuminating light illuminates the filmed original 24 supported by the film supporting frame 9 after having passed through the color separation filters 3, 4, and 5, or the monochrome conversion correcting filter 6. The light having passed through the filmed original 24 is caused by the mirror 10 to bend its optical path to form an image on the CCD line sensor 12 by the image-formation lens 11. As shown in Fig. 4, on the outer periphery of the cylindrical cover 1d, a substantially coaxial cylinder 2 with a circular shielding bottom is provided to mount the color separation filters, and others. On the center of the circular bottom 2a, a projection 2c is provided in the axial direction, and a hole 2d is cut in the center of the aforesaid projection 2c. The rotational shaft 7a of a stepping motor 7 is inserted into the aforesaid hole 2d and is fixed by a screw 2e. From the opening end 2f of the filter installation cylinder 2, the cover 1d of the aforesaid linear illumination light source 1 is fittedly inserted coaxially. On the aforesaid bottom portion 2a, a small flat piece 2b is projectedly provided to interrupt the optical path of a light emitting and receiving portion 8 so that the so-called photointerrupter is constituted. The reading of the color filmed original with the above-mentioned structure is performed by, firstly, driving the stepping motor 7 for the predetermined number of steps from the reference position of the filter installation cylinder 2 detected by the photointerrupter, so that the filter 3 is brought to a stop in the linear illumination area of the linear illumination light source 1, i.e., the location facing the slit opening 1e. In this state, the film supporting frame 9 supporting the filmed or original 24 is moved in the sub-scanning direction to allow the filmed original 24 to be read. Subsequently, the stepping motor 7 is driven for the predetermined number of steps to bring the filter 4 to a stop with respect to the linear illuminating area of the linear illumination light source 1 to allow the filmed original 24 to be read by the CCD line sensor 12 while sub-scanning the film supporting frame 9. Further, the stepping motor 7 is driven for a predetermined number of steps to bring the filter 5 to a stop with respect to the linear illuminating area of the linear illumination light source 1 to allow the filmed original 24 to be read by the CCD line sensor 12 while sub-scanning the film supporting frame 9; thus completing the reading of the filmed original 24 by the three prime colors. In the case where the color filmed original 24 is read after monochrome conversion, the stepping motor 7 is driven for the predetermined number of steps from the reference position detected by the photointerrupter so that the filter 6 is allowed to face the slit opening le to be read by the CCD line sensor 12 while the film supporting frame 9 is being subscanned. Fig. 6 and Fig. 7 are views showing the other embodiments for detecting the reference positions of the filter installation cylinder 2. In Fig. 6 and Fig. 7, slit openings 31 and 32 are provided in the locations on the filter installation cylinder 2 where the filters 3, 4, 5, and 6 are not arranged, and light from the linear illumination light source is transmitted through the slit openings 31, and 32. In Fig. 6, the slit opening 31 is arranged between the filter 3 and filter 4, i.e, within the image reading area of the CCD line sensor. Therefore, although there is an advantage that the image reading CCD line sensor can be used in combination as it is, if the density of the portion of the filmed original 24 facing the slit opening 31 is thick, the transmitting light is blocked; thus making it impossible for the CCD line sensor 12 to detect such portion. In Fig. 7, the slit opening 32 is arranged outside the image reading area of the CCD line sensor. Therefore, even if the density of the filmed original 24 is extremely thick, its detection is possible. However, it is necessary to provide a slightly longer CCD line sensor dedicated for the detection of the slit opening 32. In this respect, it is possible to perform the detection of the reference positions by means other than the photointerrupter. For example, it may be possible to structure the system so that the absolute position of the stepping motor can be detected by a rotary encoder. Also, since the filter installation cylinder 2 has light shielding property, it is possible to measure the dark current of the CCD line sensor if the cylinder can be controlled to stop at the position where no filter is installed. Also, it is possible to obtain an extremely miniaturized system as an illuminator for image reading by arranging a cylindrical rotational member on the outer periphery of a linear illumination light source and a plurality of color separation filters on the aforesaid rotational member to output plural kinds of color separation linear illumination light by controlling the rotation of the aforesaid rotational member.

Claims: An image reading apparatus having an illuminator comprising a light source (1b,1c), a filter structure (2) mounted for rotation and having a plurality of filter elements (3,4,5,6) arranged at respective angular positions around the structure (2), such that light having a desired colour can be produced by a suitable orientation of the filter structure (2), and a linear sensor (12) for reading a portion of an image illuminated by said light so that relative traveling of the image and the linear sensor allows the complete reading of the image, characterized in that said light source (1b,1c), is elongate and located inside the filter structure, said filter elements (3,4,5,6) are elongate and arranged radially around the light source, and the filter structure (2) has a light shielding portion between a pair of adjacent filter elements (3,4,5,6) so as to block any light from reaching the linear sensor at an intermediate position of the filter structure (2). Apparatus as claimed in claim 1, further comprising an elongate apertured partition disposed between the light source (1b,1c) and the filter structure (2) so that the light from the light source (1b,1c) may pass through the apertured partition to permit the light to pass through only one filter element (3,4,5,6) at any time. Apparatus as claimed in claim 1 or claim 2, wherein said elongate light source comprises an elongate diffuser (1b,1c) which is illuminated at one end thereof. Apparatus as claimed in claim 3, wherein the elongate diffuser (1b,1c) comprises a quartz rod (1b) and an elongate diffusion member (1c) disposed in proximity thereto. Apparatus according to any preceding claim, wherein said plurality of filter elements (3,4,5,6) are composed of colour separation filters (3-5) and a monochrome conversion correcting filter (6). Apparatus according to any preceding claim, wherein said filter structure (2) further comprises means for measuring dark current of said linear sensor, when said filter structure is in said intermediate position. Apparat according to any one of claims 1 to 3, wherein said filter structure (2) comprises an opening (31, 32) for permitting light from said light source to be transmitted for use in measuring a reference position of said filter structure (2). Apparatus as claimed in claim 7, wherein said opening (31) is disposed between an adjacent pair (3,4) of said filter elements (3,4,5,6). Apparatus as claimed in claim 7, wherein said opening (32) is disposed at a position along said filter structure (2) axially offset from said filter elements (3,4,5,6).

Inventors: MAEDA EISAKU, YOSHIZAWA SATORU, MAEDA, EISAKU, YOSHIZAWA, SATORU
Applicants: NIPPON KOGAKU KK, NIKON CORPORATION
Application year: 1991
Main classification: G03B27
IPC codes: H04N1, G03B27