Patent Publication Number: US-7724298-B2

Title: Image processing system and method for pick up and display of an object including division of an optical image of the object into a spectrum

Description:
TECHNICAL FIELD 
   The present invention relates to an image processing system and an image processing method, an image pickup device and an image pickup method, and an image display device and an image display method. More particularly, the present invention relates to an image processing system and an image processing method, an image pickup device and an image pickup method, and an image display device and an image display method, which can faithfully pick up and display the colors of an object. 
   BACKGROUND ART 
   In recent years, image apparatuses handling various color images, as typified by TV receivers and video cameras, are in widespread use in the world. Most of these image apparatuses pick up an object and display an image of the picked-up object, on the basis of three primary colors (such as, red, green, and blue). 
   A system which displays an optical image of an object by dividing a spectrum of the optical image into four or more wavelength bands and recording the optical image, in order to make it possible to faithfully reproduce the colors of the object by using an apparatus handling an image on the basis of three primary colors is proposed (for example, in Japanese Unexamined Patent Application Publication No. 2003-134351 (Patent Document 1)). 
   DISCLOSURE OF INVENTION 
   Problems to be Solved by the Invention 
   However, a related image apparatus handling an image on the basis of three primary colors cannot present all of the colors in the visible light region of a human being. In other words, as shown in  FIG. 1  showing the chromaticity in an XYZ color coordinate system, all of the colors which can be seen by a human being are included within a substantially horseshoe-shaped area  1 . Of these colors, the location of the colors produced by synthesizing three colors, red, green, and blue is limited to within a triangular area  2  defined by vertices R, G, and B. The vertex R represents a red coordinate in the diagram showing the chromaticity in the XYZ color coordinate system, the vertex G represents a green coordinate in the diagram showing the chromaticity in the XYZ color coordinate system, and the vertex G represents a blue coordinate in the diagram showing the chromaticity in the XYZ color coordinate system. Therefore, since the image apparatus handling an image on the basis of three primary colors cannot present the colors included in a portion which lies within the area  1  but outside the area  2 , the image apparatus cannot faithfully pick up and display the colors of an object. 
   In the invention described in Patent Document 1, it is necessary to provide a plurality of filters when shooting, to perform switching from one filter to another in order to separate and extract wavelength components of an optical image of an object, and to estimate a spectrum of the optical image of the object on the basis of various data, algorithms, and functions, from the extracted wavelength components. In addition, since the estimated spectrum of the optical image of the object is converted into display data on the basis of the various data, algorithms, and functions, not only does the processing become complicated, but also the colors which are displayable are limited by the algorithms and functions, as a result of which it is difficult to satisfactorily faithfully reproduce the colors. 
   The present invention is achieved in view of such a situation and makes it possible to faithfully pick up and display the colors of an object. 
   An image processing system according to the present invention comprises first dividing means for dividing an optical image of an object into a spectrum, detecting means for detecting the spectrum obtained by the first dividing means and outputting image data based on the detected spectrum, second dividing means for dividing white light into a spectrum, extracting means for extracting, from the spectrum of the white light divided into the spectrum by the second dividing means, spectrum portions based on the image data detected by the detecting means, synthesizing means for synthesizing the spectrum portions extracted by the extracting means, and projecting means for projecting light formed by synthesizing the spectrum portions by the synthesizing means. 
   An image processing method according to the present invention comprises the steps of performing a first dividing operation for dividing an optical image of an object into a spectrum, detecting the spectrum obtained by the first dividing operation and outputting image data based on the detected spectrum, performing a second dividing operation for dividing white light into a spectrum, extracting, from the spectrum of the white light divided into the spectrum by the second dividing operation, spectrum portions based on the image data output by the detecting operation, synthesizing the spectrum portions extracted by the extracting operation, and projecting light formed by synthesizing the spectrum portions by the synthesizing operation. 
   An image pickup device according to the present invention comprises dividing means for dividing an optical image of an object into a spectrum and detecting means for detecting the spectrum obtained by the dividing means and outputting a pixel of image data based on the detected spectrum. 
   The image pickup device may further comprise separating means for separating one line of light forming the optical image of the object and supplying the separated one line of light to the dividing means and focusing means for focusing the optical image of the object onto the detecting means, wherein the detecting means includes a plurality of photoelectric sensors disposed in a plane for detecting the strength of the light, each photoelectric sensor detecting a spectral component of each pixel of the one line of light. 
   Each photoelectric sensor may include an electron shock CCD. 
   The separating means may include a slit and adjusting means, the slit separating the one line of the optical image of the object, the adjusting means adjusting a position where the optical image of the object is incident upon the slit. 
   The image pickup device may further comprise focus means disposed just behind the slit for focusing thereon the optical image of the object, wherein the focusing means temporarily focuses the optical image of the object on the focus means. 
   It is possible for the dividing means to include a prism and the image pickup device to further comprise an optical member causing the light exiting from the slit to be incident upon the prism as parallel light and the spectrum exiting from the prism to exit as converging light to the detecting means. 
   The adjusting means may include a galvano-mirror or a polygon mirror. 
   It is possible for the adjusting means to adjust the incident position so that the entire optical image of the object is incident upon the slit every first period, and the detecting means to output the image data every second period. 
   It is possible for the first period to be a vertical scanning period and the second period to be a horizontal scanning period. 
   The image pickup device may further comprise accumulating means for accumulating the image data output by the detecting means. 
   An image pickup method according to the present invention comprises the steps of dividing an optical image of an object into a spectrum and detecting the spectrum obtained by the dividing operation and outputting a pixel of image data based on the detected spectrum. 
   An image display device according to the present invention comprises dividing means for dividing white light into a spectrum, obtaining means for obtaining image data based on a spectrum of an optical image of an object, extracting means for extracting by pixel spectrum portions based on the image data from the spectrum of the white light divided into the spectrum by the dividing means, synthesizing means for synthesizing the spectrum portions extracted by the extracting means, projecting means for projecting light formed by synthesizing the spectrum portions by the synthesizing means, and adjusting means for adjusting a position of projection by the projecting means. 
   The adjusting means may include a galvano-mirror or a polygon mirror. 
   The extracting means may include at least one reflector or transmission unit, the number of the at least one reflector or transmission unit being in correspondence with the number of pixels forming one line in a direction parallel with a line of the optical image of the object and in correspondence with the number of spectrum portions of the optical image of the object for one pixel in a direction perpendicular to the line, the at least one reflector or transmission unit controlling reflection or transmission of the spectrum of the white light on the basis of the image data obtained by the obtaining means. 
   The at least one reflector of the extracting means may include a micromirror or reflective liquid crystal. 
   The at least one transmission unit of the extracting means may include transmissive liquid crystal. 
   It is possible for the obtaining means to obtain the image data every first period and the adjusting means to adjust the projection position of the light formed by synthesizing the spectrum portions so that a line is successively displaced from another line every first period and one frame of image based on the image data is projected every second period. 
   It is possible for the first period to be a horizontal scanning period and the second period to be a vertical scanning period. 
   It is possible for the dividing means to include a lamp for emitting the white light, a condensing optical system for condensing the white light from the lamp into the form of a line, and a spectral prism for dividing the white light into the spectrum, and the synthesizing means to include a synthesizing prism for synthesizing the spectrum portions extracted by the extracting means. 
   The condensing optical system may include a cylindrical lens or a parabolic sweep mirror. 
   The image display device may further comprise a first optical member and a second optical member, the first optical member causing the light incident upon the spectral prism or the synthesizing prism to be parallel light, the second optical member causing the light exiting from the spectral prism or the synthesizing prism to be converging light. 
   It is possible for the extracting means to be the reflector, the spectral prism and the synthesizing prism to be formed as one prism, and the image display device to further comprise separating means for separating light traveling towards the reflector from light traveling away from the reflector. 
   At least one of the condensing optical system and the projecting means may be a mirror. 
   It is possible for the condensing optical system to be a parabolic sweep mirror and the projecting means to be an elliptical sweep mirror. 
   A focus of the elliptical sweep mirror may be positioned so as to optically correspond with a focus of the parabolic sweep mirror. 
   The light formed by synthesizing the spectrum portions may be projected towards the other focus of the elliptical sweep mirror. 
   It is possible for the condensing optical system to be a parabolic sweep mirror and the projecting means to be an elliptical sweep half mirror. 
   It is possible for the dividing means to include a lamp for emitting the white light, a slit for separating in the form of a line a portion of the white light from the lamp, and a spectral prism for dividing the portion of the white light into the spectrum, and the synthesizing means to include a synthesizing prism for synthesizing the spectrum portions extracted by the extracting means. 
   The image display device may further comprise a cylindrical screen for projecting thereon the light formed by synthesizing the spectrum portions. 
   An image display method according to the present invention comprises the steps of dividing white light into a spectrum, obtaining image data based on a spectrum of an optical image of an object, extracting by pixel spectrum portions based on the image data from the spectrum of the white light divided into the spectrum by the dividing operation, synthesizing the spectrum portions extracted by the extracting operation, and adjusting a position of the light formed by synthesizing the spectrum portions by the synthesizing operation. 
   In the image processing system and the image processing method according to the present invention, the optical image of the object is divided into a spectrum, the spectrum is detected, image data based on the detected spectrum is output, white light is divided into a spectrum, spectrum portions based on the output data are extracted from the spectrum of the white light divided into its spectrum, the extracted spectrum portions are synthesized, and light formed by synthesizing the spectrum portions is projected. 
   In the image pickup device and the image pickup method according to the present invention, the optical image of the object is divided into a spectrum, the spectrum is detected, and a pixel of image data based on the detected spectrum is output. 
   In the image display device and the image display method according to the present invention, white light is divided into a spectrum, image data based on a spectrum of an optical image of an object is obtained, spectrum portions based on the image data are extracted by pixel from the spectrum of the white light divided into its spectrum, the extracted spectrum portions are synthesized, and the position of light formed by synthesizing the spectrum portions is adjusted. 
   Advantages of the Invention 
   According to the present invention, it is possible to pick up an object and display a picked-up image. In particular, according to the present invention, it is possible to faithfully pick up the colors of an object and to faithfully display the colors of a picked-up image. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates the chromaticity in an XYZ color coordinate system. 
       FIG. 2  illustrates the principle of an image processing system. 
       FIG. 3  is a block diagram of a functional structure of the image processing system. 
       FIG. 4  shows a path taken by light in a sensing device of the image processing system. 
       FIG. 5  is a sectional view of a detailed structure of a lens system. 
       FIG. 6  shows a path taken by light in a display device of the image processing system. 
       FIG. 7  is a sectional view of a structure of an electron impact CCD. 
       FIG. 8  is a plan view of an arrangement of electron impact CCDs at a light sensor and an arrangement of micromirrors of a micromirror array. 
       FIG. 9  illustrates the angles of the micromirrors of the micromirror array. 
       FIG. 10  illustrates the angles of the micromirrors of the micromirror array. 
       FIG. 11  is a flowchart illustrating an image shooting process at the sensing device. 
       FIG. 12  is a flowchart illustrating in detail an image data obtaining operation in Step S 3  shown in  FIG. 11 . 
       FIG. 13  shows an example of an image of an object. 
       FIG. 14  shows an example of the image by slit light. 
       FIG. 15  shows another example of the image by slit light. 
       FIG. 16  shows still another example of the image by slit light. 
       FIG. 17  shows still another example of the image by slit light. 
       FIG. 18  is a flowchart illustrating an image display process at the display device. 
       FIG. 19  is a flowchart illustrating in detail a scanning line display operation in Step S 53  shown in  FIG. 18 . 
       FIG. 20  shows an example of a form of a galvano-mirror. 
       FIG. 21  shows a sensing device of another structure. 
       FIG. 22  shows a display device of another structure. 
       FIG. 23  shows a display device of still another structure. 
       FIG. 24  shows a display device of still another structure. 
       FIG. 25  shows a display device of still another structure. 
       FIG. 26  shows a display device of still another structure. 
   

   REFERENCE NUMERALS 
     21  image processing system,  31  sensing device,  32  transmitter,  33  accumulator,  34  display device,  41  galvano-mirror,  42  slit,  43  light divider,  44  light sensor,  45  A/D converter,  46  output section,  47  oscillator,  61  lens system,  62  prism,  71  light source,  72  slit,  73  light divider,  74  micromirror array,  75  input section,  76  driver,  77  spectrum synthesizer,  78  galvano-mirror,  79  light exiting section,  80  oscillator,  91  lens system,  92  prism,  101  prism,  102  lens system,  111  screen,  121  electron impact CCD,  151  micromirror 
   BEST MODE FOR CARRYING OUT THE INVENTION 
   An embodiment of the present invention will hereunder be described with reference to the drawings. 
     FIG. 2  illustrates the principle of the present invention. When sunlight  11  passes through a slit  12 , an elongated linear light beam having a sufficiently narrow width is separated in one direction. The sunlight  11  includes various wavelengths, with the refractive indices of the light being different according to the respective wavelengths. Therefore, when the sunlight  11  separated by the slit  12  passes through the upper surface of a prism  13 , the light is refracted at different angles due to differences in wavelengths, as a result of which the paths of the light having different wavelengths are dispersed. In addition, when the sunlight  11  passes through the lower surface of the prism  13 , the light is refracted at different angles due to differences in wavelengths, thereby increasing the difference between the paths of the light having different wavelengths. Accordingly, the light (spectrum  14 ) having various wavelengths included in the sunlight  11  exits from the lower surface of the prism  13 . In other words, the spectrum  14  of the sunlight  11  is dispersed (divided) according to the wavelengths by the prism  13 . Here, the spectrum  14  appears in an illustrated S direction (widthwise direction of the slit  12 ), and pixel components at the position of the spectrum  14  appear in an X direction perpendicular to the S direction (longitudinal direction of the slit  12 ). 
   Light (colors) seen by a human being other than sunlight (natural light), has various wavelengths, but such light is basically a reflection component of sunlight (natural light). Therefore, if it is possible to divide such light from an object into a spectrum, to precisely detect the spectrum, and to adjust a spectrum of a display image on the basis of detected data and display the spectrum, it is possible to achieve an image apparatus which can faithfully pick up and display the colors of the object compared to a related image apparatus handling an image on the basis of, for example, the three primary colors, red, green, and blue. 
   Accordingly, in the present invention, an optical image of an object is divided into a spectrum, the object is picked up on the basis of the spectrum, and a picked-up image is displayed. In other words, the spectrum of the optical image of the object is detected, image data is generated on the basis of the detected spectrum, and an image obtained by synthesizing spectrum portions extracted on the basis of the image data is displayed. 
     FIG. 3  is a block diagram of a functional structure of an image processing system  21  to which the present invention is applied.  FIG. 4  is a schematic view of a path taken by light (an optical image of an object) in a sensing device  31  of the image processing system  21 .  FIG. 5  shows an example of a specific structure of a lens system  61  shown in  FIG. 4 .  FIG. 6  is a schematic view of a path taken by light (white light and a display image) in a display device  34  of the image processing system  21 . 
   The image processing system  21  includes the sensing device  31 , a transmitter  32 , an accumulator  33 , and the display device  34 . 
   The sensing device  31  picks up an optical image of an object. More specifically, the sensing device  31  detects a spectrum of the optical image of the object and generates image data based on the detected spectrum. The sensing device  31  outputs the generated image data to the transmitter  32  or the accumulator  33 . The display device  34  displays an image based on the image data by obtaining the image data through the transmitter  32  or by obtaining the image data accumulated in the accumulator  33 . 
   The sensing device  31 , the transmitter  32 , the accumulator  33 , and the display device  34  may be disposed in the same housing or in different housings, respectively. The sensing device  31  and the accumulator  33  may be disposed in the same housing. 
   For the transmission of the image data by the transmitter  32 , for example, a transmission format based on Low Voltage Differential Signaling (LVDS) that has low noise and low power consumption and that is capable of being used in high-speed transmission may be used. 
   The transmission of the image data by the transmitter  32  may be a wired or a wireless transmission. 
   A storage medium used in the accumulator  33  may be, for example, a hard disc or a removable medium such as a semiconductor memory, an optical disc, or a magnetic disc. 
   The sensing device  31  includes a galvano-mirror  41 , a slit  42 , a light divider  43 , a light sensor  44 , an A/D converter  45 , an output section  46 , and an oscillator  47 . 
   The galvano-mirror  41  (see  FIG. 4 ) is a deflector for adjusting (deflecting) the direction of reflection of light (optical image of an object) incident upon one planar mirror which is disposed at a rotary shaft (not shown) and which rotates around the rotary shaft by a controlling operation of the oscillator  47 . The optical image of the object picked up by the sensing device  31  first impinges upon the galvano-mirror  41  and is reflected towards the slit  42 . 
   The optical image of the object reflected by the galvano-mirror  41  passes through the slit  41 , thereby separating one horizontal elongated linear light beam of the object (hereafter referred to as “slit light of the object”). With the slit light of the object separated by the slit  42  being defined as one unit (one line), the sensing device  31  divides the optical image of the object into a plurality of horizontal straight lines in a vertical direction and picks up the optical image. The display device  34  (described later) displays as one horizontal scanning line one unit of the slit light of the picked-up object, and the number of divisions in the vertical direction is the number of scanning lines in the vertical direction. 
   The galvano-mirror  41  is disposed so as to be rotatable vertically with respect to the object to be picked up. The oscillator  47  rotates the galvano-mirror  41  at a constant velocity so that the entire optical image of the object to be picked up passes through the slit  42  downward in a constant period (hereafter referred to as a vertical scanning period T). In other words, one frame of the optical image of the object is vertically scanned every vertical scanning period T by using the galvano-mirror  41 . 
   The slit light of the object separated by the slit  42  impinges upon the light divider  43 . The light divider  43  includes the lens system  61  and a prism  62 . As shown in  FIG. 4 , the slit light of the object that has passed through the lens system  61  passes through the prism  62 , so that a spectrum based on wavelength components of the slit light of the object (hereafter referred to as “object spectrum”) is separated, and is focused on a surface of the light sensor  44 . 
   The lens system  61 , like a camera lens, is a combination of a plurality of lenses and, as a whole, plays the role of a convex lens to focus the slit image of the object that has passed through the lens system  61 . In principle, it is possible to use a pinhole lens for the lens system  61 , but, practically speaking, it is desirable for the lens system  61  to have little chromatic aberration in order to reduce displacement of the position of the light incident upon the upper surface of the image pickup element  44 , the displacement being caused by differences in wavelengths when a prism is not disposed. In addition, in order to sharply focus an image on the image pickup element  44 , it is desirable to use a lens having a small diameter in the lens system  61  or to use a stop so that it is sufficiently stopped down. 
     FIG. 5  shows an example of a detailed structure of the lens system  61 . In this structure, the lens system  61  is formed by combining a plurality of lenses  61 - 1  to  61 - 5  for correcting aberration. In addition, a stop  61 - 6  is disposed between the lens  61 - 3  and the lens  61 - 4 . As mentioned above, the stop  61 - 6  to is used so that it is stopped down to the extent possible. 
   The prism  62  is desirably formed of glass having a large refractive index or other such material so as to shorten the distance between the prism  62  and the light sensor  44  (so as to divide light into a spectrum having a large width in a small distance). 
   The object spectrum focused on the surface of the light sensor  44  is converted from a light signal into an electrical signal by the light sensor  44 . 
   The light sensor  44  is, for example, a camera using an electron-impact charge coupled device (CCD).  FIG. 7  is a sectional view of a structure of an electron shock CCD  121 . When a photon  141  impinges upon a photoelectric cathode  131  of the electron shock CCD  121 , an electron  142 - 1  is emitted by photoelectric conversion. At this time, a very high voltage is applied between the photoelectric cathode  131  and a back thin-plate CCD portion  132 , causing the electron  142 - 1  to be accelerated by the applied voltage and to be driven into the back thin-plate CCD portion  132 . Therefore, the electron shock CCD  121  can intensify the electrical signal at a high S/N ratio even with respect to a very weak input light. Consequently, compared to a general CCD, the electron shock CCD  121  has high sensitivity and can precisely detect the strength (luminance) of the object spectrum that impinges upon the light sensor  44 . An electron  142 -i (i=1, 2, . . . , n) accumulated at the back thin-plate CCD portion  132  is output as an electrical signal every constant period. 
   As shown in  FIG. 8 , in the light sensor  44 , M electron shock CCDs  121  and N electron shock CCDs  121  are disposed in an x direction and an S direction, respectively, in a plane and in a lattice form within a rectangular area. A component in the direction in which the object spectrum changes (color changes) impinges upon the light sensor  44  in the S direction and a pixel component (component in the longitudinal direction of the slit  42 ) impinges upon the light sensor  44  in the x direction. At this time, spectral portions of the object spectrum having wavelengths in the visible light range (wavelengths from 380 nm to 780 nm) are incident upon the range of the light sensor  44  in the S direction. 
   The light sensor  44  outputs as an electrical signal an electron (electrical charge) that has been accumulated as a result of the object spectrum impinging upon the light sensor  44  every constant period (hereafter referred to as horizontal scanning period H). At this time, the output electrical signal is image data of one horizontal scanning line of the image to be picked up. For example, when M electron shock CCDs  121  and N electron shock CCDs  121  are disposed in the x direction and the S direction of the lattice of the light sensor  44 , respectively, the image data of one horizontal scanning line is divided into M pixels, and the pixels are detected as N spectral components having wavelengths in the visible light range (wavelengths from 380nm to 780 nm), so that the image data is output by pixel. 
   The light sensor  44  outputs image data (an f line of image data, an f line of one frame) an f number of times in the vertical scanning period T. The f number of times is the number of scanning lines of the image data in the vertical direction. In other words, the relationship among the vertical scanning period T, the horizontal scanning period H, and the number f of vertical scanning lines is as shown in Formula (1).
 
Vertical Scanning Period  T =Horizontal Scanning Period  H ×Number  f  of Vertical Scanning Lines+Return Time α  (1)
 
   The return time α represents the time required for the galvano-mirror  41  to return to its original position (where the topmost line of the optical image of the object to be picked up is picked up) after scanning the entire (one frame of the) optical image of the object to be picked up (that is, after picking up the lowest line of the optical image of the object). 
   The image data output by the light sensor  44  is input to the A/D converter  45  and is converted from analog data into digital data. At this time, the analog data is converted into n bits of digital data on the basis of the size of the image data. That is, the image data is divided into N spectral components per pixel, and the divided spectral components are represented as n bits of digital data in accordance with the strengths, so that one pixel represents N×n bits of data. 
   When the image data converted into digital data by the A/D converter  45  is to be used to display an image in real time, it is output to the transmitter  32  through the output section  46 , and is supplied to the display device  34  through the transmitter  32 . When the image data is to be recorded, the image data is output to the accumulator  33  through the output section  46  and is accumulated. 
   The display device  34  includes a light source  71 , a slit  72 , a light divider  73 , a micromirror array  74 , an input section  75 , a driver  76 , a spectrum synthesizer  77 , a galvano-mirror  78 , a light exiting section  79 , and an oscillator  80 . 
   For the light source  71 , sunlight or a lamp, such as a xenon lamp, which emits light (white light) having a spectrum corresponding to that of sunlight is used. 
   As shown in  FIG. 6 , as at the sensing device  31 , white light generated by the light source  71  is such that one light beam having the shape of an elongated line in cross section is separated from the white light by the slit  72 . The light beam is divided into a spectrum by a prism  92  of the light divider  73 . When the slit  72  is formed into a double slit or both the slit  72  and the lens system  91  are used, it is possible to focus the light beam in a form closer to a line segment. The spectrum of the divided white light is temporarily focused on a surface of the micromirror array  74 . When the slit  72  and the lens system  91  are both used, the slit  72  and the lens system  91  are disposed so that an image of the slit  72  is focused on the image pickup element  74 . Since the prism is disposed in between, “to focus” here means “to focus according to wavelength.” When only the lens system  91  is used, the lens system  91  is disposed so that a parallel light beam of the sun when sunlight is used or a light beam emitted from the light source  71  when, for example, a xenon lamp is used is focused on the image pickup element  74 . When only the slit  72  is used, the position of the slit  72  is not strictly limited. When the lens system  91  is used, a light condensing optical system capable of condensing light into a linear shape, such as a cylindrical lens, a parabolic sweep mirror (which is a mirror that looks like a flat plate whose cross section is bent into a parabolic shape), or an elliptical sweep mirror (which is a mirror that similarly looks like a flat plate whose cross section is bent into an elliptical shape), is used for the lens system  91 . A larger amount of light energy can be used when the lens system  91  is used than when the slit  72  is used. 
   In the micromirror array (Digital Micromirror Device (trademark))  74 , micromirrors (trademark), formed by finely processing silicon, are disposed as reflectors in a plane and in a lattice form and reflect predetermined spectrum portions of the spectrum of the incident white light towards the spectrum synthesizer  77 . Each micromirror is such that its angle with respect to the spectrum of the incident white light from the prism  92  is separately controlled by the driver  76 . The output of the reflection light is switched to an on setting or an off setting by this angle. Here, the term “on” refers to reflecting spectrum portions towards the spectrum synthesizer  77  (setting to a synthesizing state), while the term “off” refers to reflecting spectrum portions in a direction other than towards the spectrum synthesizer  77  (setting to a non-synthesizing state). By performing the on/off control on the output of the reflection light, the spectrum portions included in the refection light are controlled. By controlling the on/off continuation time of the output of the reflection light, the luminance of the reflection light is controlled according to the spectrum portions included in the reflection light. 
   Basically, the number and arrangement of the micromirrors of the micromirror array  74  are the same as those of the electron shock CCDs  121  of the light sensor  44  shown in  FIG. 8 . The micromirror array  74  is disposed so that the spectrum of the white light incident upon the micromirrors are the same as the object spectrum incident upon the electron shock CCDs  121  disposed at corresponding locations within the lattice of the light sensor  44 . Obviously, with the number of micromirrors being equal to or greater than N×M micromirrors, some of the may be used. If some of the N×M data are only used, a smaller number of them may be used. 
   The driver  76  obtains the image data from the transmitter  32  or the accumulator  33  through the input section  75 , and performs the on/off setting (including the on/off time) control on the output of the reflection light of the micromirrors. Here, the electron shock CCDs  121  and the micromirrors that are disposed in corresponding locations within the lattice shown in  FIG. 8  are in a one-to-one correspondence. The micromirrors are controlled on the basis of the image data output from the respective electron shock CCDs  121 . In other words, by controlling the on/off setting of the reflection of the spectrum of the white light by the respective micromirrors on the basis of the image data output from the respective electron shock CCDs  121 , the micromirror array  74  extracts spectrum portions based on the image data from the spectrum of the incident white light from the prism  92 , and causes the exiting of (reflects) with the same brightness the spectrum portions that are the same as the spectrum of the optical image of the object that has impinged upon the light sensor  44  when the image data is detected. 
   The spectrum synthesizer  77  includes a prism  101  and a lens system  102 . The spectrum portions of the reflection light exiting from the micromirror array  74  are synthesized by passing through the prism  101  of the spectrum synthesizer  77 , so that one elongated linear light beam is formed at the upper surface (light exiting surface) of the prism  101 . The linear light beam becomes light having the same components (including brightness) as the slit light of the object that has impinged upon the upper surface (incident surface) of the prism  62  of the sensing device  31  when the image data to be displayed (image data used for a controlling operation when the spectrum portions of the reflection light on which the linear light beam is based are output from the micromirror array  74 ) is detected by the sensing device  31 . Accordingly, it becomes one horizontal scanning line of the image to be displayed on a screen  111 . Hereafter, the linear light beam in which the spectrum portions have been synthesized by the prism  101  will be referred to as “display image scanning line.” The screen  111 , instead of being a planar screen, may be a cylindrical screen like a screen  111 S (described later) shown in  FIG. 22 . 
   When each micromirror of the micromirror array  74  is controlled to an on setting, the angle of each micromirror with respect to the spectrum of the white light is separately adjusted so that the spectrum is incident upon each micromirror from the prism  92  and a spectrum portion reflected by each micromirror is synthesized at the light exiting surface of the prism  101 . 
   Here, the angles of the micromirrors will be explained with reference to  FIGS. 9 and 10 . 
     FIG. 9  is a horizontal view as seen from a surface in an S direction of micromirrors  151 -i (i=1, 2, . . . , N) disposed in the micromirror array  74  (hereafter, when the individual micromirrors  151 -i (i=1, 2, . . . , N) do not need to be distinguished, they will simply be referred to as micromirrors  151 ). The solid lines in the figure refer to the directions in which spectrum portions are reflected by the micromirrors  151  that are controlled to an on setting, and the dotted lines refer to the directions in which spectrum portions are reflected by the micromirrors  151  that are controlled to an off setting. As shown in  FIG. 9 , the micromirrors  151  are disposed at an equal interval. As mentioned later with reference to  FIG. 10 , the individual micromirrors  151  have their angles previously adjusted so as to differ slightly from each other with respect to a base in order to reflect the incident spectrum in the on setting at predetermined angles. 
     FIG. 10  schematically shows the relationship between incident spectrum and spectrum portions that are reflected for the micromirrors  151 - 1 ,  151 - 6 , and  151 -N shown in  FIG. 9 . Similarly to  FIG. 9 ,  FIG. 10  is a horizontal view as seen from a surface of the micromirror array  74  in the S direction. 
   When the white light is incident upon the prism  92 , the white light is divided into its spectrum by the prism  92  and impinges upon different micromirrors  151  due to the wavelengths of the spectrum. At this time, the position of the white light incident upon the incident surface of the prism  92  and the refractive index of the prism  92  with respect to the light of each wavelength are constant. Accordingly, the path that the light having the wavelengths takes to impinge upon the micromirror  151  is constant, so that it can be easily calculated. In addition, the refractive index of the prism  101  with respect to the light having the wavelengths is constant. Accordingly, it is possible to calculate where and at what angle the light having the wavelengths should impinge upon the incident surface of the prism  101  in order to form one linear light beam by synthesizing the spectrum portions of the reflection light at a predetermined location of the light exiting surface of the prism  101 . 
   Therefore, where and at what angle each spectrum wavelength exits from the light exiting surface of the prism  92  and where and at what angle each spectrum portion having its associated wavelength is incident upon the incident surface of the prism  101  are determined. In accordance therewith, the angles of the micromirrors  151  are determined. For example, when the spectrum to be incident upon the micromirror  151 - 1  shown in  FIG. 10  is adjusted so as to exit from a point Al of the light exiting surface of the prism  92 , to be reflected at a point P 1  of a surface of the micromirror  151 - 1 , and to be incident upon a point B 1  of the incident surface of the prism  101 , the angle is determined so that the surface of the micromirror  151 - 1  is perpendicular to a bisector of an angle A 1 P 1 B 1 . 
   Similarly, when the spectrum to be incident upon the micromirror  151 - 6  shown in  FIG. 10  is adjusted so as to exit from a point A 6  of the light exiting surface of the prism  92 , to be reflected at a point P 6  of a surface of the micromirror  151 - 6 , and to be incident upon a point B 6  of the incident surface of the prism  101 , the angle is determined so that the surface of the micromirror  151 - 6  is perpendicular to a bisector of an angle A 6 P 6 B 6 . When the spectrum to be incident upon the micromirror  151 -N shown in  FIG. 10  is adjusted so as to exit from a point AN of the light exiting surface of the prism  92 , to be reflected at a point PN of a surface of the micromirror  151 -N, and to be incident upon a point BN of the incident surface of the prism  101 , the angle is determined so that the surface of the micromirror  151 -N is perpendicular to a bisector of an angle ANPNBN. 
   The reflection light (display image scanning line) in which the spectrum portions have been synthesized by the prism  101  is condensed by the lens system  102  (a light-condensing system including a cylindrical lens, a parabolic mirror, etc.) which is a combination of a plurality of lenses like the lens system  61  of the sensing device  31 , and impinges upon and is reflected by the galvano-mirror  78 . 
   Here, since the lens system  61  of the sensing device  31  and the lens system  102  of the display device  34  have the same structure, it is possible to reduce the influence of chromatic aberration of the lens systems. 
   Similarly to the galvano-mirror  41  of the sensing device  31 , the galvano-mirror  78  is a deflector for adjusting (deflecting) the direction of reflection of light (display image scanning line) incident upon one planar mirror which is disposed at a rotary shaft (not shown) and which rotates around the rotary shaft by a controlling operation of the oscillator  80 . The galvano-mirror  78  is disposed so as to rotate vertically with respect to the screen  111  of the light exiting section  79 . 
   The light exiting section  79  is formed of a black box (not shown) surrounding the screen  111  and the galvano-mirror  78 . The display image scanning line that has been condensed by the lens system  102  and reflected by the galvano-mirror  78  is focused and projected on the screen  111  of the light exiting section  79 . This causes one elongated scanning line to be displayed in the horizontal direction of the screen  111 . The black box (not shown) is effective in improving contrast ratio of an image on the screen  111 . When a sufficient contrast can be obtained, the black box may be omitted. 
   The image is displayed on the screen  111  in the following timing. In other words, the driver  76  obtains one scanning line of image data every horizontal scanning period H, and performs the on/off setting (including the on/off time) control on the output of the reflection light at the micromirrors  151  of the micromirror array  74  on the basis of the obtained image data. The oscillator  80  moves in response with the control of the exiting of the reflection light at the micromirror array  74 , adjusts the angle of the galvano-mirror  78 , and projects display image scanning lines so as to be successively displaced downward from each other on the screen  111 . f display image scanning lines forming one frame are projected onto the screen  111  during the vertical scanning period T, thereby displaying one frame of image on the screen  111 . 
   Next, the image projection process at the sensing device  31  will be described with reference to the flowcharts in  FIGS. 11 and 12 . The process is started when a user orders a shooting operation to be started and ends when the user orders the shooting operation to be ended. 
   In Step S 1 , the oscillator  47  sets the galvano-mirror  41  to an initial position. In other words, the galvano-mirror  41  is set at a reference position where the topmost line in the horizontal direction in a range (frame) in which an optical image of an object reflected by the galvano-mirror  41  is picked up is separated by the slit  42 . 
   In Step S 2 , the oscillator  47  starts rotating the galvano-mirror  41 . The galvano-mirror  41  is rotated at a constant speed so that the entire optical image of the object to be picked up passes downward through the slit  42  every vertical scanning period T. 
   In Step S 3 , an image data obtaining operation described later with reference to  FIG. 12  is performed. By this operation, as described above with reference to  FIGS. 3 and 8 , one scanning line of image formed by slit light of the object separated by the slit  42  is divided into M pixels, and the pixels are detected as N spectral components having wavelengths in the visible light range (wavelengths from 380 nm to 780 nm), so that the image is output by pixel. In this case, image data of the topmost line, in the horizontal direction of the frame, of the optical image of the object to be picked up, that is, image data of the topmost scanning line is output. 
   In Step S 4 , the A/D converter  45  converts the image data output by the light sensor  44  in the operation of Step S 3  from analog data into digital data. In other words, the image data is converted into n-bits of digital data on the basis of the size (level) of each pixel of the image data output by the operation in Step S 3 . That is, the image data is divided into N spectral components per pixel, and the divided spectral components are represented as n bits of digital data in accordance with their strengths, so that one pixel represents N×n bits of data. 
   In Step S 5 , the A/D converter  45  supplies the digital image data to the output section  46 . When the output section  46  is to display on the display device  34  in real time the image data that has been picked up on the basis of the command of the user, the image data is output to the transmitter  32 . When the image data is to be recorded, the image data is output to and is accumulated at the accumulator  33 . 
   In Step S 6 , the oscillator  47  determines whether or not the galvano-mirror  41  has rotated to the lowest reference position. In other words, it determines whether or not the galvano-mirror  41  has rotated to a location where the lowest line, in the horizontal direction of the frame, of the optical image of the object that is picked up is separated by the slit  42 . In this case, the galvano-mirror  41  is set at a position where the topmost line, in the horizontal direction of the frame, of the optical image of the object that is picked up is separated by the slit  42 . Therefore, it determines that the galvano-mirror  41  has not rotated to the lowest reference position, so that the process returns to Step S 3 . 
   Thereafter, until the oscillator  47  determines that the galvano-mirror  41  has rotated to the lowest reference position in Step S 6 , the operations from Steps S 3  to S 6  are repeated a total of f times (corresponding to the number of vertical scanning lines), so that one frame of the optical image of the object is divided into f horizontal lines (scanning lines) and picked up. The operations from Steps S 3  to S 6  are repeated at an interval corresponding to the horizontal scanning period H. 
   When the oscillator  47  determines that the galvano-mirror  41  has rotated to the lowest position in Step S 6 , the process returns to Step S 1 , so that the galvano-mirror  41  is set at the initial position and the operations subsequent to this setting operation are repeated. In other words, the second frame and subsequent frames of the optical image of the object are picked up. When the operation in Step S 1  is performed for the second time and subsequent times, the time required for setting the galvano-mirror  41  at the initial position is equal to the aforementioned return time α, the operations from Steps S 1  to S 6  are repeated at an interval corresponding to the vertical scanning period T including the return time α, and the picking up of every one frame of image is repeated, so that a plurality of frames of the image are obtained. 
   In this way, the optical image of the object is divided into f horizontal scanning lines, and one scanning line of image data is divided into M pixels. The pixels are detected as N spectral components having wavelengths in the visible light range (wavelengths from 380 nm to 780 nm), so that the optical image is output by pixel (the optical image of the object is picked up). 
   Next, the image data obtaining operation in Step S 3  shown in  FIG. 11  will be described in more detail with reference to  FIG. 12 . This operation is executed every horizontal scanning period H. 
   In Step S 21 , the optical image of the object that is picked up is incident upon the galvano-mirror  41  of the sensing device  31  and is reflected towards the slit  42 . 
   In Step S 22 , the optical image of the object reflected by the galvano-mirror  41  by the operation in Step S 21  passes through the slit  42 , so that one horizontal elongated linear light beam of the object (slit light of the object) is separated. 
   In Step S 23 , the slit light of the object separated in Step S 22  is divided into a spectrum by the light divider  43 . The slit light of the object that has passed through the lens system  61  of the light divider  43  passes through the prism  62 , so that the slit light is divided into a spectrum and the spectrum is focused on the surface of the light sensor  44 . 
   In Step S 24 , the light sensor  44  converts light signal of the object spectrum that has impinged upon the light sensor  44  into an electrical signal. As mentioned above with reference to  FIG. 8 , in the light sensor  44 , M electron shock CCDs  121  and N electron shock CCDs  121  are disposed in the x direction and the S direction, respectively, in a plane and in a lattice form within a rectangular area. By this, the object spectrum is divided into M pixels in the x direction, and each pixel is divided into N spectral components having wavelengths in the visible light range (wavelengths from 380 nm to 780 nm). The electron shock CCDs  121  convert light to electrons (electrical charges) by photoelectric effect in accordance with the strength (luminance) of the incident spectrum. 
   In Step S 25 , the light sensor  44  outputs as image data the electrical signal produced by the electrical charges accumulated at the electron shock CCDs  121  to the A/D converter  45 . 
   The slit light of the object is as illustrated from  FIGS. 13 to 17 .  FIG. 13  shows the entire image of the object. When the galvano-mirror  41  is orientated relatively upward at a first angle, as shown in  FIG. 14 , the galvano-mirror  41  takes in an image of an image frame  331 - 1  defined by the size of the galvano-mirror  41 . The light sensor  44  takes in a slit image portion  332 - 1  of the image through the slit  42 . 
   When the galvano-mirror  41  is oriented downward than in the case shown in  FIG. 14 , the galvano-mirror  41  takes in an image of an image frame  331 - 2  as shown in  FIG. 15 . The light sensor  44  takes in a slit image portion  332 - 2  of the image through the slit  42 . Thereafter, when the galvano-mirror  41  is oriented further downward and, as shown in  FIG. 16 , an image of an image frame  331 - 3  is detected, the light sensor  44  takes in a slit image portion  332 - 3  of the image. When the galvano-mirror  41  is further oriented downward, as shown in  FIG. 17 , the light sensor  44  detects a slit image portion  332 - 4  of an image of an image frame  331 - 4 . 
   In this way, the spectrum of the slit light of the object is divided into M pixels, and each pixel is divided into N spectral components having wavelengths in the visible light range (wavelengths from 380 nm to 780 nm), so that an electrical signal based on the luminance of every divided spectral component is output. In other words, the distribution and strengths of the spectrum of the optical image of the object are detected as they are, so that image data converted into electrical signals is output. 
   Next, image display at the display device  34  will be described with reference to  FIGS. 18 and 19 . This process is started when a user orders the image display to be started and ends when the user orders the image display to end. 
   In Step S 51 , the oscillator  80  sets the galvano-mirror  78  to an initial position. In other words, the galvano-mirror  78  is set at a position where a scanning line of a display image reflected by the galvano-mirror  78  is projected as a topmost scanning line on the screen  111 . 
   In Step S 52 , the driver  76  obtains one scanning line of image data of an image to be displayed from the transmitter  32  or the accumulator  33  through the input section  75 . In other words, in this case, it obtains the image data of the topmost scanning line of the first frame. 
   In Step S 53 , a scanning line display operation described later with reference to  FIG. 19  is carried out. By this operation, the image (scanning line) based on the one scanning line of image data obtained in Step S 52  is displayed on the screen  111 . In other words, in this case, the topmost scanning line of the image of the first frame is displayed on the screen  111 . 
   In Step S 54 , the oscillator  80  determines whether or not the last (lowest) scanning line of the one frame has been displayed. In other words, it determines whether or not the galvano-mirror  78  has been set at a position where the lowest scanning line is displayed on the screen  111 . In this case, since the galvano-mirror  78  is set at the position where the topmost scanning line is displayed on the screen  111 , the oscillator  80  determines that the last scanning line of the one frame is not displayed, so that the; process proceeds to Step S 55 . 
   In Step S 55 , the oscillator  80  rotates (adjusts) the galvano-mirror  78  so as to be positioned where the next scanning line, in this case, the second scanning line is displayed on the screen  111 , and the process returns to Step S 52 . 
   Thereafter, in Step S 54 , until the oscillator  80  determines that the last scanning line of the one frame has been displayed, the operations from Steps S 52  to S 55  are repeated a total of f times (corresponding to the number of vertical scanning lines), so that f scanning lines included in the one frame of image are displayed. The operations from Steps S 52  to S 55  are repeated at an interval corresponding to the horizontal scanning period H. 
   When, in Step S 54 , the oscillator  87  determines that the last scanning line of the one frame has been displayed, the process returns to Step S 51  to set the galvano-mirror  78  at the initial position and the operations subsequent to this setting operation are repeated. In other words, images of the second frame and subsequent frames are displayed. When the operation in Step S 51  is performed for the second time and subsequent times, the time required for setting the galvano-mirror  78  at the initial position is equal to the aforementioned return time α, the operations from Steps S 51  to S 56  are repeated at an interval corresponding to the vertical scanning period T including the return time α, and the display of every one frame of image is repeated. 
   In this way, an image of the image data that has been picked up by the sensing device  31  is displayed on the screen  111 . 
   Next, the scanning line display operation of Step S 53  shown in  FIG. 18  will be described in more detail with reference to  FIG. 19 . 
   In Step S 71 , white light emitted by the light source  71  passes through the slit  72  so that one elongated linear light beam (slit light of the white light) is separated from the white light. 
   In Step S 72 , the slit light separated from the white light in Step S 71  is divided into a spectrum by the prism  92  of the light divider  73 , so that the spectrum of the divided white light is temporarily focused on a surface of the micromirror array  74 . 
   In Step S 73 , the driver  76  controls the on/off setting (including the on/off time) of the output of the reflection light of the micromirrors  151  of the micromirror array on the basis of the image data obtained by the operation in Step S 52 , extracts spectrum portions based on the image data from the spectrum of the incident white light obtained in Step S 72 , and causes the exiting of (reflects) the spectrum portions that are the same as the spectrum of the image to be displayed. 
   As mentioned above, basically, the number and arrangement of the micromirrors  151  of the micromirror array  74  are the same as those of the electron shock CCDs  121  of the light sensor  44  shown in  FIG. 8 . The micromirror array  74  is disposed so that the spectrum of the white light incident upon the micromirrors  151  are the same as the object spectrum incident upon the electron shock CCDs  121  disposed at corresponding locations within the lattice of the light sensor  44 . The electron shock CCDs  121  and the micromirrors  151  that are disposed in corresponding locations within the lattice are in a one-to-one correspondence. The on/off setting (including the on/off time) of the output of the reflection light at the mircromirrors  151  is controlled on the basis of the image data output from the respective electron shock CCDs  121 . 
   The on/off setting (on/off time) of the output of the reflection light at the micromirrors  151  is controlled by a subfield method. For example, if one unit of image data is represented as 4-bit image data (that is, when each spectrum value is expressed as 4 bits (when n=4)), the time resulting from equally dividing the horizontal scanning period H into 16 (4th power of 2) parts is defined as one unit time (hereafter referred to as “unit time”). By each bit value of the image data, during a period in decimal notation expressed by the unit time×each bit, the driver  76  turns on or off the output setting of the reflection light at the micromirrors  151 . For example, if the value of the image data (one spectral value) is 1010 in binary notation, during the horizontal scanning period H, the micromirror  151  corresponding to this spectrum value is first set on for 8 unit times (=third power of 2 or the decimal notation value of the binary notation value 1000), then is set off for 4 unit times (=second power of 2 or the decimal notation value of the binary notation value 100), then is set on for 2 unit times (=first power of 2 or the decimal notation value of the binary notation value 10), and is finally set off for one unit time (=zeroth power of 2 or the decimal notation value of the binary notation value 1). 
   In this way, by controlling the on/off time of the output of the reflection light at each micromirror  151  every horizontal scanning period H on the basis of the image data value (luminance of the light incident upon the electron shock CCD  121 ), the luminance of the spectrum of the reflection light exiting from the micromirror array  74  is controlled. Since each micromirror  151  is such that the on/off setting of the reflection of the spectrum portions that are the same as the spectrum incident upon the corresponding electron shock CCD  121  is controlled, the spectrum portions that are the same as the spectrum of the optical image incident upon the light sensor  44  when the image data is obtained is extracted from the spectrum of the white light and exit from the micromirror array  74 . 
   In Step S 74 , the spectrum portions of the reflection light exiting from the micromirror array  74  in Step S 73  are synthesized as a result of the spectrum portions passing through the prism  101 , so that one elongated linear light beam (display image scanning line) is formed at the upper surface (light exiting surface) of the prism  101 . The display image scanning line becomes light having the same components (including brightness) as the slit light of the object that has impinged upon the upper surface (incident surface) of the prism  62  of the sensing device  31  when the image data of the image to be displayed (image data used for a controlling operation when the spectrum portions of the reflection light on which the linear light beam is based are output from the micromirror array  74 ) is detected by the sensing device  31 . 
   In Step S 75 , the display image scanning line formed by synthesizing the spectrum portions in Step S 74  is condensed by the lens system  102 , impinges upon the galvano-mirror  78 , and is reflected towards the screen  111 . 
   In Step S 76 , the display image scanning line that has been reflected in Step S 75  is focused and projected on the screen  111 , so that one horizontal scanning line is displayed on the screen  111 . 
   By the above-described operations in  FIGS. 18 and 19 , the image of the object that has been picked up at the sensing device  31  is displayed on the screen  111  of the display device  34  on the basis of the image data of the object that has been picked up. 
   Accordingly, the image processing system  21  can faithfully pick up the colors of an object and can display an image formed by faithfully reproducing the colors of an optical image of the object on the basis of picked-up image data. 
   Although, in the foregoing description, the micromirror array  74  is used in the display device  34 , a reflection liquid crystal display (LCD) which, like the micromirror array  74 , uses outside light (natural light) for the light source, and projects reflection outside light onto, for example, a screen may be used. Even in this case, the liquid crystal reflectivity or reflection time are controlled on the basis of image data. 
   For the galvano-mirror  41  of the sensing device  31  and the galvano-mirror  78  of the display device  34 , a galvano-mirror  201  having the form shown in  FIG. 20  may be used instead of a planar mirror which rotates around the center of a rotary shaft. The galvano-mirror  201  rotates at a constant speed in a constant direction around the center of a central axis  202 . For example, when incident light is impinging upon a surface  203 - 1  of the galvano-mirror  201 , the rotation of the galvano-mirror  201  causes the angle of the surface  203 - 1  with respect to the incident light to change, so that the angle of the reflected light also changes continuously. When the galvano-mirror  201  has rotated to a certain angle, the incident light which has been impinging upon the surface  203 - 1  starts impinging upon a surface  203 - 2 , and the angle of the reflected light becomes the same as the initial angle when the incident light was impinging upon the surface  203 - 1 . Thereafter, further rotation of the galvano-mirror  201  at the constant speed causes the angle of the reflected light to change continuously as in the case in which the incident light was impinging upon the surface  203 - 1 . By this, it is possible to adjust the angle of the reflected light in a constant period, so that the same effects as those when a planar galvano-mirror is rotated at a constant speed and is returned to its initial position when the planar galvano-mirror has rotated to a predetermined angle can be provided. 
   Instead of a galvano-mirror, it is possible to use a polygon mirror used in, for example, a laser printer. 
   By detecting and displaying a spectrum of wavelengths outside the visible light range (wavelengths from 380 nm to 780 nm) of human beings, it is possible to provide an image that approximates more closely to an object in the real world for living beings other than human beings. 
     FIG. 21  shows a sensing device  31  of another form. In this form, a slit  42  disposed downstream in a light path from the lens system  61  is formed perpendicular to the plane of the figure. The lens system  61  comprises lenses  61 - 1  to  61 - 5 , and the slit  42  is disposed at a focus of the lens system  61 . A diffuser  301  is disposed just behind the slit  42 . Accordingly, an image of an object is focused at the diffuser  301 . Although, in  FIG. 21 , only light passing through the slit  42  is shown, light is also focused on portions of the diffuser  301  other than where the slit  42  is located. However, such light is shielded, so that only the light that is focused in correspondence with the slit  42  is extracted. Although the diffuser  301  need not be used, disposing the diffuser  301  just behind the slit  42  makes it possible to restrict diffraction by the slit  42 . 
   An aplanatic lens system  61 - 6  comprising lenses  61 - 6 - 1  to  61 - 6 - 3  is disposed between the diffuser  301  and the light sensor  44 . A prism  62  is disposed between the lens  61 - 6 - 1  and the lens  61 - 6 - 2 . The lens  61 - 6 - 1  converts incident light from the diffuser  301  into parallel light and causes the parallel light to exit therefrom. Disposing the prism  62  in a parallel light path reduces chromatic aberration, and facilitates the designing of the optical system including the prism  62 . Therefore, the parallel light is incident upon the prism  62 . The lens  61 - 6 - 2  converts the parallel light back into converging light. The converging light is focused on the light sensor  44  through the lens  61 - 6 - 3 . In other words, the lens system  61  is disposed so that an image of the slit  42  is focused on the light sensor  44 . 
   Even in such an arrangement, any of the slit image portions  332 - 1  to  332 - 4  shown in  FIGS. 14 to 17  is focused on the diffuser  301  and, thus, the light sensor  44 . 
     FIG. 22  shows a display device  34  of another form. In the display device  34 , a cylindrical lens  91 S serving as the lens system  91  is used instead of the slit  72 . As in the case shown in  FIG. 6 , both the slit  72  and the lens system  71  may be used. Therefore, white light emitted from the light source  71  is condensed by the cylindrical lens  91 S, so that a spectrum of the light divided by a prism  92  is as a thin straight light beam (emission light) focused on a micromirror array  74  (a direction perpendicular to the plane of the figure corresponds to the its lengthwise direction). The focal length of the cylindrical lens  91 S is equal to the sum of a distance d between the cylindrical lens  91 S and the prism  92 , a light path length (thickness) e of the prism  92 , and a distance f between the prism  92  and the micromirror array  74  (that is, d+e+f). 
   Spectrum portions reflected by the micromirror array  74  on the basis of image data are synthesized by a prism  101  and impinge upon a cylindrical screen  111 S through a galvano-mirror  78 . 
   The focal length of a convex lens  102 - 1  is equal to the sum of a distance i between the convex lens  102 - 1  and the prism  101 , a light path length (thickness) h of the prism  101 , and a distance g between the prism  101  and the micromirror array  74  (that is, i+h+g). The micromirror array  74  is disposed at the focal length of the convex lens  102 - 1 . Therefore, light exiting from the micromirror array  74  is converted into parallel light by the convex lens  102 - 1 . The focal length of a convex lens  102 - 2  is equal to the sum of a distance j between the convex lens  102 - 2  and a galvano-mirror  78  and a distance k between the galvano-mirror  78  and the cylindrical screen  111 S (that is, j+k). Therefore, light exiting from the convex lens  102 - 2  is reflected by the galvano-mirror  78  and is focused on the cylindrical screen  111 S. 
   As shown in  FIG. 22 , the cross section of the cylindrical screen  111 S that is parallel to the plane of the figure is curved with a curvature radius k (that is, the galvano-mirror  78  is disposed so that its rotary shaft  78 A is disposed at the center of the curvature radius k of the cylindrical screen  11 S), while the cylindrical screen  111 S is not curved in a direction perpendicular to the plane of the figure. Rotation of the galvano-mirror  78  around the center of the rotary shaft  78 A causes the position of projection of a linear scanning line on the cylindrical screen  111 S to change successively. By this, an image is displayed on the cylindrical screen  111 S without distortion. 
   In this way, when the lens system  91  is used instead of the slit  72 , compared to the case in which the slit  72  is used, it is possible to more effectively condense light and to display a brighter image. If the slit  72  and the lens system  91  are both used, a thinner linear light beam can be produced. 
     FIG. 23  is a display device  34  of still another form. In this form, a lens system  91  is an aplanatic lens system including lenses  91 - 1  to  91 - 3 , in addition to a cylindrical lens  91 S. A prism  92  is disposed in a parallel light path between the lenses  91 - 1  and  91 - 2 . In addition, in this form, a transmissive LCD  401  is used instead of the micromirror array  74 . White light emitted from a light source  71  is temporarily focused as an emission line  351  by the cylindrical lens  91 S. Light from the emission line  351  is dispersed again and converted into parallel light by the lens  91 - 1 . Then, the light impinges upon the prism  92  and is divided into a spectrum there. The spectrum is formed into converging light again by the lens  91 - 2  and is focused onto the LCD  401  through the lens  91 - 3 . Therefore, an image of the emission line  351  is formed on the LCD  401 . 
   The light that has passed through the LCD  401  whose transmission setting (transmittance ratio or time) is controlled on the basis of image data is formed into an emission line  352  by an aplanatic lens system including lenses  102 - 1 ,  102 - 2 , and  102 - 3 . The lenses  102 - 1  to  102 - 3  also form the aplanatic lens system, and a prism  101  is disposed in a parallel light path between the lenses  102 - 2  and  102 - 3 . Therefore, spectrum portions emitted from the LCD  401  impinge upon the prism  101  through the lenses  102 - 1  and  102 - 2 , are synthesized at the prism  101 , and are focused by the lens  102 - 3 , so that an image of the emission line  351  is formed as the emission line  352 . 
   The light emitted from the emission line  352  is converted into parallel light by a telecentric lens unit  102 - 4  comprising lenses  102 - 4 - 1  to  102 - 4 - 5 , and then impinges upon a thin convex lens  102 - 5 . The sum of a distance b between the thin convex lens  102 - 5  and a galvano-mirror  78  and a distance a between the galvano-mirror  78  and a cylindrical screen  111 S (that is, b+a) is considered as the focal length of the thin convex lens  102 - 5 . In other words, the cylindrical screen  111 S is disposed at the focal length (b+a) of the thin convex lens  102 - 5 . a is also the curvature radius of the cylindrical screen  111 S. Therefore, an image is displayed on the cylindrical screen  111 S without any distortion. 
   The telecentric lens unit  102 - 4  and the thin convex lens  102 - 5  may be formed by zoom lenses. 
     FIG. 24  shows a display device  34  of still another form. In the form shown in  FIG. 23 , since the light path from the cylindrical lens  91 S to the galvano-mirror  78  is formed in a straight line, the overall length is long. Therefore, in the form shown in  FIG. 24 , the display device  34  is designed so that it can be reduced in size by reducing the overall length of the display device  34 . More specifically, in this form, a half mirror  371  is disposed between a cylindrical lens  91 S and an emission line  351 . Light emitted from the emission line  351 S impinges upon a micromirror array  74 , used instead of the LCD  401  shown in  FIG. 23 , through lenses  91 - 1  to  91 - 3 . A prism  92  is disposed in a parallel light path between the lenses  91 - 1  and  91 - 2 . 
   Spectrum portions exiting from the micromirror array  74  controlled on the basis of image data impinge upon the prism  92  through the lenses  91 - 3  and  91 - 2 , and are synthesized, so that the emission line  351  is formed through the lens  91 - 1 . Light emitted from the emission line  351  impinges upon and is reflected by the half mirror  371  and is separated from the incident light from the cylindrical lens  91 S. The light reflected by the half mirror  371  impinges upon a galvano-mirror  78  through a telecentric lens unit  102 - 4  and a thin convex lens  102 - 5 . Light reflected by the galvano-mirror  78  impinges upon the cylindrical screen  111 S, thereby displaying an image. 
   Accordingly, in this form, the prism  92  for dividing light into a spectrum is also used as the synthesizing prism  101 . In addition, the lenses  91 - 1  to  91 - 3  are also used as the lens  101  and lenses  102 - 1  to  102 - 3 . The other structural features are the same as those in  FIG. 23 . As a result, fewer parts are used, thereby making it possible to reduce size and costs. 
     FIG. 25  shows a display device  34  of still another form. If lenses are used as the lens systems  91  and  102 , chromatic aberration occurs. Accordingly, in this form, mirrors are used instead of lenses. More specifically, in this form, a parabolic sweep mirror  91 M is used instead of the lens system  91 , and an elliptical sweep mirror  102 M is used instead of the lens system  102 . The parabolic sweep mirror  91 M is formed by extending perpendicularly to the plane of the figure a parabolic line which is drawn in the plane of the figure. Similarly, the elliptical sweep mirror  102 M has a surface formed by extending perpendicularly to the plane of the figure a line of a portion of an ellipse which is drawn in the plane of the figure. 
   White light emitted from a light source  71  is reflected by the parabolic sweep mirror  91 M. If a prism  92  does not exist, the light is focused as an emission line (defining a focus) at a focus  421  of a parabolic line. However, the prism  92  is actually inserted between the parabolic sweep mirror  91 M and the focus  421  of the parabolic line. Therefore, a light path is bent there, causing the light to be actually focused at a transmissive LCD  401  disposed at a position that differs from the position of the focus  421 . 
   If a prism  101  does not exist, the LCD  401  is disposed at a focus  431  of the elliptical sweep mirror  102 M. However, the prism  101  is actually disposed between the elliptical sweep mirror  102 M and the focus  431 , causing a light path to be bent. Therefore, the LCD  401  is disposed at a location that is slightly displaced from the focus  431 . In other words, when the prisms  92  and  101  do not exist, the parabolic sweep mirror  91 M and the elliptical sweep mirror  102 M are disposed so that the focus  421  of the parabolic line and the focus  431  of the ellipse are disposed in correspondence with each other (that is, the two focuses are disposed at optically corresponding locations). 
   Spectrum portions exiting from the transmissive LCD  401  are synthesized by the prism  101 , and are reflected towards another focus  432  by the elliptical sweep mirror  102 M. Since a cylindrical galvano-mirror  78 S exists along the way, the spectrum portions are reflected by the galvano-mirror  78 S and are focused on a cylindrical screen  111 S. The cylindrical screen  111 S is optically disposed at the focus  432  of the ellipse of the elliptical sweep mirror  102 M. In other words, when a distance between the cylindrical galvano-mirror  78 S and the cylindrical screen  111 S is c, the distance between the cylindrical galvano-mirror  78 S and the focus  432  is also c. c is also the curvature radius of the cylindrical screen  111 S. A light incident surface of the cylindrical galvano-mirror  78 S is a convex surface as shown by a hatched cross-sectional form thereof in the figure. As a result, the length of the emission line formed perpendicular to the plane of the figure on the cylindrical screen  111 S can be made longer. 
     FIG. 26  shows a display device  34  of still another form. In this form, a prism  92  is used as the prism  92  and the prism  101  shown in  FIG. 25 , and an elliptical sweep mirror  102 M is formed as a half mirror. More specifically, after light emitted from a light source  71  is reflected by a parabolic sweep mirror  91 M, the light is actually focused upon a focus  451  of a parabolic line thereof (it is a focus of a parabolic line and, at the same time, a focus of the parabolic line of the parabolic sweep mirror  91 M). However, actually, since the prism  92  is disposed in a light path, the light is divided into a spectrum and refracted at the prism  92  and is focused on a micromirror array  74 . An elliptical sweep half mirror  102 HM is disposed between the parabolic sweep mirror  91 M and the prism  92 . The light passes through the elliptical sweep half mirror  102 HM and impinges upon the prism  92 . 
   Spectrum portions reflected by the micromirror array  74  controlled on the basis of image data impinge upon and are synthesized by the prism  92 . The light that has passed through the prism  92  impinges upon and is reflected by the elliptical sweep half mirror  102 HM. After the reflection, the light impinges upon and is reflected by a cylindrical galvano-mirror  78 S, thereby focusing the light on a cylindrical screen  111 S. In this form, the focus  451  of the parabolic sweep mirror  91 M is also one of the focuses of the elliptical sweep half mirror  102 HM. Therefore, although the light reflected by the elliptical sweep half mirror  102 HM should actually impinge upon the other focus  452  of an ellipse, since the galvano-mirror  78 S exists along the way, the light is reflected by the galvano-mirror  78 S and is focused on the cylindrical screen  111 S. Consequently, a distance c between the cylindrical galvano-mirror  78 S and the cylindrical screen  111 S is equal to a distance c between the cylindrical galvano-mirror  78 S and the other focus  452  of the ellipse. c is also the curvature radius of the cylindrical screen  111 S. 
   In this form, since mirrors are used instead of lenses, not only can chromatic aberration be restricted, but also, since the prism  92  is also used as the prism  101  shown in  FIG. 25 , size and costs can be reduced due to fewer parts. 
   In the forms shown in  FIGS. 22 to 26 , if an fθ lens is disposed in a light path (for example, between the galvano-mirror and the screen) taken by the light, formed by synthesizing the spectrum portions, traveling towards the screen, it is possible to use a flat screen. 
   In the form shown in  FIG. 25 , one of the parabolic sweep mirror  91 M and the elliptical sweep mirror  102 M may be a mirror, and the other of the parabolic sweep mirror  91 M and the elliptical sweep mirror  102 M may be a lens system. Even in the form shown in  FIG. 26 , the parabolic sweep mirror  91 M may be a lens system. 
   Further, in the specification, the term “system” refers to the entire apparatus comprising a plurality of devices.